Spatiotemporal dynamics of carbon isotope ratios and phytoplankton composition in the eastern Arabian Sea

Prachi Marathe; Anil Kumar Vijayan; B Bikram Reddy; V Sudheesh

doi:10.1016/j.marpolbul.2024.117474

Spatiotemporal dynamics of carbon isotope ratios and phytoplankton composition in the eastern Arabian Sea

Mar Pollut Bull. 2024 Dec 26:212:117474. doi: 10.1016/j.marpolbul.2024.117474. Online ahead of print.

Authors

Prachi Marathe¹, Anil Kumar Vijayan², B Bikram Reddy¹, V Sudheesh³

Affiliations

¹ Centre for Marine Living Resources and Ecology (CMLRE), Kochi, Kerala, India; Kerala University of Fisheries and Ocean Studies (KUFOS), Kochi, Kerala, India.
² Centre for Marine Living Resources and Ecology (CMLRE), Kochi, Kerala, India; Ministry of Earth Sciences (MoES), Government of India, Prithvi Bhawan, New Delhi, India. Electronic address: anilkumar.v@gov.in.
³ Centre for Marine Living Resources and Ecology (CMLRE), Kochi, Kerala, India; Central University of Kerala (CUK), Kasargod, Kerala, India.

PMID: 39729828
DOI: 10.1016/j.marpolbul.2024.117474

Abstract

This study investigated major contributors of the particulate organic matter (POM) using stable isotope ratios of particulate organic carbon (δ¹³C_POC) and its relationship with phytoplankton composition during three seasons across six coast-offshore transects in the eastern Arabian Sea (EAS). Results revealed significant spatiotemporal variations, with elevated δ¹³C_POC in coastal waters during the winter and summer monsoon (-22.40 ± 1.76‰), linked to increased phytoplankton biomass (2.26 ± 2.21 μg l^-1) and dominance of diatoms (micro-phytoplankton) (65.35 ± 30.98%). In contrast, lower δ¹³C_POC during the spring inter monsoon (SIM) and in offshore waters during WM and SM (-23.31 ± 1.32‰) were associated with cyanobacteria (pico-phytoplankton) dominance (78.27 ± 22.75%). Positive correlations of POC with Chlorophyll a (Chla) and particulate nitrogen (PN) (r > 0.5, p < 0.05), along with their ratios (POC:Chla < 200 and POC:PN < 12), indicated the autochthonous nature of POM. Distinct δ¹³C_POC ranges were identified based on phytoplankton composition; diatoms (micro-phytoplankton) dominated waters exhibited δ¹³C_POC values between -23.83 and -19.19‰, while nano and/or pico-phytoplankton dominated showed values ranging from -26.00 to -22.15‰. This study highlights spatiotemporal variability in the POM composition and emphasises the importance of δ¹³C_POC in understanding its relationship with phytoplankton composition. Baseline information on δ¹³C_POC will aid in developing stable isotope isoscapes of the EAS, enhancing our understanding of trophodynamics and animal migratory patterns.

Keywords: Convective mixing; Eastern Arabian Sea; Phytoplankton; Upwelling; δ(13)C(POC).