Climate Mediated Increases in Phytoplankton Blooms in the Northern Arabian Sea and Potential Feedback Effects

Joaquim Ignacio Goes, Lamont Doherty Earth Observatory, Palisades, New York, USA, jig@ldeo.columbia.edu
Helga do Rosario Gomes, Lamont Doherty Earth Observatory, Palisades, New York, USA, helga@ldeo.columbia.edu
Shavprasad Prabhu Matondkar, National Institute of Oceanography, Goa, India, sgpm@nio.org
John Fasullo, National Centre for Atmospheric Research, fasullo@ucar.edu
Fei Chai, Univ. of Maine, Orono, Maine, fchai@maine.edu
Sergio deRada, Naval Research Laboratory, Stennis, MS, sergio.derada@nrlssc.navy.mil
Richard Barber, Duke University, rbarber@duke.edu (Presenter)

Over the past 10 years the Arabian Sea ecosystem has witnessed rapid changes linked to the general

warming trend over Eurasia. In particular, large parts of southwest Asia (SWA) and the Himalayan-Tibetan Plateau (HTP) region have been experiencing significant decreases in spring snow persistence that have hastened and strengthened southwest monsoon (SWM) winds. Since 1998, as a result of intensification of wind-driven upwelling along the coasts of Somalia, Oman and Yemen, the western Arabian Sea has witnessed record increases in phytoplankton blooms. The impacts of the warming trend and the reduction in snow cover have not been limited to the SWM. Since 1998, winter convective mixing during the northeast monsoon (NEM) has been weakening, but despite this trend, chlorophyll (Chl a) concentrations in the Arabian Sea have been on the rise. Our collaborative studies with our Indian colleagues initiated in 2003, have allowed us to ascribe this increase in Chl a during the NEM to unprecedented blooms of a heterotrophic dinoflagellate, Noctiluca miliaris. Thick, surface dwelling blooms of Noctiluca have become a regular feature of the Arabian Sea during the NEM, replacing diatoms as the dominant winter-bloom forming phytoplankton. The extraordinary intensity of these blooms, and their persistence into the spring inter-monsoon when sea surface conditions in the Arabian Sea are most able to influence rainfall over the Indian subcontinent, demands that begin to question the feedback effects of Noctiluca blooms on heat and moisture fields over the Arabian Sea and as a consequence on the erratic monsoonal rainfall patterns being witnessed in recent years. This presentation will provide data from recent cruises on the extraordinary biooptical and ecophysiological characteristics of these blooms and also examine whether: 1) Noctiluca blooms prior to the onset of the SWM significantly increase the attenuation of light in the water column causing faster than normal heating of sea surface waters, and 2) perturbations in SST and moisture by Noctiluca blooms are large enough to induce changes in evaporation and atmospheric moisture content and stability over the Arabian Sea and rainfall over the Indian subcontinent.

Presentation: 2011_Oct04_AM_Goes_336.pptx (799k)

Presentation Type:  Plenary Talk

Session:  Poster Speed Talks:

Presentation Time:  Tue 11:00 AM  (5 minutes)