Summary of Abstract Submission

Abstract Submission No. IO50-09-0033PresentationPoster

A REDUCTION IN MARINE PRIMARY PRODUCTIVITY DRIVEN BY RAPID WARMING OVER THE TROPICAL INDIAN OCEAN

M K Roxy*1, Aditi Modi1, Raghu Murtugudde2, Vinu Valsala1, Swapna Panickal1, S Prasanna Kumar3, M Ravichandran4

1 Indian Institute of Tropical Meteorology, India
2 University of Maryland, USA
3 National Institute of Oceanography, India
4 Indian National Centre for Ocean Information Services, India

ABSTRACT :

Among the tropical oceans, the western Indian Ocean hosts one of the largest concentration of phytoplankton blooms in summer, supporting the second largest share of the most economically valuable tuna catch. Interestingly, this is also the region with the largest long-term trends in sea surface temperatures (SST) in the tropical oceans, though the contribution of such a large trend in SST to productivity changes have remained ambiguous. Earlier studies on changes in chlorophyll had described the western Indian Ocean as among the open ocean regions with the largest increase in marine phytoplankton, but based on relatively short-term records. In fact, the coastal winds over the Arabian Sea have strengthened in the recent decades and ideally, this should enhance the nutrient mixing and phytoplankton blooms in this region. On the contrary, the current study points out an alarming decrease of up to 30% in marine phytoplankton in this region over the past six decades. We find that these trends in chlorophyll are driven by enhanced ocean stratification due to the rapid warming in the Indian Ocean, which suppresses nutrient mixing from subsurface layers. Future climate projections suggest that the Indian Ocean will continue to warm, leading to further reduction in marine productivity, which combined with the fishing pressure, can drive this productive region into an ecological desert. This region may serve as a cautionary tale for other coastal and open ocean regions in terms of the marine ecosystem response in a warming world.