Time-series Sediment Trap Research Articles

Western equatorial Pacific planktic foraminiferal fluxes and assemblages during a La Niña year (1999)

A correlation between foraminiferal community dynamics and environmental conditions may provide a basis for establishing paleoclimatic proxies. We studied planktic foraminiferal shell fluxes and assemblages in samples collected in three time-series sediment trap deployments in the western equatorial Pacific under La Niña conditions from January to November 1999. Eleven species contributed about 90% of the total flux in all traps. Two sites (MT1, MT3) in the Western Pacific Warm Pool region (WPWP) were characterized by common occurrences of the species Globigerinoides ruber, Globigerinoides sacculifer, Globigerinoides tenellus, and Neogloboquadrina dutertrei. Site MT5 farther to the east in the equatorial upwelling region had common occurrences of Globigerina bulloides, Globigerinita glutinata, and Pulleniatina obliquiloculata. Very high abundances of G. bulloides and G. glutinata at MT5 indicate that equatorial upwelling (EU) occurred during the 1999 La Niña. The two western sites have similar assemblage compositions, but MT1 (∼ 135°E) has the highest fluxes (up to ∼ 3800 tests m − 2 day − 1 ), whereas MT3 (∼ 145° E) has fluxes below ∼ 2200 tests m − 2 day − 1 . Relatively high fluxes (up to ∼ 3000 tests m − 2 day − 1 ) occur at site MT5 (∼ 176° E), where upwelling occurred. The differences in faunal composition in the WPWP and EU might be attributable to differences in the way in which nutrients are supplied to the phytoplankton: large amounts of suspended material are supplied to the WPWP by advection of waters passing through the coastal region of an archipelago, whereas upwelling of nutrient-rich waters enhances primary production in the EU. At the westernmost site in the WPWP, a peak in the G. bulloides flux coincided with southward flow of the New Guinea Coastal Current (NGCC) in late February, but the highest G. ruber flux coincided with northward flow of this current in late May. Thus, the differences in species dominance at this location may be caused by monsoon-driven variability in the flow direction of the NGGC.

Seasonal rhythms of net primary production and particulate organic carbon flux to depth describe the efficiency of biological pump in the global ocean

We investigate the functioning of the ocean’s biological pump by analyzing the vertical transfer efficiency of particulate organic carbon (POC). Data evaluated include globally distributed time series of sediment trap POC flux, and remotely sensed estimates of net primary production (NPP) and sea surface temperature (SST). Mathematical techniques are developed to compare these temporally discordant time series using NPP and POC flux climatologies. The seasonal variation of NPP is mapped and shows regional‐ and basin‐scale biogeographic patterns reflecting solar, climatic, and oceanographic controls. Patterns of flux are similar, with more high‐frequency variability and a subtropical‐subpolar pattern of maximum flux delayed by about 5 days per degree latitude increase, coherent across multiple sediment trap time series. Seasonal production‐to‐flux analyses indicate during intervals of bloom production, the sinking fraction of NPP is typically half that of other seasons. This globally synchronous pattern may result from seasonally varying biodegradability or multiseasonal retention of POC. The relationship between NPP variability and flux variability reverses with latitude, and may reflect dominance by the large‐amplitude seasonal NPP signal at higher latitudes. We construct algorithms describing labile and refractory flux components as a function of remotely sensed NPP rates, NPP variability, and SST, which predict POC flux with accuracies greater than equations typically employed by global climate models. Globally mapped predictions of POC export, flux to depth, and sedimentation are supplied. Results indicate improved ocean carbon cycle forecasts may be obtained by combining satellite‐based observations and more mechanistic representations taking into account factors such as mineral ballasting and ecosystem structure.

Effects of acidification and primary production on coccolith weight: Implications for carbonate transfer from the surface to the deep ocean

The coccolithophores are not only an important group of oceanic primary producers; they are also one of the main carbonate producers in the ocean. Because the calcium carbonate plates (coccoliths) secreted by these unicellular algae are so small and light (a few picograms each), they cannot be directly weighed, with the result that very little is known about the effect of primary production and dissolution on the coccoliths. Using a new method that allows a rapid estimate of the weight of discrete coccoliths, we analyzed the effect of dissolution. The results of two acidification experiments, using cultured and fossil coccoliths, indicate that acidification does not change significantly the weight and size of coccoliths. On the basis of these experiments, we identify four parameters for identifying the effects of dissolution on a coccolith assemblage. These parameters were applied in samples from two sediment trap time series taken at the same tropical Atlantic site (EUMELI), but separated by 2000 m water depth. There was no evidence of increased dissolution with water depth between 250 and 2500 m. This is indicative of the absence of dissolution of coccoliths between the photic zone and the lysocline. Other studies have identified supra‐lysoclinal dissolution, and we propose that most of this takes place in the photic zone and possibly in the guts of grazers. Most of the coccolith weight changes observed over the duration of trap deployment were related to the occurrence of two coccolithophore blooms which resulted in significant increases in average coccolith weight of the dominant coccolithophore species during the blooms. Changes in growth rate and cell density appear to have a significant effect on the weight of coccoliths. To test this observation, we cultured E. huxleyi at different P and N concentrations. This test confirmed that coccoliths weigh more when coccolithophore production is highest. An important consequence for the carbon pump is that during higher primary production events the coccoliths will increase the ballasting of the aggregates in which they are carried to the seafloor, increasing the rate and amount of organic matter sequestered into the deep sea.

ENSO related variations in biogeochemistry of AA and HA in settling particles along the equatorial Pacific Ocean

Four year-long time-series sediment trap experiments were conducted along the equatorial Pacific Ocean in order to understand the biogeochemistry of particulate organic matter (POM) on the basis of amino acid (AA) and hexosamine (HA) compositions of the settling particles. Total mass flux in the study area varied over 4 orders of magnitude without a common seasonality among all trap sites. Planktonic blooms were apparent in terms of total mass and AA fluxes at the easternmost end of the Nino-4 region. AA fluxes closely followed the total mass flux profiles, suggesting that increased particle flux delivered a greater amount of labile OM to the deep ocean. A labile OM index (LI)-based classification showed that during the El Nino conditions in 2002, the eastern side of the equatorial Pacific transported relatively more labile OM than the western equatorial Pacific. An overall change in AA and HA composition of settling particles could be revealed with the help of discriminant analysis, suggesting that settling particles during El Nino were compositionally different from those settling during La Nina condition in the equatorial Pacific.

The impact of hurricanes on sedimenting particulate matter in the semi-arid Bahía de La Paz, Gulf of California

From 2002 through 2004, time-series sediment trap samples were collected from a depth of 410 m in Cuenca Alfonso, Bahía de La Paz, on the SW coast of the Gulf of California. The instrument recorded the impact of the local passage of hurricanes “Ignacio” (24–26 August) and “Marty” (21–23 September) in 2003. These two events accounted for 82% of the total rainfall measured in 2003, equivalent to the annual average precipitation in years without hurricanes. Mean total mass fluxes (TMFs) of 2.88 and 3.58 g m −2 d −1 were measured during the week of each hurricane as well as the following week. This may have been enough to produce a lamina in the underlying sediment with characteristics peculiar to such events. The terrigenous component was particularly abundant, with notably higher concentrations of Fe, Sc, Co and Cs and REEs. In contrast, TMFs throughout 2002–2004 (excluding the hurricane periods) averaged only 0.73 g m −2 d −1 and had a larger marine biogenic component. The extraordinary elemental fluxes during the 29 days of hurricane-influenced sedimentation represented a great proportion of the totals over an entire “normal” year: Co (67.8%) >Sc (62.6) >Fe (59.6) >Cs (53.4)>Lu (51.5)>La (51.3)>Yb (51.0)>Ce (49.5) >Tb (48.4) >Sm (44.7)>Cr (36.5) >Ca (31.0)>Eu (25.4%). The terrigenous fraction was calculated using (a) TMF minus the sum of CaCO 3, biogenic silica and organic matter and (b) the ratio of Sc in the trap samples to the average in the Earth's crust. The latter was consistently smaller, but the two methods offered similar results following hurricanes (78% vs. 63% , respectively). For normal sedimentation, however, the difference method yielded values twice as large as the Sc method (58% vs. 30%) This suggests that the mineralogy of the terrigenous fraction may also vary, with unsorted dessert soil being carried to sea by the powerful flash floods associated with hurricanes. Eolian supply of particles, particularly Sc-free quartz grains, possibly from beyond the limited fluvial drainage basin, apparently dominates normal sedimentation.

Seasonal and depth variations in molecular and isotopic alkenone composition of sinking particles from the western North Pacific

Seasonal and depth variations in alkenone flux and molecular and isotopic composition of sinking particles were examined using a 21-month time-series sediment trap experiment at a mooring station WCT-2 (39°N, 147°E) in the mid-latitude NW Pacific to assess the influences of seasonality, production depth, and degradation in the water column on the alkenone unsaturation index U K′ 37. Analysis of the underlying sediments was also conducted to evaluate the effects of alkenone degradation at the water–sediment interface on U K′ 37. Alkenone sinking flux and U K′ 37-based temperature showed strong seasonal variability. Alkenone fluxes were higher from spring to fall than they were from fall to spring. During periods of high alkenone flux, the U K′ 37-based temperatures were lower than the contemporary sea-surface temperatures (SSTs), suggesting alkenone production in a well-developed thermocline (shallower than 30 m). During low alkenone flux periods, the U K′ 37-based temperatures were nearly constant and were higher than the contemporary SSTs. The nearly constant carbon isotopic ratios of C 37:2 and C 38:2 alkenones suggest that alkenones produced in early fall were suspended in the surface water until sinking. The alkenone sinking flux decreased exponentially with increasing depth. The decreasing trend was enhanced during the periods of high alkenone flux, suggesting that fresh and labile particles sank from spring to fall, while old and stable particles sank from fall to spring. The U K′ 37-based temperature usually increased with increasing depth. The preservation efficiency of alkenones was ∼2.7–5.2% at the water–sediment interface. Despite the significant degradation of the alkenones, there was little difference in U K′ 37 levels between sinking particles and the surface sediment.

Particulate organic carbon fluxes along upwelling‐dominated continental margins: Rates and mechanisms

Time series sediment trap samples were used to examine the rates and mechanisms of particulate organic carbon (POC) flux at three continental margin locations, Santa Barbara Basin, Cariaco Basin, and Guaymas Basin, marked by seasonal upwelling and high primary production. The mean POC flux in Santa Barbara Basin (0.096 g m−2 d−1) is nearly twice that of Cariaco Basin and 4 times higher than that in Guaymas Basin, with all three sites having POC fluxes significantly higher than the open ocean average (0.007 g m−2 d−1). In Cariaco Basin, the only site with available primary production numbers, there is no significant relationship between POC flux and monthly primary production. Rather, POC fluxes in all three areas strongly correlate with mineral (carbonate, opal, and lithogenic material) fluxes. This supports the “mineral ballast” hypothesis, where it has been suggested that higher‐density minerals enhance the flux of organic matter to the deep ocean. On the basis of multiple regression analysis, the three mineral components explain 72% of the total variance in POC fluxes at the three study sites, with biogenic carbonate particles being the most effective transport mineral.

Time-series sediment trap record of alkenones from the western Sea of Okhotsk

C 37–C 39 alkenones were measured in time-series sediment trap samples collected from August 1998 to June 2000 at two depths in the seasonal sea ice region of the western Sea of Okhotsk, off Sakhalin, in order to investigate alkenone production and water-column processes in the region. Measurable export fluxes of alkenones are ranged from < 0.1 to 5.8 μg/m 2/day and clearly showed that the alkenone production was restricted to autumn. In 1998, maximum export flux of alkenones occurred in September when surface water column was well stratified with low nutrients in the surface mixing layer. In the next year, the maximum flux is observed in October. Comparison between alkenone temperature and satellite based sea surface temperature (SST) shows that the estimated alkenone temperatures in August 1998 were found to be ∼ 10 °C lower than the temporal satellite SST, suggesting that alkenones are produced in surface to subsurface thermocline layers during the period. Annual mean flux of alkenones is lower in the lower traps than that of the upper traps, suggesting rapid degradation of alkenones in water column, but the U K 37′ value is not significantly altered. This study indicates that U K 37′ values preserved in the surface sediments off Sakhalin reflect the seasonal temperature signal of near surface water, rather than annual mean surface temperature.

Seasonal and spatial variation in the sources and fluxes of long chain diols and mid-chain hydroxy methyl alkanoates in the Arabian Sea

Long chain 1,14-diols and 12-hydroxy methyl alkanoates may be useful indicators for high-nutrient conditions as their inferred sources, diatoms belonging to the genus Proboscia, are often abundant in upwelling regions. In order to test this hypothesis, the lipids of three different Proboscia species in culture were determined and the fluxes of different long chain diol isomers and mid-chain hydroxy methyl alkanoates in the Arabian Sea were studied. The culture studies showed that long chain 1,14-diols and 12-hydroxy methyl alkanoates are indeed major lipids in Proboscia indica, Proboscia inermis and Proboscia alata. Time-series sediment trap data from the Arabian Sea showed increased fluxes of long chain 1,14-diols and 12-hydroxy methyl alkanoates in periods of upwelling and low fluxes for the rest of the year. High fluxes were found primarily at stations in the upwelling area close to the coast, whereas at a station located 590 km off the coast of Oman fluxes were substantially lower. These results show that long chain 1,14-diols and 12-hydroxy methyl alkanoates can be used as proxies for upwelling conditions. Flux patterns of 1,15-diols did not, however, resemble those of 1,14-diols: 1,15-diols reached maximum flux earlier than 1,14-diols, annual flux of 1,15-diols was much lower than 1,14-diols and upwelling did not seem to affect 1,15-diol flux values. This agrees with the idea that the Eustigmatophytes rather than Proboscia spp. should be considered as the major source of 1,15-diols.

Vertical flux of particulate matter in Alfonso Basin, La Paz Bay, during 2002.

Every three months during 2002, a 1/8-m2 Technicap PPS-3 time-series sediment trap was moored 50 m above the bottom of Alfonso Basin and provided 7–8 day re...

Stable carbon and nitrogen isotopes of sinking particles in the eastern bransfield strait (Antarctica)

A time-series sediment trap was deployed at 1,034 m water depth in the eastern Bransfield Strait for a complete year from December 25, 1998 to December 24, 1999. About 99% of total mass flux was trapped during an austral summer, showing distinct seasonal variation. Biogenic particles (biogenic opal, particulate organic carbon, and calcium carbonate) account for about two thirds of annual total mass flux (49.2 g m-2), among which biogenic opal flux is the most dominant (42% of the total flux). A positive relationship (except January) between biogenic opal and total organic carbon fluxes suggests that these two variables were coupled, due to the surface-water production (mainly diatoms). The relatively low δ13C values of settling particles result from effects on C-fixation processes at low temperature and the high CO2 availability to phytoplankton. The correspondingly low δ15N values are due to intense and steady input of nitrates into surface waters, reflecting an unlikely nitrate isotope fractionation by degree of surface-water production. The δ15N and δ13C values of sinking particles increased from the beginning to the end of a presumed phytoplankton bloom, except for anomalous δ15N values. Krill and the zooplankton fecal pellets, the most important carriers of sinking particles, may have contributed gradually to the increasing δ13C values towards the unproductive period through the biomodification of the δ13C values in the food web, respiring preferentially and selectively12C atoms. Correspondingly, the increasing δ15N values in the intermediate-water trap are likely associated with a switch in source from diatom aggregates to some remains of zooplankton, because organic matter dominated by diatom may be more liable and prone to remineralization, leading to greater isotopic alteration. In particular, the tendency for abnormally high δ15N values in February seems to be enigmatic. A specific species dominancy during the production may be suggested as a possible and speculative reason.

Lunar cycles and seasonal variations in deposition fluxes of planktic foraminiferal shell carbonate to the deep South Atlantic (central Walvis Ridge)

Several authors have argued that lunar reproductive cycling controls the shell fluxes of planktic foraminifera, one of the major carbonate-producing groups in the global pelagic ocean. A time-series sediment trap at 2700 m depth on the central Walvis Ridge below the South Atlantic central gyre demonstrate for the first time that shell deposition fluxes of Hastigerina pelagica are synchronous with lunar periodicity. Spectral analysis of the 6-month time-series with 8-day resolution showed a strong 30-day cyclicity in the flux maxima of H. pelagica arriving at the ocean floor on average 12.5 days after each full moon. Given a shell settling velocity of about 400 m day −1, which implies about 7 days for settling, this coincides with the pronounced endogenous reproduction rhythm of 5±2 days after full moon as originally observed in laboratory-cultured isolates from off Bermuda in the North Atlantic. By contrast, no endogenous or exogenous lunar periodicity was observed in the deposition flux or size distribution of any of the 27 other shell species from austral winter (August 2000) to austral summer (February 2001). Instead, the deposition fluxes of shell species, the bulk carbonate and the total mass were dominated by a seasonal maximum during austral spring, without any periodicity in the 16–90-day domain of this study. Since H. pelagica exhibits low fluxes with a low burial efficiency, and continuous (re)production is shown by the deposition fluxes of other species, lunar reproductive cycling appears not to affect pelagic carbonate productivity and deep ocean sedimentation fluxes.

Sensitivity of planktic foraminifera to sea surface temperature and export production as derived from sediment trap data

Planktic foraminiferal flux data from time-series sediment trap observations have been compiled from 42 sites across the world's oceans, comprising a variety of oceanographic settings. To analyze species sensitivity to environmental parameters, distributional and optimum ranges are derived by relating fluxes and relative abundances of the following seven species to sea surface temperature (SST) and export production normalized to 1000 m water depth: Globigerinoides ruber (white and pink), G. sacculifer, Globigerinella siphonifera, Globigerina bulloides and Neogloboquadrina pachyderma (dextral and sinistral coiling varieties). Of the warm-water species, G. ruber (white) and G. sacculifer exhibit the widest SST tolerance range (9.7/9.8–31°C), followed by G. siphonifera (11.9–31°C), while G. ruber (pink) shows the narrowest SST range (16.4–29.6°C). G. bulloides and N. pachyderma (dex.) cover almost the whole SST range, N. pachyderma (dex.) exhibiting a clear preference for mid-temperatures, while the distribution pattern of G. bulloides is polymodal due to different genetic types comprised in this morphologically defined category. The polar–subpolar species N. pachyderma (sin.) is absent at SSTs above 23.7°C. The change in dominance of right- over left-coiled N. pachyderma is observed at 9°C. Derived optimum ranges for all species are in good agreement with previous plankton tow and laboratory studies, while lower temperature limits for G. ruber (white) and G. sacculifer might be several degrees lower than previously reported. With the exception of the morphospecies G. bulloides, SST has a significant effect on all investigated species. However, it seems to be a governing factor for species fluxes only at the edges of the thermal tolerance range. The influence of export production on planktic foraminiferal fluxes and relative abundances is not as pronounced. Highest relative abundances of the symbiont-bearing and thus light-dependent species G. ruber, G. sacculifer and G. siphonifera are restricted to oligotrophic and mesotrophic conditions, even though high fluxes can be observed at high export productions as well. In contrast, the asymbiotic species G. bulloides and N. pachyderma (dex.), depending more on food, reach high fluxes and relative abundances even at very high rates of export production, where they can easily outnumber the symbiotic species. Within the joint space of both SST and export production, N. pachyderma (sin.) yielded high fluxes and relative abundances coinciding mostly with medium to high export productivities.

Seasonality of biogenic particle and planktonic foraminifera fluxes: response to hydrographic variability in the Kuroshio Extension, northwestern Pacific Ocean

In order to infer the relationship between the sinking biogenic particles as well as planktonic foraminiferal fluxes to local hydrography time-series sediment trap observations were conducted at two stations, Stations WCT-3 and -7, along the Kuroshio Extension (KE) in the northwestern Pacific. The sediment trap samples were collected from 29 August 1998 to 10 August 1999 at Station WCT-3 and from 19 August 1999 to 29 August 2000 at Station WCT-7. Large seasonal, spatial and depth variations were observed in the total mass flux and the biogenic particle fluxes at both stations. The annual mean mass flux in the deep trap is ∼3 times higher than that in the shallow trap at Station WCT-3 and around twice at Station WCT-7. No distinct seasonality of biogenic particles as well as planktonic foraminiferal fluxes was observed at WCT-3 except very high fluxes during summer both in shallow and deep traps. On the other hand, a distinct bi-modal distribution of all biogenic particle fluxes was observed over almost one year at Station WCT-7, with a comparatively low value in winter and high peak in summer in both shallow and deep traps. The concentration of calcium carbonate and the organic matter decreased with depth and those of biogenic opal increased with depth at both stations. The increased fluxes of all biogenic particles in the deep traps at both stations can be explained by lateral transport. The most abundant planktonic foraminiferal species at both stations are Neogloboquadrina pachyderma (dex. and sin.), Neogloboquadrina dutertrei, Globigerina bulloides, Globigerinoides ruber, Globigerinoides sacculifer, Globigerinoides tenellus, Globigerinella aequilateralis and Globigerinita glutinata. Despite some temporal variations in relative abundance, dominant planktonic foraminiferal species showed similar distribution pattern throughout the year at both stations. Seasonal variation in species dominance also occurs at both stations, changing from G. ruber, G. tenellus and G. sacculifer in September–November to Globorotalia truncatulinoides, Globorotalia inflata and G. glutinata in January–April, and to N. pachyderma, N. dutertrei and G. bulloides in May–July. The magnitude of test fluxes and species turnover showed strong seasonality in accordance with variations in the local hydrography, which is influenced by the shift of the meandering Kuroshio and by the interaction between the subarctic water mass (Oyashio) and KE waters. The influence of local hydrography on the foraminiferal fluxes is highlighted by the simultaneous increase in total foraminiferal flux with an increase in sea-surface temperature (SST) as well as a strengthening in the stratification of the water column.

Transport of benthic diatoms across the continental shelf off southern Baja California Peninsula

Material collected with a time-series sediment trap moored in San Lázaro Basin, near the NE Pacific upwelling zone off Bahía Magdalena, Baja California Sur (Mexico), from August to November 1996 and December 1997 to June 1998, revealed temporal changes in the flux of benthic diatoms. Fluxes were highest during fall and spring. Lateral transport of benthic diatoms from the coastal zone seems to be an important phenomenon at this site. The species assemblage includes components found mainly in mangrove environments of Bahía Magdalena, as well as nearby rocky coastlines, indicating that locally the northward counter current or coastal gyres carry living cells, and possibly other particles of lagoon origin, across the continental shelf.

Calibration of Mg/Ca thermometry in planktonic foraminifera from a sediment trap time series

Paired Mg/Ca and δ18O measurements on planktonic foraminiferal species (G. ruber white, G. ruber pink, G. sacculifer, G. conglobatus, G. aequilateralis, O. universa, N. dutertrei, P. obliquiloculata, G. inflata, G. truncatulinoides, G. hirsuta, and G. crassaformis) from a 6‐year sediment trap time series in the Sargasso Sea were used to define the sensitivity of foraminiferal Mg/Ca to calcification temperature. Habitat depths and calcification temperatures were estimated from comparison of δ18O of foraminifera with equilibrium calcite, based on historical temperature and salinity data. When considered together, Mg/Ca (mmol/mol) of all species, except two, show a significant (r = 0.93) relationship with temperature (T °C) of the form Mg/Ca = 0.38 (±0.02) exp 0.090 (±0.003)T, equivalent to a 9.0 ± 0.3% change in Mg/Ca for a 1°C change in temperature. Small differences exist in calibrations between species and between different size fractions of the same species. O. universa and G. aequilateralis have higher Mg/Ca than other species, and in general, data can be best described with the same temperature sensitivity for all species and pre‐exponential constants in the sequence O. universa &gt; G. aequilateralis ≈ G. bulloides &gt; G. ruber ≈ G. sacculifer ≈ other species. This approach gives an accuracy of ±1.2°C in the estimation of calcification temperature. The ∼9% sensitivity to temperature is similar to published studies from culture and core top calibrations, but differences exist from some literature values of pre‐exponential constants. Different cleaning methodologies and artefacts of core top dissolution are probably implicated, and perhaps environmental factors yet understood. Planktonic foraminiferal Mg/Ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures (using G. ruber pink, G. ruber white, G. sacculifer, N. dutertrei, P. obliquiloculata, etc.). The existence of a single Mg thermometry equation is valuable for extinct species, although use of species‐specific equations will, where statistically significant, provide more accurate evaluation of Mg/Ca paleotemperature.

Biogenic fluxes in the Cariaco Basin: a combined study of sinking particulates and underlying sediments

The fluxes of total mass, organic carbon (OC), biogenic opal, calcite (CaCO 3) and long-chain C 37 alkenones (ΣAlk 37) were measured at three water depths (275, 455 and 930 m) in the Cariaco Basin (Venezuela) over three separate annual upwelling cycles (1996–1999) as part of the CARIACO sediment trap time-series. The strength and timing of both the primary and secondary upwelling events in the Cariaco Basin varied significantly during the study period, directly affecting the rates of primary productivity (PP) and the vertical transport of biogenic materials. OC fluxes showed a weak positive correlation ( r 2=0.3) with PP rates throughout the 3 years of the study. The fluxes of opal, CaCO 3 and ΣAlk 37 were strongly correlated (0.6< r 2<0.8) with those of OC. The major exception was the lower than expected ΣAlk 37 fluxes measured during periods of strong upwelling. All sediment trap fluxes were significantly attenuated with depth, consistent with marked losses during vertical transport. Annually, strong upwelling conditions, such as those observed during 1996–1997, led to elevated opal fluxes (e.g., 35 g m −2 yr −1 at 275 m) and diminished ΣAlk 37 fluxes (e.g., 5 mg m −2 yr −1 at 275 m). The opposite trends were evident during the year of weakest upwelling (1998–1999), indicating that diatom and haptophyte productivity in the Cariaco Basin are inversely correlated depending on upwelling conditions. The analyses of the Cariaco Basin sediments collected via a gravity core showed that the rates of OC and opal burial (10–12 g m −2 yr −1) over the past 5500 years were generally similar to the average annual water column fluxes measured in the deeper traps (10–14 g m −2 yr −1) over the 1996–1999 study period. CaCO 3 burial fluxes (30–40 g m −2 yr −1), on the other hand, were considerably higher than the fluxes measured in the deep traps (∼10 g m −2 yr −1) but comparable to those obtained from the shallowest trap (i.e. 38 g m −2 yr −1 at 275 m). In contrast, the burial rates of ΣAlk 37 (0.4–1 mg m −2 yr −1) in Cariaco sediments were significantly lower than the water column fluxes measured at all depths (4–6 mg m −2 yr −1), indicating the large attenuation in the flux of these compounds at the sediment–water interface. The major trend throughout the core was the general decrease in all biogenic fluxes with depth, most likely due to post-depositional in situ degradation. The major exception was the relatively low opal fluxes (∼5 g m −2 yr −1) and elevated ΣAlk 37 fluxes (∼2 mg m −2 yr −1) measured in the sedimentary interval corresponding to 1600–2000 yr BP. Such compositions are consistent with a period of low diatom and high haptophyte productivity, which based on the trends observed from the sediment traps, is indicative of low upwelling conditions relative to the modern day.

Growth and production of Ophiocten gracilis (Ophiuroidea: Echinodermata) on the Scottish continental slope

Growth and production of the bathyal ophiurid brittle star Ophiocten gracilis was studied from skeletal growth bands and disc size frequencies of specimens collected in sled and trawl samples taken on the continental slope off Scotland. Growth bands showed up in SEM examination as ring-like zones in surface relief and texture of the stereom microstructure of the intervertebral muscle insertions on the arm ossicles. Seasonal variability in somatic growth, presumed to underlie this growth pattern, may reflect reproduction and/or a possible non-feeding period during gonad maturation. Disc size-at-age was back-calculated from size-at-age interpreted from growth-band series on the vertebral ossicles from arms of O. gracilis. Pooled growth-band frequency data and normal-distribution mixtures based on size-at-age data were used to test for overgrowth of early growth bands on the ossicles from larger individuals. Von Bertalanffy and Gompertz growth models were fitted to the finalised back-calculated disc size-at-age data. These were used along with the modal structure of the observed disc size frequencies to develop a demographic model based on normal-distribution mixtures constrained by the growth model. These and other defining parameters were fitted by non-linear regression to size structure observed in a sample of the breeding population from 997 m depth on the Hebrides Terrace. Recruitment was estimated according to available data from sediment-trap time series. A ratio of somatic production/biomass, P S /B, in the range of 0.43–0.54 was estimated using a fitted size/mass relationship and the increment summation method (ISM) applied to the fitted growth models. A narrower, but otherwise similar, range in estimated P S /B ratios (0.48–0.49) was obtained in a parallel approach using the mass-specific growth rate method (MSGRM), whereby the same size/mass relationship was applied to the observed frequencies and growth parameters fitted to growth banding. Using previously obtained data on population density, a standing crop of 4.8 g wet weight (~0.58 mg AFDW) m−2 would provide annual wet weight production in the range of 1.9–2.4 g (~0.23–0.29 mg AFDW) m−2 in the population between ca. 700–1000 m depth. Somewhat greater production estimates (P S /B=0.73–0.98) were obtained from MSGRM by pooling the sample with size frequencies from other large samples in which postlarval sizes were more numerous, but larger sizes less numerous. Similarly high production was estimated by MSGRM from a box corer sample from the Wyville-Thomson Ridge. Explanations for variability in size structure are discussed, but even the lower estimates are comparable to boreal shallow-water brittle stars. The high rate of growth and production by accepted deep-sea standards may be related to a capability for interface feeding.

Estimation of the in‐situ settling velocity of particles in lakes using a time series sediment trap

SUMMARY 1. We outline a simple method for estimating the in‐situ settling velocity of particles in wind disturbed lakes. The total sedimentation rate (primary and secondary sedimentation) was measured during storm events in two lakes using a time series sediment trap.2. The sediment trap had 12 sample bottles which were programmed to open for periods of 3–4 h, giving total deployment times ranging from 36 to 48 h.3. Wave mixed layer theory was used to infer if and when sediment resuspension occurred and the first order rate equation was used to estimate the settling velocity of resuspended particles.4. The settling velocity during three resuspension events in Lough Neagh and one in Lough Macnean were 34.3, 29.5, 24.1 and 77.3 m day−1, respectively. These are similar to values obtained using recent in‐situ video imaging in marine environments, but much larger than previous lake sediment trap studies.

Loss Processes of Sinking Fecal Pellets of Zooplankton in the Mesopelagic Layers of the Antarctic Marginal Ice Zone

A time-series sediment trap deployment was carried out in the marginal ice zone (MIZ) of the Antarctic Ocean (64°42′ S, 139°58′E; sea depth of 2930 m), during the austral summer. Cylindrical fecal pellets were the predominant sinking particles at 537 m in the middle of January and most of them disappeared below that depth, the loss of which were 25.3 mg C m−2 day−1 in the depth range of 537–796 m. Small-sized sinking particles other than fecal pellets increased in that depth range. Analyses of fecal pellets for remnant DNA corresponding to 16S mitochondrial RNA and 28S ribosomal RNA suggested that the large cylindrical fecal pellets at 537 m were produced by Antarctic krill (Euphausia superba) and copepods. According to the presence of the DNA associated with sinking particles, E. superba fecal pellets rapidly disappeared below 537 m, while copepod fecal pellets still remained in the mesopelagic and bathypelagic layers. Small-sized amorphous sinking particles at 537 m also contained E. superba- and copepod-derived DNA. The abundance of trap-collected copepods (Oithona spp. and Oncaea spp.) which are known to be coprophagous increased at 796 m where many fecal pellets disappeared. We suggest that those rapidly sinking pellets were fragmented by copepods with intensified coprorhexy activity (fragmentation of fecal pellets) in the mesopelagic layers, reducing their sinking rates. These smaller and slower sinking particles can be important food sources for detritivorus or coprophagous animals in mesopelagic and bathypelagic layers in the MIZ.