Sediment Trap Samples Research Articles

Sapphirinid copepods as predators of doliolids: Their role in doliolid mortality and sinking flux

We investigated predatory behavior of sapphirinid copepods on doliolids around the Kuroshio Extension at stations experiencing blooms of Dolioletta gegenbauri. Onboard observations showed that adult Sapphirina nigromaculata was an active predator of doliolids, with a preference for internal tissues. When entering a doliolid body cavity, sapphirinids left a characteristic bite mark around the fringe of oral and atrial aperture or hole on the tunic of the doliolid. In situ observations with a video plankton recorder (VPR) revealed that association between sapphirinids and doliolids was common in the field. Adult sapphirinids and doliolids exhibiting the characteristic evidence of an attack (bite mark or hole) were found in sediment traps at a depth of 50 m, indicating that the association between these taxa was due to predation. Early copepodites, which were not observed in sediment‐trap samples, appeared in the VPR observations to have a semi‐parasitic phase when they attached themselves to nurse chains. The maximal daily ration of sapphirinids estimated by onboard experiments ranged between 29% and 37% of their body carbon weight. Although the mean predation effect by sapphirinids on the doliolid population biomass was only 0.7% d−1, sapphirinids potentially had a greater effect on doliolid abundance at the termination of doliolid blooms. Some of the attacked doliolids were discarded by the sapphirinids and contributed to the sinking flux below 150 m, the importance of which as a source of detritus likely increased with depth. Sapphirinids, despite their relatively low abundance in the water column, play a specific role in driving community succession and biogeochemical cycling.

Composition and provenance of terrigenous organic matter transported along submarine canyons in the Gulf of Lion (NW Mediterranean Sea)

Previous projects in the Gulf of Lion have investigated the path of terrigenous material in the Rhone deltaic system, the continental shelf and the nearby canyon heads. This study focuses on the slope region of the Gulf of Lion to further describe particulate exchanges with ocean’s interior through submarine canyons and atmospheric inputs. Nine sediment traps were deployed from the heads to the mouths of Lacaze-Duthiers and Cap de Creus submarine canyons and on the southern open slope from October 2005 to October 2006. Sediment trap samples were analyzed by CuO oxidation to investigate spatial and temporal variability in the yields and compositional characteristics of terrigenous biomarkers such as lignin-derived phenols and cutin acids. Sediment trap data show that the Dense Shelf Water Cascading event that took place in the months of winter 2006 (January, February and March) had a profound impact on particle fluxes in both canyons. This event was responsible for the majority of lignin phenol (55.4%) and cutin acid (42.8%) inputs to submarine canyons, with lignin compositions similar to those measured along the mid- and outer-continental shelf, which is consistent with the resuspension and lateral transfer of unconsolidated shelf sediment to the canyons. The highest lithogenic-normalized lignin derived phenols contents in sediment trap samples were found during late spring and summer at all stations (i.e., 193.46μgVPg−1 lithogenic at deep slope station), when river flow, wave energy and total particle fluxes were relatively low. During this period, lignin compositions were characterized by elevated cinnamyl to vanillyl phenol ratios (>3) at almost all stations, high p-coumaric to ferulic acid ratios (>3) and high yields of cutin acids relative to vanillyl phenols (>1), all trends that are consistent with high pollen inputs. Our results suggest marked differences in the sources and transport processes responsible for terrigenous material export along submarine canyons, mainly consisting of fluvial and shelf sediments during winter and atmospheric dust inputs during spring and summer.

Amino acid nitrogen isotopic composition patterns in lacustrine sedimenting matter

Amino acids (AAs) comprise a large fraction of organic nitrogen (N) in plankton and sedimenting matter. Aquatic studies of organic N compounds in general and of AAs in particular, mostly concentrate on marine environments. In order to study the cycling and fate of organic N and AAs in lakes, we measured the N isotopic composition (δ15N) of bulk organic matter (OM) and of single hydrolysable AAs in sediment trap and sediment samples from two Swiss lakes with contrasting trophic state: Lake Brienz, an oligotrophic lake with an oxic water column, and Lake Zug a eutrophic, meromictic lake. We also measured the N isotopic composition of water column nitrate, the likely inorganic N source during biosynthesis in both lakes. The δ15N–AA patterns found for the sediment trap material were consistent with published δ15N–AA data for marine plankton. The AA composition and primary δ15N–AA signatures are preserved until burial in the sediments. During early sedimentary diagenesis, the δ15N values of single AAs appear to increase, exceeding those of the bulk OM. This increase in δ15N–AA is paralleled by a decreased contribution of AAs to the total OM pool with progressed degradation, suggesting preferential AA degradation associated with a significant N isotope fractionation. Indicators for trophic level based on δ15N–AAs were determined, for the first time in lacustrine systems. In our samples, the trophic AAs were generally enriched in 15N compared to source AAs and higher trophic δ15N–AA values in Lake Zug were consistent with a higher trophic level of the bulk biomass compared to Lake Brienz. Especially the difference between average trophic δ15N–AAs and average source δ15N–AAs was sensitive to the trophic states of the two lakes. A proxy for total heterotrophic AA re-synthesis (ΣV), which is strongly associated with heterotrophic microbial reworking of the OM, was calculated based on δ15N values of trophic AAs. Higher ΣV in Lake Brienz indicate enhanced heterotrophic bacterial reworking of AAs under oligotrophic conditions. Despite changes in the δ15N–AA values within the sediments, the proxies based on these values were consistent over the studied sediment profile, indicating the preservation of trophic signatures; therefore, our results underscore that δ15N–AA analysis of sedimentary records represents a promising tool to assess trophic levels and bacterial re-synthesis in lakes.

Planktonic foraminiferal area density as a proxy for carbonate ion concentration: A calibration study using the Cariaco Basin ocean time series

AbstractBiweekly sediment trap samples and concurrent hydrographic measurements collected between March 2005 and October 2008 from the Cariaco Basin, Venezuela, are used to assess the relationship between [CO32−] and the area densities (ρA) of two species of planktonic foraminifera (Globigerinoides ruber (pink) and Globigerinoides sacculifer). Calcification temperatures were calculated for each sample using species‐appropriate oxygen isotope (δ18O) temperature equations that were then compared to monthly temperature profiles taken at the study site in order to determine calcification depth. Ambient [CO32−] was determined for these calcification depths using alkalinity, pH, temperature, salinity, and nutrient concentration measurements taken during monthly hydrographic cruises. The ρA, which is representative of calcification efficiency, is determined by dividing individual foraminiferal shell weights (±0.43 µg) by their associated silhouette areas and taking the sample average. The results of this study show a strong correlation between ρA and ambient [CO32−] for both G. ruber and G. sacculifer (R2 = 0.89 and 0.86, respectively), confirming that [CO32−] has a pronounced effect on the calcification of these species. Though the ρA for both species reveal a highly significant (p < 0.001) relationship with ambient [CO32−], linear regression reveals that the extent to which [CO32−] influences foraminiferal calcification is species specific. Hierarchical regression analyses indicate that other environmental parameters (temperature and [PO43−]) do not confound the use of G. ruber and G. sacculifer ρA as a predictor for [CO32−]. This study suggests that G. ruber and G. sacculifer ρA can be used as reliable proxies for past surface ocean [CO32−].

32Si dating of sediments from Lake Baikal

We applied the 32Si dating technique to a sediment core from Lake Baikal to obtain the sediment chronology for the last millennium. The core was recovered about 4 km offshore from the north slope of the South Basin in 1,366 m water depth. The sediment material consisted of continuously accumulated diatom-rich geogenic-terrigenous mud, intercalated with a number of dark olive-grey turbidite layers. The sediment layers containing the turbidites were excluded from 32Si sampling to obtain the chronology that is representative of the continuous sedimentation. The initial 32Si activity of 31.3 dpm kg−1 SiO2, measured in sediment trap samples, confirms the trend of 32Si specific activities of biogenic silica found in other Northern Hemisphere lakes. The four sediment core samples from depth 0–48 cm have 32Si specific activities between 23.5 and 0.5 dpm kg−1 SiO2, with corresponding ages between 60 and 860 years and constant sedimentation rate of 0.036 ± 0.004 cm year−1 over the most recent 800 years. 32Si allowed us for the first time to date the uppermost turbidites in the South Basin of Lake Baikal, to 1030, 1310 and 1670 ad. Given these dates, the last long-distance turbidity current triggered by slope instabilities had occurred 330 years before 2000 ad, and the intervals between the 1310 and 1670 ad event and between the 1030 and 1310 ad event were 360 and 280 years, respectively. The 32Si ages allow unprecedented time resolution for reconstruction of the former environmental and climatic conditions during the past millennium.

Comparison of species-specific oxygen isotope paleotemperature equations: Sensitivity analysis using planktonic foraminifera from the Cariaco Basin, Venezuela

Abstract The oxygen isotope compositions of seven species of planktonic foraminifera ( Globigerinoides ruber (pink), Globigerina bulloides , Globorotalia menardii , Globigerinoides sacculifer , Orbulina universa , Globorotalia crassaformis , and Neogloboquadrina dutertrei ) were measured from biweekly sediment trap samples collected in Cariaco Basin, Venezuela between 2003 and 2008. Sixteen published paleotemperature equations were used to estimate calcification temperatures from this δ 18 O data. As part of the CARIACO time series, routine in situ water column chemistry measurements and hydrographic monitoring has occurred since 1995. The calcification temperature estimates were compared with these monthly water column temperature measurements to ascertain species depth habitats and to determine which equations yielded the most realistic temperature estimates. No single equation provided accurate temperature estimates for all species. Rather, the equations yielded temperature estimates that varied by 2–4 °C for each species. Overall species-specific paleotemperature equations based on plankton tow samples yield the coldest temperature estimates, while generic equations produce the warmest temperatures. Our results indicate that when using planktonic foraminiferal δ 18 O to make paleotemperature estimates, equations must be carefully selected on a species by species basis. Here we provide general guidelines for selecting paleotemperature equations. We also evaluated how well the δ 18 O difference between the surface dwelling G. ruber and the deeper dwelling N. dutertrei estimates the surface to thermocline temperature gradient. The Δδ 18 O is small (0.61‰) during winter due to upwelling and increases (1.37‰) during summer as upwelling ceases and surface waters become thermally stratified.

Comparison of TEX86 and [formula omitted] temperature proxies in sinking particles in the Cariaco Basin

The Cariaco Basin, a silled, permanently anoxic basin on the continental shelf of Venezuela with a dynamic chemocline (~240–350m), has been subject of >20 years of oceanographic observation and sediment trap studies. We evaluated U37K′ and the TEX86 temperature proxies using sinking particles collected in shallow sediment trap samples at 275m (Trap A) and 455m (Trap B) (within and below the chemocline). The organic geochemical temperature proxies, U37K′ (based on coccolithophorid alkenone lipids) and TEX86 (based on archaeal glycerol dialkyl glycerol tetraether (GDGT) lipids), use observed relationships between the ratio of specific lipids and measured sea surface temperature to hindcast past sea surface temperatures. In this study, both U37K′ and TEX86 temperature proxies record seasonal temperature variations, including the cooling associated with upwelling events. U37K′-based temperatures are colder than measured sea surface temperatures, and better correlated temperature at the chlorophyll maximum. In sediment trap material collected below the chemocline (Trap B),U37K′ values are higher than those in Trap A. Warmer subchemocline U37K′ based temperatures may be related to autooxidation of sinking particles, either by small amounts of available oxygen or by alternate electron acceptors concentrated in the biologically dynamic chemocline (e.g. intermediate sulfur compounds). The absolute flux weighted TEX86 temperature values measured in sinking particles from Trap A match the measured SST well. The differences in the TEX86 values between Traps A and B are small and reflect less impact of degradation. Overall, the TEX86 temperatures in sinking particles in the Cariaco Basin reflect annual SST.

Microcystins, nutrient dynamics, and other environmental factors during blooms of non-microcystin-producing Aphanizomenon flos-aquae in Upper Klamath Lake, Oregon, 2009

Seasonal phytoplankton blooms dominated by cyanobacteria in Upper Klamath Lake, Oregon, produce toxic microcystins at concentrations that may be detrimental to local wildlife. In 2009, water column, sediment trap, and surficial sediment samples were collected to relate the occurrences of microcystins in these samples to other environmental variables. Microcystin concentrations in sediment trap and surficial sediment samples were lower than in water column samples, and sediment trap samples contained higher concentrations than surficial sediment samples, with a peak in one sample (1107 μg/g) that exceeded the maximum concentration measured in any other water or sediment sample from this area. Concentrations of microcystins and cells of Microcystis aeruginosa increased following the decline of the first bloom dominated by non-microcystin-producing Aphanizomenon flos-aquae in response to an increase in nitrogen and phosphorus concentrations. Results of this study also show that nitrogen fixation by A. flos-aquae during spring and early summer provided nitrogen for growth of toxigenic M. aeruginosa and that phosphorus availability may have played a greater role overall in determining the pattern of microcystin occurrence in the lake, given the apparent influence of phosphorus on growth and decline of the A. flos-aquae bloom. This study is the first report of microcystins in sediments of Upper Klamath Lake, the largest lake (by surface area) in Oregon, and contributes to understanding the conditions under which elevated microcystin concentrations occur. [Supplementary materials are available for this article. Go to the publisher's online edition of Lake and Reservoir Management for the following free supplemental resources: microscope images of major phytoplankton species, microcystin concentrations in surficial sediment samples from randomly selected sites, loadings of the first 2 principal components from PCA analysis of microcystin and water quality data, and the medians and ranges of measured limnological variables.]

Mesozooplankton community development at elevated CO<sub>2</sub> concentrations: results from a mesocosm experiment in an Arctic fjord

Abstract. The increasing CO2 concentration in the atmosphere caused by burning fossil fuels leads to increasing pCO2 and decreasing pH in the world ocean. These changes may have severe consequences for marine biota, especially in cold-water ecosystems due to higher solubility of CO2. However, studies on the response of mesozooplankton communities to elevated CO2 are still lacking. In order to test whether abundance and taxonomic composition change with pCO2, we have sampled nine mesocosms, which were deployed in Kongsfjorden, an Arctic fjord at Svalbard, and were adjusted to eight CO2 concentrations, initially ranging from 185 μatm to 1420 μatm. Vertical net hauls were taken weekly over about one month with an Apstein net (55 μm mesh size) in all mesocosms and the surrounding fjord. In addition, sediment trap samples, taken every second day in the mesocosms, were analysed to account for losses due to vertical migration and mortality. The taxonomic analysis revealed that meroplanktonic larvae (Cirripedia, Polychaeta, Bivalvia, Gastropoda, and Decapoda) dominated in the mesocosms while copepods (Calanus spp., Oithona similis, Acartia longiremis and Microsetella norvegica) were found in lower abundances. In the fjord copepods prevailed for most of our study. With time, abundance and taxonomic composition developed similarly in all mesocosms and the pCO2 had no significant effect on the overall community structure. Also, we did not find significant relationships between the pCO2 level and the abundance of single taxa. Changes in heterogeneous communities are, however, difficult to detect, and the exposure to elevated pCO2 was relatively short. We therefore suggest that future mesocosm experiments should be run for longer periods.

Calibration of the boron isotope proxy in the planktonic foraminifera Globigerinoides ruber for use in palaeo-CO2 reconstruction

The boron isotope-pH proxy, applied to mixed-layer planktic foraminifera, has great potential for estimating past CO2 levels, which in turn is crucial to advance our understanding of how this greenhouse gas influences Earth's climate. Previous culture experiments have shown that, although the boron isotopic compositions of various planktic foraminifera are pH dependent, they do not agree with the aqueous geochemical basis of the proxy. Here we outline the results of culture experiments on Globigerinoides ruber (white) across a range of pH (∼7.5–8.2) and analysed via multicollector inductively-coupled plasma mass spectrometry (MC-ICPMS), and compare these data to core-top and sediment-trap samples to derive a robust new species-specific boron isotope-pH calibration. Consistent with earlier culture studies, we show a reduced pH dependency of the boron isotopic composition of symbiont-bearing planktonic foraminifera compared to borate ion in seawater. We also present evidence for a size fraction effect in the δ11B of G. ruber. Finally, we reconstruct atmospheric CO2 concentrations over the last deglacial using our new calibration at two equatorial sites, ODP Site 999A and Site GeoB1523-1. These data provide further grounding for the application of the boron isotope-pH proxy in reconstructions of past atmospheric CO2 levels.

Seasonality and variability of coccolithophore fluxes in response to diverse oceanographic regimes in the Bay of Bengal: Sediment trap results

A study on coccolithophores from the sediment trap samples, collected over a period of one year (January 1992–December 1992) from three trap locations in the Bay of Bengal (BOB) were used to understand their production and export processes in relation to diverse oceanographic regimes associated with the reversing monsoons. A total of 25 species of coccolithophores were identified, which include some of the ecologically important species: viz: Gephyrocapsa oceanica, Umbilicosphaera sibogae, Florisphaera profunda, Umbellosphaera irregularis, Emiliania huxleyi, Oolithotus antillarum, U. tenuis, Helicosphaera carteri and Calcidiscus leptoporus. The total coccolithophore fluxes increased from the northern to southern Bay of Bengal where G. oceanica, U. sibogae and E. huxleyi were dominant species displaying seasonality with peak fluxes occurring during southwest (SW) and northeast (NE) monsoons reflecting their affinity for nutrient-rich waters brought in by river plumes, divergences and cyclonic eddies. U. irregularis, an indicator of oligotrophic/warm water, recorded peak abundance fluxes only during the spring intermonsoon period at all trap locations thus inferring its preference for oligotrophic conditions caused by increased Sea Surface Temperature (SST), stratification and lack of nutrient supply due to weak wind velocities. The deep dwelling species, F. profunda recorded high fluxes during the fall intermonsoon (October/November) in the northern and southern traps during the spring intermonsoon. The peak fluxes observed during the spring intermonsoon (April/May) in the central and southern traps indicated the prevalence of a deep nutricline when oligotrophic conditions prevailed at the surface. The interannual variability of coccolithophore assemblages between the years 1992 and 1994 may be attributed to the prevalence of ENSO (El Nino–Southern Oscillation) and negative IOD (Indian Ocean Dipole) during 1992 and moderate ENSO and positive IOD with different ocean dynamics in 1994. Interestingly, dissolution was encountered as evidenced by the presence of corroded coccoliths. Similarly, mechanical breakage of coccoliths was also observed. It is believed that the biologically mediated processes were the main factors responsible for both the dissolution and mechanical breakage of coccoliths.

Seasonal Flux and Assemblage Composition of Planktic Foraminifers from a Sediment-Trap Study in the Northern Gulf of Mexico

ABSTRACT Poore, R.Z.; Tedesco, K.A., and Spear, J.W., 2013. Seasonal flux and assemblage composition of planktic foraminifers from a sediment-trap study in the northern Gulf of Mexico. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 6–19, Coconut Creek (Florida), ISSN 0749-0208. Sediment-trap samples from the northern Gulf of Mexico reveal that Globorotalia truncatulinoides, Neogloboquadrina dutertrei, Pulleniatina spp. (includes P. obliquiloculata and P. finalis), and the Globorotalia menardii group (includes Gt. menardii, Gt. tumida, and Gt. ungulata) generally occur in cold months. Globigerinoides ruber (white and pink varieties) and Globigennoides sacculifer occur throughout the year. The seasonal occurrence of individual taxa of planktic foraminifers in the Gulf of Mexico have important differences with the seasonal occurrence of the same taxa ...

Wind‐formed gravel bed forms, Wright Valley, Antarctica

Bed forms composed of gravel size particles (≈50% of particles >4 mm) are observed in the Wright Valley of the McMurdo Dry Valley system in Antarctica. These bed forms are characterized by a very asymmetrical shape with a mean aspect ratio of 0.025 (standard deviation 0.005), mean wavelength of 2.7 m (±0.49 m), and a mean height of 0.06 m (±0.01 m). Particle size analysis of the bed form sediments shows bimodality with a peak near 9 mm and another between 0.5 mm and 0.25 mm. Time‐integrated sediment trap samples of horizontal saltation and creep flux indicate the flux of particles ≥4 mm during the two‐year monitoring period was extremely low. Measurements of the horizontal displacement of tracer particles (14 mm, 12 mm, 10 mm, 8 mm, and 6 mm diameter) placed onto the bed forms corroborate the low particle flux measurements and limited movement of particles. The bed forms share form and grain size characteristics with both ripples and mega‐ripples, showing poor sorting of particles across a single wavelength except for a slight coarsening at the crest similar to ripples, but their sinuosity suggest that transverse instabilities affect their formation similar to mega‐ripples. Based on the data for the prevailing environmental conditions it can be argued that the Wright Valley form is an expression of gravel particles moved solely by highly intermittent creep processes. This also argues for the need for a very long period of time for their evolution, on the order of centuries.

Contribution of zooplankton fecal pellets to deep ocean particle flux in the Sargasso Sea assessed using quantitative image analysis

Fecal pellet flux and size distribution at 500, 1500 and 3200 m depths were measured in sediment trap samples collected by the Oceanic Flux Program time-series off Bermuda, December 2006–November 2007. During the study, three mesoscale eddies passed through: a cyclonic eddy in bloom stage (February through mid-April), a decaying post-bloom mode-water eddy (late April through May), and an anticyclonic eddy (August through October). Variability associated with eddy passage masked any seasonal trends in flux or size distributions. At a depth of 1500 m, the fecal pellet flux ranged from a minimum of 100 pellets m−2 day−1 to a maximum of 500 pellets m−2 day−1 during the cyclonic eddy passage, corresponding to ranges in the fecal pellet mass and the carbon flux of 0.5–1.7 mg m−2 day−1 and 0.07–0.25 mg C m−2 day−1, respectively. Fecal pellets averaged 7 ± 3% of the organic carbon flux, a minimum estimate as disassociated pellets were not quantifiable. Size distribution shifts indicated small zooplankton and immature stages were more abundant within the cyclonic eddy, whereas larger zooplankton were present within the mode water and anticyclonic eddies. The fecal pellet number, flux and size distributions showed no consistent depth trends and indicated extensive fecal pellet reprocessing within the water column.

Dinoflagellate cyst production and flux in Gamak Bay, Korea: A sediment trap study

Abstract To develop a better understanding of the species composition and production of dinoflagellate cysts, including the ecological characteristics of Polykrikos species, a sediment trap study was conducted from June 2005 to June 2006 in Gamak Bay, Korea. Thirty-two dinoflagellate cyst taxa were identified in the sediment trap samples, and the dinoflagellate cyst assemblages were found to be dominated by cysts of Polykrikos kofoidii , Scrippsiella trochoidea , Protoperidinium spp., Polykrikos schwartzii , Gymnodinium catenatum and Ensiculifera carinata . The flux of dinoflagellate cysts ranged from 0.10 × 10 5 to 35.97 × 10 5 cysts m − 2 day − 1 , and the highest flux occurred during summer, and was driven completely by the flux in the production of P. kofoidii and P. schwartzii cysts. The timing of the production of cysts of Polykrikos species seemed to be related to the appearance of G. catenatum as prey. The assemblages of dinoflagellate cysts in surface sediments from Gamak Bay, and their seasonal changes, were very similar to those in the sediment trap samples, which suggested that the monitoring of dinoflagellate cysts in sediment samples can provide information on the environmental conditions in Gamak Bay.

Nitrogen isotopic composition of planktonic foraminifera from the modern ocean and recent sediments

We investigated the controls on the δ15N values of shell‐bound organic matter of planktonic foraminifera (foraminifera‐bound δ15N, or FB‐δ15N). The bulk biomass δ15N of live foraminifera collected from plankton tows at Sta. S in the Sargasso Sea is within ∼1‰ of the FB‐δ15N of the same species picked from surface sediments from the low‐latitude North Atlantic. The FB‐δ15N value in the surface sediments is strongly correlated with the δ15N of thermocline nitrate, the dominant source of new N to the euphotic zone. The three euphotic‐zone‐dwelling, symbiotic, spinose species, Globigerinoides ruber, Globigerinoides sacculifer, and Orbulina universa, have a FB‐δ15N similar to or slightly higher than that of the nitrate supply to the euphotic zone, whereas the deeper‐dwelling, non‐spinose, and/or asymbiotic forms have higher δ15N. In the Cariaco Basin sediment trap samples, the FB‐δ15N of O. universa varies substantially (1.2‰ between the lowest and highest value), in some cases in step with δ15N changes in the bulk sinking N, while the subeuphotic‐zone‐dwelling, asymbiotic, and/or non‐spinose species are generally higher in FB‐δ15N and less variable through the time series. The higher and less temporally variable FB‐δ15N values of the deeper dwellers are consistent with their partial reliance on subsurface suspended particulate nitrogen, the δ15N of which is elevated and relatively stable over time. As an alternative, possibly additional explanation for the lower FB‐δ15N of the euphotic‐zone dwellers (despite their likely tendency to feed on high‐δ15N zooplankton), the dinoflagellate symbionts may reduce the δ15N elevation of a foraminifera's biomass relative to its diet by reducing the efflux of low‐δ15N ammonium.

Amino acid and amino sugar transformation during sedimentation in lacustrine systems

We compared the degradation behaviour of amino sugars (ASs) and amino acids (AAs) during sedimentation in two lakes. Concentrations of individual ASs and AAs were measured in plankton, sediment trap and sediment samples from Lake Zug (LZ; eutrophic, stratified, permanently anoxic below 170m) and Lake Brienz (LB; oligotrophic, oxic throughout the water column). In the plankton samples AAs comprised 37–50% of the organic carbon (Corg) and 41–65% of the N. With increasing water depth the fraction of Corg and N as AAs almost halved in both lakes. At the sediment surface the contribution of AAs to the Corg pool was slightly greater, but in the sediments the proportion further decreased downwards to values of 1% of the Corg pool in LB and 8% in LZ, and 3% and 17% of the N pool, respectively. ASs contributed to a smaller extent to the planktonic organic matter (OM). Within the water column, the contribution decreased in both lakes. In contrast, in the sediments the contribution of ASs to the Corg and N pools increased slightly with depth, indicating AS accumulation. We applied degradation indices based on ASs, AAs and chlorins, which all revealed transformation with OM sedimentation. However, some indices were more sensitive to early degradation (e.g. reactivity index) and others to an intermediate level of degradation (e.g. chlorin index and non-protein AAs). Despite the different trophic status and redox conditions, the general pattern of degradation was similar in both lakes, but was more pronounced in the sediments of the eutrophic LZ.

Seasonal and interannual changes of planktic foraminiferal fluxes in the Gulf of Lions (NW Mediterranean) and their implications for paleoceanographic studies: Two 12-year sediment trap records

In order to investigate the seasonal and interannual variability of planktic foraminiferal fluxes in the NW Mediterranean, 266 samples from two 12-year-long sediment traps were analyzed. Two mooring lines were deployed at the east (Station Planier) and the west (Station Lacaze Duthiers) of the Gulf of Lions. The moorings were deployed at a water depth of around 1000m and were equipped with sediment traps at 500m above bottom (mab). In addition, an array of 13 core-tops recovered from different key areas of the Gulf of Lions is described. At Lacaze Duthiers, average foraminiferal fluxes were about double (411.8shellsm−2d−1) those found at the Planier sampling site (225.4shellsm−2d−1), probably due to the fertilizing effect of the Rhone river plume and the general oceanographic circulation. The annual total foraminiferal fluxes exhibited a unimodal trend, with maxima recorded during the winter–spring transition, i.e. the spring bloom, and minima during summer. Therefore, planktic foraminifers found in the sedimentary record in the Gulf of Lions may reflect the flux during the winter–spring period, rather than throughout the annual cycle. A total of eleven planktic foraminiferal species were identified in the sediment trap and core-top samples but only four species were dominant in the assemblages: Globigerina bulloides Neogloboquadrina pachyderma (dex.), Globorotalia inflata and Globorotalia truncatulinoides. The foraminiferal assemblages in the Gulf of Lions reflected the relatively cold conditions of the Northern Basin. No clear relationship between the NAO (North Atlantic Oscillation) and planktic foraminiferal fluxes was found in the sediment trap records. The low planktic foraminiferal fluxes recorded during the spring of 1998 were probably related to the anomalous environmental conditions triggered by the 1997–98 El Niño event. Furthermore, sediment trap samples were compared with surficial sediments recovered from different environmental and sedimentary settings of the Gulf of Lions and the application of these results in paleoceanographic reconstructions is discussed.

Climate variability and silicoflagellate fluxes in Alfonso Basin (southern Gulf of California)

Abstract We conducted a study from January 2002 to February 2008 on silicoflagellate fluxes in Alfonso Basin at the entrance to the Gulf of California. Thirteen taxa were identified in sediment trap samples, with Octactis pulchra as the dominant species. Total flux climatology reached a maximum value of 5×106 skeletons m-2 day-1 in December and then sharply decreased to a minimum value in February (2.3×103 skeletons m-2 day-1) concurrently with the climatological sea surface temperature (SST) minimum. Subsequently, there was a positive trend with a second relative maximum of 1.6×106 skeletons m-2 day-1 in September coincident with a maximum in climatological SST. During this period, there was a similar increase to 1.4×106 skeletons m-2 day-1 in May. Factor analysis identified three patterns of variation: “subtropical oceanic,” “subarctic,” and “equatorial El Niño.” Factors had reasonable correlations with the Pacific decadal oscillation (PDO), North Pacific Gyre oscillation (NPGO), and El Niño Modoki indices (r=0.53, 0.67, and 0.63, respectively). The first and second modes were apparently linked to decadal climatic conditions correlated to PDO and NPGO, as suggested by the silicoflagellate species Dictyocha messanensis forma messanensis and the assemblage of D. epiodon and Distephanus speculum, respectively; the third mode was related to the presence of warm equatorial-oceanic waters identified by D. messanensis forma spinosa, which defines El Niño influence. These results demonstrate the importance of the region where there is a confluence of the low-frequency, high-latitude PDO, NPGO, and high-frequency El Niño signals.

Museum archives of the 19 years long time-series sediment trap samples collected at central subarctic Pacific Station SA and Bering Sea Station AB during 1990-2010

PARLUX type sediment traps were moored at 600 m above the sea-floor at Station SA (water depth: 5,406m) in the central subarctic Pacific and at Station AB (water depth: 3,788m) in the Aleutian Basin of the Bering Sea. The time-series flux samples were obtained during 1990-2010 for nineteen years. This allowed us to characterize primary fluxes of biogenic particles primarily produced near the surface layers of the deep water columns as well as to decipher the environmental variations associated with climate changes. Based on the samples various studies were conducted thus far, including the followings types: quantitative plankton taxon-numerical studies on diatoms, silicoflagellates, radiolarians, coccolithophores and planktic foraminfers; and geochemical aspects of chemical compounds such as biogenic opal, calcium carbonate and hexosamine as well as elements such as rare earth elements. Such studies published thus far are cited in this paper. The sediment trap samples are archived at the Kyushu University Museum for permanent preservation. The grand total of the currently archived samples, including membrane filters and microslides for the two stations, is 3,552. The details of the samples are described herein and spreadsheet tables of the archives will also be electronically published by the Museum. This makes it possible for future scientists and students, who need to examine the relevant sediment trap samples, to access them properly.