Joaquim Goes, Ph.D.
Bigelow Laboratory for Ocean Sciences
Shrinking Snow Caps and Increasing Phytoplankton -
Is Global Warming Making the Arabian Sea More Productive?
Wednesday – December 12, 2007
Pacific Forum – 3:00 p.m.
Over the past eight years, the ecosystem of the Arabian Sea has been showing signs of rapid and profound changes. First seen as a year-to -year increase in ocean color-derived chlorophyll, this unusual escalation in phytoplankton biomass was found to be the result of atypically strong southwest monsoon (SWM) winds and enhanced wind-driven upwelling off the coasts of Somalia, Oman, and Yemen. Detailed investigations revealed that these changes were not occuring in isolation. They were in fact part of a sequence of events whose origins could be traced to the Eurasian warming, which in turn triggered a decline in winter and spring-time snow over the Himalayan-Tibetan plateau region. More recent studies show that the decline in snowfall in winter is also undermining convection mixing, responsible for nutrient enrichment during the boreal winter component of the monsoon cycle. Consistent with the weakening trend of winter convective mixing, phytoplankton concentrations in the eastern Arabian Sea have been on the decline. In contrast, the western and central regions of the Arabian Sea have been experiencing large increases in chlorophyll, fuelled by large and unprecedented blooms of the green dinoflagellate Noctiluca miliaris Suriray (synonym Noctiluca scintillans Macartney). This increase in phytoplankton biomass in the Arabian Sea and the unusual appearance of N. miliaris, has raised the intriguing question whether the warming trend over Eurasia is making the Arabian Sea more productive and altering its biodiversity as well.