Labrador Sea boundary currents (Greenland)

The Labrador Sea is one of the few regions of the world ocean where deep convection takes place. The boundary currents play an essential role in the Labrador Sea as heat and freshwater sources. Surface drifters combined with several hydrographic sections show that the boundary current is constituted of two main components: a more baroclinic component close to the shelf break, and a more barotropic component closer to the 3000 m isobath. Temperature and salinity profiles collected by PALACE floats show that the Irminger Sea Water carried by the boundary currents around the Labrador Sea is cooled by along isopycnal mixing with the fresh and cold interior surface waters. Several moorings across the Labrador continental slope just north of Hamilton Bank show that convection does take place within the Labrador Current. Mixing above the lower Labrador slope is facilitated by the onshore along isopycnal intrusions of low PV eddies which waken the stratification. Above the shelf break, the Irminger Sea Water core is displaced onshore while the stratification weakens with the increase in isopycnal slope. The change in stratification is partially due to the onshore shift of the ‘classical’ Labrador Current and possibly slantwise convection. The 20 year time series from a 1000 m deep instrument at the shelf break shows some trends in speed and temperature. Volume, freshwater and heat transport through Davis Strait, the northern boundary of the Labrador Basin, are computed using a mooring array deployed for three consecutive years. The transports include significant seasonal variability dictated by the variability in the main water masses transport: Irminger Sea Water, West Greenland shelf water, surface meltwater, and a Cold Intermediate Layer originating from the Canadian Archipelago. The southward freshwater transport amplitude is dominated by the Cold Intermediate Layer transport rather than the surface meltwater layer. The northward heat transport anomaly is due simultaneously to the northward flowing Irminger Sea Water and the southward flowing sub-zero Cold Intermediate Layer. The Irminger Sea Water long term salinity variations at Davis Strait follows the trend of the main other water masses in the subpolar gyre while the Cold Intermediate Layer shows an unexplained opposite trend.