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This study presents a comprehensive analysis on the variations in the tropical cyclone (TC) frequencies during 1980–2021, including the linear trends, periodicities, and their variabilities on both global and basin-wise scales. An increasing trend in the annual number of global TCs is identified, with a significant rising trend in the numbers of tropical storms (maximum sustained wind 35   k t s ≤ U m a x < 64   k t s ) and intense typhoons ( U m a x ≥ 96   k t s ) and a deceasing trend for weak typhoons ( 64   k t s ≤ U m a x < 96   k t s ). There is no statistically significant trend shown in the global Accumulated Cyclone Energy (ACE). On a regional scale, the Western North Pacific (WNP) and Eastern North Pacific (ENP) are the regions of the first- and second-largest numbers of TCs, respectively, while the increased TC activity in the North Atlantic (NA) contributes the most to the global increase in TCs. It is revealed in the wavelet transformation for periodicity analysis that the variations in the annual number of TCs with different intensities mostly show an inter-annual period of 3–7 years and an inter-decadal one of 10–13 years. The inter-annual and inter-decadal periods are consistent with those in the ENSO-related ocean drivers (via the Niño 3.4 index), Southern Oscillation Index (SOI), and Inter-decadal Pacific Oscillation (IPO) index. The inter-decadal variation in 10–13 years is also observed in the North Atlantic Oscillation (NAO) index. The Tropical North Atlantic (TNA) index and Atlantic Multi-decadal Oscillation (AMO) index, on the other hand, present the same inter-annual period of 7–10 years as that in the frequencies of all the named TCs in the NA. Further, the correlations between TC frequencies and ocean drivers are also quantified using the Pearson correlation coefficient. These findings contribute to an enhanced understanding of TC activity, thereby facilitating efforts to predict particular TC activity and mitigate the inflicted damage. [ABSTRACT FROM AUTHOR]

The World Ocean's surface, particularly in the North Atlantic, has been heating up for decades. There was concern that the thermohaline circulation and essential climate variables, such as the temperature and salinity of seawater, could undergo substantial changes in response to this surface warming. The Atlantic Meridional Overturning Circulation (AMOC) has changed noticeably over the last centennial and possibly slowed down in recent decades. Therefore, concerns about the future of the North Atlantic Ocean climate are warranted. The key to understanding the North Atlantic current climate trajectory is to identify how the decadal climate responds to ongoing surface warming. This issue is addressed using in-situ data from the World Ocean Atlas covering 1955-1964 to 2005-2017 and from the SODA reanalysis project for the most recent decades of 1980-2019 as fingerprints of the North Atlantic three-dimensional circulation and AMOC's dynamics. It is shown that although the entire North Atlantic is systematically warming, the climate trajectories in different sub-regions of the North Atlantic reveal radically different characteristics of regional decadal variability. There is also a slowdown of the thermohaline geostrophic circulation everywhere in the North Atlantic during the most recent decade. The warming trends in the subpolar North Atlantic lag behind the subtropical gyre and Nordic Seas warming by at least a decade. The climate and circulation in the North Atlantic remained robust from 1955-1994, with the last two decades (1995-2017) marked by a noticeable reduction in AMOC strength, which may be closely linked to changes in the geometry and strength of the Gulf Stream system. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive analysis on the variations in the tropical cyclone (TC) frequencies during 1980–2021, including the linear trends, periodicities, and their variabilities on both global and basin-wise scales. An increasing trend in the annual number of global TCs is identified, with a significant rising trend in the numbers of tropical storms (maximum sustained wind 35 kts≤Umax<64 kts) and intense typhoons (Umax≥96 kts) and a deceasing trend for weak typhoons (64 kts≤Umax<96 kts). There is no statistically significant trend shown in the global Accumulated Cyclone Energy (ACE). On a regional scale, the Western North Pacific (WNP) and Eastern North Pacific (ENP) are the regions of the first- and second-largest numbers of TCs, respectively, while the increased TC activity in the North Atlantic (NA) contributes the most to the global increase in TCs. It is revealed in the wavelet transformation for periodicity analysis that the variations in the annual number of TCs with different intensities mostly show an inter-annual period of 3–7 years and an inter-decadal one of 10–13 years. The inter-annual and inter-decadal periods are consistent with those in the ENSO-related ocean drivers (via the Niño 3.4 index), Southern Oscillation Index (SOI), and Inter-decadal Pacific Oscillation (IPO) index. The inter-decadal variation in 10–13 years is also observed in the North Atlantic Oscillation (NAO) index. The Tropical North Atlantic (TNA) index and Atlantic Multi-decadal Oscillation (AMO) index, on the other hand, present the same inter-annual period of 7–10 years as that in the frequencies of all the named TCs in the NA. Further, the correlations between TC frequencies and ocean drivers are also quantified using the Pearson correlation coefficient. These findings contribute to an enhanced understanding of TC activity, thereby facilitating efforts to predict particular TC activity and mitigate the inflicted damage.

The World Ocean’s surface, particularly in the North Atlantic, has been heating up for decades. There was concern that the thermohaline circulation and essential climate variables, such as the temperature and salinity of seawater, could undergo substantial changes in response to this surface warming. The Atlantic Meridional Overturning Circulation (AMOC) has changed noticeably over the last centennial and possibly slowed down in recent decades. Therefore, concerns about the future of the North Atlantic Ocean climate are warranted. The key to understanding the North Atlantic current climate trajectory is to identify how the decadal climate responds to ongoing surface warming. This issue is addressed using in-situ data from the World Ocean Atlas covering 1955-1964 to 2005-2017 and from the SODA reanalysis project for the most recent decades of 1980-2019 as fingerprints of the North Atlantic three-dimensional circulation and AMOC’s dynamics. It is shown that although the entire North Atlantic is systematically warming, the climate trajectories in different sub-regions of the North Atlantic reveal radically different characteristics of regional decadal variability. There is also a slowdown of the thermohaline geostrophic circulation everywhere in the North Atlantic during the most recent decade. The warming trends in the subpolar North Atlantic lag behind the subtropical gyre and Nordic Seas warming by at least a decade. The climate and circulation in the North Atlantic remained robust from 1955-1994, with the last two decades (1995-2017) marked by a noticeable reduction in AMOC strength, which may be closely linked to changes in the geometry and strength of the Gulf Stream system.

A new mean sea surface (MSS) was determined by focusing on the accuracy provided by exact-repeat altimetric missions (ERM) and the high spatial coverage of geodetic (or drifting) missions. The goal was to obtain a high-resolution MSS that would provide centimeter-level precision. Particular attention was paid to the homogeneity of the oceanic content of this MSS, and specific processing was also carried out, particularly on the data from the geodetic missions. For instance, CryoSat-2 and SARAL/AltiKa data sampled at high frequencies were enhanced using a dedicated filtering process and corrected from oceanic variability using the results of the objective analysis of sea-level anomalies provided by DUACS multi-missions gridded sea-level anomalies fields (MSLA). Particular attention was also paid to the Arctic area by combining traditional sea-surface height (SSH) with the sea levels estimated within fractures in the ice (leads). The MSS was determined using a local least-squares collocation technique, which provided an estimation of the calibrated error. Furthermore, our technique takes into account altimetric noises, ocean-variability-correlated noises, and along-track biases, which are determined independently for each observation. Moreover, variable cross-covariance models were fitted locally for a more precise determination of the shortest wavelengths, which were shorter than 30 km. The validations performed on this new MSS showed an improvement in the finest topographic structures, with amplitudes exceeding several cm, while also continuing to refine the correction of the oceanic variability. Overall, the analysis of the precision of this new CNES_CLS 2022 MSS revealed an improvement of 40% compared to the previous model, from 2015. [ABSTRACT FROM AUTHOR]

The mean sea surface (MSS) has an important role, both, in the calculation of the mean dynamic topography and in the area of sea-level change as a reference surface. This paper presents a new approach to estimate a continuous spatiotemporal MSS from along-track altimetric sea surface height measurements. A parametric function continuously defined in the spatial as well as temporal domain is constructed from a C 1 -smooth finite element space to represent the MSS. Least-squares observation equations are set up, to estimate the unknown scaling coefficients from the sea surface height measurements as collected by altimetric exact repeat missions and geodetic missions. An advantage of the proposed method is that the surface is represented by an analytic model and the unknown parameters can be physically interpreted. Whereas the static component of the function represents the MSS, the temporal component is used to absorb the ocean variability. Within this initial study, 10 years of satellite altimetry over the period 2010–2019 are analyzed in a small study region around the Agulhas Current. To obtain the best possible data coverage, all missions available via AVISO, which provide data in the study region and period, are included, i.e., geodetic missions and mission phases as well as exact repeat missions. Besides the static MSS, the temporal component, which is co-estimated to absorb the dominating ocean variability, is modeled with different basis functions to study their performance. On the one hand, global basis functions considering a linear trend and periodic functions are compared with B-Spline basis functions. The comparison of the static component to the global CNES_CLS15 MSS shows a reasonable agreement with a root-mean-square error in the range of 1–4 cm for the well-suited model configurations. To validate the modeling approach and the different analyzed configurations, the temporal model component is compared to gridded sea-level anomaly products. Although it is not (yet) a target quantity, the analysis can serve as a quality check of the MSS and the proposed modeling approach as well. It is shown that in regions with relatively low ocean variability the combination of a linear trend with an annual period is well suited to model the dominant temporal signal, whereas it is not sufficient in regions with strong ocean variability, e.g., close to the Agulhas Current. In those regions, the scenario which utilizes B-Splines in the temporal domain performs significantly better. In general, it is demonstrated that the proposed approach can be an alternative to the well-established MSS estimation procedures. [ABSTRACT FROM AUTHOR]

The Ross Sea has been the site of extensive investigations since the earliest days of polar exploration. The International Geophysical Year of 1957-58 enhanced research activities with the establishment of scientific stations and the collection of oceanographic observations in the area. While many features of its oceanography, ecology, physics, glaciology, geology, and biogeochemistry are known, recent advances provide new insights into its structure and function, as well as into its relationship to global climate. We present a comprehensive review of the advances of understanding the main processes occurring in the area, such as the formation of dense shelf water and the production of Antarctic Bottom Water (AABW), as well as the main drivers (at both large and local scales) of local dynamics and water mass variability. We also summarize the main modeling applications, which are still limited and need to be improved using high-resolution models and, locally, limited-area models to explain processes driven mainly by thermodynamics and water-mass transformations. The Ross Sea forms the most saline AABW due to the activity of two polynyas in the western sector. A salinity gradient occurs on the shelf, with fresh Low Salinity Shelf Waters concentrated in the eastern Ross Sea, which is influenced by the inflow of fresh water from the Amundsen and Bellingshausen Seas. This freshwater inflow was thought to be the cause of a multi-decadal freshening of the High Salinity Shelf Water, precursor to the AABW, although a rebound in salinity in the Ross Sea has been observed since 2014. The increase in salinity has also affected the production of AABW, with the respective rebound occurring almost simultaneously. [ABSTRACT FROM AUTHOR]

The Tomini is one of the largest gulf in Indonesia. The gulf also has a unique profile and adjacent to Maluku Sea which is the eastern route of the Indonesian Throughflow. The purpose of this research is to investigate and analyze the circulation patterns that occur inside the gulf of Tomini and Maluku Sea as well as the variability of physical parameters such as temperature, salinity and transport volume and to correlate the driving factors of ocean-atmosphere phenomena that affect these physical parameters using the INDESO model dataset from January 2008 to December 2014 (7 years). The results showed that the surface circulation in the gulf and Maluku Sea flows southeastward to the Lifamatola Strait during the northwest and 1st transition, during the southeastern season the circulation flows leaving Maluku Sea through the ITF entry to the Pacific and Sulawesi Seas, and then flows southeastward during 2nd transition. The seawater temperature in the study area ranges between 28.6 - 32.0°C and the salinity varies between 32.2-34.4 psu. Vertical structure of zonal current in the gulf reveals velocity range from 0.02-0.3 Sv and the surface layer current is dominated by the westward flow, while at 20-60 m depth the flow is eastward. The mean transport volume at transects 123°E is about -0.028 (±0.2578) Sv. Variability of transport volume revealed spatial anomalies and periodicity on the intra-seasonal, semi-annual, annual, and inter-annual time-scales. Those are significantly coherence with zonal and meridional winds forcing in the Indo-Pacific region. [ABSTRACT FROM AUTHOR]

Abstract Among the regions of the Southern Ocean, the northern Antarctic Peninsula (NAP) has emerged as a hotspot of climate change investigation. Nonetheless, studies have indicated issues and knowledge gaps that must be addressed to expand the understanding of the carbonate system in the region. Therefore, we focused on identifying current knowledge about sea-air CO2 fluxes (FCO2), anthropogenic carbon (Cant) and ocean acidification along NAP and provide a better comprehension of the key physical processes controlling the carbonate system. Regarding physical dynamics, we discuss the role of water masses formation, climate modes, upwelling and intrusions of Circumpolar Deep Water, and mesoscale processes. For FCO2, we show that the summer season corresponds to a strong sink in coastal areas, leading to CO2 uptake that is greater than or equal to that of the open ocean. We highlight that the prevalence of summer studies prevents comprehending processes occurring throughout the year and the net annual CO2 balance in the region. Thus, temporal investigations are necessary to determine natural environmental fluctuations and to distinguish natural variability from anthropogenically driven changes. We emphasize the importance of more studies regarding Cant uptake rate, accumulation, and export to global oceans.

Numerous indicators show that multi-annual and longer oceanic baroclinic variability retains a complicated spatial structure out to decades and longer. With time-averaging, the sub-basin scales connected to abyssal topography and meteorological structures emerge in the fields. Here, using 26-years of an oceanic state estimate (ECCO), an attempt is made to extract simpler patterns from the vertical average (whole water column) annual mean temperature anomalies and, separately, the vertical structures at each horizontal position. Singular vectors (SVs)/empirical orthogonal functions (EOFs) successfully simplify vertical and horizontal fields, but principal observation patterns (POPs) do not do so. About 3 horizontal spatial patterns account for more than 95% of the interannual and longer variances. A breakdown of the purely vertical structure at each grid point leads in contrast to an intricate variability with depth. Results have implications both for future sampling strategies, and for estimates, e.g. of the accuracy of any mean oceanic scalar.

GLORYS12 is a global eddy-resolving physical ocean and sea ice reanalysis at 1/12° horizontal resolution covering the 1993-present altimetry period, designed and implemented in the framework of the Copernicus Marine Environment Monitoring Service (CMEMS). The model component is the NEMO platform driven at the surface by atmospheric conditions from the ECMWF ERA-Interim reanalysis. Ocean observations are assimilated by means of a reduced-order Kalman filter. Along track altimeter sea level anomaly, satellite sea surface temperature and sea ice concentration, as well as in situ temperature and salinity vertical profiles are jointly assimilated. A 3D-VAR scheme provides an additional correction for the slowly-evolving large-scale biases in temperature and salinity. The performance of the reanalysis shows a clear dependency on the time-dependent in situ observation system. The general assessment of GLORYS12 highlights a level of performance at the state-of-the-art and the capacity of the system to capture the main expected climatic interannual variability signals for ocean and sea ice, the general circulation and the inter-basins exchanges. In terms of trends, GLORYS12 shows a higher than observed warming trend together with a slightly lower than observed global mean sea level rise. Comparisons made with an experiment carried out on the same platform without assimilation show the benefit of data assimilation in controlling water mass properties and sea ice cover and their low frequency variability. Moreover, GLORYS12 represents particularly well the small-scale variability of surface dynamics and compares well with independent (non-assimilated) data. Comparisons made with a twin experiment carried out at 1/4° resolution allows characterizing and quantifying the strengthened contribution of the 1/12° resolution onto the downscaled dynamics. GLORYS12 provides a reliable physical ocean state for climate variability and supports applications such as seasonal forecasts. In addition, this reanalysis has strong assets to serve regional applications and provide relevant physical conditions for applications such as marine biogeochemistry. In the near future, GLORYS12 will be maintained to be as close as possible to real time and could therefore provide relevant and continuous reference past ocean states for many operational applications.

Satellite radar altimetry collected during a number of geodetic missions has provided a new understanding of the topography and tectonics of the deep oceans. As altimeter performance and coverage improves, smaller structures are revealed. Here we investigate the contribution of six altimeter missions that have been placed into geodetic mapping phases for more than one year. Two types of evaluations are performed. We first compare the composite (all six altimeters) grids of east and north vertical deflection to matching grids where one altimeter has been omitted evaluate their contribution versus latitude. We then estimate the noise in each altimeter by computing the median absolute deviation of the profiles with the best composite grid. Both analyses show that SARAL/AltiKa provides the greatest contribution and ERS-1 no longer provides any significant improvement. The major limitation for recovering small scale gravity features is the sea surface roughness from ocean waves. There have been steady improvements in instrumentation and processing methods that will continue into the future with higher frequency radars and interferometric swath altimeters planned for future missions. [ABSTRACT FROM AUTHOR]

Recent investigations suggest that global warming is likely to alter temperature regimes along the southeastern coastline of South Africa through the increased frequency of upwelling events. Identifying thermal thresholds is fundamental in predicting the response of marine ectotherms to rapidly changing ocean temperatures. The aim of this study was to determine the thermal tolerance of the endemic sparid Boopsoidea inornata. To achieve this, 20 wild fish were captured from near Noordhoek in Gqeberha (Port Elizabeth). The fish were exposed to laboratory-simulated upwelling and heat-plume conditions until sublethal endpoints were identified to estimate the critical lower (CTmin) and critical upper (CTmax) thermal limits, respectively. During the simulated cooling or heating events, the opercular beat (OB) rates were recorded, their sublethal endpoints (loss of equilibrium) were identified, and their CTmin and CTmax were estimated. Breakpoint analyses of the OB rates identified the lower and upper thermal stress limits to occur at an average of 9 °C and 25 °C, respectively. The CTmin was estimated to be 7.8 °C and the CTmax 30 °C. When compared with in situ temperatures, these limits suggest that B. inornata is susceptible to small reductions in the minimum temperature. Given that the frequency and magnitude of upwelling events are expected to increase in response to global warming, this may have significant consequences for this and other sympatric, resident species. [ABSTRACT FROM AUTHOR]

A major uncertainty in Antarctica's contribution to future sea‐level rise is the ice sheet response timescales to ocean warming. Totten Glacier drains a region containing 3.9 m global sea level equivalent and has been losing mass over recent decades. We use an ice sheet model coupled to an ice‐shelf cavity combined ocean box and plume model to investigate Totten's response to variable ocean forcing. Totten's grounding line is stable for a limited range of ocean temperatures near current observations (i.e., −0.95°C to −0.75°C), with topography influencing the discharge periodicity. For increases of ≥0.2°C in temperatures beyond this range, grounding line retreat occurs. Variable ocean forcing can reduce retreat relative to constant forcing, and different variability amplitudes can cause centennial‐scale delays in retreat through interactions with topography. Our results highlight the need for long‐term ocean state observations and to include forcing variability in ice sheet model simulations of future change. Plain Language Summary: Antarctica's contribution to future sea‐level rise is dominated by uncertainties in how the ice sheet will respond to ocean warming. Totten Glacier, East Antarctica, currently contributes to sea‐level rise and is the major outlet glacier in a region with potential to significantly raise sea levels. We use an ice sheet model coupled to a combined box and plume ocean model to investigate how variability in ocean temperatures can impact ice mass loss in this region. For scenarios of ocean temperatures that are near observed, the grounding line position is close to its present‐day location. In these scenarios, interactions between the ice shelf and topography are important in controlling the timing between peak ice shelf melting and peak mass changes. For small increases in background ocean temperature, we see grounding line retreat. In these scenarios, variability in ocean temperatures can reduce ice flux across the grounding line compared with when the ocean temperature is constant. Certain amplitudes of variability can delay grounding line retreat by centuries through interactions with the topography. This highlights the need for long‐term ocean observations in this region and to include ocean variability in ice sheet model simulations of future change. Key Points: Totten's grounding line is steady and close to present‐day only for current ocean temperatures and retreats for small temperature increasesOcean variability of various amplitudes can reduce discharge and cause centennial scale delays in grounding line migrationForcing variability needs to be taken into account in ice sheet model simulations of future climate change [ABSTRACT FROM AUTHOR]

Increased ocean‐to‐ice heat fluxes play a key role in the accelerated mass loss of Greenland's marine‐terminating glaciers. Ocean current variability leads to variations in this heat flux. A year‐long time series of ocean currents at all gateways to the ocean cavity under Greenland's largest remaining floating ice tongue at the Nioghalvfjerdsfjorden Glacier (79NG) was analyzed. The variability of the exchange flow at intra‐annual to near‐daily timescales was characterized. The currents exhibit considerable variability with standard deviations exceeding the time mean flow strength by a factor of 2. The inflow of warm Atlantic Intermediate Water into the cavity and the outflow via the northernmost calving front were directly coupled on intra‐annual timescales (periods, T > 30 days) with enhanced fluctuations in the winter months. A strong correlation between the variability of the deep inflow and currents in the subsurface boundary current on the continental shelf suggests a link between cavity and continental shelf circulation. Variability on higher frequencies (T < 30 days) in the outflow was only partly induced by the inflow variability. Two export branches of the cavity circulation were identified, which were potentially constrained by subglacial meltwater channels. The relative importance of the two export branches varies on monthly time scales. This research has provided evidence that the large intra‐annual ocean current variability at the 79NG is strongly influenced by the continental shelf circulation. Temporally varying preferred export routes increase the complexity of the cavity circulation. Plain Language Summary: The 79 North Glacier (79NG) in northeastern Greenland has the largest remaining floating ice tongue in Greenland. Like many others, the glacier tongue is melting, likely due to rising ocean temperatures. The amount of heat available for melting varies with the ocean temperatures and velocities supplying the cavity below the tongue with heat from the ocean. We wanted to better understand how and why the ocean speeds at the 79NG varied. Therefore, we deployed sensors that measured ocean velocities, temperature, and salinity next to the calving fronts between August 2016 and September 2017. We found that the ocean velocities varied strongly on timescales from several months to days. Comparing the variability at different gateways to the cavity revealed that more than half of the warm water flowing into the cavity is transported out via the calving front to the north. We showed that the variability in the inflow to the cavity is connected to the ocean currents transporting the warm water masses to the glacier from the continental shelf. This connection means that changes in the ocean currents several hundred kilometers away from the 79NG can have an impact on its melting. Key Points: Ocean exchange flow at the 79 North Glacier exhibits considerable variability with standard deviations twice as large as the time mean flowCoherent, intra‐seasonal fluctuations of the main ocean exchange flow across the calving fronts is enhanced in wintertimeIntra‐annual variability in the Atlantic water flow velocities at the glacier and upstream on the continental shelf co‐vary at zero lag [ABSTRACT FROM AUTHOR]

Numerous indicators show that multi-annual and longer oceanic baroclinic variability retains a complicated spatial structure out to decades and longer. With time-averaging, the sub-basin scales connected to abyssal topography and meteorological structures emerge in the fields. Here, using 26-years of an oceanic state estimate (ECCO), an attempt is made to extract simpler patterns from the vertical average (whole water column) annual mean temperature anomalies and, separately, the vertical structures at each horizontal position. Singular vectors (SVs)/empirical orthogonal functions (EOFs) successfully simplify vertical and horizontal fields, but principal observation patterns (POPs) do not do so. About 3 horizontal spatial patterns account for more than 95% of the interannual and longer variances. A breakdown of the purely vertical structure at each grid point leads in contrast to an intricate variability with depth. Results have implications both for future sampling strategies, and for estimates, e.g. of the accuracy of any mean oceanic scalar. [ABSTRACT FROM AUTHOR]

The Mediterranean community represented in this paper is the result of more than 30 years of EU and nationally funded coordination, which has led to key contributions in science concepts and operational initiatives. Together with the establishment of operational services, the community has coordinated with universities, research centers, research infrastructures and private companies to implement advanced multi-platform and integrated observing and forecasting systems that facilitate the advancement of operational services, scientific achievements and mission-oriented innovation. Thus, the community can respond to societal challenges and stakeholders needs, developing a variety of fit-for-purpose services such as the Copernicus Marine Service. The combination of state-of-the-art observations and forecasting provides new opportunities for downstream services in response to the needs of the heavily populated Mediterranean coastal areas and to climate change. The challenge over the next decade is to sustain ocean observations within the research community, to monitor the variability at small scales, e.g., the mesoscale/submesoscale, to resolve the sub-basin/seasonal and inter-annual variability in the circulation, and thus establish the decadal variability, understand and correct the model-associated biases and to enhance model-data integration and ensemble forecasting for uncertainty estimation. Better knowledge and understanding of the level of Mediterranean variability will enable a subsequent evaluation of the impacts and mitigation of the effect of human activities and climate change on the biodiversity and the ecosystem, which will support environmental assessments and decisions. Further challenges include extending the science-based added-value products into societal relevant downstream services and engaging with communities to build initiatives that will contribute to the 2030 Agenda and more specifically to SDG14 and the UN's Decade of Ocean Science for sustainable development, by this contributing to bridge the science-policy gap. The Mediterranean observing and forecasting capacity was built on the basis of community best practices in monitoring and modeling, and can serve as a basis for the development of an integrated global ocean observing system.

In the last 10 years, new monitoring and modelling technologies have emerged allowing real-time observation and forecasting of the coastal ocean at regional and local scales. These technologies are at the core of multi-platform integrated observing and forecasting systems, such as the Balearic Islands Coastal Ocean Observing and Forecasting System (SOCIB). New capabilities to characterise the state of the ocean and its variability at finer spatial and temporal scales are emerging, supporting science and products for society. SOCIB has a well-defined mission to deliver ocean observing for the benefit of science and society. From initiation in 2010, SOCIB has provided high-quality, free and open data. In order to increase our utility, we developed a Products and Services Strategy rooted in business best practice. Ten sectors – groups of users with common data needs – were identified, for which SOCIB has information and knowledge of high value. Dedicated products were developed in cooperation with the end-users: beach lifeguards/managers and sustainable marine resources managers. We illustrate an integrative approach, combining business concepts with collaborative software development methodologies and ocean observing science, to turn ocean observations and forecasts into products and services, with benefits for society in the sustainable blue economy era. [ABSTRACT FROM AUTHOR]

In 2010–2011, three projects combined to characterize the temporal and spatial distributions of Modified Circumpolar Deep Water (MCDW) in the Ross Sea using icebreaker-based sampling, gliders, instrumented seals, and hindcasts from a numerical circulation model. The fieldwork clearly identified MCDW throughout the Ross Sea, and the data were used to determine its influence on potential heat and nutrient inputs and biotic distributions. Furthermore, the numerical simulations confirm its apparent trajectory and location. Substantial small-scale variability in oceanographic and biological distributions suggests that such variability may play an important role in biogeochemical cycles. Data from the three projects provide a view of hydrographic variability in the Ross Sea that is impossible to obtain using traditional sampling. Multiplatform investigations are promising approaches to future polar experiments where logistical considerations are of paramount importance.

Investigating the variability of Agulhas leakage, the volume transport of water from the Indian Ocean to the South Atlantic Ocean, is highly relevant due to its potential contribution to the Atlantic Meridional Overturning Circulation as well as the global circulation of heat and salt and hence global climate. Quantifying Agulhas leakage is challenging due to the non-linear nature of this process; current observations are insufficient to estimate its variability and ocean models all have biases in this region, even at high resolution . An Eulerian threshold integration method is developed to examine the mechanisms of Agulhas leakage variability in six ocean model simulations of varying resolution. This intercomparison, based on the circulation and thermohaline structure at the Good Hope line, a transect to the south west of the southern tip of Africa , is used to identify features that are robust regardless of the model used and takes into account the thermohaline biases of each model. When determined by a passive tracer method, 60 % of the magnitude of Agulhas leakage is captured and more than 80 % of its temporal fluctuations, suggesting that the method is appropriate for investigating the variability of Agulhas leakage. In all simulations but one, the major driver of variability is associated with mesoscale features passing through the section. High resolution ( $${<} 1/10^{\circ }$$ ) hindcast models agree on the temporal (2-4 cycles per year) and spatial (300-500 km) scales of these features corresponding to observed Agulhas Rings. Coarser resolution models ( $${<} 1/4^{\circ }$$ ) reproduce similar time scale of variability of Agulhas leakage in spite of their difficulties in representing the Agulhas rings properties. A coarser resolution climate model ( $$2^{\circ }$$ ) does not resolve the spatio-temporal mechanism of variability of Agulhas leakage. Hence it is expected to underestimate the contribution of Agulhas Current System to climate variability. [ABSTRACT FROM AUTHOR]

Explosive cyclones are intense extra-tropical low pressure systems featuring large deepening rates. In the Euro-Atlantic sector, they are a major source of life-threatening weather impacts due to their associated strong wind gusts, heavy precipitation and storm surges. The wintertime variability of the North Atlantic cyclonic activity is primarily modulated by the North Atlantic Oscillation (NAO). In this study, we investigate the interannual and multi-decadal variability of explosive North Atlantic cyclones using track density data from two reanalysis datasets (NCEP and ERA-40) and a control simulation of an atmosphere/ocean coupled General Circulation Model (GCM-ECHAM5/MPIOM1). The leading interannual and multi-decadal modes of variability of explosive cyclone track density are characterized by a strengthening/weakening pattern between Newfoundland and Iceland, which is mainly modulated by the NAO at both timescales. However, the NAO control of interannual cyclone variability is not stationary in time and abruptly fluctuates during periods of 20-25 years long both in NCEP and ECHAM5/MPIOM1. These transitions are accompanied by structural changes in the leading mode of explosive cyclone variability, and by decreased/enhanced baroclinicity over the sub-polar/sub-tropical North Atlantic. The influence of the ocean is apparently important for both the occurrence and persistence of such anomalous periods. In the GCM, the Atlantic Meridional Overturning Circulation appears to influence the large-scale baroclinicity and explosive cyclone development over the North Atlantic. These results permit a better understanding of explosive cyclogenesis variability at different climatic timescales and might help to improve predictions of these hazardous events. [ABSTRACT FROM AUTHOR]

Velocity data from 81 globally distributed current meters are used to characterize the vertical structure of ocean current fluctuations. The primary empirical orthogonal functions from most of the moorings are similar, decreasing monotonically with depth to a value near zero at the bottom. This contrasts with the standard barotropic (BT) and baroclinic (BC) modes, which have flow at the bottom. However, the structure is very similar to the first baroclinic (BC1) mode with zero horizontal flow at the bottom, as is appropriate over a rough or steeply sloping bottom. This mode captures a greater fraction of the observed variance than the standard flat bottom BC1 mode. Also, an analytical approximation of the first mode, obtained assuming exponential stratification, is as accurate as the numerically generated BC mode. This suggests a simple way to project surface velocities into the interior. [ABSTRACT FROM AUTHOR]

Abstract: The ice-loaded Labrador Current (LC) is an important component of the western North Atlantic circulation that influences the position and strength of the northern limb of the North Atlantic Current (NAC). This flow of cold and fresh Polar Waters originating from the Arctic has a marked impact on the North Atlantic climate, yet little is known about its variability beyond the instrumental period. In this study, we present the first sub-decadal alkenone-based 2000-year long sea-surface temperature (SST) records from the western Labrador Sea, a climatically crucial region at the boundary between the LC and the NAC. Our results show a clear link between the LC strength and the Northern Annular Mode (NAM), with a stronger NAM and a more vigorous LC during the Medieval Climate Anomaly (MCA). This suggests enhanced LC activity upon future global warming with implications for the Atlantic meridional overturning circulation (AMOC). [Copyright &y& Elsevier]

The North Atlantic and Europe experienced two extreme climate events in 2015: exceptionally cold ocean surface temperatures and a summer heat wave ranked in the top ten over the past 65 years. Here, we show that the cold ocean temperatures were the most extreme in the modern record over much of the mid-high latitude North-East Atlantic. Further, by considering surface heat loss, ocean heat content and wind driven upwelling we explain for the first time the genesis of this cold ocean anomaly. We find that it is primarily due to extreme ocean heat loss driven by atmospheric circulation changes in the preceding two winters combined with the re-emergence of cold ocean water masses. Furthermore, we reveal that a similar cold Atlantic anomaly was also present prior to the most extreme European heat waves since the 1980s indicating that it is a common factor in the development of these events. For the specific case of 2015, we show that the ocean anomaly is linked to a stationary position of the Jet Stream that favours the development of high surface temperatures over Central Europe during the heat wave. Our study calls for an urgent assessment of the impact of ocean drivers on major European summer temperature extremes in order to provide better advance warning measures of these high societal impact events.

Using the National Center for Atmospheric Research Community Climate System Model Version 3.5, this paper examines the climatic effects of afforestation in the East China monsoon region with a focus on land-atmosphere interactions and the modulating influence of ocean variability. In response to afforestation, the local surface air temperature significantly decreases in summer and increases in winter. The summer cooling is attributed to enhanced evapotranspiration from increased tree cover. During winter, afforestation induces greater roughness and weaker winds over the adjacent coastal ocean, leading to diminished latent heat flux and increased sea-surface temperature (SST). The enhanced SST supports greater atmospheric water vapor, which is accompanied by anomalous wind, and transported into the East China monsoon region. The increase in atmospheric water vapor favors more cloud cover and precipitation, especially in the eastern afforestation region. Furthermore, the increase in atmospheric water vapor and cloud cover produce a greenhouse effect, raising the wintertime surface air temperature. By comparing simulations in which ocean temperature are either fixed or variable, we demonstrate that a significant hydrologic response in East China to afforestation only occurs if ocean temperatures are allowed to vary and the oceanic source of moisture to the continent is enhanced. [ABSTRACT FROM AUTHOR]

This article focuses on the determination and the validation of the new Mean Sea Surface from the CNES/CLS. This new model merges multiple satellite altimeters over 16 years of observations. Particular attention was paid on the analysis of the oceanic variability. Then a novel method was applied to remove this variability and to take into account different kinds of errors that affect the data. Several types of validations were performed to estimate the quality of the shortest topographic structures and to quantify the accuracy of the mean oceanic content at a larger scale. [ABSTRACT FROM AUTHOR]

Summary: Reconstructions of hydrologic variables are commonly created using tree-ring chronologies. Incorporating climate signals and regionally specific sea surface temperature (SST) indices can greatly improve reconstructive skill. This study performed several reconstructions in the Upper Green River Basin (UGRB), located in the northern portion of the Upper Colorado River Basin. Reconstructed snowpack (April 1st snow water equivalent (SWE)) for the UGRB will provide information on the long-term variability of snowpack and assist in determining the effectiveness of current weather modification efforts. Previous attempts to reconstruct regional snowpack in the UGRB were unsuccessful due to a limited number of tree-ring chronologies. This study increased the number of stations used to represent regional SWE and expanded the spatial area of the study. This resulted in the first reconstruction of UGRB SWE using tree-ring chronologies (R 2 =0.34). Next, the predictor variable pool is increased by adding climate signals (Southern Oscillation Index (SOI), Pacific Decadal Oscillation (PDO)) and Pacific Ocean SSTs from regions that were determined to be teleconnected with UGRB SWE. Singular value decomposition (SVD) was performed on Pacific Ocean SSTs and UGRB SWE to identify coupled regions of climate (SSTs) and hydrology (SWE). Stepwise linear regression was used to identify the best predictor combinations. Including climate data (SOI) in the model improved the R 2 value from 0.34 to 0.57. The addition of Pacific Ocean SST data further improved the skill of the model (R 2 =0.63). Reconstructions using Pacific Ocean SST data identified by SVD and climate signals explained a higher degree of SWE variance than reconstructions using tree-ring chronologies and climate data, indicating that Pacific Ocean SSTs and climate signals are useful predictors for snowpack reconstruction in the UGRB. This methodology is transferable to other regions. [Copyright &y& Elsevier]

The first results on simulating the intra-annual variability of the World Ocean circulation by use of the eddy-resolving model are considered. For this purpose, a model of the World Ocean with a 1/10° horizontal resolution and 49 vertical levels was developed (a 1/10 × 1/10 × 49 model of the World Ocean). This model is based on the traditional system of three-dimensional equations of the large-scale dynamics of the ocean and boundary conditions with an explicit allowance for water fluxes on the free surface of the ocean. The equations are written in the tripolar coordinate system. The numerical method is based on the separation of the barotropic and baroclinic components of the solution. Discretization in time is implemented using explicit schemes allowing effective parallelization for a large number of processors. The model uses the sub-models of the boundary layer of the atmosphere and the submodel of sea-ice thermodynamics. The model of the World Ocean was developed at the Institute of Numerical Mathematics of the Russian Academy of Sciences (INM RAS) and the P.P. Shirshov Institute of Oceanogy (IO RAS). The formulation of the problem of simulating the intra-annual variability of thermohydrodynamic processes of the World Ocean and the parameterizations that were used are considered. In the numerical experiment, the temporal evolution of the atmospheric effect is determined by the normal annual cycle according to the conditions of the international Coordinated Ocean-Ice Reference Experiment (CORE-I). The calculation was carried out on a multiprocessor computer with distributed memory; 1601 computational cores were used. The presented analysis demonstrates that the obtained results are quite satisfactory when compared to the results that were obtained by other eddy-resolving models of the global ocean. The analysis of the model solution is, to a larger extent, of a descriptive character. A detailed analysis of the results is to be presented in following works. This experiment is a significant first step in developing the eddy-resolving model of the World Ocean. [ABSTRACT FROM AUTHOR]

Ocean bottom pressure (OBP) from the Gravity Recovery and Climate Experiment (GRACE) and the Ocean Model for Circulation and Tides (OMCT) are compared globally with OBP computed from altimetry corrected for steric variations from Argo floats from January 2005 to December 2007. Two methods of smoothing the GRACE data are examined. The first uses a standard Gaussian smoother with a radius of 300 km. The second method projects those smoothed maps onto empirical orthogonal functions derived from OMCT in a least squares estimation in order to produce maps that better agree with the physical processes embodied by the model. These new maps agree significantly better with estimates from the steric-corrected altimetry, reducing the variance on average by 30% over 70% of the ocean. This is compared to smaller reductions over only 14% of the ocean using the 300-km Gaussian maps and 56% of the ocean using OMCT maps. The OMCT maps do not reduce variance as much in the Southern Ocean where OBP variations are largest, whereas the GRACE maps do. Based on this analysis, it is estimated that the local, or point-to-point, uncertainty of new EOF filtered maps of GRACE OBP is 1.3 (one standard deviation). [ABSTRACT FROM AUTHOR]

The global and regional climate response to a warming of the Indian Ocean is examined in an ensemble of atmospheric general circulation model experiments. The most marked changes occur over the Indian Ocean, where the increase in tropical SST is found to drive enhanced convection throughout the troposphere. In the extratropics, the warming Indian Ocean is found to induce a significant trend toward the positive phase of the northern annular mode and also to enhance the Southern Hemisphere storm track over Indian Ocean longitudes as a result of stronger meridional temperature gradients. Convective outflow in the upper levels over the warming Indian Ocean leads to a trend in subsidence over the Indian and Asian monsoon regions extending southeastward to Indonesia, the eastern Pacific, and northern Australia. Regional changes in Australia reveal that this anomalous zone of subsidence induces a drying trend in the northern regions of the continent. The long-term rainfall trend is exacerbated over northeastern Australia by the anomalous anticyclonic circulation, which leads to an offshore trend in near-surface winds. The confluence of these two factors leads to a drying signal over northeastern Australia, which is detectable during austral autumn. The rapid, late twentieth-century warming of the Indian Ocean may have contributed to a component of the observed drying trend over northeastern Australia in this season via modifications to the vertical structure of the tropical wind field. [ABSTRACT FROM AUTHOR]

Rainfall variability over the Amazon basin has often been linked to variations in Pacific sea surface temperature (SST), and in particular, to the El Niño/Southern Oscillation (ENSO). However, only a fraction of Amazon rainfall variability can be explained by ENSO. Building upon the recent work of Zeng (Environ Res Lett 3:014002, ), here we provide further evidence for an influence on Amazon rainfall from the tropical Atlantic Ocean. The strength of the North Atlantic influence is found to be comparable to the better-known Pacific ENSO connection. The tropical South Atlantic Ocean also shows some influence during the wet-to-dry season transition period. The Atlantic influence is through changes in the north-south divergent circulation and the movement of the ITCZ following warm SST. Therefore, it is strongest in the southern part of the Amazon basin during the Amazon’s dry season (July–October). In contrast, the ENSO related teleconnection is through anomalous east-west Walker circulation with largely concentrated in the eastern (lower) Amazon. This ENSO connection is seasonally locked to boreal winter. A complication due to the influence of ENSO on Atlantic SST causes an apparent North Atlantic SST lag of Amazon rainfall. Removing ENSO from North Atlantic SST via linear regression resolves this causality problem in that the residual Atlantic variability correlates well and is in phase with the Amazon rainfall. A strong Atlantic influence during boreal summer and autumn is particularly significant in terms of the impact on the hydro-ecosystem which is most vulnerable during the dry season, as highlighted by the severe 2005 Amazon drought. Such findings have implications for both seasonal-interannual climate prediction and understanding the longer-term changes of the Amazon rainforest. [ABSTRACT FROM AUTHOR]

Global mean temperature at the Earth's surface responds both to externally imposed forcings, such as those arising from anthropo- genic greenhouse gases, as well as to natural modes of variability internal to the climate system. Variability associated with these latter processes, generally referred to as natural long-term climate variability, arises primarily from changes in oceanic circulation. Here we present a technique that objectively identifies the com- ponent of inter-decadal global mean surface temperature attrib- utable to natural long-term climate variability. Removal of that hidden variability from the actual observed global mean surface temperature record delineates the externally forced climate signal, which is monotonic, accelerating warming during the 20th century. [ABSTRACT FROM AUTHOR]

Abstract: Daily observations of sea-surface temperature (SST) have been acquired at the southern end of Monterey Bay in Pacific Grove, California since 1919. It is one of the longest oceanographic records off the west coast of North America. The record is examined to determine the major sources of variability in Monterey Bay and beyond, on time scales from seasonal to interdecadal. On seasonal time scales, the spring transition to coastal upwelling, often a major event along the coast of central California, is not well-expressed inside the bay but is detectable, occurring, on average, between mid-March and mid-April. The onset of the Davidson Current in Monterey Bay is well-defined, occurring, on average, in mid-October, ±2–3 weeks. Intraseasonal changes also occur during the spring and summer that may correspond to intrusions of warmer offshore waters into Monterey Bay. Intraseasonal oscillations with periods in the range of 40–50 days occur in Monterey Bay, but compared to their signature along the open coast, their event-like behavior is modified. The annual cycle of surface temperature in Monterey Bay is asymmetric with seasonal warming occurring during the spring and summer, and cooling during the fall. This asymmetry is primarily due to the net surface heat exchange which is positive for most of the year, and, to a lesser extent, the influence cold upwelled waters that are advected into the bay during the spring and summer, observations supported by a simple model that combines both the net surface heat exchange and thermal advection. On interannual time scales, the influence of El Niño warming events is strong. A comparison with the Northern Oscillation Index (NOI) using Singular Spectrum Analysis (SSA), shows that the El Niño signal is often as strong in SST at Pacific Grove as it is in the NOI. On interdecadal time scales, the influence of the Pacific Decadal Oscillation (PDO) is also relatively strong in Monterey Bay, again based on SSA. The integrated anomaly was calculated from the record and reveals regime shifts in Monterey Bay that occurred in 1929, an event that was apparently regional in scale, reflecting a transition from unusually cold to warmer conditions, and the regime change in the PDO that occurred in 1976. Each regime change can be approximated by a step-wise increase in temperature. Finally, linear trends were estimated for the entire record (∼+0.01°C/year), and for the 72-year period from 1930 to 2001 (+0.0042°C/year), i.e., following the regional regime change in 1929. The estimated trend for the last 72 years is not statistically significant; however, it is in close agreement with the long-term trend for the Intergovernmental Panel on Climate Change (IPCC) record of global surface temperature that spans almost 140 years (∼+0.005°C/year). Although the long-term increase in SST at Pacific Grove appears to be consistent with global warming, the integrated anomaly suggests that temperature increases in Monterey Bay have occurred rather abruptly and thus it becomes more difficult to invoke the global warming scenario. Finally, based on the monthly averaged data, the annual cycle, El Niño warming episodes, the PDO, the long-term trend, and the semiannual cycle account for approximately 44%, 18%, 6%, 4%, and 3% of the total variance, respectively, in SST at Pacific Grove. [Copyright &y& Elsevier]

This paper proposes a genetic algorithm (GA) for path planning of an autonomous underwater vehicle in an ocean environment characterized by strong currents and enhanced space-time variability. The goal is to find a safe path that takes the vehicle from its starting location to a mission-specified destination, minimizing the energy cost. The GA includes novel genetic operators that ensure the convergence to the global minimum even in cases where the structure (in space and time) of the current field implies the existence of different local minima. The performance of these operators is discussed. The proposed algorithm is suitable for situations in which the vehicle has to operate energy-exhaustive missions. [ABSTRACT FROM AUTHOR]

This is a synthesis of published and unpublished research on euphausiid and fish populations using the south-west coast of Vancouver Island. Overall, the studies covered 1985–98, when there were two ENSO events and considerable variation in upwelling. The population biology of the dominant euphausiids (Thysanoessa spinifera , Euphausia pacifica ) was monitored during 1991–98. The species abundance trends differed. Results of simple correlation analyses suggested that variations in temperature, salinity and upwelling do not explain variations in the abundance of larval or adult euphausiids, or in the abundance of portions of euphausiid populations on which fish feed. I found significant interannual variations in daily ration of the dominant planktivorous fish species, but euphausiids remained the most important prey. Pacific hake (Merluccius productus ), the dominant planktivore, fed on larger (>17 mm) T. spinifera , even though the biomass of this part of the euphausiid biomass decreased by 75% between 1991 and 1997, but Pacific herring (Clupea pallasi ) may have begun feeding on smaller E. pacifica . Therefore, any study of the relationship between fish production and krill biology must consider that part of the euphausiid biomass exploited by fish. In addition, some fish species and/or life history stages appeared to adapt to changes in euphausiid availability, while others did not. Such variation in adaptations also has to be described and considered to understand how changes in euphausiid biology affect fish productivity. [ABSTRACT FROM AUTHOR]

Six years of quasi-meridional crossings of the Antarctic Ocean from Antarctica to southern Africa between 4°W and 16°E longitude are analyzed, with emphasis on temperature and salinity distributions. Data are sparse, but (particularly in the southern part of the sections) adequate to show significant variations in the latitude/depth distributions and T-S characteristics of the principal water masses. In particular, the cross-sectional area occupied by Warm Deep Water ( Weddell Deep Water) dropped by about one third in 1968. Positions of major features associated with the Antarctic Divergence varied by up to 5 degrees of latitude. The surface temperature gradient often observed at the Antarctic Divergence appears to be the surface expression of a shallow (possibly seasonal) thermocline which sometimes slopes upward to intersect the sea surface. There is a clear need for more closely spaced and consistently planned data from Antarctic cruises, particularly those on which physical oceanography is an ancillary activity. As a bare minimum, much more closely spaced surface temperature (and if possible also salinity) measurements would be useful. [ABSTRACT FROM AUTHOR]

Argo, an international, global observational array of nearly 4,000 autonomous robotic profiling floats, each measuring ocean temperature and salinity from 0 to 2,000 m on nominal 10-day cycles, has revolutionized physical oceanography. Argo started at the turn of the millennium,growing out of advances in float technology over the previous several decades. After two decades, with well over 2 million profiles made publicly available in real time, Argo data have underpinned more than 4,000 scientific publications and improved countless nowcasts, forecasts, and projections. We review a small subset of those accomplishments, such as elucidating remarkable zonal jets spanning the deep tropical Pacific; increasing understanding of ocean eddies and the roles of mixing in shaping water masses and circulation; illuminating interannual to decadal ocean variability; quantifying, in concert with satellite data, contributions of ocean warming and ice melting to sea level rise; improving coupled numerical weather predictions; and underpinning decadal climate forecasts.