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Abstract.Remotely sensed chlorophyll pigment concentrations from the Coastal Zone Color Scanner (CZCS) are used to estimate biological heating rate and investigate the biological modulation of the sea surface temperature (SST) in a bulk mixed layer model, embedded in the ocean isopycnal general circulation model (OPYC). A higher abundance of chlorophyll in October than in April in the Arabian Sea increases absorption of solar irradiance and heating rate in the upper ocean, resulting in decreasing the mixed layer thickness and lowering temperatures in the layers below the mixed layer than they would be under clear water condition. These changes in the model mixed layer were consistent with Joint Global Ocean Flux Study (JGOFS) observations during the 1994-1995 Arabian Sea experiment. In order to study the effect of chlorophyll pigment on compared different mixed layer models for some simple, idealized forcing cases and tested the models using mixed-

[1] Phytoplankton alter the absorption of solar radiation, affecting upper ocean temperature and circulation. These changes, in turn, influence the atmosphere through modification of the sea surface temperature (SST). To investigate the effects of the present-day phytoplankton concentration on the atmosphere, an atmospheric general circulation model was forced by SST changes due to phytoplankton. The modified SST was obtained from ocean general circulation model runs with space-and time-varying phytoplankton abundances from Coastal Zone Color Scanner data. The atmospheric simulations indicate that phytoplankton amplify the seasonal cycle of the lowest atmospheric layer temperature. This amplification has an average magnitude of 0.3°K but may reach over 1°K locally. The surface warming in the summer is marginally larger than the cooling in the winter, so that on average annually and globally, phytoplankton warm the lowest layer by about 0.05°K. Over the ocean the surface air temperature changes closely follow the SST changes. Significant, often amplified, temperature changes also occur over land. The climatic effect of phytoplankton extends throughout the troposphere, especially in middle latitudes where increased subsidence during summer traps heat. The amplification of the seasonal cycle of air temperature strengthens tropical convection in the summer hemisphere. In the eastern tropical Pacific Ocean a decreased SST strengthens the Walker circulation and weakens the Hadley circulation. These significant atmospheric changes indicate that the radiative effects of phytoplankton should not be overlooked in studies of climate change.

Interdecadal sea surface temperature (SST) anoma-1 We use the term "interdecadal" to loosely refer to timescales that are longer than interannual (ENSO) and shorter than centennial (greenhouse gas forcing).lies show a "canonical" structure (e.g., Tanimoto et al. 1993;Zhang et al. 1997), with central North Pacific SSTs near the subtropical front bracketed to the east, north, and south by oppositely signed SSTs. A second SST pattern is centered around the subpolar front in the Kuroshio-Oyashio Extension region (Deser and Blackmon 1995;Nakamura et al. 1997) and tends to lag the subpolar front SST anomalies by a few years on interdecadal timescales (Miller and Schneider