Abstract
Continuous measurements from the OSNAP (Overturning in the Subpolar North Atlantic Program) array yield the first estimates of trans-basin heat and salinity transports in the subpolar latitudes. For the period from August 2014 to May 2018, there is a poleward heat transport of 0.50 ± 0.05 PW and a poleward salinity transport of 12.5 ± 1.0 Sv across the OSNAP section. Based on the mass and salt budget analyses, we estimate that a surface freshwater input of 0.36 ± 0.05 Sv over the broad subpolar-Arctic region is needed to balance the ocean salinity change created by the OSNAP transports. The overturning circulation is largely responsible for setting these heat and salinity transports (and the derived surface freshwater input) derived from the OSNAP array, while the gyre (isopycnal) circulation contributes to a lesser, but still significant, extent. Despite its relatively weak overturning and heat transport, the Labrador Sea is a strong contributor to salinity and freshwater changes in the subpolar region. Combined with trans-basin transport estimates at other locations, we provide new estimates for the time-mean surface heat and freshwater divergences over a wide domain of the Arctic-North Atlantic region to the north and south of the OSNAP line. Furthermore, we estimate the total heat and freshwater exchanges across the surface area of the extratropical North Atlantic between the OSNAP and the RAPID-MOCHA (RAPID Meridional Overturning Circulation and Heat-flux Array) arrays, by combining the cross-sectional transports with vertically-integrated ocean heat and salinity content. Comparisons with the air-sea heat and freshwater fluxes from atmospheric reanalysis products show an overall consistency, yet with notable differences in the magnitudes during the observation time period.
Highlights
The ocean’s role in the climate system stems from its ability to store and transport large amounts of heat (Rhein et al, 2014)
The Overturning in the Subpolar North Atlantic Program (OSNAP) array has resulted in 4-year continuous measurements of the trans-basin volume, heat and salinity transports in the subpolar re gion
A majority of the subpolar heat transport is contained in the eastern subpolar gyre, which has profound implications for the strength of deep convection north of the OSNAP East line that has been linked to the sub polar overturning variability (Lozier et al, 2019)
Summary
The ocean’s role in the climate system stems from its ability to store and transport large amounts of heat (Rhein et al, 2014). More important than the OHT or OFT is the ocean heat or freshwater convergence/divergence for an enclosed basin, which induces changes in the ocean heat or salinity storage that can impact the basin-scale surface temperature and salinity patterns (Fig. 1) The latter are closely related to the air-sea heat and freshwater fluxes, which may influence the atmospheric circulation and provide potential feedbacks on the oceanic transports (e.g., Sutton et al, 2018). The OSNAP records have provided observational constraints of volume, heat and salinity transports in the region They are key measurements as variations in these transports can cause property changes throughout the water columns and affect the ocean circulation. We compare surface heat and fresh water fluxes from atmospheric reanalyses with these new ocean observation-based estimates
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
