Spatio-temporal variations in upwelling indices in Arabian Sea coastal upwelling systems and associated biological productivity using remote sensing observations

ABSTRACT

In this paper, the spatio-temporal variations of Yemen, Oman and west coast of India upwelling are studied using wind and Sea Surface Temperature (SST) based upwelling indices. The relative contributions of offshore Ekman transport and Ekman pumping are compared in these upwelling regions. It has been found that offshore Ekman transport is the more dominant mechanism in coastal areas of Oman from 17°N to 21°N with upwelling indices reaching up to 3–4 m²/s during June-July while for the Yemen coast (13–16.5°N), Ekman pumping is stronger. The west coast of India has much weaker upwelling during the southwest monsoon. Offshore Ekman transport is the main mechanism for upwelling activity during the southwest monsoon for the west coast of India. A combined upwelling index was developed, adding the contributions of Ekman transport and integrated Ekman pumping. Chlorophyll data from 1998 to 2017 showed an increase in chlorophyll concentration during southwest monsoon season for all three upwelling regions. The maximum increase in southwest monsoon chlorophyll was observed for northern Yemen (15–16.5°N) with an increase of 10–20 times. This is followed by coastal region of Oman (17–19°N) and southern part of west coast of India (8–10°N).

KEYWORDS:

• Ekman mass transport
• Ekman pumping
• upwelling indices
• wind stress
• chlorophyll concentration

Acknowledgements

The authors are thankful to Remote Sensing Systems and Globcolour project for access to wind and chlorophyll data, respectively. The authors are also grateful to Director, Space Applications Centre for his active support.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

All data for this study are publicly available. CCMP wind data is available at www.remss.com. Chlorophyll data is available publicly at ftp://ftp.hermes.acri.fr. MODIS SST data are available openly at https://urs.earthdata.nasa.gov. Modelled 3D temperature data used for thermocline depth computation is available openly at https://marine.copernicus.eu.