Equatorial Phytoplankton and Millennial Forcing;Who Responds, Who Does Not, and Why With Respect to Tropical Climate Dynamics.

A. McIntyre (LDEO, Palisades, N.Y. 10964; ph. 914-365-8333; fax. 914-365-2312; Internet barbclim@ldeo.columbia.edu); B. Molfino (Central Intelligence Agency, Washington, D.C. 20505)

The Tropics is the "boiler" of the thermodynamic engine that is climate. Small changes in energy received produces rapid response of the turbulent boundary layer of the Equatorial Atlantic, e.g. seasonal insolation and trade wind variation occurs on annual to orbital time scales. Theoretically the biota record this but response is species dependent. Partitioning response of organisms defines climate regime control of equatorial oceanography.

Two coccolithophorid species, indigenous to the equatorial euphotic zone, have quite different signals. Florisphaera profunda, indigenous to the deep euphotic zone that, at ten degrees West, is below the nutricline/thermocline, maintains a uniform concentration. through time. The ratio of F. profunda versus all other coccolithophorids indigenous to the upper euphotic zone defines climate change at the atmosphere-ocean interface. This ratio has 60% of it's spectral variance associated with insolation variation; 8% is in millennial periods of 11-8.4ky (equivalent to Heinrich events) and 10% at a period of 1.47ky. The latter is correlative, coherent, and in phase with Greenland dust. Because both signals are a response to tropospheric dynamics we posit one possible mechanism: seasonal relaxation of zonal wind stress in the tropics permits increased seasonal advection of energy to the N. Atlantic region of winter latent heat flux which modulates the Boreal Winter Subpolar Cyclone.

Unlike other species in the upper euphotic zone, Gephyrocapsa oceanica is not dominated by precessional forcing. Instead, it's signal is correlative with oxygen isotopes. It's spectra is dominated by 100ky, lacks both primary precessional and 11 to 8.4ky groups but does contain the 1.47ky period which accounts for only 3% of total variance. Evidence from Ironex I indicates that G. oceanica is Fe dependent, and that it records delivery of aeolian Fe, indicative of african aridity through time. Or is it Cosmic dust?