title: Mean and eddy induced transport in the ocean region adjacent to the Greenland-Scotland Ridge
Creators: name: Lundrigan, Sarah
Publisher: name: Memorial University of Newfoundland
Year: 2019

description: The circulation and transport in the ocean region adjacent to the Greenland-
 Scotland Ridge (GSR) are crucial for maintaining heat, freshwater, and sea-ice exchange
 between the Nordic Seas and Subpolar North Atlantic Ocean. The Nordic
 Seas receive low-density Atlantic Water and transform it into dense water. The dense
 water overflow contributes to the North Atlantic Deep Water mass formation, which
 feeds the lower limb of the Atlantic Meridional Overturning Circulation. The thesis
 presents results from a study of the temperature and salinity transport in the ocean
 region adjacent to the GSR consisting of three sub-projects.
 The first sub-project is focused on model simulations of interannual to decadal
 variability of the exchange through the GSR and its impact on the variability of the
 temperature and salinity in the Nordic Seas. The model results demonstrate that
 the increase in the transport of fresh and cold waters through Fram Strait in the
 1960s was concurrent with a reduction in the exchange over the GSR. The resulting
 imbalance in salinity and heat fluxes through the strait and over the ridge contributed
 to the freshening of the water masses of the Nordic Seas and intensified the Great
 Salinity Anomaly in the 1960s. In the late 1980s the AW transport over the GSR was
 stronger than normal while the exchange through Fram Strait was close to normal.
 The related imbalance in the lateral heat fluxes through the strait and over the ridge
 warmed the Nordic Seas and caused an increase in the temperature of the AW inflow
 to the Arctic Ocean in the late 1980s (i.e., about a decade earlier than the warming
 of the subpolar North Atlantic Ocean in the mid-1990s).
 The second sub-project is focused on observational estimates of the heat flux convergence of the ocean region adjacent to the GSR. Along-track altimeter and
 sea surface temperature satellite observations and ARGO in-situ measurements of
 temperature and salinity are used to investigate the heat transport by mean currents
 and eddies in the ocean region adjacent to the GSR from 2003 to 2008. The results
 from the analysis show that the heat advection by the mean flow in the surface layer
 is zonally asymmetric with a higher magnitude in the western part of the region. This
 asymmetry is associated with an excessive mean heat advection in an area adjacent
 to the Denmark Strait. The advection of heat is high and positive south of the strait
 and low and negative north of it. We suggest that this heat advection impacts the
 local budgets of heat and potential energy of the mean flow in the surface layer.
 The third sub-project studies the vertical structure of the convergence of advective
 fluxes of heat (HFC) and salt (SFC) in the ocean region adjacent to the GSR. The
 study is based on SODA (Simple Ocean Data Assimilation) ocean reanalysis for the
 period between 1965 and 2010. The SODA based estimates show that the high
 values found in satellite based estimates of HFC over the Denmark Strait are part
 of a pattern of high HFC and SFC in the whole water column. In this region, the
 HFC has a maximum at the surface. The highest values of SFC there are found in
 the subsurface layer at depths between 500 and 1500 m. A similar structure of high
 positive SFC and HFC are observed at intermediate depths over the Iceland-Faroe
 Ridge. The EOF analysis of the HFC and SFC shows that the variability of the HFC
 and SFC in these two regions are dominated by modes of coherent variations in the
 SFC and HFC. During warming period in the late 1980s these modes drove strong
 variations of the HFC and SFC over Denmark Strait and Iceland-Faroe Ridge which
 correlated well with the variations in the surface wind stress curl.