Dissolved iron cycling in the Arabian Sea and sub-tropical gyre region of the Indian Ocean

Chinni, Venkatesh; Singh, Sunil Kumar

doi:10.1016/j.gca.2021.10.026

Cited by 26 publications

(15 citation statements)

References 107 publications

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“…In calculating the nutrient concentration‐based N 2 fixation rate, we are unlikely to have fully accounted for this local P excess (i.e., low N* input) in our P and N budgets, leading to an underestimation of N 2 fixation. Upper ocean dissolved iron measurements from across the Indian basin, albeit limited, reveal generally higher concentrations in the northern versus southern basin (0.1–1.3 nM vs. 0.05–0.5 nM) and near the south‐western and south‐eastern margins versus the south‐central basin (reaching 1.4 vs. 0.2 nM) (Chinni & Singh, 2022; Grand, Measures, Hatta, Hiscock, et al., 2015; Grand, Measures, Hatta, Morton, et al., 2015; Nishioka et al., 2013; Shiozaki et al., 2014; Siefert et al., 1999). Dissolved iron concentrations measured during the WOCE IO5 and IO6 expeditions that sampled the Agulhas region were high, >1 nM at the shelf and >0.3 nM in the current, and attributed to the entrainment of sedimentary iron by the Agulhas Current, augmented by local iron deposition (Grand, Measures, Hatta, Morton, et al., 2015).…”

Section: Discussionmentioning

confidence: 99%

The Agulhas Current Transports Signals of Local and Remote Indian Ocean Nitrogen Cycling

et al. 2023

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Section: Discussionmentioning

confidence: 99%

The Agulhas Current Transports Signals of Local and Remote Indian Ocean Nitrogen Cycling

et al. 2023

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“…A large portion of the modern Arabian Sea acts as a high nutrient low chlorophyll (HNLC) region due to Fe limitation (Naqvi et al., 2010; Wiggert & Murtugudde, 2007). A recent water column study of dissolved Fe in the Arabian Sea suggests that the surface ocean Fe budget is dominantly controlled by the inputs from lateral and vertical advection with a secondary role of dust deposition (Chinni & Singh, 2022). Lateral advection and upwelling of Fe‐deficient AAIW and deeper waters in the Arabian Sea could be responsible for the Fe limitation (Chinni & Singh, 2022).…”

Section: Discussionmentioning

confidence: 99%

“…A recent water column study of dissolved Fe in the Arabian Sea suggests that the surface ocean Fe budget is dominantly controlled by the inputs from lateral and vertical advection with a secondary role of dust deposition (Chinni & Singh, 2022). Lateral advection and upwelling of Fe‐deficient AAIW and deeper waters in the Arabian Sea could be responsible for the Fe limitation (Chinni & Singh, 2022). Despite higher dust supply during the cold HS and YD (Deplazes et al., 2014; McGee et al., 2013; Figure S8 in Supporting Information ), we observe strong CO 2 degassing suggesting upwelling of Fe‐deficient AAIW responsible for Fe limitation and reduced productivity.…”

Section: Discussionmentioning

confidence: 99%

Enhanced CO₂ Degassing From the Tropical Indian Ocean During Cold Climatic Events of the Last Glacial Cycle

Tarique,

Rahaman,

Lathika

et al. 2023

Paleoceanog and Paleoclimatol

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Atmospheric CO2 variability on the glacial–interglacial (G–IG) timescale reflects a balance between oceanic and terrestrial processes involving carbon uptake and release. The Southern Ocean CO2 uptake is considered as an important modulator for the G–IG atmospheric CO2 variability, while the role of tropical ocean ventilation remains enigmatic. We present critical evidence for CO2 ventilation from the tropical Indian Ocean through the reconstruction of the Arabian Sea‐surface pCO2 for the past ∼136 ka utilizing boron isotope (δ11B) record of planktic foraminifera, Globigerinoides ruber. Our site in the Arabian Sea presently acts as a significant source of CO2. The reconstructed ΔpCO2 (ΔpCO2 = pCO2 Seawater − pCO2 Atmosphere) record shows an enhanced CO2 degassing up to ∼50 ppm during the major cooling events, such as the Last Glacial Maximum, Younger Dryas, and Heinrich‐Stadials. Our investigation based on multiproxy records of sea‐surface temperature, salinity, and productivity suggests that the northward invasion and shoaling of southern source CO2‐rich water, coupled with stronger upwelling, resulted in CO2 degassing during these cold intervals. This finding is in align with the tropical Atlantic which also demonstrated an enhanced CO2 degassing during the cold intervals; however, most of the upwelled CO2 was consumed as the water moved away from the upwelling sites. Therefore, our finding, when considered alongside tropical Atlantic records, suggests that tropical oceans played a minor role in reducing atmospheric CO2 levels during the cold intervals of the last glacial cycle, supporting the prevailing hypothesis.

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“…In the Indian Ocean, biogeochemical feedbacks dominate, especially in the BoB (R >1, figure 1(b)) where they appear to explain the counter-intuitive reduction of O 2 concentration in the OXYBIO simulation with respect to CTRL (figure 2(b)) as treated in section 3.3. It is noteworthy that the different biogeochemical responses between the AS and BoB is likely due to different levels of oxygen deficiency [34].…”

Section: Mechanisms Involved In the Evolution Of Omzsmentioning

confidence: 99%

Contrasting responses of the ocean’s oxygen minimum zones to artificial re-oxygenation

Beghoura

Gorguès

Fransner

et al. 2023

Environ. Res. Lett.

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Studies assessing potential measures to counteract the marine deoxygenation attributed to anthropogenic activities have been conducted in a few coastal environments and at regional scale, but not yet on a global scale. One way toward global scale artificial oxygenation would be to use oxygen produced as a by-product from hydrogen-production through electrolysis. The low-carbon footprint renewable production of hydrogen from offshore wind energy offers such a possibility. Here, we assessed the potential of this artificial oxygenation method on a global scale using a coupled physical-biogeochemical numerical model. The anthropogenic oxygen source scenario assumes worldwide adoption of hydrogen, considering demographic changes and the feasibility of offshore wind turbine deployment. Following this scenario, artificial oxygenation had a negligible effect on the overall oxygen inventory (an increase of 0,07 %) but showed a reduction in the overall volume of Oxygen Minimum Zones (OMZ) between 1,1–2,4 %. Despite the decrease in the mean OMZ volume globally, OMZs display distinct and contrasting regional patterns notably due to the oxygen impacts on the nitrogen cycle. Artificial oxygenation can inhibit denitrification resulting in a net gain of nitrate that promotes locally and remotely increased biological productivity and consequent respiration. Increased respiration could ultimately lead to an oxygen loss at and beyond injection sites as in the Tropical Pacific and Indian Ocean and particularly expand the Bay of Bengal OMZ. In contrast, the tropical OMZ shrinkage in the Atlantic Ocean is attributed to oxygen enrichment induced by advective transport into the OMZ, while the absence of denitrification in this area precludes any biochemical feedback effect on oxygen levels. These results suggest that the impacts of artificial oxygenation on oxygen concentrations and ecosystems are highly non-linear. It can produce unexpected regional responses that can occur beyond the injection sites which make them difficult to forecast.

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Dissolved iron cycling in the Arabian Sea and sub-tropical gyre region of the Indian Ocean

Cited by 26 publications

References 107 publications

The Agulhas Current Transports Signals of Local and Remote Indian Ocean Nitrogen Cycling

The Agulhas Current Transports Signals of Local and Remote Indian Ocean Nitrogen Cycling

Enhanced CO₂ Degassing From the Tropical Indian Ocean During Cold Climatic Events of the Last Glacial Cycle

Contrasting responses of the ocean’s oxygen minimum zones to artificial re-oxygenation

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Dissolved iron cycling in the Arabian Sea and sub-tropical gyre region of the Indian Ocean

Cited by 26 publications

References 107 publications

The Agulhas Current Transports Signals of Local and Remote Indian Ocean Nitrogen Cycling

The Agulhas Current Transports Signals of Local and Remote Indian Ocean Nitrogen Cycling

Enhanced CO2 Degassing From the Tropical Indian Ocean During Cold Climatic Events of the Last Glacial Cycle

Contrasting responses of the ocean’s oxygen minimum zones to artificial re-oxygenation

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Product

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Enhanced CO₂ Degassing From the Tropical Indian Ocean During Cold Climatic Events of the Last Glacial Cycle