Decline and partial rebound of the Labrador Current 1993–2004: Monitoring ocean currents from altimetric and conductivity‐temperature‐depth data

Abstract

Monitoring and understanding of Labrador Current variability is important because it is intimately linked to the meridional overturning circulation and the marine ecosystem off northeast North America. Nevertheless, knowledge of its decadal variability is inadequate because of scarcity of current meter data. By using a novel synthesis of satellite altimetry with conductivity‐temperature‐depth (CTD) data, we assess the Labrador Current variability north of the Hamilton Bank (56°N) over 1993–2004. Our analysis shows a decline of the surface‐to‐bottom transport of current by 6.3 ± 1.5 Sv (1 Sv = 106 m3 s−1) in the 1990s (significant at the 99% confidence level) and a likely partial rebound of 3.2 ± 1.7 Sv in the early 2000s (significant at the 89% confidence level only). The inferred multiyear changes in the Labrador Current transport seem to be primarily barotropic and positively correlated (at the 99% level) with the North Atlantic Oscillation at zero lag implying a fast response of the regional circulation to the atmospheric forcing variability. The results compare favorably with direct current measurements and recent model‐based findings on the multiyear variability of the subpolar gyre and its underlying mechanisms. The study demonstrates the feasibility of combining altimetry and CTD data for assessing the climatic variability of the boundary currents.