Biological-physical coupling in the equatorial Pacific during the 1997-1998 El Niņo

Pete Strutton, Ph.D.
Monterey Bay Aquarium Research Institute

Friday, February 26, 1999
12:00 Noon—Pacific Forum (Video conference to UC Berkeley)

Since December 1996, MBARI has maintained bio-optical and chemical sensors at two sites in the equatorial Pacific. During 1998, this program was expanded to include smaller self-contained packages at four additional sites in the Tropical Atmosphere Ocean (TAO) Array. These instruments, together with ocean color data from the SeaWiFS satellite and in situ data from a total of 11 cruises during 1997-98, have enabled us to document the rise and fall of the 1997-98 El Niņo at a level of detail not previously possible.

This presentation will focus on the transition from warm to cool conditions that occurred in the equatorial Pacific during 1998. During this transition, chlorophyll levels increased more than 40-fold as the trade winds resumed and upwelling of macro- and micronutrients recommenced along the equator. Associated with this phytoplankton bloom, a series of Tropical Instability Waves (TIWs) distorted the tongue of high chlorophyll and low temperature, as they propagated from east to west across the Pacific at a velocity of approximately 50 km/day. At the same time, but in the opposite direction, a patch of very high chlorophyll (>1 ug/l) migrated from west to east at a velocity of approximately 120 km/day. Using mooring, satellite and in situ data, the biological-physical coupling associated with these phenomena will be described. The significance of these observations will be discussed in the context of oceanic productivity and global carbon cycling.

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