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Increased ocean heat transport into the Nordic Seas and Arctic Ocean over the period 1993–2016


Warm water of subtropical origin flows northward in the Atlantic Ocean and transports heat to high latitudes. This poleward heat transport has been implicated as one possible cause of the declining sea-ice extent and increasing ocean temperatures across the Nordic Seas and the Arctic Ocean, but robust estimates are still lacking. Here, we use a box inverse model and more than 20 years of volume transport measurements to show that the mean ocean heat transport was 305 ± 26 TW for 1993–2016. A significant increase of 21 TW occurred after 2001, which is sufficient to account for the recent accumulation of heat in the northern seas. Ocean heat transport may therefore have been a major contributor to climate change since the late 1990s. This increased heat transport contrasts with the Atlantic Meridional Overturning Circulation (AMOC) slowdown at mid-latitudes and indicates a discontinuity of the overturning circulation measured at different latitudes in the Atlantic Ocean.

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Fig. 1: Major ocean currents of the region and data coverage.
Fig. 2: Mass-balanced volume transport across the boundary of the Arctic Mediterranean.
Fig. 3: Mass-balanced ocean heat transport across the boundary of the Arctic Mediterranean.
Fig. 4: Filtered ocean heat and temperature transport changes referenced to January 1997.
Fig. 5: Summary of ocean and sea ice heat transport estimates in the North Atlantic and Arctic Mediterranean.

Data availability

The mass-balanced ocean volume and heat transports are available at the Norwegian Marine Data Centre repository at volume transport time series for GSR branches (IF, FSC, NIIC, DS and FBC) are available at Oceansites website The WTR data are available through The objectively mapped sections in Davis Strait are available via The Bering Strait data are available at project website The Arctic Ocean heat transport estimates during 2004–2010 are available at The ERA-Interim reanalysis data were obtained from European Centre for Medium-Range Weather Forecasts ( The PIOMAS were obtained from the Polar Science Centre at University of Washington (


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Support for this work was provided by the Trond Mohn Foundation under grant no. BFS2016REK01 (T.T. and K.V.), the European Union’s FP7 grant no. 308299, NACLIM project (C.J.) and the European Union’s Horizon 2020 research and innovation programme under grant no. 727852, Blue-Action project (B.H., K.M.H.L., S.Ø., S.J. and H.V.). We acknowledge R. Dickson’s active role in initiating and promoting the integration of the Nordic Seas and Arctic Ocean boundary observation arrays over recent decades. The sustained mooring observations across GSR during 1993–2016 were funded through many national and international research projects including EU research projects such as VEINS (EU contract no. MAST-III MAS3960070), THOR (EU grant no. 212643) and NACLIM (EU grant no. 308299). Bering Strait data and analysis were supported by various NSF, NOAA and ONR grants, including NSF grant no. NFS-0856786 and the NOAA-RUSALCA programme. The Davis Strait programme was supported by the US National Science Foundation under grant nos. ARC0632231 and ARC1022472.

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T.T. and K.V. conceived and developed the study. T.T. integrated and analysed the data with inputs from all authors. T.T. and K.V. wrote the paper. All authors interpreted the results and clarified the implications.

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Correspondence to Takamasa Tsubouchi.

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Peer review information Nature Climate Change thanks Andrea Storto and Andrey Pnyushkov for their contribution to the peer review of this work.

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Supplementary Tables 1–3 and Figs. 1–5.

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Tsubouchi, T., Våge, K., Hansen, B. et al. Increased ocean heat transport into the Nordic Seas and Arctic Ocean over the period 1993–2016. Nat. Clim. Chang. 11, 21–26 (2021).

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