Planktonic Ecosystem
Response to
Changing Sea Ice and Upper Ocean Physics in the
Chukchi and Beaufort Seas: Modeling, Satellite and In Situ Observations
Funded
by
NASA
Ocean
Biology
&
Biogeochemistry
and
Cryosphere
Programs
Jinlun Zhang and Mike Steele (University of Washington)
Carin J. Ashjian (Woods Hole
Oceanographic Institution)
Robert G. Campbell (University
of Rhode Island)
Victoria Hill (Old Dominion University) Yvette H. Spitz (OregonStateUniversity)
Significant
decline
of
arctic sea ice has been observed in recent
years. The
decline
was
particularly dramatic during summers 2007–2009,
when
the
arctic sea ice extent decreased to the lowest
levels observed in the satellite era (1979–present).The dramatic decline
occurred
after years of shrinking and thinning of the ice cover, closely linked
to
increasing surface air temperature (SAT).The ice cover has
been shrinking
in every season and in every sector of the Arctic Ocean. However, the summer
ice retreat
during 2007–2009 was most severe in the Pacific sector including the
Chukchi
and Beaufort seas (CBS), indicating that sea ice in that region may be
particularly vulnerable to arctic warming.
Despite the extreme polar conditions, the
CBS
shelves
are ranked among the most productive in the
world, supporting a complex pelagic food
web that
includes zooplankton, fish, birds, seals, walruses, whales and the top
predator, the polar bear. At the base of the food chain, supporting all
the
marine life, are the phytoplankton and algae that produce organic
carbon.
Light,
temperature, and nutrients govern the
variability of the biological productivity in the CBS. Advection of
nutrient-rich Pacific water, input of freshwater and nutrients from
rivers,
upwelling/downwelling, and cross-shelf exchange between shelf and basin
influence
biological and chemical distributions and processes in the CBS. Changes
in the
ice cover affect the penetration of light into the water column, mixing
due to
wind stirring and buoyancy flux at the ocean surface, the oceanic mixed
layer
temperature, upwelling and shelf–basin exchange of nutrients, and
air–sea
exchange of biogenic gases. Thus, the
decline of sea
ice in the CBS may have a profound effect on the marine ecosystem.
The central science
question for our
research is “What is the impact of climate change (natural and
anthropogenic) on the biogeochemistry and ecology of the Chukchi and
Beaufort
seas?" as raised by the NASA
Ocean Biology & Biogeochemistry Program. Our main hypothesis
is that reduction in
summer ice cover and changes in upper ocean physics will substantially
impact
the CBS ecosystem, via changes in primary production, ecosystem
structure and
function, and alteration in the strength of benthic-pelagic coupling.
Our
objectives in addressing the central science question and the main
hypothesis are:
1) Synthesize the historical evolution
of the
biology/ice/ocean system in the Chukchi and Beaufort seas from 1978 to
the
present through modeling and analyses of satellite and in
situ observations; quantify and understand the large-scale
changes that have occurred in sea ice, upper ocean, and the marine
planktonic
ecosystem over the shelves and the basin.
2) Identify key linkages and
interactions between sea ice,
upper ocean, and the planktonic ecosystem to understand how changes in
sea ice,
water temperature, vertical mixing, and upper ocean stratification
affect light
availability, nutrient distribution, biogeochemical processes, food-web
dynamics, and the strength of benthic-pelagic coupling.
3) Examine how the Chukchi/Beaufort
planktonic ecosystem
responds to changes in nutrient-rich Pacific water inflow at Bering
Strait and
advection on the shelves, in the Beaufort shelfbreak jet, and in
mesoscale
physical processes that enhance shelf-basin exchange such as eddy and
filament
formation and shelf-break upwelling.
To achieve these
goals
we will conduct observational analyses using satellite ocean color, sea
ice, and
sea surface temperature (SST) data, and in situ data. We will also
develop a
fully coupled 3D high-resolution Biology/Ice/OceanModeling and Assimilation System
(BIOMAS)
for
synthesis and modeling of the Chukchi and Beaufort seas. BIOMAS will
combine
advanced sea ice and ocean models with a tested arctic marine
planktonic
ecosystem model (Zhang
et al. 2010) and assimilate
satellite sea ice concentration and SST.
SeaWiFS-derived chlorophyll and primary productivity and in situ
biophysical
data will be used for model calibration/validation. This unique system
will
enhance our understanding of how the planktonic ecosystem responds to
changing
sea ice and upper ocean physics in the Chukchi and Beaufort seas. Our
work is
part of the NASA Impacts of Climate change on the Eco-Systems
and
Chemistry of the Arctic Pacific Environment
(ICESCAPE)
project which
aims to pursue the above central science question and associated issues
through
an interdisciplinary, cross cutting approach integrating field
expeditions,
modeling, and satellite remote sensing. Movies:
