Current Intensity Trends in the Labrador and Irminger Seas Based on Satellite Altimetry Data

Abstract

Sea level measurements from an absolute dynamic typography dataset for the period of 1993–2015 were used to study the variability in geostrophic circulation in the Labrador and Irminger seas. Analysis of current intensity trends calculated by geostrophic formulas has shown a weakening in cyclonic circulation observed in these two convection centers. The intensity trends are negative in all the main currents making up the Subpolar Gyre: the Labrador, East Greenland, West Greenland, and Irminger currents. On average, the negative intensity trends in the indicated currents are –0.3 cm s^–1 yr^–1, in individual areas reaching –0.5 cm s^–1 yr^–1, which corresponds to a decrease in current speed of 6.9–11.5 cm/s for the 23-year interval. Weakening of cyclonic circulation is likely predetermined by weakening convection processes and a decrease in the dome-shaped curvature of isopycnal surfaces generated by upwelling of weakly stratified water closer to the surface. This is confirmed by analysis of satellite data: in periods when deep convection weakens, the intensity of cyclonic circulation decreases at the margin of the Labrador and Irminger seas. Simultaneously with weakening currents, an increase in intensity is observed from the outer (with respect to the convection centers) margin of the considered currents, including in coastal zones.