Carbonate Flux Research Articles

Distribution and fluxes of calcium carbonate along the continental margin in the Gulf of Biscay

Compositions of major components in suspended matter,collected by centrifugation, in situ pumping andsediment traps, in the Gulf of Biscay during the OMEXproject were determined and compared. The resultsshow a strong and rapid decrease in the concentrationof biogenic fraction in the upper 200 m of the watercolumn which may be attributed to the preferentialremoval of this component due to the production offaecal pellets and to the formation of marine snow. Concurrent decrease with depth of the organic andinorganic carbon contents demonstrate the importanceof the respiration of organic matter and thedissolution of calcium carbonate in the oceanic carboncycling. Lithogenic and carbonate fluxes across thecontinental slope in the Goban Spur area wereevaluated based on sediment trap records. The rate ofproduction of calcium carbonate in the surface waters(100 g CaCO3 m-2y-1), deduced from theprimary production measurements, is much largercompared to the fluxes of this component observed inthe sediment traps (5–21 g CaCO3 m-2y-1)and to its rate of burial (9–31 gCaCO3 m-2y-1). It strongly suggeststhe occurrence of carbonate dissolution, even inwaters oversaturated with respect to the mineral phaseconsidered. This is likely to be associated with therespiration of organic matter within the faecalpellets, or at the surface of biogenic calcite oraragonite

Export flux of particles at the equator in the western and central Pacific ocean

Export of particles was studied at the equator during an El Nin˜o warm event (October 1994) as part of the French ORSTOM/FLUPAC program. Particulate mass, carbon (organic and inorganic) (C), nitrogen (N), and phosphorus (P) export fluxes were measured at the equator in the western and central Pacific during two 6–7 day-long time-series stations located in the warm pool (TS-I at 0°, 167°E) and in the equatorial HNLC situation (TS-II at 0°, 150°W), using drifting sediment traps deployed for 48 h at four depths (between, approximately, 100 and 300 m). The particulate organic carbon (POC) fluxes at the base of the euphotic zone (0.1 % light level), were approximately four times lower at TS-I than at TS-11 (4.1 vs. 17.0 mmol C m -2 day -1). Conversely, fluxes measured at 300 m were similar at both sites (3.6 vs. 3.7 mmol C m −2 day −1 at TS-I and TS-11, respectively). This change in export fluxes was in good agreement with food-web dynamics in the euphotic zone characterized by an increase in plankton biomasses and metabolic rates and a shift towards larger size from TS-1 to TS-II. The POC flux profiles indicated high remineralization (up to 78%) of the exported particles at TS-II, between 100 and 200 m in the Equatorial Undercurrent. According to zooplankton ingestion estimates from 100 – 300 m, 60% of this POC loss could be accounted for by zooplankton grazing. At TS-I, no marked increase of flux with depth was observed, and we assume that loss of particles was compensated by in-situ particle production by zooplankton. Fluxes of particulate nitrogen and phosphorus followed the same general patterns as the POC fluxes. The elemental and pigment composition of the exported particles was not very different between the two stations. In particular, the POCYN flux molar ratio at the base of the euphotic zone was low, 6.9 and 6.2 at TS-1 and TS-II, respectively. For particulate inorganic carbon (mainly carbonate) flux, values at the base of the euphotic zone averaged 0.9 mmol C m-2 day-1 at TS-I and 2.3 mmol C m-2 day-1 at TS-11 (corresponding to a 2.6-fold increase) and showed low depth changes at both stations. POC export flux (including active flux associated with the interzonal migrants) at the 0.1 % light level depth represented only 8% of primary production (1°C uptake) measured at TS-1 and 19% at TS-II. For the time and space scales considered in the present study, new primary production, as measured by the 15N method, was in good agreement with the total export flux in the HNLC situation, thus leading to negligible dissolved organic carbon (DOC) or nitrogen (DON) losses from the photic zone. Conversely, export flux was found to be only 50% (C units) and 60% (N) of new production in the oligotrophic system, either because of an overestimation by the 15N method or of a significant export of DOC and DON. Comparison with other oceanic regions shows that export flux in the warm pool was within the same range as in the central gyres. On the other hand, comparison with EgPac data in the central Pacific suggests that there is no straightforward relation between the magnitude of the export and surface nitrate concentrations.

Late Quaternary productivity changes in the western equatorial Atlantic: Evidence from 230Th-normalized carbonate and organic carbon accumulation rates

Paleoproductivity changes in the western equatorial Atlantic have been estimated from carbonate and marine organic carbon accumulation for the last 180,000 yr from a CearáRise sediment core GeoB 1523-1. Accumulation rates were calculated by normalizing to excess 230Th activity. Paleoproductivity from carbonate accumulation was estimated by a correlation between carbonate and organic carbon fluxes derived from sediment traps deployed in oligotrophic waters. Results indicate minor productivity changes varying around 30 gC m −2 yr −1 for organic carbon-derived estimations and around 45 gC m −2 yr −1 for carbonate-derived estimations, suggesting that the study area remained a low productivity region throughout the time period examined. Maxima in western Atlantic paleoproductivity occurred during the warm substages of glacials and interglacials, in contrast to the eastern tropical Atlantic where maxima are recorded in the cold substages. This contrast might be caused by a deepening of the thermocline and nutricline in the west connected with a synchronous shallowing in the east. The carbonate preservation record was examined for the last 380,000 yr based on variations in percent planktonic foraminiferal fragments and percent coarse fraction. Only minor carbonate dissolution above 3300 m water depth is observed, except for three main dissolution events at isotope stages 4, 8.4 and 10. Considerable carbonate loss during these intervals is attributed to a decreased production of North Atlantic Deep Water which is associated with vertical expansion of Southern-Source Deep Water.

Stratigraphy, sedimentology, and isotopic geochemistry of Australian Neoproterozoic postglacial cap dolostones; deglaciation, delta 13 C excursions, and carbonate precipitation

ABSTRACT Thin (d13C excursions in the geologic record, they are interpreted to record a brief postglacial anomaly in ocean chemistry. In Australia, the Marinoan (Varanger equivalent 600 Ma) cap dolostone units exhibit many of the characteristics displayed by such deposits elsewhere around the globe, including fine-grained dolomitic mineralogy, lateral persistenc at basinal scales, thin laminae, graded beds, intervals with abundant marine cements, crystal fans, and a distinctive negative d13C isotopic signature of up to -5 PDB. On the basis of these features, the Australian examples are interpreted here to be deeper-water deposits (below storm wave base) resulting from an anomalous flux of inorganic carbonate to the sea floor during postglacial transgression. Detailed isotopic analysis of Australian cap dolostones indicates d13C values ranging from -1 to -5 and gen rally becoming more depleted in 13C upsection. Trace-element data indicate some diagenetic stabilization, but textural evidence and the presence of similar profiles in different basins argue against a pervasive recrystallization event. The range in d13C values between sections as well as more negative 13C values appear to correlate with greater paleobathymetry within basins. This implies either (1) only partial preservation of the complete oceanic variation of d13C or (2) precipitation of this peculiar facies owes its genesis to basinal-specific oceanographic processes such as proximi y of a given section to a postglacial upwelling zone. In the later case, d13C values would not represent whole ocean values. Stratigraphic constraints and paleoenvironmental interpretations suggest that much of this excursion lies within the geologically brief period of postglacial transgression. This implies that the cause(s) of d13C variation likely operated on time scales significantly less than the residence time of carbon in the oceans (105 yr). The continent-wide and perhaps global nature of cap dolostones indicates that large volumes of carbonate were precipitated during the postglacial transgressive period. Such large-scale carbonate precipitation over the hypothesized short time interval of postglacial transgression must have caused (or have been the product of) profound changes in the carbon cycle and global climate at tha time. Similar evidence for transgression and increased carbonate deposition in the Holocene are attributed to the changing basin shape and pH of the oceans (the Coral Reef Hypothesis of Berger 1982). Cap dolostones may record a Proterozoic equivalent of this process with the substitution of abiotic carbonate precipitation for skeletal precipitation by reef organisms.

Equatorial Pacific sea surface temperatures, faunal patterns, and carbonate burial during the Pliocene

A high-resolution record of radiolarian faunal abundances from the eastern equatorial Pacific is compared to records of carbonate and noncarbonate burial to examine the evolution of eastern tropical Pacific climate processes during the Pliocene. These data provide a means to evaluate the sensitivity of the equatorial Pacific to the onset of Northern Hemisphere glaciation around 2.8−2.5 Ma, to the closure of the Isthmus of Panama around 4.4−3.2 Ma, and to orogeny-related weathering changes before 4.0 Ma. Radiolarian faunal assemblages and sea surface temperature (SST) estimates indicate a gradual cooling from early to late Pliocene, but no significant changes occur near the onset of northern hemisphere glaciation. Records of carbonate and noncarbonate mass accumulation show a long term decrease from the Miocene/Pliocene boundary to the upper Pliocene. Greater carbonate burial in the early Pliocene relative to the late Pliocene parallels a gradual cooling from early to late Pliocene, and may reflect changes related to Isthmus closure or widespread orogeny. No significant time domain changes are seen in the eastern equatorial Pacific that could be related to the onset of Northern Hemisphere glaciation. Evolutive spectral analyses of these equatorial Pacific climate parameters indicate that variance in SST and seasonality commonly concentrate at frequencies not linearly related to orbital variations. Furthermore, cross spectral comparisons with a high resolution benthic δ 18O record indicate that the surface ocean and carbonate flux share little coherent variance with high latitude climate processes during the Pliocene. Given the high degree of chronostratigraphic control in these records, these results suggest that Milankovitch-band surface ocean processes as well as carbonate burial in the equatorial Pacific are decoupled from high latitude climate processes during the Pliocene.

Significance of ocean carbonate budgets for the global carbon cycle

AbstractChanges in the trace gas composition of the atmosphere over glacial–interglacial cycles are linked to changes in the oceanic carbon cycle. This paper examines the role of biologically driven fluxes of organic and inorganic carbon in modifying the carbon dioxide chemistry of the oceans, and the corresponding implications for the partitioning of CO2 between the atmosphere and ocean. Relevant details of the marine carbon system are presented together with an assessment of the significance of remineralization and dissolution processes. Recent estimates of the marine carbonate fluxes show significant uncertainties and inconsistencies which must be resolved in order to assess fully the role of the oceans' biota in the marine carbon system. Various types of ocean carbon cycle models have been developed in order to interpret the changes in past atmospheric carbon dioxide. Some take account of the role of the oceans' biota, focussing in the main on the cycling of organic matter. Relatively few have considered the role of the carbonate pump and the subtle interactions between organic and inorganic carbon cycling. The significance of carbonate formation and dissolution, and of the effects of global change on the marine carbonate system, for air–sea fluxes of CO2 are discussed. Finally some recommendations for future research are made in order to improve our understanding of how spatial and temporal variation in marine carbonate fluxes, in conjunction with processes determining the oxidation and burial of organic matter in the oceans, affect levels of CO2 in the atmosphere.

Distinct year-to-year particle flux variations off Cape Blanc during 1988–1991: Relation to δ<SUP>18</SUP>O-deduced sea-surface temperatures and trade winds

Particle fluxes measured from 1988 to 1991 adjacent to a coastal upwelling site off Cape Blanc showed significant interannual variability of fluxes and sea-surface temperatures (SST) deduced from stable oxygen isotope analysis of the planktonic foraminifera Globigerinoides ruber and, partly, of the pteropod Limacina inflata. For the duration of the study period, a decrease in the seasonality of SST's was observed, as well as a significant decrease in the average annual SST from 24.4° to 20.8°C. This cooling trend was mainly the effect of a drastic decrease in the summer to fall SST (from 27.2° to 21.8°C). In comparison, the winter-spring SST decreased only slightly from 20.3° in 1988 to 19.8°C in 1991. Concomitantly, we measured decreasing annual total, carbonate, biogenic opal and lithogenic fluxes and, in contrast, increasing marine organic carbon fluxes. During 1991, when cold SST's prevailed and the trade winds were rather high throughout, annual biogenic and lithogenic fluxes (except organic carbon) were lower by approximately a factor of two compared to the other years. Colder SST's, generally corresponding to stronger trade winds and upwelling intensity, did not result in increased biogenic opal and lithogenic matter sedimentation ; but higher marine organic carbon fluxes were recorded. Decreasing summer-fall SST from 1988 to 1991 coincided with decreased carbonate sedimentation maxima which generally occurred during the warm summer season. In the summer of 1989, when SST's were the highest of the four-year sampling period and upwelling was less intense due to weak spring-summer trades, a large sedimentation pulse of pteropod shells was observed. Our data set does not yet provide conclusive evidence that the observed year-to-year flux and SST variations represent larger-scale, periodically occurring climatic variations in the eastern Atlantic but it offers insight into the prevailing large variability in biochemical cycles and processes in the eastern Atlantic.

Micro- and mesoprotozooplankton at 140*W in the equatorial Pacific: heterotrophs and mixotrophs

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 10:273-282 (1996) - doi:10.3354/ame010273 Micro- and mesoprotozooplankton at 140*W in the equatorial Pacific: heterotrophs and mixotrophs Stoecker DK, Gustafson DE, Verity PG Abundance, biomass and presence or absence of plastids in micro- (&GT20 to 200 um) and meso- (&GT200 um to 2 mm size range) protozooplankton were determined during March-April and October 1992 at 140*W on the equator as part of the United States' participation in the Joint Global Ocean Flux Study (JGOFS). The March-April cruise took place during strong El Niño conditions but the October 1992 cruise was during a relaxation in El Niño. Protistan zooplankton biomass in the 20 to 64 um size range was dominated by planktonic ciliates, in the &GT64 to 200 um size range by ciliates, heterotrophic dinoflagellates, foraminifera and acantharia, and in the &GT200 um size range by acantharia, foraminifera and polycystine radiolaria. Presence of algal plastids, indicating mixotrophic nutrition, was common. In October, plastidic cells contributed ~27, 47 and 56% of the protozooplankton biomass in the 20-64, &GT64-200 and &GT200 um size classes, respectively. During October, the protistan micro- and mesozooplankton biomass was generally higher than in March-April 1992. Most of the increase in biomass was due to ciliates and foraminifera. These data suggest that the numerical responses of ciliates may be important in coupling changes in primary productivity of nanoplankton to their removal by grazing in the equatorial Pacific. The increased biomass of foraminifera in October may be linked to the relaxation in El Niño. Foraminifera may be particularly important in the coupling between primary production and biogenic flux of organic carbon and carbonate in the equatorial Pacific. El Niño . Ciliates . Heterotrophic dinoflagellates . Sarcodines . Foraminifera . Radiolaria . Acantharia . Mixotrophy . JGOFS . Microzooplankton . EqPac . Equatorial Pacific Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 10, No. 3. Publication date: June 27, 1996 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1996 Inter-Research.

Decadal and annual changes in biogenic opal and carbonate fluxes to the deep Sargasso Sea

Analyses of samples from a 14-year series of sediment-trap deployments in the deep Sargasso Sea reveal a significant trend in the ratio of the sinking fluxes of biogenic calcium carbonate and silica. Although there are pronounced seasonal cycles for both flux components, the overall opal/CaCO 3 ratio changed by 50% from 1978 to 1991 (largely due to a decrease of opal flux), while total flux had no significant trend. These results suggest that plankton communities respond rapidly to subtle climate change, such as is evident in regional variations of wind speed, precipitation, wintertime ventilation and midwater temperatures. If the trends we observe in the makeup of sinking particulate matter occur on a large scale, they may in turn modify climate by modulating ocean-atmosphere CO 2 exchange and albedo over the ocean.

Carbonate preservation history in the Peru Basin: Paleoceanographic implications

We studied preservation/dissolution cycles and paleoproductivity in eight sediment cores from the Peru Basin south of the highly productive surface waters of the eastern equatorial Pacific. Stratigraphy is based on stable oxygen isotopes and on combined magnetostratigraphy and biostratigraphy. Sediment cores which span the last 8 m.y., were retrieved during cruise 79 with RV SONNE close to the carbonate compensation depth (CCD). In general, sediments show Pacific‐type carbonate cycles. We interpret a pronounced carbonate peak between 6 and 7 Ma as the result of a western and northern extension of the highly productive Peru Current. Decreased carbonate contents from the late Miocene to the late Pliocene might be associated with a slow contraction of the latitudinal extent of the high‐productivity belt north of the study areas. During the Pliocene, carbonate variations showed 400 kyr cycles indicating the growth and decay of ice sheets, which should have been associated with pulsations of the Antarctic ice cap. An abrupt collapse of the carbonate system occurred at 2.4 Ma. Higher frequency variations of the carbonate record indicate the major increase of the northern hemisphere glaciation. During the Quaternary, carbonate fluxes are high during glacials and low during interglacials. Large amplitude variations with long broad minima and maxima, associated with small migrations of the lysocline and the CCD (< 200 m), are indicative of the preservation/dissolution history in the Peru Basin. During the early Pleistocene, climatic forcing by the 41 kyr obliquity cycle is not observed in the carbonate record. During the last 800 kyr, variability in the carbonate record was dominated by the 100 kyr eccentricity cycle. Fluxes of biogenic material (calcium carbonate, organic carbon, opal, and barium) were greatest during glacials, which imply higher productivity and export production of the Peru Current during cold climatic periods. Dissolution was greatest during interglacials as inferred from the relatively poor preservation of planktonic foraminifera and from the low accumulation rate of carbonate. After the Mid‐Brunhes Event (400 ka), we observe a plateaulike shift to enhanced dissolution and to intensified productivity.

Quaternary deposits and sediment fluxes at the toe of the Barbados Accretionary Prism

Sedimentologic and stratigraphic investigations on four cores collected close to the front of the Barbados accretionary prism provided information about the Quaternary depositional processes and sediment fluxes in the region. The morphology of the prism is marked by N—Soriented anticlinal ridges separated by troughs. The deposits are hemipelagic on top of the ridges and in the abyssal plain, with a mean global flux of 1.35–1.40 g cm−2 10−3 yr. The carbonate flux decreases from the prism to the abyssal plain (0.49 and 0.3 g cm−2 10−3 yr, respectively). Terrigenous material is provided by distal turbiditic plumes. It decreases slightly from the abyssal plain to the prism (1.06 and 0.9 g cm−2 10−3 yr, respectively). During cold climatic stages, it is up to 1.4 g cm−2 10−3 yr. The global flux is much higher (7.1 g cm−2 10−3 yr) in the interridge troughs, which act as sediment traps for distal turbidity currents.

Depositional fluxes, palaeoproductivity, and ice rafting in the NE Atlantic over the past 30 ka

Over the last 30 ka, sediment flux to the northeast Atlantic Ocean has been strongly influenced by the growth and decay of northern hemisphere ice sheets, input of ice‐rafted detritus, the migration of the polar front, and associated changes in patterns of biological productivity. We examined cores from 47°N to 60°N along 20°W to determine the flux of components including carbonate, organic carbon and terrigenous material and divided into size fractions. During the glacial period, fine carbonate flux was low and ice‐rafted input high. Burial flux during the Holocene became dominated by coccolith and foraminiferal carbonate, with minor organic matter and biogenic silica. Estimates of palaeoproductivity are ambiguous: a method which corrects for water depth and sedimentation rate suggests no clear glacial to Holocene change, whereas a method based on percentage of organic carbon suggests increased productivity from glacial to Holocene of around 60%. Sites of sediment focusing saw a change from enhanced fine terrrigenous flux in the glacial to enhanced fine carbonate in the Holocene. After compensating for sediment focusing, glacial ice‐rafted flux distribution shows a decrease from south to north across the area, reflecting cyclonic surface water circulation. Deposition of ice‐rafted detritus during Heinrich events H1 and H2 led to enhanced preservation of organic matter immediately beneath the layers, indicating a rapid accumulation rate.

Comparative evolution of material flux through two DSDP successions from Central Atlantic and Gulf of Mexico. Preliminary results of a new approach to sedimentary dynamics in pelagic environments

A method for gaining knowledge of sedimentary fluxes is applied to Early Cretaceous sequences containing high-frequency sedimentary cycles. The cycles are used to determine the relative fluctuations of (1) the sedimentation rate and (2) carbonate and silicate terrigenous fluxes expressed as linear values proportional to the real fluxes. Visual and automatic image analysis of black-and-white core photographs have been used to calculate the masses of different materials deposited in equal time intervals and to determine the distribution of the material within lithological units of cores according to a scale of grey intensities. Characters of these distributions allow definition of a flux variability index, assumed to be negatively correlated to ocean-continent distance related itself to sea level. At DSDP Sites 534 (western Atlantic off Florida) and 535 (Gulf of Mexico), the Valanginian-Hauterivian interval has been chosen for determining the relative variations of carbonate and silicate terrigenous linear fluxes, their variability and their distribution within lithological cycles. These data provide information about the relative importance of carbonate sources (lands, platforms and plankton) and their evolution, and of other forcings upon planktonic productivity such as supply of nutrients from the continents and upwelling. By comparing the data in the two sites, it is possible to detect common (climate and eustasy) and local factors (tectonics and upwelling) which have controlled the material fluxes. Compared with Site 534, Site 535 was supplied by more numerous, active and close carbonate sources and less active but closer terrigenous sources. At the two sites, carbonate flux was controlled by common factors, sea level being the most prominent one. Terrigenous flux was submitted to more local controls. This new method for investigating pelagic deposits should be tested on other deep-sea sedimentary sequences.

Export production of coccolithophores in an upwelling region: Results from San Pedro Basin, Southern California Borderlands

A seven month-long time series sediment trap project was carried out in San Pedro Basin (Southern California Borderlands) in order to evaluate the response of calcareous nannoplankton to seasonal hydrographic changes. This region is periodically influenced by upwelling, particularly during the spring and early summer. The highest fluxes of both whole coccospheres and individual coccoliths occurred during winter (January-February), a period when the fluxes of diatoms and planktic foraminifera were low. The highest coccolithophore fluxes were recorded in the mid-February with 860 × 10 6 coccoliths m −2 day −1, 8 × 10 6 whole coccospheres m −2 day −1, and 80 mg of coccolith carbonate m −2 day −1. Coccolith carbonate fluxes in January and February account for most of the total carbonate fluxes measured during this period. The season of maximum coccolithophore production in this region (winter) is correlated with weak stratification of the upper water column, low total primary production, low nutrient contents, and low temperatures. Emiliania huxleyi and Florisphaera profunda are the two most abundant species in this region. While E. huxleyi displays no distinct seasonal changes in flux, F. profunda shows a clear preference for cold, low nutrient water conditions and low light levels. Helicosphaera spp. flux is positively correlated to the total coccosphere fluxes and is indicative of high coccolithophore productivity.

Bank-derived carbonate sediment transport and dissolution in the Hawaiian Archipelago

This investigation used two approaches to examine the flux of bank-derived carbonate particles and determine the potential influence of benthic carbonate particle dissolution on the carbon chemistry of the waters around the Hawaiian Archipelago. First, the particle flux near several representative carbonate banks in the Hawaiian Archipelago was measured and compared with the flux at a distal site (ALOHA) approximately 100 km north of Oahu, Hawaii. The results of four sediment trap deployments on three carbonate banks in the Hawaiian Archipelago demonstrate that the flux of bank-derived carbonate particles are consistently one to two orders of magnitude higher than the fluxes at the distal station. Furthermore, the mineralogy of the carbonate flux near the banks, which includes very soluble bank-derived aragonite and magnesian calcite particles, is distinctly different from that of the distal fluxes. Second, the chemistry of the waters at each bank station along the archipelago was characterized and compared with the chemistry of the distal waters to determine if differences in the particle flux were reflected in the carbon chemistry. Higher alkalinity and carbonate ion concentrations were observed around all of the banks studied. The saturation state of these waters suggests that the dissolution of some magnesian calcite and aragonite phases could explain the higher alkalinity values. Calculations suggest that the dissolution of benthically-derived aragonite and magnesian calcite may be an important component of the North Pacific alkalinity budget and a potential sink for anthropogenic CO2.

Determination of thorium and uranium in mineral sands by ion chromatography

Thorium and uranium can be determined by ion chromatography using a C 18 reversed-phase column and a complexing eluent of hydroxyisobutyric acid followed by post-column derivatization with Arsenazo III and detection at 658 nm. A number of sample dissolution and clean-up procedures were evaluated in order to permit the application of the chromatographic method to the analysis of mineral sands. Dissolution procedures investigated included a variety of acid digestions and alkali fusion with peroxide, borate, carbonate, hydroxide and pyrosulphate fluxes. Sample clean-up protocols were then studied in order to overcome matrix interference effects. The optimal sample preparation procedure involved a tetraborate fusion/nitric acid leach followed by either cation-exchange pretreatment, or simply dilution in concentrated hydroxyisobutyric acid, depending upon the sample type. The results obtained using the chromatographic method showed good agreement with X-ray fluorescence and inductively coupled plasma mass spectrometry for ilmenite, synthetic rutile, zircon and rutile mineral sands with detection limits (in the original mineral sand) in the order of 1.0 μg/ml for the two analytes.

Lunar-influenced carbonate flux of the planktic foraminifer Globigerinoides sacculifer (Brady) from the central Red Sea

Two phenomena control the rate of sedimentation of planktic foraminifers: (1) changes in the populations structure with time; and (2) size-dependent settling velocities of empty shells. As a result, the total flux and the flux per-size-fraction change significantly during a reproductive cycle. This implies that timing and duration of collection of trap devices are important parameters for interpreting sediment trap-collected samples. Using data on the distribution and abundance of living Globigerinoides sacculifer (Brady) from the central Red Sea, a shell flux was modelled. The simulations demonstrate that the sedimentation pattern oscillates on a lunar basis. The foremost result of this study is that the timing of trap deployment within the lunar cycle does not influence the collection if the deployment time of the trap is equal to or a multiple of the reproductive cycle. The effect of two variables on the daily calcite flux was investigated: (1) the reproduction rate; and (2) the length of the reproductive period. A decrease in the reproduction rate shifts the calcite flux maximum from full moon to new moon. A short reproduction period intensifies the full moon flux maximum, especially at high reproduction rates. The total monthly calcite flux, however, is independent of these variables. An estimate for the carbonate flux in the Red Sea due to G. sacculifer alone is 1 g m −2 year −1.

Glacial/interglacial changes in sediment rain rate in the SW Indian Sector of subantarctic Waters as recorded by 230Th, 231Pa, U, and δ15N

High‐resolution records of opal, carbonate, and terrigenous fluxes have been obtained from a high‐sedimentation rate core (MD84‐527: 43°50′S; 51°19;′E; 3269 m) by normalization to 230Th. This method estimates paleofluxes to the seafloor on a point‐by‐point basis and distinguishes changes in sediment accumulation due to variations in vertical rain rates from those due to changes in syndepositional sediment redistribution by bottom currents. We also measured sediment δ15N to evaluate the changes in nitrate utilization in the overlying surface waters associated with paleoflux variations. Our results show that opal accumulation rates on the seafloor during the Holocene and stage 3, based on 14C dating, were respectively tenfold and fivefold higher than the vertical rain rates, At this particular location, changes in opal accumulation on the seafloor appear to be mainly controlled by sediment redistribution by bottom currents rather than variations in opal fluxes from the overlying water column. Correction for syndepositional sediment redistribution and the improved time resolution that can be achieved by normalization to 230Th disclose important variations in opal rain rates. We found relatively high but variable opal paleoflux during stage 3, with two maxima centered at 36 and 30 kyr B.P., low opal paleoflux during stage 2 and deglaciation and a pronounced maximum during the early Holocene, We interpret this record as reflecting variations in opal production rates associated with climate‐induced latitudinal migration of the southern ocean frontal system. Sediments deposited during periods of high opal paleoflux also have high authigenic U concentrations, suggesting more reducing conditions in the sediment, and high Pa‐231/Th‐230 ratios, suggesting increased scavenging from the water column. Sediment δ15N is circa 1.5 per mil higher during isotopic stage 2 and deglaciation. The low opal rain rates recorded during that period appear to have been associated with increased nitrate depletion. This suggests that opal paleofluxes do not simply reflect latitudinal migration of the frontal system but also changes in the structure of the upper water column. Increased stratification during isotopic stage 2 and deglaciation could have been produced by a meltwater lid, leading to lower nitrate supply rates to surface waters.

Seasonal patterns of vertical particle flux in equatorial and coastal upwelling areas of the eastern Atlantic

Eight time-series sediment traps were deployed on moored arrays off Mauritania (Cap Blanc), in the northern and southern Guinea Basin, and off Namibia (Walvis Ridge). The highest total fluxes (66.8 and 59.1 g m−2y−1), as well as carbonate (28.7 and 32.9 g m−2y−1) and biogenic opal fluxes (5.4 and 8.2 g m−2y−1) were recorded at the two coastal sites, off Mauritania and off Namibia, respectively. Intermediate rates were recorded north and low rates south of the equator. Surprisingly, carbonate-producing organisms dominated total fluxes at all sites, whereas biogenic opal was only a minor contributor. The most distinct flux maxima were in July–August both at the Cap Blanc and the northern Guinea Basin site (2°N). Carbonate fluxes also peaked during that period. In contrast, highest opal fluxes were measured there in late winter/early spring. At the Cap Blanc site, high lithogenic fluxes correlate well with fluxes of biogenic components. At both equatorial sites, prominent flux maxima were observed in boreal spring, attributed to the southermost penetration of the ITCZ. These fluxes were characterized by a relatively high lithogenic contribution. South of the equator (2°S), sedimentation decreased rapidly to almost zero after May when the ITCZ started to migrate northwards. Seasonality was most expressed at the Walvis Ridge site, where a distinct bi-modal flux pattern occurred (June–July and October–November). In austral spring, elevated fluxes were determined for a relatively long period when wind-driven upwelling is strongest and the Namibia upwelling cell shows the greatest extension to the west approaching the trap position. Contribution of lithogenic material to total fluxes was very low at this site.

Seasonality and interannual variability of particle fluxes to the deep Arabian sea

Long-term sediment trap studies have been carried out since 1986 at three locations in the western, central and eastern Arabian Sea. Here we present total and bulk component fluxes measured for 3 years at the central station and for 4 years at the western and eastern stations. Particulate fluxes to the deep sea are controlled by the monsoons with generally higher fluxes during the SW and NE monsoons and lower fluxes during the intermonsoon periods. The increase of particle fluxes occurs simultaneously with a drop in surface water temperature, induced by wind-or convective-mixing and an associated entrainment of nutrients into the euphotic zone. More than 50% of the annual particle fluxes to the deep sea occurs during the SW monsoon at the western location due to the prolonged influence of the monsoonal upwelling as indicated by increased biogenic carbonate and opal fluxes. However, the opal fluxes peak a month later than the carbonate fluxes. The delayed onset of opal flux peak appears to be controlled by the observed premonsoon silica distribution in the Arabian Sea, where the subsurface waters are silica depleted down to the thermocline at 150 m. At the central location particle fluxes are of similar magnitude during the SW and NE monsoons. The interannual variability of particle fluxes at the eastern location is determined by the NE monsoon. At the western and central locations, on the other hand, maximum interannual variability of fluxes occurs during the SW monsoon and particle fluxes were higher during years of stronger SW monsoon. The results further suggest that, apart from monsoon strength, geographic shifts of the area of maximum wind-stress may produce significant variabilities in particle fluxes to the deep ocean at the western Arabian Sea site.