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I/Ca in epifaunal benthic foraminifera: A semi-quantitative proxy for bottom water oxygen in a multi-proxy compilation for glacial ocean deoxygenation

Abstract.

"The decline in dissolved oxygen in global oceans (ocean deoxygenation) is a potential consequence of global warming which may have important impacts on ocean biogeochemistry and marine ecosystems. Current climate models do not agree on the trajectory of future deoxygenation on different timescales, in part due to uncertainties in the complex, linked effects of changes in ocean circulation, productivity and organic matter respiration. [...]"

Source: Earth and Planetary Science Letters
Authors: Wanyi Lu et al.
DOI: 10.1016/j.epsl.2019.116055


Neritic ecosystem response to Oceanic Anoxic Event 2 in the Cretaceous Western Interior Seaway, USA

Abstract.

"Cretaceous oceanic anoxic events (OAEs) were periods of geologically short (<1 million years) global change characterized by elevated temperatures, changes in ocean biogeochemistry, ecological turnover, and the global-scale deposition of black shales. After decades of OAE research, the intensity and spatiotemporal heterogeneity of ocean anoxia and its direct effects on marine ecology remain areas of active study. We present high-resolution organic geochemical and foraminiferal records from the western margin of the Western Interior Seaway (WIS) during the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE2, ~94 Ma) that indicate reorganization of a neritic ecosystem in response to sea-level rise, and dynamic changes in redox conditions that were likely driven by enhanced marine productivity. [...]"

Source: Palaeogeography, Palaeoclimatology, Palaeoecology
Authors: F. Garrett Boudinot et al.
DOI: 10.1016/j.palaeo.2020.109673

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Organic Heterogeneities in Foraminiferal Calcite Traced Through the Distribution of N, S, and I Measured With NanoSIMS:

A New Challenge for Element-Ratio-Based Paleoproxies?

 

Abstract.

"Oceanic oxygen decline due to anthropogenic climate change is a matter of growing concern. A quantitative oxygen proxy is highly desirable in order to identify and monitor recent dynamics as well as to reconstruct pre-Anthropocene changes in amplitude and extension of oxygen depletion. Geochemical proxies like foraminiferal I/Ca ratios seem to be promising redox proxies. [...]"

Source: Frontiers in Earth Science
Authors: Nicolaas Glock et al.
DOI: 10.3389/feart.2019.00175

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Nitrogen isotope evidence for expanded ocean suboxia in the early Cenozoic

Abstract.

"The million-year variability of the marine nitrogen cycle is poorly understood. Before 57 million years (Ma) ago, the 15N/14N ratio (δ15N) of foraminifera shell-bound organic matter from three sediment cores was high, indicating expanded water column suboxia and denitrification. [...]"

Source: Science
Authors: Emma R. Kast et al.
DOI: 10.1126/science.aau5784

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Metabolic preference of nitrate over oxygen as an electron acceptor in foraminifera from the Peruvian oxygen minimum zone

Abstract.

"Benthic foraminifera populate a diverse range of marine habitats. Their ability to use alternative electron acceptors—nitrate (NO3−) or oxygen (O2)—makes them important mediators of benthic nitrogen cycling. Nevertheless, the metabolic scaling of the two alternative respiration pathways and the environmental determinants of foraminiferal denitrification rates are yet unknown. We measured denitrification and O2 respiration rates for 10 benthic foraminifer species sampled in the Peruvian oxygen minimum zone (OMZ). [...]"

Source: PNAS
Authors: Nicolaas Glock et al.
DOI: 10.1073/pnas.1813887116

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Mid-Holocene deepening of the Southeast Pacific oxycline

Abstract.

"This study presents new high resolution sedimentary δ15N records from piston cores collected within and outside the present-day eastern south Pacific oxygen minimum zone along a latitudinal transect from 3.5°S to 15°S. Radiocarbon dating of foraminifera and organic matter show that the cores cover the Holocene and the last deglaciation with high sedimentation rate allowing interpretations at millennial to centennial timescale. [...]"

Source: Global and Planetary Change
Authors: Elfi Mollier-Vogel et al.
DOI: 10.1016/j.gloplacha.2018.10.020

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Deep-Water Dynamics in the Subpolar North Atlantic at the End of the Quaternary

Abstract.

"In the subpolar North Atlantic, four sediment cores were taken. All of them were suitable for reconstructing the dynamics of the meridional overturning circulation in the late Quaternary. Stratigraphy of the cores was performed by carbonate analyses, study of planktonic foraminifera, and oxygen isotopic composition in Neogloboquadrina pachyderma sin. Study of benthonic foraminifera assemblages has shown significant differences in the deep-water dynamics in the late Quaternary related to water exchange between the North Atlantic and Arctic seas. [...]"

Source: Oceanology
Authors: N.P. Lukashina
DOI: 10.1134/S0001

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Last interglacial ocean changes in the Bahamas: climate teleconnections between low and high latitudes

Abstract.

"Paleorecords and modeling studies suggest that instabilities in the Atlantic Meridional Overturning Circulation (AMOC) strongly affect the low-latitude climate, namely via feedbacks on the Atlantic Intertropical Convergence Zone (ITCZ). Despite the pronounced millennial-scale overturning and climatic variability documented in the subpolar North Atlantic during the last interglacial period (MIS 5e), studies on cross-latitudinal teleconnections remain very limited. This precludes a full understanding of the mechanisms controlling subtropical climate evolution across the last warm cycle. [...]"

Source: Climate of the Past
Authors: Anastasia Zhuravleva and Henning A. Bauch
DOI: 10.5194/cp-14-1361-2018

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A Novel Eukaryotic Denitrification Pathway in Foraminifera

Abstract.

"Benthic foraminifera are unicellular eukaryotes inhabiting sediments of aquatic environments. Several species were shown to store and use nitrate for complete denitrification, a unique energy metabolism among eukaryotes. The population of benthic foraminifera reaches high densities in oxygen-depleted marine habitats, where they play a key role in the marine nitrogen cycle. However, the mechanisms of denitrification in foraminifera are still unknown, and the possibility of a contribution of associated bacteria is debated. Here, we present evidence for a novel eukaryotic denitrification pathway that is encoded in foraminiferal genomes. [...]"

Source: Current Biology
Authors: Christian Woehle et al.
DOI: 10.1016/j.cub.2018.06.027

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How nutrients are removed in oxygen-depleted regions of the ocean

"In the course of global climate change, scientists are observing the increase of low-oxygen areas in the ocean, also termed oxygen minimum zones (OMZs). Large-scale OMZs exist, for example, in the Pacific off the coast of South America or in the Indian Ocean. Since little to no oxygen is present in these regions - depending on the depth of the water - organisms whose metabolisms is independent of oxygen have a distinct advantage. These organisms include some representatives of the foraminifera: unicellular, shell-forming microorganisms, which have a nucleus and thus belong to the eukaryotes. Their life style involves a particular metabolic pathway termed anaerobic respiration. In the absence of oxygen, they convert nitrate present in the water into molecular nitrogen. [...]"

Source: Kiel University

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