Peña, M. Angelica

Institute of Ocean Sciences, P.O. Box 6000, Sidney, BC, Canada, V8L 4B2, Tel: 250-363-6576, Fax: 250-363 6746, E-mail: penaa@pac.dfo-mpo.gc.ca

Modeling the response of the planktonic food web to iron fertilization and warming in the NE subarctic Pacific

A one-dimensional ecosystem model with two explicit size classes of phytoplankton was developed for the NE subarctic Pacific to investigate variations in the export of organic particles to the ocean interior due to potential changes in the environment. Specifically, the responses of the planktonic ecosystem to permanent removal of iron limitation and to warming (of 2º and 5º C) were explored. The ecosystem model consists of 5 components (small and large phytoplankton, microzooplankton, detritus and nitrogen) and includes grazing by mesozooplankton, which varies in time according to long-term observations from OSP. The ecosystem model was forced with annual wind and solar heating from OSP. The model best reproduced the low chlorophyll high nitrate conditions of the NE subarctic Pacific when both small and large phytoplankton were limited by iron such that their maximum specific growth rate was reduced by 10 and 70% respectively. When compared with the standard case, model simulations indicated that both permanent removal of iron limitation and warming cause changes in food web structure and the carbon cycle. The response was more dramatic in the iron release case where the phytoplankton community structure in spring changed from one dominated by pico- and nanoplankton to one dominated by large phytoplankton. These changes in food web structure influenced the magnitude, composition and seasonal cycle of sinking particles.