CONFIGURATION

20160329_OSNAP_planeview

OSNAP observing system: From west to east: Canadian (CA) shelfbreak array and German (DE) 53°N western boundary array; US West Greenland boundary array; US/UK East Greenland boundary array; Netherlands (NL) western Mid-Atlantic Ridge array; US eastern Mid-Atlantic Ridge array; Chinese (CN) glide survey in the Icealand Basin; UK glider survey over the Hatton-Rockall Bank; UK Scottish Slope current array. Cyan dots: 2014 US float launch sites. Gray solid line: Chinese glider; gray dashed line: UK glider. Blue circles: US sound sources. Note: white triangles illustrate three French (FR) moorings as part of the RREX program. The light grey lines represent the 1000m-, 2000m- and 3000m-isobaths.

 

OSNAP array superposed on climatological salinity along the OSNAP West and East lines. Color shading is 2005-2012 mean salinity from WOA13; black dashed lines are isopycnals of 27.5, 27.75, 27.8, and 27.88 kg m-3. OSNAP mooring locations (vertical gray lines) and glider domain (shaded white box) are indicated. Vertical black lines over the western flank of the Reykjanes Ridge illustrate three moorings as part of the RREX program.

OSNAP array superposed on climatological salinity along the OSNAP West and East lines. Color shading is 2005-2012 mean salinity from WOA13; black dashed lines are isopycnals of 27.5, 27.75, 27.8, and 27.88 kg m-3. OSNAP mooring locations (vertical gray lines) and glider domain (shaded white box) are indicated. Vertical black lines over the western flank of the Reykjanes Ridge illustrate three moorings as part of the RREX program.

Enlarged Maps

Iceland to Scotland Instrument Locations and OSNAP-East Mooring Diagram
Irminger Sea Instrument Locations and OSNAP-East Mooring Diagram
Labrador Sea Instrument Locations and OSNAP-West Mooring Diagram

OSNAP is configured as a transbasin observing system, across which AMOC metrics are measured using a combination of fixed current meter arrays, repeat hydrographic occupations and gliders. The OSNAP line consists of two legs: OSNAP West extends from southern Labrador to southwestern Greenland and OSNAP East from southeastern Greenland to the coast of Scotland. Flow through these lines are connected via subsurface RAFOS floats that track the pathways of the overflow waters and help interpret observed variability in fluxes across the OSNAP lines. Though alternate configurations were considered, including a single zonal line across the subpolar region, two lines were chosen due to several advantages: water mass transformations and Arctic export pathways west (Davis Strait and Labrador Sea) and east (Fram Strait and Nordic Seas) of Greenland are physically separated; the equatorward evolution of the DWBC and its constituent water masses can be assessed; and the two lines optimize transport calculations since they are nearly normal to the mean flow in the region.  This configuration also allows for detailed studies of water mass transformation within the three sub-basins:  Iceland, Irminger and Labrador.

The two legs are situated to capitalize on a number of existing and planned long-term observational efforts in the subpolar North Atlantic: the Canadian repeat AR7W program in the Labrador Sea (although the OSNAP West line is shifted slightly southeastward to capture the export of all LSW from the Labrador Sea); the German Labrador Sea western boundary mooring array at 53°N; the US Global OOI (Ocean Observatories Initiative) node placed in the southwest Irminger Sea; the repeat A1E/AR7E hydrographic sections across the Irminger and Iceland Basins (approximately coincident with OSNAP East); and the Ellett line in the Rockall region.