Dissolved Oxygen Recovery in the Oxygen Minimum Zone of the Arabian Sea in Recent Decade as Observed by BGC‐Argo Floats

Liu, Tongtong; Qiu, Yun; Lin, Xinyu; Ni, Xutao; Wang, Lei; Li, Hongliang; Jing, Chunsheng

doi:10.1029/2024gl108841

Geophysical Research Letters

2024

DOI: 10.1029/2024gl108841

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Dissolved Oxygen Recovery in the Oxygen Minimum Zone of the Arabian Sea in Recent Decade as Observed by BGC‐Argo Floats

Tongtong Liu,

Yun Qiu,

Xinyu Lin

et al.

Abstract: The Arabian Sea (AS) hosts the world's thickest and most intense oxygen minimum zone (OMZ), and previous studies have documented a dramatic decline of dissolved oxygen (DO) in the northeastern AS in recent decades. In this study, using the recently released data from Biogeochemical‐Argo floats, we found a surprising trend of recovery in deoxygenation within the core region of the OMZ in the AS (ASOMZ) since 2013. The average DO concentration increased by approximately threefold, from ∼0.63 μM in 2013 to ∼1.68 … Show more

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Cited by 2 publications

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Monitoring low-oxygen-adapted subsurface phytoplankton distribution in a changing ocean

Cox,

Brewin,

Sheen

et al. 2024

Front. Mar. Sci.

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Recent decadal trends of deoxygenation in the global ocean interior have resulted in the expansion and shoaling of oxygen minimum zones (OMZs). When the OMZs upper bound nears the euphotic zone a unique community of phytoplankton, residing in extremely low light (<0.1% surface irradiance) and dissolved oxygen concentrations (<1-2 μmol kg-1), can appear. In this mini-review paper we synthesize our current understanding of the phytoplankton community that resides in an OMZ chlorophyll maximum (OMZ-CM), below the depths of the deep chlorophyll maximum found in permanently and seasonally stratified regions, and its role in OMZ biogeochemical cycles. Uncultivated basal lineages of the cyanobacterium Prochlorococcus dominate this community, forming an OMZ-CM that can contribute to integrated stocks of chlorophyll a, in some cases with a similar magnitude to the deep chlorophyll maximum. Photosynthesis by Prochlorococcus in the OMZ-CM provides a significant source of oxygen, that fuels the aerobic oxidation of nitrite and organic matter, impacting elemental biogeochemical cycling, including that of carbon and nitrogen. Yet, on a global scale, there is a lack of understanding and quantification of the spatial distribution of these OMZ-CM, their stocks of phytoplankton, their influence on fluxes of carbon and nitrogen, and how these may respond to climate change. Monitoring the dynamics of the OMZ-CM and biogeochemical cycles in OMZs is challenging, and requires a multidisciplinary approach, combining ship-based observations with autonomous platforms, satellite data, and conceptual models. Only then can the implications of enhanced deoxygenation on the future marine ecosystem be understood.

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Monitoring low-oxygen-adapted subsurface phytoplankton distribution in a changing ocean

Cox,

Brewin,

Sheen

et al. 2024

Front. Mar. Sci.

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Sedimentary organic matter signature hints at the phytoplankton-driven biological carbon pump in the central Arabian Sea

Pandey,

Biswas,

Birgel

et al. 2024

Biogeosciences

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Abstract. The central Arabian Sea, a unique tropical basin, is profoundly impacted by monsoon wind reversal affecting its surface circulation and biogeochemistry. Phytoplankton blooms associated with high biological productivity and particle flux occur in the northern part of the central Arabian Sea due to summer-monsoon-induced open-ocean upwelling and winter convection. The core oxygen minimum zone (OMZ) at intermediate water depths is another important feature of the northern central Arabian Sea and fades southward. In this study, we attempt to interlink how these factors collectively impact phytodetrital export to the sediment. Short sediment core-top (1 cm) samples representing the recent particle flux signatures were analysed from five locations (21 to 11° N; 64° E) in the central Arabian Sea. Previously, we used core-top (0–0.5 cm) samples and observed a trend between diatom frustule abundance and diversity with bulk sedimentary parameters indicating a spatial variability in phytodetrital export to the sediment. To verify this observation further, lipid biomarkers of key phytoplankton groups and a sea surface temperature (SST) proxy have been analysed in addition to diatom frustules. The C37 alkenone-based SST proxy indicated cooler SST (27.6 ± 0.25 °C) in the north (21–15° N) mostly due to upwelling (summer) and convective mixing (winter). Warmer SSTs (+0.4 °C) are measured in the south, which usually remains nutrient-poor. This trend was consistent with satellite-derived average SST values (2017–2020). Lipid biomarker analysis suggests that dinoflagellates were likely to be the highest contributor, as indicated by dinosterol and its degradative product dinostanol, followed by brassicasterol and C37 alkenone, likely representing diatoms and coccolithophores, respectively. The north, which largely experiences periodic phytoplankton blooms and is influenced by the thick OMZ, revealed the highest contents of organic matter, diatom frustules (diversity and abundance), dominated by large, thickly silicified cells (e.g. Coscinodiscus and Rhizosolenia) and phytoplankton lipid biomarkers, as well as lower contents of zooplankton biomarkers (cholesterol and cholestanol). In contrast, relatively smaller chain-forming centric (e.g. Thalassiosira) and pennate (e.g. Pseudo-nitzschia, Nitzschia, Thalassionema) diatom frustules along with lower phytoplankton lipid biomarker contents were found in the south, where zooplankton biomarkers and silicious radiolarians were more abundant. The possible impacts of the OMZ on particle flux related to the phytoplankton community, including zooplankton grazing and other factors, have been discussed.

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Dissolved Oxygen Recovery in the Oxygen Minimum Zone of the Arabian Sea in Recent Decade as Observed by BGC‐Argo Floats

Cited by 2 publications

References 78 publications

Monitoring low-oxygen-adapted subsurface phytoplankton distribution in a changing ocean

Monitoring low-oxygen-adapted subsurface phytoplankton distribution in a changing ocean

Sedimentary organic matter signature hints at the phytoplankton-driven biological carbon pump in the central Arabian Sea

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