Intellectual Merit: The Denmark Strait overflow is an important contributor to the deep limb of the global Meridional Overturning Circulation. However, considerable uncertainty remains regarding the source(s) of the overflow water, and the causes of its transport and temperature/salinity variability. A better description of the dense water pathways leading to Denmark Strait through the Iceland Sea is needed to understand, and ultimately predict, changes in the overflow entering the North Atlantic Ocean.
Recent studies have proposed that there are two pathways for dense water to enter the Denmark Strait: one from the Greenland Sea via the East Greenland Current, and another from the interior Iceland Sea via the North Icelandic Jet. A recent modeling study suggests that these pathways may alternate with changing wind conditions, in particular the wind stress curl in the region around Iceland. During years with high (low) wind stress curl, the East Greenland Current (North Icelandic Jet) is thought to be the dominant pathway.
Subsurface Lagrangian observations, which directly measure fluid parcel pathways, are not presently available in the Iceland Sea. This project will deploy acoustically tracked floats set at a depth of 500 m, just above the sill depth of Denmark Strait, to directly observe dense water pathways in the Iceland Sea over a two-year period. A total of 35 float trajectories, tracked with an array of six sound sources, will be combined with atmospheric, hydrographic and altimetry data to define the relationship between the observed pathways and the forcing conditions during the experiment. An ocean general circulation model simulation of particle trajectories in the Iceland Sea, forced with the conditions observed during the experiment, will be compared with the float trajectories. The field work is heavily leveraged, with the Institute for Marine Research in Bergen, Norway providing the sound source array, the ship time for sound source and float deployment and about 40% of the floats. Overall, this study will help to better understand the Denmark Strait overflow and its variability as well as shed light on the general subsurface circulation of the Iceland Sea.
Broader impacts: This project has bearing on the variability of the lower limb of the Meridional Overturning Circulation, and thus is relevant to the broader topic of the ocean?s role in global climate change. The research is highly collaborative with several international partners, including the Institute of Marine Research in Bergen, Norway, the Marine Research Institute in Reykjavik, Iceland and the Institute of Oceanography in Hamburg, Germany. This experiment will also provide an opportunity for an early career scientist to lead her first field project.
