Sediment Trap Material Research Articles

Performance of biochemical tools as fish waste particle tracers in a dispersive marine system

As finfish aquaculture expands to more dispersive coastal environments, inputs of aquaculture-derived organic matter become more diffuse, but widespread. Significant amounts of organic material are likely to be exported beyond the near-farm area, where it may encounter sensitive habitats. Biochemical tracers of organic matter, such as stable isotopes and fatty acids may be useful tools for detecting diffuse waste deposition. We used numerical modelling of direct and resuspended farm waste deposition and empirical environmental measurements to evaluate a range of biochemical indicators (major nutrients, bulk stable isotopes, fatty acids, minor and trace elements) for their efficacy as particle tracers of fish waste around a shallow water (∼30 m) salmon farm, in a dispersive coastal farming area. We also compared their efficacy across a range of sampling approaches (in sediment trap material, sediment and Mytilus edulis as a bio-indicator). Elemental carbon, nitrogen and zinc indicators could accurately reflect predicted waste deposition close to the farm, but only terrestrial fatty acid indicators were able to reflect diffuse wastes farther afield suggesting they are more sensitive tracers of fish waste. Their performance as tracers also differed between sediment trap and sediment samples, with most performing better in sediment trap samples. Although translocated mussels showed evidence of fish waste assimilation in areas of high waste deposition, tissue concentrations of fish waste tracers correlated relatively poorly with modelled waste deposition. Our results highlight the sensitivity of terrestrial fatty acids as fish waste tracers for detecting diffuse waste deposition, and demonstrate that concentrations of a number of elements can be used for mapping acute waste deposition. Our findings can inform selection of biochemical tracers for improved monitoring and management of farm wastes in dispersive marine systems.

Deep carbon export peaks are driven by different biological pathways during the extended Scotia Sea (Southern Ocean) bloom

Estimating the amount of organic carbon leaving the upper water column and becoming sequestered in the deep ocean is a major challenge in our understanding the oceanic C cycle. This study investigate deep sediment trap material collected at a 5 day resolution over a 4 month period covering the bloom in the northern Scotia Sea. This region is characterised by extensive and long-lived phytoplankton blooms that collectively take up the greatest amount of atmospheric carbon dioxide yet measured in the Southern Ocean. In particular, the study resolved multiple peaks of POC flux during the northern Scotia Sea bloom resulting from distinctly different export processes. This work also examine the contribution of diatoms and calcifying species to the POC flux as well as determining FP (faecal pellet) characteristics, including biogeochemical composition and sinking velocity. Results showed that POC flux during the bloom was concentrated in three major POC peak events. The first two POC peaks were large, of similar intensity (24.5 mg C m−2 d−1 in early November and 22.5 mg C m−2 d−1 in early December), and were dominated by faecal pellets (FPs, 60–66%). FP biogeochemical composition during these two POC peaks was characterised by a dominance of carbonate (>48%), as well as a higher sinking speed (up to 347 m d−1) compared with other FP in the rest of the samples. Results suggest that the large presence of calcium carbonate in these FPs contributed to their relatively high sinking velocity which, in turn, promoted their higher level of POC export to bathypelagic depths. Intact single cell diatoms were relatively important in the first POC peak (mainly characterised by Fragilariopsis kerguelensis and Thalassionema nitzschioides), while detritus including semi-grazed phytodetritus were more abundant during the second POC peak, suggesting a change in the upper ocean C cycle between the two POC peaks. A third, smaller, POC peak (12.7 mg C m−2 d−1 in January) was dominated by diatom resting spores, mainly Chaetoceros Hyalochaete sp. (>70% of total diatoms contribution), which were, almost exclusively, fully intact cells. Our high resolution sampling allowed insights into short time-scale processes that influence the ultimate magnitude of the substantial annual POC flux in this region. Overall our findings highlights that the temporal sequence of biological events in the surface layers during the bloom has a strong influence on both the magnitude and the composition of the fluxes.

First long-term evidence of microplastic pollution in the deep subtropical Northeast Atlantic

No anthropogenic pollutant is more widespread in the aquatic and terrestrial environment than microplastic; however, there are large knowledge gaps regarding its origin, fate, or temporal variations in the oceans. In this study, we analyzed sediment trap material from the deep subtropical Northeast Atlantic (2000 m) in a long-term record (2003–2015) to assess the role of the deep ocean as a potential sink of microplastics. Microplastic particles were identified in all 110 analyzed samples with flux rates of 1.13–3146.81 items d−1 m−2. Calculated microplastic mass fluxes ranged between 0.10 and 1977.96 μg d−1 m−2, representing up to 8% of the particle flux. Between years, the composition of the different polymers changed significantly, dominated by polyethylene, whose amount was correlated with the lithogenic input. The correlation between polyethylene and the lithogenic fraction was attributed to an air transport pathway from northeast Africa and surrounding regions. The second most abundant polymer detected in our study was polyvinyl chloride, which is not correlated with lithogenic or biogenic particle flux fractions. Instead, we observed seasonality for polyvinyl chloride with recurring high fluxes in winter before the plankton bloom and significantly lower amounts in summer. Other polymers identified were polypropylene, polyethylene terephthalate, and lower numbers of polystyrene and polymethyl methacrylate. The average microplastic particle size for all samples and polymers was 88.44 ± 113.46 μm, with polyethylene and polyvinyl chloride having the highest proportion of small particles (<100 μm). Our findings provide first insights into temporal variations of sinking microplastics, which are crucial for understanding the fate of plastic in the oceans.

Coupling between physical processes and biogeochemistry of suspended particles over the inner shelf mud in the East China Sea

This study examines how geochemical signals regarding the source and transformation in suspended particles are transported in the marine portion of the sediment dispersal system. In the source-to-sink sedimentary continuum of a world major river, the Changjiang (Yangtze) River, is used to demonstrate the close coupling between the marine physical processes and the geochemical signals carried by suspended particles. A sediment trap mooring configured with a non-sequential sediment trap, a downward-looking ADCP, CTD, LISST-100× were deployed for 29 days in the winter of 2014 off the coast of Zhejiang Province, China in water depth of 22.5 m. The mooring rendered two types of data. Physical processes included temporal changes of water depth, currents at 11 depths, temperature at two depths, and salinity at one depth. There was 15-cm accumulation of captured particles in the trap, which rendered the total mass flux of 233.3 g/cm2/day. The trap material was analyzed for grain-size composition, total 210Pb, minerals including mica/illite, kaolinite, chlorite, k-feldspar, plagioclase, quartz, and dolomite. Organic material (TOC, TN) and carbon isotope δ13C were also measured. The range of terrestrial fraction (Ft) of the trap material was between 45–60%. EOF analysis was used to examine the covariability in both data sets. For the physical data set, 37 variables were used in the analysis. For the sediment trap material, 15 variables were used. The EOF results of the physical processes indicate the tidal flow was the most important physical forcing for the transport of suspended particles and water masses that carried marine- and terrestrial-sourced particles. Wave and current combined resuspension entrained reworked sediment off the seabed, which was then transported landward or seaward. The most important covariability of the particle properties in the sediment trap was caused by hydrodynamic sorting that separated the clay from silt and sand sizes. Geochemical signals of the particles were carried by clay and the particle mass (dry weight) was associated with silt and sand. The temporal characteristics of the sorting show the spring-neap tidal cycle. The next major distinction was the contrast between terrestrial- and marine-sourced materials. The EOF analysis further distinguish contributions from the distal Changjiang River and proximal small rivers at the tertiary level of the covariability. The coverabilities in both data sets show close correspondence. Our findings give firm evidence to show marine processes dominated the transport of land-derived fluvial sediment and the incorporation of marine-sourced particles into the dispersal system. There is complexity in both physical processes and geochemical signals of suspended particles. However, our study points out the close coupling between the two.

Mercury accumulation in the sediment of the Western Mediterranean abyssal plain: A reliable archive of the late Holocene

Temporal reconstruction of Hg deposition from sediment archives is relatively straightforward in organic-rich or high sedimentation rate environments, such as lakes and ocean margins. To retrieve long-term records at regional or global scales, deep-sea sediments are more appropriate, but such records are scarce and their reliability has been questioned because of possible post-depositional Hg diagenetic remobilization. Here, we investigated the accumulation of Hg in the Balearic Abyssal Plain (2850 m deep) of the Western Mediterranean through a comprehensive characterization of the chemical and isotopic composition (organic carbon, nitrogen, sulfur, major and redox-sensitive elements) of sediment trap material and sediment cores. The analysis of material collected in the sediment traps, deployed at 250, 1440, and 2820 m, indicates that Hg is (i) partially re-emitted to the atmosphere and mobilized in the twilight zone and that (ii) the Hg downward flux depends on the primary production in surface waters, suggesting that organic matter (OM) acts as the main Hg-carrier phase. As the Hg concentrations of material collected in the traps vary little with depth but the Hg:Corg ratio of the settling particulate matter decreases with depth, Hg must be re-adsorbed onto the more refractory fraction of the settling OM. Results of selective chemical extractions of the sediment indicate that Hg is very weakly coupled to the iron cycle but strongly associated with sulfur, supporting the assumption that its vertical distribution was only weakly altered by diagenetic remobilization. In addition, the distributions of S and δ34S in the sedimentary column exclude the possibility that local volcanism impacted on Hg enrichment of the sediments. Accordingly, a reconstruction of Hg accumulation rates (Hg-AR) during the Late Holocene is readily achieved. Biological mixing and smoothing of the sediment record, as revealed by the distribution of radionuclides in surface sediments, was considered in the interpretation of the Hg-AR record. The first anthropogenic Hg signal recorded in the studied cores corresponds to the Iron Age and the Roman Empire period, as Hg-ARs rose from the baseline (0.7 ± 0.2 µg m−2 yr−1) to an average value of 2.2 ± 0.5 µg m−2 yr−1. The Hg-ARs return to baseline values at the decline of the Roman Empire, display a small increase during the Medieval Period (1.5 ± 0.5 µg m−2 yr−1), increase abruptly at the onset of the Industrial Era, leading to a ~ 10-fold increase in Hg deposition in the last 120 years (8.9 ± 1.4 µg m−2 yr−1), and retreat progressively over the past 50 years.

Siliceous micro- and nanoplankton fluxes over the Northwind Ridge and their relationship to environmental conditions in the western Arctic Ocean

Siliceous planktons are valuable indicators of the environmental conditions in both modern and past marine settings. However, in contrast to diatoms and radiolarians, other siliceous micro- and nanoplankton in the Arctic Ocean have been rarely explored. In this study, silicoflagellates, endoskeletal dinoflagellate Actiniscus pentasterias and chrysophyte cysts were investigated in one-year mooring sediment trap material (from August 2008 to September 2009) collected in the Northwind Ridge, western Arctic Ocean. The silicoflagellate assemblage was dominated by Stephanocha speculum, accounting for > 71% of the total silicoflagellate composition. While S. speculum was overwhelmingly abundant in summer, S. medianoctisol and S. octonaria were more frequent during winter. The export fluxes of endoskeletal dinoflagellate A. pentasterias did not show clear seasonal pattern except for a peak value in September 2009. We suggest that high flux of A. pentasterias reflects nutrient rich environment at sea ice edge rather than cold under sea ice conditions. High fluxes of chrysophyte cysts were recorded in summer 2009 peaking in late July and early August, ~10 times higher than in summer 2008. Peak of chrysophyte cysts and sea ice melting occurred simultaneously. In addition, observed encystment might be triggered by the population density, hence indicating a favorable environment for phytoplankton blooming. These siliceous micro- and nanoplankton provides information on the modern Arctic Ocean environment but requires further investigations to consolidate knowledge for robust use in paleoceanography.

Why productive lakes are larger mercury sedimentary sinks than oligotrophic brown water lakes

AbstractMercury accumulation in lake sediments is a widespread environmental problem due to the biomagnification of Hg in the aquatic food chain. Soil Hg concentrations, catchment vegetation, erosion, and lake productivity are major factors controlling the accumulation of Hg in lakes. However, their influence on the Hg mass balance in lakes with different catchment characteristics and trophic state is poorly understood. In this multilake study, we decipher the effects of catchment vegetation (coniferous vs. deciduous forest), soil Hg content, and trophic state on Hg sedimentation at six lakes in Germany. We investigated Hg concentrations in leaves, soils, and the lake's water phase. Soils under coniferous stands show slightly higher Hg concentrations than under deciduous forest. Hg concentrations in the water phase were higher in the oligotrophic brown water lakes (8.1 ± 5.6 ng L−1 vs. 3.0 ± 1.9 ng L−1). Lower Hg concentrations in sediment trap material indicate dilution by algae organic matter in the mesotrophic lakes (0.12–0.17 μg g−1 vs. 0.57–0.89 μg g−1). However, Hg accumulation rates in sediment traps were up to 14‐fold higher in the mesotrophic lakes (113–443 μg m−2 yr−1) than in the brown water lakes (32–144 μg m−2 yr−1), which could not be explained by higher Hg fluxes to the productive lakes. Hg mass balance calculation reveals that water phase Hg scavenging by algae is the major reason for the intense Hg export to the sediments of productive lakes which makes them significantly larger sedimentary sinks than oligotrophic brown water lakes.

Abundance and characteristics of microfibers detected in sediment trap material from the deep subtropical North Atlantic Ocean

Plastics and microplastics increasingly gain importance due to their perils and wide distribution in the marine environment. Microfibers account for the largest percentage of anthropogenic-induced microparticles, which inter alia, consist of plastic, and are found in deep-sea sediments. However, the sinking of fibers from the surface through the water column to the seafloor is still poorly understood. The present study investigates microfibers extracted from sediment trap samples, which were deployed in the North Atlantic Subtropical Gyre (NASG). The average result of eleven analyzed samples showed 913 microfibers per gram of collected particle flux material, with a predominant fiber length shorter than 1 mm (75.6%) and a distribution maximum between 0.2 and 0.4 mm. Further, the average number of microfibers found in this study was used to derive microfiber fluxes for the NASG based on the deployment time of the sediment trap. Extrapolating the computed flux of 94 microfibers m−2 day−1 to the entire NASG area would correspond to a total microfiber mass flux of 9800 t a−1 or 73 × 1013 microfibers a−1 of sinking microfibers through the water column. These findings offer an extended application of sediment traps to monitor microfiber fluxes, which reveals the opportunity to investigate the mechanism driving sinking of microfibers and microplastics into the deep open ocean.

Diatom composition and fluxes over the Northwind Ridge, western Arctic Ocean: Impacts of marine surface circulation and sea ice distribution

Over the last decades, the western Arctic Ocean has undergone unprecedented environmental changes. However, long-term in situ observations of marine phytoplankton are still rare and therefore insufficient to fully characterize their evolutionary trends. This study investigated the diatom fluxes and composition in sediment trap material collected from the Northwind Ridge, western Arctic Ocean, from August 2008 to September 2009. Our data showed that Chaetoceros resting spores were the predominant species, accounting for >40% of the diatom composition. The sea ice diatom group, which included Fossula arctica, Fragilariopsis cylindrus and F. oceanica, dominated the rest of the assemblage throughout the observation period. While diatom fluxes in winter were extremely low, higher flux values were found in summer, and summer 2009 flux values were twice as high as those in 2008. The high total mass and diatom fluxes in summer 2009 were attributed to the combined effect of a weakened Beaufort Gyre, a strengthened Pacific water inflow (PWI) and the distribution pattern of the sea ice. The higher levels of coastal diatoms and terrigenous proxies in summer 2009 were consistent with the intensified PWI. Sea ice diatoms and sea ice biomarker IP25 fluxes were both high during the sea ice melting season and were significantly correlated with each other (r2 = 0.64, p < 0.01). Our data also suggest that sea ice diatoms are prone to selective dissolution in the water column and sediments, implying the existence of biases in diatom assemblage data and subsequently in paleoceanographic reconstructions.

Reconstructing N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;-fixing cyanobacterial blooms in the Baltic Sea beyond observations using 6- and 7-methylheptadecane in sediments as specific biomarkers

Abstract. Summer cyanobacterial blooms represent a threat to the Baltic Sea ecosystem, causing deoxygenation of the bottom water and the spread of the so-called dead zones. The history of the Baltic Sea cyanobacterial blooms is known from in situ and satellite observations since the early 1980s but is still not well understood. By comparing both weekly resolved sediment trap material and a well-dated sediment core from the eastern Gotland Basin with monitoring and satellite cyanobacterial data of the last ca. 35 years, it is shown here that 6- and 7-methylheptadecane lipids (expressed as 6+7Me-C17 : 0) may be potentially considered semiquantitative biomarkers for diazotrophic cyanobacteria, and more specifically for Nodularia spumigena. Using this organic proxy, it was thus possible to reconstruct the history of cyanobacterial blooms beyond the observational period with a resolution of 2–4 years since 1860. Cyanobacteria were constantly present but in relatively low abundance until 1920, when they started to alternate between periods with high and low abundance. Interestingly, there seems to be no significant increase in cyanobacterial abundance in the 1950s, when eutrophication and deoxygenation of the Baltic Sea increased considerably. While the early increase in cyanobacteria may be related to a small increase in phosphorus loading, decadal to multi-decadal fluctuations are likely related to variability in the Baltic Sea surface temperature and, ultimately, to the Atlantic Multi-decadal Oscillation. A 7000-year 6+7Me-C17 : 0 record from the Bothnian Sea also suggests a relationship with the mean summer temperature in the Baltic Sea region but at a multi-centennial to multi-millennial timescale. The intensity of the cyanobacterial blooms in the Baltic Sea is thus likely mainly related to natural processes such as temperature variability, at least at a multi-decadal to multi-millennial timescale.

Seasonal Toxicity Observed with Amphipods (Eohaustorius estuarius) at Paleta Creek, San Diego Bay, USA.

To assess potential impacts on receiving systems, associated with storm water contaminants, laboratory 10-d amphipod (Eohaustorius estuarius) survival toxicity tests were performed using intact sediment cores collected from Paleta Creek (San Diego Bay, CA, USA) on 5 occasions between 2015 and 2017. The approach included deposition-associated sediment particles collected from sediment traps placed at each of 4 locations during the 2015 to 2016 wet seasons. The bioassays demonstrated wet season toxicity, especially closest to the creek mouth, and greater mortality associated with particles deposited in the wet season compared with dry season samples. Grain size analysis of sediment trap material indicated coarser sediment at the mouth of the creek and finer sediment in the outer depositional areas. Contaminant concentrations of metals (Cd, Cu, Hg, Ni, Pb, and Zn) and organic compounds (polycyclic aromatic hydrocarbons [PAHs], polychlorinated biphenyls [PCBs], and pesticides) were quantified to assess possible causes of toxicity. Contaminant concentrations were determined in the top 5 cm of sediment and porewater (using passive samplers). Whereas metals, PAHs, and PCBs were rarely detected at sufficient concentrations to elicit a response, pyrethroid pesticides were highly correlated with amphipod toxicity. Summing individual pyrethroid constituents using a toxic unit approach suggested that toxicity to E. estuarius could be associated with pyrethroids. This unique test design allowed delineation of spatial and temporal differences in toxicity, suggesting that storm water discharge from Paleta Creek may be the source of seasonal toxicity. Environ Toxicol Chem 2019;39:229-239. © 2019 SETAC.

Oxygen consumption in seasonally stratified lakes decreases only below a marginal phosphorus threshold

Areal oxygen (O2) consumption in deeper layers of stratified lakes and reservoirs depends on the amount of settling organic matter. As phosphorus (P) limits primary production in most lakes, protective and remediation efforts often seek to reduce P input. However, lower P concentrations do not always lead to lower O2 consumption rates. This study used a large hydrochemical dataset to show that hypolimnetic O2 consumption rates in seasonally stratified European lakes remain consistently elevated within a narrow range (1.06 ± 0.08 g O2 m−2 d−1) as long as areal P supply (APS) exceeded 0.54 ± 0.06 g P m−2 during the productive season. APS consists of the sum of total P present in the productive top 15 m of the water column after winter mixing plus the load of total dissolved P imported during the stratified season, normalized to the lake area. Only when APS sank below this threshold, the areal hypolimnetic mineralization rate (AHM) decreased in proportion to APS. Sediment trap material showed increasing carbon:phosphorus (C:P) ratios in settling particulate matter when APS declined. This suggests that a decreasing P load results in lower P concentration but not necessarily in lower AHM rates because the phytoplankton community is able to maintain maximum biomass production by counteracting the decreasing P supply by a more efficient P utilization. In other words, in-lake organic matter production depends only on APS if the latter falls below the threshold of 0.54 g P m−2 and correspondingly, the atomic C:P ratio of the settling material exceeds ~155.

Cyanobacteria and cyanophage contributions to carbon and nitrogen cycling in an oligotrophic oxygen-deficient zone

Up to half of marine N losses occur in oxygen-deficient zones (ODZs). Organic matter flux from productive surface waters is considered a primary control on N2 production. Here we investigate the offshore Eastern Tropical North Pacific (ETNP) where a secondary chlorophyll a maximum resides within the ODZ. Rates of primary production and carbon export from the mixed layer and productivity in the primary chlorophyll a maximum were consistent with oligotrophic waters. However, sediment trap carbon and nitrogen fluxes increased between 105 and 150 m, indicating organic matter production within the ODZ. Metagenomic and metaproteomic characterization indicated that the secondary chlorophyll a maximum was attributable to the cyanobacterium Prochlorococcus, and numerous photosynthesis and carbon fixation proteins were detected. The presence of chemoautotrophic ammonia-oxidizing archaea and the nitrite oxidizer Nitrospina and detection of nitrate oxidoreductase was consistent with cyanobacterial oxygen production within the ODZ. Cyanobacteria and cyanophage were also present on large (>30 μm) particles and in sediment trap material. Particle cyanophage-to-host ratio exceeded 50, suggesting that viruses help convert cyanobacteria into sinking organic matter. Nitrate reduction and anammox proteins were detected, congruent with previously reported N2 production. We suggest that autochthonous organic matter production within the ODZ contributes to N2 production in the offshore ETNP.

Diagenesis of amino compounds in water column and sediment of Lake Baikal

The diagenesis of amino compounds in Lake Baikal was studied in sediment trap material (18 different water depths between 50–1350m) and underlying sediment (0–40 cm). Total hydrolysable amino acids (THAA), the amino acid (AA) composition including d- and l-enantiomers and amino sugars were analyzed. The study provides information on early diagenesis (<1 year) of settling material as well as on longer-term diagenesis (up to 600 years) occurring in the sediment. AA based diagenetic indicators were successfully applied to reveal changes at the different diagenetic stages. With increasing water and sediment depth, consistent decreases were found in: (1) the contributions of AA to total organic carbon (%TAAC, from 20 to 7%) and total nitrogen (%TAAN, from 54 to 20%); (2) the ratios of protein AA and their respective non-protein degradation products (aspartic acid:β-alanine, from 15 to 2; glutamic acid:γ-aminobutyric acid, from 28 to 2; arginine:ornithine, from 19 to 2); and (3) the AA based degradation index (from 0.7 to −1.1). There was multiple evidence that diagenesis went along with a progressive transformation of phytoplankton and zooplankton into bacterial organic material. Glycine, which is enriched in bacterial peptidoglycan, increased in relative abundance and bacteria-derived d-AA preferentially accumulated over proteinaceous l-AA. Molar ratios of glucosamine and galactosamine decreased towards a ratio of 1.0 ± 0.1 in the sediment, similar to ratios previously reported for detrital marine organic material. The general pattern of amino compound diagenesis in Lake Baikal resembles the pattern observed in marine systems, indicating a universal character of the processes controlling diagenesis in aquatic environments.

Calcification depths of planktonic foraminifera from the southwestern Atlantic derived from oxygen isotope analyses of sediment trap material

Abstract We present a multi-year record of shell fluxes and δ18O of six planktonic foraminifera species (Globigerinoides ruber pink, Globigerinoides ruber white, Trilobatus sacculifer, Orbulina universa, Neogloboquadrina dutertrei, Globorotalia menardii) from sediment traps located in the southwestern Atlantic. Among the six species, only the fluxes of G. ruber white and N. dutertrei exhibit a significant seasonal component, with G. ruber white showing a single flux peak in austral summer, and N. dutertrei exhibiting two flux peaks in spring and autumn. To estimate calcification depths of the studied species, we then compare their measured δ18O to vertical δ18O profiles predicted for each collection time from in-situ temperature profiles and climatological salinity profiles. For the majority of the cases, the measured δ18O could be accounted for by in-situ calcification, assuming species-specific temperature-δ18O calibrations. The resulting estimates of the calcification depth imply that each species exhibits a characteristic typical mean calcification depth. The estimated calcification depths for N. dutertrei (mode 60–70 m) and G. menardii (mode 70–80 m) appear to track the depth of the thermocline in the region, whereas the calcification depths of the remaining four species correspond to conditions in the mixed layer. Among the apparent mixed-layer calcifiers, G. ruber pink and white appeared to calcify consistently shallower (mode 30–40 m) while T. sacculifer calcified deeper (mode 50–60 m). Because of the low flux seasonality, the observed oxygen isotope offsets among the species are similar to the flux-weighted mean annual δ18O offsets, indicating that isotopic offsets among the species in sediment samples are mainly due to different calcification depths. Since the habitat offsets among the species are consistent across seasons, δ18O in sedimentary shells can be used to track conditions in different parts of the water column and the difference in the oxygen-isotope composition between surface species (best represented by G. ruber pink) and thermocline species (best represented by N. dutertrei) can be used as a proxy for stratification in the southwestern Atlantic.

Diversity and taxonomic identification of Shionodiscus spp. in the Australian sector of the Subantarctic Zone

Diatoms are siliceous phytoplankton that play a major role in global carbon fixation, as well as forming the basis of most marine food webs. In the Southern Ocean, diatoms are responsible for significant volumes of carbon export and sequestration in the deep sea. Diatoms are unicellular and microscopic, thus diatom taxonomy has naturally progressed as imaging and molecular technologies have developed. Despite recent advancements, some aspects of diatom taxonomy remain unclear. The genus Shionodiscus was separated from Thalassiosira in 2006, and possesses, as a group, internal extensions of the marginal strutted processes as well as a labiate process on the valve face, usually distant from the margin. The features distinguishing Shionodiscus from Thalassiosira, and Shionodiscus spp. from each other, are difficult to examine under light microscopy, and most taxonomists will group similar Shionodiscus species together when encountered, rather than discriminating species. As a result, the full extent of Shionodiscus diversity is rarely examined in individual studies. In this study, sediment trap material captured in the Australian sector of the Subantarctic Zone was examined using both light and scanning electron microscopy, and compared to known measurements on Shionodiscus species and varieties. This study had two aims; to catalogue for the first time the diversity of Shionodiscus spp. within the Australian sector, and to create a formalized set of criteria for grouping Shionodiscus species, when only light microscopy analysis is possible. By documenting Shionodiscus diversity in the Australian sector and establishing a standard identification protocol, researchers will be better able to determine the ecological significance of the genus in diatom assemblages.

Influence of inter-annual environmental variability on chrysophyte cyst assemblages: insight from a 2-years sediment trap study in lakes from northern Poland

&lt;p&gt;Quantitative paleonvironmental studies using transfer functions are developed from training sets. However, changes in some variables (&lt;em&gt;e.g&lt;/em&gt;., climatic) can be difficult to identify from short-term monitoring (&lt;em&gt;e.g.,&lt;/em&gt; less than one year). Here, we present the study of the chrysophyte cyst assemblages from sediment traps deployed during two consecutive years (November 2011-November 2013) in 14 lakes from Northern Poland. The studied lakes are distributed along a W-E climatological gradient, with very different physical, chemical and morphological characteristics, and land-uses. Field surveys were carried out to recover the sediment trap material during autumn, along with the measurement of several environmental variables (nutrients, major water ions, conductivity, pH, dissolved oxygen and chlorophyll&lt;em&gt;-a&lt;/em&gt;). During the study, one year experienced mild seasonal changes in air temperature (November 2011-November 2012; TS1), typical of oceanic climate, while the other year was characterized by colder winter and spring (November 2012-November 2013; TS2), and higher summer temperatures, more characteristic of continental climate. Other environmental variables (&lt;em&gt;e.g&lt;/em&gt;., nutrients) did not show great changes between both years. Multivariate statistical analyses (RDA and DCA) were performed on individual TS1 and TS2 datasets. Water chemistry and nutrients (pH, TN and TP) explained the largest portion of the variance of the chrysophyte data for the individual years. However, analyses of the combined TS1 and TS2 datasets show that strong changes between summer and autumn (warm period, ice-free period with thermal stratification) and winter and spring (cold period, ice-cover period) play the most important role in the inter-annual variability in the chrysophyte assemblages. We show how inter-annual sampling maximizes ecological gradients of interest, particularly in regions with large environmental diversity, and low climatic variability. This methodology could help to identify distinct seasonal and inter-annual changes of biological communities to improve its application in paleoclimate studies.&lt;/p&gt;

Selective quantification of DOSS in marine sediment and sediment-trap solids by LC-QTOF-MS.

At the onset of the 2010 Gulf oil spill, analytical methods for the quantification of the surfactants in Corexit did not exist in the peer-reviewed literature. To date, only a single study reports the presence of bis-(2-ethylhexyl) sodium sulfosuccinate (DOSS) in deep-sea Gulf sediment collected in 2010 from a single location. There are no data on the occurrence of DOSS in association with settling solids (i.e., sediment-trap solids). To address this data gap, DOSS was initially quantified by liquid chromatography tandem quadrupole mass spectrometry (LC-MS/MS) in sediment and sediment-trap solids collected from multiple sites in the Gulf between 2010 and 2013. However, interferences confounded analyses using only a quadrupole (MS/MS) system; therefore, a LC-high mass accuracy quadruple time of flight mass spectrometry (LC-QTOF-MS) method was developed. The LC-QTOF method was validated and applied to eight representative samples of sediment and of sediment-trap solids. The presented method quantifies DOSS in solids of marine origin at concentrations above the limit of quantification of 0.23μgkg-1 with recoveries of 97 ± 20% (mean ± 95 CI). Gulf sediment and sediment-trap solids gave DOSS concentrations of <LOQ-25 and 1.5-6.3μgkg-1, respectively. Graphical Abstract Sediment core and sediment trap materials were collected in the Gulf and analyzed for DOSS by LCQTOF.

Effectiveness of preservatives and poisons on sediment trap material in freshwater environments

To estimate the effectiveness of preservative/poisons on sediment trap material in freshwater environments, we measured the ratio of particulate organic matter retention [particulate organic carbon (POC) and nitrogen (PON), particulate phosphorus (PP)] using simulated sediment trap material (SSTM). SSTM was collected in summer and fall from depths of 30 and 85 m in the mesotrophic northern basin of Lake Biwa, Japan. All SSTM was incubated in buffered formalin, sodium azide (NaN3) and mercuric chloride (HgCl2) solutions for a period of 56 days. The retention ratio of POC, PON and PP of SSTM was measured throughout the course of the experiments. Results showed that buffered formalin and HgCl2 were very effective in preserving POC. Although NaN3 was less effective at preventing degradation of POC, the degradation process as a function of time was described with the double-exponential decay equation extremely well. Buffered formalin and HgCl2 were also effective in preserving PON, but less effective than for POC. To ensure accurate measurements of PON vertical flux, therefore, one should estimate the decomposition kinetics of PON in sediment trap material. None of the preservatives used in this study was effective for preserving PP, which was rapidly degraded within a week. However, the degradation process was also fully described by the equation, and this will make it possible to accurately estimate PP vertical flux.

Fractionation of iron isotopes during leaching of natural particles by acidic and circumneutral leaches and development of an optimal leach for marine particulate iron isotopes

Iron (Fe) is an essential nutrient for life on land and in the oceans. Iron stable isotope ratios (δ56Fe) can be used to study the biogeochemical cycling of Fe between particulate and dissolved phases in terrestrial and marine environments. We have investigated the dissolution of Fe from natural particles both to understand the mechanisms of Fe dissolution, and to choose a leach appropriate for extracting labile Fe phases of marine particles. With a goal of finding leaches which would be appropriate for studying dissolved-particle interactions in an oxic water column, three particle types were chosen including oxic seafloor sediments (MESS-3), terrestrial dust (Arizona Test Dust – A2 Fine), and ocean sediment trap material from the Cariaco basin. Four leaches were tested, including three acidic leaches similar to leaches previously applied to marine particles and sediments (25% acetic acid, 0.01N HCl, and 0.5N HCl) and a pH 8 oxalate-EDTA leach meant to mimic the dissolution of particles by organic complexation, as occurs in natural seawater. Each leach was applied for three different times (10min, 2h, 24h) at three different temperatures (25°C, 60°C, 90°C). MESS-3 was also leached under various redox conditions (0.02M hydroxylamine hydrochloride or 0.02M hydrogen peroxide). For all three sample types tested, we find a consistent relationship between the amount of Fe leached and leachate δ56Fe for all of the acidic leaches, and a different relationship between the amount of Fe leached and leachate δ56Fe for the oxalate-EDTA leach, suggesting that Fe was released through proton-promoted dissolution for all acidic leaches and by ligand-promoted dissolution for the oxalate-EDTA leach. Fe isotope fractionations of up to 2‰ were observed during acidic leaching of MESS-3 and Cariaco sediment trap material, but not for Arizona Test Dust, suggesting that sample composition influences fractionation, perhaps because Fe isotopes are greatly fractionated during leaching of silicates and clays but only minimally fractionated during dissolution of Fe oxyhydroxides. Two different analytical models were developed to explain the relationship between amount of Fe leached and δ56Fe, one of which assumes mixing between two Fe phases with different δ56Fe and different dissolution rates, and the other of which assumes dissolution of a single phase with a kinetic isotope effect. We apply both models to fit results from the acidic leaches of MESS-3 and find that the fit for both models is very similar, suggesting that isotope data will never be sufficient to distinguish between these two processes for natural materials. Next, we utilize our data to choose an optimal leach for application to marine particles. The oxalate-EDTA leach is well-suited to this purpose because it does not greatly fractionate Fe isotopes for a diversity of particle types over a wide variety of leaching conditions, and because it approximates the conditions by which particulate Fe dissolves in the oceans. We recommend a 2h leach at 90°C with 0.1M oxalate and 0.05M EDTA at pH 8 to measure labile “ligand-leachable” particulate δ56Fe on natural marine materials with a range of compositions.