Oceanic Mixing over the Northern Arabian Sea in a Warming Scenario: Tug of War between Wind and Buoyancy Forces

Abstract

A consensus of the twenty-first-century climate change in the ocean is surface warming, stratification due to extreme freshening and subsequent weakening of mixing, overturning circulation, and biological production. Counterintuitively, certain parts of the tropical ocean may develop a resistance to changes in mixing, where the climate change impacts of atmosphere and ocean are complementary to each other. Under the poleward shift of monsoon low-level jet (LLJ) in the twenty-first century, a part of the northern Arabian Sea has a tendency to maintain the mixed layer depth intact. The process is studied using a set of high-resolution regional ocean model downscaling experiments for the present and future climate. It is found that the wind intensification caused by the shift in LLJ tends to counteract the stratification gained by surface ocean warming and maintains the mixing process in a warming scenario. The mixing energetics shed light on the way in which this is achieved. Intensified winds promote shear production and surface ocean warming demotes buoyancy production of turbulent kinetic energy (TKE), with a net effect of an increase in TKE. However, TKE appears to be dissipating quickly because of the presence of a larger number of small-scale eddies. This causes the mixing length and mixed layer depth to remain intact. Therefore, the interpretations of impacts of future climate change in ocean mixing should be viewed with caution, at least regionally, by focusing on the detailed changes of the governing mechanisms.

The IOD Impacts on the Indian Ocean Carbon Cycle

“…These unique equatorial winds make the Indian Ocean tropical thermocline flatter than a classical east‐west tilt pattern found in the Pacific and Atlantic (Schott et al, 2009). The seasonal reversal of monsoon winds and concurrent ocean currents not only drive the physical dynamics of the Indian Ocean (Shankar et al, 2002) but also control the seasonal variability of biogeochemical properties strongly coupled with physical dynamics (Praveen et al, 2016, 2020; Roxy et al, 2016; Sarma et al, 2013; Sreeush et al, 2018; Valsala & Maksyutov, 2013).…”

Evaluating the Arabian Sea as a regional source of atmospheric CO<sub>2</sub>: seasonal variability and drivers

“…Even though winds represent such a major variable in determining AS CO 2 flux timing, the variability in total flux due to different pCO 2 products leads to a 2x range in magnitude. These results suggest that in addition to the expected increase of surface ocean pCO 2 due to anthropogenic climate change, possible changes in the timing, location, and magnitude of monsoon winds (Lachkar et al, 2018;Praveen et al, 01 Apr. 2020) will have downstream impacts on seasonal air-sea flux.…”

Evaluating the Arabian Sea as a regional source of atmospheric CO<sub>2</sub>: seasonal variability and drivers

“…Even though winds represent such a major variable in determining AS CO 2 flux timing, the variability in total flux due to different pCO 2 products leads to a 2× range in magnitude. These results suggest that in addition to the expected increase in surface ocean pCO 2 due to anthropogenic climate change, possible changes in the timing, location, and magnitude of monsoon winds (Lachkar et al, 2018;Praveen et al, 2020) will have downstream impacts on seasonal air-sea flux.…”

“…For this study, we choose to focus on the seasonal cycle due to the strength of the monsoon in the AS and because it is resolved by the in situ data, although models suggest interannual (Valsala and Maksyutov, 2013;Valsala et al, 2020) and intraseasonal (Valsala and Murtugudde, 2015) variability exists. The study begins with a description of pCO 2 datasets used, along with the model configuration and methods of analysis in Sect.…”