On the hydrography of Denmark Strait

Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 306–321, doi:10.1002/2016JC012007.Using 111 shipboard hydrographic sections across Denmark Strait occupied between 1990 and 2012, we characterize the mean conditions at the sill, quantify the water mass constituents, and describe the dominant features of the Denmark Strait Overflow Water (DSOW). The mean vertical sections of temperature, salinity, and density reveal the presence of circulation components found upstream of the sill, in particular the shelfbreak East Greenland Current (EGC) and the separated EGC. These correspond to hydrographic fronts consistent with surface-intensified southward flow. Deeper in the water column the isopycnals slope oppositely, indicative of bottom-intensified flow of DSOW. An end-member analysis indicates that the deepest part of Denmark Strait is dominated by Arctic-Origin Water with only small amounts of Atlantic-Origin Water. On the western side of the strait, the overflow water is a mixture of both constituents, with a contribution from Polar Surface Water. Weakly stratified “boluses” of dense water are present in 41% of the occupations, revealing that this is a common configuration of DSOW. The bolus water is primarily Arctic-Origin Water and constitutes the densest portion of the overflow. The boluses have become warmer and saltier over the 22 year record, which can be explained by changes in end-member properties and their relative contributions to bolus composition.US National Science Foundation (RP and DM) Grant Number: OCE-0959381; ;Norwegian Research Council Grant Number: 231647 (KV)2017-07-2

The North Icelandic Jet and its relationship to the North Icelandic Irminger Current

Author Posting. © The Authors, 2017. This article is posted here by permission of Sears Foundation for Marine Research for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 75 (2017): 605-639, doi:10.1357/002224017822109505.Shipboard hydrographic and velocity sections are used to quantify aspects of the North Icelandic Jet (NIJ), which transports dense overflow water to Denmark Strait, and the North Icelandic Irminger Current (NIIC), which imports Atlantic water to the Iceland Sea. The mean transports of the two currents are comparable, in line with previous notions that there is a local overturning cell in the Iceland Sea that transforms the Atlantic water to dense overflow water. As the NIJ and NIIC flow along the north side of Iceland, they appear to share a common front when the bottom topography steers them close together, but even when they are separate there is a poleward flow inshore of the NIJ. The interannual variability in salinity of the inflowing NIIC is in phase with that of the outflowing NIJ. It is suggested, however, that the NIIC signal does not dictate that of the NIJ. Instead, the combination of liquid and solid freshwater flux from the east Greenland boundary can account for the observed net freshening of the NIIC to the NIJ for the densest half of the overturning circulation in the northwest Iceland Sea. This implies that the remaining overturning must occur in a different geographic area, consistent with earlier model results. The year-to-year variability in salinity of the NIJ can be explained by applying annual anomalies of evaporation minus precipitation over the Iceland Sea to a one-dimensional mixing model. These anomalies vary in phase with the wind stress curl over the North Atlantic subpolar gyre, which previous studies have shown drives the interannual variation in salinity of the inflowing NIIC.Funding for the project was provided by the National Science Foundation under grants OCE-1558742 (RSP, MAS, DJT, CN), OCE-1433170 (MAS), and OCE-0959381 (DM); the Norwegian Research Council under grant agreement no. 231647 (KV); the Bergen Research Foundation (KV); the European Union Seventh Framework Programme (FP7 2007-2013) under grant agreement 308299 (NACLIM project, KV, HV, and SJ); and the Natural Sciences and Engineering Research Council of Canada (GWKM)

Hydrographic structure of overflow water passing through the Denmark Strait

Thesis: S.M., Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2015.Cataloged from PDF version of thesis.Includes bibliographical references (pages 63-66).Denmark Strait Overflow Water (DSOW) constitutes the densest portion of North Atlantic Deep Water, which feeds the lower limb of the Atlantic Meridional Overturning Circulation (AMOC). As such, it is critical to understand how DSOW is transferred from the upstream basins in the Nordic Seas, across the Greenland-Scotland Ridge, and to the North Atlantic Ocean. The goal of this study is to characterize the hydrographic structure of the different DSOW constituents at the sill before the water descends into the Irminger Sea using temperature and salinity (T/S) data from 111 shipboard crossings in the vicinity of the sill, collected between 1990 and 2012. The individual realizations indicate that weakly stratified "boluses" of DSOW frequent the sill and contribute the densest water to the overflow. This study also characterizes the structure, size, and location of the boluses and relates them to the T/S modes found at the sill. Lastly, historical hydrographic data from the Nordic Seas are used to make inferences regarding the origin of the boluses.by Dana M. Mastropole.S.M