In high-latitude environments such as the Arctic Ocean, phytoplankton
growth is strongly constrained by light availability. Because light
penetration into the upper ocean is attenuated by snow and ice cover, it
was generally believed until recently that phytoplankton growth was
limited to areas of open water, with negligible growth under the ice.
However, under-ice phytoplankton blooms have been reported multiple
times over the past several decades [e.g. Fukuchi et al. (1989);
Legendre, Ingram, and Poulin (1989)]. In July 2011, Arrigo et al.
(2012) observed a massive phytoplankton bloom beneath sea ice in the
Chukchi Sea. Observational evidence suggests that this bloom was not an
isolated case, and that under-ice blooms maybe widespread on Arctic
continental shelves (Arrigo et al., 2014; Lowry, van Dijken, & Arrigo,
2014). Arrigo and van Dijken (2011) estimate the total primary
production north of the Arctic Circle to be 438 +/- 21.5 Tg C yr -1.
However, due to observational limitations, this estimate did not include
under sea ice production. Therefore, an open question remains: How
important are under-ice phytoplankton blooms to the total Arctic primary
production? RASM is a high-resolution, fully-coupled, regional model
with a domain encompassing the entire marine cryosphere of the Northern
Hemisphere, including the major inflow and outflow pathways, with
extensions into North Pacific and Atlantic oceans. The components of
RASM include: atmosphere, sea ice, ocean, biogeochemical, and land
hydrology (Maslowski et al. 2012, Roberts et al. 2015, DuVivier et al.
2016, Hamman et al. 2016, Hamman et al. 2017, Cassano et al. 2017). The
ocean BGC component in RASM is a medium-complexity
Nutrients-Phytoplankton-Zoo-plankton-Detritus (NPZD) model (Jin et al.
2018). The model has three phytoplankton categories: diatoms, small
phytoplankton and diazotrophs. RASM results show that under-ice pelagic
chl-a and primary production values can at times be very high,
particularly during the spring and early summer. Our numerical model
results produce a mean of 495 Tg C yr -1 north of the Arctic Circle
during 1980-1998 (and 507 Tg C yr -1 during 1980-2018). We also see an
increase in primary production over the last several decades. This
increase is attributed to the reduced sea ice cover, which increases
light availability to the upper ocean. We conclude that under-sea-ice
pelagic primary production makes up a large fraction of the total
production and cannot be considered negligible.