ASLO/TOS Ocean Research Conference, Honolulu, HI, February 2004, p. 16.

Temporal variations in phytoplankton community structure and physical forcing at Station ALOHA (22.75N, 158W)

R. R. Bidigare¹, Y. Chao², R. Lukas¹, R. M. Letelier³, S. Christensen¹ and D. M. Karl¹

¹University of Hawaii, Honolulu, USA

²Jet Propulsion Laboratory, Pasadena, USA

³Oregon State University, Corvallis, USA

Potential biological responses to basin-scale climate forcing in the Pacific are assessed based on temporal variations in phytoplankton community structure observed at Station ALOHA (1989-2002) and the output of a Regional Ocean Modeling System (ROMS) model. Phytoplankton populations were monitored monthly during this period using taxon-specific pigment analyses. These analyses revealed distinct temporal patterns, with highest pelagophyte abundance during the periods 1990-1993 and 1998-2002. For other key groups, such as the haptophytes and cyanobacteria, there appears to be a recent post-1998 enhancement in their biomass relative to the previous 7-year period of observation. An Ocean General Circulation Model based on the terrain-following vertical coordinate primitive equation ROMS model, was used to simulate hydrographic dynamics at Station ALOHA. Preliminary analysis comparing the model emulation with TAO observations has shown that the model can realistically reproduce the low-frequency (seasonal-to-interannual) variability. The ROMS simulation during 1989-2002 will be first compared against the HOT physical measurements and then used to help interpret the observed changes in phytoplankton communty structure at Station ALOHA.