Abstract. Carbon and nitrogen uptake rates by small phytoplankton (0.7–5 µm)
in the Kara, Laptev, and East Siberian seas in the Arctic Ocean were
quantified using in situ isotope labeling experiments; this research, which
was novel and part of the NABOS (Nansen and Amundsen Basins Observational
System) program, took place from 21 August to 22 September 2013. The
depth-integrated carbon (C), nitrate (NO3-), and ammonium
(NH4+) uptake rates by small phytoplankton ranged from 0.54 to
15.96 mg C m−2 h−1, 0.05 to 1.02 mg C m−2 h−1,
and 0.11 to 3.73 mg N m−2 h−1, respectively. The contributions
of small phytoplankton towards the total C, NO3-, and
NH4+ varied from 25 % to 89 %, 31 % to 89 %, and
28 % to 91 %, respectively. The turnover times for NO3-
and NH4+ by small phytoplankton found in the present study
indicate the longer residence times (years) of the nutrients in the deeper
waters, particularly for NO3-. Additionally, the relatively
higher C and N uptake rates by small phytoplankton obtained in the present
study from locations with less sea ice concentration indicate the possibility
that small phytoplankton thrive under the retreat of sea ice as a result of
warming conditions. The high contributions of small phytoplankton to the
total C and N uptake rates suggest the capability of small autotrophs to
withstand the adverse hydrographic conditions introduced by climate change.