Abstract
Over the past decades, Arctic sea ice has declined in thickness and
extent and is shifting towards a seasonal ice regime, with accelerated
ice drift and an increase in the seasonal ice zone. The changing Arctic
ice cover will impact the trans-border exchange of sea ice between the
Exclusive Economic Zones (EEZs) of the Arctic nations, with important
implications for ice-rafted contaminant transport. To investigate
projected changes to transnational ice exchange, we use the Lagrangian
Ice Tracking System (LITS) to follow ice floes from the location of
their formation to where they ultimately melt. We apply this tool to
output from two ensembles of the Community Earth System Model (CESM):
the CESM Large Ensemble, which uses a high emission scenario (RCP8.5)
that leads to over 4°C global warming by 2100, and the CESM Low Warming
ensemble, with reduced emissions that lead to a stabilized warming of
2°C by 2060. We also use the National Snow and Ice Data Center Polar
Pathfinder and Climate Data Record products to evaluate the fidelity of
the CESM present-day tracking simulations. Transnational ice exchange is
well represented in CESM except for ice traveling from Russia to Norway,
with twice as much ice following this pathway compared to observations.
Initial results suggest this might be due to a combination of internal
variability and speed biases in the observational data. The CESM
projects that by mid-century, transnational ice exchange will expand,
with a large increase in the fraction of transnational ice originating
from Russia and the Central Arctic. As the seasonal ice zone grows, ice
floes accelerate and transit times decrease, eventually cutting off ice
exchange between longer pathways. By the end of the 21st century, we see
a large impact of the emission scenario on ice exchange: consistent
ice-free summers under the high emission scenario act to reduce the
total fraction of transnational ice exchange compared to mid-century.
The low emission scenario on the other hand continues to see an increase
in transnational ice exchange by 2100. Under both scenarios, all
pathways have decreased to average transit times of less than 2 years,
compared to a maximum of 6 years under present-day conditions and 3
years by mid-century, effectively bringing the Arctic nations closer
together.