Arctic Field Projects



Project Title: Collaborative Research: Submarine Melting and Freshwater Export in Greenland's Glacial Fjords: The Role of Subglacial Discharge, Fjord Topography and Shelf Properties (Award# 1434041)

PI: Cenedese, Claudia (ccenedese@whoi.edu)
Phone: (508) 289.2696 
Institute/Department: Woods Hole Oceanographic Institution,  
IPY Project?
Funding Agency: US\Federal\NSF\GEO\OCE
Program Manager: Dr. Baris Uz (bmuz@nsf.gov)
Discipline(s): | Oceanography |

Project Web Site(s):
NSF_Award_Info: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1...

Science Summary:
Increased submarine melting of Greenland's glaciers has emerged as a plausible trigger for their recent acceleration in mass loss and for quadrupling Greenland's contribution to sea-level rise from 1992-2000 to 2001-2011. Notwithstanding its importance, current understanding of submarine melting is limited, and it is presently absent or crudely represented in glacier, ice sheet and climate models. Ocean models are beginning to include freshwater discharge from Greenland, but where and when this freshwater enters the continental shelves is largely unknown. Understanding the dynamics that govern the magnitude and spatial distribution of both submarine melt and freshwater export to the open ocean is a key step in projecting sea level rise and the consequences of the Greenland-induced ocean freshening. A multifaceted approach that includes the analysis of existing observations, a series of laboratory experiments and high-resolution numerical simulations will seek to quantify the sensitivity of submarine melting and freshwater export distribution to the dominant controls, and to derive basic parameterizations that relate submarine melt rates and freshwater export to large-scale parameters including subglacial discharge, fjord size and topography (i.e. sill), and continental shelf hydrography and stratification. The project involves collaborations with international experts from complementary fields and will contribute to fostering interactions between the multiple disciplines involved and beyond national boundaries. One student and one post-doctoral fellow will be exposed to a cutting-edge problem and work within a multidisciplinary team of researchers. Results from this project will be widely disseminated to scientists across disciplines, as demonstrated by the project team's long track record of organizing summer schools and working groups, and to the public through different media outlets, including a blog on polar science. Recent Greenland related work by the project team has been featured in the New York Times, the Weather Channel and Italian National Television, amongst other media. The exchange of heat and freshwater between the ocean and Greenland's outlet glaciers, typically grounded hundreds of meters below sea level, occurs at the head of long, deep fjords that connect the ice sheet margins to the continental shelves and the large-scale North Atlantic circulation. Recent work by the project team, and others, has shown, for several idealized or specific cases, that the fjord's temperature and stratification, as well as the summer discharge of surface melt at the base of the glacier (subglacial discharge) have a first order impact on the magnitude, distribution and timing of submarine melting. These results will be generalized by formulating parameterizations, suitable for large-scale ice sheet and climate models, of submarine melting and associated freshwater export distributions as a function of large-scale controls. Two specific tasks will be carried out: 1) Establishing dynamical links between submarine melting, and the associated freshwater export from the glacier, and its dominant controls, which include: the magnitude and spatial distribution of subglacial discharge; hydrographic properties and stratification on the continental shelf; and fjord size and topography, in particular the presence and height of a sill. 2) Formulating two complementary parameterizations: one for the magnitude and spatial distribution of submarine melting as a function of the fjord's topography and size, the shelf stratification and the subglacial discharge, to be used in glacier and ice sheet models; and one for the magnitude and vertical distribution of the freshwater export from the fjords to be used in large scale ocean and climate models which do not resolve the fjords. This project involves the analysis of existing data, laboratory experiments and high-resolution numerical simulations. It will be carried out in collaboration with two international experts: a glacial hydrologist (Ian Hewitt at the University of Oxford) and a fjord oceanographer (Lars Arneborg at the University of Goteborg). The work is aimed at understanding a newly discovered "wiring" of our climate system and is timely because of the large and unanticipated changes that are occurring at Greenland's margins. It is complementary to the study of ice sheet/ocean interactions around Antarctica (the more studied of the two) since both the large-scale ocean circulation and the presence of narrow, long fjords in Greenland contribute a unique set of relevant dynamical mechanisms.

Logistics Summary:
This collaborative project between Cenedese (1434041, WHOI) and Heimbach (1434149, MIT) will continue work begun under NSF 1130008. Warming of the atmosphere and ocean around Greenland, over the last few decades, has resulted in excess melting of the Greenland Ice Sheet. The ice loss is, in part, due to increased melting of glaciers that reach the ocean. This submarine melting, however, is poorly understood and challenging to observe or model. One important consequence of a shrinking Greenland Ice Sheet is a rise in sea level. A second, less understood, consequence is what impact the excess meltwater will have on the ocean circulation. If this meltwater ends up at the surface, it can form sea-ice easily and also become barrier to heat exchanges between the subsurface ocean and the atmosphere, which, in turn, can affect the circulation of the entire Atlantic Ocean. But if the meltwater is released below the surface, for example because the glaciers and icebergs extend hundreds of meters below the surface, its fate and its impact on the ocean are unclear. Improving our understanding of submarine melting and of where the meltwater from Greenland ends up is thus key to future projections of sea level rise and changes in the ocean, and the marine ecosystems, around Greenland. This project has addressed the physics of submarine melting, and meltwater spreading, by combining laboratory experiments, numerical models and the analysis of data collected from the margins of Greenland. Through these complementary approaches, we have been able to study melting and the meltwater spreading in realistic environments and improve understanding of what controls variations in melting of glaciers and icebergs. One key result from this project has been to show that the melting of icebergs, and meltwater spreading, is strongly sensitive to the speed at which the ocean waters are moving past the icebergs. Laboratory experiments, guided by data from Greenland's margins, have provided us with a tool to visualize and quantify these effects and improve existing representations of this process. A second, important result has been the first estimate of submarine melting for Greenland's three remaining floating ice shelves (this is the floating portion of a glacier that reaches the ocean) using a new method and ultra-high resolution satellite data. A third, area of focus of this work has targeted the plumes of surface melt discharged at the glacier/ocean margin, hundreds of meters below the surface, and their impact on melting of the glacier and the spreading of sediments near the coastal margins. Results from this project have been: published in 10 scientific papers, presented at scientific meetings, used in lectures during summer courses, used in the training of multiple graduate students and presented to the public through a series of media pieces. No fieldwork was conducted.




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