Dependence of subsurface chlorophyll on seasonal water masses in the Chukchi Sea

During the late summer, phytoplankton in the northeastern Chukchi Sea are typically found in subsurface layers. These layers and their sensitivity to local changes in hydrography and nutrient concentrations are characterized by combining data from a high-resolution towed sampling platform with traditional shipboard observations. The replacement of surface meltwater and deeper nutrient-rich Chukchi Winter Water by northward flowing nutrient-poor Chukchi Summer Water and Remnant Winter Water leads to a net decrease in biomass and smaller phytoplankton. Between 17 and 67% of phytoplankton biomass is contained within the subsurface layers. This estimate is nearly twice as high as previous estimates from sparser shipboard data and suggests subsurface phytoplankton contribute significantly to the net biomass in the Chukchi Sea in late summer.