Controls on organic matter distribution in oxygen minimum zone sediments from the continental slope off western India

Kurian, Siby; Kessarkar, Pratima M.; Rao, V. Purnachandra; Reshma, K.; Sarkar, Amit; Pattan, J.N.; Naqvi, S.W.A.

doi:10.1016/j.jmarsys.2018.09.003

Cited by 9 publications

(4 citation statements)

References 44 publications

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“…It is certainly clear that faunal digestive processes are recorded in the composition of organic matter deposited across the margins (e.g., Jeffreys et al, 2009;Smallwood et al, 1999). In summary, oxygen-dependent cross-margin variability in benthic communities and ecosystem function (feeding, bioturbation, and bio-irrigation) may be important contributors to the role that oxygen exposure plays in controlling organic carbon distribution and burial across Arabian Sea margins, although other factors, most notably hydrodynamic processes, are also important (e.g., Cowie, 2005;Koho et al, 2013;Kurian et al, 2018).…”

Section: Benthic Ecosystem Functionmentioning

confidence: 99%

Reviews and syntheses: Present, past, and future of the oxygen minimum zone in the northern Indian Ocean

et al. 2020

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Abstract. Decreasing concentrations of dissolved oxygen in the ocean are considered one of the main threats to marine ecosystems as they jeopardize the growth of higher organisms. They also alter the marine nitrogen cycle, which is strongly bound to the carbon cycle and climate. While higher organisms in general start to suffer from oxygen concentrations < ∼ 63 µM (hypoxia), the marine nitrogen cycle responds to oxygen concentration below a threshold of about 20 µM (microbial hypoxia), whereas anoxic processes dominate the nitrogen cycle at oxygen concentrations of < ∼ 0.05 µM (functional anoxia). The Arabian Sea and the Bay of Bengal are home to approximately 21 % of the total volume of ocean waters revealing microbial hypoxia. While in the Arabian Sea this oxygen minimum zone (OMZ) is also functionally anoxic, the Bay of Bengal OMZ seems to be on the verge of becoming so. Even though there are a few isolated reports on the occurrence of anoxia prior to 1960, anoxic events have so far not been reported from the open northern Indian Ocean (i.e., other than on shelves) during the last 60 years. Maintenance of functional anoxia in the Arabian Sea OMZ with oxygen concentrations ranging between > 0 and ∼ 0.05 µM is highly extraordinary considering that the monsoon reverses the surface ocean circulation twice a year and turns vast areas of the Arabian Sea from an oligotrophic oceanic desert into one of the most productive regions of the oceans within a few weeks. Thus, the comparably low variability of oxygen concentration in the OMZ implies stable balances between the physical oxygen supply and the biological oxygen consumption, which includes negative feedback mechanisms such as reducing oxygen consumption at decreasing oxygen concentrations (e.g., reduced respiration). Lower biological oxygen consumption is also assumed to be responsible for a less intense OMZ in the Bay of Bengal. According to numerical model results, a decreasing physical oxygen supply via the inflow of water masses from the south intensified the Arabian Sea OMZ during the last 6000 years, whereas a reduced oxygen supply via the inflow of Persian Gulf Water from the north intensifies the OMZ today in response to global warming. The first is supported by data derived from the sedimentary records, and the latter concurs with observations of decreasing oxygen concentrations and a spreading of functional anoxia during the last decades in the Arabian Sea. In the Arabian Sea decreasing oxygen concentrations seem to have initiated a regime shift within the pelagic ecosystem structure, and this trend is also seen in benthic ecosystems. Consequences for biogeochemical cycles are as yet unknown, which, in addition to the poor representation of mesoscale features in global Earth system models, reduces the reliability of estimates of the future OMZ development in the northern Indian Ocean.

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Section: Benthic Ecosystem Functionmentioning

confidence: 99%

Reviews and syntheses: Present, past, and future of the oxygen minimum zone in the northern Indian Ocean

et al. 2020

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“…It is certainly clear that faunal digestive processes are recorded in the composition of organic matter deposited across the margins (e.g., Jeffreys et al, 2009;Smallwood et al, 1999). In summary, oxygen-dependent crossmargin variability in benthic communities and ecosystem function (feeding, bioturbation and bioirrigation etc) may be important contributors to the role that oxygen exposure plays in controlling organic carbon distribution and burial across Arabian Sea margins, although other factors, most notably hydrodynamic processes, are also important (e.g., Cowie, 2005;Cowie et al, 2009b;Koho et al, 2013;Kurian et al, 2018).…”

Section: Benthic Ecosystem Functionmentioning

confidence: 99%

Present past and future of the OMZ in the northern Indian Ocean

Rixen¹,

Cowie²,

Gaye³

et al. 2020

Preprint

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Abstract. Decreasing concentrations of dissolved oxygen and the resulting expansion of anaerobic ecosystems is a major threat to marine ecosystem services because it favors the formation of greenhouse gases such as methane, endangers the growth of economically important species, and increases the loss nitrate. Nitrate is one of the potential primary nutrients, which availability controls the marine productivity. The Arabian Sea and the Bay of Bengal are home to ~ 59 % of the Earth's marine sediments exposed to severe oxygen depletion and approximately 21 % of the total volume of oxygen-depleted waters (oxygen minimum zones, OMZs). The balance between physical oxygen supply and the biological oxygen consumption controlled the oxygen concentrations. In the Arabian Sea and most likely also in the Bay of Bengal the supply of oxygen sustained by mixing and advection associated with mesoscale eddies compensated the biological oxygen consumption. These steady states maintain low (hypoxic) oxygen concentrations allowing the competition between anaerobic and aerobic processes. However, due to slightly higher oxygen concentrations, the aerobic nitrite oxidization inhibits the anaerobic nitrite reduction and thus denitrification (the reduction of nitrate to N2) to become significant in the Bay of Bengal. A feedback mechanism caused by the negative influence of decreasing oxygen concentrations on the biological oxygen demand helped to maintain these steady states. Furthermore, it might have also counteracted a reduced physical oxygen supply into the Arabian Sea caused by climate-driven changes in the ocean's circulation during the last 6000 years. However, due to human-induced global changes, the OMZs in Arabian Sea and the Bay of Bengal intensified and expanded, which included also the occurrence of anoxic events on the Indian shelf. This affects benthic ecosystems, and in the Arabian Sea it seems to have initiated a regime shift within the pelagic ecosystem structure. Consequences for biogeochemical cycles are unknown, which, in addition to the poor representation of mesoscale features reduces the reliability of predictions of the future OMZ development in the northern Indian Ocean.

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“…After 55 days, DO concentration showed an upward trend, which resulted from the reduction by the reducing substances. As depicted in Figure 4d, injecting oxygen enriched water could effectively improve DO concentration of the sludge-water interface [36], whereas injecting ordinary water could not inhibit the reduction of the DO concentration.…”

Section: Characteristic Change Of Sedimentmentioning

confidence: 99%

Biological Reduction of Organic Matter in Buji River Sediment (Shenzhen, China) with Artificial Oxygenation

Che

Jin

Zhou

et al. 2020

Water

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In this work, artificial oxygenation treatment (pure oxygen aeration or oxygen enriched water injection) combined with the introduction of exogenous microorganisms was employed to purify urban river sediment for the first time. Results showed that the developed in situ remediation strategy could increase the dissolved oxygen (DO) concentration and oxidation-reduction potential (ORP) value of the sediments. Benefiting from the increase of DO concentration, the bacterial diversity was enhanced. The highest removal efficiencies of organic matter were 18.4% and 22.3% through pure oxygen aeration and oxygen enriched water injection, respectively. More importantly, overlying water quality was not affected. By comparison, oxygen enriched water injection treatment could achieve better performance on sediment purification. Introducing exogenous microorganisms further reduced the organic matter content of the sediment. In short, the current work not only proposed a promising strategy for controlling urban river sediment pollution, but also provided novel insight for the understanding of river sediment containing highly concentrated organic matter.

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Controls on organic matter distribution in oxygen minimum zone sediments from the continental slope off western India

Cited by 9 publications

References 44 publications

Reviews and syntheses: Present, past, and future of the oxygen minimum zone in the northern Indian Ocean

Reviews and syntheses: Present, past, and future of the oxygen minimum zone in the northern Indian Ocean

Present past and future of the OMZ in the northern Indian Ocean

Biological Reduction of Organic Matter in Buji River Sediment (Shenzhen, China) with Artificial Oxygenation

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