Assessing decadal changes in the Deep Western Boundary Current absolute transport southeast of Cape Farewell, Greenland, from hydrography and altimetry

Abstract

In earlier studies, the decadal variability of the Deep Western Boundary Current (DWBC) transport in the vicinity of Cape Farewell, Greenland, has been assessed from changes in the baroclinic velocities computed from hydrographic data and referenced to 1000 m depth. The main limitation of using such an estimate as an index for the DWBC absolute transport variability comes from the unaccounted for decadal velocity changes at the reference level (1000 m). These changes may substantially contribute to the DWBC absolute transport variability by compensating for or adding to the baroclinic transport changes. To assess this contribution to variability, we quantify the decadal velocity changes which occurred at 1000 m depth southeast of Cape Farewell since the mid‐1990s. The analysis combines estimates of the baroclinic velocity changes in the water column derived from repeat hydrography at ∼59.5°N and the velocity changes at the sea surface derived from altimetry. An increase in the southward velocity at 1000 m above the DWBC between the periods of 1994–1997 and 2000–2007 is inferred. It indicates that the increase in the DWBC absolute transport was larger than the 2 Sv (1 Sv = 106 m3 s−1) increase in its baroclinic component referenced to 1000 m. This result and the observed coherence of the DWBC absolute and baroclinic transport changes between individual observations imply that the DWBC absolute transport variability in the region is underestimated but qualitatively well represented by its baroclinic component on decadal and shorter time scales.