Edwards, C. A. University of California, cae@socrates.berkeley.edu
Batchelder, H. A. University of California, halbatch@socrates.berkeley.edu
Powell, T. M. University of California, zackp@socrates.berkeley.edu

The response of a coastal microzooplankton population to an upwelling event is studied using simple coupled biological and physical models. In particular, we investigate the behavior of the Franks and Walstad (1997) model in a parameter range that applies to microzooplankton with large ingestion rates but low assimilation efficiency and compare our results with those generated by more conventional (i.e., mesozooplankton) parameters. Within this range, the model exhibits limit-cycle behavior that is stabilized by the added modification of a density-dependent zooplankton mortality. The physical circulation results from a simple 2-dimensional (x-z), hydrostatic, finite-difference model that includes the KPP mixed layer formulation and a mixing-length bottom boundary layer. When driven by an upwelling-favorable wind-stress, the coupled model generates a substantial phytoplankton bloom within the frontal region that is narrow in zonal extent, limited by the strong grazing pressure of the enhanced zooplankton population further offshore. The magnitude of the zooplankton maximum is significant compared to steady-state values but considerably smaller than the phytoplankton peak magnitudes owing to the poor efficiency of the grazers. The comparable calculations for mesozooplankton parameters lead to wider spatial extent of the phytoplankton bloom and no associated zooplankton maximum. We conclude that the rates of biological processes can have substantial impact on the spatial patterns biological productivity.
Day: Thursday, Feb. 4
Time: 10:45 - 11:00am
Location: Hilton of Santa Fe
Code: SS04TH1045H