23 May 2022
23 May 2022
Status: this preprint is open for discussion.

Interannual to decadal sea level variability in the subpolar North Atlantic: The role of propagating signals

Denis L. Volkov1,2, Claudia Schmid2, Leah Chomiak3, Cyril Germineaud4, Shenfu Dong2, and Marlos Goes1,2 Denis L. Volkov et al.
  • 1Cooperative Institute for Marine and Atmospheric Studies, University of Miami, Miami, Florida 33149, USA
  • 2NOAA Atlantic Oceanographic and Meteorological Laboratory, Miami, Florida 33149, USA
  • 3Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida 33149, USA
  • 4Mercator Ocean International, Toulouse, France

Abstract. The gyre-scale, dynamic sea surface height (SSH) variability signifies the spatial redistribution of heat and freshwater in the ocean, influencing the ocean circulation, weather, climate, sea level, and ecosystems. It is known that the first empirical orthogonal function (EOF) mode of the interannual SSH variability in the North Atlantic exhibits a tripole gyre pattern, with the subtropical gyre varying out-of-phase with both the subpolar gyre and the tropics, influenced by the low-frequency North Atlantic Oscillation. Here, we show that the first EOF mode explains the majority (60–90 %) of the interannual SSH variance in the Labrador and Irminger Seas, whereas the second EOF mode is more influential in the northeastern part of the subpolar North Atlantic (SPNA), explaining up to 60–80 % of the regional interannual SSH variability. We find that the two leading modes do not represent physically independent phenomena. On the contrary, they evolve as a quadrature pair associated with a propagation of SSH anomalies from the eastern to the western SPNA. This is confirmed by the complex EOF analysis, which can detect propagating (as opposed to stationary) signals. The analysis shows that it takes about 2 years for sea level signals to propagate from the Iceland Basin to the Labrador Sea, and it takes 7–10 years for the entire cycle of the North Atlantic SSH tripole to complete. The observed westward propagation of SSH anomalies is linked to shifting wind stress curl patterns and to the cyclonic pattern of the mean ocean circulation in the SPNA. The analysis of regional surface buoyancy fluxes in combination with the upper-ocean temperature and salinity changes suggests a time-dependent dominance of either air-sea heat fluxes or advection in driving the observed SSH tendencies, while the contribution of surface freshwater fluxes (precipitation and evaporation) is negligible. We demonstrate that the most recent cooling and freshening observed in the SPNA since about 2010 was mostly driven by advection associated with the North Atlantic Current. The results of this study indicate that signal propagation is an important component of the North Atlantic SSH tripole, as it applies to the SPNA.

Denis L. Volkov et al.

Status: open (until 28 Jul 2022)

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Denis L. Volkov et al.

Denis L. Volkov et al.


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Short summary
Ocean and atmosphere dynamics redistribute heat and freshwater, which drives regional sea level changes. This study reports on the east-to-west propagation of sea level anomalies in the subpolar North Atlantic, mainly associated with advection by the mean flow – an important component of the leading mode of interannual sea level variability in the region. This variability mainly results from oceanic advection and air-sea heat fluxes, whose relative contributions are space- and time-dependent.