Leading modes of the sea surface temperature large-scale variability in the Atlantic sector of the Arctic.

The study presents an analysis of the large-scale spatiotemporal variability of sea surface temperature (SST) in the Atlantic sector of the Arctic, a key region for the transformation of Atlantic waters and heat exchange between the North Atlantic and the Arctic Ocean. To achieve this, the Empirical Orthogonal Function (EOF) decomposition method was applied to the original monthly mean SST anomalies from the ERA5 reanalysis over the period 1950–2024. Three leading modes have been identified, collectively accounting for 55,8 % of the total SST variance. The first mode (25 % of the variance) exhibits a spatial dipole structure, separating the study area into western and eastern parts. It reflects the mechanism of intensified advection of Atlantic waters northward and eastward, correlating with the heat flux through Fram Strait (R = 0.42) and the Arctic Dipole index (R = 0.27). The second mode (16,4 % of the variance) is characterized by a latitude-oriented dipole structure. Its temporal evolution and significant correlation (R = 0.58) with the Atlantic Meridional Overturning Circulation (AMOC) index reflect the influence of low-frequency oceanic variability. The third mode (14,4 % of the variance) exhibits a complex structure with a positive anomaly in the western and central parts of the basin. It   is interpreted by the authors as an indicator of deep convection intensity in the Greenland Sea, a finding supported by its correlation with temperature in the 500–1750 m layer (R = –0.48). It is established that the spatial structures identified are formed under the combined influence of advective heat transport by Atlantic waters, multi-decadal variability in the intensity of the AMOC, and atmospheric circulation patterns associated with the Arctic Dipole and the Arctic Oscillation. The results obtained quantitatively determine the contribution of the leading modes to the total SST variability in the Atlantic sector of the Arctic, which is essential for understanding the regional climate response to global changes and for refining the mechanisms of Arctic amplification.

1. Reynolds R.W., Smith T.M., Liu C., Chelton D.B., Casey K.S., Schlax M.G. Daily high resolution-blended analyses for sea surface temperature. J. Clim. 2007;20:5473–5496. https://doi.org/10.1175/2007JCLI1824.1

2. Deser C., Alexander M.A., Xie S.P., Phillips A.S. Sea surface temperature variability: Patterns and mechanisms. Annual review of marine science. 2010;2(1):115–143. https://doi.org/10.1146/annurev-marine-120408-151453

3. Intergovernmental Panel on Climate Change (IPCC). Climate Change 2021 — The Physical Science Basis: Working Group I Contribution to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press; 2023. 2391 p. https://doi.org/10.1017/9781009157896

4. Carvalho K.S., Wang S. Sea surface temperature variability in the Arctic Ocean and its marginal seas in a changing climate: Patterns and mechanisms. Global and Planetary Change. 2020;193:103265. https://doi.org/10.1016/j.gloplacha.2020.103265

5. Tsubouchi T., Våge K., Hansen B., Larsen K.M.H., Østerhus S., Johnson C., Jónsson S., Valdimarsson H. Increased ocean heat transport into the Nordic Seas and Arctic Ocean over the period 1993–2016. Nature Climate Change. 2021;11(1):21–26. https://doi.org/10.1038/s41558-020-00941-3

6. Screen J.A., Simmonds I. The central role of diminishing sea ice in recent Arctic temperature amplification. Nature. 2010;464(7293):1334–1337. https://doi.org/10.1038/nature09051

7. Dai A. Arctic amplification is the main cause of the Atlantic meridional overturning circulation weakening under large CO2 increases. Climate Dynamics. 2022;58(11):3243–3259. https://doi.org/10.1007/s00382-021-06096-x

8. Smedsrud L.H., Muilwijk M., Brakstad A., Madonna E., Lauvset S.K., Spensberger C., Born A., Eldevik T., Drange H., Jeansson E., Li C., Olsen A., Skagseth Ø., Slater D.A., Straneo F., Våge K., Årthun M. Nordic Seas heat loss, Atlantic inflow, and Arctic sea ice cover over the last century. Reviews of Geophysics. 2022;60(1):e2020RG000725. https://doi.org/10.1029/2020RG000725

9. Lis N.A., Cherniavskaia E.A., Timokhov L.A. SST trends in certain areas of the Barents Sea in the winter season and mechanisms of their formation. Arctic and Antarctic Research. 2024;70(3):276–294. (In Russ.). https://doi.org/10.30758/0555-2648-2024-70-3-276-294

10. Årthun M., Eldevik T., Smedsrud L.H., Skagseth Ø., Ingvaldsen R.B. Quantifying the influence of Atlantic heat on Barents Sea ice variability and retreat. Journal of Climate. 2012;25(13):4736– 4743. https://doi.org/10.1175/JCLI-D-11-00466.1

11. Asbjørnsen H., Årthun M., Skagseth Ø., Eldevik T. Mechanisms underlying recent Arctic atlantification. Geophysical Research Letters. 2020;47(15):e2020GL088036. https://doi.org/10.1029/2020GL088036

12. Asbjørnsen H., Årthun M., Skagseth Ø., Eldevik T. Mechanisms of ocean heat anomalies in the Norwegian Sea. Journal of Geophysical Research: Oceans. 2019;124(4):2908–2923. https://doi.org/10.1029/2018JC014649

13. Selyuzhenok V., Bashmachnikov I., Ricker R., Vesman A., Bobylev L. Sea ice volume variability and water temperature in the Greenland Sea. The Cryosphere. 2020;14(2):477–495. https://doi.org/10.5194/tc-14-477-2020

14. Efstathiou E., Eldevik T., Årthun M., Lind S. Spatial patterns, mechanisms, and predictability of Barents Sea ice change. Journal of Climate. 2022;35(10):2961–2973. https://doi.org/10.1175/JCLI-D-21-0044.1

15. Volkov D.L., Schmid C., Chomiak L., Germineaud C., Dong S., Goes M. Interannual to decadal sea level variability in the subpolar North Atlantic: the role of propagating signals. Ocean science. 2022;18(6):1741–1762. https://doi.org/10.5194/os-18-1741-2022

16. Saes M.J., Gjelstrup C.V., Visser A.W., Stedmon C.A. Separating annual, interannual and regional change in sea surface temperature in the Northeastern Atlantic and Nordic seas. Journal of Geophysical Research: Oceans. 2022;127(8):e2022JC018630. https://doi.org/10.1029/2022JC018630

17. Smedsrud L.H., Esau I., Ingvaldsen R.B., Eldevik T., Haugan P.M., Li C., Lien V.S., Olsen A., Omar A.M., Risebrobakken B., Sandø A.B., Semenov V.A., Sorokina S.A. The role of the Barents Sea in the Arctic climate system. Reviews of Geophysics. 2013;51(3):415–449. https://doi.org/10.1002/rog.20017

18. Hannachi A., Jolliffe I.T., Stephenson D.B. Empirical orthogonal functions and related techniques in atmospheric science: A review. International journal of climatology. 2007;27(9):1119–1152.

19. ERA5 monthly mean Sea Surface Temperature (SST) data from 1940 to present. Available at: https://cds.climate.copernicus.eu/datasets/reanalysis-era5-single-levels-monthly-means?tab=overview (accessed 31.03.2025).

20. Yang C., Leonelli F.E., Marullo S., Artale V., Beggs H., Nardelli B.B., Chin T.M., De Toma V., Good S., Huang B., Merchant C.J., Sakurai T., Santoleri R., Vazquez-Cuervo J., Zhang H.-M., Pisano A. Sea Surface Temperature intercomparison in the framework of the Copernicus Climate Change Service (C3S). Journal of Climate. 2021;34(13):5257–5283. https://doi.org/10.1175/JCLI-D-20-0793.1

21. Mayer J., Haimberger L., Mayer M. A quantitative assessment of air-sea heat flux trends from ERA5 since 1950 in the North Atlantic basin. Earth Syst. Dynam. 2023;14:1085–1105.

22. North G.R., Bell T.L., Cahalan R.F., Moeng F.J. Sampling errors in the estimation of empirical orthogonal functions. Monthly weather review. 1982;110(7):699–706.

23. ORAS5 global ocean reanalysis monthly data from 1958 to present. Available at: https://cds. climate.copernicus.eu/datasets/reanalysis-oras5?tab=download (accessed 30.10.2025).

24. Фалеев В.И, Горшков С.Г. (ред.). Атлас океанов: Северный Ледовитый океан. Л.: Гл. упр. навигации и океанографии Мин. обороны СССР; 1980. 188 с.

25. Global Ocean Ensemble Physics Reanalysis (GLORYS2V4, ORAS5 и C-GLORSv7). Available at: https://doi.org/10.48670/moi-00024 (accessed 08.08.2025).

26. Smirnov A.V., Ivanov V.V., Sokolov A.A. Comparison analysis of heat and mass transport through Fram strait calculated using the mooring and Ocean reanalysis data. Physical Oceanography. 2024;31(3):354–386.

27. Sumkina A.A., Kivva K.K., Ivanov V.V., Smirnov A.V. Seasonal ice removal in the Barents Sea and its dependence on heat advection by Atlantic waters. Fundamental and Applied Hydrophysics. 2022;15(1):82–97. (In Russ.). https://doi.org/10.59887/fpg/1krp-xbuk-6gpz

28. Monthly mean NAO index from January 1950 until present. Available at: https://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/nao.shtml (accessed 31.03.2025).

29. ERA5 monthly mean data on single (SST) and pressure (SLP) levels from 1940 to present. Available at: https://cds.climate.copernicus.eu/ (accessed 15.07.2025).

30. AO index, obtained by projecting the AO loading pattern to the daily anomaly 1000 millibar height field over 20° N–90° N latitude. Available at: https://www.ncei.noaa.gov/access/monitoring/ao/ (accessed 02.05.2024).

31. Ensemble Mean of Atlantic Meridional Overturning Circulation strength (maximum at 26.5N) from January 1993 to December 2023. Available at: https://data.marine.copernicus.eu/viewer/expert?view=datasetServices&dataset=GLOBAL_OMI_NATLANTIC_amoc_max26N_timeseries (accessed 30.01.2026).

32. Korablev A., Smirnov A., Baranova O.K. Climatological Atlas of the Nordic Seas and Northern North Atlantic (NCEI Accession 0118478). NOAA National Centers for Environmental Information. Dataset. 2014. Available at: https://doi.org/10.7289/v54b2z78. (accessed 27.07.2025).

33. Barton B.I., Lenn Y.D., Lique C. Observed Atlantification of the Barents Sea causes the Polar Front to limit the expansion of winter sea ice. Journal of Physical Oceanography. 2018;48(8):1849–1866.

34. Hátún H., Sandø A.B., Drange H., Hansen B., Valdimarsson H. Influence of the Atlantic subpolar gyre on the thermohaline circulation. Science. 2005;309(5742):1841–1844. https://doi.org/10.1126/science.111477

35. Diansky N.A., Solomonova I.V., Gusev A.V. Predictive estimates of climate changes in the Arctic based on the combined scenario. Russian Arctic. 2018;4:24–33. (In Russ.). https://doi.org/10.24411/2658-4255-2018-00003

36. Smeed D.A., Josey S.A, Beaulieu C., Johns W.E., Moat B.I., Frajka-Williams E., Rayner D., Meinen C.S., Baringer M.O., Bryden H.L., McCarthy G.D. The North Atlantic Ocean is in a state of reduced overturning. Geophysical Research Letters. 2018;45(3):1527–1533. https://doi.org/10.1002/2017GL076350

37. Oldenburg D., Armour K.C., Thompson L., Bitz C.M. Distinct mechanisms of Ocean heat transport into the Arctic under internal variability and climate change. Geophysical Research Letters. 2018;45(15):7692–7700. https://doi.org/10.1029/2018GL078719

38. Cayan D.R. Latent and sensible heat flux anomalies over the northern oceans: Driving the sea surface temperature. Journal of Physical Oceanography. 1992;22(8):859–881.

39. Visbeck M.H., Hurrell J.W., Polvani L., Cullen H.M. The North Atlantic Oscillation: past, present, and future. Proceedings of the National Academy of Sciences.2001;98(23):12876–12877. https://doi.org/10.1073/pnas.23139159

40. Dickson R.R., Meincke J., Malmberg S.A., Lee A.J. The “great salinity anomaly” in the northern North Atlantic 1968–1982. Progress in Oceanography. 1988;20(2):103–151.

41.

42.