The Overturning in the Subpolar North Atlantic Program (OSNAP) is an international project designed to study the mechanistic link between

water mass An oceanographic water mass is an identifiable body of water with a common formation history which has physical properties distinct from surrounding water. Properties include temperature, salinity, chemical - isotopic ratios, and other physical ...

transformation at high

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...

s and the

meridional overturning circulation Thermohaline circulation (THC) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. The adjective ''thermohaline'' derives from '' thermo-'' referring to tem ...

in the North Atlantic (

AMOC The Atlantic meridional overturning circulation (AMOC) is part of a global thermohaline circulation in the oceans and is the zonally integrated component of surface and deep currents in the Atlantic Ocean. It is characterized by a northward f ...

) on interannual time scales. Though this linkage is evident in climate models on decadal time scales, to date there has been no clear demonstration of AMOC variability in response to changes in deep water formation on interannual and decadal time scales. OSNAP intends to fill that gap by providing a continuous record of the trans-basin fluxes of heat, mass and freshwater for a comparison to records of convective activity and water mass transformation at high latitudes in the North Atlantic. The OSNAP observing system, fully deployed in the summer of 2014, consists of moorings, gliders and

RAFOS float RAFOS floatsThe RAFOS system
T. Rossby D. Dorson J. Fontaine ...

s spanning the subpolar North Atlantic from Labrador to Greenland to Scotland. Measurement contributions come from the US, the UK, Germany, the Netherlands, Canada, China and France. Vigorous boundary currents crossing the OSNAP line are directly measured in the

Labrador , nickname = "The Big Land" , etymology = , subdivision_type = Country , subdivision_name = Canada , subdivision_type1 = Province , subdivision_name1 ...

and

Irminger Sea The Irminger Sea is a marginal sea of the North Atlantic Ocean. It is bordered to the west by southern Greenland, to the north by Iceland and the Denmark Strait, to the east by the Reykjanes Ridge (a northern part of the Mid-Atlantic Ridge), ...

s by

current meter A current meter is an oceanographic device for flow measurement by mechanical, tilt, acoustical or electrical means. Different reference frames In physics, one distinguishes different reference frames depending on where the observer is located ...

arrays, and over the eastern flank of the

Reykjanes Ridge The Mid-Atlantic Ridge is a mid-ocean ridge (a divergent or constructive plate boundary) located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. In the North Atlantic, the ridge separates the North Am ...

by deep arrays.

Geostrophic current A geostrophic current is an oceanic current in which the pressure gradient force is balanced by the Coriolis effect. The direction of geostrophic flow is parallel to the isobars, with the high pressure to the right of the flow in the Northern H ...

s in the basin interior are estimated using temperature and

salinity Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...

measurements from moorings and gliders. The AMOC is calculated on the basis of the directly measured

boundary current Boundary currents are ocean currents with dynamics determined by the presence of a coastline, and fall into two distinct categories: western boundary currents and eastern boundary currents. Eastern boundary currents Eastern boundary currents are ...

s, the geostrophic currents and the

Ekman transport Ekman transport is part of Ekman motion theory, first investigated in 1902 by Vagn Walfrid Ekman. Winds are the main source of energy for ocean circulation, and Ekman Transport is a component of wind-driven ocean current. Ekman transport occurs w ...

s estimated from the surface

wind stress In physical oceanography and fluid dynamics, the wind stress is the shear stress exerted by the wind on the surface of large bodies of water – such as oceans, seas, estuaries and lakes. Stress is the quantity that describes the magnitude of a for ...

. In conjunction with the RAPID/MOCHA array at 26⁰N, the EU THOR/NACLIM program and other observational elements, OSNAP will provide a comprehensive measure of the three-dimensional AMOC in the North Atlantic and an understanding of what drives its variability. The first OSNAP data products are expected in the fall of 2017.

External links

* OSNAP http://www.o-snap.org * RAPID/MOCHA http://www.rapid.ac.uk/rapidmoc/ * EU THOR/NACLIM http://www.eu-thor.eu/index.php?id=1994 * ATLAS http://www.eu-atlas.org

References

{{authority control Physical oceanography Water masses Oceanographic organizations

See also

External links

References