Post-bloom Conditions Research Articles

Iodide, iodate & dissolved organic iodine in the temperate coastal ocean

The surface ocean is the main source of iodine to the atmosphere, where it plays a crucial role including in the catalytic removal of tropospheric ozone. The availability of surface oceanic iodine is governed by its biogeochemical cycling, the controls of which are poorly constrained. Here we show a near two-year time series of the primary iodine species, iodide, iodate and dissolved organic iodine (DOI) in inner shelf marine surface waters of the Western English Channel (UK). The median ± standard deviation concentrations between November 2019 and September 2021 (n=76) were: iodide 88 ± 17 nM (range 61-149 nM), iodate 293 ± 28 nM (198-382 nM), DOI 16 ± 16 nM (<0.12-75 nM) and total dissolved iodine (dIT) 399 ± 30 nM (314-477 nM). Though lower than inorganic iodine ion concentrations, DOI was a persistent and non-negligible component of dIT, which is consistent with previous studies in coastal waters. Over the time series, dIT was not conserved and the missing pool of iodine accounted for ~6% of the observed concentration suggesting complex mechanisms governing dIT removal and renewal. The contribution of excess iodine (I*) sourced from the coastal margin towards dIT was generally low (3 ± 29 nM) but exceptional events influenced dIT concentrations by up to ±100 nM. The seasonal variability in iodine speciation was asynchronous with the observed phytoplankton primary productivity. Nevertheless, iodate reduction began as light levels and then biomass increased in spring and iodide attained its peak concentration in mid to late autumn during post-bloom conditions. Dissolved organic iodine was present, but variable, throughout the year. During winter, iodate concentrations increased due to the advection of North Atlantic surface waters. The timing of changes in iodine speciation and the magnitude of I* subsumed by seawater processes supports the paradigm that transformations between iodine species are biologically mediated, though not directly linked.

Local variability of Arctic mesozooplankton biomass and production: A case summer study

The Barents Sea is a highly productive ecosystem within the Arctic Ocean. The overall biological productivity in this region relies heavily on the secondary mesozooplankton production (MZP). Previous research has primarily focused on mesozooplankton abundance (MZA) and biomass (MZB), lacking a comprehensive analysis of the environmental factors that influence MZP in the Arctic marine environment. The primary objective of this study was to examine the key factors responsible for the spatial variability in the community structure and MZP during the summer season. Data were collected from 52 stations in the central Barents Sea, specifically during post-bloom conditions in 2015. Through cluster analysis, two distinct groups of stations were identified, differing in terms of mesozooplankton taxa abundance. Copepods were found to dominate the mesozooplankton assemblages, comprising 89% of total MZA, 83% of MZB, and 68% of MZP. The biomass stocks in the study area varied from 8 to 102 mg dry mass (DM) m−3, with an average of 44 mg DM m−3. MZP rates ranged from 0.34 to 2.33 mg DM m−3 day−1, with an average of 1.16 mg DM m−3 day−1. The highest MZB and MZP values were observed at frontal zones that separated relatively warm and cold waters. Through redundancy analysis, it was determined that the primary environmental factors affected the distribution of mesozooplankton were longitude, latitude, and sampling depth. Temperature, salinity, and chlorophyll a concentration were found to have a less significant impact. These findings emphasize the importance of oceanographic conditions as the main predictors of mesozooplankton distribution during the summer season in the Arctic marine environment. This study highlights the essential role of environmental forcing in determining the productivity of Arctic marine zooplankton. Given the ongoing climatic changes, the results of this report can serve as a valuable tool for monitoring pelagic ecosystems in the Arctic.

Absence of photophysiological response to iron addition in autumn phytoplankton in the Antarctic sea-ice zone

Abstract. The high nutrient–low chlorophyll condition of the Southern Ocean is generally thought to be caused by the low bioavailability of micronutrients, particularly iron, which plays an integral role in phytoplankton photosynthesis. Nevertheless, the Southern Ocean experiences seasonal blooms that generally initiate in austral spring, peak in summer, and extend into autumn. This seasonal increase in primary productivity is typically linked to the seasonal characteristics of nutrient and light supply. To better understand the potential limitations on productivity in the Antarctic sea-ice zone (SIZ), the photophysiological response of phytoplankton to iron addition (2.0 nM FeCl3) was investigated during autumn along the Antarctic coast off Dronning Maud Land. Five short-term (24 h) incubation experiments were conducted around Astrid Ridge (68∘ S) and along a 6∘ E transect, where an autumn bloom was identified in the region of the western SIZ. Surface iron concentrations ranged from 0.27 to 1.39 nM around Astrid Ridge, and 0.56 to 0.63 nM along the 6∘ E transect. Contrary to expectation, the photophysiological response of phytoplankton to iron addition, measured through the photosynthetic efficiency and the absorption cross-section for photosystem II, showed no significant responses. It is thus proposed that since the autumn phytoplankton in the SIZ exhibited a lack of an iron limitation at the time of sampling, the ambient iron concentrations may have been sufficient to fulfil the cellular requirements. This provides new insights into extended iron replete post-bloom conditions in the typically assumed iron deficient high nutrient–low chlorophyll Southern Ocean.

Contrasting sea ice conditions shape microbial food webs in Hudson Bay (Canadian Arctic)

The transition from ice-covered to open water is a recurring feature of the Arctic and sub-Arctic, but microbial diversity and cascading effects on the microbial food webs is poorly known. Here, we investigated microbial eukaryote, bacterial and archaeal communities in Hudson Bay (sub-Arctic, Canada) under sea-ice cover and open waters conditions. Co-occurrence networks revealed a <3 µm pico‒phytoplankton-based food web under the ice and a >3 µm nano‒microphytoplankton-based food web in the open waters. The ice-edge communities were characteristic of post-bloom conditions with high proportions of the picophytoplankton Micromonas and Bathycoccus. Nano‒ to micro‒phytoplankton and ice associated diatoms were detected throughout the water column, with the sympagic Melosira arctica exclusive to ice-covered central Hudson Bay and Thalassiosira in open northwestern Hudson Bay. Heterotrophic microbial eukaryotes and prokaryotes also differed by ice-state, suggesting a linkage between microbes at depth and surface phytoplankton bloom state. The findings suggest that a longer open water season may favor the establishment of a large phytoplankton-based food web at the subsurface chlorophyll maxima (SCM), increasing carbon export from pelagic diatoms to deeper waters and affect higher trophic levels in the deep Hudson Bay.

Temperature enhances the functional diversity of dissolved organic matter utilization by coastal marine bacteria.

Although bulk bacterial metabolism in response to temperature has been determined for different oceanic regions, the impact of temperature on the functional diversity of dissolved organic matter (DOM) utilization has been largely unexplored. Here, we hypothesized that besides modifying the rates of carbon utilization, temperature can also alter the diversity of substrates utilized. The patterns of utilization of 31 model DOM compounds (as represented in Biolog EcoPlate™) by bacterioplankton were assessed using inocula from surface waters of the southern Bay of Biscay continental shelf over 1 year. Bacteria utilized more polymers and carbohydrates in late spring and summer than in winter, likely reflecting changes in substrate availability linked to the release and accumulation of DOM in phytoplankton post-bloom conditions. Seawater temperature correlated positively with the number of substrates utilized (i.e. functional richness) and this relationship was maintained in monthly experimental incubations spanning 3°C below and above in situ values. The enhancement of functional richness with experimental warming displayed a unimodal response to ambient temperature, peaking at 16°C. This temperature acted as a threshold separating nutrient-sufficient from nutrient-deficient conditions at the study site, suggesting that trophic conditions will be critical in the response of microbial DOM utilization to future warming.

Spatial occurrence and abundance of marine zooplankton in Northeast Greenland

We present a large-scale survey of mesozooplankton (size range 0.2–20 mm) across coastal, shelf, and slope locations in Northeast Greenland (latitudes 74–79° N, August 2015 and September 2017). Our study is centred on the Video Plankton Recorder (VPR) for non-invasive in situ observations of taxa distribution and abundance while simultaneously recording oceanographic profiles. A modified WP-2 plankton net (85-μm mesh size) was used primarily not only to verify taxa detected by the VPR but also to make a preliminary comparison of abundance estimates by the two gears. A total of 35 zooplankton taxa were identified with 10 genera alone among copepods (Hexanauplia). Selected taxa from the VPR (N=16) were associated with the temperature-salinity spaces and the chlorophyll a-depth profiles in the study area. From surface to > 900 m depth, the overall temperature and salinity ranged between −1.9 and 6.8 °C and 26.6 and 35.3, respectively. Two copepod genera dominated, i.e. Pseudocalanus prevailed in the upper sub-zero layers in coastal waters whereas Calanus was omnipresent, but mainly abundant in the warmer Atlantic waters at the shelf break. Chlorophyll a levels were in general very low (< 2 mg m-3) and peaked at 30–50 m depth, suggesting post-bloom conditions. Overall, zooplankton abundances tended to increase from the coast towards the slope (9–344×103 individuals m-2). Biodiversity in terms of taxon richness, on the other hand, showed the opposite trend and decreased from 16 taxa at the coast to 5 taxa further offshore.

New insights into trace metal speciation and interaction with phytoplankton in estuarine coastal waters

In coastal productive zones, phytoplankton activity may influence trace metal speciation and partitioning at short temporal scale. We coupled hourly in situ voltammetry quantification of the lead (Pb), cadmium (Cd), and copper (Cu) potentially bioavailable fractions, using an innovative submersible sensing probe (the TracMetal), to surface water sampling for the quantification of the targeted trace metals in the dissolved <0.2 μm and <0.02 μm fractions, suspended particles, and phytoplankton nets in the Gironde Estuary mouth. The in situ TracMetal monitoring reflected real-time dynamic Cd and Cu regeneration related to algal cells under post-bloom conditions as well as Pb remobilization due to photoreduction of colloids. The potentially bioavailable fraction consisted in 30, 30–50 and <10 % of the total dissolved fraction for Pb, Cd, and Cu, respectively, representing crucial ecotoxicological information. Metal bioconcentration factors using the dynamic fraction concentrations showed levels up to 107 for Cu in phytoplankton.

Total lipid and fatty acid composition of mesozooplankton functional group members in the NE Pacific over a range of productivity regimes

Fish, whales, and seabirds along the productive west coast of Vancouver Island (WCVI), NE Pacific, rely on copepod prey that are assumed to be rich in lipid. However, the total lipid (TL) and fatty acid content of most copepod species and other mesozooplankton in this region have not been measured. To assess the diets and quality of zooplankton prey off the WCVI, we investigated differences in lipid content and composition of mesozooplankton according to their taxonomic versus functional group identities. Copepods, chaetognaths, euphausiids, and amphipods, belonging to 3 different functional groups, were sampled on the WCVI during pre-, mid-, and post-bloom conditions. Compared to taxonomic classifications, the functional group approach was superior in its ability to discern statistical differences in TL among zooplankton and between seasons. Furthermore, multivariate analyses using zooplankton fatty acid composition from all oceanographic regimes produced 3 to 4 statistically different clusters of species that corroborated functional group designations. However, some trophic flexibility was observed in several copepod species, particularly Calanus marshallae, that may relate to food scarcity or the presence of potentially noxious prey. The omnivorous-herbivorous functional group frequently contained higher amounts of TL and masses of essential fatty acids than the carnivorous group. Euphausiids and C. marshallae contributed the most lipid (mg m-3) to the pelagic ‘lipid pool’, due to very high lipid content and high abundance, respectively. However, on the continental slope and shelf break, chaetognaths and Neocalanus spp. copepods contributed substantially to the lipid pool.

Role of mesoscale eddies in the sustenance of high biological productivity in North Eastern Arabian Sea during the winter-spring transition period

Convective mixing, mesoscale eddies and regenerated production sustain an above-average biological productivity in the North East Arabian Sea (NEAS) during the winter-spring transition period. Satellite-derived long-term data sets on Chlorophyll-a (Chl-a), Sea Surface Height Anomaly (SSHA), Sea Surface Temperature (SST) and Okubo-Weiss parameterization show existence of number of mesoscale eddies, propagating and non-propagating, that contribute to the regional production. The dominance of Eddy Kinetic Energy (EKE) over the Available Potential Energy (APE) in the core depth and the diameter (120km) of the observed eddy being wider than the Rossby Radius of Deformation (RRD, 55 km), it is suggested that the baroclinic instability is a possible mechanism for the eddy formation. Spatial variation in APE and its influences on the regional dynamics, including chemical and biological response are explained. In the non-eddy areas, where convective mixing is active, diatoms (96.74%) dominated than dinoflagellates (3.14%), and the Chl-a in the Cold Core Eddy (CCE) were two to three folds higher to non-eddy regions. The abundance increased from core (58,152 cells L−1) to periphery (5.95 × 105 cells L−1) where the water column is less dynamic. Extensive blooms of the dinoflagellate green Noctiluca (N. scintillans) contribute to the very high cell density in the periphery of the CCE, where the currents were comparatively weak, and water column was more stable. Active mixing is associated with diatom dominance, followed by Noctiluca when the mixing slackens, making use of the available nutrients and supported by regenerated production. The bloom dynamics is explained for pre-bloom, bloom and post-bloom conditions with measurements on nutrients and plankton assemblages. The Noctiluca bloom (mid-March) is succeeded by Trichodesmium (April–May), in the stratified nutrient depleted, abundant light environment and propagated southwards. Observed increasing trends in the SSHA over the period indicate strengthening of stratification and hence altered production patterns in the NEAS.

Earth Observation Techniques to Assess Water Quality Monitoring in the Murray Darling Basin of Australia

The Murray Darling Basin Authority (MDBA) currently has been using a discrete field sampling technique for water quality monitoring that is expensive, time consuming and may not adequately represent the spatial variability of water quality relative to the entire water body. A pilot project was executed to assess the effectiveness of using earth observation data, supported by archived field-based observations for quantitative estimation of Water Quality Parameters (WQP) and detection of algal blooms in the River Murray. The selected pilot study area includes a 100km stretch of the River Murray between the Hume Dam and Yarrawonga Weir. The time frame for the archived field samples was between November 2008 and March 2011, when major algal blooms were occurring in this stretch of the Murray River.Analysis of the 2009 data shows that waters in sites in the Murray River downstream of the Hume Dam to the Yarrawonga Weir show more temporal than spatial variability in Chl-a and PC levels. The Chl-a concentration is relatively less in the Yarrawonga Weir than in the Murray River. The scatter plot of PC vs. Turbidity suggests that PC is a more significant parameter for the detection of Cyanobacteria than Chl-a. The field data represents the temporal bio-optical variability across the 2009 algal bloom events by successfully capturing the co-variations among Chlorophyll-a, Chycocyanin and turbidity at pre, during and post bloom conditions. The methodology has proved that the usefulness of an integrated earth observation and field based WQP technique to accurately map algal bloom events. The long term MDBA RMWQMP data for the 2009 bloom event is found partially compatible to the NOW Pilot study data in that only the data for the Heywood site that was used together for testing the WQP monitoring technique. The incompatibility of the RMWQMP data downstream of Yarrawonga Weir may be due to differing techniques used for determining Chlorophyll. The 2010 data was suitable for testing the technique for complex spatial bio-optical variability during the peak of the bloom in a large water storage. Lack of Chlorophyll measurements in 2010 data poses challenges in interpreting the relationship of bio-optical variability with the spatial distributions of bio-optical parameters. As relational parameters are absent, local information and expert advice will be required to develop plausible assumptions between the Chlorophyll - Phycocyanin relationship. The field sampled data for the 2010 bloom event acquired from the Hume Dam was used for comparative investigation of both moderate resolution sensors (MODIS and MERIS) and high resolution sensors (TM/TM+). The 2009 bloom event field samples of sites in the Yarrawonga Weir was used as an input with MODIS and MERIS and the data from all the sites was applied with TM/TM+. This paper will present an integrated earth observation and field based WQP technique to accurately map algal bloom events, and discuss challenges for real time earth observation data initiatives and future collaborative projects.

Extreme Levels of Ocean Acidification Restructure the Plankton Community and Biogeochemistry of a Temperate Coastal Ecosystem: A Mesocosm Study

The oceans’ uptake of anthropogenic carbon dioxide (CO2) decreases seawater pH and alters the inorganic carbon speciation – summarized in the term ocean acidification (OA). Already today, coastal regions experience episodic pH events during which surface layer pH drops below values projected for the surface ocean at the end of the century. Future OA is expected to further enhance the intensity of these coastal extreme pH events. To evaluate the influence of such episodic OA events in coastal regions, we deployed eight pelagic mesocosms for 53 days in Raunefjord, Norway, and enclosed 56–61 m3 of local seawater containing a natural plankton community under nutrient limited post-bloom conditions. Four mesocosms were enriched with CO2 to simulate extreme pCO2 levels of 1978 – 2069 μatm while the other four served as untreated controls. Here, we present results from multivariate analyses on OA-induced changes in the phyto-, micro-, and mesozooplankton community structure. Pronounced differences in the plankton community emerged early in the experiment, and were amplified by enhanced top-down control throughout the study period. The plankton groups responding most profoundly to high CO2 conditions were cyanobacteria (negative), chlorophyceae (negative), auto- and heterotrophic microzooplankton (negative), and a variety of mesozooplanktonic taxa, including copepoda (mixed), appendicularia (positive), hydrozoa (positive), fish larvae (positive), and gastropoda (negative). The restructuring of the community coincided with significant changes in the concentration and elemental stoichiometry of particulate organic matter. Results imply that extreme CO2 events can lead to a substantial reorganization of the planktonic food web, affecting multiple trophic levels from phytoplankton to primary and secondary consumers.

Carbon Export in the Seasonal Sea Ice Zone North of Svalbard From Winter to Late Summer

Phytoplankton blooms in the Arctic Ocean's seasonal sea ice zone are expected to start earlier and occur further north with retreating and thinning sea ice cover. The current study is the first compilation of phytoplankton bloom development and fate in the seasonally variable sea ice zone north of Svalbard from winter to late summer, using short-term sediment trap deployments. Clear seasonal patterns were discovered, with low winter and pre-bloom phytoplankton standing stocks and export fluxes, a short and intense productive season in May and June, and low Chl a standing stocks but moderate carbon export fluxes in the autumn post-bloom conditions. We observed intense phytoplankton blooms with Chl a standing stocks of &amp;gt;350 mg m−2 below consolidated sea ice cover, dominated by the prymnesiophyte Phaeocystis pouchetii. The largest vertical organic carbon export fluxes to 100 m, of up to 513 mg C m−2 day−1, were recorded at stations dominated by diatoms, while those dominated by P. pouchetii recorded carbon export fluxes up to 310 mg C m−2 day−1. Fecal pellets from krill and copepods contributed a substantial fraction to carbon export in certain areas, especially where blooms of P. pouchetii dominated and Atlantic water advection was prominent. The interplay between the taxonomic composition of protist assemblages, large grazers, distance to open water, and Atlantic water advection was found to be crucial in determining the fate of the blooms and the magnitude of organic carbon exported out of the surface water column. Previously, the marginal ice zone was considered the most productive region in the area, but our study reveals intense blooms and high export events in ice-covered waters. This is the first comprehensive study on carbon export fluxes for under-ice phytoplankton blooms, a phenomenon suggested to have increased in importance under the new Arctic sea ice regime.

Transcriptional Patterns of Biogeochemically Relevant Marker Genes by Temperate Marine Bacteria.

Environmental microbial gene expression patterns remain largely unexplored, particularly at interannual time scales. We analyzed the variability in the expression of marker genes involved in ecologically relevant biogeochemical processes at a temperate Atlantic site over two consecutive years. Most of nifH transcripts, involved in nitrogen (N) fixation, were affiliated with the symbiotic cyanobacterium Candidatus Atelocyanobacterium thalassa, suggesting a key role as N providers in this system. The expression of nifH and amoA (i.e., marker for ammonia oxidation) showed consistent maxima in summer and autumn, respectively, suggesting a temporal succession of these important N cycling processes. The patterns of expression of genes related to the oxidation of carbon monoxide (coxL) and reduced sulfur (soxB) were different from that of amoA, indicating alternate timings for these energy conservation strategies. We detected expression of alkaline phosphatases, induced under phosphorus limitation, in agreement with the reported co-limitation by this nutrient at the study site. In contrast, low-affinity phosphate membrane transporters (pit) typically expressed under phosphorus luxury conditions, were mainly detected in post-bloom conditions. Rhodobacteraceae dominated the expression of soxB, coxL and ureases, while Pelagibacteraceae dominated the expression of proteorhodopsins. Bacteroidetes and Gammaproteobacteria were major contributors to the uptake of inorganic nutrients (pit and amt transporters). Yet, in autumn, Thauma- and Euryarchaeota unexpectedly contributed importantly to the uptake of ammonia and phosphate, respectively. We provide new hints on the active players and potential dynamics of ecologically relevant functions in situ, highlighting the potential of metatranscriptomics to provide significant input to future omics-driven marine ecosystem assessment.

Fe(II) stability in coastal seawater during experiments in Patagonia, Svalbard, and Gran Canaria

Abstract. The speciation of dissolved iron (DFe) in the ocean is widely assumed to consist almost exclusively of Fe(III)-ligand complexes. Yet in most aqueous environments a poorly defined fraction of DFe also exists as Fe(II), the speciation of which is uncertain. Here we deploy flow injection analysis to measure in situ Fe(II) concentrations during a series of mesocosm/microcosm/multistressor experiments in coastal environments in addition to the decay rate of this Fe(II) when moved into the dark. During five mesocosm/microcosm/multistressor experiments in Svalbard and Patagonia, where dissolved (0.2 µm) Fe and Fe(II) were quantified simultaneously, Fe(II) constituted 24 %–65 % of DFe, suggesting that Fe(II) was a large fraction of the DFe pool. When this Fe(II) was allowed to decay in the dark, the vast majority of measured oxidation rate constants were less than calculated constants derived from ambient temperature, salinity, pH, and dissolved O2. The oxidation rates of Fe(II) spikes added to Atlantic seawater more closely matched calculated rate constants. The difference between observed and theoretical decay rates in Svalbard and Patagonia was most pronounced at Fe(II) concentrations &lt;2 nM, suggesting that the effect may have arisen from organic Fe(II) ligands. This apparent enhancement of Fe(II) stability under post-bloom conditions and the existence of such a high fraction of DFe as Fe(II) challenge the assumption that DFe speciation in coastal seawater is dominated by ligand bound-Fe(III) species.

Arctic (Svalbard islands) active and exported diatom stocks and cell health status

Abstract. Diatoms tend to dominate the Arctic spring phytoplankton bloom, a key event in the ecosystem including a rapid decline in surface-water pCO2. While a mass sedimentation event of diatoms at the bloom terminus is commonly observed, there are few reports on the status of diatoms' health during Arctic blooms and its possible role on sedimentary fluxes. Thus, we examine the idea that the major diatom-sinking event which occurs at the end of the regional bloom is driven by physiologically deteriorated cells. Here we quantify, using the Bottle-Net, Arctic diatom stocks below and above the photic zone and assess their cell health status. The communities were sampled around the Svalbard islands and encompassed pre- to post-bloom conditions. A mean of 24.2±6.7 % SE (standard error) of the total water column (max. 415 m) diatom standing stock was found below the photic zone, indicating significant diatom sedimentation. The fraction of living diatom cells in the photic zone averaged 59.4±6.3 % but showed the highest mean percentages (72.0 %) in stations supporting active blooms. In contrast, populations below the photic layer were dominated by dead cells (20.8±4.9 % living cells). The percentage of diatoms' standing stock found below the photic layer was negatively related to the percentage of living diatoms in the surface, indicating that healthy populations remained in the surface layer. Shipboard manipulation experiments demonstrated that (1) dead diatom cells sank faster than living cells, and (2) diatom cell mortality increased in darkness, showing an average half-life among diatom groups of 1.025±0.075 d. The results conform to a conceptual model where diatoms grow during the bloom until resources are depleted and supports a link between diatom cell health status (affected by multiple factors) and sedimentation fluxes in the Arctic. Healthy Arctic phytoplankton communities remained at the photic layer, whereas the physiologically compromised (e.g., dying) communities exported a large fraction of the biomass to the aphotic zone, fueling carbon sequestration to the mesopelagic and material to benthic ecosystems.

Paralytic shellfish toxin profiles in mussel, cockle and razor shell under post-bloom natural conditions: Evidence of higher biotransformation in razor shells and cockles

Concentrations of the paralytic shellfish toxins GTX6, C1+2, GTX5, C3+4, dcSTX, dcNEO and dcGTX2+3 were determined by LC-FLD in composite samples of whole soft tissues of mussels (Mytilus galloprovincialis), cockles (Cerastoderma edule) and razor shells (Solen marginatus) after exposure to a Gymnodinium catenatum bloom. Specimens were harvested weekly during three months under natural depuration conditions in the Mira branch of Aveiro lagoon, Portugal. Under the decline of G. catenatum cell densities, elimination or transformation of the uptake toxins associated with the ingestion of toxic cells differed among the surveyed species. Ratio between the toxins dcSTX plus dcGTX2+3 plus dcNEO and toxins GTX6 plus GTX5 plus C1+2 plus C3+4 was used to illustrate the biotransformation occurring in the bivalves. Enhancement of the ratios was observed for razor shells and cockles seven weeks after the peak of the algal bloom. Most likely it reflects more intense biotransformation in razor shells and cockles than in mussels. Conversion into toxins of higher toxicity may prolong the bivalve toxicity. These results show the complexity of toxin elimination in bivalves under post-bloom conditions and emphasize the pertinence of monitoring programs of bivalve toxicity in order to protect human health.

Impacts of phytoplankton blooms on trace metal recycling and bioavailability during dredging events in the Sado estuary (Portugal)

This work evaluates the impact of phytoplankton blooms on metal availability driven by dredging, in an area of the Sado estuary (Portugal), subject to ongoing dredging operations during the entire sampling period. In situ changes of chlorophyll a concentration, bioavailable trace metals (Cr, Mn, Co, Ni, Cu, Zn, Cd and Pb) in the water column, metal content in particulate matter, and particulate metal to bioavailable metal ratios were investigated during pre-bloom, bloom and post-bloom conditions to evaluate the potential of the phytoplankton-mediated metal removal. Metals in particulate matter significantly enhanced concomitantly with the decline of metals (mostly Mn, Co, Cu, Zn, and Pb) in the water column during the bloom, in comparison with pre- and post-bloom periods. During the peak of the phytoplankton bloom, bioavailable Cr, Mn, Co, Ni, Cu, Zn, Cd and Pb were reduced to 30, 99, 100, 87, 98, 72, 84 and 88% of their original levels (pre-bloom values). Copper and Pb, and to a lesser extent, Zn and Mn, were ranked as more particle reactive. Volume particulate matter concentrations of Mn, Ni, Cu and Pb much higher than the bioavailable concentrations, indicated that phytoplankton is likely to be a dominant sink of these metals during the bloom period. Thus, Mn, Ni, Cu and Pb are prone to be transferred and biomagnified into the marine food web. These results highlight phytoplankton blooms as important biological sinks of trace metals during dredging, which should be taken into consideration in planning and management of dredging, to minimise environmental impacts and protect estuarine and coastal ecosystems.

Relationship Between Carbon- and Oxygen-Based Primary Productivity in the Arctic Ocean, Svalbard Archipelago

Phytoplankton contribute half of the primary production in the biosphere and are the major source of energy for the Arctic Ocean ecosystem. While primary production measurements are therefore fundamental to our understanding of marine biogeochemical cycling, the extent to which current methods provide a definitive estimate of this process remains uncertain given differences in their underlying approaches and assumptions. This is especially the case in the Arctic Ocean, a region of the planet undergoing rapid evolution as a result of climate change, yet where primary production measurements are sparse. In this study, we compared three common methods for estimating primary production in the European Arctic Ocean: 1) production of 18O-labeled oxygen (GPP-18O), 2) changes in dissolved oxygen (GPP-DO) and 3) incorporation rates of 14C-labelled carbon into particulate organic carbon (14C-POC) and into total organic carbon (14C-TOC, the sum of dissolved and particulate organic carbon). Results show that primary production rates derived using oxygen methods showed good agreement across season and were strongly positively correlated. While also strongly correlated, higher scatter associated with seasonal changes was observed between 14C-POC and 14C-TOC. The 14C-TOC-derived rates were, on average, approximately 50 % of the oxygen-based estimates. However, the relationship between these estimates changed seasonally. In May, during a spring bloom of Phaeocystis sp., 14C-TOC was 52 % and 50 % of GPP-DO and GPP-18O respectively, while in August, during post-bloom conditions dominated by flagellates, 14C-TOC was 125 % of GPP-DO and 14C-TOC was 175 % of GPP-18O. Varying relationship between C and O rates may be the result of varying importance of respiration, where C-based rates estimate Net Primary Production (NPP) and O-based rates estimate Gross Primary Production (GPP).However, uncertainty remains in this comparison, given differing assumptions of the methods and the photosynthetic quotients.The median O:C ratio of 4.75 in May is within the range of that observed for other regions of the world’s ocean. However, the median O:C ratio for August is < 1, lower than in any other reported region. Our results suggest further research is needed to estimate O:C in Arctic waters, and at different times of the seasonal cycle.

Phytoplankton biomass, primary production and chemoautotrophic production of the Western Black Sea in April 2003

Abstract The multilayered surface waters of the Black Sea contain aerobic, suboxic and anoxic layers that support both photoautotrophic (PP) and chemoautotrophic (ChP) biological production. During the R/V Knorr cruise from 15 to 25 April 2003, phytoplankton biomass (represented as chlorophyll-a), photoautotrophic and chemoautotrophic production (ChP) rates were determined in the southwestern Black Sea. Surface Chl-a concentrations ranged from 0.06 and 0.62 μg/ l for the whole study area. These low values suggest post-bloom conditions. Integrated chlorophyll-a concentrations in the euphotic zone were as low as 2.4 mg m−2 in the central gyre, while they were as high as 22 mg m−2 in the Rim current. Integrated photoautotrophic production rates ranged from 70 to 664 mgC m−2 d−1. The lowest values were observed in the western central gyre and the highest values were found at the regions around Sakarya Canyon. Integrated ChP rates were 282 and 1013 mgC m−2 d−1, which were equivalent to 45% and 83% of the overall water-column production for the central gyre and Rim current regions, respectively. Maximum rates are observed in the upper layer of the sulfide zone. The highest values of integrated ChP were in the vicinity of the Sakarya shelf and Rim current region. Extremely high values of ChP can occur in the Black Sea and appear to be driven by oxygen ventilation and redox cycling.

Evidence of high N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fixation rates in the temperate northeast Atlantic

Abstract. Diazotrophic activity and primary production (PP) were investigated along two transects (Belgica BG2014/14 and GEOVIDE cruises) off the western Iberian Margin and the Bay of Biscay in May 2014. Substantial N2 fixation activity was observed at 8 of the 10 stations sampled, ranging overall from 81 to 384 µmol N m−2 d−1 (0.7 to 8.2 nmol N L−1 d−1), with two sites close to the Iberian Margin situated between 38.8 and 40.7∘ N yielding rates reaching up to 1355 and 1533 µmol N m−2 d−1. Primary production was relatively lower along the Iberian Margin, with rates ranging from 33 to 59 mmol C m−2 d−1, while it increased towards the northwest away from the peninsula, reaching as high as 135 mmol C m−2 d−1. In agreement with the area-averaged Chl a satellite data contemporaneous with our study period, our results revealed that post-bloom conditions prevailed at most sites, while at the northwesternmost station the bloom was still ongoing. When converted to carbon uptake using Redfield stoichiometry, N2 fixation could support 1 % to 3 % of daily PP in the euphotic layer at most sites, except at the two most active sites where this contribution to daily PP could reach up to 25 %. At the two sites where N2 fixation activity was the highest, the prymnesiophyte–symbiont Candidatus Atelocyanobacterium thalassa (UCYN-A) dominated the nifH sequence pool, while the remaining recovered sequences belonged to non-cyanobacterial phylotypes. At all the other sites, however, the recovered nifH sequences were exclusively assigned phylogenetically to non-cyanobacterial phylotypes. The intense N2 fixation activities recorded at the time of our study were likely promoted by the availability of phytoplankton-derived organic matter produced during the spring bloom, as evidenced by the significant surface particulate organic carbon concentrations. Also, the presence of excess phosphorus signature in surface waters seemed to contribute to sustaining N2 fixation, particularly at the sites with extreme activities. These results provide a mechanistic understanding of the unexpectedly high N2 fixation in productive waters of the temperate North Atlantic and highlight the importance of N2 fixation for future assessment of the global N inventory.