Primary Productivity in the Gulf of Alaska in a High-Resolution Global Climate Model

Abstract

The Gulf of Alaska is a major fishery that plays a vital role in the economic development and success of Alaska. The fishery’s success is dependent on several factors, one being primary production. Primary producers, such as phytoplankton, form the base of the oceanic food web and supply energy and materials to secondary consumers. The Gulf of Alaska is a high nitrate low chlorophyll (HNLC) region often limited by iron. Phytoplankton require iron to synthesize chlorophyll and reduce other nutrients. Sources of iron include suspended sediments transported via rivers, dust deposition from drier lands, and sediments released by melting glaciers transported from the coast to the interior of the gyre via Haida Eddies. This study focuses on identifying the factors that control the seasonal succession of phytoplankton at Ocean Station Papa in the Gulf of Alaska. Using a high-resolution global climate model, the interannual variability of surface nutrients, mixed layer depth, phytoplankton biomass, zooplankton biomass, and irradiance are examined in order to draw conclusions regarding the cause of two distinct chlorophyll regimes that occur over a 15 year period. Irradiance turns out to be the main culprit behind the diverging chlorophyll regimes. Lastly, a preliminary investigation is conducted on the role that Haida Eddies play in iron transport and primary production in the Gulf of Alaska. Elevated iron concentrations within the eddy cause phytoplankton biomass to reach a maximum a month earlier than the surrounding waters.