Spatial variability of nutrient sources determining phytoplankton Chlorophyll-a concentrations in the Bay of Bengal

Abstract

Primary production is a key marine ecosystem driver in the Bay of Bengal and is important for the societies and economies of the surrounding countries. Although the availability of inorganic nutrients is known to control primary production in this region, the specific nutrient sources that affect primary production in different parts of the bay have not been identified. In this study, we assess the importance of nutrients from different sources in determining chlorophyll-a concentration, an indicator of primary production, in the Bay of Bengal by conducting multiple linear regression of satellite-derived chlorophyll-a concentration, sea surface height anomaly, and sea surface temperature; modelled dust deposition; and in situ river discharge from 1997 to 2016. River-borne nutrients were important up to approximately 200 km from the coast. Deep-ocean nutrients influenced chlorophyll-a concentrations mainly in the south-western and western bay, whereas wind-borne nutrients were more important in the central and eastern bay. Any attempt to understand the impact of nutrients from a certain source should also consider the potential impacts of other nutrient sources. Although climate impacts on chlorophyll-a concentrations through river discharge were observed in our study, future studies should investigate climate-change impacts through atmospheric aerosols and mesoscale eddies.

Mesoscale eddies with anomalous sea surface temperature and its relation with atmospheric convection over the North Indian Ocean

“…The cyclonic eddies that bring the subsurface nutrients to the surface through upwelling have positive chlorophyll anomalies at the centre of eddies. Results signifies that the presence of cyclonic eddies are responsible for the increase of sea surface chlorophyll anomalies in the BoB (Sridevi et al ., 2019; Mathew et al ., 2021; Siswanto et al ., 2022) and reduction of chlorophyll is evident due to the presence of anti‐cyclonic eddies in the BoB (Mathew et al ., 2021; Peter et al ., 2022). Cyclonic eddies that are associated with the upward movement of thermocline, which is associated with the upward velocities can carry nutrients from subsurface to surface of ocean (Falkowski et al ., 1991; Prasanna Kumar et al ., 2002, 2004, 2009; Vidya and Kumar, 2013).…”

Phytoplankton Blooms with Sequential Cyclonic and Anticyclonic Eddies During the Passage of Tropical Cyclone Hibaru

“…Additionally,the variability of chlorophyll in the southwestern and western regions is more sensitive to nutrients from the deep sea than that in other regions of the Bay of Bengal (Siswanto et al, 2022). The absence of the barrier layer was conducive to the nutrient updraft caused by ocean cyclonic eddies and surface chlorophyll blooms (Balaguru et al, 2012;Li et al, 2022).…”

“…This implies that a decrease in SST can reflect, to some extent, the vertical transport of nutrients from the deep sea. SST decreases are usually associated with high nutrient vertical supply (Siswanto et al, 2022). During the passage of TC Hibaru, SST decreased on 13 January (Figure 7), PAR increased over time (Figure 10).…”

Variations of phytoplankton chlorophyll in the Bay of Bengal: Impact of climate changes and nutrients from different sources

“…There are at least three major sources of inorganic nutrients that support primary production in the BoB. Previous studies have mentioned how inputs of inorganic nutrients from rivers and ocean subsurface waters cause seasonal variations in CHL in the BoB (e.g., Gomes et al, 2000;Levy et al, 2007;Vinayachandran, 2009;Siswanto et al, 2022). The GBR, which globally ranks fourth with respect to freshwater discharge into the sea (an average of 1,032 km 3 year −1 ) (Dai and Trenberth, 2002), supplies nutrients that elevate CHL along the northern coast of the bay during the boreal summer (e.g., Vinayachandran, 2009;Kay et al, 2018).…”