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 (NO 3 − , NH 4 + , Si(OH) 4 , and PO 4 3− ) decreased markedly from west to east, with minima in NO 3 − and NH 4 + 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 (ρNO 3 − ) and ammonium (ρNH 4 + ) 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 ρNO 3 − 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, ρNO 3 − , 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 NO 3 − concentrations were lower.