Holocene strengthening of the Oxygen Minimum Zone in the northwestern Arabian Sea linked to changes in intermediate water circulation or Indian monsoon intensity?

Das, Moumita; Singh, Raj K.; Gupta, Anil K.; Bhaumik, Ajoy K.

doi:10.1016/j.palaeo.2016.10.035

Cited by 42 publications

(48 citation statements)

References 62 publications

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“…However, the simulated OMZ in the Arabian Sea is too weak in this very coarse resolution model, raising concern about its reliability in the region. In the Holocene, large-scale ventilation changes may have played an important role together with the fluctuations in monsoon intensity as suggested by recent studies (Rixen et al, 2014;Gaye et al, submitted;Das et al, 2017). For instance, recent paleo-reconstructions by Das et al (2017) suggest an intensification of the Arabian Sea OMZ from the middle to late Holocene despite a weakening of the SWM winds.…”

Section: Implications For Paleo-studiesmentioning

confidence: 86%

“…Oxygen and nitrate initial and boundary conditions are derived from Garcia et al (2010a, b) dataset. The atmospheric bound-ary conditions for heat and freshwater fluxes are based on the Comprehensive Ocean-Atmosphere Data Set (COADS; da Silva et al, 1994). We applied surface restoring to COADS-observed surface temperatures and salinities using kinematic flux corrections described in Barnier et al (1995).…”

Section: Experimental Designmentioning

confidence: 99%

“…Located near major coastal upwelling systems, the OMZs are indeed highly vulnerable to changes in alongshore winds. In most eastern boundary upwelling systems as well as in the western Arabian Sea, upwelling-favorable wind intensification has been shown to occur under warming scenarios (Wang et al, 2015;deCastro et al, 2016). Bakun (1990) has linked this to increased land-sea thermal gradient under warmer climates, strengthening the land-sea pressure gradient and hence alongshore winds.…”

Section: Introductionmentioning

confidence: 99%

“…This high productivity in conjunction with a sluggish circulation sustains the world's thickest OMZ, responsible for up to 40 % of global pelagic denitrification despite occupying less than 2 % of the World Ocean area (Bange et al, 2005). Future climate projections suggest that Indian summer monsoon may intensify in the future under a warmer climate (e.g., Wang et al, 2013;Sandeep and Ajayamohan, 2015;Praveen et al, 2016;deCastro et al, 2016). Praveen et al (2016) found that the future upwelling intensification will affect essentially the coast of Oman.…”

Section: Introductionmentioning

confidence: 99%

“…Praveen et al (2016) found that the future upwelling intensification will affect essentially the coast of Oman. Using an ensemble of global and regional model simulations for the 21st century, deCastro et al (2016) show a strengthening of the Somali coastal upwelling that increases with latitude. Furthermore, these authors show that the intensification of upwelling in the western Arabian Sea is even higher than what is predicted for the eastern boundary upwelling systems.…”

Section: Introductionmentioning

confidence: 99%

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Intensification and deepening of the Arabian Sea oxygen minimum zone in response to increase in Indian monsoon wind intensity

2018

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Abstract. The decline in oxygen supply to the ocean associated with global warming is expected to expand oxygen minimum zones (OMZs). This global trend can be attenuated or amplified by regional processes. In the Arabian Sea, the world's thickest OMZ is highly vulnerable to changes in the Indian monsoon wind. Evidence from paleorecords and future climate projections indicates strong variations of the Indian monsoon wind intensity over climatic timescales. Yet, the response of the OMZ to these wind changes remains poorly understood and its amplitude and timescale unexplored. Here, we investigate the impacts of perturbations in Indian monsoon wind intensity (from −50 to +50 %) on the size and intensity of the Arabian Sea OMZ, and examine the biogeochemical and ecological implications of these changes. To this end, we conducted a series of eddy-resolving simulations of the Arabian Sea using the Regional Ocean Modeling System (ROMS) coupled to a nitrogen-based nutrient-phytoplankton-zooplanktondetritus (NPZD) ecosystem model that includes a representation of the O 2 cycle. We show that the Arabian Sea productivity increases and its OMZ expands and deepens in response to monsoon wind intensification. These responses are dominated by the perturbation of the summer monsoon wind, whereas the changes in the winter monsoon wind play a secondary role. While the productivity responds quickly and nearly linearly to wind increase (i.e., on a timescale of years), the OMZ response is much slower (i.e., a timescale of decades). Our analysis reveals that the OMZ expansion at depth is driven by increased oxygen biological consumption, whereas its surface weakening is induced by increased ventilation. The enhanced ventilation favors episodic intrusions of oxic waters in the lower epipelagic zone (100-200 m) of the western and central Arabian Sea, leading to intermittent expansions of marine habitats and a more frequent alternation of hypoxic and oxic conditions there. The increased productivity and deepening of the OMZ also lead to a strong intensification of denitrification at depth, resulting in a substantial amplification of fixed nitrogen depletion in the Arabian Sea. We conclude that changes in the Indian monsoon can affect, on longer timescales, the large-scale biogeochemical cycles of nitrogen and carbon, with a positive feedback on climate change in the case of stronger winds. Additional potential changes in large-scale ocean ventilation and stratification may affect the sensitivity of the Arabian Sea OMZ to monsoon intensification.

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Section: Implications For Paleo-studiesmentioning

confidence: 86%

Section: Experimental Designmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Intensification and deepening of the Arabian Sea oxygen minimum zone in response to increase in Indian monsoon wind intensity

2018

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Linkages between East China Sea Deep-sea Oxygenation and the Variability of the East Asian Summer Monsoon and Kuroshio Current over last 400,000 years

Vats

Singh

Das

et al. 2021

Preprint

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The East China Sea (ECS) seasonally receives a high organic input due to the terrestrial organic matter influx, which is controlled by the East Asian Summer Monsoon (EASM), and the increased productivity driven by upwelling of the subsurface Kuroshio Current (KC). Changes in benthic foraminiferal assemblage composition in combination with paleoceanographic proxy data (CaCO3 (%), TOC (%), δ 13 Cpf, and δ 18 Obf) are used to reconstruct bottom water oxygenation and organic export flux variability over the last 400 kyr in the ECS. Multivariate analyses of benthic foraminiferal census data identified six biofacies characteristic of varying environmental conditions. These results suggest that enhanced EASM precipitation and KC upwelling directly influenced organic export flux and bottom water oxygen content in the ECS. The ECS bottom water was suboxic during Marine Isotope Stage (MIS) 11 to 8; suboxic to dysoxic between MIS 7 and 6, strongly dysoxic between mid-MIS 5 and 4, and exhibited high variability between MIS 3 and 1. Spectral analysis of relative abundances of representative genera Quinqueloculina (oxic), Bulimina (suboxic), and Globobulimina (dysoxic) reveals a robust 23 kyr signal, which we attribute to precessionally-paced changes in surface productivity and bottom water oxygenation related to KC variability over the past 400 kyr.

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Multiproxy analysis constraining climatic control over the Cenozoic depositional history of Kachchh, Western India

Chaudhuri

Srivastava

et al. 2022

Geological Journal

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A well‐developed 86 m‐thick Cenozoic sedimentary succession in the Matanomadh area, western Kachchh, was studied to assess the stratigraphic positions of different units, ascertain depositional environments, and the degree of climatic controls over time depositional processes. Age‐diagnostic nannoplankton species Cyclicargolithus floridanus (46.29–12.1 Ma), Reticulofenestra dictyoda (53–30.8 Ma), Reticulofenestra minuta (50.5–2.59 Ma) and foraminiferal species, for example, Orbulinoides beckmanni (41–39.5 Ma) found across studied units envisage the stratigraphic age and palaeoenvironment. CaO with strong negative elemental correlation, binary/ternary discriminant tectonic and depositional regimes cross‐plot from units indicate the biogenic origin of limestones and shales were formed in typical passive, marginal, shallow littoral settings with plausible detritus influx from Deccan basaltic provenance. Total organic carbon with TE‐REE respectively connotes a sedimentation process in a nearly consistent open shallow marine, locally transient semi‐restricted marginal basin in a tropical‐equatorial region. Furthermore, principal component analysis (PCA) of weathering indices based on elemental abundance and X‐ray diffraction data of clays deterministically suggest with empirical relation between humid tropical climate‐induced weathering and fluctuant terrestrial influx. Palaeoredox indices with biological data demonstrate localized redox‐stratified conditions. However, coherent signatures of the global events such as Eocene Thermal Maximum‐2, Middle Eocene Climatic Optimum, and Mid Miocene Climatic Optimum can be traced and validated by synthesizing geochemical data for direct/indirect estimation of sediment routing, rainfall (αAlMg and αAlCa) and climate proxies (PCA), productivity indices (Babio, Cubio and Nibio), and localized periodic oxic‐dysoxic environment (V/Cr, U/Th, Ni/Co) from core samples.

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Holocene strengthening of the Oxygen Minimum Zone in the northwestern Arabian Sea linked to changes in intermediate water circulation or Indian monsoon intensity?

Cited by 42 publications

References 62 publications

Intensification and deepening of the Arabian Sea oxygen minimum zone in response to increase in Indian monsoon wind intensity

Intensification and deepening of the Arabian Sea oxygen minimum zone in response to increase in Indian monsoon wind intensity

Linkages between East China Sea Deep-sea Oxygenation and the Variability of the East Asian Summer Monsoon and Kuroshio Current over last 400,000 years

Multiproxy analysis constraining climatic control over the Cenozoic depositional history of Kachchh, Western India

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