Possible solar control on primary production along the Indian west coast on decadal to centennial timescale

Abstract

Using multiple geochemical proxies including specific biomarkers (dinosterol, phytol, stigmasterol and beta-sitosterol) measured in a high-sedimentation rate core collected from the inner shelf (depth approx. 45 m) off Goa (India). Surface productivity is reconstructed, which is mainly controlled by the monsoon upwelling in this region, during the last ca. 700 a. Surface productivity appears to have varied in tandem with the Konkan–Goa rainfall and sunspot activity during the instrumental period (last 250 a). The productivity proxies also covary with the total solar irradiance reconstructed for the period beyond the instrumental era, within the considerable uncertainty of the age model. This suggests that solar forcing may control coastal upwelling intensity and biological productivity in the eastern Arabian Sea on decadal to centennial timescales. During the late Anthropocene (last ca. 50 a), steep increases in all four biomarkers indicate greatly enhanced productivity in response to high solar irradiance as well as anthropogenic inputs of nutrients