Spatial and year-to-year patterns in new and primary productivity in sea ice melt regions of the eastern Bering Sea

Four years of data on for new (nitrate), regenerated (ammonium), and primary (carbon) productivity (2007 through 2010) confirm the elevated productivity associated with the marginal ice zone (MIZ) of the eastern Bering Sea (EBS) in spring. The greatest levels of productivity were associated with ice-melt regions along the western edge of the ice pack. Population seeding and the shallowing of the mixed-layer depth near the ice edge were less important in the development of elevated MIZ productivity than was the amount of ice melt entering surface water, suggesting that ice contributed substances stimulating phytoplankton growth. Based on ice melt as an index of bloom development, primary productivity continued to increase after new productivity peaked. At the MIZ environments with optimal growth conditions, new productivity averaged 18.6 mmol N m−2 d−1, with a ƒ-ratio of 0.61 and primary productivity averaged 492 mmol C m−2 d−1. Although these features were consistently recorded in late April/early May, they varied with the dynamics of ice cover, whose retreat was later in 2008 relative to 2007 and 2009. The intense but localized MIZ blooms appear to be under-sampled in ocean-color imagery. Under ice productivity was generally low (ave. ρNO3=0.45 mmol N m−2 d−1; ave. primary prod.=4.16 mmol C m−2 d−1), although larger values were measured under the western edge of the ice pack and in the St. Lawrence polynya region. The advection of ice and water may contribute to the large values under the western ice edge and the highly transparent new ice may play a role in the polynya. New and primary productivity rates of under-ice samples were significantly inhibited when exposed to ice-free irradiance levels. In situ productivity could be estimated to ±35% from rates measured on-deck by adjusting for the impact of ice on submarine light. The carbon to nitrate uptake ratio was closely related to specific carbon production in the in situ incubations.