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Responses of quasi‐6‐day waves (Q6DWs) to the extreme 2019 Antarctic stratospheric sudden warming (SSW) have been widely reported in the ionosphere, while the excitation mechanism of the global Q6DWs is still unclear in the mesosphere and lower thermosphere (MLT) region. According to the Aura satellite measurements, the amplitudes of the Q6DWs in the upper MLT region are found to be higher than their climatological activities from 2005 to 2020 at mid‐latitudes in both Northern and Southern Hemispheres. Combined with the Modern‐Era Retrospective Analysis for Research and Applications, version 2 data, the trigger mechanisms of the global enhanced Q6DWs are investigated by tracing their sources and propagations. Our analysis indicates that the equatorward propagation induced by the SSW is the main reason for the enhanced Q6DWs in the upper MLT at mid‐latitudes in the Southern Hemisphere, and the main source of the Q6DWs in the Northern Hemisphere is the seasonal variability. Besides, interhemispheric propagations also contribute to the amplification of Q6DWs during the 2019 Antarctic SSW. Key Points: The sources and propagations of the global extremely excited quasi‐6‐day waves (Q6DWs) in September 2019 are revealedThe Antarctic warming and climatology are respectively responsible for the enhanced Q6DWs in the Southern and Northern HemispheresInterhemispheric propagations have additional contributions to the global enhanced Q6DWs [ABSTRACT FROM AUTHOR]

We provide a detailed description of the spatial distribution, seasonality and transformation of the main water masses within MacKenzie Polynya (MP) in Prydz Bay, East Antarctica, using data from instrumented southern elephant seals. Dense Shelf Water (DSW) formation in MP shows large spatial variability that is related to the (a) local bathymetry, (b) water column preconditioning from the presence/absence of different water masses, and (c) proximity to the Amery Ice Shelf meltwater outflow. MP exhibits sustained sea ice production and brine rejection (thus, salinity increase) from April to October. However, new DSW is only formed from June onward, when the mixed layer deepens and convection is strong enough to break the stratification set by Antarctic Surface Water above and Ice Shelf Water below. We found no evidence of DSW export from MP to Darnley polynya, as previously suggested. Rather, our observations suggest some DSW formed in Darnley Polynya may drain toward the western Prydz Bay. Then, DSW is exported offshore from Prydz Bay through the Prydz Channel. The interplay between sea ice formation, meltwater input, and sea floor topography is likely to explain why some coastal polynyas form more DSW than others, as well as the temporal variability in DSW formation within a particular polynya. Plain Language Summary: Coastal polynyas are regions of open water surrounded by sea ice. They form when strong winds from the Antarctic continent push newly formed sea ice away from the coast, as rapidly as it forms. Polynyas are therefore important sea ice factories. When sea ice forms, salt is released into the water below, increasing its salinity and density. The densest water in the World Ocean can be traced back to a few coastal polynyas along the Antarctic continent. This dense water formed in polynyas supplies the deep limb of a network of ocean currents that influences climate on global scales. Despite their importance, coastal polynyas remain poorly understood as they are difficult to reach and observe. Using data collected by instrumented elephant seals, we investigated seasonal changes in the MacKenzie Polynya in Prydz Bay, East Antarctica. Our study shows that dense water production is regulated by a complex interplay between three factors: strength of sea ice formation, the input of meltwater from ice shelves, and steering of the flow by sea floor topography. These new observations collected by seals contribute to a better understanding of dense water formation and the vulnerability of the global overturning circulation to future change. Key Points: High resolution sampling of seasonal water‐mass evolution in MacKenzie Polynya reveals processes regulating dense shelf water productionDense water formation is concentrated in the relatively shallow western polynya where topography blocks inflow of Ice Shelf WaterThe interplay between sea ice formation, meltwater input and topography regulates the amount of Dense Shelf Water formed in coastal polynyas [ABSTRACT FROM AUTHOR]

Global warming changes the Earth's climate in different ways, in particular it influences extreme weather events like storms. Strong storms cause large surges and thus have a signature in the sea level record. While previous studies focused on long‐term changes of storm surge amplitude or frequency, changes in the timing of extreme surge events have not been investigated so far. We employed the more than 150 yr long tide gauge record of Brest (France) and found a distinct shift of storm surge timing between the years 1950 and 2000. This caused extreme events to happen about three weeks earlier during the year. We developed for this study two different methods based on statistical extreme value analysis; both methods show this shift of the seasons consistently. Furthermore, by analyzing eight additional stations, we found evidence that this timing shift happened similarly over a large part of the European Atlantic coast. Therefore, we speculate that our measured shift is part of a large‐scale climate process. Plain Language Summary: Climate change leads to an increase of the sea level all over the world. This means not only that the average sea level rises, but also that extreme sea levels become higher, which presents a major threat for coastal communities. To prepare for this growing natural hazard, it is important to understand how extreme sea levels evolve in a warming climate. One of the best places to study this is the harbor of Brest, France, which has one of the longest sea level records in the world (over 150 yr). From this time series, we extracted the surge, which is the part of the sea level that is created by large‐scale atmospheric forcing, like storms. We used two statistical methods to analyze the extreme surge levels in Brest, and we found that between 1950 and 2000, the season of large surge levels shifted forward. In 2000, extreme storm surge events happened three weeks earlier than 50 yr before. We then analyzed sea level records of other stations and found the same shift over large parts of the European Atlantic coast. So we conclude that this shift of the extreme surge season might be the signature of a large‐scale climate process. Key Points: Extreme storm surge events occurred three weeks earlier in Brest in the winter 2000 than in the 1950sShift of winter storm surge timing was calculated consistently with two statistical methodsAnalysis of additional stations in Europe suggests a large‐scale process [ABSTRACT FROM AUTHOR]

Accelerated loss of the sea‐ice cover and increased human activities in the Arctic emphasize the need for skillful prediction of sea‐ice conditions at subseasonal to seasonal (S2S) timescales. To assess the quality of predictions, dynamical forecast systems can be benchmarked against reference forecasts based on present and past observations of the ice edge. However, the simplest types of reference forecasts—persistence of the present state and climatology—do not exploit the observations optimally and thus lead to an overestimation of forecast skill. For spatial objects such as the ice‐edge location, the development of damped‐persistence forecasts that combine persistence and climatology in a meaningful way poses a challenge. We have developed a probabilistic reference forecast method that combines the climatologically derived probability of ice presence with initial anomalies of the ice‐edge location, both derived from satellite sea‐ice concentration data. No other observations, such as sea‐surface temperature or sea‐ice thickness, are used. We have tested and optimized the method based on minimization of the Spatial Probability Score. The resulting Spatial Damped Anomaly Persistence forecasts clearly outperform both simple persistence and climatology at subseasonal timescales. The benchmark is about as skillful as the best‐performing dynamical forecast system in the S2S database. Despite using only sea‐ice concentration observations, the method provides a challenging benchmark to assess the added value of dynamical forecast systems. Plain Language Summary: The Arctic is becoming more ice free and seeing more human activities, which means it is important to have reliable forecasts of sea ice conditions weeks to months ahead. The accuracy of a forecast system is typically compared against reference forecasts based on present and past observations of the ice edge. However, most widely used references either simply maintain the current state or consider states at the same time of the year during previous years. Such simple benchmarks can lead to an overestimation of how "skillful" a forecast system is considered. For sea ice edge, creating a better reference forecast combining both historical and current observations can be challenging. We have addressed this challenge and developed a method where we find the historical probability of ice presence along the current ice edge and use this probability to predict ice presence at future dates. The new method clearly outperforms the simpler methods and remains slightly better than historical‐based forecasts even 2 months ahead. Despite using only observed sea ice concentration data (like the simpler benchmarks), the new benchmark is about as good as modern model‐based forecast systems. The method therefore provides a good reference to study how well the latest forecast systems are actually performing. Key Points: We have developed a new method that combines climatological sea‐ice probability and initial‐state anomaly to forecast sea‐ice presenceIce‐edge forecasts derived from this method can outperform climatological benchmarks at lead times of up to 2 monthsSpatial damped anomaly persistence forecasts have a higher predictive skill than most models from the subseasonal to seasonal database [ABSTRACT FROM AUTHOR]

Mixed‐layer dynamics exert a first order control on nutrient and light availability for phytoplankton. In this study, we examine the influence of mixed‐layer dynamics on net community production (NCP) in the Southern Ocean on intra‐seasonal, seasonal, interannual, and decadal timescales, using biogeochemical Argo floats and satellite‐derived NCP estimates during the period from 1997 to 2020. On intraseasonal timescales, the shoaling of the mixed layer is more likely to enhance NCP in austral spring and winter, suggesting an alleviation of light limitation. As expected, NCP generally increases with light availability on seasonal timescales. On interannual timescales, NCP is correlated with mixed layer depth (MLD) and mixed‐layer‐averaged photosynthetically active radiation (PAR) in austral spring and winter, especially in regions with deeper mixed layers. Though recent studies have argued that winter MLD controls the subsequent growing season's iron and light availability, the limited number of Argo float observations contemporaneous with our satellite observations do not show a significant correlation between NCP and the previous‐winter's MLD on interannual timescales. Over the 1997–2020 period, we observe regional trends in NCP (e.g., increasing around S. America), but no trend for the entire Southern Ocean. Overall, our results show that the dependence of NCP on MLD is a complex function of timescales. Plain Language Summary: We examine the influence of mixed‐layer dynamics on net community production (NCP) in the Southern Ocean on intra‐seasonal, seasonal, interannual, and decadal timescales, using automated observations and satellite data during the period from 1997 to 2020. On intra‐seasonal timescales, the shoaling of the mixed layer is more likely to enhance NCP in austral spring and winter. As expected, NCP generally increases with light availability on seasonal timescales. On interannual timescales, NCP is correlated with mixed layer depth (MLD) and light within the mixed layer in austral spring and winter, especially in regions with deeper mixed layers. Our results do not show a significant correlation between NCP and the previous‐winter's MLD on interannual timescales. Over the 1997–2020 period, we observe regional trends in NCP, but no trend for the entire Southern Ocean. Overall, our results show that the dependence of NCP on MLD is a complex function of timescales. Key Points: Net community production (NCP) is correlated with mixed layer depth (MLD) and mixed‐layer‐averaged photosynthetically active radiation (PAR) on seasonal timescales, and on interannual timescales for spring and winterOn intraseasonal timescales, the impact of mixed‐layer dynamics on NCP is most pronounced in the austral springOn longer timescales, NCP is changing in various regions (e.g., around S. America), but no trend is evident for the entire Southern Ocean [ABSTRACT FROM AUTHOR]

Nitrification is a central process of the aquatic nitrogen cycle that controls the supply of nitrate used in other key processes, such as phytoplankton growth and denitrification. Through time series observation and modeling of a seasonally stratified, eutrophic coastal basin, we demonstrate that physical dilution of nitrifying microorganisms bywater column mixing can delay and decouple nitrification. The findings are based on a 4-y, weekly time series in the subsurface water of Bedford Basin, Nova Scotia, Canada, that included measurement of functional (amoA) and phylogenetic (16S rRNA) marker genes. In years with colder winters, more intense winter mixing resulted in strong dilution of resident nitrifiers in subsurface water, delaying nitrification for weeks to months despite availability of ammonium and oxygen. Delayed regrowth of nitrifiers also led to transient accumulation of nitrite (3 to 8 µmol · kgsw-1) due to decoupling of ammonia and nitrite oxidation. Nitrite accumulation was enhanced by ammonia-oxidizing bacteria (Nitrosomonadaceae) with fast enzyme kinetics, which temporarily outcompeted the ammonia-oxidizing archaea (Nitrosopumilus) that dominated under more stable conditions. The study reveals how physical mixing can drive seasonal and interannual variations in nitrification through control of microbial biomass and diversity. Variable, mixing-induced effects on functionally specialized microbial communities are likely relevant to biogeochemical transformation rates in other seasonally stratified water columns. The detailed study reveals a complex mechanism through which weather and climate variability impacts nitrogen speciation, with implications for coastal ecosystem productivity. It also emphasizes the value of high-frequency, multiparameter time series for identifying complex controls of biogeochemical processes in aquatic systems. [ABSTRACT FROM AUTHOR]

Systematic surveys to examine seasonal variation, degradation, and bioavailability of dissolved organic matter (DOM) in the Changjiang Estuary and the adjacent East China Sea were conducted in July 2016 and February 2017. Concentrations of dissolved organic carbon (DOC) and total hydrolyzable amino acids (THAA) were higher in July than in February. THAA and chlorophyll a (Chl‐a) were positively correlated in July, but not in February. The carbon normalized yields of THAA (THAA‐C%) in surface waters in July and February were not significantly different. However, degradation index (DI) values in the surface water were higher in February than in July. Compared with outer estuary, the inner estuary had lower THAA‐C% and DI values in both surveys. Solar radiation experiments showed that THAA and THAA‐C% values increased with time at station A6‐11 in the oceanic water but declined at C3 in the freshwater, possibly due to the different origins, chemical compositions, or initial degradation states of the DOM at the time of collection. Microbial incubation experiments showed that accumulated DOC and DON in surface waters were bioavailable to the microbial community of the surface layer, but recalcitrant to the microbial fauna from the bottom layer. Leucine (Leu) was selectively consumed, while glycine (Gly), threonine, and alanine appeared to be recalcitrant in summer (July) microbial incubations; and histidine, Gly, and methionine were preferentially consumed, while aspartic acid, serine, phenylalanine, and Leu were recalcitrant in winter (February) incubations. Plain Language Summary: As one of the most abundant components of labile dissolved organic matter (DOM), amino acids are an important reservoir of organic carbon and nitrogen in the ocean, and amino acid cycling is closely associated with phytoplankton and bacteria. Photochemical reactions and microbial consumption are crucial parts of the transformation and degradation pathways of DOM in marine environments. Analysis of amino acids can be used to evaluate the quality and degradation state of organic matter. In this study, we investigated the temporal and spatial distributions and compositions of total hydrolyzable amino acids (THAA), evaluated the bioavailability of DOM based on amino acids, and investigated the removal mechanisms of DOM via seawater photochemical and microbial incubation experiments. This study indicated that phytoplankton and terrestrial runoff played the important roles in controlling dissolved organic carbon and THAA concentrations. The bioavailability of DOM was higher at offshore sites than the inner Changjiang Estuary sites. We suspect that accumulated DOM in surface waters were removed via bacterial consumption and then transported to the bottom layer. Individual amino acids were selectively utilized by heterotrophic bacteria. Key Points: The concentrations of dissolved organic carbon (DOC) and total hydrolyzable amino acids and the bioavailability of dissolved organic matter showed significant spatial and seasonal variationsAccumulated DOC and dissolved organic nitrogen in surface waters were removed via bacterial consumption and then transported to the bottom layerIndividual amino acids were selectively utilized by heterotrophic bacteria [ABSTRACT FROM AUTHOR]

Seasonal and interannual variability of the New Guinea Coastal Current (NGCC) and New Guinea Coastal Undercurrent (NGCUC) were investigated with 3 years of mooring measurements off the northern coast of New Guinea and outputs from the Ocean General Circulation Model for the Earth Simulator during 1980–2018. Acoustic Doppler Current Profilers mounted on the two moorings captured variations of the currents in the upper 800 m off the New Guinea coast during 2015–2018. NGCC is a seasonally reversing current in the upper 100 m, which flows southeastward in boreal winter with maximum velocity of 63 cm/s near the surface, and flows northwestward in boreal summer with maximum velocity of −55 cm/s at 80 m. NGCUC flows northwestward all year round between 100 and 400 m, and its temporal mean velocity reaches −40 cm/s at 200 m. A seasonally reversing current named New Guinea Coastal Intermediate Current with speed of 10 cm/s is detected below the NGCUC, which is in phase with the NGCC on seasonal time scale. Seasonal variation of the NGCUC is also in phase with that of the NGCC, and it is strong in boreal summer and weak in winter. Such seasonal signal reaches down to the depth of 800 m. Both mooring measurements and model outputs indicate that NGCUC demonstrates significant interannual variations associated with El Nino‐Southern Oscillation (ENSO), with its velocity core shoaling during El Nino and deepening during La Nina, but the net transport of NGCUC exhibits no significant relationship with ENSO. Plain Language Summary: The currents north of the New Guinea coast transport water masses crossing the equator from the Southern Hemisphere to the Northern Hemisphere, and modulate the thermohaline structure in the equatorial Pacific, playing an important role in the El Nino‐Southern Oscillation cycle and the interhemisphere water exchange. To better understand the structure and variability of these currents, we deployed two subsurface moorings and obtained the velocity time series measurements down to 800 m. A seasonally reversing current is detected below the traditionally known upper‐ocean currents, and the monsoon wind forcing is noticed to reach the depth of 800 m, much deeper than the previously acknowledged 150 m. The velocity core of the New Guinea Coastal Undercurrent is revealed shoaling and deepening during El Nino and La Nina, respectively, but the transport of this current exhibits no close relationship with ENSO, which is probably due to the transport restriction through Vitiaz Strait. This research improved our understanding of the vertical structure and variability of the currents off the New Guinea coast. Key Points: Vertical structure of currents in the upper 800 m off the New Guinea coast is revealed with mooring measurementsMonsoon‐induced seasonality is not trapped in upper ocean, a seasonally reversing flow is detected below New Guinea Coastal Undercurrent (NGCUC)Velocity core of NGCUC shoals/deepens in El Nino/La Nina, the transport shows no significant relation with ENSO [ABSTRACT FROM AUTHOR]

We identify and analyze tropical instability waves (TIWs) in the equatorial Atlantic Ocean during 2010–2018 using satellite derived observations of sea surface salinity (SSS), sea surface temperature (SST), sea level anomaly, and Argo profiles. In particular, the weekly 50‐km resolution SSS time series from the climate change initiative project provides an unprecedented opportunity to observe the salinity structure at a scale closer to the SST scale. We examine the relative contributions of SSS and SST to the horizontal surface density gradient on seasonal and interannual time scales and how they contribute to the TIW properties and energetics. For the central Atlantic TIWs, the maximum of the SST contribution to the density anomaly lags the SSS one by approximately one month. Argo vertical profiles indicate that temperature and salinity both significantly contribute to TIW‐related density anomalies. In May–June, salinity contributes to 50% of the perturbation potential energy in the top 60 m, and between 30% and 45% from July to September. While variations in SST appear to be related to dynamic processes, the interannual variability of SSS is also influenced by precipitations. However, the two leading modes of variability in the region (Atlantic Meridional and Zonal modes) do not well explain at 1°N these interannual variations. Plain Language Summary: Density is a key variable, influenced by both salinity and temperature and essential to understand the equatorial Atlantic dynamics. Each spring and summer, the horizontal density gradient generated by the equatorial upwelling is subject to undulations associated with tropical instability waves (TIWs). These waves are important features that influence both the ocean dynamics and air‐sea interactions. The scarcity of historical salinity observations has been a limiting factor in the study of the relative role of salinity and temperature (and therefore density) in the TIWs dynamics. To do so, we use here an unprecedented 9‐year satellite‐based dataset together with sea surface temperature and in situ Argo floats data. We show that the Atlantic TIWs seasonal and interannual variations are different in salinity and temperature. The TIWs surface salinity seasonal cycle leads the temperature one by one month. Concerning the wave energetics, salinity is responsible for almost half of the potential energy generated by the density gradient. Contributions of temperature and salinity are similar in May and June, while temperature dominates in July to September. Further characterization of the seasonal cycle, interannual variations, and energetics of TIWs will be necessary to better understand their role in climate. Key Points: Satellite and in situ data highlight large seasonal and interannual variability in the respective roles of salinity and temperature on tropical instability waves (TIWs)TIWs maximum surface salinity signal leads the temperature one by one monthIn the top 60‐m of the ocean, salinity and temperature each contribute to about 50% of the TIWs perturbation potential energy [ABSTRACT FROM AUTHOR]

A new high‐resolution global analysis product is constructed from a fully coupled surface wave‐tide‐circulation Ocean Model developed by the First Institute of Oceanography Coupled Ocean Model (FIO‐COM). The performance of the FIO‐COM analysis data set is assessed based on comparisons with two other widely used high‐resolution global analysis products (Copernicus marine and environment monitoring service and HYbrid isopycnal‐sigma‐pressure coordinate ocean model), and observations in tropical oceans. Through comparison with observations, the FIO‐COM analysis is shown to be able to accurately capture the large‐scale mixed layer depth (MLD) structures in the tropical oceans during all seasons. Seasonal variations of MLDs can exceed ±80% in the southern and northern tropical oceans (10°‐25°S and 10°‐25°N) in both boreal winter and summer, as inferred from observations and FIO‐COM analysis data. Quantitative assessments of the 20°C isothermal depth, temperature at 5°m depth, and temperature and salinity profiles, among the analyses and in situ observations are also conducted. The capability of the FIO‐COM analysis to reflect the observed sea surface temperature variability during the 2015 El Niño episode is further investigated through comparisons with observations from 19 TAO buoys located in the Niño 3.4 region. All indicate the high quality of the new data set. Plain Language Summary: We present a new high‐resolution global analysis data set, which is for the first time constructed from a surface wave‐tide‐circulation fully coupled model system. To evaluate the accuracy of the analysis data set, we present intercomparisons with two other high‐resolution global analysis datasets, as well as observations from tropical ocean areas. We show that the new analysis data set simulates the large‐scale ocean mixed layer depth structures accurately during all seasons over a two‐year period. Specifically, we make comparisons with in situ observations of the 20°C isothermal depth, temperature at 5°m depth, and the temperature and salinity profiles. The new data set exhibits high quality in all of these variables. Key Points: This is a first attempt to generate analysis data based on a surface wave‐tide‐circulation fully coupled model system, First Institute of Oceanography Coupled Ocean ModelThe quality of this data set is comprehensively verified through comparison with two other analysis datasets and observationsThe new data set can well capture the seasonal variation of sea surface temperature, mixed layer depth, El Niño, Indian Ocean dipole, and Atlantic meridional mode [ABSTRACT FROM AUTHOR]

Neoehrlichia mikurensis is a tick‐borne pathogen widespread among ticks and rodents in Europe and Asia. A previous study on Ixodes ricinus ticks in Norway suggested that N. mikurensis was scarce or absent on the south‐west coast of Norway, but abundant elsewhere. The aim of this study was to further investigate the prevalence and distribution of N. mikurensis along the western seaboard of Norway in comparison with more eastern and northern areas. The second aim of the study was to examine seasonal variation of the bacterium in one specific location in the south‐eastern part of Norway. Questing I. ricinus were collected from 13 locations along the coast of Norway, from Brønnøysund in Nordland County to Spjærøy in Østfold County. In total, 11,113 nymphs in 1,113 pools and 718 individual adult ticks were analysed for N. mikurensis by real‐time PCR. The mean prevalence of N. mikurensis in adult ticks was 7.9% while the estimated pooled prevalence in nymphs was 3.5%. The prevalence ranged from 0% to 25.5%, with the highest prevalence in the southernmost and the northernmost locations. The pathogen was absent, or present only at low prevalence (<5%), at eight locations, all located in the west, from 58.9°N to 64.9°N. The prevalence of N. mikurensis was significantly different between counties (p <.0001). No significant seasonal variation of N. mikurensis prevalence was observed in the period May to October 2015. Our results confirm earlier findings of a low prevalence of N. mikurensis in the western seaboard of Norway. [ABSTRACT FROM AUTHOR]

Aim: Conservation of highly mobile species often requires identifying locations or time periods of elevated vulnerability. Since both extrinsic habitat conditions and intrinsic behavioural and energetic requirements contribute to habitat use at the landscape scale, identifying spatial or temporal foci for conservation intervention requires understanding how habitat needs and distributions vary across the annual cycle. Nearshore marine birds inhabit highly dynamic systems and have widely varying habitat needs among breeding, moult and non‐breeding seasons, making them a useful case study for testing the relative contributions of individual resource requirements and environmental conditions in driving annual variation in distribution patterns. Location: Northern Gulf of Mexico (USA). Methods: We tracked Brown Pelicans using bird‐borne GPS transmitters and used a combination of Hidden Markov Models and multivariate selectivity analysis to compare the characteristics of preferred resident habitats used throughout the annual cycle. Results: Habitat selection was driven by dynamic oceanographic variables during all stages of the annual cycle. Key habitat characteristics varied between seasons, with particularly strong selection on high productivity, low temperature and low salinity during the breeding and post‐breeding moult periods. The post‐breeding moult also corresponded to a time of limited availability of preferred habitats, resulting in extensive overlap between breeding populations from different administrative planning areas. Main conclusions: By incorporating seasonal variation in individual behaviour and resource requirements into our habitat models, we were able to identify the post‐breeding moult as a period of high selectivity and restricted availability of preferred habitats for Brown Pelicans. Locations meeting preferred habitat criteria during the post‐breeding period, particularly estuarine habitats with high productivity and low salinity, would therefore be high‐value targets for management and restoration. Our analysis demonstrates the importance of accounting for both intrinsic and extrinsic temporal variation in evaluating habitat selection. [ABSTRACT FROM AUTHOR]

We present a 3-year record of seasonal variations in ice speed and frontal ablation of 10 marine-terminating outlet glaciers along the coast of Prudhoe Land in northwestern Greenland. The glaciers showed seasonal speedup initiated between late May and early June, and terminated between late June and early July. Ice speed subsequently decreased from July to September. The timing of the speedup coincided with the onset of the air temperature rise to above freezing, suggesting an influence of meltwater availability on the glacier dynamics. No clear relationship was found between the speedup and the terminus position or the sea-ice/ice-mélange conditions. These results suggest that the meltwater input to the glacier bed triggered the summer speedup. The excess of summer speed (June–August) over the mean for the rest of the year accounted for 0.5–13% of the annual ice motion. Several glaciers showed seasonal frontal variations, i.e. retreat in summer and advance in winter. This was not due to ice-speed variations, but was driven by seasonal variations in frontal ablation. The results demonstrate the dominant effect of glacier surface melting on the seasonal speedup, and the importance of seasonal speed patterns on longer-term ice motion of marine-terminating outlet glaciers in Greenland. [ABSTRACT FROM AUTHOR]

Middle East surface air temperature (ME-SAT), during boreal summer (June to August: JJA), shows robust multidecadal variations for the period 1948−2016. Here, using observational and reanalysis datasets, as well as coupled atmosphere–ocean model simulations, we linked the observed summer ME-SAT variability to the multidecadal variability of sea surface temperature (SST) in the North Atlantic Ocean (AMV). This Atlantic−ME connection during summer involves ocean–atmosphere interactions through multiple ocean basins, with an influence from the Indian Ocean and the Arabian Sea. The downstream response to Atlantic SST is a weakening of the subtropical westerly jet stream that impacts summer ME-SAT variability through a wave-like pattern in the upper tropospheric levels. The Atlantic SST response is further characterized by positive geopotential height anomalies in the upper levels over the Eurasian region and a dipole-like pressure distribution over the ME in lower levels. For positive Atlantic SST anomalies this pressure gradient initiates anomalous low-level southerly flow, which transports moisture from the neighboring water bodies toward the extremely hot and dry ME landmass. The increase in atmospheric moisture reduces the longwave radiation damping of the SAT anomaly, increasing further ME-SAT. A suite of Atlantic Pacemaker experiments skillfully reproduces the North Atlantic–ME teleconnection. Our findings reveal that in observations and models the Atlantic Ocean acts as a critical pacemaker for summer ME-SAT multidecadal variability and that a positive AMV can lead to enhanced summer warming over the Middle East. [ABSTRACT FROM AUTHOR]

The sea ice modeling community is progressing towards pan-Arctic simulations that explicitly resolve leads in the simulated sea ice cover. Evaluating these simulations against observations poses new challenges. A new feature-based evaluation of simulated deformation fields is introduced, and the results are compared to a scaling analysis of sea ice deformation. Leads and pressure ridges – here combined into linear kinematic features (LKFs) – are detected and tracked automatically from deformation and drift data. LKFs in two pan-Arctic sea ice simulations with a horizontal grid spacing of 2 km are compared with an LKF dataset derived from the RADARSAT Geophysical Processor System (RGPS). One simulation uses a five-class ice thickness distribution (ITD). The simulated sea ice deformation follows a multi-fractal spatial and temporal scaling, as observed from RGPS. The heavy-tailed distribution of LKF lengths and the scale invariance of LKF curvature, which points to the self-similar nature of sea ice deformation fields, are reproduced by the model. Interannual and seasonal variations in the number of LKFs, LKF densities, and LKF orientations in the ITD simulation are found to be consistent with RGPS observations. The lifetimes and growth rates follow a distribution with an exponential tail. The model overestimates the intersection angle of LKFs, which is attributed to the model's viscous-plastic rheology with an elliptical yield curve. In conclusion, the new feature-based analysis of LKF statistics is found to be useful for a comprehensive evaluation of simulated deformation features, which is required before the simulated features can be used with confidence in the context of climate studies. As such, it complements the commonly used scaling analysis and provides new useful information for comparing deformation statistics. The ITD simulation is shown to reproduce LKFs sufficiently well for it to be used for studying the effect of directly resolved leads in climate simulations. The feature-based analysis of LKFs also identifies specific model deficits that may be addressed by specific parameterizations, for example, a damage parameter, a grounding scheme, and a Mohr–Coulombic yield curve. [ABSTRACT FROM AUTHOR]

This study was carried out to investigate plastic pollution in the Black Sea Coast of the Anatolian side of Istanbul, Turkey. In the study, the plastic particles in the collected samples (beach sands) were classified depending on size. The abundance of microplastics (1-5 mm) and large plastics (>5 mm) by number and weight were determined. The spatial and seasonal variations in the abundance by number and weight were also reported. The highest abundances by number were found at Riva station, whereas the lowest abundances by number were found at Sile Port. [ABSTRACT FROM AUTHOR]

Sponges play an important ecological function in many benthic habitats. They filter large volumes of water, retain suspended particles with high efficiency, and process dissolved compounds. Nevertheless, the factors that regulate sponge pumping rate and its relation to environmental factors have been rarely studied. We examined, in situ , the variation of pumping rates for five Mediterranean sponge species and its relationship to temperature, particulate food abundance and sponge size over two annual cycles. Surprisingly, temperature and food concentration had only a small effect on pumping rates, and the seasonal variation of pumping rates was small (1.9–2.5 folds). Sponge size was the main determinant of the specific pumping rate (pumping normalized to sponge volume or mass). Within the natural size distribution of each species, the volume-specific pumping rate [PR V , ml min−1 (cm sponge)−3] decreased (up to 33 folds) with the increase in sponge volume (V , cm3), conforming to an allometric power function (PR V = aVb) with negative exponents. The strong dependence of the size-specific pumping rate on the sponge size suggests that the simplistic use of this value to categorize sponge species and predict their activity may be misleading. For example, for small specimens, size-specific pumping rates of the two low-microbial-abundance (LMA) species (allometric exponent b of −0.2 and −0.3) were similar to those of two of the high-microbial-abundance (HMA) species (b of −0.5 and −0.7). However, for larger specimens, size-specific pumping rates were markedly different. Our results suggest that the pumping rate of the sponges we studied can be approximated using the measured allometric constants alone in conjunction with surveys of sponge abundance and size distribution. This information is essential for the quantification of in situ feeding and respiration rates and for estimates of the magnitude of sponge-mediated energy and nutrient fluxes at the community level. Further work is required to establish if and to what extent the low seasonal effect and the strong size dependency of pumping rate can be generalized to other sponges and habitats. [ABSTRACT FROM AUTHOR]

The Ross Ice Shelf (RIS) is host to a broadband, multimode seismic wavefield that is excited in response to atmospheric, oceanic and solid Earth source processes. A 34-station broadband seismographic network installed on the RIS from late 2014 through early 2017 produced continuous vibrational observations of Earth's largest ice shelf at both floating and grounded locations. We characterize temporal and spatial variations in broadband ambient wavefield power, with a focus on period bands associated with primary (10–20 s) and secondary (5–10 s) microseism signals, and an oceanic source process near the ice front (0.4–4.0 s). Horizontal component signals on floating stations overwhelmingly reflect oceanic excitations year-round due to near-complete isolation from solid Earth shear waves. The spectrum at all periods is shown to be strongly modulated by the concentration of sea ice near the ice shelf front. Contiguous and extensive sea ice damps ocean wave coupling sufficiently so that wintertime background levels can approach or surpass those of land-sited stations in Antarctica. [ABSTRACT FROM AUTHOR]

Although there have been many previous studies that have interpreted the variability of Indonesian Throughflow transport, the processes that determine its vertical structure have rarely been investigated due to limited observations and model inefficiencies. In this study, a regionally coupled model is developed to address this issue. The model adopts an unstructured model grid, with an ~3‐km resolution within the Indonesian seas and straits, and reveals somewhat inconsistent results compared to previous models with coarser resolutions. The results suggest that the seasonal variability of the depth of the Indonesian Throughflow velocity maximum is partially controlled by the seasonally reversed Karimata throughflow, while the remainder primarily originated from the Mindanao–Sulawesi inflow rather than the Sibutu Strait throughflow. The Mindanao–Sulawesi inflow possesses a subsurface velocity core similar to that of the Makassar Strait, with a deep (shallow) maximum during El Niño (La Niña) years that plays a crucial role in determining the downstream Makassar throughflow profile in the interannual time scale. A sensitivity experiment by fixing Indian Ocean boundary condition shows that the impacts from the Indian Ocean might be significant only within the intraseasonal to seasonal time scales. Key Points: A high‐resolution regional coupled model is developed to investigate the Makassar throughflow profile variabilityThe seasonal variability of Makassar throughflow profile is determined by both Karimata Strait flow, Mindanao Current intrusion, and downstream Kelvin wavesIndian Ocean impact is significant within the seasonal time scale, whereas the Pacific Ocean impact is predominated in the interannual time scale [ABSTRACT FROM AUTHOR]

The Bhagirathi streams are a major source of fresh water in the form of glaciers meltwater streams and monsoonal phenomena. The watersheds of the Bhagirathi basin is trending towards water chemistry as well as changing morphological and land cover features due to the climatic and anthropogenic activity. To understand seasonal hydrochemistry and the impact of watershed morphology a total of 32 stream water samples collected during post and pre-monsoon seasons. The bicarbonate is the most dominant ion in the streams water followed by Na+, Ca+2, SO4−2, Cl−, SiO2, K+, and Mg+2. The results were found that HCO3− is in very good correlation with the base cations Ca+2, Mg+2 and Na+ in both pre and post-monsoon seasons. The higher concentration of HCO3− in Bhagirathi stream water and its positive correlation with Ca+2 and Mg+2 indicates that their main source comes from the dissolution of carbonates. Most of the hydro-chemical parameters (EC, pH) and ions (Ca+2, Mg+2, Na+, K+, HCOf−, SO4−2, Cl−, and F−) indicated a relationship with morphometric and land cover and these parameters vary with the season. It is observed that elevation, relief, basin length, area, and perimeter impact on stream water chemistry. Due to the processes of chemical weathering, mixing of the groundwater, snow/glacier meltwater, and surface water components responsible for the seasonal variation in the hydro-chemistry of streams. Impact of agriculture land is more dominant than any land cover followed by barren land and glacier cover that influence the hydrochemistry of streams. [ABSTRACT FROM AUTHOR]

Seasonal variations in environmental variables, chlorophyll a (Chl-a), particulate carbon and nitrogen (PC and PN, respectively), phytoplankton carbon biomass (Ph-C) and primary production were investigated at a neritic station in Sagami Bay, Kanagawa, from January 2008 to December 2013. Size-fractionated Ph-C was converted from cell volume by microscopic observation, adding valuable data for this area. During spring blooms, the micro-size fraction (>20 μm) comprised the majority of the total Chl-a and total Ph-C, whereas during other periods the pico- and nanosize fraction (<20 μm) comprised a larger proportion, indicating that phytoplankton standing crops were affected by sunlight conditions and physicochemical properties of the water. In February-March, phytoplankton biomass increased and formed the first peak of spring blooms under increasing sunlight intensities (>15.7 MJ m-2 d-1), high nutrient concentrations and balanced molar ratios. From the regression equations of size-fractionated Ph-C-Chl-a relationships, the mean Ph-C/Chl-a ratio was 5.3-7.7, 29.2-32.6 and 22.1-25.1 for the <20 μm, >20 μm and total fraction, respectively. The Ph-C/Chl-a ratio (1.8-128.8) was regulated by irradiance and nutrients. Growth rate (ca. 0-3.7 d-1) was positively correlated with irradiance and assimilation number, and negatively with the Ph-C/Chl-a ratio. The depth-integrated primary production (DIPP) was 0.15-5.43 g C m-2 d-1. On the basis of the 0-50 m depth-integrated values, the total Ph-C and DIPP accounted for 1.3-34.4% and 1.3-30.9% d-1 of PC, respectively, indicating that PC variations depended on the total Ph-C and DIPP. [ABSTRACT FROM AUTHOR]

Paralytic shellfish toxins (PSTs) are a group of the most harmful neurotoxins distributed worldwide. Marine organism samples, including mollusks, crustaceans and fish, collected from 11 sites around the coastal water of the South China Sea, were analyzed in terms of the PST and toxicity via high–performance liquid chromatography. The PST geographical distribution, detectable rate for PST and toxin content all increased slightly from 2006 to 2008 to 2015. High PST content with more than 2 nmol g−1 appeared in Shantou (ST), Shanwei (SW), Zhanjiang (ZJ), Beihai (BH), Xuwen (XW), Haikou (HK), Dongfang (DF), Wanning (WN) and Sanya (SY). Low PST content with less than 2 nmol g−1 appeared in Shenzhen (SZ) and Yangjiang (YJ). High PST toxicity over the safety limit 800 μg STXeq/kg appeared in ST, SW, ZJ, BH, DF, SY and XW. PST has significant seasonal characteristics and was mostly detected in spring, early summer (March–June) and autumn (September–November) in the coastal water of the South China Sea. PST was usually detected in some specific species of scallop, mussel, bloody clam, hard clam, razor clam, oyster, crab, shrimp and fish. Toxin profile variation of marine organism samples was influenced greatly by species, sampling time and site. • PST was mostly detected in spring, early summer and autumn in the South China Sea. • High PST mainly distributed in Shantou, Shanwei, Zhanjiang, Beihai and Dongfang. • The highest toxicity 5906 μg STXeq/kg appeared in clam Spondylus cruentus Lischke. [ABSTRACT FROM AUTHOR]

The spatial and temporal variation of phytoplankton communities including HAB species in relation to the environmental characteristics was investigated in the protected meso-oligotrophic Mellah lagoon located in the South Western Mediterranean. During 2016, a biweekly monitoring of phytoplankton assemblages and the main abiotic factors were realized at three representative stations. Taxonomic composition, abundance, and diversity index were determined. In total, 227 phytoplankton species (160 diatoms and 53 dinoflagellates) were inventoried. There was a clear dominance of diatoms (62.9%) compared with dinoflagellates (36.8%). Diatoms dominated in spring and dinoflagellates developed in summer and early autumn in Mellah showing a marked seasonal trend. Data showed that the dynamic of the phytoplankton taxa evolving in the lagoon was mainly driven by temperature and salinity. For the first time, a number of potentially toxic species have been identified, including 2 diatoms (Pseudo-nitzschia group delicatissima, Pseudo-nitzschia group seriata) and 5 dinoflagellates (Alexandrium minutum, Alexandrium tamarense/catenella, Dinophysis acuminata, Dinophysis sacculus, Prorocentrum lima). These harmful species could threat the functioning of the Mellah lagoon and human health and require the establishment of a monitoring network. Finally, our study suggests that the observed decrease of the phytoplankton diversity between 2001 and 2016 could result from the reduction in water exchanges between the lagoon and the adjacent coast following the gradual clogging of the channel. [ABSTRACT FROM AUTHOR]

The seasonal habitat use of bearded seals is important information in terms of conservation of this species. However, their distribution outside the breeding season has not been well documented. We investigated seasonal variations in the call occurrence of bearded seals by using passive acoustic monitoring in the southern Chukchi Sea, which has some of the greatest benthic biomass in the Pacific sector of the Arctic Ocean. Underwater sounds were recorded between 2012 and 2015. Calls of bearded seals were detected from mid-September or early October to the end of each recording period (mid-May 2013, early March 2014, and mid-June 2015). Two peaks in call occurrence were noted; the first peak occurred during the open-water periods in November, and the second peak occurred during ice-covered periods. This suggest that bearded seals utilize the southern Chukchi Sea not only for the breeding site but also for the autumn foraging site. We could complement the information about the southward autumn migration pattern of bearded seals, and the southern Chukchi Sea was suggested as the south limit of bearded seals' autumn distribution. Additionally, their vocal activity during autumn in this site was suggested to have some role in social interaction. Our results indicated that the southern Chukchi Sea would be an important monitoring site for understanding the habitat use and the vocal activity of bearded seals, especially outside the breeding season. [ABSTRACT FROM AUTHOR]

Shelf circulation on the North West Shelf (NWS) of Australia is dominated by seasonal variations of the alongshore Holloway Current forced by the monsoonal winds. However, the intra-annual variability of the current remains poorly understood. In this study, a combination of model outputs and two years of mooring time series data were used to analyse the intra-annual variability of the Holloway Current. The dominant intra-annual variability of the alongshore current on the NWS were at intraseasonal and semiannual frequencies, as revealed by sea level data. Whereas the interannual variability in the region is mostly forced remotely by tropical Pacific processes, the intraseasonal and semiannual signals are mostly driven by variations of regional winds off the northern coast of Australia. Phase analysis of sea level anomalies indicated that the excitation and propagation of Coastally Trapped Waves (CTWs) are forced by Madden-Julian Oscillations (MJO; intraseasonal) and semiannual wind anomalies. Intraseasonal CTWs are excited over the eastern parts of the Kimberley shelf, whereas semiannual waves are generated further to the east, over the northern Australian coast. The phase speed of intraseasonal CTWs is ~5.5 ms−1, characteristic of the first CTW mode, and 2.5 ms−1for semiannual CTWs, characteristic of the second CTW mode. The fluctuations in the velocity field over the NWS translates into significant alongshore current transport anomalies, ranging on average from ~0.4 Sv to ~0.6 Sv, for intraseasonal and semiannual frequency, respectively. Southwestward (northeastward) intraseasonal transport anomalies peak during Phase 1 (Phase 5) of the MJO cycle (out of the 8 phases of MJO) on the Kimberley shelf, whereas the corresponding transport anomalies on the Pilbara shelf peak during Phase 3 (Phase 7). Semiannual southwestward (northeastward) transport anomalies on the Kimberley shelf peak in April and October (January and July), preceding those on the Pilbara shelf by one month. • Strong intra-seasonal and semiannual variability in North West Shelf Australian waters forced by remote offshore winds. • Alongshore wind anomalies drive anomalous sea level along the shelf via Ekman transport. • Excitement and propagation of coastally trapped waves along the North West shelf. • Strength of the Holloway Current highly influenced by the propagation of coastally trapped waves. [ABSTRACT FROM AUTHOR]

Monthly phytoplankton samples were collected from January 2013 to December 2015 at a fixed sampling site in Bahía de La Paz, Gulf of California. During this study 26 samplings were Amphidinium cf. carterae positive. The highest densities of A. cf. carterae (754.2 × 103 to 1022.4 × 103 cells L−1) were recorded during a bloom detected in January 2015 when water temperatures were 20–22 °C. This dinoflagellate showed a well-marked seasonal variation, being found mainly from November to April. Blooms of the species were linked to the upwelled water due to the northwesterly wind. Cysts surrounded by a mucilaginous membrane of A. cf. carterae were found. We also observed these hyaline cysts inside zooplankton fecal pellets. Other benthic/tychoplanktonic dinoflagellates and diatoms, including some potentially toxic species were also found. The occurrence of blooms of A. cf. carterae in Bahía de La Paz could represent a risk for aquaculture activities and human health. • Amphidinium cf. carterae is a potentially toxic dinoflagellate in Mexican waters. • Its highest densities (1022.4 × 103 cells L−1) were recorded in January 2015. • Blooms of Amphidinium cf. carterae in Bahía de La Paz were found at 22 °C. • Blooms of the species are linked to the upwelled water due to the northwestern wind. • No apparent detrimental effects on the marine fauna were observed during the blooms. [ABSTRACT FROM AUTHOR]

The experimental data given in the article show a perturbation of currents in the northeastern Caspian Sea near Peschanomysskoe uplift, which is caused by the interaction between cyclonic circulation and the southern slope of the uplift. This interaction results in that the water of the cyclonic circulation forks into lower and upper branches. The lower, bottom branch is reflected southwestward by the uplift, where, at the head of the uplift, it meets water flowing southeastward over the bed of the Yuzhno-Buzachinskii depression, while the upper branch, consisting of the surface and intermediate cold water, is pushed upward and flows over the uplift. The rise of cold water forms upwelling in the top layer, which extends over the entire northeastern part of the sea. [ABSTRACT FROM AUTHOR]

The modelling of chlorophyll-a concentration helps to restrict the harmful effects in marine species caused by increased nutrient loads. The derived satellite data are often used for the monitoring of marine ecology. The common usage of satellite data is monthly average data to avoid the problem of missing values. In order to reduce the effect of missing data, this study employed the cubic spline model by using a satellite data for investigating seasonal variations of chlorophyll-a mapped in an eight-day interval consisting of missing values in Pattani Bay, Thailand from the year 2003 to 2017. This study further used the spline-fitted data for creating the baseline model of chlorophyll-a in Pattani Bay, and for examining the difference between spline fitted and monthly average data. This study revealed that the cubic spline method was able to handle the missing values in satellite data to gain the smoothness in data. When both models were compared, the spline-fitted observation yielded a smoother curve pattern than the monthly average observation. The spline fitted model was also able to display the chlorophyll-a data at any particular day of the year. It was also shown that the chlorophyll-a concentration level in the coastal area of Pattani Bay was higher in the inshore pixels, especially in rainy season. [ABSTRACT FROM AUTHOR]

Iceberg discharge is estimated to account for up to 50% of the freshwater flux delivered to glacial fjords. The amount, timing, and location of iceberg melting impacts fjord‐water circulation and heat budget, with implications for glacier dynamics, nutrient cycling, and fjord productivity. We use Sentinel‐2 imagery to examine seasonal variations in freshwater flux from open‐water icebergs in Sermilik Fjord, Greenland during summer and fall of 2017–2018. Using iceberg velocities derived from visual‐tracking and changes in total iceberg volume with distance down‐fjord from Helheim Glacier, we estimate maximum average two‐month full‐fjord iceberg‐derived freshwater fluxes of ~1,060 ± 615, 1,270 ± 735, 1,200 ± 700, 3,410 ± 1,975, and 1,150 ± 670 m3/s for May–June, June–July, July–August, August–September, and September–November, respectively. Fluxes decrease with distance down‐fjord, and on average, 86–91% of iceberg volume is lost before reaching the fjord mouth. This method provides a simple, invaluable tool for monitoring seasonal and interannual iceberg freshwater fluxes across a range of Greenlandic fjords. Plain Language Summary: Recent studies have shown that the freshwater produced via the melting of icebergs can dominate the freshwater budget in glacial fjords surrounding the Greenland Ice Sheet, which has important implications for fjord circulation and heat budget, nutrient availability, and primary productivity. Here we use satellite imagery to estimate both iceberg velocity and the seasonal changes in iceberg volume in Sermilik Fjord in southeast Greenland in 2017–2018, from which meltwater fluxes are derived. Iceberg meltwater fluxes are highest in the late summer and fall, when fjord water temperatures are warmer than in the spring and early summer, and when more icebergs have been calved into the fjord. Throughout the year, the volume of freshwater generated from the melting of icebergs is greater than the freshwater entering the fjord at the base of the glacier and sourced from melting at the ice sheet surface. As such, the melting of icebergs provides a significant volume of freshwater to the fjord system, with important implications for fjord‐scale circulation and heat budget, nutrient cycling, and primary productivity. The methodology presented here is effective, simple and inexpensive, and can be applied to a variety of glacial fjord systems, particularly those that are remote and inaccessible. Key Points: Freshwater fluxes from iceberg melt in Sermilik Fjord have a seasonal signal, peaking across August and September in 2017 and 2018Fluxes decrease with distance down‐fjord from Helheim Glacier, with ~86–91% of iceberg volume lost before reaching the fjord mouthWe present a simple and effective tool for monitoring iceberg freshwater fluxes across a range of Greenlandic fjords [ABSTRACT FROM AUTHOR]

Global mass redistribution between the Earth subsystems oceans, atmosphere and continental hydrosphere causes a predominantly seasonal signal in Earth rotation excitation that superimposes the effects of each individual Earth subsystem. Especially for annual length-of-day variations a consistent consideration of the global mass balance among atmosphere, ocean and continental water is necessary to compare the simulated effective angular momentum functions for Earth rotation from geophysical models with geodetic observations. In addition to atmospheric, oceanic and hydrological contributions, we estimate the contributions due to the global mass balance effect using the new ESMGFZ SLAM product as well as estimates of the barystatic ocean bottom pressure anomalies from the GRACE Level 3 GravIS products. For the annual cycle the global mass balance effect overcompensates the contributions to length-of-day variations from terrestrial hydrology. Moreover, most of the atmospheric surface pressure contribution is also compensated. The global mass balance effect has to be calculated for each combination of geophysical Earth system models individually. Considering the global mass balance, model based mass induced excitation on seasonal length-of-day variations coincide well with estimates from satellite gravimetry. Moreover, the mass terms can be determined accurate enough to attribute the remaining gap in the length-of-day excitation budget between models and observation clearly to an underestimation of atmospheric wind speeds in the global European weather forecast model. Magnifying its wind speeds by +7 per cent the sum of all ESMGFZ angular momentum functions can almost perfectly explain the total length-of-day excitation. [ABSTRACT FROM AUTHOR]

The oxygen minimum zone (OMZ) of the central Arabian Sea is investigated with a biogeochemical model that couples the marine nitrogen and oxygen cycles and includes euphotic, aphotic, aerobic and anaerobic processes. The model is used to quantify the strength, location and relative timing of governing processes, in particular, nitrite generation, nitrogen losses and oxygen consumption. In an idealized two-dimensional physical environment the model is able to reproduce the observed meridional-vertical structure of oxygen and nitrate, as well as the secondary nitrite maximum layer. Characteristic features of vertical profiles are well represented and the modelled nitrogen transformation rates are in good agreement with observed values. The model results show that (i) the OMZ is neither vertically nor horizontally homogeneous, (ii) minute differences in oxygen concentration determine the thickness of the nitrite layer, (iii) there is hardly any seasonal cycle in the extent of the OMZ but a pronounced seasonal cycle in nitrite, and (iv) the nitrogen loss in the OMZ is accomplished by a succession of denitrification and anammox, based on the seasonal supply of labile detritus. We conclude that the nitrogen loss in the Arabian Sea can only be understood by taking into account the diversity, vertical arrangement and temporal succession of microbial processes. [ABSTRACT FROM AUTHOR]

A floating plastic monitoring program was conducted for two years on a weekly basis in Banderas Bay, Mexico. A total of 94 samples were collected from May 2016 to April 2018 in the southern part of the bay. Half (57%) of them contained plastic debris; 79% of it being <5 mm in length. Polypropylene and Polyethylene were the most abundant polymers, accounting for 45% and 43% of the plastic pieces (pp), respectively. The highest abundance of plastic pieces was found in July 2016, with a maximum of 0.3 pp/m3 found in one sample. The amount of floating plastics was significantly higher in the hurricane season compared to the dry season (p < 0.001). This suggests that rainfall may play a significant role in the offload of plastics from land-based sources into the bay. Unlabelled Image • Two years of floating plastic monitoring was conducted from 2016 to 2018. • Microplastics (<5 mm) accounted for 79% of collected plastic pieces. • A significant seasonal signal was detected in the two years of monitoring. • The mean abundance is lower than most of the floating plastic debris studies. [ABSTRACT FROM AUTHOR]

Studies of krill (Crustacea: Euphausiacea) in oceanic waters of the Bay of Biscay are scarce and restricted to the epipelagic zone, overlooking vertical dynamics such as diurnal vertical migration (DVM). There is a growing interest in acoustically evaluating the biomass of krill in this area, but this requires a good knowledge of its vertical dynamics and aggregation patterns. In this work we employed acoustic data and net samples from two consecutive annual surveys covering a wide off-shelf area of the Bay of Biscay (JUVENA surveys of 2013 and 2014) and four seasonal surveys covering slope and oceanic waters in the Cantabrian Sea (SCAPA surveys of 2015). Vertical dynamics of krill were analyzed in the frame of the environmental seascape. High interannual and seasonal variations in the vertical distribution and aggregation patterns (small swarms, dense aggregations, or loose layers) of krill were observed. The vertical distribution covaried with dissolved oxygen and salinity. According to our findings, the best season to acoustically evaluate krill in the Bay of Biscay is spring, with the bulk of the biomass located above 600 m depth. Moreover, extending the acoustic recording beyond the epipelagic zone is mandatory for any season. [ABSTRACT FROM AUTHOR]

Microzooplankton communities in the coastal Gulf of Alaska (CGOA) were studied during two contrasting years: 2011, with a greatly reduced spring phytoplankton bloom, and 2013, with a robust spring bloom. Other sampling contrasts were season (spring, summer, fall) and region (eastern versus western shelf waters). Ciliates and dinoflagellates comprised nearly all microzooplankton in the ≥ 15 µm size class. Many of the strongest contrasts in the biomass and taxonomic composition of the microzooplankton community were regional. The east had generally lower microzooplankton biomass levels and a greater proportion of ciliates than the west, even in the face of basin-wide seasonal and interannual contrasts. This difference is likely a consequence of the narrower shelf in the east, which leads to a lower productivity environment. Interannual differences in spring bloom intensity were reflected in microzooplankton biomass (higher in spring 2013, especially in the east), while interannual differences in taxonomic composition persisted throughout the year, with a greater representation of ciliates in 2011. Ciliate dominance could reflect adaptations to lower productivity conditions, with many of the largest taxa likely retaining chloroplasts as a strategy (mixotrophy) for survival during times of prey scarcity. Microzooplankton: phytoplankton biomass ratios varied widely over time and space. These ratios indicate that lower productivity regions (east) and seasons (summer) also tend to be locations and times of reduced trophic transfer efficiency from phytoplankton to ciliates and dinoflagellates. Ciliates and dinoflagellates can be preferred prey of mesozooplankton, including dominant CGOA copepod species. Thus multiple mechanisms conspire to reduce the flow of matter and energy to higher trophic levels in low productivity locations and time periods in the CGOA. [ABSTRACT FROM AUTHOR]

Previous studies have indicated that most of the net sinking associated with the downward branch of the Atlantic Meridional Overturning Circulation (AMOC) must occur near the subpolar North Atlantic boundaries. In this work we have used monthly mean fields of a high-resolution ocean model (0.1 ∘ at the Equator) to quantify this sinking. To this end we have calculated the Eulerian net vertical transport (W∑) from the modeled vertical velocities, its seasonal variability, and its spatial distribution under repeated climatological atmospheric forcing conditions. Based on this simulation, we find that for the whole subpolar North Atlantic W∑ peaks at about -14 Sv at a depth of 1139 m, matching both the mean depth and the magnitude of the meridional transport of the AMOC at 45∘ N. It displays a seasonal variability of around 10 Sv. Three sinking regimes are identified according to the characteristics of the accumulated W∑ with respect to the distance to the shelf: one within the first 90 km and onto the bathymetric slope at around the peak of the boundary current speed (regime I), the second between 90 and 250 km covering the remainder of the shelf where mesoscale eddies exchange properties (momentum, heat, mass) between the interior and the boundary (regime II), and the third at larger distances from the shelf where W∑ is mostly driven by the ocean's interior eddies (regime III). Regimes I and II accumulate ∼90% of the total sinking and display smaller seasonal changes and spatial variability than regime III. We find that such a distinction in regimes is also useful to describe the characteristics of W∑ in marginal seas located far from the overflow areas, although the regime boundaries can shift a few tens of kilometers inshore or offshore depending on the bathymetric slope and shelf width of each marginal sea. The largest contributions to the sinking come from the Labrador Sea, the Newfoundland region, and the overflow regions. The magnitude, seasonal variability, and depth at which W∑ peaks vary for each region, thus revealing a complex picture of sinking in the subpolar North Atlantic. [ABSTRACT FROM AUTHOR]

Estuarine food webs are generally considered to be supported by marine pelagic and benthic primary producers and by the import of dead organic matter from the open sea. Although estuaries receive considerable amounts of freshwater phytoplankton and organic compounds from adjacent rivers, the potential contribution of these living and dead matter to estuarine food webs is often assumed to be negligible and, therefore, not examined. Based on stable isotope analyses, we report the importance of freshwater suspended particulate organic matter (FW-SPOM) for fuelling estuarine food webs in comparison to estuarine SPOM and microphytobenthos. This previously neglected food source contributed 50–60% (annual average) of food intake of suspension-feeding bivalves such as cockles (Cerastoderma edule), mussels (Mytilus edulis) and Pacific oysters (Magallana gigas) at the Balgzand tidal flats, an estuarine site in the western Wadden Sea (12–32 psu). For these species, this proportion was particularly high in autumn during strong run-off of SPOM-rich freshwater, whilst estuarine SPOM (20%-25%) and microphytobenthos (15%-30%) were relatively important in summer when the freshwater run-off was very low. These findings have implications for our understanding of the trophic interactions within coastal food webs and for freshwater management of estuarine ecosystems. [ABSTRACT FROM AUTHOR]

The seasonal variations of rainfall over the island of Hawaii are studied using the archives of the daily model run from the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) from June 2004 to February 2010. Local effects mainly drive the rainfall on the Kona coast in the early morning and the lower slopes in the afternoon. During the summer, the incoming trade winds are more persistent and moister than in winter. The moisture content in the wake zone is higher than open-ocean values because of the convergent airflow associated with dual counterrotating vortices. As the westerly reversed flow moves toward the Kona coast, it decelerates with increasing moisture and a moisture maximum over the coastal area, especially in the afternoon hours in summer months. The higher afternoon rainfall on the Kona lower slopes in summer than in winter is caused by a moister (>6 mm) westerly reversed flow bringing moisture inland and merging with a stronger upslope flow resulting from solar heating. Higher nocturnal rainfall off the Kona coast in summer than in winter is caused by the low-level convergence between a moister westerly reversed flow and offshore flow. On the windward slopes, the simulated rainfall accumulation in winter is higher because of frequently occurring synoptic disturbances during the winter storm season. Nevertheless, early morning rainfall along the windward coast and afternoon rainfall over the windward slopes of the Kohala Mountains is lower in winter because the incoming trades are drier. [ABSTRACT FROM AUTHOR]

This paper reports on the long-term statistics of ambient noise (50–2000 Hz) in the northeast South China Sea. The data were collected from July 2016 to March 2018. The long-term statistics, seasonal, and diel variations of ambient noise are analyzed. There are significant seasonal variations from 500 to 2000 Hz. The ambient noise level at 1000 Hz is 6–10 dB higher in winter than in summer. There is only a small difference between the day and night comparison (less than 1.6 dB). The results are significant to evaluate and improve the performance of underwater acoustic systems in this area. [ABSTRACT FROM AUTHOR]

We present a first assessment of the Sea Surface Temperature (SST) and 300m Heat Content (HC) ensemble mean skill of the Australian Community Climate and Earth-System Simulator-Seasonal v1.0 (ACCESS-S1) around New Zealand on seasonal timescales, using a set of retrospective ensemble forecasts for 1990-2012. This was verified against Reynolds AVHRR analysis and Bluelink ReANalysis 3.5 (BRAN3.5). For inshore areas with depth <300m, the model shows skill forecasting for summer at a lead time of 0 months, with 66% and 65% of model grid cells having correlation coefficients exceeding 0.6 for SST and 300m HC respectively. Regions of lower skill seem to be associated with the model representation of the complex and variable frontal systems around New Zealand, and an overly-strong response to the El Niño Southern-Oscillation (ENSO). Nevertheless, the skill of ACCESS-S1 around New Zealand suggests there is potential for the development of useful seasonal forecast products for the region. [ABSTRACT FROM AUTHOR]

Abstract Seasonal variation of sea breeze (SB) characteristics and its effect on turbulence spectra at Visakhapatnam (17.7°N, 83.3°E) located at east coast of Peninsular India are investigated by considering 244 sea breeze events during December 2012 to March 2014. The delayed onset of backdoor SB during winter occurs due to the southward component of shore-parallel background winds while the prevailing northward component of background wind enable the early onset of corkscrew SB during pre-monsoon and summer monsoon. The turbulence spectral peak of horizontal winds shifts to higher frequency side after SB onset. Highlights Seasonal variation of sea breeze (SB) characteristics and its effect on turbulence spectra at a coastal station, Visakhapatnam (17.7°N, 83.3°E) located in the east coast of Peninsular India are investigated using fast-response micro-meteorological observations carried out at 10 m level during December 2012 to March 2014. The study is based on 244 days with unambiguous identification of sea breeze circulation and brings out the following highlights: • Sea breeze activity exists more or less throughout the year, though it is most prominent in winter and rather weak during summer monsoon season. The most probable onset time of sea breeze is between 08 and 11 LT during winter and around 07–10 LT during pre-monsoon and summer monsoon seasons. • The prevailing wind direction and diurnal variation of winds observed at Visakhapatnam show that the occurrence of pure or backdoor sea breeze (the later characterized by veering of wind and potentially delayed sea breeze onset) might be more frequent during winter while corkscrew sea breeze (characterized by backing of wind and early sea breeze onset) might be more frequent during pre-monsoon and summer monsoon seasons. • The turbulence spectral peak of horizontal winds shifts to higher frequency side after SB onset, due to the development of thermal internal boundary layer. [ABSTRACT FROM AUTHOR]

The seasonal and interannual variations of the barrier layer thickness (BLT) in the tropical Indian Ocean (TIO) is investigated in this study using the Simple Ocean Data Assimilation (SODA) version 3 reanalysis dataset from 1980 to 2015. BLT presents a significant seasonal variation in the TIO, mainly attributed to the variations of the sea surface salinity (SSS) and the thermocline. In particular, BLT anomalies are negatively correlated to SSS anomalies in the western TIO, except in summer. In the eastern TIO, the thermocline anomalies positively impact BLT anomalies in all seasons. However, the dependency of BLT anomalies on thermocline in the western TIO is only observed during winter. Furthermore, It is found that BLT could feedback on SSS, as BLT of the spring-time can negatively affect the SSS of the summer-time in the western TIO. In terms of the interannual BLT variation, we found that both the Indian Ocean Dipole (IOD)and El Niño South Oscillation (ENSO) events could impact the variation of BLT by affecting the thermocline, especially in the eastern TIO. In addition, BLT in the western TIO presents remarkable seasonal phase locking feature during the El Niño years. During the developing and mature phases of El Niño, thicker BLT is due to the change of thermocline, while during the decaying phase of El Niño BLT opposing to the weakened thermocline change becomes more significant because of the change of SSS. [ABSTRACT FROM AUTHOR]

Beaufort Sea ice motion is episodic in winter, on average following the anticyclonic motion of the Beaufort Gyre. Weather systems cause the ice pack to fracture in characteristic patterns that depend on the location and trajectory of the weather system in relation to the coast. The majority of leads associated with anticyclonic motion in the Beaufort Sea are coastal leads that form perpendicular from promontories along the coast and landfast ice edge. Between 40% and 90% (depending on location along the Beaufort coast) winter sea ice motion is associated with leads, including coastal leads, coastal flaw leads, and interior lead patterns. In winter much of the Beaufort Gyre ice drift results from ice‐coast interaction, with high ice drift localized on the leeward side of fractures that propagate from the coast. In the vicinity of Point Barrow, which has the largest occurrence of coastal leads, ice drift rates are enhanced due to this ice‐coast interaction. No trends in occurrence of these leads are found over the 20 winters from December 1993 to May 2013. Seasonality in the occurrence of the leads follows seasonality in the location of the Beaufort High. In order for ice to be transported from the northeast part of the Beaufort Gyre to the southwest in a single winter, anticyclones would need to break their geospatial climatic norm, needing a higher prevalence of anticyclones in the eastern Beaufort early in the season and higher prevalence in the west Canada Basin later in the season. Key Points: Leads in the Beaufort Sea are classified and their occurrence linked to location and trajectory of weather systemsSeasonality in lead distributions generally follows seasonality of the Beaufort High locationVariability in the location of weather systems controls variability of winter sea ice motion in the Beaufort Sea [ABSTRACT FROM AUTHOR]

The seasonal and interannual variability of photosynthetically available radiation (PAR) over the tropical oceans is examined using satellite imagery acquired from 1997 to 2017. Spatial and temporal biases between monthly PAR estimates from different instruments are determined and corrected, resulting in a consistent time series over the 20‐year record. Uncertainty is evaluated in comparisons with in situ measurements at various sites. Empirical orthogonal function (EOF) analysis is performed with both seasonal and nonseasonal PAR signals, and linear trends are quantified. Seasonal cycles dominate PAR variability, with the first three seasonal EOF modes explaining 84.7% of the total variance. The seasonal patterns are related to solar position and monsoon. Canonical El Niño–Southern Oscillation (ENSO) and Modoki ENSO are related to the two leading nonseasonal EOF modes, with a correlation coefficient of 0.84 between the first mode and the multivariate ENSO index and of 0.48 between the second mode and the El Niño Modoki index. Trend analysis reveals that PAR tends to decrease by 0.2%/year in the central Pacific north of the equator and to increase by 0.2%/year in the central Pacific around 5°S. The tendency is also for PAR to increase west of Central and South America. These changes are consistent with patterns of cloud change evidenced in the satellite cloud record and predicted by global climate models. The long‐term satellite PAR data set, together with information of nutrient availability and temperature, enables further studies to elucidate the causes of phytoplankton variability in the tropical oceans. Plain Language Summary: Knowing the spatial and temporal distribution of photosynthetically available radiation (PAR) over the global oceans is critical to understanding biogeochemical cycles of carbon, nutrients, and oxygen and to address important climate issues such as the fate of anthropogenic atmospheric carbon dioxide. This paper examines the seasonal and interannual variability of PAR at the surface of the tropical oceans using 20‐year satellite imagery. It is found that the seasonal patterns are related to solar position and monsoon and nonseasonal patterns are affected by El Niño events. The PAR time series exhibits significant trends in some regions due to cloudiness change. Such long‐term satellite PAR data set, together with information of nutrient availability and temperature, enables further studies to elucidate the causes of phytoplankton variability (spatial, seasonal, and interannual) in the tropical oceans. Key Points: A 20‐year consistent time series of satellite‐derived PAR over the tropical oceans is generatedThe seasonal patterns of PAR are related to solar position and monsoon, and nonseasonal variability is associated to El NiñoPAR trends in the tropical oceans are connected to cloud cover and albedo changes [ABSTRACT FROM AUTHOR]

In this study we analyzed sediment trap time series from five tropical sites to assess seasonal variations in concentrations and fluxes of long-chain diols (LCDs) and associated proxies with emphasis on the long-chain diol index (LDI) temperature proxy. For the tropical Atlantic, we observe that generally less than 2 % of LCDs settling from the water column are preserved in the sediment. The Atlantic and Mozambique Channel traps reveal minimal seasonal variations in the LDI, similar to the two other lipid-based temperature proxies TEX 86 and U37K′. In addition, annual mean LDI-derived temperatures are in good agreement with the annual mean satellite-derived sea surface temperatures (SSTs). In contrast, the LDI in the Cariaco Basin shows larger seasonal variation, as do the TEX 86 and U37K′. Here, the LDI underestimates SST during the warmest months, which is possibly due to summer stratification and the habitat depth of the diol producers deepening to around 20–30 m. Surface sediment LDI temperatures in the Atlantic and Mozambique Channel compare well with the average LDI-derived temperatures from the overlying sediment traps, as well as with decadal annual mean SST. Lastly, we observed large seasonal variations in the diol index, as an indicator of upwelling conditions, at three sites: in the eastern Atlantic, potentially linked to Guinea Dome upwelling; in the Cariaco Basin, likely caused by seasonal upwelling; and in the Mozambique Channel, where diol index variations may be driven by upwelling from favorable winds and/or eddy migration. [ABSTRACT FROM AUTHOR]

Six years of mooring data from the Alaskan Beaufort Sea slope, together with meteorological observations and reanalysis fields, are used to quantify the occurrence of wind-driven upwelling and the associated atmospheric forcing. The canonical upwelling event, composited from 115 individual events, reveals that when the easterly wind is strongest the entire shelfbreak jet is reversed to the west. At the end of the event a bottom-intensified, eastward-flowing "rebound jet" spins up that is stronger than the normal shelfbreak jet. The cross-isobath flow has a three-layer structure with onshore flow in the surface layer, offshore flow in the middle of the water column, and onshore flow near the bottom. This is because the reversed shelfbreak jet is oriented slightly onshore which overwhelms the cross-isobath surface Ekman transport. The vertically-integrated along-isobath momentum balance supports this interpretation and indicates that the rebound jet is driven by the zonal gradient in sea surface height. During over two thirds of the events, Atlantic Water (AW) is upwelled to the shelfbreak, while for the remaining events only Pacific Water (PW) is upwelled. The primary driving factor behind this is the seasonal variation in the PW-AW interface depth offshore of the shelfbreak, which is controlled by the local wind stress curl. During summer, when PW-type events dominate, Ekman pumping associated with negative wind stress curl deepens the interface depth, limiting access to the Atlantic layer. Over the remainder of the year, when AW events dominate, Ekman suction associated with positive wind stress curl raises the interface. These variations are due to the influence of the two regional atmospheric centers of action — the Aleutian Low and the Beaufort High. [ABSTRACT FROM AUTHOR]

Abstract This study presents the distribution, seasonal variations and factors influencing phosphorus (P) forms in surface sediments from the Maowei Sea. P forms were measured using the sequential extraction (SEDEX) procedures. Inorganic P (IP) was the predominant chemical form of total P (TP). Fe-bound P (Fe P) was the main IP form. Sediment particle sizes, organic matter distribution, terrestrial input and aquaculture activity were responsible for the seasonal variations of different forms of P in sediment. In summer, the average proportions of P fractions in TP followed the order of organic P (OP) > Fe-P > authigenic P (Ca P) > detrital P (De-P) > exchangeable P (Ex-P); in winter, the corresponding order was OP > Fe-P > De-P > Ca-P > Ex-P. The potential bio-available P accounted for 71.1 ± 4.9% and 70.6 ± 6.3% of TP in summer and winter, respectively. Sedimentary organic matter mainly came from land-based sources in winter. Highlights • Seasonal variations in P chemical speciation between summer and winter were obvious. • Inorganic P was the dominant component of sedimentary total P in summer and winter. • Fe-bound P was the main chemical forms of inorganic P in the surface sediments. • Grain size and organic matter co-affected the behaviors of P in both seasons. • Surface sediment was a potentially important source of P in the aquaculture bay. [ABSTRACT FROM AUTHOR]

The basic biology and ecology of the South African east coast round herring Etrumeus wongratanai was investigated from samples of fish collected between 2013 and 2016. This species is short‐lived and reaches a maximum of 3 years of age, with rapid growth in its first year of life. It reproduces from June to December (austral summer) and condition factor was lowest in May through to August and increased from September, probably reflecting the physiological strain before and during spawning. Fish larvae were the most important food items consumed during summer, whereas eucalanid copepods were the most important prey at other times of the year. Stable‐isotope data suggest that there are gradual changes in the trophic level with increasing fish size, δ15N and δ13C values also differed between seasons. The results obtained here are compared with those of other Etrumeus species, regionally and globally. [ABSTRACT FROM AUTHOR]

Abstract Dalk Glacier, which has been monitored by CHINARE since 2007, is a calving outlet glacier near the Chinese Zhongshan Station in East Antarctica. Using in situ observational azimuthal data from 2007 to 2012, 67 high-precision spatial intersection points were calculated. Consequently, the ice-flow features of the tongue of Dalk Glacier were explored via ground measurements. The maximum observed ice-flow velocity (IV) was 192.72 m/a, at stake P9. The velocities then decreased with the distance from the central flow line on both sides of the glacier in a cross section. Further analysis showed the following: the velocities of each stake increased annually; the closer to the terminus, the faster the ice flowed; and the ascent ratio of the IVs was approximately 10.67 m/a2 in the main flow area. We also observed seasonal variations in the ice-flow velocities, including a speed-up in January 2009 preceding an ice-calving event. The elevation change measurements at the stakes showed fluctuations along the central flow line, which indicates ice-shelf grounding over a seamount that had not been previously identified. [ABSTRACT FROM AUTHOR]

Seasonal variations in iodine concentrations were investigated for two years in a brown alga (Ecklonia cava Kjellman) and a seagrass (Zostera marina L.) occurring in the northwestern Pacific coast of central Japan. The iodine concentration in E. cava was 0.92-5.6 mg per gram dry weight (g‒ 1 DW) (mean ± SD:2.3 ± 1.1 mg g‒1 DW), and its variation was similar to that of other brown algae. In Z. marina, the iodine concentration was 17-110 μg g‒1 DW (61 ± 28 μg g‒ 1 DW) and displayed seasonal variation, as it was high in winter and spring and low in autumn. [ABSTRACT FROM AUTHOR]