Sediment Trap Study Research Articles

Annual record of particle fluxes, geochemistry and diatoms in Effingham Inlet, British Columbia, Canada, and the impact of the 1999 La Niña event

Sediment traps were deployed inside the anoxic inner basin of Effingham Inlet and at the oxygenated mouth of the inlet from May 1999 to September 2000 in a pilot study to determine the annual depositional cycle and impact of the 1999 La Niña event within a western Canadian inlet facing the open Pacific Ocean. Total mass flux, geochemical parameters (carbon, nitrogen, opal, major and minor element contents, and stable isotope ratios) and diatom assemblages were determined and compared with meteorological and oceanographic data. Deposition was seasonal, with coarser grained terrestrial components and benthic diatoms settling in the autumn and winter, coincident with the rainy season. Marine sedimentary components and abundant pelagic diatoms were coincident with coastal upwelling in the spring and summer. Despite the seasonal differences in deposition, the typical temperate-zone Thalassiosira – Skeletonema – Chaetoceros bloom succession was muted. A July 1999 total mass flux peak and an increase in biogenous components coincided with a rare bottom-water oxygen renewal event in the inlet. Likewise, there were cooler-than-average sea surface temperatures (SSTs) just outside the inlet, and unusually high abundances of a previously undescribed cool-water marine diatom ( Fragilariopsis pacifica sp. nov.) within the inlet. Each of these occurrences likely reflects a response to the strong La Niña that followed the year after the strongest-ever recorded El Niño event of 1997–1998. By the autumn of 1999, SSTs had returned to average, and F. pacifica had all but disappeared from the remaining trap record, indicating that oceanographic conditions had returned to normal. Oxygenation events were not witnessed in the inlet in the years before or after 1999, suggesting that a rare oceanographic and climatic event was captured by this sediment trap time series. The data from this record can therefore be used as a benchmark for identifying anomalous environmental conditions on this coast. ► Only sediment trap study done in a western Canadian inlet facing the open Pacific ► Deposition of settling particles is clearly seasonal. ► Deposition of settling particles is also influenced by the 1999 La Niña event. ► 1999 La Niña had a strong oceanographic and biological effect on the coast. ► Sediment trap data can be used as benchmarks recording anomalous climatic events.

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 ...

Deposition signatures in Onondaga Lake, New York: Observations from a 28‐year sediment‐trap study

We tested paradigms and models that relate deposition of phytoplankton constituents to lake metabolism based on analyses of long‐term sediment‐trap collections (28 yr of the 1980–2010 period) from a dimictic urban lake, Onondaga Lake, New York. There were major changes in a number of important drivers of deposition, including decreases in the concentration of a divalent cation (Ca2+), nutrient loading and primary production, and variations in food‐web effects. The summertime downward fluxes of particulate organic carbon (DFPOC), particulate nitrogen, particulate phosphorus (P), and chlorophyll were greater than values reported in the literature at the start of the program and decreased > 70% in response to decreases in Ca2+ and P loading. Results include (1) the positive dependence of DFPOC on primary production, (2) the positive dependence of the rate of hypolimnetic oxygen depletion on DFPOC, (3) the negative effect of Daphnia grazing on DFPOC under eutrophic and hypereutrophic conditions, and (4) the dependence of the stoichiometry of depositing material on particle origins and nutrient status of the phytoplankton community. The relationship between the export ratio, the fraction of gross primary production lost to deposition, and primary production reported in the literature was extended based on inclusion of Onondaga Lake data, and described by a nonlinear (polynomial function) relationship.

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.

Organic biomarkers to describe the major carbon inputs and cycling of organic matter in the central Great Barrier Reef region

Controversy surrounds the sources and transport of land derived pollutants in the Great Barrier Reef ecosystem because there is insufficient knowledge of the mechanism of movement of organic contaminants and the cycling of organic matter in this dynamic system. Thus a sediment and sediment trap study was used to describe the composition of resuspended and surface sediments in the south central Great Barrier Reef and its lagoon. This region is characterised by strong tides (6–8 m at Mackay) and trade winds regularly about 15–20 knots. A series of organic biomarkers detailed the cyclical processes of sediment resuspension, recolonising with marine algae and bacteria, packaging into zooplankton faecal pellets and resettlement to sediments where the organics undergo further diagenesis. With each cycle the inshore sediments are diluted with CaCO 3 reef sediments and moved further offshore with the strong ebb tide currents. This results in transport of land derived materials offshore and little storage of organic materials in the lagoon or reef sediments. These processes were detailed by inorganic measurements such as %CaCO 3 and Al/Ca ratios, and by the compositions of hydrocarbon, sterol, alcohol, and fatty acid lipid fractions. Persistent contaminants such as coal dust from a coastal loading facility can be detected in high concentration inshore and decreasing out to the shelf break at 180 m approximately 40 nautical miles offshore. The normal processes would likely be amplified during cyclonic and other storms. The lipids show the sources of carbon to include diatoms and other phytoplankton, creanaerchaeota, sulfate reducing and other bacteria, land plants including mangrove leaves, plus coal dust and other petroleum contaminants.

High-resolution sediment trap study of organic-walled dinoflagellate cyst production and biogenic silica flux in Saanich Inlet (BC, Canada)

Dinoflagellate cyst fluxes and assemblage composition were investigated from November 2007 to February 2010 in Patricia Bay, Saanich Inlet (BC, Canada). Samples were collected using a sediment trap deployed at ~ 97 m water depth. The sampling interval ranged from 0.5 to 19.5 days, allowing for a high-resolution study of dinoflagellate cyst production in relation to measured environmental parameters. Ninety-six samples were collected and a total of 42 dinoflagellate cyst taxa were identified. The dinoflagellate cyst flux was very high and ranged from ~ 149,000 to ~ 2,400,000 cysts m− 2 day− 1, with an average of ~ 777,000 cysts m− 2 day− 1. Seasonal and interannual variation in cyst assemblage was recorded. It reflects changes in environmental parameters such as sea-surface temperature, sea-surface salinity, solar insolation, river discharge, and biogenic silica flux. Fluxes of cysts produced by autotrophic dinoflagellates, particularly Spiniferites spp. and Spiniferites bentorii, were greatest during winter. Spring dinoflagellate cyst assemblages were dominated by Brigantedinium spp. and Quinquecuspis concreta. In summer the assemblages were characterized by an increase of cysts produced by heterotrophic dinoflagellates, in particular by Echinidinium delicatum, E. cf. delicatum, Votadinium spinosum and cysts of Protoperidinium minutum. Multivariate statistical analysis performed on the data supports the observed seasonal trends, where winter taxa are associated with low sea-surface temperatures, low salinity, and high Cowichan River discharge, whereas summer taxa are associated with warmer sea-surface temperatures, higher solar insolation and increased biogenic silica flux. The cyst assemblage from nearby surface sediment was shown to be very similar to an annual average sediment trap assemblage.

Organic-walled dinoflagellate cyst production, composition and flux from 1996 to 1998 in the central Strait of Georgia (BC, Canada): A sediment trap study

Bi-weekly fluxes of dinoflagellate cysts and assemblage composition were recorded from March 1996 to January 1999 in the central part of the Strait of Georgia (BC, Canada). The study period captured the 1997–98 El Niño event, which was characterized locally by increased Fraser River discharge resulting from earlier than usual snowmelt in 1997 and warmer sea-surface temperatures in 1998. Thirty dinoflagellate cyst taxa were identified in the sediment trap samples. The dinoflagellate cyst flux varied from ∼ 600 to 336,200 cysts m − 2 day − 1 , with an average of 20,000 cysts m − 2 day − 1 . In general, dinoflagellate cyst flux and species composition reflected seasonal variation of water conditions in the Strait of Georgia. Throughout the study period, assemblages were dominated by cysts produced by heterotrophic dinoflagellates, such as Protoperidineaceae ( Brigantedinium spp., Quinquecuspis concreta , and Protoperidinium americanum ). The greatest abundance of cysts of the potentially toxic Alexandrium spp. was recorded in the spring of 1996. Our results demonstrate that cysts produced by heterotrophic dinoflagellates peak in June each year, during or following diatom blooms, as indicated by biogenic silica flux. Cysts produced by autotrophic taxa were most abundant during August–September. The total annual dinoflagellate cyst flux was lower in 1997 and 1998 than in 1996, mostly due to the bloom of Alexandrium spp. in 1996. Warmer sea-surface temperature and the early spring of 1998 had a positive effect on the production of both autotrophic and heterotrophic dinoflagellates as reflected in the cyst fluxes. Cyst assemblages from sediment trap samples were consistent with a cyst assemblage recovered from a core sample at the same site.

Fluxes and fate of petroleum hydrocarbons in the Timor Sea ecosystem with special reference to active natural hydrocarbon seepage

A sediment and sediment trap study of natural oil seeps in the Timor Sea off the north coast of Australia has been conducted. Sediment traps were set at 40 m below sea level on top of a benthic carbonate dome, formed near the Cornea oil and gas field, which was visibly leaking oil and gas around its edges in ∼ 90 m of water. Other traps were set at the continental shelf edge at 100 m and 400 m below sea level on the 500 m bathymetric contour to gauge the long range dispersion of the Cornea seep. Sediment cores from the trap sites and other relevant sites were also collected. Sea surface microlayer samples of the oil slicks emerging with gas bubbles were also sampled. These were used to characterize the oil as it moved from surface slicks, through settling particles, to surface sediment. Downward fluxes of total hydrocarbons (THC) ranged from ∼ 500 µg m − 2 d − 1 at the shallow Cornea seep site to ∼ 100 µg m − 2 d − 1 in 100 m depth traps at the offshore stations. Fluxes of oil polynuclear aromatic hydrocarbons (PAH) ranged from ∼ 6000 ng m − 2 d − 1 at Cornea to ∼ 1000 ng m − 2 d − 1 at off shore stations. Principal Hierarchical Cluster Analysis and Principal Component Analysis (HCA–PCA) of the petroleum biomarkers confirmed that the surface slick samples and sediment traps from Cornea and some of the offshore traps had similar hydrocarbon compositions. However, some of the offshore traps also contained hydrocarbons from an apparently different source. This second source appeared to be “background oil”, probably due to a mixture of natural seeps, oil industry activities, or release from shipping traffic, and was similar in composition to that seen in previous sediment trap studies on the Northwest shelf. The Cornea seep area was deemed a significant point source of oil and gas to the coastal environment that was dispersed by tidal movements across the continental shelf and contributed to settling particles up to 300 km away on the continental slope of the Timor Sea. An extension of a diagenesis model showed that 44 to 77% of the (THC) and 27 to 83% of the (PAH) were degraded in the water column. Of the remaining oil reaching the sediment surface 99 to ∼ 100% of THC and 98 to ∼ 100% of PAH were degraded in the near surface sediments. Microbial biomarkers indicated the presence of sulphate reducing bacteria in both sediment traps and sediments and only trace amounts of the markers associated with Archaea which together accomplish the anoxic oxidation of methane (AOM). Rather than this well known deep sea microbial consortia, aerobic hydrocarbon oxidizing bacteria constituted a small proportion of the bacterial community in the surface sediment layer associated with the largest seep plume observed at the Cornea seep area. These hydrocarbon degraders were not visible in the offshore sediments against the background of other microbes. The rapid water column and surface sediment degradation rates indicated that the Timor Sea is well adapted to degrade natural oil seeps. This rapid degradation rate makes detection difficult for specific oil biomarkers due to low hydrocarbon concentrations in sediments. Such studies are more successfully accomplished with sediment trap deployments.

Reduced calcification in modern Southern Ocean planktonic foraminifera

The oceans are becoming more acidic as they absorb anthropogenic carbon dioxide—this may limit the ability of marine organisms to secrete carbonate. A sediment-trap study shows that in the Southern Ocean the shell weights of a surface-dwelling single-celled organism with a calcite shell are lower than pre-industrial values, probably as a result of increasing ocean acidity. Anthropogenic carbon dioxide has been accumulating in the oceans, lowering both the concentration of carbonate ions and the pH (ref. 1), resulting in the acidification of sea water. Previous laboratory experiments have shown that decreased carbonate ion concentrations cause many marine calcareous organisms to show reduced calcification rates2,3,4,5. If these results are widely applicable to ocean settings, ocean acidification could lead to ecosystem shifts. Planktonic foraminifera are single-celled calcite-secreting organisms that represent between 25 and 50% of the total open-ocean marine carbonate flux6 and influence the transport of organic carbon to the ocean interior7. Here we compare the shell weights of the modern foraminifer Globigerina bulloides collected from sediment traps in the Southern Ocean with the weights of shells preserved in the underlying Holocene-aged sediments. We find that modern shell weights are 30–35% lower than those from the sediments, consistent with reduced calcification today induced by ocean acidification. We also find a link between higher atmospheric carbon dioxide and low shell weights in a 50,000-year-long record obtained from a Southern Ocean marine sediment core. It is unclear whether reduced calcification will affect the survival of this and other species, but a decline in the abundance of foraminifera caused by acidification could affect both marine ecosystems and the oceanic uptake of atmospheric carbon dioxide.

Low‐latitude control on seasonal and interannual changes in planktonic foraminiferal flux and shell geochemistry off south Java: A sediment trap study

Results from sediment trap experiments conducted in the seasonal upwelling area off south Java from November 2000 until July 2003 revealed significant monsoon‐, El Niño–Southern Oscillation–, and Indian Ocean Dipole–induced seasonal and interannual variations in flux and shell geochemistry of planktonic foraminifera. Surface net primary production rates together with total and species‐specific planktonic foraminiferal flux rates were highest during the SE monsoon‐induced coastal upwelling period from July to October, with three species Globigerina bulloides, Neogloboquadrina pachyderma dex., and Globigerinita glutinata contributing to 40% of the total foraminiferal flux. Shell stable oxygen isotopes (δ18O) and Mg/Ca data of Globigerinoides ruber sensu stricto (s.s.), G. ruber sensu lato (s.l.), Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, and Globorotalia menardii in the sediment trap time series recorded surface and subsurface conditions. We infer habitats of 0–30 m for G. ruber at the mixed layer depth, 60–80 m (60–90 m) for P. obliquiloculata (N. dutertrei) at the upper thermocline depth, and 90–110 m (100–150 m) for G. menardii in the 355–500 μm (>500 μm) size fraction corresponding to the (lower) thermocline depth in the study area. Shell Mg/Ca ratio of G. ruber (s.l. and s.s.) reveals an exponential relationship with temperature that agrees with published relationships particularly with the Anand et al. (2003) equations. Flux‐weighted foraminiferal data in sediment trap are consistent with average values in surface sediment samples off SW Indonesia. This consistency confirms the excellent potential of these proxies for reconstructing past environmental conditions in this part of the ocean realm.

Seasonal and interannual dynamics of diatom assemblages in Sacrower See (NE Germany): a sediment trap study

Diatom assemblages from sediment trap samples collected during ten intervals between October 2003 and October 2005 in Sacrower See (NE Germany) were related to limnological and meteorological data. Sacrower See is a dimictic, 38 m deep, hypertrophic lowland lake (29.5 m a.s.l.). We identified distinct seasonal and interannual changes of diatom assemblages for the studied period. Diatoms showed a typical seasonal succession for temperate, dimictic, and eutrophic lakes. Stephanodiscus parvus, S. hantzschii, S. neoastraea, and S. alpinus had high accumulation rates during winter and spring, whereas species of the genera Stephanodiscus, Fragilaria, and Nitzschia were the predominant diatoms during summer and autumn. In a Canonical Correspondence Analysis, precipitation, air and water temperatures, epilimnetic calcium, pH, and total phosphorus concentrations together explained 70% of the variance of the diatom data. Interannual variability in the diatom assemblages during the two sampled years mainly seems to reflect changes in the total phosphorus concentration and temperature and secondarily the onset of the growing season and of stratification.

Global Radiation and Onset of Stratification as Forcing Factors of Seasonal Carbonate and Organic Matter Flux Dynamics in a Hypertrophic Hardwater Lake (Sacrower See, Northeastern Germany)

A 2-year (October 2003–October 2005) high-resolution sediment trap study was conducted in Sacrower See, a dimictic hardwater lake in northeastern Germany. Geochemical and diatom data from sediment trap samples were compared with a broad range of limnological and meteorological parameters to quantify the impact of single parameters on biochemical calcite precipitation and organic matter production. Our goals were to disentangle how carbonaceous varves and their sublaminae form during the annual cycle to better understand the palaeorecords and to detect influences of dissolution, resuspension as well as of global radiation and stratification on lake internal particle formation. Total particle fluxes in both investigated years were highest during spring and summer. Sedimentation was dominated by autochthonous organic matter and biochemically precipitated calcite. Main calcite precipitation occurred between April and July and was preceded and followed by smaller flux peaks caused by resuspension during winter and blooms of the calcified green algae Phacotus lenticularis during summer. In some of the trap intervals during summer up to 100% of the precipitated calcite was dissolved in the hypolimnion. High primary production due to stable insolation conditions in epilimnic waters began with stratification of the water column. Start and development of stratification is closely related to air and water surface temperatures. It is assumed that global radiation influences the onset and stability of water column stratification and thereby determining the intensity of primary production and consequently of timing and amount of calcite precipitation which is triggered by phytoplanktonic CO2 consumption. Sediment fluxes of organic matter and calcite are also related to the winter NAO-Index. Therefore these fluxes will be used as a proxy for ongoing reconstruction of Holocene climate conditions.

Organic carbon and nutrient fluxes to the coastal zone from the Sepik River outflow

The Sepik River is a major contributor of water, sediment and associated organic loads to the coastal waters of northern New Guinea and the Bismarck Sea. We compare dissolved and particulate organic carbon data from September 1997 during an extremely dry El Nino year with those from 1996, 1999 and 2000 during La Nina wet season discharges. Estimated Sepik River flux of DOC is 3.2×10 10 mol yr −1 and POC is 1.1×10 11 mol yr −1. The estimates for total river nutrient fluxes to the sea are 1.1×10 10 mol yr −1 for nitrogen and 4.6×10 8 mol yr −1 for phosphorus. The Sepik DOC flux is about equal to that combined from all four major rivers that enter the Gulf of Papua on the south coast of PNG. The Sepik inorganic PIC flux is low (1.4×10 8 mol yr −1) as the river does not drain carbonate soils. With a narrow continental shelf, and strong coastal currents, much of this exported material is available for long distance transport into the coastal Bismarck Sea and beyond. With data from the water column, a sediment trap study, and analysis of a series of sediment cores, we estimate total fluxes for carbon in this relatively remote coastal system. For the mass balance of organic carbon we calculated primary production in the area as 5.6×10 10 mol yr −1. These terrestrial and marine inputs gave a total of ∼2×10 11 mol OC yr −1 entering the near coastal system. Approximately 40% of the total OC load is degraded in the coastal water column or advected away from the immediate area in coastal currents. Approximately 13% of the annual river organic carbon load of exported sediments settles on the narrow coastal fringe and upper continental slope. About 2% of the total is lost through early diagenesis and 5% preserved in the shelf and upper slope sediments. The remaining ∼53% of the sediment organic carbon apparently flows with sediments along the coastal slope or into the deep sea. The carbon/nutrient regime leaving the Sepik River has a C/N molar ratio of 12, and a C/P ratio of 284 which is in between the Atkinson ratio of 550 and the Redfield ratio of 106. The particles settling through the water column in the nearby coastal waters retain a high C/N ratio; while the dissolved organic matter changes to a lower, more marine, Redfield ratio with distance offshore and with depth.

A study of the TEX86 paleothermometer in the water column and sediments of the Santa Barbara Basin, California

Particulate organic matter collected during a 2‐year period, as part of an ongoing sediment trap study, and a high‐resolution sediment record from 1850 to 1987 A.D. from the Santa Barbara Basin were analyzed for TEX86, a temperature proxy based on marine crenarchaeotal membrane lipids. Highest fluxes of crenarchaeotal lipids in the water column were found in May–June 1996 and from October 1996 to January 1997 and, in general, showed a good correlation with mass fluxes. TEX86 reconstructed temperatures from the sediment trap series ranged from 8 to 11°C and were usually substantially lower than sea surface temperatures (SST), indicating that unlike in previous studies, the TEX86 corresponds to subsurface temperatures, likely between 100 and 150 m. TEX86 temperature variations observed in trap samples were not coupled to changes in SST or deep‐water temperatures and only to some degree with crenarchaeotal lipid fluxes. This suggests that a complex combination of different depth origins and seasonal growth periods of Crenarchaeota contributed to the variations in TEX86 signal during the annual cycle. TEX86 temperatures in the two sediment cores studied (8–13°C) were also substantially lower than those of instrumental SST records (14–17.5°C) confirming that TEX86 records a subsurface temperature signal in the Santa Barbara Basin. This result highlights the importance of performing calibration studies using sediment traps and core tops before applying the TEX86 temperature proxy in a given study area.

Lithogenic and biogenic particle deposition in an Antarctic coastal environment (Marian Cove, King George Island): Seasonal patterns from a sediment trap study

Particulate suspended material was recovered over a 23-month period using two sediment traps deployed in shallow water (∼30 m deep) off the King Sejong Station located in Marian Cove of King George Island, West Antarctica. Variability in seasonal flux and geochemical characteristics of the sediment particles highlights seasonal patterns of sedimentation of both lithogenic (terrigenous) and biogenic particles in the coastal glaciomarine environment. All components including total mass flux, lithogenic particle flux and biogenic particle flux show distinct seasonal variation, with high recovery rates during the summer and low rates under winter fast ice. The major contributor to total mass flux is the lithogenic component, comprising from 88% during the summer months (about 21 g m −2 d −1) up to 97% during the winter season (about 2 g m −2 d −1). The lithogenic particle flux depends mainly on the amount of snow-melt (snow accumulation) delivered into the coastal region as well as on the resuspension of sedimentary materials. These fine-grained lithogenic particles are silt-to-clay sized, composed mostly of clay minerals weathered on King George Island. Biogenic particle flux is also seasonal. Winter flux is ∼0.2 g m −2 d −1, whereas the summer contribution increases more than tenfold, up to 2.6 g m −2 d −1. Different biogenic flux between the two summers indicates inter-annual variability to the spring–summer phytoplankton bloom. The maximum of lithogenic particle flux occurs over a short period of time, and follows the peak of biogenic particle flux, which lasts longer. The seasonal warming and sea-ice retreat result in change in seawater nutrient status and subsequent ice-edge phytoplankton production. Meanwhile, the meltwater input to Marian Cove from the coastal drainage in January to February plays a major role in transporting lithogenic particles into the shallow water environment, although the tidal currents may be the main agents of resuspension in this kind of sheltered bay.

Cyst formation: an important mechanism for the termination of Scrippsiella trochoidea (Dinophyceae) bloom

A sediment trap study was conducted at Daya Bay, South China Sea, to investigate the relationships between encystment and population dynamics of Scrippsiella trochoidea from December 1999 to January 2001. A dense bloom of S. trochoidea occurred during the study period from August to September 2000, with the maximum cell number of 3.18 × 10 4 cells mL −1 . Two morphotypes of cysts, one with a thick calcareous wall (calcified cyst) and another without the obvious calcareous cover (non-calcified cyst), were observed during this investigation. The morphological and excystment characteristics of these two cyst types were studied as well. Mass encystments of S. trochoidea, with the maximum of 3.05 × 10 5 cysts m −2 d −1 for calcified cyst, and 1.54 × 10 7 cysts m −2 d −1 for non-calcified cyst, coincided with the maximum abundance of the vegetative cells. Encystment caused the transfer of a total of 2.24-4.49 × 10 8 cells m −2 vegetative cells from the water column to the sea bottom during the bloom and resulted in a considerable loss of the bloom population. High assemblages of cysts of S. trochoidea were detected in the surface sediments as well. This rich ‘seed bed’ in the surface sediments caused by the high efficiency of encystment after blooms acting as a benthic reservoir for future vegetative population, together with the short dormant period (15-26 days) and high germination rate (50-90%), may explain the repeated occurrence of S. trochoidea blooms in Daya Bay.

A sediment trap and radioisotope study to determine resuspension of particle reactive substances in the sound between Sweden and Denmark

Sediment traps and the radioisotopes 137Cs, 210Pb, 7Be, 234Th and 228Th were used to study downward fluxes and resuspension of sediments in the shallow sound (Øresund) between Sweden and Denmark connecting the Baltic Sea with the North Sea. The water transport through Øresund covers approximately 30% of the total water transport between the North Sea and the Baltic Sea. The heavy boat traffic and the densely populated surroundings coupled to a shallow sound makes resuspension events an important factor in transporting released pollutants. Over the time period studied mass-fluxes recorded by the sediment traps ranged between 175 g m −2 day −1 near bottom during winter time to less than 1 g m −2 day −1 during late spring when the water column was stratified. A combination of sediment traps at different levels in the water column and radioisotope ratios shows that resuspended seabed sediments accounts for a large portion of the collected trap material, ranging from nearly 100% during the winter period to some 50% during stratified periods in late spring. In general the flux of all radioisotopes studied showed a linear relation with the mass-flux. The correlation of flux with organic carbon was better than with mass-flux. A comparison between atmospheric fluxes of 7Be and 210Pb and the fluxes of these isotope measured in the sediment traps shows that the agreement for 7Be is within a factor of two while for 210Pb the sediment trap fluxes are totally dominated by resuspended matter. The fraction of resuspended sediments in the traps may be quantified partly by using the 7Be/ 210Pb or 228Th/ 232Th ratios.

PAH transport by sinking particles in the open Mediterranean Sea: A 1 year sediment trap study

One year time series of sinking particles were collected at two depths in the open Mediterranean Sea and analysed for polycyclic aromatic hydrocarbons (PAH). Average total PAH concentrations were 593 ± 284 ng g −1 at 250 m and 551 ± 198 ng g −1 at 2850 m. Total PAH fluxes averaged 73 ± 58 ng m −2 d −1 at 250 m and 53 ± 39 ng m −2 d −1 at 2850 m. Contamination levels and, thus, exposure of marine organisms to PAH are comparable in surface and deep waters. Deep waters appear as a significant, yet overlooked, PAH sink. PAH temporal patterns show noticeable seasonality. This is partly due to varying levels of specific components such as the winter increase of pyrolytic PAH. Downward transport processes and the nature of sinking particles also impact on PAH fluxes, as inferred during periods of increasing productivity. Different phase-associations and interactions with particulate organic carbon for low-MW fossil PAH and high-MW pyrolytic PAH influence their downward transport efficiency.

Calibration of the planktonic foraminiferal Mg/Ca paleothermometer: Sediment trap results from the Guaymas Basin, Gulf of California

The Mg/Ca ratio has been measured in two surface‐dwelling species of planktonic foraminifera, Globigerinoides ruber and Globigerina bulloides, from biweekly sediment trap samples collected in Guaymas Basin, Gulf of California, between August 1992 and November 1997. The Guaymas Basin experiences significant seasonal changes in sea surface temperature (SST) (∼16°–33°C) and thus is an ideal location for testing the temperature dependence of Mg incorporation into foraminiferal calcite. The planktonic foraminiferal Mg/Ca ratios are directly compared with concurrent temperature measurements from the study site. The results from the sediment trap study reveal a strong positive correlation between SST and the Mg/Ca ratio in both G. ruber (r2 = 0.86) and G. bulloides (r2 = 0.90). The Mg/Ca ratio increases exponentially by 7% per 1°C change in temperature for G. ruber and by 6% for G. bulloides. These results indicate that the Mg/Ca ratio in G. ruber and G. bulloides accurately records the measured seasonal surface temperature cycle and interannual variability in the Guaymas Basin within ±1°C. The greatest deviation between Mg/Ca–estimated SST and observed SST occurs in the spring and fall for both species. This variability is attributed to rapidly changing hydrographic conditions and possible offset between the time of calcification and the temperature measurements. In addition, G. ruber and G. bulloides exhibit very high Mg/Ca ratios during the strong El Niño–Southern Oscillation years of 1992 and 1997, verifying their potential to record SST up to 33°C and 28°C, respectively. The trace metal data are compared with foraminiferal oxygen isotope and alkenone measurements made on the same suite of sediment trap samples to assess the internal consistency of these temperature proxies. Strong correlations exist between the δ18O and Mg/Ca for G. ruber (r2 = 0.86) and G. bulloides (r2 = 0.79). Similarly, sea surface temperature estimates from Mg/Ca ratios are in good agreement with alkenone‐derived temperature estimates (r2 = 0.89 for G. ruber and r2 = 0.81 for G. bulloides).

Lipids and their oxidation products as biomarkers for carbon cycling in the northwestern Mediterranean Sea: results from a sediment trap study

Classical lipid biomarkers (sterols, fatty acids and pigments) and their photo-oxidation and autoxidation products were measured in sediment trap samples collected during the summer of 1998 at the DYFAMED time-series station in the northwestern Mediterranean Sea to investigate changes in phytoplanktonic composition and alteration of particulate organic matter (POM). The study period covered a transitional situation from bloom event to oligotrophic conditions. At the beginning of the study, the phytoplankton community appeared to be mainly composed of diatoms, prymnesiophytes, pelagophytes and dinoflagellates. During the transition to the oligotrophic period, the contribution of small cells (pico- and nanoplankton) increased. Quantification of a “pool” of oxidation products resulting from photo-oxidation and autoxidation of phytoplanktonic sterols, monounsaturated fatty acids and chlorophyll phytyl side-chain provided very useful indications concerning the alteration state of POM during the investigated period. This “pool,” composed of some oxidation products which are very sensitive (but labile) indicators and of others which are less sensitive (but more refractory), allowed us to obtain a large range of diagnostic information about organic matter behaviour. Thanks to these indicators, visible light-induced and autoxidative degradative processes, which have been virtually ignored to date owing to the lack of suitable tracers, may be easily distinguished and appear to act intensively in the northwestern Mediterranean Sea.