Data for Enhanced monsoon-driven upwelling in Southeast Asia during the Little Ice Age

Global climate models predict that surface ocean nutrient concentrations will significantly decrease over the next 100 years as our climate changes. However, in the world’s marginal seas, which human populations depend on most heavily for food security, the surface ocean biogeochemical changes are still difficult to predict with global-scale models. Here, using coral-based paleoclimate proxies, we reconstruct changes to surface phosphate concentration and to sources of surface nitrogen over the past four centuries in the South China Sea. Combined with box model simulations, our data reveal a 65% decline in phosphate and an 8-48% decline in subsurface nitrate supply from the 1600s to present. Such a decline implies a significant decrease in primary productivity and likely a community shift towards nitrogen-fixing phytoplankton. Importantly, our data indicate that the decrease in nutrient supply was driven by weakened monsoon-induced upwelling, demonstrating strong ties between nutrient supply and monsoon strength in the South China Sea. Climate change is predicted to strengthen the East Asian Summer Monsoon, and our results suggest that primary productivity in this economically important region may increase, contrary to the widely predicted decreases in average global ocean productivity.