Pelagic primary productivity and upper ocean nutrient dynamics across Subarctic and Arctic Seas

Abstract

Phytoplankton and nutrient dynamics were investigated during the 2007 and 2008 summers in the euphotic zone of five broad domains across Subarctic and Arctic Seas: the Eastern Subarctic North Pacific Ocean, ESNP; Bering and Chukchi Seas, BE-CH; Beaufort Sea and Canada Basin, BS-CB; Canadian Arctic Archipelago, CAA; and Baffin Bay and Labrador Sea, BB-LS. Average concentrations of nutrients (NO3-, NH4+, Si(OH) 4, and PO43-) decreased markedly from west to east, with minima in NO3- and NH4+ in surface BS-CB waters, but relatively invariant urea-N concentrations across the entire region. In the BS-CB domain, low uptake rates of nitrate (ρNO3-) and ammonium (ρNH4+) were exceeded by uptake of urea (ρUrea-N). Whereas average ρNO 3- was highest in the BE-CH domain, ρUrea-N was maximal in BB-LS. Average depth-integrated f-ratios ranged from 0.27 in the BS-CB domain to 0.57 in BE-CH, while chlorophyll a (chl a) and primary productivity (ρC) were highest in BE-CH and BB-LS, and consistently low in the BS-CB domain. The >5 μm phytoplankton fraction dominated ρC and ρNO3- in the BE-CH and CAA domains, whereas ESNP and BS-CB were dominated by the <5 μm fraction. In the BB-LS domain, the larger cells were responsible for ∼50% of ρC, ρNO3-, and ρUrea-N. This study highlights the contrast in ice-corrected average new production between the BE-CH (396 mg C m-2 d-1) and BS-CB (5.50 mg C m-2 d-1) domains in summer, and the larger contribution of urea-N uptake to total N uptake in central and eastern regions where NO3- concentrations were lower. Key Points Canada Basin had the lowest primary and new production rates High new production in the Chukchi Sea was dominated by >5 um phytoplankton Urea was an important nitrogen source for phytoplankton when nitrate was low ©2013. American Geophysical Union. All Rights Reserved.