Pelagic Regions Research Articles

Geographic distribution of modern dinoflagellate cysts in surface sediments of the Arabian Sea: significance of taxa and morphometry as potential ecological indicators.

Studies on dinoflagellate cysts in the Arabian Sea (AS) are limited to the coastal waters, but no information from the deeper depths. The dinoflagellate cyst assemblages in surface sediment samples (0-2cm) from the deeper depths (up to ~ 4500m) of central (oxygen minimum zone (OMZ)) and southeastern (oligotrophic) AS revealed that the relatively good numbers of cyst concentrations reach deeper depths of OMZ (3505m) and oligotrophic (4368m) regions, but the former harbored more cyst concentrations than the latter. The cyst concentration and species count (including HAB species) recorded here are lower compared to the eastern (EAS) and western (WAS) AS, but the autotrophic cyst dominance (74-83%) at deeper depths is in contrast with the heterotrophic dominance in coastal AS. Of the recorded 41 cyst species (belonging to 18 genera), four species (cyst of Cladopyxis sp., Operculodinium janduchenei, Stelladinium bifurcatum, and Protoperidinium monospinum) from the deepest part of oligotrophic AS form the first report. In contrast, Spiniferites and Lingulodinium cysts were common occurrences. Taxonomic comparison with literature revealed (i) the prevalence of more cosmopolitan species (32 species) which could be due to the prevalence of large and small-scale lateral transport of cysts in oligotrophic regions followed by OMZ and coastal regions, respectively, and (ii) very few region-specific species, i.e., cyst of Protoperidinium latissimum, Lejeunecysta sabrina, cyst of Protoperidinium denticulatum in EAS and Impagidinium patulum, and I. strialatum, in WAS. Interestingly, variability in the morphometry was evident between the coastal and open oceans in some cosmopolitan cysts, e.g., Operculodinium centrocarpum and Lingulodinium machaerophorum. These findings from the less studied pelagic regions will contribute to the growing knowledge of dinoflagellate cyst distribution patterns and highlight the significance of cyst taxa and morphology as potential ecological indicators for AS.

Source and fate of atmospheric iron supplied to the subarctic North Pacific traced by stable iron isotope ratios

The availability of dissolved iron (Fe) limits primary production over some regions of the surface ocean, especially in regions such as the subarctic North Pacific. In this work, we use Fe stable isotope ratios (δ56Fe) in bulk and size-fractionated marine aerosol particles and dissolved Fe of surface seawater in the subarctic North Pacific on Japanese GEOTRACES cruise GP02 (Summer 2017) as a tracer to clarify the relative contribution of combustion and natural Fe in both marine aerosol particles and surface seawater. The bulk aerosols collected in the coastal regions of both East Asia and western North Pacific have total δ56Fe values that are as low as −0.5 ‰ when compared to crustal (+0.1 ‰), with both the water-soluble phase and the fine particles even more fractionated (as low as −1.9 and −2.8 ‰, respectively). The negative correlation between the aerosol δ56Fe signatures and the enrichment factors of Fe and other elements dominated by anthropogenic sources (e.g., lead and cadmium) in these coastal regions indicates the presence of Fe emitted from high-temperature combustion sources, such as coal combustion and metal smelting. In these regions, combustion Fe accounts for 4–13 and 13–45 % of the total and water-soluble aerosol Fe, respectively. The results demonstrate that soluble aerosol Fe sourced from combustion Fe can be equivalent to that sourced from natural dust Fe in these coastal regions. By contrast, the aerosol particles in pelagic regions were near crustal δ56Fe in all particle size fractions, indicating the dominance of natural Fe and little to no combustion Fe. The relationships among the fractional Fe solubility, major ion concentration, Fe species, and δ56Fe indicate that the presence of combustion Fe is the dominant reason for the solubility increase in the coastal regions and that the atmospheric processing of mineral dust during transport is more important in the pelagic regions. The dissolved Fe of the surface seawater at 10 m depth had a consistently higher δ56Fe by up to +1.5 ‰ than that of the simultaneously collected water-soluble aerosol Fe. The pattern of the elevated δ56Fe in the surface seawater corresponds to decreasing Fe concentrations and can be approximated by Rayleigh fractionation; we attribute these elevated surface δ56Fe values to the effect of biological uptake. New Fe fluxes from both the atmosphere and deeper depths are limited at least in summer compared with the biological uptake in the open ocean of the subarctic North Pacific.

Niche partitioning and plastisphere core microbiomes in the two most plastic polluted zones of the world ocean.

Plastics are offering a new niche for microorganisms colonizing their surface, the so-called "plastisphere," in which diversity and community structure remain to be characterized and compared across ocean pelagic regions. Here, we compared the bacterial diversity of microorganisms living on plastic marine debris (PMD) and the surrounding free-living (FL) and organic particle-attached (PA) lifestyles sampled during the Tara expeditions in two of the most plastic polluted zones in the world ocean, i.e., the North Pacific gyre and the Mediterranean Sea. The 16S rRNA gene sequencing analysis confirmed that PMD are a new anthropogenic ocean habitat for marine microbes at the ocean-basin-scale, with clear niche partitioning compared to FL and PA lifestyles. At an ocean-basin-scale, the composition of the plastisphere communities was mainly driven by environmental selection, rather than polymer types or dispersal effect. A plastisphere "core microbiome" could be identified, mainly dominated by Rhodobacteraceae and Cyanobacteria. Predicted functions indicated the dominance of carbon, nitrogen and sulfur metabolisms on PMD that open new questions on the role of the plastisphere in a large number of important ecological processes in the marine ecosystem.

Characterizing oceanographic conditions near Coiba Island and Pacific Panama using 20 years of satellite-based wind stress, SST and chlorophyll-a measurements

Coiba Island and the associated Special Zone of Marine Protection represent an important, yet poorly studied marine reserve along the Pacific coast of Panama. While efforts have recently began to establish monitoring programs in the region, a range of historical, marine-related environmental measurements already exist, derived from satellite-based observations. The goal of this paper was to use long-term datasets for key variables to provide qualitative insights (i.e. descriptive oceanography) of climatological conditions and interannual variability in the Pacific Panama region. These are underpinned with numerical assessments, providing an important baseline for ongoing and future studies, particularly in the Coiba Island/Gulf of Chiriqui region. In particular, we examined 20 years (January 2003-December 2022) of wind stress, sea surface temperature (SST), and chlorophyll-a (Chl-a), spanning the neritic and pelagic regions of the Pacific Panama coast. During the dry season (northern winter), the well-known, seasonal, regional Panama wind jet appeared across the Gulf of Panama, leading to surface mixing and SST cooling that eventually extended across most of the Panama Bight. West of the Azuero Peninsula, SST increased and surface warming extended further offshore from January through April. The SST in the Gulf of Chiriqui during this period was about 1 °C warmer on average than east of Coiba Island. By July and August, offshore SST gradients became largely longitudinal, cooling occured across the season, and the SST on either side of Coiba Island was nearly the same. The influence of the Panama jet in the Gulf of Panama was clear in the Chl-a data as well, with upwelling-driven values peaking in February/March (up to 11 mg m-3, with a monthly climatological value of around 2 mg m-3 during this period). During the rest of the year, the Chl-a concentration in this region averaged around 0.5-1.0 mg m-3. In the Gulf of Chiriqui and the region east of Coiba Island, the climatological monthly averages were roughly 0.3-0.5 mg m-3 and 0.4-0.6 mg m-3, respectively. Somewhat surprisingly, very high Chl-a values were present in the satellite data for the Gulf of Chiriqui during May 2007 and June 2008, peaking at 16 mg m-3 and 32 mg m-3 at a location just west of Coiba Island, respectively. It remains unclear as to the cause of these apparent blooms. Even when the high Chl-a values were excluded in the calculation of climatological averages in the Gulf of Chiriqui, however, there is a suggestion of modest seasonality in Chl-a values, with slightly elevated values (~ 0.4 mg m-3) peaking around May and October. During the extreme El Niño event of 2015-2016, the monthly-averaged SST along the Panama Pacific coast was warmer than average, with elevated levels of up to + 2 °C and lasting 12 months in the Gulf of Chiriqui. In the Gulf of Panama, the monthly-averaged SST anomalies were up to + 1.7 °C, although the temperatures returned to near-seasonal averages after roughly 5 months.

Large Methane Emission from the River Inlet Region of Eutrophic Lake: A Case Study of Lake Taihu

Lakes are important natural sources of atmospheric methane (CH4), which should be considered in global CH4 budget estimations. However, the CH4 emissions from lakes can be highly variable, and the emissions from the river inlet region were less studied, which seriously hamper our understanding of CH4 budget estimates of lakes. Here, field measurements from over six years (2012 to 2017) at Lake Taihu, a large eutrophic shallow lake with a complicated river network, were conducted to address the issue. Results show that the river inlet region of the lake was a hot spot of CH4 emission. The CH4 emission at the river inlet region with an annual mean value of 0.183 mmol m−2 d−1 was seven times higher than that at pelagic region (0.028 mmol m−2 d−1). Peak CH4 emission occurred in warm seasons, and the lowest in cold seasons at the pelagic region, but peak emission occurred in cold seasons at the river inlet region. The seasonal CH4 emission at the pelagic region can be explained by water temperature; however, less temperature dependency of CH4 emission at the river inlet region was found. The variability of CH4 emission was linked to pollution loadings, and CH4-rich water in the inflowing river likely sustained the large CH4 emission of river inlet region.

Factors influencing mercury levels in Leach's storm-petrels at northwest Atlantic colonies

Mercury (Hg) is a globally distributed heavy metal, with negative effects on wildlife. Its most toxic form, methylmercury (MeHg), predominates in aquatic systems. Levels of MeHg in marine predators can vary widely among individuals and populations. Leach's storm-petrels (Hydrobates leucorhous) have elevated levels of Hg but the role of Hg in storm-petrel population declines is unknown. In this study, we used egg and blood samples to study variation in Hg exposure among several northwest Atlantic colonies during breeding seasons, thereby evaluating relative toxicity risk within and among colonies. Total mercury (THg) concentrations were higher with increasing colony latitude, and were more pronounced in blood than in eggs. THg concentrations in blood were mostly associated with low toxicity risk in birds from the southern colonies and moderate risks in birds from the northern colonies; however, those values did not affect hatching or fledging success. THg concentrations in both eggs and blood were positively correlated with δ34S, emphasizing the role of sulfate-reducing bacteria in methylation of THg acquired through marine food webs, which is consistent with enriched δ34S profiles. By associating tracking data from foraging trips with THg from blood, we determined that blood THg levels were higher when storm-petrel's intensive search locations were over deeper waters. We conclude that spatial variation in THg concentrations in Leach's storm-petrels is attributable to differences in ocean depth at foraging locations, both at individual and colony levels. Differences in diet among colonies observed previously are the most likely cause for observed blood THg differences. As one of the few pelagic seabird species breeding in Atlantic Canada, with limited overlap in core foraging areas among colonies, Leach's storm-petrels can be used as biomonitors for less sampled offshore pelagic regions. The global trend in Hg emissions combined with legacy levels warrant continued monitoring for toxicity effects in seabirds.

Vertical distribution of picophytoplankton in the NW shelf and deep-water area of the Black Sea in spring

Structure and functions of picophytoplankton and their links to the water column density stratification and nutrient vertical profiles were studied in the Black Sea open waters along a transect from the Western Gyre to the NW shelf during spring homothermy in April of 2017. Abundances of picocyanobacteria of the genus Synechococcus (0.85 ± 0.96 (SD) × 10 3 cells ml −1 ) and eukaryotic picoalgae (5.74 ± 5.99 × 10 3 cells ml −1 ) and their intracellular pigment (chl a , phycoerythrin) contents were quantified using flow cytometry. The distribution of these variables in the upper 100-m layer was non-uniform. Along the whole transect, Synechococcus and picoeukaryote abundance maxima (up to 4 × 10 3 and 3 × 10 4 cells ml −1 , respectively) were observed at the water temperature of 8–8.5°С in the depth range between 30 and 40 m. Picoeukaryotes dominated the total community. The share of Synecococcus averaged about 22% and increased with depth up to 80%. Picophytoplankton abundance dropped abruptly through the oxycline but the cells were found in the suboxic layer at about 10 3 cells ml −1 and in a sample from the anoxic zone at 10 2 cells ml −1 . Intracellular chl a maxima were revealed in the nitrate peak at sigma- t density of 15.5. In the surface and suboxic layers, non-specific green autofluorescence (GAF) was detected in picophytoplankton cells that might provide evidence of their stress state in adverse environment. Multivariate analysis has revealed tight coupling between abiotic and microbiological variables in three statistically distinct pelagic regions of the transect, corresponding to the abyss, the continental slope and the shelf. • Picoeukaryotes dominated picophytoplankton but the proportion of Synecococcus increased with depth. • Picophytoplankton abundance dropped abruptly through oxycline but still survived in suboxic layer. • Non-specific green autofluorescence (GAF) was detected in picophytoplankton by flow cytometry. • Picophytoplankton GAF maxima were revealed in surface and suboxic layers, indicating stress conditions.

Isotopic evolution of dissolved Ni, Cu, and Zn along the Kuroshio through the East China Sea

In this study, we have investigated the evolution of concentrations and isotope ratios of dissolved nickel (Ni), copper (Cu), and zinc (Zn) from the North Equatorial Current in the western North Pacific to the Kuroshio in the East China Sea, where the inputs of anthropogenic and lithogenic materials through riverine and aeolian pathways are relatively high. The concentrations and isotope ratios for Ni, Cu, and Zn in the deep water of the East China Sea are similar to those of the western North Pacific. The concentrations of Ni, Cu, and Zn in the Changjiang diluted water (<34.0 of salinity) are 3.0–4.1 nmol/kg, 2.0–2.7 nmol/kg, and 0.5–1.1 nmol/kg, respectively, which are significantly higher than those in the surface water of the western North Pacific, thereby indicating the impact of the riverine input. In the Changjiang diluted water, isotope ratios of Ni range from +0.8 to +1.4‰, which is lower than +1.7‰ observed in the surface water (<150 m) of the western North Pacific. The distribution of concentrations and isotope ratios for dissolved Ni fit with simple mixing among the three endmembers, Changjiang diluted water, Kuroshio surface water, and deep water in the western North Pacific. A mixing model using isotope ratios and concentrations for Ni quantitatively evaluates the sources of dissolved Ni in the East China Sea. The ranges of the isotope ratios are +0.4 to +0.5‰ for Cu and −0.1 to +0.2‰ for Zn in the Changjiang diluted water, which are similar to those in the surface water of the Okinawa Trough but lower than those in the distal ocean, such as the central Pacific. Compared with published data from the global ocean, dissolved Ni, Cu, and Zn are isotopically lighter in the surface water of some coastal regions than in the pelagic regions, indicating that isotopically light Ni, Cu, and Zn are supplied from the continents.

Mechanistic approach and elements of metacommunity structure of the zooplankton of palm swamps in the Neotropical region

AbstractStudies of metacommunities are of great importance for ecological knowledge because they assess how the processes related to the species' niche and the dispersion processes structure the communities. In this context, the objective of the present study was to investigate the main assembly mechanisms responsible for the structuring of the zooplankton community in a complex of neotropical palm swamps (“veredas”), consisting of sets of small common ponds in the Brazilian savannah, similar to swamps. Zooplankton were sampled in the pelagic region of 15 veredas in April 2018. The zooplankton total community showed a distribution related to spatial and environmental factors. For Rotifera the relative importance of environmental factors was greater, while Cladocera and Copepoda were more structured by space. The community was still structured according to the Gleasonian model of distribution, where Rotifera presented a Gleasonian structure, Cladocera quasi‐Gleasonian, and Copepoda quasi‐nested random. The influence of environmental and spatial factors and the resulting structure of the zooplankton metacommunity seem to be directly related to the dispersal capacity in each group. Differences in relative importance of the factors that shaped the community highlight the idiosyncratic characteristics of zooplankton species. Thus, we emphasize the importance of using the two approaches of metacommunity studies to help to elucidate the processes that govern the structuring of metacommunities.

Underwater frazil ice and its suspension depth detected from ADCP backscatter data around sea ice edge in the Sea of Okhotsk

Small sea ice crystals, so-called frazil ice, are created during initial ice formation in the water column. Frazil ice can be suspended under turbulent conditions, and it can scavenge particulate matter through interaction with resuspended sediment. This study examined the suspension depth of frazil ice based on backscatter data from 150-kHz Acoustic Doppler Current Profilers (ADCPs) moored in the pelagic regions east of Sakhalin Island in the Sea of Okhotsk with bottom depths from 800 to 1700 m during 1998–2000. ADCP backscatter strength revealed dominant signals from the diurnal vertical migration of zooplankton. In addition, the backscatter was enhanced by suspended frazil ice that extended down the water column from the surface. Frazil ice was detected several times at each mooring site during sea-ice seasons. These events occurred when the mooring sites were on the edge of the sea ice regions and the wind speed was high, typically exceeding 8 m/s. The estimated mean suspension depth of frazil ice was 35 m as long as valid ADCP backscatter data from depths greater than ~15 m were used. The maximum suspension depth reached ~100 m, which was much deeper than that previously reported in various sea-ice regions as frazil ice originating from the atmospheric heat absorption at the surface. These results suggest that frazil ice comes into contact with the bottom and scavenges seafloor sediment in shallower regions, resulting in incorporation of sediment-origin macronutrients into sea ice, which would play an important role in bio-related material cycle.

Structure of phytoplankton functional groups in shallow lakes with different equilibrium states

Changes in equilibrium states in shallow lakes are associated with disturbances and resilience. The study evaluated the structure and composition of phytoplankton functional groups in two lakes, Lagoa do Paó (turbid waters) and Santa Lúcia (clear waters). Monthly collections of limnological variables and phytoplankton occurred between August 2014 and June 2015 in the pelagic region. The lakes shared five functional groups: K, S1 , X1 , W2 and P, formed by coccoid and filamentous cyanobacteria, coccoid chlorophytes and euglenophytes, and desmids, respectively. The canonical correspondence analysis evidenced a clear separation, highlighting the groups TD, N, W2 and S1 in Santa Lúcia and functional groups composed of potentially toxic cyanobacteria in Lagoa do Paó (SN, Lo), indicating that the submerged macrophyte coverage can act promoting the phosphorous stabilization in the sediment in Santa Lúcia, reducing its contribution to the water column and inhibiting the dominance of the mentioned species. Temperature, pH, phosphorus and light attenuation coefficient influenced the occurrence of H1 , SN, S1 , W2 , X1 , D, and Lo , in the Lagoa do Paó. The composition and structure of the functional groups responded in the two lakes with some functional groups associated with toxic cyanobacteria occurring exclusively in Lagoa do Paó, having also been observed the sharing of some functional groups.

Long-term tracking of an Arctic-breeding seabird indicates high fidelity to pelagic wintering areas

Site fidelity is driven by predictable resource distributions in time and space. However, intrinsic factors related to an individual’s physiology and life-history traits can contribute to consistent foraging behaviour and movement patterns. Using 11 yr of continuous geolocation tracking data (fall 2008 to spring 2019), we investigated spatiotemporal consistency in non-breeding movements in a pelagic seabird population of black-legged kittiwakes Rissa tridactyla breeding in the High Arctic (Svalbard). Our objective was to assess the relative importance of spatial versus temporal repeatability behind inter-annual movement consistency during winter. Most kittiwakes used pelagic regions of the western North Atlantic. Winter site fidelity was high both within and across individuals and at meso (100-1000 km) and macro scales (&gt;1000 km). Spatial consistency in non-breeding movement was higher within than among individuals, suggesting that site fidelity might emerge from individuals’ memory to return to locations with predictable resource availability. Consistency was also stronger in space than in time, suggesting that it was driven by consistent resource pulses that may vary in time more so than in space. Nonetheless, some individuals displayed more flexibility by adopting a strategy of itinerancy during winter, and the causes of this flexibility are unclear. Specialization for key wintering areas can indicate vulnerability to environmental perturbations, with winter survival and carry-over effects arising from winter conditions as potential drivers of population dynamics.

Scarcity of chert in upper Lower Triassic Panthalassic deep-sea successions of Japan records elevated clastic inputs rather than depressed biogenic silica burial flux following the end-Permian extinction

Lower Triassic sedimentary rocks deposited in pelagic regions of Panthalassa show anomalously clay-rich and silica-poor lithologies compared with the deep marine chert-dominated successions that characterise older and younger strata. The end-Permian mass extinction, which impacted radiolarians, has been proposed as an explanation for this so-called “chert gap” through its inferred impact on biogenic silica production. To test this hypothesis, we evaluated linear sedimentation rates (LSRs) for an upper Olenekian (upper Lower Triassic) siliceous claystone succession in Tsukumi, Oita Prefecture, Southwest Japan. Correlation of conodont biohorizons allows extrapolation of absolute ages obtained by previous studies in South China onto our studied sections. Results show that LSR is higher in the Lower Triassic claystone than in typical Mesozoic radiolarian bedded chert. This implies that increased burial flux of clastic material, not decreased biogenic silica burial flux, drove deposition of clay-rich sediments in pelagic Panthalassa during the late Olenekian. • Lithostratigraphy of upper Lower Triassic pelagic Panthalassic deep-sea claystone. • Most detailed conodont biostratigraphy from Olenekian Panthalassic deep-sea strata. • Much of the Lower Triassic claystone was formed by high inputs of clastic material. • Collapse in radiolarian deposition during the Early Triassic needs reconsideration.

Mercury levels in commercial mid-trophic level fishes along the Portuguese coast – Relationships with trophic niche and oxidative damage

Abstract Sardines (Sardina pilchardus) and mackerels (Scomber spp. and Trachurus spp.) are amongst the most common fish caught along the Iberian coast for human consumption and, as mid-trophic level organisms, they constitute essential prey in the diet of several marine predators. Thus, the assessment of trophic ecology, contamination exposure, and stress responses in such organisms provides valuable information on the environmental health in the mid-trophic chain and the potential risks for consumers. This study aims to contribute for an integrative mercury assessment of the marine ecosystem by measuring stable isotopes, mercury levels, and oxidative stress parameters in five commercial fish species in the northeast Atlantic. Samples of muscle and liver were collected from a total of 116 individuals in two fisheries assessment surveys (Spring and Autumn) along the whole Portuguese coast. Mercury concentrations and stable isotope analysis (δ13C and δ15N) were performed in the muscle, while oxidative stress parameters (lipid peroxidation and DNA damage) were measured in both muscle and liver. Mercury concentrations were found to be considerably lower than values recorded in previous studies and the limits set by the European Union law, which confirms the non-toxic status of these species along the Portuguese coast, concerning this harmful element. Interestingly, no differences were found among the three genera, despite clear differences in trophic niches. Still, mercury concentrations were significantly higher during Autumn than Spring, possibly due to upwelling events during the Summer. Moreover, no relationships between the mercury concentrations and oxidative stress parameters were found. Overall, this work provided an integrative mercury assessment of commercial fishes from the mid-trophic chain, particularly from pelagic (and neritic) regions in the northeast Atlantic, showing that mercury concentration in these species is low. However, it is important to note that this study focused on small- and medium-sized specimens (overall ranging from 13–25 cm in length), and thus higher concentrations of mercury may be present in larger fish due to bioaccumulation.

Aalenian–Lower Bajocian Foraminiferal Fauna from the Ammonitico Rosso Series of Bakonycsernye (Hungary). Part 1: Taxonomy and Biostratigraphy

AbstractThis paper provides the first record of isolated foraminiferal assemblages from the continuous Aalenian–lower Bajocian succession from the pelagic region of the Neotethys. The studied Tűzkövesárok section B of Bakonycsernye (Hungary) has been well dated by ammonites and consists of Ammonitico Rosso type limestones. The foraminiferal fauna extracted by glacial acetic acid yielded 49 benthic taxa (species and subspecies); protoglobigerinids also occurred. Most specimens belonged to the suborder Spirillinina, followed by the suborder Lagenina and Rotaliina; agglutinated forms were subordinate and miliolids were absent. The majority of the species have wide stratigraphic ranges; moreover, the distributions of 11 species changed based on their appearances in this section. Nevertheless, the Aalenian and Bajocian parts of the section could be distinguished based upon the stratigraphic distributions of some species.

Aalenian–Lower Bajocian Foraminiferal Fauna from the Ammonitico Rosso Series of Bakonycsernye (Hungary). Part 2: Palaeoecological and Palaeobiogeographical Aspects

AbstractThis paper provides the first assessment of the paleoecology and biogeography of foraminiferal assemblages from the continuous Aalenian–lower Bajocian succession from the pelagic region of the Neotethys. Foraminiferal assemblages were extracted by glacial acetic acid from the Tűzkövesárok section B of Bakonycsernye (Hungary), which is well dated by ammonites and consists of Ammonitico Rosso type limestones. Palaeoenvironmental changes were evaluated based on microfacies studies, taxonomic and palaeoecological analyses (abundance, diversity, morphogroups, and ecozones) of the 49 benthic and one planktic taxa. The grazer-dominated foraminiferal assemblages indicated normal marine salinity and well-oxygenated conditions in a pelagic swell-graben environment below the photic zone. The majority of the foraminifera likely grazed on a biofilm or mat produced by microbes and/or fungi and also may have fed on marine snow. At the Aalenian–Bajocian transition, the decrease in abundance and diversity was linked with a sea-level fall event (JBj1). In the upper Bajocian, dissolution due to deepening resulted in the gradual and selective impoverishment of the fauna. In addition, two biomes, Boreal-Atlantic and Mediterranean, were distinguished within the area of the Boreal-Atlantic-Caucasian Province, based on the review of the coeval faunas.

Browning reduces the availability—but not the transfer—of essential fatty acids in temperate lakes

Abstract Atmospheric changes are leading to the browning of northern lakes (i.e. increases in catchment‐derived dissolved organic matter [DOM]), consequently altering phytoplankton biomass and community composition. We hypothesised that lake browning and the concurrent increase in nutrients drive a shift towards greater cyanobacteria biomass. We further hypothesised that, as a consequence of this shift in phytoplankton, the content of ω‐3 (n‐3) essential fatty acids (EFA) in seston would decline, affecting the subsequent transfer of EFA to consumers across the plant–animal interface in pelagic regions of lakes. We tested these hypotheses in the epilimnion of 30 temperate lakes in Ontario (Canada), representing a gradient of lake browning, with dissolved organic carbon (DOC) ranging from 2 to 10 mg/L and total phosphorus ranging from 6.0 to 48.5 μg/L. In each of these lakes, the concentration and composition of DOM, the biomass of phytoplankton and cyanobacteria, and the EFA content of seston, cladocerans, and copepods were measured. An increase in aromatic DOM was associated with increased phytoplankton and cyanobacteria biomass. Due to the lower content of the EFA eicosapentaenoic acid (EPA; 20:5n‐3) and docosahexaenoic acid (DHA; 22:6n‐3) in cyanobacteria, this increase in phytoplankton biomass was associated with a decline in EPA and DHA content in lake seston. However, there was no significant change in EFA content of cladocerans and copepods. This homeostatic (diet‐independent) EFA composition in zooplankton suggested that, as the phytoplankton community shifted towards more cyanobacteria with lower EFA content, the cladocerans and copepods may have met their nutritional requirements by relying on alternative food sources (e.g. heterotrophic ciliates and flagellates) capable of either trophically upgrading phytoplankton‐produced EPA and DHA, or synthesising EPA and DHA de novo. Results from this study indicate that increasing DOC from low (2 mg DOC/L) to moderate levels (15 mg DOC/L) may increase the importance of the microbial pathway in the trophic transfer of EPA and DHA from basal resources to zooplankton. However, this supplementary transfer of EFA through the microbial food web may not sustain high EPA and DHA levels in zooplankton when lake browning starts to limit primary production (&gt;15 mg DOC/L).

From bi-polar to regional distribution of modern dinoflagellate cysts, an overview of their biogeography

This paper examines the distribution of 91 modern dinoflagellate cyst taxa from 3636 locations across the world's oceans. Patterns of distributions among the taxa included bi-polarity, cosmopolitan, northern versus southern hemispheres, and geographically restricted. Of the 91 taxa, three dominate these 3636 assemblages at the global scale, Brigantedinium species, Operculodinium centrocarpum sensu Wall and Dale 1966 and some species of Spiniferites . Whereas Brigantedinium is a true cosmopolitan taxon, with high abundances in each ocean, Operculodinium centrocarpum sensu Wall and Dale 1966 shows high abundances in polar to temperate regions in the Northern Hemisphere, and in tropical to sub-tropical waters in the Southern Hemisphere. Spiniferites species show highest occurrences in the Southern Hemisphere. This study also highlights three true bi-polar species, Impagidinium pallidum , Islandinium minutum and cyst of Polarella glacialis . Only a few taxa are strictly endemic, either being relics of ancient seas such as the Paratethys ( Spiniferites cruciformis ) or linked to specific environmental conditions. However, recent studies have shown recent worldwide dispersal of these endemic species possibly due to human activities. Overall, this compilation has highlighted the progress made since the early 1970s on our understanding of these important tracers of environmental conditions but also gaps in our knowledge of their distribution in pelagic regions of the Pacific and Indian Oceans as well as under Arctic sea ice. • 3636 assemblages of modern dinoflagellate cysts were compiled to discuss patterns of distribution. • Of the 91 taxa, only three dominate globally, Brigantedinium spp., Operculodinium centrocarpum and Spiniferites species. • Only three taxa are truly bi-polar: Impagidinium pallidum , Islandinium minutum and Polarella glacialis.

Different circulation history of mercury in aquatic biota from King George Island of the Antarctic

To trace the circulation history of aquatic bioavailable Hg in the Antarctic, the species and isotopic compositions of Hg in sediment, Archaeogastropoda (Agas), Neogastropoda (Ngas), and fish collected from King George Island were studied in detail. Positive mass independent fractionation (MIF) was observed and positively correlated with the percentages of methylmercury (MeHg%) in Agas and Ngas, suggesting an effect of MeHg accumulation during trophic transfer on MIF signatures. However, both the ratios of Δ199Hg/δ202Hg and Δ199Hg/Δ201Hg indicated different circulation histories of Hg in Agas, Ngas, and fish. The microbial methylation in sediment was the primary source of MeHg in Agas and Ngas (Δ199Hg/δ202Hg ∼0, Δ199Hg/Δ201Hg ∼1.00). In contrast, the MeHg in fish (Δ199Hg/δ202Hg = 0.55 ± 0.06, Δ199Hg/Δ201Hg = 1.19 ± 0.17) came from the combined sources of residual MeHg which had sunk from the surface water and microbial-methylated MeHg in sediments, and the bioavailable Hg in the sediments contributed to approximately 44% of the total Hg in fish. Subsequently, the Δ199Hg values of bioavailable MeHg and IHg in sediments were quantitatively calculated, which provided key end-member information for future source apportionment in the Antarctic and other pelagic regions. It was also found that the Hg accumulated in Agas and Ngas had no history of MeHg photo-degradation, indicating that the methylated Hg in benthic zones suffered little photo-degradation and thus presented high bioavailability and environmental risk.

On the separation between inorganic and organic fractions of suspended matter in a marine coastal environment

A central aspect of coastal biogeochemistry is to determine how nutrients, lithogenic and organic matter are distributed and transformed within coastal and estuarine environments. Analyses of the spatio-temporal changes of total suspended matter (TSM) concentration indicate strong and variable linkages between intertidal fringes and pelagic regions. In particular, knowledge about the organic fraction of TSM provides insight to how biogenic and lithogenic particulate matter are distributed in suspension. In our study we take advantage of a set of over 3000 in situ Loss on Ignition (LoI) data from the Southern North Sea that represent fractions of particulate organic matter (POM) relative to TSM (LoI ≡ POM:TSM). We introduce a parameterization (POM-TSM model) that distinguishes between two POM fractions incorporated in TSM. One fraction is described in association with mineral particles. The other represents a seasonally varying fresh pool of POM. The performance of the POM-TSM model is tested against data derived from MERIS/ENVISAT-TSM products of the German Bight. Our analysis of remote sensing data exhibits specific qualitative features of TSM that can be attributed to distinct coastal zones. Most interestingly, a transition zone between the Wadden Sea and seasonally stratified regions of the Southern North Sea is identified where mineral associated POM appears in concentrations comparable to those of freshly produced POM. We will discuss how this transition is indicative for a zone of effective particle interaction and sedimentation.The dimension of this transition zone varies between seasons and with location. Our proposed POM-TSM model is generic and can be calibrated against in situ data of other coastal regions.