Recent changes in atmospheric input and primary productivity in the north Indian Ocean

Global oceanic regions are rapidly changing in terms of their temperature, oxygen, heat content, salinity and biogeochemistry. Since the biogeochemistry of the oceans is important and pivotal for global food production, and a major part of the world population relies on marine resources for their daily life and livelihood, it is imperative to monitor and find the spatio-temporal changes in the primary productivity of oceans. Here, we estimate the changes in Chlorophyll-a (Chl-a) and Net Primary Productivity (NPP) in the north Indian Ocean (NIO) basins of Bay of Bengal and Arabian Sea for the period 1998-2019. We find a substantial reduction of NPP in NIO since 1998 (-0.048 mg m- 3 day-1 yr- 1) and the increase in sea surface temperature (SST) (+0.02 degrees C yr- 1) is the primary driver of this change. Furthermore, there is a significant (10-20%) change in the air mass or dust transport to NIO from the period Decade 1 (1998-2008) to Decade 2 (2009-2019). This change in air mass trajectories has also altered NPP in both basins through the changes in nutrient input and associated biogeochemistry. Henceforth, this study cautions the changes in primary productivity of NIO, and suggests regular assessments and continuous monitoring of the physical and biological processes from a perspective of food security and ecosystem dynamics.

Automated summary

Global oceanic regions are experiencing significant changes in temperature, oxygen levels, heat content, salinity, and biogeochemistry. This study focuses on estimating the changes in Chlorophyll-a (Chl-a) and Net Primary Productivity (NPP) in the north Indian Ocean (NIO), specifically the Bay of Bengal and Arabian Sea, from 1998 to 2019. The findings reveal a considerable reduction in NPP since 1998, primarily due to the increase in sea surface temperature and changes in air mass trajectories affecting nutrient input and biogeochemical processes.