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Geochemistry of sediments in contact with oxygen minimum zone of the eastern Arabian Sea: Proxy for palaeo-studies

Abstract. 

"The Arabian Sea encompasses oxygen minimum zone with denitrifying conditions. For the present study, sediments were collected across three transects off Goa transect (GT), Mangalore transect (MT) and Kochi transect (KT) in contact with water column dissolved oxygen (DO) range of 1.4–118.0 µM. Sediments were investigated for texture, clay mineralogy, total organic carbon (Corg), total nitrogen, CaCO3, δ15N, δ13C, metal content to infer their distribution with changing DO and their use as possible palaeo-proxies. The Corg (0.9–8.6%) is largely marine and δ15N from GT and MT preserves signatures of higher water column denitrification. [...]". 

 

Source: Journal of Earth System Science 

Authors: Pratima M. Kessarkar et al. 

DOI: https://doi.org/10.1007/s12040-022-01823-2 

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Anaerobic methane oxidation in a coastal oxygen minimum zone: spatial and temporal dynamics

Abstract. 

"Coastal waters are a major source of marine methane to the atmosphere. Particularly high concentrations of this potent greenhouse gas are found in anoxic waters, but it remains unclear if and to what extent anaerobic methanotrophs mitigate the methane flux. Here we investigate the long-term dynamics in methanotrophic activity and the methanotroph community in the coastal oxygen minimum zone (OMZ) of Golfo Dulce, Costa Rica, combining biogeochemical analyses, experimental incubations and 16S rRNA gene sequencing over 3 consecutive years. [...]".

 

Source: Environmental Microbiology

Authors: Herdís G. R. Steinsdóttir et al. 

DOI: https://doi.org/10.1111/1462-2920.16003

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Sensitivity of Global Ocean Deoxygenation to Vertical and Isopycnal Mixing in an Ocean Biogeochemistry Model

Abstract. 

"Large-scale loss of oxygen under global warming is termed “ocean deoxygenation” and is caused by the imbalance between physical supply and biological consumption of oxygen in the ocean interior. Significant progress has been made in the theoretical understanding of ocean deoxygenation; however, many questions remain unresolved. The oxygen change in the tropical thermocline is poorly understood, with diverging projections among different models. Physical oxygen supply is controlled by a suite of processes that transport oxygen-rich surface waters into the interior ocean, which is expected to weaken due to increasing stratification under global warming. [...]".

 

Source: Wiley Online Library

Authors: Taka Ito et al.

DOI: https://doi.org/10.1029/2021GB007151

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Marine anoxia as a trigger for the largest Phanerozoic positive carbon isotope excursion: Evidence from carbonate barium isotope record

Abstract. 

"The mid-Ludfordian Lau carbon isotope excursion (Lau CIE) represents the largest positive carbon isotope excursion in the Phanerozoic (~9‰), coincident with the biodiversity loss of many marine animal clades. Two main explanations for the Lau CIE are enhanced organic carbon burial via increased marine productivity and preservation-driven expansion of anoxia. While these two explanations are not mutually exclusive, the main driver of Lau CIE is yet to be constrained. Here, we resolve this longstanding debate using barium isotopes (δ138 Ba) of marine carbonates deposited across the Lau CIE. [...]". 

 

Source: Science Direct

Authors: Feifei Zhang et al.

DOI: https://doi.org/10.1016/j.epsl.2022.117421

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Temperature and oxygen supply shape the demersal community in a tropical Oxygen Minimum Zone

Abstract. 

"The organisms that inhabit Oxygen Minimum Zones (OMZ) have specialized adaptations that allow them to survive within a very narrow range of environmental conditions. Consequently, even small environmental perturbations can result in local species distribution shifts that alter ecosystem trophodynamics. Here, we examined the effect of changing sea water temperatures and oxygen levels on the physiological performance and metabolic traits of the species forming marine demersal communities along the OMZ margins in the Costa Rican Pacific. The strong temperature and oxygen gradients along this OMZ margin provide a “natural experiment” to explore the effects of warming and hypoxia on marine demersal communities. [...]".

 

Source: Environmental Biology of Fishes

Authors: Tayler M. Clarke et al. 

DOI: https://doi.org/10.1007/s10641-022-01256-2

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Mid-Holocene intensification of the oxygen minimum zone in the northeastern Arabian Sea

Abstract. 

"The Arabian Sea is characterized by a strong Oxygen Minimum Zone (OMZ) bearing sub-oxic conditions at the intermediate water depth. We analyzed a sediment core near the upper margin of OMZ (174 m water depth) from offshore Saurashtra, northeastern (NE) Arabian Sea to reconstruct multi-proxy biogeochemical response in the area during the Early-Middle Holocene (∼10–4 ka before present). The results indicate lower foraminiferal productivity (both benthic and planktic) and weak sub-surface denitrification causing mild OMZ conditions at the study site during the early Holocene (∼10–8 ka). Subsequently, an increased foraminiferal productivity and sub-surface (both the water column and sediment) denitrification in the area led to intensified OMZ conditions during the mid-Holocene (after ∼8 ka). [...]".

 

Source: Science Direct

Authors: Syed Azharuddin et al. 

DOI: https://doi.org/10.1016/j.jseaes.2022.105094

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Uranium isotope evidence for extensive shallow water anoxia in the early Tonian oceans

Abstract. 

"The Earth's redox evolution has been commonly assumed to have played a key role in shaping the evolutionary history of the biosphere. However, whether and how shifts in marine redox conditions are linked to key biotic events – foremost the rise of animals and the ecological expansion of eukaryotic algae in the late Proterozoic oceans – remains heavily debated. Our current picture of global marine redox evolution during this critical interval is incomplete. This is particularly the case for the Tonian Period (∼1.0 to ∼0.717 Ga), when animals may have diverged and when eukaryotic algae began their rise in ecological importance. Here, we present new uranium isotope (U) measurements from Tonian carbonates to fill this outstanding gap. [...]".

 

Source: Science Direct 

Authors: Feifei Zhang et al.

DOI: https://doi.org/10.1016/j.epsl.2022.117437

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Chromium isotope evidence for oxygenation events in the Ediacaran ocean

Abstract. 

"Pulses of the Ediacaran ocean oxygenation were inferred from strong enrichments of redox-sensitive elements (RSEs; particularly Mo, V, U, Re) and negative pyritesulfur isotopes (δ34Spy) in black shales of the Doushantuo Formation in South China. These oceanic oxygenation events (OOEs) have been challenged by the lack of comparable RSE enrichments in correlative strata of northwestern Canada. Here we report four positive chromium isotope (δ53Cr) excursions with peak values (+0.79 ± 0.03‰ to +1.45 ± 0.06‰; 2SD) close to the average δ53Cr value of the modern ocean (+1.0 ± 0.3‰) at the intervals of OOEs, which are separated by low δ53Cr values close to that of the bulk silicate Earth (BSE, −0.124 ± 0.101‰). The positive δ53Cr excursions could be explained by episodic input of oxygenated water from the open ocean to the restricted Nanhua basin, or pulses of ocean oxygenation during the Ediacaran-early Cambrian. The two interpretations can explain the majority of the geochemical data available from the Wuhe section, but both have limitations. [...]". 

 

Source: Science Direct

Authors: Dongtao Xu et al.

DOI: https://doi.org/10.1016/j.gca.2022.02.019

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Evidence of hypoxia in the eastern coast of the Gulf of California as induced by stable nitrogen isotopes in surface sediments

Abstract. 

"The Gulf of California is a highly biodiverse marine basin located in the northeast Mexican Pacific Ocean. In the past three decades, this basin has experienced increased hypoxia in shallow waters, which threatens its coastal ecosystems. The aim of this study is to analyze δ15N and δ13C isotopes of organic matter in coastal sediments to characterize sources of primary production and shifts in biogeochemical processes that reflect increasing oxygen deficiency in the shallow coast of the eastern Gulf of California. Surface sediments samples were collected from 8 to 47 m deep along the coastal margin of Sinaloa and Sonora. This region is characterized by the development of anthropogenic activities, which could be the main source of organic matter evidenced in the marine environment. [...]". 

 

Source: Science Direct

Authors: Alberto Sánchez et al. 

DOI: https://doi.org/10.1016/j.csr.2022.104716

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