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

2000 ◽  
Vol 161 (3-4) ◽  
pp. 337-359 ◽  
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

scholarly journals Live foraminiferal faunas (Rose Bengal stained) from the northern Arabian Sea: links with bottom-water oxygenation

2013 ◽  
Vol 10 (9) ◽  
pp. 15257-15304 ◽  
Author(s):  
C. Caulle ◽  
K. A. Koho ◽  
M. Mojtahid ◽  
G. J. Reichart ◽  
F. J. Jorissen
Keyword(s):  
Rose Bengal ◽  
Arabian Sea ◽  
Bottom Water ◽  
Principal Component ◽  
Environmental Parameters ◽  
Low Oxygen ◽  
The Core ◽  
Northern Arabian Sea ◽  
Transitional Group ◽  
Epistominella Exigua

Abstract. Live (Rose Bengal stained) benthic foraminifera from the Murray Ridge, within and below the northern Arabian Sea Oxygen Minimum Zone (OMZ), were studied in order to determine the relationship between faunal composition, bottom-water oxygenation (BWO), pore-water chemistry and organic matter (organic carbon and phytopigment) distribution. A series of multicores were recovered from a ten-station oxygen (BWO: 2–78 μM) and bathymetric (885–3010 m depth) transect during the winter monsoon in January 2009. Foraminifera were investigated from three different size fractions (63–125 μm, 125–150 μm and > 150 μm). The larger foraminifera (> 125 μm) were strongly dominated by agglutinated species (e.g. Reophax spp.). In contrast, in the 63–125 μm fraction, calcareous taxa were more abundant, especially in the core of the OMZ, suggesting an opportunistic behaviour. On the basis of a Principal Component Analysis, three foraminiferal groups were identified, reflecting the environmental parameters along the study transect. The faunas from the shallowest stations, in the core of the OMZ (BWO: 2 μM), were composed of "low oxygen" species, typical of the Arabian Sea OMZ (e.g., Rotaliatinopsis semiinvoluta, Praeglobobulimina spp. , Bulimina exilis, Uvigerina peregrina typeparva). These taxa are adapted to the very low BWO conditions and to high phytodetritus supplies. The transitional group, typical for the lower part of the OMZ (BWO: 5–16 μM), is composed of more cosmopolitan taxa tolerant to low-oxygen concentrations (Globocassidulina subglobosa, Ehrenbergina trigona). Below the OMZ (BWO: 26–78 μM), where food availability is more limited and becomes increasingly restricted to surficial sediments, more cosmopolitan calcareous taxa were present, such as Bulimina aculeata, Melonis barleeanus, Uvigerina peregrina and Epistominella exigua. Miliolids were uniquely observed in this last group, reflecting the higher BWO. At these deeper sites, the faunas exhibit a clear depth succession of superficial, intermediate and deep-infaunal microhabitats, because of the deeper oxygen and nitrate penetration into the sediment.

scholarly journals Sedimentary phosphorus and iron cycling in and below the oxygen minimum zone of the northern Arabian Sea

2012 ◽  
Vol 9 (7) ◽  
pp. 2603-2624 ◽  
Author(s):  
P. Kraal ◽  
C. P. Slomp ◽  
D. C. Reed ◽  
G.-J. Reichart ◽  
S. W. Poulton
Keyword(s):  
Arabian Sea ◽  
Bottom Water ◽  
Surface Sediments ◽  
Lower Boundary ◽  
Oxygen Minimum Zone ◽  
Apatite Formation ◽  
Northern Arabian Sea ◽  
Minimum Zone ◽  
Oxygen Minimum ◽  
Burial Efficiency

Abstract. In this study, we investigate phosphorus (P) and iron (Fe) cycling in sediments along a depth transect from within to well below the oxygen minimum zone (OMZ) in the northern Arabian Sea (Murray Ridge). Pore-water and solid-phase analyses show that authigenic formation of calcium phosphate minerals (Ca-P) is largely restricted to where the OMZ intersects the seafloor topography, likely due to higher depositional fluxes of reactive P. Nonetheless, increased ratios of organic carbon to organic P (Corg/Porg) and to total reactive P (Corg/Preactive) in surface sediments indicate that the overall burial efficiency of P relative to Corg decreases under the low bottom water oxygen concentrations (BWO) in the OMZ. The relatively constant Fe/Al ratio in surface sediments along the depth transect suggest that corresponding changes in Fe burial are limited. Sedimentary pyrite contents are low throughout the ~25 cm sediment cores at most stations, as commonly observed in the Arabian Sea OMZ. However, pyrite is an important sink for reactive Fe at one station in the OMZ. A reactive transport model (RTM) was applied to quantitatively investigate P and Fe diagenesis at an intermediate station at the lower boundary of the OMZ (bottom water O2: ~14 μmol L−1). The RTM results contrast with earlier findings in showing that Fe redox cycling can control authigenic apatite formation and P burial in Arabian Sea sediment. In addition, results suggest that a large fraction of the sedimentary Ca-P is not authigenic, but is instead deposited from the water column and buried. Dust is likely a major source of this Ca-P. Inclusion of the unreactive Ca-P pool in the Corg/P ratio leads to an overestimation of the burial efficiency of reactive P relative to Corg along the depth transect. Moreover, the unreactive Ca-P accounts for ~85% of total Ca-P burial. In general, our results reveal large differences in P and Fe chemistry between stations in the OMZ, indicating dynamic sedimentary conditions under these oxygen-depleted waters.

Surface- and deep-water response to the Early Aptian OAE 1a in the western Tethys

2021 ◽  
Author(s):  
Cinzia Bottini ◽  
Victor M. Giraldo-Gómez ◽  
Maria Rose Petrizzo ◽  
Elisabetta Erba
Keyword(s):  
Deep Water ◽  
Surface Waters ◽  
Benthic Foraminifera ◽  
Bottom Water ◽  
Black Shales ◽  
Ontong Java Plateau ◽  
Western Tethys ◽  
Organic Carbon Flux ◽  
Water Response ◽  
Matter Flux

<p>The Cretaceous was punctuated by interludes of widespread deposition of organic-rich sediments (black shales) in the oceans and epicontinental seas, named Oceanic Anoxic Events (OAE)s, representing major alterations in the global carbon budget. The early Aptian OAE 1a (ca. 120 Ma) coincided with a global paleoclimatic and paleoenvironmental perturbation which lasted for ca. 1.1 Myrs probably triggered by volcanogenic CO<sub>2 </sub>emissions associated with the emplacement of the Ontong Java Plateau. To date, there is a comprehensive characterization of OAE 1a paleoceanographic conditions and paleoecology of surface-waters while less information is available for bottom-water evolution. In this regard, benthic foraminifera are ideal to characterize deep-water oxygen levels and the organic carbon flux. We present a high-resolution study of benthic foraminiferal assemblages across OAE 1a in the Cismon Core (western Tethys, Lombardy Basin, Northern Italy). Contrarily to many sites, the Cismon Core yields benthic foraminifera also in the Selli Level thus providing information about deep-water conditions during OAE 1a. Our data are indicative of fluctuations in bottom-water oxygenation and organic-matter flux to the sea-floor prior to, during and after OAE 1a. The integration of the new benthic foraminiferal data with calcareous nannofossil and planktonic foraminiferal datasets is here used to produce a model of surface- to bottom-water paleowater evolution through the latest Barremian-early late Aptian. In particular, the new data show coeval changes in bottom- and surface-waters conditions prior to and at the onset of OAE 1a. Anoxia was reached during the core of the negative carbon isotope anomaly, under maximum warming and higher surface-water fertility. Conversely, the repopulation of benthic foraminifera postponed the plankton recovery. Benthic foraminifera data at Cismon show, for the first time, evidence of a repopulation event during the OAE 1a suggestive for a slight increase in the supply of oxygen to the seafloor during the Selli Level deposition.</p>

scholarly journals A multi-proxy analysis of Late Quaternary ocean and climate variability for the Maldives, Inner Sea

2017 ◽  
Vol 13 (12) ◽  
pp. 1791-1813 ◽  
Author(s):  
Dorothea Bunzel ◽  
Gerhard Schmiedl ◽  
Sebastian Lindhorst ◽  
Andreas Mackensen ◽  
Jesús Reolid ◽  
...  
Keyword(s):  
Oxygen Consumption ◽  
Indian Ocean ◽  
Organic Carbon ◽  
Sea Level ◽  
Benthic Foraminifera ◽  
Arabian Sea ◽  
Bottom Water ◽  
Winter Monsoon ◽  
Intermediate Water ◽  
Combined Effects

Abstract. As a natural sediment trap, the marine sediments of the sheltered central part of the Maldives Inner Sea represent an exceptional archive for paleoenvironmental and climate changes in the equatorial Indian Ocean. To evaluate the complex interplay between high-latitude and monsoonal climate variability, related dust fluxes, and regional oceanographic responses, we focused on Fe ∕ Al, Ti ∕ Al and Si ∕ Ca ratios as proxies for terrigenous sediment delivery and total organic carbon (TOC) and Br XRF counts as proxies for marine productivity. Benthic foraminiferal fauna distributions, grain size and stable δ18O and δ13C data were used for evaluating changes in the benthic ecosystem and changes in the intermediate water circulation, bottom water current velocity and oxygenation. Our multi-proxy data record reveals an enhanced dust supply during the glacial intervals, causing elevated Fe ∕ Al and Si ∕ Ca ratios, an overall coarsening of the sediment and an increasing amount of agglutinated benthic foraminifera. The enhanced dust fluxes can be attributed to higher dust availability in the Asian desert and loess areas and its transport by intensified winter monsoon winds during glacial conditions. These combined effects of wind-induced mixing of surface waters and dust fertilization during the cold phases resulted in an increased surface water productivity and related organic carbon fluxes. Thus, the development of highly diverse benthic foraminiferal faunas with certain detritus and suspension feeders was fostered. The difference in the δ13C signal between epifaunal and deep infaunal benthic foraminifera reveals intermediate water oxygen concentrations between approximately 40 and 100 µmol kg−1 during this time. The precessional fluctuation pattern of oxygen changes resembles that from the deep Arabian Sea, suggesting an expansion of the oxygen minimum zone (OMZ) from the Arabian Sea into the tropical Indian Ocean with a probable regional signal of strengthened winter-monsoon-induced organic matter fluxes and oxygen consumption further controlled by the varying inflow intensity of the Antarctic Intermediate Water (AAIW). In addition, the bottom water oxygenation pattern of the Maldives Inner Sea reveals a long phase of reduced ventilation during the last glacial period. This process is likely linked to the combined effects of generally enhanced oxygen consumption rates during high-productivity phases, reduced AAIW production and the restriction of upper bathyal environments in the Inner Sea during sea-level lowstands. Thus, our multi-proxy record reflects a close linkage between the Indian monsoon oscillation, intermediate water circulation, productivity and sea-level changes on orbital timescale.

scholarly journals Sedimentary phosphorus and iron cycling in and below the oxygen minimum zone of the northern Arabian Sea

2012 ◽  
Vol 9 (3) ◽  
pp. 3829-3880 ◽  
Author(s):  
P. Kraal ◽  
C. P. Slomp ◽  
D. C. Reed ◽  
G.-J. Reichart ◽  
S. W. Poulton
Keyword(s):  
Arabian Sea ◽  
Bottom Water ◽  
Surface Sediments ◽  
Lower Boundary ◽  
Oxygen Minimum Zone ◽  
Apatite Formation ◽  
Northern Arabian Sea ◽  
Minimum Zone ◽  
Oxygen Minimum ◽  
Burial Efficiency

Abstract. In this study, we investigate phosphorus (P) and iron (Fe) cycling in sediments along a depth transect from within to well below the oxygen minimum zone (OMZ) in the northern Arabian Sea (Murray Ridge). Pore-water and solid-phase analyses show that authigenic formation of calcium phosphate minerals (Ca-P) is largely restricted to where the OMZ intersects the seafloor topography, likely due to higher depositional fluxes of reactive P. Nonetheless, increased ratios of organic carbon to organic P (Corg/Porg) and to total reactive P (Corg/Preactive) in surface sediments indicate that the overall burial efficiency of P relative to Corg decreases under the low bottom water oxygen concentrations (BWO) in the OMZ. The relatively constant Fe/Al ratio in surface sediments along the depth transect suggest that corresponding changes in Fe burial are limited. Sedimentary pyrite contents are low throughout the ~25-cm sediment cores at most stations, as commonly observed in the Arabian Sea OMZ. However, pyrite is an important sink for reactive Fe at one station in the OMZ. A reactive transport model (RTM) was applied to quantitatively investigate P and Fe diagenesis at an intermediate station at the lower boundary of the OMZ (bottom water O2: ~14 μ mol l−1). The RTM results contrast with earlier findings in showing that Fe redox cycling can control authigenic apatite formation and P burial in Arabian Sea sediment. In addition, results suggest that a large fraction of the sedimentary Ca-P is not authigenic, but is instead deposited from the water column and buried. Dust is likely a major source of this Ca-P. Inclusion of the unreactive Ca-P pool in the Corg/P ratio leads to an overestimation of the burial efficiency of reactive P relative to Corg along the depth transect. Moreover, the unreactive Ca-P accounts for ~85% of total Ca-P burial. In general, our results reveal large differences in P and Fe chemistry between stations in the OMZ, indicating dynamic sedimentary conditions under these oxygen-depleted waters.

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