Relationships between primary productivity and bottom-water oxygenation off northwest Africa during the last deglaciation

2011 ◽  
Vol 26 (4) ◽  
pp. 448-456 ◽  
Author(s):  
Helena L. Filipsson ◽  
Oscar E. Romero ◽  
Jan-Berend W. Stuut ◽  
Barbara Donner
Keyword(s):  
Primary Productivity ◽  
Bottom Water ◽  
Last Deglaciation ◽  
Northwest Africa ◽  
The Last Deglaciation

scholarly journals Changes in productivity and intermediate circulation in the northern Indian Ocean since the last deglaciation: new insights from benthic foraminiferal Cd /thinsp;Ca records and benthic assemblage analyses

2020 ◽  
Author(s):  
Ruifang Ma ◽  
Sophie Sépulcre ◽  
Laetitia Licari ◽  
Frédéric Haurine ◽  
Franck Bassinot ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Primary Productivity ◽  
Arabian Sea ◽  
Bottom Water ◽  
Geochemical Data ◽  
Intermediate Water ◽  
Last Deglaciation ◽  
Northern Indian Ocean ◽  
Surface Productivity ◽  
The Last Deglaciation

Abstract. We have measured Cd / Ca ratios of several benthic foraminiferal species and studied benthic foraminiferal assemblages on two cores from the northern Indian Ocean (Arabian Sea and northern Bay of Bengal, BoB), in order to reconstruct variations in intermediate water circulation and paleo-nutrient content since the last deglaciation. Intermediate water Cdw records estimated from the benthic Cd / Ca reflect past changes in surface productivity and/or intermediate-bottom water ventilation. The benthic foraminiferal assemblages are consistent with the geochemical data. These results suggest that during the last deglaciation, the Heinrich Stadial 1 and Younger Dryas (HS1 and YD, respectively) millennial-scale events were marked by a decrease in Cdw values, indicating an enhanced ventilation of intermediate-bottom water masses. Benthic foraminifer assemblages indicate that surface primary productivity was low during the early Holocene (from 10 to 6 cal kyr BP), resulting in low intermediate water Cdw at both sites. From ~ 5.2 to 2.4 cal kyr BP, the benthic foraminiferal assemblages indicate meso- to eutrophic intermediate water conditions, which correspond to high surface productivity. This is consistent with a significant increase in the intermediate water Cdw in the southeastern Arabian Sea and the northeastern BoB. The comparison of intermediate water Cdw records with previous reconstructions of past Indian monsoon evolution during the Holocene suggests a direct control of intermediate water Cdw by monsoon-induced changes in upper water stratification and surface primary productivity.

Millennial-scale changes of surface and bottom water conditions in the northwestern Pacific during the last deglaciation

2017 ◽  
Vol 154 ◽  
pp. 33-43 ◽  
Author(s):  
Sunghan Kim ◽  
Boo-Keun Khim ◽  
Ken Ikehara ◽  
Takuya Itaki ◽  
Akihiko Shibahara ◽  
...  
Keyword(s):  
Bottom Water ◽  
Northwestern Pacific ◽  
Last Deglaciation ◽  
Water Conditions ◽  
The Last Deglaciation ◽  
Millennial Scale

scholarly journals Supplementary material to "Bottom-water deoxygenation at the Peruvian Margin during the last deglaciation recorded by benthic foraminifera"

2019 ◽  
Author(s):  
Zeynep Erdem ◽  
Joachim Schönfeld ◽  
Anthony E. Rathburn ◽  
Maria-Elena Pérez ◽  
Jorge Cardich ◽  
...  
Keyword(s):  
Benthic Foraminifera ◽  
Bottom Water ◽  
Last Deglaciation ◽  
Water Deoxygenation ◽  
Supplementary Material ◽  
The Last Deglaciation

scholarly journals Bottom-water deoxygenation at the Peruvian margin during the last deglaciation recorded by benthic foraminifera

2020 ◽  
Vol 17 (12) ◽  
pp. 3165-3182
Author(s):  
Zeynep Erdem ◽  
Joachim Schönfeld ◽  
Anthony E. Rathburn ◽  
Maria-Elena Pérez ◽  
Jorge Cardich ◽  
...  
Keyword(s):  
Bottom Water ◽  
Sediment Cores ◽  
Lower Boundary ◽  
Climatic Conditions ◽  
Last Deglaciation ◽  
Oxygen Minimum Zones ◽  
Proxy Records ◽  
Water Deoxygenation ◽  
The Last Deglaciation ◽  
Oxygen Minimum

Abstract. Deciphering the dynamics of dissolved oxygen in the mid-depth ocean during the last deglaciation is essential to understand the influence of climate change on modern oxygen minimum zones (OMZs). Many paleo-proxy records from the eastern Pacific Ocean indicate an extension of oxygen-depleted conditions during the deglaciation, but the degree of deoxygenation has not been quantified to date. The Peruvian OMZ, one of the largest OMZs in the world, is a key area to monitor such changes in near-bottom-water oxygenation in relation to changing climatic conditions. Here, we analysed the potential to use the composition of foraminiferal assemblages from the Peruvian OMZ as a quantitative redox proxy. A multiple regression analysis was applied to a joint dataset of living (rose-bengal-stained, fossilizable calcareous species) benthic foraminiferal distributions from the Peruvian continental margin. Bottom-water oxygen concentrations ([O2]BW) during sampling were used as the dependant variable. The correlation was significant (R2=0.82; p<0.05), indicating that the foraminiferal assemblages are rather governed by oxygen availability than by the deposition of particulate organic matter (R2=0.53; p=0.31). We applied the regression formula to three sediment cores from the northern part of the Peruvian OMZ between 3 and 8∘ S and 997 and 1250 m water depth, thereby recording oxygenation changes at the lower boundary of the Peruvian OMZ. Each core displayed a similar trend of decreasing oxygen levels since the Last Glacial Maximum (LGM). The overall [O2]BW change from the LGM and the Holocene was constrained to 30 µmol kg−1 at the lower boundary of the OMZ.

scholarly journals Bottom-water deoxygenation at the Peruvian Margin during the last deglaciation recorded by benthic foraminifera

2019 ◽  
Author(s):  
Zeynep Erdem ◽  
Joachim Schönfeld ◽  
Anthony E. Rathburn ◽  
Maria-Elena Pérez ◽  
Jorge Cardich ◽  
...  
Keyword(s):  
Bottom Water ◽  
Climatic Conditions ◽  
Eastern Pacific Ocean ◽  
Last Deglaciation ◽  
Oxygen Minimum Zones ◽  
Proxy Records ◽  
Water Oxygen ◽  
Water Deoxygenation ◽  
The Last Deglaciation ◽  
Oxygen Minimum

Abstract. Deciphering the dynamics of dissolved oxygen in the mid-depth ocean during the last deglaciation is essential to understand the influence of climate change on modern oxygen minimum zones (OMZs). Many paleo-proxy records from the Eastern Pacific Ocean indicate an extension of oxygen depleted conditions during the deglaciation but the degree of deoxygenation has not been quantified to date. The Peruvian OMZ, one of the largest OMZs in the world, is a key area to monitor such changes in near-bottom water oxygenation in relation to changing climatic conditions. Here, we analysed the potential to use the composition of foraminiferal assemblages from the Peruvian OMZ as a quantitative redox-proxy. A multiple regression analysis was applied to a joint dataset of living (rose Bengal stained, fossilizable calcareous species) benthic foraminiferal distributions from the Peruvian continental margin. Bottom-water oxygen concentrations ([O2]BW) during sampling were used as dependant variable. The correlation was significant (R2 = 0.82; p 

scholarly journals Eastern Mediterranean Sea circulation inferred from the conditions of S1 sapropel deposition

2015 ◽  
Vol 11 (6) ◽  
pp. 855-867 ◽  
Author(s):  
K. Tachikawa ◽  
L. Vidal ◽  
M. Cornuault ◽  
M. Garcia ◽  
A. Pothin ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Benthic Foraminifera ◽  
Bottom Water ◽  
Eastern Mediterranean ◽  
Last Deglaciation ◽  
Short Term ◽  
Total Recovery ◽  
Eastern Mediterranean Sea ◽  
The Last Deglaciation ◽  
Freshwater Inputs

Abstract. Holocene eastern Mediterranean Sea sediments contain an organic-rich sapropel S1 layer that was formed in oxygen-depleted waters. The spatial distribution of this layer revealed that during S1 deposition, deep waters were anoxic below a depth of 1800 m. However, whether this boundary permanently existed from the early to the mid-Holocene has not been examined yet. To answer this question, a multi-proxy approach was applied to a core retrieved close to the 1800 m boundary (at 1780 m). We measured the bulk sediment elemental composition, the stable isotopic composition of the planktonic foraminifer Globigerinoides ruber and the abundance of benthic foraminifera since the last deglaciation. The result indicates that authigenic U and Mo accumulation began around 13–12 cal ka BP, in concert with surface water freshening estimated from the G. ruber δ18O record. The onset of bottom and pore water oxygen depletion occurred prior to S1 deposition inferred from barium enrichment. In the middle of the S1 deposition period, reduced authigenic V, Fe and As contents and the Br/Cl ratio indicated short-term bottom-water re-oxygenation. A sharp Mn peak and maximal abundance for benthic foraminifera marked a total recovery for circulation at approximately 7 cal ka BP. Based on our results and existing data, we suggest that S1 formation within the upper 1780 m of the eastern Mediterranean Sea was preconditioned by reduced ventilation, resulting from excess freshwater inputs due to insolation changes under deglacial conditions that initiated between 15 and 12 cal ka BP within the upper 1780 m. Short-term re-oxygenation in the Levantine Basin is estimated to have affected bottom water at least as deep as 1780 m in response to cooling and/or the reduction of freshwater inputs. We tentatively propose that complete ventilation recovery at the S1 termination was depth-dependent, with earlier oxygenation within the upper 1780 m. Our results provide new constraints on vertical water column structure in the eastern Mediterranean Sea since the last deglaciation.

On new developments in accelerator mass spectrometry and how they promote our understanding of global carbon cycle dynamics during the last deglaciation

2020 ◽  
Author(s):  
Julia Gottschalk ◽  
Robert F. Anderson ◽  
David A. Hodell ◽  
Alfredo Martinez-Garcia ◽  
Alain Mazaud ◽  
...  
Keyword(s):  
High Resolution ◽  
Southern Ocean ◽  
Bottom Water ◽  
Deep Ocean ◽  
Global Ocean ◽  
Last Deglaciation ◽  
Surface Ocean ◽  
Ocean Atmosphere ◽  
The Last Deglaciation ◽  
Reservoir Age

&lt;p&gt;Ocean-atmosphere &lt;sup&gt;14&lt;/sup&gt;C disequilibria of the surface and deep ocean reflect past changes in the efficiency of ocean-atmosphere CO&lt;sub&gt;2&lt;/sub&gt; exchange and ocean mixing, while it may also be related to variations in global-ocean respired carbon content. A full assessment of the oceanic mechanisms controlling deglacial changes in atmospheric CO&lt;sub&gt;2&lt;/sub&gt; is complicated by a lack of high-resolution &lt;sup&gt;14&lt;/sup&gt;C ventilation age estimates from the Southern Ocean and other key regions due to low foraminiferal abundances in marine sediments in those areas. Here we present high-resolution deglacial &lt;sup&gt;14&lt;/sup&gt;C ventilation age records from key sites in the Atlantic and Indian Sector of the Southern Ocean obtained by radiocarbon analyses of small benthic and planktic foraminiferal samples (&lt;1 mg CaCO&lt;sub&gt;3&lt;/sub&gt;) with the UniBe Mini-Carbon Dating System (MICADAS). Our analyses specifically circumvent foraminiferal sample size requirements related to &amp;#8220;conventional&amp;#8221; accelerator mass spectrometer analyses involving sample graphitization (&gt;1 mg CaCO&lt;sub&gt;3&lt;/sub&gt; in most laboratories). Complementing multi-proxy analyses of sea surface temperature (SST) changes at these sites allow the construction of a radiocarbon-independent age model through a stratigraphic alignment of SST changes to Antarctic (ice core) temperature variations. We demonstrate the value of refining the age models of our study cores on the basis of high-resolution sedimentary U- and Th flux estimates, which allows an improved quantification of surface ocean reservoir age variations in the past. The resulting deep-ocean ventilation age changes are compared against qualitative and quantitative indicators of bottom water [O&lt;sub&gt;2&lt;/sub&gt;] variations, in order to assess the role of Southern Ocean overturning dynamics in respired carbon changes at our study sites. We discuss the implications of our new radiocarbon- and bottom water [O&lt;sub&gt;2&lt;/sub&gt;] data for the ocean&amp;#8217;s role in atmospheric CO&lt;sub&gt;2&lt;/sub&gt; changes throughout the last deglaciation, and evaluate down-stream effects of southern high-latitude surface ocean reservoir age anomalies.&lt;/p&gt;

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