Carbon Isotopes of Live Benthic Foraminifera from the South Atlantic: Sensitivity to Bottom Water Carbonate Saturation State and Organic Matter Rain Rates

The Baltic Sea is characterized by a restricted exchange of deep waters due to permanent stratification of the water column. The aim of the present study is to investigate the distribution of benthic foraminifera in the south-eastern part of the Baltic Sea in relation to environmental parameters. The distribution of benthic foraminifera was analyzed in 26 surface sediment samples collected in the south-eastern part of the Baltic Sea and in the Bornholm Basin during springtime and wintertime 2016. Foraminiferal diversity in the studied region was extremely low. Agglutinated specimens dominated the assemblages and were represented by small-sized individuals which belong to Psammosphaera, Pseudothurammina, Saccammina, and Reophax genera. Calcareous foraminifera were dominated by Cribroelphidium genus. Micropaleontological data were compared to the environmental parameters characterizing bottom water (temperature, salinity, and dissolved oxygen content) and substrate conditions (grain size composition and total organic carbon content). Higher foraminiferal concentrations and diversity were found in deeper parts of the study region where fine-grained sediments with a higher total organic carbon content were accumulated under stable hydrographical conditions. Calcareous tests were found only at the stations with elevated salinity, indicating that bottom water salinity is the main factor limiting the distribution of calcareous foraminifera. On the other hand, substrate parameters and hydrodynamic conditions appear to play a major role in the distribution of agglutinated foraminifera.

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Relationships between bottom water carbonate saturation and element/Ca ratios in coretop samples of the benthic foraminifera <i>Oridorsalis umbonatus</i>

Biogeosciences Discussions ◽

10.5194/bgd-9-1483-2012 ◽

2012 ◽

Vol 9 (2) ◽

pp. 1483-1510 ◽

Cited By ~ 1

Author(s):

C. F. Dawber ◽

A. Tripati

Keyword(s):

Benthic Foraminifera ◽

Partition Coefficients ◽

Bottom Water ◽

Energetic Cost ◽

Individual Element ◽

Fractionation Factor ◽

Bottom Water Temperature ◽

Rayleigh Fractionation ◽

Wide Range ◽

Water Carbonate

Abstract. Elemental ratios in benthic foraminifera have been used to reconstruct bottom water temperature and carbonate saturation (Δ[CO32−]). We present elemental data for the long-ranging benthic foraminifera Oridorsalis umbonatus from sediment core tops that span a narrow range of temperatures and a wide range of saturation states. B/Ca, Li/Ca, Sr/Ca and Mg/Ca ratios exhibit positive correlations with bottom water carbonate saturation. The sensitivity of individual element/calcium ratios to bottom water Δ [CO32−] varies considerably, with B/Ca being most sensitive and Sr/Ca the least sensitive. The empirically derived sensitivity of B/Ca, Li/Ca, Mg/Ca and Sr/Ca to bottom water Δ [CO32−] are 0.433 ± 0.053 and 0.0561 ± 0.0084 μmol mol−1 per μmol kg−1 and 0.0164 ± 0.0015 and 0.00241 ± 0.0004 μmol mol−1 per μmol kg−1, respectively. To assess the fidelity of these relationships and the possibility of applying these relationships to earlier periods of Earth history, we examine the mechanisms governing elemental incorporation into foraminiferal calcite. Empirical partition coefficients for Li and Sr are consistent with Rayleigh fractionation from an internal pool used for calcification. For O. umbonatus and other benthic species, we show that the fraction of Ca remaining in the pool is a function of bottom water Δ [CO32−], and can be explained by either a growth rate effect and/or the energetic cost of raising vesicle pH at the site of calcification. Empirical partition coefficients for Mg and B may also be controlled by Rayleigh fractionation, but require that either the fractionation factor from the internal pool is smaller than the inorganic partition coefficient and/or additional fractionation mechanisms. O. umbonatus element ratio data may also be consistent with fractionation according to the surface entrapment model and/or the presence of discrete high- and low-Mg calcite phases. However at present we are limited in our ability to assess these mechanisms. The new X/Ca data for O. umbonatus provide constraints to test the role of these mechanisms in the future.

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Terrigenous particle transports as indicators of late Quaternary deep and bottom water circulation in the South Atlantic and adjoining Southern Ocean

Zeitschrift der Deutschen Geologischen Gesellschaft ◽

10.1127/zdgg/148/1997/405 ◽

1997 ◽

Vol 148 (3-4) ◽

pp. 405-429

Author(s):

Bernhard Diekmann ◽

Gerhard Kuhn

Keyword(s):

Southern Ocean ◽

Bottom Water ◽

Late Quaternary ◽

South Atlantic ◽

Water Circulation ◽

The South

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Benthic foraminifera as proxies of organic matter flux and bottom water oxygenation? A case history from the northern Arabian Sea

Palaeogeography Palaeoclimatology Palaeoecology ◽

10.1016/s0031-0182(00)00074-2 ◽

2000 ◽

Vol 161 (3-4) ◽

pp. 337-359 ◽

Cited By ~ 111

Author(s):

M den Dulk ◽

G.J Reichart ◽

S van Heyst ◽

W.J Zachariasse ◽

G.J Van der Zwaan

Keyword(s):

Organic Matter ◽

Case History ◽

Benthic Foraminifera ◽

Arabian Sea ◽

Bottom Water ◽

Northern Arabian Sea ◽

Matter Flux

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Mg/Ca and Mn/Ca ratios in benthic foraminifera: the potential to reconstruct past variations in temperature and hypoxia in shelf regions

Biogeosciences ◽

10.5194/bg-10-5125-2013 ◽

2013 ◽

Vol 10 (7) ◽

pp. 5125-5138 ◽

Cited By ~ 33

Author(s):

J. Groeneveld ◽

H. L. Filipsson

Keyword(s):

Dissolved Oxygen ◽

Trace Metal ◽

Benthic Foraminifera ◽

Bottom Water ◽

Oxygen Depletion ◽

Open Ocean ◽

Low Oxygen ◽

Saturation State ◽

Bottom Water Temperature ◽

Fish And Shellfish

Abstract. Shelf and coastal regions are exceptionally important for many countries as they provide the main habitat for many economically important fish and shellfish species. With ongoing climate change and human-induced eutrophication the shelf regions are especially affected, resulting in increased temperatures and stratification as well as oxygen depletion of the bottom waters. In order to be able to predict the magnitude of these changes in the future, it is necessary to study how they varied in the past. Commonly used foraminiferal climate and environmental proxies, e.g., stable isotopes and trace metal/Ca ratios, that are applied in open-ocean settings are not necessarily applicable in shelf regions, either as faunas are significantly different or as conditions can change much faster compared to the open ocean. In this study we explore the use of Mg/Ca as paleothermometer and Mn/Ca as a potential proxy for changing dissolved oxygen conditions in bottom water on the benthic foraminifera Bulimina marginata and Globobulimina turgida. Living specimens were collected from the Skagerrak and the Gullmar Fjord (SW Sweden); the latter is hypoxic for several months a year. As the specimens were alive when collected, we assume it unlikely that any diagenetic coatings have already significantly affected the trace metal/Ca ratios. The Mg/Ca ratios are similar to previously published values but display much larger variation than would be expected from the annual temperature change of less than 2 °C. An additional impact of the difference in the calcite saturation state between the Skagerrak and the Gullmar Fjord could explain the results. Mn/Ca ratios from G. turgida can potentially be related to variations in dissolved oxygen of the habitat where the foraminifera calcify. Samples from the Skagerrak display increased Mn/Ca in specimens that lived deeper in the sediment than those that lived near the surface. G. turgida samples from the low-oxygen Gullmar Fjord showed significantly increased Mn/Ca, being highest when bottom water dissolved oxygen was at a minimum. Our study suggests that trace metal/Ca ratios in benthic foraminifera from shelf regions have the potential to record past variations in bottom water temperature and dissolved oxygen concentrations, but an additional impact of the inorganic carbonate chemistry cannot be excluded.

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Exploring the controls on element ratios in middle Eocene samples of the benthic foraminifera <i>Oridorsalis umbonatus</i>

Climate of the Past ◽

10.5194/cp-8-1957-2012 ◽

2012 ◽

Vol 8 (6) ◽

pp. 1957-1971 ◽

Cited By ~ 2

Author(s):

C. F. Dawber ◽

A. K. Tripati

Keyword(s):

Benthic Foraminifera ◽

Bottom Water ◽

Middle Eocene ◽

Environmental Parameters ◽

Intermediate Water ◽

Saturation State ◽

Bottom Water Temperature ◽

Elemental Ratios ◽

Elemental Ratio ◽

Element Ratios

Abstract. Culturing studies and empirically based core top calibrations have been used to infer that elemental ratios in benthic foraminifera can be used as proxies to reconstruct past variations in bottom water temperature and saturation state (Δ [CO32−]). However the mechanisms linking elemental ratios to these parameters are poorly constrained. Here, we explore the environmental parameters influencing the incorporation of B, Li, Sr and Mg in Oridorsalis umbonatus in early Cenozoic sediments from Ocean Drilling Program Site 1209. We investigate the influence of middle Eocene variations in intermediate water Δ [CO32−] using relationships developed from core top samples. The fidelity of bottom water Δ[CO32−] reconstructions based on single element ratios is assessed by comparing the X/Ca-based reconstructions to each other and to carbon cycle proxy records (benthic foraminifera δ13C, organic carbon content, foraminifera dissolution indices), and a seawater δ18O reconstruction for Site 1209. Discrepancies in the reconstructed Δ[CO32−] values based on these different metal ratios suggest that there are still gaps in our understanding of the parameters influencing X/Ca and demonstrate that caution is required when interpreting palaeo-reconstructions that are derived from a single elemental ratio. The downcore record of O. umbonatus Mg/Ca does not exhibit any similarities with the Li/Ca, B/Ca and Sr/Ca records, suggesting that the environmental parameters influencing Mg/Ca may be different for this species, consistent with temperature as the strongest control on this elemental ratio. This hypothesis is supported by the coefficients of multiple linear regression models on published Mg/Ca data. An incomplete understanding of the controls on elemental incorporation into benthic foraminifera hinders our ability to confidently quantify changes in saturation state using single X/Ca reconstructions over a range of timescales.

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