Deconstructing the seasonality of the West Greenland boundary current system

The seasonal variability of the West Greenland boundary current system is analyzed using data from a high-resolution mooring array deployed across the shelf and slope near Cape Farewell from 2014-2018. The array is part of the Overturning of the Subpolar North Atlantic Program (OSNAP). Three velocity cores transporting five distinct water masses are identified: the West Greenland Coastal Current, which transports cold and fresh Polar Water (PW); the Irminger Current, which advects warm and salty Irminger Water (IW) as well as cold and fresh PW at the surface; and the Deep Western Boundary Current, which carries dense overflow waters (Denmark Strait Overflow Water and Northeast Atlantic Deep Water). Labrador Sea Water (LSW) resides in the interior of the basin and is also present in the deep part of the Irminger Current on a seasonal basis. The four-year mean transport of the boundary current is 31.3 ±7.4 Sv, with no clear seasonal signal. However, the individual water mass components show statistically significant seasonal cycles in temperature, salinity, and transport. LSW exhibits maximum transport in springtime, due to an increase in LSW presence in the Irminger Current rather than changes in LSW velocity. IW seasonal transport is anti-correlated with that of LSW; when the presence of LSW is enhanced, the amount of IW is reduced. By using four additional upstream mooring arrays distributed around the Irminger Sea along the IW pathway, it is demonstrated that IW is diluted and transformed into LSW from air-sea interaction and mixing with LSW in the boundary current during winter. Finally, PW exhibits a maximum in transport in winter, due to intensification of wind stress along the east coast of Greenland and the propagation of this signal through coastally trapped waves.