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 Systematics of past changes in ocean ventilation: a comparison of Cretaceous Ocean Anoxic Event 2 and Pleistocene to Holocene Oxygen Minimum Zones

2014 ◽  
Vol 11 (9) ◽  
pp. 13343-13387 ◽  
Author(s):  
J. Schönfeld ◽  
W. Kuhnt ◽  
Z. Erdem ◽  
S. Flögel ◽  
N. Glock ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Bottom Water ◽  
Sediment Cores ◽  
Carbon Accumulation ◽  
Accumulation Rates ◽  
Oxygen Minimum Zones ◽  
Oxygen Levels ◽  
Water Oxygen ◽  
Oxygen Minimum

Abstract. Present day oceans are generally well ventilated except mid-depth oxygen minimum zones (OMZs) under high surface water productivity regimes, regions of sluggish circulation, and restricted marginal basins. In the Mesozoic, however, entire oceanic basins transiently became dysoxic or even anoxic. In particular the Cretaceous Ocean Anoxic Events (OAEs) were characterised by laminated organic-carbon rich shales and low-oxygen indicating trace fossil assemblages preserved in the sedimentary record. Yet both, qualitative and quantitative assessments of intensity and extent of Cretaceous near-bottom water oxygenation have been hampered by deep or long-term diagenesis and the evolution of marine biota serving as oxygen indicators in today's ocean. Sedimentary features similar to those found in Cretaceous strata were observed in deposits underlying Recent OMZs, where bottom-water oxygen levels, the flux of organic matter, and benthic life are well known. Their implications for constraining past bottom-water oxygenation are addressed in this review, with emphasis on comparing OMZ sediments from the Peruvian upwelling with deposits of the late Cenomanian OAE 2 from the Atlantic NW African shelf. Holocene laminated sediments were encountered at bottom-water oxygen levels of <7 μmol kg−1 under the Peruvian upwelling and <5 μmol kg−1 in California Borderland basins and the Pakistan Margin. Changes of sediment input on seasonal to decadal time scales are necessary to create laminae of different composition. However, bottom currents may shape similar textures that are difficult to discern from primary seasonal laminae in sediment cores. The millimetre-sized trace fossil Chondrites was commonly found in Cretaceous strata and Recent oxygen-depleted environments where its diameter increased with oxygen levels from 5 to 45 μmol kg−1. This ichnogenus has not been reported from Peruvian sediments but cm-sized crab burrows appeared around 10 μmol kg−1, which may indicate a minimum oxygen value for bioturbated Cretaceous strata. Organic carbon accumulation rates ranged from 0.7 and 2.8 g C cm−2 kyr−1 in laminated sections of OAE 2 in the Tarfaya Basin, Morocco, matching late Holocene accumulation rates of the majority of laminated Peruvian sediment cores under Recent oxygen levels below 5 μmol kg−1. Sediments deposited at >10 μmol kg−1 showed an inverse exponential relationship of bottom-water oxygen levels and organic carbon accumulation depicting enhanced bioirrigation and decomposition of organic matter with increased oxygen supply. In absence of seasonal laminations and under conditions of low burial diagenesis, this relationship may facilitate quantitative estimates of paleo-oxygenation under suboxic conditions. Similarities and differences between Cretaceous OAEs and late Quaternary OMZs have to be further explored to improve our understanding of sedimentary systems under hypoxic conditions.

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

Towards model-data comparison of the deglacial temperature evolution in space and time

2021 ◽  
Author(s):  
Nils Weitzel ◽  
Heather Andres ◽  
Jean-Philippe Baudouin ◽  
Oliver Bothe ◽  
Andrew Dolman ◽  
...  
Keyword(s):  
Earth System ◽  
Sources Of Information ◽  
Last Deglaciation ◽  
Model Data ◽  
Glacial Cycle ◽  
Data Comparison ◽  
Space And Time ◽  
Proxy Records ◽  
Scale Temperature ◽  
The Last Deglaciation

&lt;div&gt; &lt;p&gt;The increasing number of Earth system model simulations that try to simulate the climate during the last deglaciation (ca 20 to 10 thousand years ago) creates a demand for benchmarking against environmental proxy records synthesized for the same time period. Comparing these two data sources over a period with changing background conditions requires new methods for model-data comparison that incorporate multiple types and sources of uncertainty.&lt;/p&gt; &lt;p&gt;Natural archives of past reality are distributed sparsely and non-uniformly in space and time. Signals that can be obtained are in addition perturbed by uncertainties related to dating, the relationship between the proxy sensor and environmental fields, the archive build-up, and measurement. On the other hand, paleoclimate simulations are four-dimensional, complete, and physically consistent representations of the climate. However, they are subject to errors due to model inadequacies and sensitivity to the forcing protocol, and will not reproduce any particular history of unforced variability.&amp;#160;&lt;/p&gt; &lt;/div&gt;&lt;div&gt; &lt;p&gt;We present a method for probabilistic, multivariate quantification of the deviation between paleo-data and paleoclimate simulations that draws on the strengths of both sources of information and accounts for the aforementioned uncertainties. We compare the shape and magnitude of orbital- and millennial-scale temperature fluctuations during the last deglaciation and compute metrics of regional and global model-data mismatches. We test our algorithm with an ensemble of published simulations of the deglaciation and simulations from the ongoing PalMod project, which aims at the simulation of the last glacial cycle with comprehensive Earth system models. These are evaluated against a compilation of temperature reconstructions from multiple archives. Our work aims for a standardized model-data comparison workflow that will be used in PalMod. This workflow can be extended subsequently with additional proxy data, new simulations, and improved representations of proxy uncertainties.&amp;#160;&lt;/p&gt; &lt;/div&gt;

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.

scholarly journals Macrofaunal colonization across the Indian Margin oxygen minimum zone

2013 ◽  
Vol 10 (6) ◽  
pp. 9451-9492 ◽  
Author(s):  
L. A. Levin ◽  
A. L. McGregor ◽  
G. F. Mendoza ◽  
C. Woulds ◽  
P. Cross ◽  
...  
Keyword(s):  
Community Structure ◽  
Oxygen Concentration ◽  
Sediment Cores ◽  
Oxygen Minimum Zone ◽  
Continental Margins ◽  
Benthic Community Structure ◽  
Oxygen Minimum Zones ◽  
Minimum Zone ◽  
Oxygen Minimum ◽  
Oxygen Concentrations

Abstract. There is a growing need to understand the ability of bathyal assemblages to recover from disturbance and oxygen stress, as human activities and expanding oxygen minimum zones increasingly affect deep continental margins. The effects of a pronounced oxygen minimum zone (OMZ) on slope benthic community structure have been studied in both the Western and Eastern Arabian Sea; however, little is known about the dynamics or resilience of these benthic populations. To examine the influence of oxygen and phytodetritus on short-term settlement patterns we conducted colonization experiments along two cross-OMZ transects on the West Indian continental margin. Four colonization trays were deployed at each depth for 4 days at 542 and 802 m (16°58′ N) and for 9 days at 817 m and 1147 m (17°31′ N). Oxygen concentrations ranged from 0.9 μM (0.02 mL L−1) at 542 m to 22 μM (0.5 mL L−1) at 1147 m. All trays contained local defaunated sediments; half of the trays at each depth also contained 13C/15N-labeled phytodetritus mixed into the sediments. Sediment cores were collected between 535 m and 1140 m for analysis of background (source) macrofaunal (> 300 μm) densities and composition. Background densities ranged from 0 ind. m−2 (at 535–542 m) to 7400 ind. m−2, with maximum values on both transects at 700–800 m. Macrofaunal colonizer densities ranged from 0 ind. m−2 at 542 m, where oxygen was lowest, to average values of 142 ind. m−2 at 800 m, and 3074 ind. m−2 at 1147 m, where oxygen concentration was highest. These were equal to 4.3% and 151% of the ambient background community at 800 m and 1147 m, respectively. Community structure of settlers showed no response to the presence of phytodetritus. Increasing depth and oxygen concentration, however, significantly influenced the community composition and abundance of colonizing macrofauna. Polychaetes constituted 92.4% of the total colonizers, followed by crustaceans (4.2%), mollusks (2.5%), and echinoderms (0.8%). The majority of colonizers were found at 1147m; 88.5% of these were Capitella sp., although they were rare in the background community. Colonists at 800 and 1147 m also included ampharetid, spionid, syllid, lumbrinerid, cirratulid, cossurid and sabellid polychaetes. Consumption of δ13C/ δ15N-labeled phytodetritus was observed for macrofaunal foraminifera (too large to be colonizers) at the 542 and 802/817 m sites, and by metazoan macrofauna mainly at the deepest, better oxygenated site. Calcareous foraminifera (Uvigerina, Hoeglundina sp.), capitellid polychaetes and cumaceans were among the major consumers. These preliminary experiments suggest that bottom-water oxygen concentrations may strongly influence ecosystem services on continental margins, as reflected in rates of colonization by benthos and colonizer processing of carbon following disturbance.

scholarly journals Records of past mid-depth ventilation: Cretaceous ocean anoxic event 2 vs. Recent oxygen minimum zones

2015 ◽  
Vol 12 (4) ◽  
pp. 1169-1189 ◽  
Author(s):  
J. Schönfeld ◽  
W. Kuhnt ◽  
Z. Erdem ◽  
S. Flögel ◽  
N. Glock ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Bottom Water ◽  
Carbon Accumulation ◽  
Marine Biota ◽  
Accumulation Rates ◽  
Oxygen Minimum Zones ◽  
Oxygen Levels ◽  
Water Oxygen ◽  
Oxygen Minimum

Abstract. Present day oceans are well ventilated, with the exception of mid-depth oxygen minimum zones (OMZs) under high surface water productivity, regions of sluggish circulation, and restricted marginal basins. In the Mesozoic, however, entire oceanic basins transiently became dysoxic or anoxic. The Cretaceous ocean anoxic events (OAEs) were characterised by laminated organic-carbon rich shales and low-oxygen indicating trace fossils preserved in the sedimentary record. Yet assessments of the intensity and extent of Cretaceous near-bottom water oxygenation have been hampered by deep or long-term diagenesis and the evolution of marine biota serving as oxygen indicators in today's ocean. Sedimentary features similar to those found in Cretaceous strata were observed in deposits underlying Recent OMZs, where bottom-water oxygen levels, the flux of organic matter, and benthic life have been studied thoroughly. Their implications for constraining past bottom-water oxygenation are addressed in this review. We compared OMZ sediments from the Peruvian upwelling with deposits of the late Cenomanian OAE 2 from the north-west African shelf. Holocene laminated sediments are encountered at bottom-water oxygen levels of < 7 μmol kg−1 under the Peruvian upwelling and < 5 μmol kg−1 in California Borderland basins and the Pakistan Margin. Seasonal to decadal changes of sediment input are necessary to create laminae of different composition. However, bottom currents may shape similar textures that are difficult to discern from primary seasonal laminae. The millimetre-sized trace fossil Chondrites was commonly found in Cretaceous strata and Recent oxygen-depleted environments where its diameter increased with oxygen levels from 5 to 45 μmol kg−1. Chondrites has not been reported in Peruvian sediments but centimetre-sized crab burrows appeared around 10 μmol kg−1, which may indicate a minimum oxygen value for bioturbated Cretaceous strata. Organic carbon accumulation rates ranged from 0.7 and 2.8 g C cm−2 kyr−1 in laminated OAE 2 sections in Tarfaya Basin, Morocco, matching late Holocene accumulation rates of laminated Peruvian sediments under Recent oxygen levels below 5 μmol kg−1. Sediments deposited at > 10 μmol kg−1 showed an inverse exponential relationship of bottom-water oxygen levels and organic carbon accumulation depicting enhanced bioirrigation and decomposition of organic matter with increased oxygen supply. In the absence of seasonal laminations and under conditions of low burial diagenesis, this relationship may facilitate quantitative estimates of palaeo-oxygenation. Similarities and differences between Cretaceous OAEs and late Quaternary OMZs have to be further explored to improve our understanding of sedimentary systems under hypoxic conditions.

Dating rapid climate change in the North Atlantic during Heinrich Stadial 1

2020 ◽  
Author(s):  
Andrea Burke ◽  
Rosanna Greenop ◽  
James Rae ◽  
Rhian Rees-Owen ◽  
Paula Reimer ◽  
...  
Keyword(s):  
Climate Change ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Sediment Cores ◽  
Last Deglaciation ◽  
Large Reservoir ◽  
The North ◽  
The Last Deglaciation ◽  
The North Atlantic ◽  
Reservoir Age

&lt;p&gt;Paleoclimate records from the North Atlantic show some of the most iconic signals of abrupt climate change during the ice ages. Here we use radiocarbon as a tracer of ocean circulation and air-sea gas exchange to investigate potential mechanisms for the abrupt climate changes seen in the North Atlantic over the last deglaciation. We have created a stack of North Atlantic surface radiocarbon reservoir ages over the past 20,000 years, using new synchronized age models from thirteen sediment cores refined with thorium normalization between tie-points. This stack shows consistent and large reservoir age increases of more than 1000 years from the LGM into HS1, dropping abruptly back to approximately modern reservoir ages before the onset of the Bolling-Allerod. We use the intermediate complexity earth system model cGENIE to investigate the potential drivers of these reservoir age changes. We find that sea ice, circulation and CO&lt;sub&gt;2&lt;/sub&gt; all play important roles in setting the reservoir age. We use these coherently dated records to revisit the sequence and timing of climatic events during HS1 and the last deglaciation, and show that Laurentide Heinrich Events are a response to stadial conditions, rather than their root cause.&lt;/p&gt;

scholarly journals Seemingly divergent sea surface temperature proxy records in the central Mediterranean during the last deglaciation

2013 ◽  
Vol 9 (3) ◽  
pp. 1375-1383 ◽  
Author(s):  
M.-A. Sicre ◽  
G. Siani ◽  
D. Genty ◽  
N. Kallel ◽  
L. Essallami
Keyword(s):  
Adriatic Sea ◽  
Planktonic Foraminifera ◽  
Sea Surface ◽  
Last Deglaciation ◽  
Central Mediterranean ◽  
Proxy Record ◽  
Proxy Records ◽  
The Last Deglaciation ◽  
Temperature Proxy ◽  
Two Temperature

Abstract. Sea surface temperatures (SSTs) were reconstructed over the last 25 000 yr using alkenone paleothermometry and planktonic foraminifera assemblages from two cores of the central Mediterranean Sea: the MD04-2797 core (Siculo–Tunisian channel) and the MD90-917 core (South Adriatic Sea). Comparison of the centennial scale structure of the two temperature signals during the last deglaciation period reveals significant differences in timing and amplitude. We suggest that seasonal changes likely account for seemingly proxy record divergences during abrupt transitions from glacial to interglacial climates and for the apparent short duration of the Younger Dryas (YD) depicted by the alkenone time series, a feature that has already been stressed in earlier studies on the Mediterranean deglaciation.

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