Project: Tracking Greenland Melt in the Ocean Using Noble Gas Fingerprints

NSF Award Abstract:
Rapid land-ice loss from the Greenland Ice Sheet is resulting in increased fresh water discharge into the ocean. One consequence is a rise in global sea level. Another consequence, that has attracted less attention, is the freshening of ocean waters at Greenland's coastal margins. Locally, this impacts sea-ice formation, air-sea exchange, the marine ecosystems and local communities. On larger scales, it can impact dense water formation and hence the global circulation. Beyond bulk estimates based on ice sheet-wide assessments, however, the limited knowledge of where, when and how fresh water enters the ocean makes it difficult to assess its present and future impact. One consequence of this uncertainty is the large discrepancy in the formulation of the fresh water forcing used in model studies to investigate the oceanic impact of Greenland melt. Greenland's fresh water discharge occurs at the head of fjords in the form of icebergs, submarine melt and discharge of surface melt at base of glaciers often hundreds of meters beneath sea level. This discharge drives a non-trivial transformation of the fjords' waters and forms a new water class, glacially modified waters. It is through the export of these glacially modified waters, much of it occurring below the surface, that Greenland's fresh water reaches the large-scale ocean circulation. Traditional measurements do not provide an unambiguous means of tracking glacially modified waters nor can they be used to quantify the relative fraction of surface and submarine melt. Yet knowing how Greenland's fresh water is exported, and differentiating pathways and rates for submarine or surface melt, which may vary at different rates, is key to the ability to assess present and future local and large-scale impacts. By providing the first measurements of how different melt components spread into Greenland's fjords and onto the continental shelves, this project will contribute to ensuring appropriate representation of the relevant dynamics in climate models, which do not resolve ice-ocean exchanges or fjord dynamics. The cross-disciplinary nature of this project will benefit the training of a post-doc. As part of this project, the scientists have interested a media science program (NOVA) in the largely neglected impact of Greenland's increasing fresh water discharge on the ocean. Pending obtaining separate funding, NOVA will be sending a professional producer in the field with the scientists and use material for this project to produce several media pieces on the problem of melting glaciers. In addition, the material from this research will used to raise public awareness on changes occurring in the oceans near Greenland.

Land-ice loss at both poles is predicted to increase in a warming climate and will further increase the fresh water discharge into the oceans. Understanding the mechanisms that govern the fate of this fresh water is key to the ability to predict both its local and global impacts. This project utilizes the unique signature of noble gases, and other tracers (tritium, oxygen and helium isotopes), in each type of glacial meltwater to identify and track different kinds of Greenland fresh water in a major glacier-fjord system and on the continental shelves. The method builds on work in Antarctica and, more recently, on a pilot study conducted by the project's scientists in a small glacier-fjord system in West Greenland. The field observations will take advantage of two existing cruises, one to a large glacial fjord system in Southeast Greenland and the other to the continental shelves at the southern tip of Greenland, to collect geochemical tracer data in regions influenced by Greenland's meltwater. Synoptic and moored measurements, collected as part of these cruises, will provide context to the geochemical tracer analysis. The first goal of the project is to develop a method that can be used to track glacial melt water both in Greenland and Antarctica and at the margins of other ice caps and glaciers. A second objective is to provide an ocean-based assessment of the glacial melt water transport out of a major fjord, and along Greenland's continental shelves, at the peak of the melt season.