Decadal variability and anthropogenic influence on trace element dynamics in the Bay of Bengal: Evidence from high-resolution coral records

Abstract

The Bay of Bengal (BoB) exhibits dynamic trace element (TE) chemistry shaped by a complex interplay of natural processes and anthropogenic influences. Despite its significance, the temporal variability of TEs in this region is poorly understood. This study investigates decadal (2011–2022) TE dynamics by analyzing trace element-to-calcium ratios (TEs/Ca: B/Ca, Mn/Ca, Fe/Ca, Ba/Ca, P/Ca, As/Ca, Zn/Ca, Cd/Ca, and Sn/Ca) and strontium-to-calcium (Sr/Ca) ratios in modern Porites corals, supplemented by data from a sub-fossil coral as a benchmark. The results reveal distinct seasonal cycles in B/Ca, Sr/Ca, and Ba/Ca, with B/Ca and Sr/Ca being predominantly controlled by sea surface temperature (SST), while Ba/Ca variability is influenced by terrestrial inputs associated with river discharge. B/Ca has been validated as a reliable SST proxy for riverine runoff-influenced BoB. Elevated Fe/Ca, Mn/Ca, and As/Ca ratios are associated with anthropogenic activities, such as the construction of significant infrastructure projects (e.g., Padma Multipurpose Bridge, Payra Sea Port, and Matarbari Deep Sea Port) and the establishment of the Rohingya refugee camp. Additionally, increases in P/Ca, Zn/Ca, and Cd/Ca reflect intensified fertilizer use, whereas rising Sn/Ca levels suggest inputs from antifouling agents, pesticides, and tourism. Principal component analysis combined with multiple linear regression (PCA-MLR) indicates that anthropogenic activities account for approximately 70 % of the TE variability. These findings underscore the significant role of human activities in altering the TE dynamics in the BoB, providing valuable insights for coastal management and pollution mitigation strategies in similarly impacted regions worldwide.