Observational evidence of stratification control of upwelling and pelagic fishery in the eastern Arabian Sea

Jayu Narvekar,S Prasanna Kumar,P K Dinesh Kumar,Diksha Gaonkar,Riyanka Roy Chowdhury

doi:10.1038/s41598-021-86594-4

Jayu Narvekar, S Prasanna Kumar + Show 3 more

Open Access

https://doi.org/10.1038/s41598-021-86594-4

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Abstract

Upwelling is a physical phenomenon that occurs globally along the eastern boundary of the ocean and supports pelagic fishery which is an important source of protein for the coastal population. Though upwelling and associated small pelagic fishery along the eastern Arabian Sea (EAS) is known to exist at least for the past six decades, our understanding of the factors controlling them are still elusive. Based on observation and data analysis we hypothesize that upwelling in the EAS during 2017 was modulated by freshwater-induced stratification. To validate this hypothesis, we examined 17 years of data from 2001 and show that inter-annual variability of freshwater influx indeed controls the upwelling in the EAS through stratification, a mechanism hitherto unexplored. The upper ocean stratification in turn is regulated by the fresh water influx through a combination of precipitation and river runoff. We further show that the oil sardine which is one of the dominant fish of the small pelagic fishery of the EAS varied inversely with stratification. Our study for the first time underscored the role of freshwater influx in regulating the coastal upwelling and upper ocean stratification controlling the regional pelagic fishery of the EAS.

Highlights

Upwelling is a physical phenomenon that occurs globally along the eastern boundary of the ocean and supports pelagic fishery which is an important source of protein for the coastal population
Though upwelling regions occupy only 5% of the total ocean area, it accounts for 25% of the global marine fish catch[2]
Though the magnitude of upwelling in the eastern Arabian Sea (EAS) is much smaller compared to the other eastern boundary upwelling regions, it supports a substantial pelagic fishery like oil sardine, mackerel, and anchovies[8,9,10,11,12,13] that supplements the nutrition requirement of the population in this region

Summary

Introduction

Upwelling is a physical phenomenon that occurs globally along the eastern boundary of the ocean and supports pelagic fishery which is an important source of protein for the coastal population. Thereafter, the latitudinal variability of the depth of 24 °C isotherm ( D24, a proxy for upwelling), upper water column (0–1 m) static stability (an indicator of stratification) and wind forcing via Ekman vertical velocity and Ekman mass transport (EMT) were analysed to infer about the forcing that controls upwelling process.

Results

Conclusion