The Arctic Ocean plays a key role in Earth’s climate because it is the northernmost part of the Atlantic Meridional Overturning Circulation (AMOC). The Arctic Ocean is almost enclosed, with only a few openings (i.e. straits) where seawater can flow in and out. Warm, salty water from the Atlantic enters mainly through the Barents Sea Opening and Fram Strait. Once inside the Arctic Ocean, this water cools, mixes with fresher water, and interacts with sea ice, which changes its temperature and salt content (salinity). On the Pacific side, fresher water flows in through the Bering Strait, with high-volume Siberian and North American rivers add further freshwater. Fresh, colder seawater and sea ice leave the Arctic mainly through the East Greenland Current and Davis Strait.
Researchers have maintained mooring arrays in the four Arctic gateways (Fram Strait, Barents Sea Opening, Bering Strait and Davis Strait) since the late 1990s / early 2000s. These instruments measure ocean velocity, temperature, and salinity. Temperature and salinity are also measured by research vessels when they collect hydrographic sections (lines of measurements taken from the sea surface down to the seafloor), showing how ocean properties change with depth and distance.
The EPOC team interpolated these observations onto a grid for each gateway, then ran an inverse model. This method adjusts observed velocities slightly to balance the volume of water flowing into and out of the Arctic. From these adjusted fields, the team derived net heat and freshwater transport through the Arctic gateways.
Earlier studies covered periods of one to five years. This record runs from 2004 to 2022, long enough to show seasonal change, year-to-year difference, and long-term trend.
The Arctic gateways carry about 162 terawatts of heat into the Arctic Ocean and 168 millisverdrups of freshwater out, on average, across the record. Both figures show a significant downward trend between 2004 and 2022: heat transport falls by about 1.3 terawatts per year, freshwater transport by about 2.2 millisverdrups per year.
Season affects both. Heat transport peaks in November and drops to its lowest in May, a seasonal swing of about 102 terawatts. Freshwater transport peaks in March and falls to its lowest in June, a swing of about 164 millisverdrups. Ocean currents drive most of this exchange. Sea ice adds a further seasonal cycle, peaking in March and dipping in August.
This work connects to EPOC’s wider Arctic research.
EPOC Deliverable 1.2 Heat and freshwater transport variability through Arctic gateways (2004-2022). Report by Hege-Beate Fredriksen & Laura de Steur, October 2025.
The full report will be available for download when the EC review process is complete.