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COrona VIrus Disease (COVID) 2019 pandemic forced most countries to go into complete lockdown and India went on complete lockdown from 24th March 2020 to 8th June 2020. To understand the possible implications of lockdown, we analyze the long-term distribution of Net Primary Productivity (NPP) in the North Indian Ocean (NIO) and the factors that influence NPP directly and indirectly, for the period 2003–2019 and 2020 separately. There exists a seasonal cycle in the relationship between Aerosol Optical Depth (AOD), Chlorophyll-a (Chl-a) and NPP in agreement with the seasonal transport of aerosols and dust into these oceanic regions. In Arabian Sea (AS), the highest Chl-a (0.58 mg/m3), NPP (696.57 mg/C/m2/day) and AOD (0.39) are observed in June, July, August, and September (JJAS). Similarly, maximum Chl-a (0.48 mg/m3) and NPP (486.39 mg/C/m2/day) are found in JJAS and AOD (0.27) in March, April, and May (MAM) in Bay of Bengal. The interannual variability of Chl-a and NPP with wind speed and Sea Surface Temperature (SST) is also examined, where the former has a positive and the latter has a negative feedback to NPP. The interannual variability of NPP reveals a decreasing trend in NPP, which is interlinked with the increasing trend in SST and AOD. The analysis of wind, SST, Chl-a, and AOD for the pre-lockdown, lockdown, and post lockdown periods of 2020 is employed to understand the impact of COVID-19 lockdown on NPP. The assessment shows the reduction in AOD, decreased wind speeds, increased SST and reduced NPP during the lockdown period as compared to the pre-lockdown, post-lockdown and climatology. This analysis is expected to help to understand the impact of aerosols on the ocean biogeochemistry, nutrient cycles in the ocean biogeochemical models, and to study the effects of climate change on ocean ecosystems.

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Anthropogenic emissions have produced significant amount of carbon dioxide (CO2) in the atmosphere since the beginning of the industrial revolution. High levels of atmospheric CO2 increases global temperature as CO2 absorbs outgoing longwave radiation and re-emits. Though a well-mixed greenhouse gas, CO2 concentration is not uniform in the atmosphere across different altitudes and latitudes. Here, we uncover a region of high CO2 concentration (i.e. CO2 pool) in the middle troposphere (500–300 hPa) over the Indo-Pacific Warm Pool (IPWP, 40° E–140° W, 25° S–25° N), in which the CO2 concentration is higher than that of other regions in the same latitude band (20° N–20° S), by using CO2 satellite measurements for the period 2002–2017. This CO2 pool extends from the western Pacific to the eastern Indian Ocean. Much of the CO2 pool is over the western Pacific Ocean (74.87%), and the remaining lies over the eastern Indian Ocean (25.13%). The rising branch of Walker circulation acts as a “CO2 Chimney” that constantly transports CO2 released from the natural, human-induced and ocean outgassing processes to the middle and upper troposphere. The CO2 pool evolves throughout the year with an average annual trend of about 2.17 ppm yr−1, as estimated for the period 2003–2016. Our analysis further reveals that La Niña (El Niño) events strengthen (weaken) the CO2 pool in the mid-troposphere. The radiative forcing for the CO2 pool suggests more warming in the region and is a grave concern for global warming and climate change.

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