Abstract
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.
Highlights
About half of the global net oceanic primary productivity (NPP) is contributed by the phytoplankton (Field et al, 1998; Käse and Geuer, 2018)
The main aim of the study is the estimation of variability of primary productivity in North Indian Ocean (NIO) and examine them in the context of COrona VIrus Disease (COVID)-19 lockdown
Our analysis suggests that Aerosol Optical Depth (AOD) shows an increasing trend over Arabian Sea (AS) and Bay of Bengal (BoB), while Chl-a and NPP show a decreasing trend in AS, in the southern AS where an increasing trend in Sea Surface Temperature (SST) is observed; implying the reduction in oceanic productivity with global ocean warming
Summary
About half of the global net oceanic primary productivity (NPP) is contributed by the phytoplankton (Field et al, 1998; Käse and Geuer, 2018). The major environmental drivers of oceanic NPP are light, nutrients and temperature. These are, in turn, altered by the changes in associated oceanic and atmospheric processes, and are sensitive to the changes and variability of climate (Field et al, 1998; Chavez et al, 2011). A few of the Essential Climate Variables (ECVs) identified by the Global Climate Observation System (GCOS, 2011) are surface winds, phytoplankton, SST, and aerosols, which are either directly or indirectly connected to the amount of regional and global oceanic NPP. Previous studies show a positive (Martin et al, 1994; Jickells et al, 2005; Patra et al, 2007; Banerjee and Prasanna Kumar, 2014), negative (Mallet et al, 2009; Paytan et al, 2009; Jordi et al, 2012) and even no correlation between aerosols and oceanic NPP at different world oceanic regions (Cropp et al, 2005; Gallisai et al, 2014)
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