High Phytoplankton Productivity Research Articles

Classification of optical water groups in the subarctic pacific and adjacent seas using satellite-derived light absorption spectra of chromophoric dissolved organic matter

The characteristics of the water masses that contribute to high biological production in the subarctic Pacific and adjacent seas (SPA) could change because of recent climate change. This study reports on a method to classify water in the SPA into distinct optical water groups using the light absorption coefficient of chromophoric dissolved organic matter (CDOM), aCDOM(λ), captured using an ocean color satellite. In situ samples obtained from ship surveys between 2006 and 2021 were classified into five optical group numbers (OGN1–OGN5) based on aCDOM parameters in the ultraviolet (UV) region: aCDOM(λ) at 350 nm (aCDOM(350)) and the spectral slopes at 275–295 nm (S275–295) and at 350–400 nm (S350–400). We were also able to identify OGN with a new method using machine learning technique developed in this study that adopted satellite-derived aCDOM(λ) in the visible (VIS) region. The distribution and characteristics of OGN classified using the in situ aCDOM parameters in the UV region supplement the interpretation of the origin and mixing of the water masses classified by temperature and salinity. Relative to in situ samples, the accuracy of the OGN estimation from the ocean color satellites was 83.3%. The satellite-derived OGN were able to distinguish high chlorophyll-a areas where high phytoplankton productivity is expected. In addition, identifying the distribution of OGN from satellites supports improved understanding of the bloom process. This method has potential to help to understand the impact of phenomena from accelerating ocean warming (e.g., sea ice decline, enhancement of stratification and increase in riverine input) on water masses structure and the consequent changes in the phytoplankton productivity in the SPA.

Seasonal stratification leads to changes within the benthic food web of the Gulf of Lions (northwestern Mediterranean)

Due to its extensive continental shelf, the Gulf of Lions, situated in the northwestern Mediterranean Sea, plays a crucial role in providing ecological services amidst various natural and anthropogenic pressures. Exposed to the impacts of climate change and suitable for marine energy development projects, the conservation of marine biodiversity in this environment raises significant concerns. To detect any potential disturbances in the functioning of the terrigenous mud community on the continental shelf, we conducted stable carbon and nitrogen isotope analyses on suspended particulate organic matter, sediments, and benthic fauna. Since seasonality is a structuring factor for the functioning of such an oligotrophic ecosystem, we conducted two sampling campaigns in 2018 to capture contrasting scenarios of water column stratification — one in April during well-mixed conditions and high phytoplankton production, and another in September at the end of the summer thermal stratification period characterized by low primary productivity. Stable isotope analysis revealed changes in the structure of the benthic food web in response to seasonal stratification of the water column. While isotopic niches of taxa remained evenly distributed, the total niche space contracted between sampling dates, primarily affecting low trophic level consumers. The observed contraction aligns with that reported at the base of the pelagic food web. These results enhance our understanding of the functioning of the continental shelf of the Gulf of Lions. The intense trawling pressure on the study site affected sampling. In this context, this research contributes not only to the knowledge of seasonal trophic variations but also provides a reference state to understand the future of this Mediterranean continental shelf.

Diversity, Composition and Environmental Relations of Periphytic Rotifer Assemblages in Lentic Freshwater Bodies (Flanders, Lower Belgium)

Periphytic rotifer assemblages from lentic habitats are understudied. To improve knowledge on the principal environmental determinants of their structure and composition, we examined summer periphyton from 184 freshwater bodies from a taxonomic and multi-trait-based perspective. Only the latter allowed consideration of all bdelloids. Alpha diversity decreased with electrolyte and aluminium concentration but increased with macrophyte richness, pointing at salinization, metal toxicity and loss of structural niche heterogeneity as potential threats for rotifer diversity. Replacement was the prominent component of beta diversity, with acidified sites showing the highest local contributions. Variation partitioning indicated that local conditions explained variation in species composition best, but general setting (soil type, land cover, connectivity) and spatial context were also not insignificant. Redundancy analysis related species composition more particularly to gradients of pH and trophic status, whereas the representation of functional groups was structured mainly by phytoplankton productivity. Mirroring shifts observed in the plankton, high phytoplankton productivity associated with larger size and more detritibacterivory. Dominance of collectors constrained variation in guild ratios, underlining the need for more refined functional approaches. To aid the use of periphytic rotifers in regional water quality assessment, we identified indicators and community thresholds for pH and trophic variables and determined optima and tolerances for individual taxa.

Microfossils, High-Resolution Stratigraphy, Geochemistry and Lithology of the Upper Jurassic and Lower Cretaceous (Urdyuk-Khaya and Paksa Formations) in the Nordvik Peninsula, Anabar Bay, Laptev Sea

Abstract —The goal of this study was to improve the high-resolution biostratigraphy of the Upper Jurassic and Lower Cretaceous in the type section on the Nordvik Peninsula, Anabar Bay, Laptev Sea. The results were used to identify a succession of 13 foraminiferal biostratigraphic units, 9 dinocyst units, and 8 palynofloral biostratigraphic units in the rank of zones and local zones. Based on new data, the stratigraphic continuity of this section is proved for the Lower and Middle Volgian, where a major stratigraphic hiatus was previously assumed. The established zones have variable correlation potential. Different versions of the subdivision of the section based on ammonites are discussed and the proposed scale is justified. A reference level based on calcispheres/calcareous dinocysts is defined providing global correlations and calibration of beds near Jurassic–Cretaceous boundary in the Tethyan and Arctic regions. The magnetostratigraphic subdivision of the studied section and its comparison with the Tethyan regions are discussed. Together with biostratigraphic data, the proposed δ13Corg curve in the Upper Jurassic and lower part of the Valanginian can be a tool for detailed correlations in different regions of the Northern Hemisphere. The cyclicity of carbon isotope composition in the Upper Volgian and Boreal Berriasian and isotope events in the Volgian and Lower Valanginian are determined within the Arctic region. The distribution of geochemical parameters (Corg, δ13Corg and hydrogen index) is determined in studied section, geochemical stratification of the section and variations in major oxide compositions are demonstrated. A sharp change in geochemical parameters is identified at the base of the Paksa Formation (Upper Volgian). The distribution interval of the “subsurface chlorophyll maximum” is determined. The study shows that high concentrations of isotopically light organic carbon in the first diasterene geochemical subhorizon were caused by high phytoplankton productivity and were deposited under reducing conditions favorable for preservation of organic matter. The analysis of major oxide compositions of the studied rocks revealed that variations in the chemical composition of the studied rocks reflect changes in their mineralogy and petrography.

Physical mechanisms affecting phytoplankton variability along the Chilean coast

Chile has high phytoplankton production due to being a classic example of an Eastern Boundary Upwelling System. Monthly averaged chlorophyll-α (Chl) and physical parameters (sea surface temperature, precipitation rate, southerly and westerly winds) were studied off the Chilean coast from 2002 to 2018, in order to understand the primary production along this important ocean margin. The coastal margin was split into three zones and ten sub-sections. The Northern Zone had a low phytoplankton production with small seasonal variability, except in its north. This pattern is due to a narrow shelf, weak winds, lack of precipitation and relatively stable weather conditions driven by the Southeast Pacific Subtropical Anticyclone (SPSA). The Central Zone presented a seasonally varying production, with a high Chl concentration in summer and early spring. This is linked to the SPSA movement and sunlight reduction during the winter. A high Chl activity is seen in the Southern Zone despite this Zone being at the limits of the SPSA effect, leading to weak longshore winds only during the warm season. Overall, this study has demonstrated the importance of shelf width and the upwelling driven by the presence or absence of the SPSA for ocean primary production. Thus, the most productive region is from 35°S to 45°S owing to both variables being present.

Biomarker Records of Environmental Shifts on the Labrador Shelf During the Holocene

AbstractThe ultimate demise of the Laurentide Ice Sheet (LIS) and the preceding and succeeding oceanographic changes along the western Labrador Sea offer insights critically important to improve climate predictions of expected future climate warming and further melting of the Greenland ice cap. However, while the final disappearance of the LIS during the Holocene is rather well constrained, the response of sea ice during the resulting meltwater events is not fully understood. Here, we present reconstructions of paleoceanographic changes over the past 9.3 Kyr BP on the northwestern Labrador Shelf, with a special focus on the interaction between the final meltwater event around 8.2 Kyr BP and sea ice and phytoplankton productivity (e.g., IP25, HBI III (Z), brassicasterol, dinosterol, biogenic opal, total organic carbon). Our records indicate low sea‐ice cover and high phytoplankton productivity on the Labrador Shelf prior to 8.9 Kyr BP, sea‐ice formation was favored by decreased surface salinities due to the meltwater events from Lake Agassiz‐Ojibway and the Hudson Bay Ice Saddle from 8.55 Kyr BP onwards. For the past ca. 7.5 Kyr BP sea ice is mainly transported to the study area by local ocean currents such as the inner Labrador and Baffin Current. Our findings provide new insights into the response of sea ice to increased meltwater discharge as well as shifts in atmospheric and oceanic circulation.

Glacier retreat alters downstream fjord ecosystem structure and function in Greenland

The melting of the Greenland Ice Sheet is accelerating, with glaciers shifting from marine to land termination and potential consequences for fjord ecosystems downstream. Monthly samples in 2016 in two fjords in southwest Greenland show that subglacial discharge from marine-terminating glaciers sustains high phytoplankton productivity that is dominated by diatoms and grazed by larger mesozooplankton throughout summer. In contrast, melting of land-terminating glaciers results in a fjord ecosystem dominated by bacteria, picophytoplankton and smaller zooplankton, which has only one-third of the annual productivity and half the CO2 uptake compared to the fjord downstream from marine-terminating glaciers.

Insights into Toxic Prymnesium parvum Blooms as a Cause of the Ecological Disaster on the Odra River

In 2022, Poland and Germany experienced a prolonged and extensive mass fish kill in the Odra River. During the period from the end of July to the beginning of September 2022, a high level of incidental disease and mortality was observed in various fish species (dozens of different species were found dead). The fish mortality affected five Polish provinces (Silesia, Opole, Lower Silesia, Lubuskie, and Western Pomerania) and involved reservoir systems covering most of the river (the Odra River is 854 km long, of which 742 km are in Poland). Fatal cases were investigated using toxicological, anatomopathological, and histopathological tests. Water samples were collected to determine nutrient status in the water column, phytoplankton biomass, and community composition. High nutrient concentrations indicated high phytoplankton productivity, with favorable conditions for golden algal blooms. The harmful toxins (prymnesins secreted by Prymnesium parvum habitats) had not been found in Poland before, but it was only a matter of time, especially in the Odra River, whose waters are permanently saline and still used for navigation. The observed fish mortality resulted in a 50% decrease in the fish population in the river and affected mainly cold-blooded species. Histopathological examinations of fish showed acute damage to the most perfused organs (gills, spleen, kidneys). The disruption to hematopoietic processes and damage to the gills were due to the action of hemolytic toxins (prymnesins). An evaluation of the collected hydrological, meteorological, biological, and physico-chemical data on the observed spatio-temporal course of the catastrophe, as well as the detection of three compounds from the group of B-type prymnesins in the analyzed material (the presence of prymnesins was confirmed using an analysis of the fragmentation spectrum and the accurate tandem mass spectrometry (MS/MS) measurement, in combination with high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS), allowed the formulation and subsequent testing of the hypothesis for a direct link between the observed fish mortality and the presence of prymnesins in the Odra River. This article systematizes what is known about the causes of the fish kill in the Odra River in 2022, based on official government reports (one Polish and one German) and the EU technical report by the Joint Research Centre. A review and critical analysis of government findings (Polish and German) on this disaster were conducted in the context of what is known to date about similar cases of mass fish kills.

Identification of Phytoplankton-Based Production of the Clam Corbicula japonica in a Low-Turbidity Temperate Estuary Using Fatty Acid and Stable Isotope Analyses

The brackish water clam, Corbicula japonica, acts as an ecosystem engineer in estuaries. To identify its resource-use patterns in the low-turbidity temperate Seomjin River estuary of Korea, we analyzed stable isotope and fatty acid (FA) biomarkers to differentiate allochthonous and autochthonous dietary sources, and examined the effects of clam size, salinity gradient, and season. The δ13C and δ15N values were consistent across the three factors. The δ13C values of the clams were similar to those of both riverine- and estuarine-suspended particulate organic matter (R- and E-SPOM), while their δ15N values were 2–4‰ higher, indicating an equal contribution of both sources to the clam diet. Biogeochemical proxies and FA compositions of SPOM indicate that estuarine phytoplankton significantly contribute to the E-SPOM pool. Moreover, the similarity in FA profiles between Corbicula and E-SPOM indicates that phytoplankton-derived organic matter is the primary source of nutrition for the clam, with minimal impact from growth, salinity gradient, or seasonal changes. Our study suggests that in low-turbidity estuaries with high phytoplankton production, allochthonous organic matter makes a negligible contribution to clam nutrition, compared to high-turbidity estuaries. This finding could provide insights into the variations in the trophic structure of estuarine food webs across diverse regions.

Phytoplankton productivity and community structure changes in the middle Okinawa Trough since the last deglaciation

Marine phytoplankton plays an important role in the ocean biological pump, whereas our understandings of phytoplankton growth in response to global climate and enviromment changes are still debated. Due to the forcing from the strong land-ocean interaction between the East Asia and the Indo-Pacific Warm Pool, the Okinawa Trough is characterized by high phytoplankton productivity and fast sediment accumulation, therefore it provides ideal archives to study marine productivity changes on millennial-to-orbital timescales. In this study, lipid biomarkers of C37 alkenones, dinosterol and brassicasterol, were analyzed in a sediment core M063–05 retrieved from the middle Okinawa Trough to reconstruct phytoplankton productivity and community structure changes over the last 15.8 kyr. We find that temporal variations of these lipid biomarker contents are parallel with precipitation changes in the Changjiang drainage basin during the last deglaciation, with high values during increased precipitation interval (14.5–12.7 ka) and low values during decreased precipitation intervals (15.8–15.0 ka and 12.7–11.5 ka). We propose that precipitation-induced terrestrial nutrient supply controlled phytoplankton growth in the middle Okinawa Trough during the last deglaciation. Lipid biomarker ratios reveal high (low) contributions of diatoms and dinoflagellates to total phytoplankton productivity during increased (decreased) precipitation intervals. The phytoplankton community structure record is also consistent with precipitation-induced terrestrial nutrient forcing during the deglacial stage, with higher nutrient condition favored diatom and dinoflagellate growth. Precipitation in the Changjiang drainage basin was mainly controlled by the East Asian summer monsoon change and the Intertropical Convergence Zone migration, however the deglacial sea level rise also modulated the forcing of precipitation on phytoplankton growth by affecting the delivery distance of terrestrial nutrients to our site. From the last deglaciation to the Holocene, the biomarker content decreased and the contribution of coccolithophorids to total phytoplankton productivity increased at the expense of dinoflagellates and diatoms. The most likely explanation is the regime shift of major nutrient sources supporting phytoplankton growth, from terrestrial riverine nutrients during the deglaciation to the Kuroshio subsurface water nutrients during the Holocene. Our results provide new insight of past phytoplankton responses to climate and environment changes.

Nutrient Pollution and Its Dynamic Source-Sink Pattern in the Pearl River Estuary (South China)

Nutrient enrichment and its quantitative cause-effect chains of the biogeochemical processes have scarcely been documented in the Pearl River Estuary (South China). Field investigations of nutrient samples taken between 1996 and 2018 showed significant differences in nitrogen and phosphorus with times and sites. The concentrations of DIN and DIP gradually increased over the past two decades, with good fitted linear curves (R2 = 0.31 for DIN, R2 = 0.92 for DIP); while the temporal variation in DSi was non-significant. Higher levels of nitrogen and silicate mainly appeared in the upper estuary because of the riverine influence. The phosphorus pollution was accumulated in the northeast (e.g., Shenzhen bay). The aquatic environment was highly sensitive to nutrient pollution and eutrophication risk, which accordingly corresponded to high phytoplankton production and biodiversity. Phosphorus was the limiting factor of phytoplankton growth in this estuary, and more frequently caused the eutrophication risks and blooms. The nutrient pollution was largely influenced by riverine inputs, quantified by PCA-generation, and the contributions of coastal emission and atmospheric deposition were followed. The two-end member mixing model differentiated the physical alterations from the biological activity and identified the dynamic source-sink patterns of nutrient species. Nitrogen and silicate had relatively conservative behaviors in the estuary and phosphate showed an active pattern.

Causes and timing of recurring subarctic Pacific hypoxia.

Several North Pacific studies of the last deglaciation show hypoxia throughout the ocean margins and attribute this phenomenon to the effects of abrupt warming and meltwater inputs. Yet, because of the lack of long records spanning multiple glacial cycles and deglaciation events, it is unclear whether deoxygenation was a regular occurrence of warming events and whether deglaciation and/or other conditions promoted hypoxia throughout time. Here, subarctic Pacific laminated sediments from the past 1.2 million years demonstrate that hypoxic events recurred throughout the Pleistocene as episodes of highly productive phytoplankton growth and were generally associated with interglacial climates, high sea levels, and enhanced nitrate utilization-but not with deglaciations. We suggest that hypoxia was typically stimulated by high productivity from iron fertilization facilitated by redox-remobilized iron from flooded continental shelves.

The water column of the Yamal tundra lakes as a microbial filter preventing methane emission

Abstract. Microbiological, molecular ecological, biogeochemical, and isotope geochemical research was carried out in four lakes of the central part of the Yamal Peninsula in the area of continuous permafrost. Two of them were large (73.6 and 118.6 ha) and deep (up to 10.6 and 12.3 m) mature lakes embedded into all geomorphological levels of the peninsula, and two others were smaller (3.2 and 4.2 ha) shallow (2.3 and 1.8 m) lakes which were formed as a result of thermokarst on constitutional (segregated) ground ice. Samples were collected in August 2019. The Yamal tundra lakes were found to exhibit high phytoplankton production (340–1200 mg C m−2 d−1) during the short summer season. Allochthonous and autochthonous, particulate and dissolved organic matter was deposited onto the bottom sediments, where methane was the main product of anaerobic degradation, and its content was 33–990 µmol CH4 dm−3. The rates of hydrogenotrophic methanogenesis appeared to be higher in the sediments of deep lakes than in those of the shallow ones. In the sediments of all lakes, Methanoregula and Methanosaeta were predominant components of the archaeal methanogenic community. Methane oxidation (1.4–9.9 µmol dm−3 d−1) occurred in the upper sediment layers simultaneously with methanogenesis. Methylobacter tundripaludum (family Methylococcaceae) predominated in the methanotrophic community of the sediments and the water column. The activity of methanotrophic bacteria in deep mature lakes resulted in a decrease in the dissolved methane concentration in lake water from 0.8–4.1 to 0.4 µmol CH4 L−1 d−1, while in shallow thermokarst lakes the geochemical effect of methanotrophs was much less pronounced. Thus, only small, shallow Yamal lakes may contribute significantly to the overall diffusive methane emissions from the water surface during the warm summer season. The water column of large, deep lakes on Yamal acts, however, as a microbial filter preventing methane emission into the atmosphere. It can be assumed that climate warming will lead to an increase in the total area of thermokarst lakes, which will enhance the effect of methane release into the atmosphere.

ECOSYSTEM METABOLISM AND OXYGEN DEFICIT IN LAKE MANINJAU: INSIGHT FROM HIGH-FREQUENCY MEASUREMENT

High-frequency measurement provides a sophisticated insight in capturing environmental pattern. Compared to traditional discrete measurement, high-frequency sensors allow better understanding of any processes particularly those with temporal scale characteristics. Lake metabolism is one of the exemplars getting advantage of such better resolution measurement. The dynamics of dissolved oxygen concentration (DO) observed in hourly manner, even in minutes, may explain the balance of photosynthetic activity as expressed by gross primary production (GPP) and respiration (R), and atmospheric exchange. Using a coupled thermistor-chain and oxygen sensor, we computed lake metabolism of the eutrophic Lake Maninjau. Characterized by high phytoplankton productivity fueled by the abundance of nutrient availability, DO concentration in Lake Maninjau is likely to be supersaturated. On the other hand, floating cage aquaculture operated in the lake may have a consequence in increasing water column heterotrophy, oxygen demanding community. Through a simple mathematical model we revealed that water column respiration in Lake Maninjau is higher than gross primary production (R > GPP) with an average of 12.1 mg O 2 L -1 day -1 and 9.0 mg O 2 L -1 day -1 , respectively. Our findings highlight that as heterotrophy in eutrophic lakes may relatively be high, oxygen depletion in the water column may occur in any instance, especially in lakes where dense floating cage aquaculture is in place. Keywords: lake metabolism, dissolved oxygen, high-frequency monitoring, heterotrophy

Seasonal and Spatial Variability in the Biogenic Production and Consumption of Volatile Organic Compounds (VOCs) by Marine Plankton in the North Atlantic Ocean

Marine-derived volatile organic compounds (VOCs) influence global carbon cycling, atmospheric reactions, and climate. Yet, the biogenic production (sources) and consumption (sink) rates of marine VOCs are not well-constrained and are currently excluded from global chemical transport models. We directly measured the net biogenic production rates of seven VOCs (acetaldehyde, acetone, acetonitrile, dimethylsulfide, isoprene, methanethiol, and methanol) in surface seawater during four field campaigns in the North Atlantic Ocean that targeted different stages of the phytoplankton annual cycle. All of the VOCs exhibited strong seasonal trends, with generally positive rates during May (peak spring bloom) and lower, sometimes negative rates (net consumption), during November and/or March (the winter bloom minimum transition). Strong latitudinal gradients were identified for most VOCs during May and September, with greater production observed in the northern regions compared to the southern regions. These gradients reflect the interplay between high phytoplankton and bacterial productivity. During the bloom transition stages (March and September), acetaldehyde and acetone exhibited net production rates that bracketed zero, suggesting that biogenic production was either very low or indicative of a tightly coupled system with more complex underlying microbial VOC cycling. Our data provides the first direct evidence for widespread biogenic acetonitrile production and consumption in the surface ocean and the first net biogenic production rates for methanethiol in natural seawater.

A comparison of spring body condition, maturation status, and diet in the European sardine, Sardina pilchardus (Teleostei: Clupeidae) from contrasting environments off the Moroccan Atlantic coast

ABSTRACT The bulk of marine fish production in Morocco comprises small pelagic with a large predominance of the European sardine Sardina pilchardus. Information on feeding intensity and diet composition of small pelagic fish are of great importance for understanding species ecology and life-history traits and fisheries management. In the present study, we compared body condition, sexual maturation, feeding intensity and diet composition (stomach content analysis) in sardines from contrasting fishing environments representative of the three Moroccan Atlantic stocks (North: Larache; central: Safi; and south: Dakhla) in spring 2016. The body condition factor increased from north to south and varied inversely with gonado- and hepato-somatic ratios. The feeding intensity was low in Larache and Dakhla and higher in Safi, related to the reproductive status. Sardines are generalist feeders selecting primarily zooplankton (copepods and cnidarians) in Larache and phytoplankton (diatoms and dinoflagellates) in Dakhla and Safi. However, based on carbon content, sardines from the three locations are rather zooplanktivorous. Great similarity in numerical specific abundance was found between the diets in sardines from Dakhla and Safi, which are areas of high phytoplankton productivity in the spring. In contrast, there was a low similarity in diet between sardines from Dakhla and Larache in relation to the low productivity and differences in sexual maturation of sardines from the latter. We concluded that in spring, the feeding intensity and diet composition of sardines depend on their reproductive status and ecosystem productivity, which affect their body condition.

Depth-Differentiation and Seasonality of Planktonic Microbial Assemblages in the Monterey Bay Upwelling System.

Coastal upwelling regions are hotspots of biological productivity, supporting diverse communities of microbial life and metabolisms. Monterey Bay (MB), a coastal ocean embayment in central California, experiences seasonal upwelling of cold, nutrient-rich waters that sustain episodes of high phytoplankton production in surface waters. While productivity in surface waters is intimately linked to metabolisms of diverse communities of Archaea and Bacteria, a comprehensive understanding of the microbial community in MB is missing thus far, particularly in relation to the distinct hydrographic seasons characteristic of the MB system. Here we present the results of a 2-year microbial time-series survey in MB, investigating community composition and structure across spatiotemporal gradients. In deciphering these patterns, we used unique sequence variants (SVs) of the 16S rRNA gene (V4–V5 region), complemented with metagenomes and metatranscriptomes representing multiple depth profiles. We found clear depth-differentiation and recurring seasonal abundance patterns within planktonic communities, particularly when analyzed at finer taxonomic levels. Compositional changes were more pronounced in the upper 0–40 m of the water column, whereas deeper depths were characterized by temporally stable populations. In accordance with the dynamic nutrient profiles, the system appears to change from a Bacteroidetes- and Rhodobacterales-dominated upwelling period to an oceanic season dominated by oligotrophic groups such as SAR11 and picocyanobacteria. The cascade of environmental changes brought about by upwelling and relaxation events thus impacts microbial community structure in the bay, with important implications for the temporal variability of nutrient and energy fluxes within the MB ecosystem. Our observations emphasize the need for continued monitoring of planktonic microbial communities in order to predict and manage the behavior of this sensitive marine sanctuary ecosystem, over projected intensification of upwelling in the region.

Distribution and grazing of the dominant mesozooplankton species in the Yenisei estuary and adjacent shelf in early summer (July 2016)

Estuaries of large Siberian rivers, Yenisei and Ob, play a pivotal role in transformation and sedimentation of the suspended matter from the riverine runoff. The mesozooplankton community is one of the key players in estuarine functioning. Most of the studies in the Yenisei region were performed at the end of the productive season (August–September) and concentrated on the structure of zooplankton community. The main goal of this study was to characterize structure and grazing of the zooplankton community in the Yenisei estuarine and plume-affected shelf region in early summer soon after the discharge maximum. More specifically, we assessed zooplankton biomass and analyzed the distribution patterns of the dominant species in July; assessed herbivorous feeding rates; and grazing pressure of these species during the period of high phytoplankton production. Zooplankton were collected and feeding rates were studied along a quasi-latitudinal transect in the Yenisei Estuary and the adjacent shelf in July 2016. Freshwater zone (FWZ), frontal zone of the Yenisei plume (YFZ) and shelf zone outside the plume (MSZ) were distinguished according to salinity and temperature. Highest biomass (12–101 mg DW m−3) was recorded in the YFZ. Several specific aspects of distribution and grazing were distinguished. Cladocera were highly abundant in the FWZ and grazed up to 14% of phytoplankton there. Species which dominated zooplankton in the YFZ avoided the upper freshened layer, and maximum abundance of both marine and brackish species coincided with the gradient layer. The brackish Limnocalanus macrurus penetrated far into the north where this species was supposedly exported earlier with the maximal runoff. Low ingestion (0.1–0.9% body carbon) and demographic structure of L. macrurus suggest termination of seasonal development of the population. Herbivorous feeding of the marine copepods exceeded their metabolic demands in the estuarine zone and was insufficient in the marine shelf zone. The highest daily grazing pressure in the YFZ (up to 21% phytoplankton biomass) was exerted by Calanus glacialis. Analysis of our results together with the published data implies that timing of ice retreat is among the main factors controlling seasonal development of the dominant zooplankton populations.

Estimating Carbon Flux From Optically Recording Total Particle Volume at Depths Below the Primary Pycnocline

Optical instruments can rapidly determine numbers and characteristics of water column particles with high sensitivity. Here we show the usefulness of optically assessed total particle volume below the main pycnocline to estimate carbon export in two systems: the open subarctic North Atlantic and the Ross Sea, Antarctica. Both regions exhibit seasonally high phytoplankton production and efficient export (i.e., a strong biological pump). Total particle volumes in the mesopelagic (200-300 m) were significantly correlated with those in the overlying surface mixed layer (50 - 60 m), indicating that most particles at depth reflect export from the surface. This connectivity, however, is modulated by the physical structure of the water column and by particle type (e.g., the presence of colonies of the haptophyte Phaeocystis antarctica versus diatoms). Evidence from both regions show that a strong pycnocline can delay or may even prevent particles from settling to deeper layers, which then succumb to disintegration, or microbial and/or zooplankton consumption. Strong katabatic winds in the Ross Sea may deepen the mixed layer, causing a rapid transfer of particles to mesopelagic depths through the mixed-layer pump. Independent estimates of seasonally integrated export production in the Ross Sea, based on upper water column carbon mass balance, were significantly correlated (in the order of shared variance) with 1) total particle volumes from images, 2) particulate organic carbon, and 3) chlorophyll fluorescence, all recorded at a depth range of 200 – 300 m. Carbon export was not significantly correlated with particle abundance measured by a Coulter Counter at the same depth range. Measuring total particle volume below the primary pycnocline is therefore a useful approach to estimate carbon export at least in regions characterized by seasonally high particle export.

From Land to the Ocean: The Interplay Between Allochthonous and Autochthonous Contribution to Particles in Nepheloid Layers of the Cariaco Basin, Venezuela

AbstractLithogenic sediment input to the Cariaco Basin on the eastern Venezuelan shelf is controlled by small mountainous rivers (SMRs). The Cariaco Basin is also an area of high phytoplankton productivity as a result of strong Trade Wind‐driven coastal upwelling. Characterizing the sources that supply particulate organic carbon (POC) to the deep Cariaco Basin is important for interpreting the paleoclimate record stored in its sediments. We measured suspended POC in the four main rivers draining into the Caraiaco Basin, the Tuy, Unare, Neveri, and Manzanares, between September 2008 and September 2009 and conducted basin‐wide oceanographic cruises in September 2008 (rainy season) and March 2009 (upwelling season). Riverine concentrations of dissolved organic carbon (DOC) and POC in the four rivers were comparable to observations made in similar tropical SMR systems (POC was between 0.3–2 mg C l−1; DOC was between 100–300 μM). Within the basin, the geochemical composition of surface particles and bottom nepheloid layers (BNLs) changed with season. During the rainy season, the isotopic composition of both surface particles and BNL was characteristic of continentally derived material (δ13Corg, approximately −30 to −26‰), while during upwelling, the composition shifted to values more typical of marine sources (δ13Corg, approximately −24 to −20‰). SMRs represent an important component of the global carbon budget, which are often overlooked in ocean carbon budgets and also in paleoclimate studies of coastal environments.