LAUSR

Labrador Sea Water (LSW) is a major component of the deep limb of the Atlantic Meridional Overturning Circulation, yet LSW transport pathways and their variability lack a complete description. A portion of the LSW exported from the subpolar gyre is advected eastward along the North Atlantic Current and must contend with the Mid‐Atlantic Ridge before reaching the eastern basins of the North Atlantic. Here, we analyze observations from a mooring array and satellite altimetry, together with outputs from a hindcast ocean model simulation, to estimate the mean transport of LSW across the Charlie‐Gibbs Fracture Zone (CGFZ), a primary gateway for the eastward transport of the water mass. The LSW transport estimated from the 25‐year altimetry record is 5.3 ± 2.9 Sv, where the error represents the combination of observational variability and the uncertainty in the projection of the surface velocities to the LSW layer. Current velocities modulate the interannual to higher‐frequency variability of the LSW transport at the CGFZ, while the LSW thickness becomes important on longer time scales. The modeled mean LSW transport for 1993–2012 is higher than the estimate from altimetry, at 8.2 ± 4.1 Sv. The modeled LSW thickness decreases substantially at the CGFZ between 1996 and 2009, consistent with an observed decline in LSW volume in the Labrador Sea after 1994. We suggest that satellite altimetry and continuous hydrographic measurements in the central Labrador Sea, supplemented by profiles from Argo floats, could be sufficient to quantify the LSW transport at the CGFZ. Plain Language Summary Wintertime cooling of the Labrador Sea creates a pool of dense water and a fast track for anthropogenic CO2 to enter the deep ocean. Stored for up to centuries before the Labrador Sea Water returns to the surface, the carbon captured within this layer does not contribute to the greenhouse effect. Despite playing this important role in the climate system, we still lack a complete understanding of the circulation pathways and spreading rates of the Labrador SeaWater. Here, we combine information from ocean‐ and satellite‐based sensors with ocean model outputs to assess the flow rate of Labrador SeaWater through a fracture in theMid‐Atlantic Ridge, the main gateway between the eastern and western basins of the North Atlantic. We find that the fluctuating speed of the Labrador Sea Water transport across the Mid‐Atlantic Ridge can be effectively inferred from satellite‐observed surface currents. Additionally, changes in wintertime conditions in the Labrador Sea water can perturb the spreading rates onto the eastern Atlantic. By combining satellite‐based estimates of surface speed and subsurface estimates of the water properties from floating sensors, we can monitor the transport of the carbon‐rich water from the Labrador Sea in a changing ocean.