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Because of the difficulties in tracking a water mass over time and conducting synoptic surveys over large spatial scales, measurements of biological variables in the ocean are often restricted to isolated Eulerian observations. Here a proof‐of‐concept of a pseudo‐Lagrangian transformation was applied to a time series of chlorophyll‐a profiles acquired at a single fixed station to diagnose the shape of a phytoplankton patch, and its physical‐biological rates of transformation. During August 2013, a 27‐hr time series of observations of horizontal currents, hydrographic properties, turbulent mixing and chlorophyll‐a was acquired at a central station of the Ría de Vigo (NW Iberian Peninsula). A chlorophyll‐a patch, tilted upward toward the inner part of the Ría, was observed moving back and forth past the sampling station. Its shape and position during the sampling period were modulated by the semi‐diurnal (M2) tidal currents and the vertically sheared upwelling circulation. The pseudo‐Lagrangian transformation allowed estimation of chlorophyll‐a net rates of change. These rates were positive between 12 and 14 m depth, and negative elsewhere, with a mean value of −0.001 ± 0.449 days−1 within the patch maximum. After accounting for the effects of diffusion and sinking, the mean net biological production rate in the upper 15 m (0.53 ± 0.25 days−1) was comparable with in vitro estimates of the balance between phytoplankton growth and mortality obtained from dilution experiments carried out under similar conditions (0.2 ± 0.7 days−1). This pseudo‐Lagrangian transformation is complementary to traditional analyses for the quantification of ecological processes and biogeochemical budgets. Plain Language Summary: Oceanography distinguishes two ways to make observations: Eulerian and Lagrangian. Eulerian approaches measure properties at fixed locations in space as a function of time as water flows past the instrument. In contrast, Lagrangian approaches quantify temporal changes in fluid parcels while following the flow. Isolated Eulerian observations are the most common approach to investigate biological properties. However, temporal variations in Eulerian observations result from combinations of physical and biological processes whose effects are often difficult to separate. We applied a pseudo‐Lagrangian methodology to reconstruct the spatial structure of a phytoplankton (microscopic algae) patch observed at a single station in a coastal embayment. Because the flow was dominated by tidal currents, some water parcels were sampled multiple times, allowing to compute the rate of change of properties in the phytoplankton patch. Biological production, or the rate of change due to biological processes, was comparable with traditional estimates from in vitro experiments performed in the region under similar hydrographic conditions. Our findings show that the pseudo‐Lagrangian transformation is a useful complement to data obtained from traditional analyses for the quantification of ecological processes and biogeochemical budgets. Key Points: A pseudo‐Lagrangian transformation was applied to diagnose the shape of a phytoplankton patchThe pseudo‐Lagrangian transformation allowed estimation of Chl‐a fluorescence net rates of changeNet biological production was comparable with in vitro estimates from dilution experiments under similar hydrographic conditions [ABSTRACT FROM AUTHOR]

Saffir-Simpson Category-4 Typhoon Malakas crossed the Kuroshio, the Western Boundary Current of the North Pacific Ocean, and moved along the path of the Kuroshio for eight days between September 12 and 20, 2016. Malakas induced a 3-4°C sea surface cooling and an increase in sea surface Chlorophyll-a concentration to 0.8 mg/m3. The total cooling area was approximately 18,000 km2. Satellite observations show that Malakas triggered two upwelling regions associated with two mesoscale eddies, both to the northeast of Taiwan. The Regional Oceanic Modeling System (ROMS) was employed to offer insights into the dynamical mechanisms on the ocean response to a typhoon. The numerical model results reveal that a coastal upwelling event was induced by southeasterly winds blowing prior to the arrival of Malakas' outer band, and caused a surface cooling near Taiwan's northeast coast. A branch of the Taiwan Warm Current interacted with the offshore Kuroshio current to form an eddy prior to the typhoon's arrival. Malakas then facilitated the development of the near-coastal eddy. An open ocean eddy was triggered by inertial-Ekman pumping under the forcing effect of Malakas. The interaction between the southward current caused by Malakas and the northeastward flowing Kuroshio maintained these two induced mesoscale eddies. Numerical results show a near-inertial oscillation (IO) of about a 26-h period with an e-folding time scale of ~5 days was magnified and modulated by Malakas. The typhoon-induced oceanic phenomena were very well revealed in this combined observational and numerical modeling study. Plain Language Summary Typhoon Malakas passed through and affected the ocean to the northeast of Taiwan from September 12 to 20, 2016. Two surface cooling regions were observed by geostationary satellites after Typhoon Malakas passed by the area. The revelation of the factors responsible for inducing the oceanic surface cooling is crucial in understanding atmosphere-ocean dynamic processes and managing the local ecosystem resources. A numerical ocean model was employed in an attempt to replicate the oceanic phenomena that were observed. The model results suggest that a coastal upwelling event and an oceanic eddy were induced near the northeast coast of Taiwan prior to the arrival of the typhoon and subsequently enhanced by Malakas. An open ocean eddy was also triggered to the northeast of Taiwan by Malakas. The dynamic balance analyses of numerical model results reveal that inertial-Ekman pumping caused by Malakas was the critical factor in the induction of these phenomena. Eddyinduced upwelling was triggered and subsequently cooled down ocean surface temperatures. In addition, the variant typhoon wind magnified a near-inertial oscillation of about a 26-h period, in the current field, with a ~5-day e-folding time scale, to the northeast of Taiwan, which was imbedded into the growth and decay of the eddies. [ABSTRACT FROM AUTHOR]

The year‐to‐year seasonal variability of the vertical distribution of concentration of chlorophyll‐a (Chla) in the Black Sea, its relation to light (photosynthetically available irradiance [PAR]), and mixing conditions were studied based on the 6‐year (2014–2019) measurements of Bio‐Argo floats. Variations in PAR caused by changes in incoming solar radiation and light attenuation determine the position of the deep chlorophyll maximum (DCM). During all seasons, the DCM was located between isolume of daily integrated PAR of 0.080 and 10.0 mole photons m−2 d−1. Analysis of Bio‐Argo data allowed to distinguish seven different stages of Chla seasonal variability. In February, the minimum of Chla in the entire water column was often observed in areas with a deep mixed layer (Stage 1), followed by the March early spring peak, occupying both the mixed layer and the seasonal thermocline (Stage 2). In April–May, Chla decreased throughout the 0–40 m layer, which was accompanied by the maximum in light penetration and an increase in Chla in the deepest layers (Stage 3). In summer, two deep peaks of Chla were distinguished: the first, a thin and shallow peak in June, and the second, a large and deeper peak in August (Stage 4 and 5). The August peak was followed by the deepest seasonal minimum of Chla in September–October, coincided with the autumn rise of the zooplankton biomass (Stage 6). Autumn–winter convection in November–January led to the third seasonal peak of Chla (Stage 7). The study discusses the role of various abiotic and biotic factors in the formation of each of these stages. Plain Language Summary: Continuous measurements of four Bio‐Argo for more than 5 years floats were used to study in detail the seasonal variability of the vertical distribution of chlorophyll‐a (Chla) in the Black Sea and its relation with different factors. These data allowed us to distinguish seven different stages of Chla vertical distribution, including four seasonal maximums and three minimums. In this article, we investigated and discussed the impact of light, mixing, and grazing on the observed stages of Chla variations in the Black Sea. Key Points: Six years of Bio‐Argo data are used to study vertical distribution of chlorophyll‐a (Chla) and its relation to photosynthetically available irradiance (PAR)Variability of PAR controls the position of Chla maximum, which in all seasons is located between isolumes 3 and 330 µmole photons m−2 s−1Seven stages of Chla are observed, including three seasonal minimums and four maximums; their physical and biological reasons are discussed [ABSTRACT FROM AUTHOR]

This study investigates extreme phytoplankton blooms in the southern tropical Indian Ocean (TIO) in January–April 2011 using the extended ocean color products and in situ data. The amplitude of the blooms was approximately 4 times higher than the climatological value and 2 times higher than that in 1998–1999. The anomalous enhancement of surface chlorophyll‐a concentration (Chla) was associated with the strong upwelling Rossby waves that forced by the extraordinary strong wind stress curl in the southeastern TIO during 2010–2011 La Niña, which was much stronger than that of 1998–1999 La Niña. The Rossby waves uplifted the thermocline, which was shoaled by more than 70 m relative to the climatology. The results of the nonlinear 1.5‐layer reduced‐gravity model further suggest that the thermocline variations are mainly due to the wind stress curl over the interior TIO. In the vertical direction, the Argo data show a distinct upward and westward propagation of subsurface cooling, indicating that the upwelling of cold nutrient‐rich waters leads to the abnormally high Chla. The strong upwelling processes are also well captured by the Moored Array for African‐Asian‐Australian Monsoon Analysis and Prediction observations at 8°S, 80.5°E. Based on the climatological in situ nitrate data, the Rossby wave‐induced nitrate supply and potential new production at the mooring site are estimated. The potential f ratio ranges from 50% to 87% when the water brought to the surface is assumed to have originated from 60 to 200 m, thus indicating the dominant role of nutrient supply by the upwelling processes. Plain Language Summary: Taking advantage of extended ocean color products and observation from Argo and Moored Array for African‐Asian‐Australian Monsoon Analysis and Prediction, this study investigates extreme phytoplankton blooms in the southern TIO during the 2010–2011 La Niña event. The amplitude of the blooms was approximately 4 times higher than the climatological value and 2 times higher than that in another La Niña year 1998–1999. The anomalous enhancement of surface chlorophyll‐a concentration was associated with the strong upwelling Rossby waves that forced by the extraordinary strong wind stress curl in the southeastern TIO during 2010–2011 La Niña. The in situ data reveal the dominant role of Rossby wave‐induced upwelling in triggering the extreme blooms in the southern TIO. Key Points: The extreme high chlorophyll‐a in the southern TIO in 2011 is identified from two‐decade satellite observationThe in situ data reveal the dominant role of Rossby wave‐induced upwelling in triggering the bloomsLa Niña‐induced wind stress curl in the southeastern TIO is much stronger in 2010–2011 than that in 1998–1999, accounting for the Rossby waves [ABSTRACT FROM AUTHOR]

A rapid, high‐resolution shipboard survey, using a combination of lowered and expendable hydrographic measurements and vessel‐mounted acoustic Doppler current profiler data, provided a unique three‐dimensional view of an Arctic anti‐cyclonic cold‐core eddy. The eddy was situated 50‐km seaward of the Chukchi Sea shelfbreak over the 1,000 m isobath, embedded in the offshore side of the Chukchi slope current. The eddy core, centered near 150‐m depth, consisted of newly ventilated Pacific winter water which was high in nitrate and dissolved oxygen. Its fluorescence signal was due to phaeopigments rather than chlorophyll, indicating that photosynthesis was no longer active, consistent with an eddy age on the order of months. Subtracting out the slope current signal demonstrated that the eddy velocity field was symmetrical with a peak azimuthal speed of order 10 cm s−1. Its Rossby number was ~0.4, consistent with the fact that the measured cyclogeostrophic velocity was dominated by the geostrophic component. Different scenarios are discussed regarding how the eddy became embedded in the slope current, and what the associated ramifications are with respect to eddy spin‐down and ventilation of the Canada Basin halocline. Plain Language Summary: A critical feature of the interior Arctic Ocean is the sharp vertical change in salinity between roughly 100‐m to 200‐m depth, known as the cold halocline. This shields the warm Atlantic‐origin water below from mixing upward to the surface and melting the pack ice. The cold halocline is believed to be partially maintained by eddies of cold water emanating from the Chukchi Sea continental shelf. This paper presents measurements from a rapid, high‐resolution shipboard survey of a cold‐core Arctic eddy offshore of the shelf edge, providing a unique three‐dimensional view of the feature. The eddy's core contained water near the freezing point with a high level of nitrate, but the biological activity had largely ceased because the eddy had descended below the part of the water column exposed to sunlight. The eddy was imbedded in the offshore edge of the westward‐flowing Chukchi slope current. Different scenarios are discussed regarding how the eddy became embedded in the slope current, and what the associated ramifications are with respect to disintegration of the eddy and the manner in which the cold water feeds the halocline. Key Points: A rapid, high‐resolution shipboard survey provided a unique 3‐D view of an Arctic anti‐cyclonic cold‐core eddy on the Chukchi slopeThe winter water in the core contained high levels of nitrate, but the biological activity had largely ceased due to lack of sunlightThe eddy was imbedded in the seaward edge of the Chukchi slope current and likely formed in the vicinity of Barrow Canyon [ABSTRACT FROM AUTHOR]

The occurrence of phytoplankton blooms in estuarine and coastal waters is codetermined by the export of fluvial nutrients and other water properties such as turbidity. In this study, the Changjiang River Estuary was used as an example to investigate the intrinsic link between river plume dynamics, riverine nutrient loading, suspended sediment concentration, and phytoplankton blooms with a coupled hydrodynamic‐sediment‐ecosystem numerical model. Suspended sediment concentration from the sediment module was used to parameterize light attenuation in waters, which, in association with river plume dynamics, was found to impact phytoplankton distribution. Data that was collected in situ, in addition to satellite data for chlorophyll, nutrients, and suspended sediments, were used to validate the model, which performed well. The surface high chlorophyll centers exhibited a patch‐like pattern from the northeast to the south off the Changjiang River mouth. The high chlorophyll concentration within the river plume was mainly determined by riverine nutrient exports, and potential phosphate limitation occurred away from the river mouth. The chlorophyll concentration decreased dramatically shoreward of the sediment front, which was controlled by the bottom river plume front. The bottom plume front was an intrinsic feature of the Changjiang River plume and similar river plume systems, which set a boundary separating the well‐mixed (turbid) nearshore waters and stratified (clear) offshore waters. Without considering the sediment shading effect, the model yielded an unrealistic chlorophyll distribution with artificially high values in the turbid area. This indicated that light attenuation was a key factor limiting phytoplankton blooms in turbid river estuaries. Plain Language Summary: In estuaries and coastal waters, the aquatic environment is affected by both riverine nutrient input and water properties such as turbidity. The associated river plume may play an essential role in controlling water properties, thus influencing the aquatic environment such as the algal blooms. In the current study, a well‐validated hydrodynamic‐sediment‐ecosystem model was used to simulate phytoplankton blooms and the dynamic link with the Changjiang River plume. The results showed that the surface suspended sediment front was of vital importance in determining the shoreward boundary of the phytoplankton bloom area. Light attenuation due to high turbidity became a major factor limiting phytoplankton blooms in turbid nearshore waters. In environments with a strong tidal influence, the surface suspended sediment front was closely related to the bottom river plume front, which gave rise to differences in water stabilization and thus resulted in turbid conditions on either side. The results of this study provided a good reference for understanding the phytoplankton distribution characteristics in estuaries with high turbidity. Key Points: High chlorophyll concentrations are located seaward of the surface suspended sediment front in the Changjiang River plume areaThe surface suspended sediment front is controlled by the bottom plume front seaward of which the water is stratifiedLight attenuation due to high turbidity limits phytoplankton blooms in turbid nearshore waters [ABSTRACT FROM AUTHOR]

The article discusses a study in which a global Earth system model (ESM) is used to predict seasonal to multiannual marine ecosystem or chlorophyll fluctuations. Topics include the anticipation of interannual fish-catch variations in selected large marine ecosystems from predicted chlorophyll and sea surface temperature anomalies, and the use of ESM-based marine biogeochemical predictions for dynamic marine resource management.

Abstract The dynamics of nutrients, phytoplankton, zooplankton and water clarity of the iconic Great Barrier Reef World Heritage Area (GBRWHA) are influenced by seasonal variation in coastal and oceanic conditions, and anthropogenic inputs. We use the 3-dimensional coupled catchment-hydrodynamic-sediment-wave-optical-biogeochemical eReefs model to hindcast nutrient and planktonic responses to changes in seasonal and annual variability over a six-year period (2011–2016). In this paper we present a comparison of the eReefs model conducted against a range of in situ observations that included 24 water quality moorings, 2 nutrient sampling programs (with a total of 18 stations) and time-series of taxon-specific plankton abundance. At 14 near-coastal stations the simulated chlorophyll a (Chl a), when compared with chlorophyll extractions from water samples, had an average root mean square (RMS) error of 0.30 mg m−3 and a Willmott index of 0.59. For the same sites, simulated turbidity, when compared with turbidity sensors, had a Willmott index of 0.58 and simulated nitrate + nitrite had a Willmott index of 0.41 when compared with tri-annual water samples. Comparison with a spatially-resolved statistical model of zooplankton based on >900 observations in the region showed similarities in the relationship and spatial distribution of simulated and observed biomass, where both show zooplankton biomass is greatest inshore, biomass is highest around shallow reef areas and in the southern and central GBRWHA, and greater in summer than winter. Additionally, we investigate planktonic and nutrient responses to climatic variation. The first two years of the simulation coincided with La Niña events that drive greater than average winds, rainfall and river discharge. Throughout all years, simulated Chl a increases from north to south and from outer to inner coastal regions. Dissolved inorganic nitrogen, primary production and phytoplankton biomass were higher during La Niña in inshore and mid-shelf waters, while offshore regions were similar in all years from 2011 to 2016. Simulated Secchi depth was deeper offshore and decreased from offshore to inner coastal regions and from north to south. The eReefs simulation contributes to the understanding at a high spatial and temporal resolution of where and how nutrients and plankton originate and interact within the Great Barrier Reef. Highlights • Use of a 3D-catchment-hydrodynamic-sediment-wave-optical-biogeochemical model • Model encompasses the 2300 km long Great Barrier Reef from coast to Coral Sea. • Comparison of observations with simulated plankton & nutrients • Observations include remote sensing, moorings and water samples. • Simulated nutrients and plankton show realistic seasonal and interannual variation. [ABSTRACT FROM AUTHOR]

Large-scale spatial synchrony is ubiquitous in ecology. We examined 56 years of data representing chlorophyll density in 26 areas in British seas monitored by the Continuous Plankton Recorder survey. We used wavelet methods to disaggregate synchronous fluctuations by timescale and determine that drivers of synchrony include both biotic and abiotic variables. We tested these drivers for statistical significance by comparison with spatially synchronous surrogate data. Identification of causes of synchrony is distinct from, and goes beyond, determining drivers of local population dynamics. We generated timescale-specific models, accounting for 61% of long-timescale (> 4yrs) synchrony in a chlorophyll density index, but only 3% of observed short-timescale (< 4yrs) synchrony. Thus synchrony and its causes are timescale-specific. The dominant source of long-timescale chlorophyll synchrony was closely related to sea surface temperature, through a climatic Moran effect, though likely via complex oceanographic mechanisms. The top-down action of Calanus finmarchicus predation enhances this environmental synchronising mechanism and interacts with it non-additively to produce more long-timescale synchrony than top-down and climatic drivers would produce independently. Our principal result is therefore a demonstration of interaction effects between Moran drivers of synchrony, a new mechanism for synchrony that may influence many ecosystems at large spatial scales. [ABSTRACT FROM AUTHOR]

Abstract Oceanic chlorophyll-a concentration (Chl, mg m−3) maps derived from satellite ocean color measurements are the only data source which provides synoptic information of phytoplankton abundance on global scale. However, after excluding data collected under non-optimal observing conditions such as strong sun glint, clouds, thick aerosols, straylight, and large viewing angles, only ~5% of MODIS ocean measurements lead to valid Chl retrievals, regardless of the fact that about 25–30% of the global ocean is cloud free. A recently developed ocean color index (CI) is effective in deriving relative ocean color patterns under most non-optimal observing conditions to improve coverage, but these patterns cannot be interpreted as Chl. In this study, we combine the advantage of the high-quality, low-coverage Chl and lower-quality, higher-coverage CI to improve spatial and temporal coverage of Chl through machine learning, specifically via a random forest based regression ensemble (RFRE) approach. For every MODIS scene, the machine learning requires CI, Rayleigh-corrected reflectance (R rc (λ = 469, 555, 645 nm), dimensionless), and high-quality low-coverage Chl from the common pixels where they all have valid data to develop an RFRE-based model to convert CI and R rc (λ) to Chl. The model is then applied to all valid CI pixels of the same scene to derive Chl. This process is repeated for each scene, and the model parameterization is optimized for each scene independently. The approach has been tested for the Yellow Sea and East China Sea (YSECS) where non-optimal observing conditions frequently occur. Validations using extensive field measurements and image-based statistics for 2017 show very promising results, where coverage in the new Chl maps is increased by ~3.5 times without noticeable degradation in quality as compared with the original Chl data products. The improvement in Chl coverage without compromising data quality is not only critical in revealing otherwise unknown bloom patterns, but also important in reducing uncertainties in time-series analysis. Tests of the RFRE approach for several other regions such as the East Caribbean, Arabian Sea, and Gulf of Mexico suggest its general applicability in improving Chl coverage of other regions. Highlights • Standard MODIS daily Chl data products have many gaps due to several reasons. • An approach is developed to fill the gaps for the Yellow Sea and East China Sea. • Parameterization of the machine learning approach is optimized for each image. • Chl data quantity is increased by 3.5 times without noticeable degrading quality. • The approach shows potentials for other oceanic regions to improve Chl coverage. [ABSTRACT FROM AUTHOR]

Subsurface chlorophyll maximum layers (SCMLs) are nearly ubiquitous in stratified water columns and exist at horizontal scales ranging from the submesoscale to the extent of oligotrophic gyres. These layers of heightened chlorophyll and/or phytoplankton concentrations are generally thought to be a consequence of a balance between light energy from above and a limiting nutrient flux from below, typically nitrate (NO3). Here we present multiple lines of evidence demonstrating that iron (Fe) limits or with light colimits phytoplankton communities in SCMLs along a primary productivity gradient from coastal to oligotrophic offshore waters in the southern California Current ecosystem. SCML phytoplankton responded markedly to added Fe or Fe/light in experimental incubations and transcripts of diatom and picoeukaryote Fe stress genes were strikingly abundant in SCML metatranscriptomes. Using a biogeochemical proxy with data from a 40-y time series, we find that diatoms growing in California Current SCMLs are persistently Fe deficient during the spring and summer growing season. We also find that the spatial extent of Fe deficiency within California Current SCMLs has significantly increased over the last 25 y in line with a regional climate index. Finally, we show that diatom Fe deficiency may be common in the subsurface of major upwelling zones worldwide. Our results have important implications for our understanding of the biogeochemical consequences of marine SCML formation and maintenance. [ABSTRACT FROM AUTHOR]

San Jorge Gulf (SJG) is a region of high biological productivity that supports important shrimp (Pleoticus muelleri) and hake (Merluccius hubbsi) fisheries, as well as high marine biodiversity associated, in part, with a tidal front located in the southern part of the gulf. In situ high-resolution cross-frontal measurements were collected using a remotely operated towed vehicle to characterize the three-dimensional structure of the tidal front and to investigate how its position varies during the semidiurnal tidal cycle (high/low) and the spring to neap transition, together with its impact on the distribution of nutrients and chlorophyll-a. Estimates of tidal height and flow velocity derived from a numerical model support the conclusion that frontal displacements mostly result from advection by cross-frontal tidal currents. The frontal position was also modified by baroclinic instabilities that significantly distort the front. Measurements reveal intrusions of lowsalinity, nutrient-rich waters from the mixed side into the pycnocline on the stratified side cause a subsurface chlorophyll-a peak near the neap phase. Most prior studies of fronts in the SJG have been limited to their surface manifestations because they were conducted using satellite images. This article aims to contribute to the understanding of the complex southern tidal front dynamics, highlighting that maximum primary productivity occurs in a subsurface layer that is not visible by satellite sensors. [ABSTRACT FROM AUTHOR]

Given projected changes in river flow to coastal regions worldwide due to climate change and increasing human freshwater demands, it is necessary to determine the role hydrology plays in regulating the biogeochemistry of estuaries. A climatic gradient exists along the Texas coast where freshwater inflow balance ranges from hydrologically positive to negative (where evaporation exceeds inflow) within a narrow latitudinal band, providing a natural experiment for examining inflow effects. Four Texas estuaries ranging from mesosaline to hypersaline were studied for 3 yr to determine how hydrological changes alter the biogeochemistry within and among the estuaries. Trends in dissolved inorganic nutrients, chlorophyll, dissolved organic matter, and carbonate chemistry indicated that these estuaries had drastically different biogeochemical signatures. Nutrients and chlorophyll patterns illustrated an emerging paradigm where phytoplankton biomass in positive estuaries is supported by "new" nitrogen from riverine input, while high concentrations of reduced nitrogen (organic, ammonium) allowed for high chlorophyll in the negative estuary. For carbonate chemistry, a positive estuary receiving river input from a limestone‐dominated watershed was well‐buffered under moderate to high freshwater inflow conditions. When weathering products were diluted during high‐flow conditions, there is carbonate undersaturation (for aragonite) and decreases in pH. However, "acidification" was not observed in the negative estuary because evaporation concentrated the dissolved species and increased buffering capacity. Hydrological changes over spatial gradients are analogous to climatic changes over time, meaning climate change forecasts of higher temperatures and decreased precipitation can make the biogeochemistry of fresher estuaries change to the patterns of saltier estuaries. [ABSTRACT FROM AUTHOR]

Rates of phytoplankton growth and mortality are poorly defined over short‐time scales (hours to days), despite these scales being relevant over the daily tidal cycle in coastal marine areas. To assess the influence of tidal variability on phytoplankton rates, we performed eight, same‐day dilution experiments at high and low tide (6‐h intervals) in the Skidaway River Estuary, Georgia, measuring phytoplankton growth, microzooplankton grazing, and virus‐induced mortality. Chlorophyll and group‐specific biomass (Synechococcus spp., picoeukaryotes, and nanoeukaryotes) varied between tides and multidimensional scaling clustering of tidal biomass revealed separation in community composition based on tide. Rates also varied significantly over the tidal cycle, especially microzooplankton grazing, which was higher at low tide in most experiments with rates ranging from 0–3.77 d−1 at low tide to 0–1.51 d−1 at high tide. Virus‐induced mortality rates were rarely detected, only being observed in Synechococcus spp. in three experiments (0.3–0.8 d−1) and picoeukaryotes twice (~ 0.36 d−1). The differences in grazing and growth rates observed between the two tides were not explained by temperature, salinity, or sunlight (i.e., time of day) and grazing was only weakly explained by initial chlorophyll concentration (R2 = 0.36), highlighting the influence of community composition on rate measurements. These results suggest that within tidally influenced areas, short‐term sampling over the tidal cycle is essential to accurately characterize daily phytoplankton dynamics and reliably monitor and predict shifts in primary production and coastal ecosystem health. [ABSTRACT FROM AUTHOR]

The contribution of terrestrially derived carbon to micro‐crustacean zooplankton biomass (i.e., allochthony) has been previously studied in lakes, reservoirs, and estuaries, but little is known about zooplankton allochthony in rivers. In lacustrine environments, allochthony is regulated by distinct selective feeding behavior of different taxa. However, we hypothesized that restricted possibility for selective grazing in turbulent environments such as rivers would decouple zooplankton from specific microbial and algal food resources, such that their allochthony would mirror the terrestrial contribution to the surrounding bulk particle pool. We tested this idea by analyzing allochthony in 13 widely distributed Swedish rivers, using a dual‐isotope mixing model. Zooplankton biomasses were generally low, and allochthony in different micro‐crustacean groups (Cladocera, Cyclopoida, Calanoida) varied from 2% to 77%. As predicted, there were no correlations between allochthony and variables indicating the supply of algal and microbial food resources, such as chlorophyll a and bacterial production. Instead, the allochthony was generally similar to the share allochthonous contribution in bulk particulate organic matter, with relationships close to the 1 : 1 line. The zooplankton community allochthony was strongly regulated by the ecosystem metabolic balance between production and respiration, which in turn was dependent upon the ratio between total autochthonous organic carbon concentrations and water color. Our study for the first time shows that micro‐crustacean allochthony is regulated differently in rivers compared to in lacustrine systems, and points to inefficient support of zooplankton biomass by algal resources in turbulent waters. [ABSTRACT FROM AUTHOR]

Various empirical relationships have been developed in the past nine decades to link the Secchi‐disk depth (ZSD) with the diffuse attenuation coefficient (KPAR), the euphotic zone depth (Zeu), and chlorophyll (Chl) concentration, where the latter two are important for the quantification and evaluation of photosynthesis in aquatic environments. There was also a classical theory regarding Secchi‐disk sighting, but large gaps existed between the observations and model outcomes. These gaps have puzzled the ocean community for > 60 yr and have resulted in contradictory conclusions regarding the interpretation and usefulness of ZSD. Here, we compare these measurements with data simulated based on an innovative theory and model regarding ZSD, and we found remarkable agreements between theoretical predictions and these century‐long observations. The results not only resolve the long‐standing puzzles associated with these observations, but also unify the relationships published in the literature. In particular, the ratio of Zeu to ZSD is found to be ∼ 3.5 for all waters, which is ∼ 45% greater than the consensus value of ∼ 2.4 suggested in the past for clear waters. In addition, the new model validates an empirical relationship between ZSD and Chl developed for global oceanic waters, thus providing strong support for using historical ZSD data to study changes of phytoplankton in global oceans in the past century. [ABSTRACT FROM AUTHOR]

Highlights • Sweet flag could tolerate nitrite up to 30 mg/L. • Nitrite (≥30 mg/L) could trigger physiological protection system of sweet flag. • High nitrite level (40 mg/L) could cause significant increase in PEL and MDA. • Sweet flag membrane system was badly damaged when nitrite increased to 40 mg/L. Abstract Various newly discovered novel biological nitrogen removal (BNR) routes via nitrite offer great potential for improving nitrogen removal efficiency of constructed wetlands. In these novel routes, nitrite is required as the substrate or intermediary media. Hence, in the present study, the tolerance and physiological responses of sweet flag (Acorus calamus L.) to nitrite stress were investigated. Results showed that the physiology of sweet flag was not significantly affected when exposed to nitrite up to 20 mg/L. High nitrite levels (≥30 mg/L) led to changes in its cell membrane permeability, plant photosynthesis and activities of antioxidant enzymes. Particularly, when exposed to a nitrite level of 40 mg/L, sweet flag displayed trends of significant increase in the percentage of electrolyte leakage and contents of malondialdehyde and proline, whereas the chlorophyll content and plant height decreased and antioxidant defence systems were disrupted. Therefore, for CWs with sweet flag, 30 mg/L is the recommended threshold value for nitrite. [ABSTRACT FROM AUTHOR]

Impact of four major cyclones: Phailin, Helen, Lehar, and Madi have been studied in terms of changes in ocean productivity utilizing Indian satellite Oceansat-2 ocean color monitor and MODIS-Aqua data during October-December 2013. The 8-day and monthly composite chlorophyll images have been generated owing to the pre-, during, and post-stages of four cyclones; out of which, three were very severe cyclonic storms and the Helen was severe cyclonic storm. The chlorophyll concentration increased two- to threefolds due to the aftereffect of cyclone in the coastal water, and the concentration was very high (around 2-3 mg/m3). To understand the possible links of cyclones to cooling and upwelling, MODIS-Aqua sea surface temperature (SST) images have been processed. The SST images have shown the cooling effect near the cyclone track pass, over Bay of Bengal. The cooling was observed by 2-3 degree Celsius during the above cyclones. To understand the in situ surface water and water column salinity and temperature variability, the Argo float data are plotted and interpreted. The surface contour shows the lowering of salinity and temperature with effects of cyclones. In addition, the Argo depth profile data have shown possible mixed layer deepening in few profiles around halocline and thermocline depths. This study will be useful for mapping potential fishing zone, ocean biogeochemistry and other useful applications and research. [ABSTRACT FROM AUTHOR]

Accurate simulation of the underwater light climate is a requirement to understanding and predicting the ecological benefits from initiatives to manage land-derived inputs of nutrients and suspended solids to the coast. The goal of this work was to derive an empirical light model to be used in the water quality module of a coupled physical-biogeochemical model, developed to estimate habitat suitability for seagrasses in a metropolitan region (Adelaide, South Australia) affected by wastewater and stormwater discharges. Paired measurements of water quality and the vertical attenuation coefficient (K d ) obtained at six fixed sites between summer and winter were used in a multiple regression analysis to optimize local specific attenuation coefficients for coloured dissolved organic matter (CDOM) (2.623 cm m −1 , measured as absorption at 254 nm), chlorophyll a (0.071 m 2 mg −1 ), suspended solids (SS) < 63 μm (0.032 m 2 g −1 ) and >63 μm (0.001 m 2 g −1 ). The fitted relation explained 65% of the variability in K d , with a standard error of 0.10 m -1 . This error is small considering a mean K d value of 0.35 m -1 , varying between 0.12 and 0.89 m -1 . Fine SS contributed on average 6 times more light attenuation (34%) than coarse SS (6%). CDOM was the second largest contributor to K d (36%). The contribution of chlorophyll a to K d (13%) was only marginally higher than the background imparted by seawater (12%). In shallow waters (3–5 m), K d values were >0.4 m -1 and heavily influenced by sediment resuspension. In deeper waters (12–15 m), K d values decreased and were dominated by CDOM. The light climate in the north of the study region was also heavily influenced by CDOM inputs, not only from point sources but also from mangroves and seagrass beds. This analysis suggests the control of fine SS as the most powerful management option to deter further nearshore seagrass losses in the region, and promote seagrass restoration. [ABSTRACT FROM AUTHOR]

Phytoplankton patterns, tightly linked to the dynamics of the ocean surface layer and its atmospheric forcing, have major impacts on ecosystem functioning and are valuable indicators of its response to environmental variability and change. Phytoplankton phenology and its underlying drivers are spatially variable, and the study of its patterns, particularly over heterogeneous regions, benefits from a delineation of regions with specific phenological properties, or phenoregions. The area Southwest off the Iberian Peninsula (SWIP, NE Atlantic) integrates a highly complex set of coastal and ocean domains that collectively challenge the understanding of regional phytoplankton phenology and related forcing mechanisms. This study aims to evaluate phytoplankton phenology patterns over the SWIP area, during an 18-year period (September 1997 – August 2015), using an objective, unsupervised partition strategy (Hierarchical Agglomerative Clustering – HAC) based on phenological indices derived from satellite ocean colour data. The partition is then used to describe region-specific phytoplankton phenological patterns related to bloom magnitude, frequency, duration and timing. Region-specific variability patterns in phenological indices and their linkages with environmental determinants, including local ocean physical-chemical variables, hydrodynamic variables and large scale climate indices, were explored using Generalized Additive Models (GAM). HAC analyses identified five coherent phenoregions over SWIP, with distinctive phytoplankton phenological properties: two open ocean and three coastal regions. Over the open ocean, a single, low magnitude and long bloom event per year, was regularly observed. Coastal phenoregions exhibited up to six short bloom events per year, and higher intra-annual and variability. GAM models explained 50–90% of the variance of all phenological indices except bloom initiation timing, and revealed that interannual patterns in phytoplankton phenology and their environmental drivers varied markedly among the five phenoregions. Over the oceanic phenoregions, large-scale climate indices (Eastern Atlantic Pattern, Atlantic Meridional Oscillation), mixed layer depth (MLD) and nitrate concentration preceding primary bloom events were influential predictors, reflecting the relevance of nutrient limitation. For the Coastal-Slope, a relatively more light-limited phenoregion, North Atlantic Oscillation and wind speed were more relevant, and bloom magnitude was also positively influenced by riverine discharge. This variable was a significant predictor of bloom frequency, magnitude and duration over the Riverine-influenced region. Over the Upwelling-influenced region, upwelling intensity and mean annual MLD showed stronger partial effects on phytoplankton phenology. Overall, our phenology-based unsupervised approach produced a biologically-relevant SWIP partition, providing an evaluation of the complexity of interactions between phytoplankton and multiple environmental forcing, particularly over coastal areas. [ABSTRACT FROM AUTHOR]

Abstract: It has been hypothesized that global warming will strengthen upwelling‐favorable winds in the Northern Humboldt Current System (NHCS) as a consequence of the increase of the land–sea thermal gradient along the Peruvian coast. The effect of strengthened winds in this region is assessed with the use of a coupled physical–biogeochemical model forced with projected and climatological winds. Strengthened winds induce an increase in primary production of 2% per latitudinal degree from 9.5°S to 5°S. In some important coastal upwelling sites primary production is reduced. This is due to a complex balance between nutrient availability, nutrient use efficiency, as well as eddy‐ and wind‐driven factors. Mesoscale activity induces a net offshore transport of inorganic nutrients, thus reducing primary production in the coastal upwelling region. Wind mixing, in general disadvantageous for primary producers, leads to shorter residence times in the southern and central coastal zones. Overall, instead of a proportional enhancement in primary production due to increased winds, the NHCS becomes only 5% more productive (+5 mol C m−2 year−1), 10% less limited by nutrients and 15% less efficient due to eddy‐driven effects. It is found that regions with a initial strong nutrient limitation are more efficient in terms of nutrient assimilation which makes them more resilient in face of the acceleration of the upwelling circulation. [ABSTRACT FROM AUTHOR]

Abstract: Benthic fluxes of chlorophyll a (Chl a) and particulate organic carbon (POC) and nitrogen (PON) were quantified on Tallon reef, a strongly tide‐dominated (spring range > 8 m) reef located in the Kimberley region of northwestern Australia, over a 2‐week period. Extensive hydrodynamic observations were used to construct a reef‐scale mass balance to estimate material exchange between the reef and ocean over individual tidal cycles. Additionally, a one‐dimensional control volume approach was used to estimate fluxes of Chl a in waters traversing the reef platform. Particulate material was delivered to the reef platform in a pulse during flood tide, and benthic uptake of Chl a declined to negligible values toward the end of ebb tide. On the scale of tidal cycles, a net uptake of Chl a was observed on the reef platform (on average 1.3 mg Chl a m−2 d−1), which was lower than previous studies of many reef communities. Fluxes showed variability depending on the magnitude of individual tidal cycles, which was likely related to volumes of oceanic Chl a inputs. Tallon reef was a net source of detrital POC and PON to the surrounding coastal ocean, with average POC exports ∼ 3% of the reef's benthic gross primary production. Seasonal measurements of water quality reported here are among the first records for the coastal Kimberley, and suggest that reefs in the west Kimberley may experience naturally elevated levels of phytoplankton and particulate nutrients, especially during the wet season. [ABSTRACT FROM AUTHOR]

Chlorophyll (Chl) concentration is one of the key indicators identifying changes in the Arctic marine ecosystem. However, current Chl algorithms are not accurate in the Arctic Ocean due to different bio-optical properties from those in the lower latitude oceans. In this study, we evaluated the current Chl algorithms and analyzed the cause of the error in the western coastal waters of Svalbard, which are known to be sensitive to climate change. The NASA standard algorithms showed to overestimate the Chl concentration in the region. This was due to the high non-algal particles (NAP) absorption and colored dissolved organic matter (CDOM) variability at the blue wavelength. In addition, at lower Chl concentrations (0.1–0.3 mg m −3 ), chlorophyll-specific absorption coefficients were ∼2.3 times higher than those of other Arctic oceans. This was another reason for the overestimation of Chl concentration. OC4 algorithm-based regionally tuned-Svalbard Chl (SC4) algorithm for retrieving more accurate Chl estimates reduced the mean absolute percentage difference (APD) error from 215% to 49%, the mean relative percentage difference (RPD) error from 212% to 16%, and the normalized root mean square (RMS) error from 211% to 68%. This region has abundant suspended matter due to the melting of tidal glaciers. We evaluated the performance of total suspended matter (TSM) algorithms. Previous published TSM algorithms generally overestimated the TSM concentration in this region. The Svalbard TSM-single band algorithm for low TSM range (ST-SB-L) decreased the APD and RPD errors by 52% and 14%, respectively, but the RMS error still remained high (105%). [ABSTRACT FROM AUTHOR]

Abstract: Models of dissolved organic nitrogen (DON) production and consumption indicate that marine DON is produced in the euphotic zone, especially in upwelling environments, and is consumed as it transits into more oligotrophic regions where it may support export production. However, evaluation of such models is data limited, and in particular, few measurements of DON concentration and/or nitrogen isotopic composition (“δ15N”) exist from the South Pacific. Here we present measurements of the concentration and δ15N of DON collected in the eastern tropical South Pacific during the austral summers of 2010 (El Niño) and 2011 (La Niña). The concentration and δ15N of DON from the eastern tropical South Pacific are broadly consistent with prior measurements elsewhere, that is, DON concentrations of 5 ± 1 μM and DON δ15N of 5 ± 1‰, but variations were associated with DON production and consumption. Specifically, surface ocean chlorophyll a concentrations were highly correlated with upper 50‐m DON stocks (r = 0.96), consistent with a photosynthetic source for DON. Additionally, upper 50‐m DON stocks and their δ15N were significantly negatively correlated (r = −0.84, p = 0.0006), indicating that DON was consumed in surface waters with an isotope effect of 5.5 ± 1.2‰. These results inform our understanding of the controls of DON distributions in the surface ocean and indicate that DON may support export production in nitrate‐poor surface waters, which may decouple new from gross production. [ABSTRACT FROM AUTHOR]

We estimated monthly air-sea CO2 fluxes in the Arctic Ocean and its adjacent seas north of 60° N from 1997 to 2014. This was done by mapping partial pressure of CO2 in the surface water (pCO2w) using a self-organizing map (SOM) technique incorporating chlorophyll a concentration (Chl a), sea surface temperature, sea surface salinity, sea ice concentration, atmospheric CO2 mixing ratio, and geographical position. We applied new algorithms for extracting Chl a from satellite remote sensing reflectance with close examination of uncertainty of the obtained Chl a values. The overall relationship between pCO2w and Chl a was negative, whereas the relationship varied among seasons and regions. The addition of Chl a as a parameter in the SOM process enabled us to improve the estimate of pCO2w, particularly via better representation of its decline in spring, which resulted from biologically mediated pCO2w reduction. As a result of the inclusion of Chl a, the uncertainty in the CO2 flux estimate was reduced, with a net annual Arctic Ocean CO2 uptake of 180±130 TgCyr-1. Seasonal to interannual variation in the CO2 influx was also calculated. [ABSTRACT FROM AUTHOR]

Seychelles-Chagos Thermocline Ridge (SCTR, 5°- 10°S, 50°-75°E) in the southwestern tropical Indian Ocean is a unique area that experiences year-round upwelling. This is a response to the upward Ekman pumping prevalent in the region. Satellite data, model data and objectively analysed Argo temperature/ salinity data have been used to study the seasonal surface chlorophyll a (chl a) variability in SCTR. Variability of surface chl a concentration in SCTR showed a weak semiannual signature. The western part of SCTR (WSCTR, 50°-62°E) is characterized by higher chl a concentration than the eastern part (ESCTR, 63°-75°E). Average chl a concentration in WSCTR/ESCTR showed a primary peak in July- August (~0.26/~0.16 mg/m3) and a secondary peak in January (~0.14/~0.12 mg/m3). Minimum chl a concentration (~0.12/~0.1 mg/m3) was observed during March- April and December-January. The high amplitude of chl a variability observed during July-August is associated with weak stratification and deep mixed layer depth (MLD). Deep MLD reaching to nutrient-rich thermocline entrains nutrients to the surface and thereby increases the surface chl a concentration. However, the low surface chl a concentration is a result of shallow MLD in the region. The deep MLD (30-40 m) observed during June-October is dominated by wind mixing and supported by buoyancy mixing. Shallow MLD (<30 m) observed during rest of the year is due to weak wind mixing and high surface buoyancy. The high surface buoyancy is a manifestation of ocean surface warming and presence of low saline surface waters in the SCTR region. [ABSTRACT FROM AUTHOR]

Chlorophyll and phytoplankton distribution and concentration in the Gulf of Cadiz were studied during 2014 and 2015. In both years the highest chlorophyll concentrations are found at coastal stations during spring. Pico- and nanophytoplankton are the main contributors to total chlorophyll, with highest concentrations at the outer limit of the continental shelf. Microphytoplankton is responsible for most of the inshore chlorophyll. Picophytoplankton was analyzed to determine density, biomass and distribution. Prochlorococcus and Synechococcus show differences in distribution depending on distance from the coast and depth. Our results suggest temperature and consequent water stratification seem to be the main factors determining deep fluorescence maxima (DFM), mainly formed by picophytoplankton, especially Prochlorococcus . Pigment identification assisted by CHEMTAX analysis was carried out to analyze relative concentrations of larger phytoplankton. [ABSTRACT FROM AUTHOR]

To evaluate the sources and budgets of sedimentary organic matter in the East China Sea (ECS), bulk organic matter properties (total organic carbon (TOC), C/N ratio, carbon and nitrogen isotopic composition (δ 13 C and δ 15 N)) and sterols in surface sediments were analyzed. The distributions of bulk organic matter properties and sterols showed a strong regionality with higher contents in the southern inner shelf as well as the offshore upwelling area. It was consistent with the increasing mud and chlorophyll a ( Chl a) contents southwards. These distribution patterns were attributed to the terrestrial inputs by shelf circulations and phytoplankton contribution. Both of bulk organic matter properties and sterols indicated a mixture of terrestrial and marine derived organic matter inputs with marine source as a dominant input. Budgets suggested that organic carbon (OC) and sterol influxes from terrestrial source were 5.15 × 10 6 and 3.32 × 10 3 t/yr, with the Changjiang River input as the primary contributor; and while their influxes from marine source were 26.3 × 10 6 and 2.19 × 10 3 t/yr, respectively. The burial fluxes of OC and sterol were 3.99 × 10 6 t C/yr and 0.21 × 10 3 t/yr, with the inner shelf as main accumulation area. Although there was a huge amount of OC influx from terrestrial and marine sources, but only 24.6% and 10% of them could be preserved in sediments. Consequently, the combined effect of riverine input, marine primary productivity and deposition decided the organic matter behaviors in the ECS. [ABSTRACT FROM AUTHOR]

A recent revision of the NASA global ocean colour record shows changes in global ocean chlorophyll trends. This new 18-year time series now includes three global satellite sensors, the Sea-viewing Wide Field of view Sensor (SeaWiFS), Moderate Resolution Imaging Spectroradiometer (MODIS-Aqua), and Visible Infrared Imaging Radiometer Suite (VIIRS). The major changes are radiometric drift correction, a new algorithm for chlorophyll, and a new sensor VIIRS. The new satellite data record shows no significant trend in global annual median chlorophyll from 1998 to 2015, in contrast to a statistically significant negative trend from 1998 to 2012 in the previous version. When revised satellite data are assimilated into a global ocean biogeochemical model, no trend is observed in global annual median chlorophyll. This is consistent with previous findings for the 1998–2012 time period using the previous processing version and only two sensors (SeaWiFS and MODIS). Detecting trends in ocean chlorophyll with satellites is sensitive to data processing options and radiometric drift correction. The assimilation of these data, however, reduces sensitivity to algorithms and radiometry, as well as the addition of a new sensor. This suggests the assimilation model has skill in detecting trends in global ocean colour. Using the assimilation model, spatial distributions of significant trends for the 18-year record (1998–2015) show recent decadal changes. Most notable are the North and Equatorial Indian Oceans basins, which exhibit a striking decline in chlorophyll. It is exemplified by declines in diatoms and chlorophytes, which in the model are large and intermediate size phytoplankton. This decline is partially compensated by significant increases in cyanobacteria, which represent very small phytoplankton. This suggests the beginning of a shift in phytoplankton composition in these tropical and subtropical Indian basins. [ABSTRACT FROM PUBLISHER]

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The Southern Ocean is the largest high nutrient, low chlorophyll region in the global ocean and is subject to strong iron limitation. Iron availability is associated with the interaction between the Antarctic Circumpolar Current (ACC) and topographic features such as the Kerguelen Plateau in the Indian Sector of the Southern Ocean. The fronts of the ACC also provide important environmental delineations for Southern Ocean ecosystem structure. Here, we implement a NPZD (nitrogen, phytoplankton, zooplankton, detritus) model together with an optimal control algorithm along three meridional transects across the Antarctic Circumpolar Current. Our study represents the first spatial application of this model, and considers potential environmental drivers of parameter variability and community dynamics. In iron-limited open ocean regions, this model captures seasonal processes well but does not converge in more complex regions, such as the iron fertilized Kerguelen Plateau and sea ice areas. All variables show marked meridional changes, which are likely associated with the fronts of the Antarctic Circumpolar Current. This technique indicates that the different bodies of water associated with the circumpolar current exhibit different ecosystem dynamics, a result that is likely caused by distinct NPZD communities. Overall, our findings contribute to broadscale understanding of the drivers of lower trophic level ecosystem dynamics across physical boundaries in the Indian Sector of the Southern Ocean, and can be used to help guide further modelling efforts. [ABSTRACT FROM AUTHOR]

The biomass and productivity of primary producers in the surf zone of the ocean beach at Wrightsville Beach, North Carolina, USA, were measured during all seasons, along with environmental parameters and nutrient levels. Variation in biomass (chlorophyll a ) was associated with temperature. Primary production (PP), measured by in situ 14-C incubations, was a function of chlorophyll a , tide height at the start of incubations, and rainfall in the preceding 24-hr period. Biomass-normalized production (P B ) was also a function of tide height and rainfall in the preceding 24-hr period. We interpreted these results as evidence of surf production 1) as combined contributions of phytoplankton and suspended benthic microalgae, which may confound application of simple P-E models to surf zone production, and 2) being regulated by nutrient source/supply fluctuations independently from other factors. Surf zone biomass and production levels are intermediate between relatively high estuarine values and much lower coastal ocean values. Surf zone production may represent an important trophic connection between these two important ecosystems. [ABSTRACT FROM AUTHOR]

Field morpho-physiological characterization of barley is essential for selecting salt-tolerant genotypes and for predicting yield reduction. A field experiment was conducted for two consecutive growing seasons (2012-13 and 2013-14) in Kairouan (semi arid, Central Tunisia) and in Medenine (arid, South-East Tunisia), where 4 widely grown varieties, 23 local landraces originated from saline and non-saline agro-ecosystems, and 13 genotypes from the Near East North Africa (NENA) region, were tested. In each location, saline groundwater and drinking water were used. Grain yield, plant ion content (Na + , K + and Ca 2+ ), flag leaf chlorophyll content index (CCI), relative water content (RWC), specific leaf area (LA) and plant earliness at heading (E60) were measured for each genotype. Grain yield reduction ratio (YRR) was calculated for all genotypes to estimate their tolerance to salinity. [ABSTRACT FROM AUTHOR]

Atmospheric dust loads and chemical compositions serve as a key link between global climate patterns and marine biogeochemical cycles. The primary source of atmospheric dust in the world today is the Sahara-Arabian desert belt. Although this source was also active during the Quaternary, the interpretation of paleo-dust records and their effects on marine ecosystems is complicated by the scarcely reported atmospheric load patterns of bioavailable phases (i.e., water and acid leachable phases) and present-day contamination of anthropogenic components. This study reports a multi-annual time series of atmospheric dust loads (2006–2016) and their chemical compositions (2006–2010) collected in the north Gulf of Aqaba (north Red Sea) at a weekly to bi-weekly resolution. Major and trace element abundances in each sample are reported for three fractions: water-soluble salts, carbonates and oxides (weak acid leach), and Al-silicates. Dust loads vary seasonally from low values in late summer (∼20–30 μg m −3 ) to higher values in the fall, and highest values in late winter and early spring (∼150–250 μg m −3 ). Major and trace element abundances allow to distinguish between the sources and chemical compositions that dominate high and low dust loads in each season. The water leachable fraction (L0) is relatively enriched in Na, Ca, K and Mg, the acid-leachable fraction (L1) is enriched in Ca as well as Na, Al, Mg, Zn, Cd and Pb, and the silicate residue (L2) in Al and Fe. High dust loads occurring mainly during winter and spring months are characterized by low Mg/Ca (L1, L2), low K/Al and Na/Al (L1) and high Ca/Al (L1), high Mg/Al (L2) and relatively un-weathered (L2) contents. High dust load intervals during winter months are characterized by low passing air masses originating from the Sahara, while the ambient winter dust (low dust load) is associated with proximal source regions from the East Sahara and Arabian Peninsula. During late winter and spring months, high dust loads originate from central and west Sahara and to a lesser extent from north Sahara. Low dust loads characterize the summer with limited compositional variability relative to winter-spring months. Summer dust is generally characterized by high K/Al (L1) ratios relative to late winter and spring. It is also relatively high in anthropogenic trace elements in the L0 and L1 fractions (e.g., Zn/Al, Pb/Al, Cr/Al, Ni/Al and V/Al), whereby back trajectories indicate the source of these components is primarily from south and east Europe. The total load (ng m −3 ) of anthropogenic trace elements however, remains higher during winter and spring, stemming from the overall significantly higher dust loads characterizing this time window. The temporal load patterns of important micronutrients such as Fe, Cd, Zn, Cu, Ni and others in the bio-available phases (L0, L1) are not correlated with major nutrients or Chlorophyll-a sea surface concentrations, suggesting that the atmospheric dust plays a limited role in driving primary productivity in the oligotrophic surface waters of the Gulf of Aqaba. On a wider scale, the results provide unique chemical fingerprinting of Sahara-Arabian dust that can be applied to reconstruct past trends in dust loads recorded in deep-sea cores and other geological archives from this and other regions. [ABSTRACT FROM AUTHOR]

Understanding how phytoplankton respond to their physical environment is key to predicting how bloom dynamics might change under future climate change scenarios. Phytoplankton are at the base of most marine food webs and play an important role in drawing CO 2 out of the atmosphere. Using nearly 5 years of simultaneous CTD, irradiance, chlorophyll a fluorescence and optical backscattering observations obtained from Slocum glider missions, we observed the subsurface phytoplankton populations across the Scotian Shelf, near Halifax (Nova Scotia, Canada) along with their physical environment. Bloom conditions were observed in each of the 5 springs, with the average chlorophyll in the upper 60 m of water generally exceeding 3 mg m − 3 . These blooms occurred when the upper water column stratification was at its lowest, in apparent contradiction of the critical depth hypothesis. A subsurface chlorophyll layer was observed each summer at about 30 m depth, which was below the base of the mixed layer. This subsurface layer lasted 3–4 months and contained, on average, 1/4 of the integrated water column chlorophyll found during the spring bloom. This suggests that a significant portion of the primary productivity over the Scotian Shelf occurs at depths that cannot be observed by satellites—highlighting the importance of including subsurface observations in the monitoring of future changes to primary productivity in the ocean. [ABSTRACT FROM AUTHOR]

Phaeocystis antarctica is an abundant phytoplankton species in the Southern Ocean, where growth is frequently limited by iron and light. Being able to grow under low iron conditions is essential to the species’ success, but there have been hints that this ability differs among clones. Here, we compare the growth, cell size and chlorophyll a concentrations of four P. antarctica clones cultured under different iron and light conditions. Iron was provided either as unchelated iron (Fe′) or bound to the bacterial siderophore desferrioxamine B, representing, respectively, the most and least bioavailable forms of iron which phytoplankton encounter in the marine environment. The growth rate data demonstrate that the clones vary in their ability to grow using organically bound iron, and that this ability is not related to their ability to grow at low inorganic iron concentrations. These results are consistent at low and high light. Physiologically, only three of the four clones shrink or decrease the concentration of chlorophyll a in response to iron limitation, and only one clone decreases colony formation. Together, our data show that P. antarctica clones 1) respond to the same degree of iron limitation using different acclimation strategies, and 2) vary in their ability to grow under the same external iron and light conditions. This physiological diversity is surprisingly large for isolates of a single phytoplankton species. [ABSTRACT FROM AUTHOR]

This paper presents data on various parameters of primary production (chlorophyll concentration, carbon uptake, nitrogen uptake, phytoplankton groups) measured in 4 cruises in the Saudi Arabian waters of the Red Sea between 2012 and 2015. The results showed that while there was a tendency for an increase from north to south, the meridional distributions were distinguished by alternating high and low concentrations of chlorophyll, carbon uptake rates and cell densities of various phytoplankton groups, with the higher levels being associated with zonal currents and the lower values lying in between. These patterns of distributions lead us to conclude that the biological production in the Red Sea is influenced more by anticyclonic eddy, and less by meridional, circulations at any time of the year. Synthesizing the present results with earlier ones on the patterns of distributions of nutrients and the flow of Gulf of Aden Intermediate Water (GAIW), we also conclude that entrainment of GAIW in successive eddies is the cause for higher nutrients and biological production in the regions of eddy boundary currents. Data on size-fractionated carbon uptake and nitrogen uptake showed that the eddies in Red Sea favour the proliferation of producers across a range of size classes rather than one class. The amount of nutrients injected into the euphotic zone in the eddy boundary currents is probably not high enough to induce a definite shift in phytoplankton size classes, and the primary production still remains to a significant extent regenerated nutrient-driven. [ABSTRACT FROM AUTHOR]

The article studies the accumulation of the diatoms Anaulus australis and Asterionellopsis glacialis species complex in the low-latitude sand beaches in Bahia, eastern Brazilian coast. It discusses the environmental data of study area, sampling of surf-zone diatoms and use principal component analysis (PCA) to understand the trend. Dark patches, high chlorophyll concentration and high nutrient contents were observed at Cururupe beach.

An optical method is developed to estimate water transparency (or underwater visibility) in terms of Secchi depth ( Z ), which follows the remote sensing and contrast transmittance theory. The major factors governing the variation in Z , namely, turbidity and length attenuation coefficient (1/( c + K ), c = beam attenuation coefficient; K = diffuse attenuation coefficient at 531 nm), are obtained based on band rationing techniques. It was found that the band ratio of remote sensing reflectance (expressed as ( R (443) + R (490))/( R (555) + R (670)) contains essential information about the water column optical properties and thereby positively correlates to turbidity. The beam attenuation coefficient ( c) at 531 nm is obtained by a linear relationship with turbidity. To derive the vertical diffuse attenuation coefficient ( K ) at 531 nm, K (490) is estimated as a function of reflectance ratio ( R (670)/ R (490)), which provides the bio-optical link between chlorophyll concentration and K (531). The present algorithm was applied to MODIS-Aqua images, and the results were evaluated by matchup comparisons between the remotely estimated Z and in situ Z in coastal waters off Point Calimere and its adjoining regions on the southeast coast of India. The results showed the pattern of increasing Z from shallow turbid waters to deep clear waters. The statistical evaluation of the results showed that the percent mean relative error between the MODIS-Aqua-derived Z and in situ Z values was within ±25%. A close agreement achieved in spatial contours of MODIS-Aqua-derived Z and in situ Z for the month of January 2014 and August 2013 promises the model capability to yield accurate estimates of Z in coastal, estuarine, and inland waters. The spatial contours have been included to provide the best data visualization of the measured, modeled (in situ), and satellite-derived Z products. The modeled and satellite-derived Z values were compared with measurement data which yielded RMSE = 0.079, MRE = −0.016, and R = 0.95 for the modeled Z and RMSE = 0.075, MRE = 0.020, and R = 0.95 for the satellite-derived Z products. [ABSTRACT FROM AUTHOR]

The Gulf of Guinea represents a wide tract of the African coast with complex and rich coastal ecosystems undergoing various pressures. The seasonal variations of chlorophyll-a concentration (Chla) along the Gulf of Guinea (GoG) and their relations with physical oceanographic variables were analyzed using satellite observations covering the period 2002–2012. The effects of sea surface temperature (SST), sea level anomalies (SLA), winds, geostrophic currents, eddy kinetic energy (EKE), mesoscale eddies and fronts were considered on a monthly time scale. The analysis for each unit area was carried out on a chlorophyll index (IChla) computed as the product of the mean distance from the coast to the eutrophic threshold (1 mg m −3 isoline) and the average Chla in the eutrophic area. The study, based on satellite-derived Chla, was allowed by the unprecedented coverage given by the products distributed by the ESA Ocean Colour Climate Change Initiative (OC_CCI) resulting from the merging of data from several satellite missions. The physical variables served as potential predictors in a statistical Boosted Regression Tree (BRT) model. To account for the heterogeneous nature of the GoG, the analysis was conducted on eight systems that made up a partition of the whole region defined on the basis of the BRT model results and climatological properties. The western-most domain, from Guinea-Bissau to Sierra Leone, was associated with upwelling properties in boreal winter and appeared to share some characteristics with the overall Northwest African upwelling system. The region of Ivory Coast and Ghana also had upwelling properties but the main upwelling season was in boreal summer. In general upwelling conditions with cold SST, negative SLA, fairly strong frontal activity, and moderate winds, appeared as the environmental window most favorable to high IChla values. For these systems, the BRT model fitted the IChla data well with a percentage of explained total deviance D 2 between 70% and 91% when using only physical oceanographic variables. Finally, the systems associated with the coasts of Nigeria to Gabon showed some mixed properties, with D 2 values of 54–60%. Among these systems, a common feature seemed to be the importance of river discharge to explain IChla variations. Where possible (for the Niger River in the Nigeria system), the addition of river data as predictor in the BRT model resulted in a significant increase of D 2 to 75%. Further progress is needed to understand the observed relationships and to predict how they can evolve in the face of climate change. [ABSTRACT FROM AUTHOR]

The phenology of the winter–spring phytoplankton bloom in the Black Sea was investigated on the basis of the satellite-derived chlorophyll concentration (Chl) for the recent 18-year period. Data for the 8-day Chl were analysed, together with changes in the nutrient concentration, sea surface temperature (SST), photosynthetically available radiation, wind velocity and duration. Based on Sverdrup’s Critical Depth hypothesis and its recent refinements, the Pulsing-Bloom hypothesis was proposed for the highly stratified waters of the Black Sea. This hypothesis relates the biological response to physical forcing and chemical fluxes to the photic zone and predicts the pulsing growth of phytoplankton and different patterns of phytoplankton changes in the upper layer in winter–spring during cold and regular years. The hypothesis was supported by Chl dynamics and several Chl peaks were observed during winter-spring. Normally, the highest Chl occurred in winter and a spring peak was absent, whereas in cold years, a relatively low Chl in winter was followed by a spring bloom. These events were observed only in 15% of cases and the magnitude of the bloom was associated with the intensity of winter convection that was revealed by the negative inter-annual correlation between the March Chl and the February SST. In contrast, the February Chl was positively correlated with the SST. The proposed hypothesis provides an explanation of this phenomenon on the basis of an alternation between the low-turbulence and deep-mixing regimes. This mechanism was confirmed by the positive relationships between Chl and the duration of light wind during the current period and strong wind in the previous period. Inorganic nitrogen was depleted disproportionately during the winter–spring, whereas the phosphate concentration remained relatively high. Following a cold winter, the highest phosphate concentration and extremely low nitrogen-to-phosphorus molar ratios (2) were observed in the upper 25-m layer in late spring. The regular absence of spring blooms might represent one of the consequences of the regional climate change. [ABSTRACT FROM AUTHOR]

Ofunato Bay was a semi-closed area because of the breakwater effect at the entrance; however, the breakwater was destroyed by a massive tsunami generated by the 2011 off the Pacific coast of Tohoku Earthquake. Consequently, the physical environment of Ofunato Bay has been changed significantly, i.e., the modification of the stratified structure of seawater inside the bay and the intermittent intrusion of seawater outside the bay. These alterations of physical environment are considered to have an influence on the chemical and biological environment in Ofunato Bay. To elucidate the influence of the tsunami on the aquatic environment, we measured dissolved nutrients, chlorophyll a and dissolved oxygen concentrations, and heterotrophic bacteria abundance inside and outside of Ofunato Bay from 2012 to 2014, and compared these data with those obtained before the earthquake. As compared with before the earthquake, significant changes after the earthquake were (1) decrease of ammonium and phosphate concentrations, (2) increase of chlorophyll a concentration, (3) increase of dissolved oxygen concentration in the bottom, and (4) decrease of heterotrophic bacteria abundance. The collapse of the breakwater and consequential enhanced water exchange were considered to have brought the decrease of nutrient concentration inside the bay. Furthermore, washout of shellfish mariculture rafts by the tsunami decreased the shellfish biodeposits along with the elution of nutrients by heterotrophic bacteria. Decrease of cultivated shellfish further caused a decline in feeding pressure on phytoplankton and, subsequently, increased the phytoplankton biomass that contributed to the decrease of nutrients inside the bay. [ABSTRACT FROM AUTHOR]

In this study, the relationships between sea surface temperature (SST), chlorophyll-a (Chl-a) concentration and catch locations of sardine (Sardina pilchardus) and Atlantic chub mackerel (Scomber colias) were explored using satellite-derived SST and Chl-a together with fishing activity data for the southern and southwestern Portuguese coasts for the period January 2014 to December 2015. Chl-a and SST conditions linked with high catches differed between sardine and chub mackerel. On the southwestern Portuguese coast, sardine catches were highest for SST ranging from 16 °C to 20°C and Chl-a concentration below 4mgm-3, while high chub mackerel catches were associated with a broader range of SST values (15-21 °C) and lower values of Chl-a (<2mgm-3). On the south coast, both species had high catches for a broad range of SST conditions (14-22 °C for sardine and 12-24 °C for chub mackerel) and low Chl-a concentrations (<2.5 mgm-3 for sardine and <1.5 mgm-3 for chub mackerel). Daily presence-absence maps based on these intervals are part of the System for Integrated Monitoring of the Ocean platform. [ABSTRACT FROM AUTHOR]

From summer to autumn, in the southwestern Japan Sea, the maximum subsurface nutrient (DIN: nitrate + nitrite) concentration and minimum dissolved oxygen (DO) concentration layers lie at depths of approximately 75-125 dbar. The subsurface nutrient-rich water originates from the East China Sea through the lower layer (50-100-dbar depths) of the Tsushima Straits. On a smaller scale, in the subsurface nutrient-rich layer, submesoscale structures (~10 km) with high DO and chlorophyll- a (Chl- a) concentrations were observed below the surface euphotic zone and the minimum Chl- a layer in late October 2008. Considering that photosynthesis cannot occur in the minimum Chl- a layer, the submesoscale Chl- a maxima did not coincide with the normal maximum subsurface chlorophyll layer, where phytoplankton can mature, in the seasonal pycnocline in summer. The subsurface submesoscale water masses were zonally distributed from west to east downstream of the Tsushima Warm Current. In late November 2008, high DO and Chl- a water subducted from the surface density front to the subsurface layers along the isopycnal surface. In the large-scale frontal region of the Tsushima Warm Current, the subsurface isopycnals were convex upward both in October and November 2008, suggesting meso- and submesoscale upwellings. [ABSTRACT FROM AUTHOR]

The patterns of sea surface Chlorophyll-a (Chl-a) have regional and dynamic features. An understanding of the Chl-a dynamics and whether its trends in the past will be persistent in the future is important for restoration of ecosystem. Spatial and temporal variations of sea surface Chl-a concentrations in the Bohai Sea were investigated with data remotely sensed by MODIS from 2003 to 2014. The goals of this research are to identify the phytoplankton dynamics and detect their correlation with environmental changes and anthropogenic activities. Based on an indicator system built with Mann–Kendall Test and Hurst Exponent, our research shows that the Chl-a concentration in the surface layer is heterogeneous in both temporal and spatial scale. It is higher in costal zones, particularly near the Qinhuangdao coast. The occurrence of spring and summer blooms has a one-month time lag from south to north. An increasing trend that was persistent is evident offshore and a decreasing trend that was persistent is seen near the coast, which may indicate an expansion of eutrophication from coast to deep sea. The seasonality of the phytoplankton bloom is basically driven by vertical structure of water column. Climate and mariculture activity are significant correlated with the Chl-a trends. River discharge and suspended sediment also influence Chl-a. [ABSTRACT FROM AUTHOR]

Using ASCAT, QuikSCAT, and MODIS data, we analyzed the sea surface wind field, temperature, salinity, and chlorophyll concentrations in the mixed zone between the Bohai Sea and Yellow Sea in the winter (the period of winter 2013 included December 2013 and January-February 2014) from 2002 to 2013. We found that the intrusion of the Yellow Sea Warm Current into the Bohai Sea occurred three times in the winters of 2007 (strongest), 2004, and 2013 (weakest) during this 12-year period. We present detailed validation of the intrusion in 2013. This study shows that the intrusion of the Yellow Sea Warm Current into the Bohai Sea occurred when the wind speed, sea surface temperature, and salinity were above (or close to) the multiyear average and the chlorophyll concentration was less than the multiyear average. [ABSTRACT FROM AUTHOR]

The effect of ocean acidification and changing water conditions on primary (and secondary) marine aerosol emissions is not well understood on a regional or a global scale. To investigate this effect as well as the indirect effect on aerosol that changing biogeochemical parameters can have, ~52m³ pelagic mesocosms were deployed for several weeks in the Mediterranean Sea during both winter pre-bloom and summer oligotrophic conditions and were subjected to various levels of CO2 to simulate the conditions foreseen in this region for the coming decades. After seawater sampling, primary bubble-bursting aerosol experiments were performed using a plunging water jet system to test both chemical and physical aerosol parameters (10-400 nm). Comparing results obtained during pre-bloom and oligotrophic conditions, we find the same four lognormal modal diameters (18.5±0.6, 37.5±1.4, 91.5±2.0, 260±3.2 nm) describing the aerosol size distribution during both campaigns, yet pre-bloom conditions significantly increased the number fraction of the second (Aitken) mode, with an amplitude correlated to virus-like particles, heterotrophic prokaryotes, TEPs (transparent exopolymeric particles), chlorophyll a and other pigments. Organic fractions determined from kappa closure calculations for the diameter, Dp ~50 nm, were much larger during the pre-bloom period (64%) than during the oligotrophic period (38%), and the organic fraction decreased as the particle size increased. Combining data from both campaigns together, strong positive correlations were found between the organic fraction of the aerosol and chlorophyll a concentrations, heterotrophic and autotrophic bacteria abundance, and dissolved organic carbon (DOC) concentrations. As a consequence of the changes in the organic fraction and the size distributions between pre-bloom and oligotrophic periods, we find that the ratio of cloud condensation nuclei (CCN) to condensation nuclei (CN) slightly decreased during the pre-bloom period. The enrichment of the seawater samples with microlayer samples did not have any effect on the size distribution, organic content or the CCN activity of the generated primary aerosol. Partial pressure of CO2, pCO2, perturbations had little effect on the physical or chemical parameters of the aerosol emissions, with larger effects observed due to the differences between a pre-bloom and oligotrophic environment. [ABSTRACT FROM AUTHOR]

A new method for the calculating propagation of brackish waters from the Ob-Yenisei estuary in the Kara Sea is proposed. This method is based on satellite altimetry measurements and meteorological data. Surface currents in the upper layer are estimated as the sum of geostrophic and parameterized wind-driven transport. Geostrophic velocities are calculated using altimetry-derived sea-level anomalies and mean dynamic topography. The method has been used previously to calculate surface currents in the Black Sea [7, 12]. In this paper it has been successfully verified on the basis of comparisons with field observations of surface salinity and satellite images of sea-surface chlorophyll in the Kara Sea. [ABSTRACT FROM AUTHOR]

The distribution and composition of aliphatic and polycyclic aromatic hydrocarbons (HC) in dissolved and particulate forms, as well as in bottom sediments, was studied along the route of a vessel and at stations. It was found that the widest variability of HC concentrations in surface waters was characteristic for the frontal zones of the Yenisei River mouth (4.8-69 µg/L) and for the western branch of the St. Anna Trough (5.5-80.4 µg/L). The increased concentrations of aliphatic HC coincide with those of chlorophyll and particulate matter, as well as with the growth of the intensity of fluorescence, and are caused by natural processes. This is confirmed by HC composition. Bottom sediments are characterized by low HC concentrations, both in terms of dry mass (14 µg/g on average, with the maximum of 36.8 µg/g at station 5018 in the layer of 3-17 cm) and within C compositions (0.88%). Natural terrigenous homologues are prevailing in alkane composition of the sediments. The marginal filters of the Ob and Yenisei rivers were compared. It is shown that oil HC transferred by the rivers are deposited in the zone of marginal filters without reaching the open waters of the Kara Sea. [ABSTRACT FROM AUTHOR]

This study examines the spatio-temporal variations in the sea-surface chlorophyll-a (Chl-a) concentration and their associated underlying driving forces in the northern South China Sea (SCS) from 2004 - 2010. A stratified analysis method and the Moderate Resolution Imaging Spectroradiometer (MODIS) Chl-a product, the National Centers for Environmental Prediction (NCEP) reanalysis data, with maps of monsoon winds and current systems were used in this work. Validation indicated that the MODIS-derived Chl-a is in good agreement with in-situ measurements (R2 = 0.815), accurate enough for analyzing the temporal-spatial variations of Chl-a in the northern SCS. The results show that the spatial heterogeneity of the Chl-a concentration was lowest in winter and increased in spring. The seasonal Chl-a concentration dynamics varied spatially and depended predominantly on the distance from the coastline. The most important factors that affect the Chl-a concentration spatial variability were identified as the monsoon, surface current and sea surface temperature (SST). [ABSTRACT FROM AUTHOR]