Atmospheric Drivers of Subseasonal Variability in North Atlantic Phytoplankton Phenologies

Atmospheric forcing is known to drive annual cycles of phytoplankton dynamics in both the open oceans and the continental margins. Much attention has been paid to the role of subseasonal (10-30 day) variability in atmospheric forcing on the initiation of spring phytoplankton blooms in the North Atlantic, indicating that subseasonal changes in net surface heating may contribute to a restratification of the upper mixed layer and thus initating a spring bloom. However, the effects of subseasonal forcings on late summer and early fall phytoplankton dynamics have yet to be explored in the same detail. A 1/12 deg. coupled physics-sea ice-biogeochemistry Northwest Atlantic regional model is used to explore the late summer dynamics of phytoplankton biomass and Nitrogen inventory in the Grand Banks of Newfoundland. During the control run, a series of biomass accumulation events in July-August 2015 were identified and associated with a passing storm event which included elevated surface wind stress and net surface cooling. Sensitivity experiments were then conducted in which the subseasonal component (<30 days) of wind stress, surface air temperature, and surface humidity were removed from the forcing to assess their individual roles on the biomass accumulation events. The removal of subseasonal wind stress was associated with a 21% decrease in peak total Nitrogen, while the peak phytoplankton biomass only saw a 2% decrease, indicating that subseasonal surface wind stress alone could not account for the rapid increase in nutrient inventory and phytoplankton biomass that was observed.

Presentation Preference: Poster

Primary Presenter: Shaun Eisner, University of Maryland at College Park (seisner1@umd.edu)

Authors:

Shaun Eisner, University of Maryland, College Park  (seisner1@umd.edu)

Katja Fennel, Dalhousie University  (katja.fennel@dal.ca)

Arnaud Laurent, Dalhousie University  (arnaud.laurent@dal.ca)