Abstract
Present day thinking contends that Labrador Sea Water (LSW), one of the major watermasses of the North Atlantic, is formed exclusively in the Labrador basin via deep wintertime convection. It is argued herein that LSW is likely formed at a second location—the southwest Irminger Sea. We base this on two pieces of evidence: (1) tracer observations in the western subpolar gyre are inconsistent with a single source and (2) the combination of oceanic and atmospheric conditions that lead to convection in the Labrador Sea is present as well east of Greenland. Hydrographic data (both recent and climatological) are used, in conjunction with an advective–diffusive numerical model, to demonstrate that the spatial distribution of LSW and its inferred spreading rate are inconsistent with a Labrador Sea-only source. The spreading would have to be unrealistically fast, and could not produce the extrema of LSW properties observed in the Irminger basin. At the same time, the set of conditions necessary for deep convection to occur—a preconditioned water column, cyclonic circulation, and strong air–sea buoyancy fluxes—are satisfied in the Irminger Sea. Using observed parameters, a mixed-layer model shows that, under the right conditions, overturning can occur in the Irminger Sea to a depth of 1500– 2000 m , forming LSW.
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