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Ocean Surface Topography from Space
SCIENCE
Linking Sea Surface Height Variations with Hydrographic Variability around the Greenland Ice Sheet to Improve Understanding of Sea Level Rise


Author:

Ian Fenty - (Jet Propulsion Laboratory)

Co-Investigator(s):
  Dr. Dimitris Menemenlis
Prof. Robert Nerem
(Jet Propulsion Laboratory)
(Jet Propulsion Laboratory)


Collaborator(s):
  Dr. Gael Forget
Dr. Ichiro Fukumori
Dr. Ronald Kwok
Dr. Kristin Laidre
Luc Rainville
(Jet Propulsion Laboratory)
(Jet Propulsion Laboratory)
(Jet Propulsion Laboratory
(Jet Propulsion Laboratory)
(Jet Propulsion Laboratory)


Abstract:
The acceleration of global mean sea level rise in the past several decades has been driven, in part, by increased melting of the Greenland Ice Sheet. Over the satellite altimetry period, the rate of global mean sea level rise has nearly doubled relative to its 20th century average to 3.2 mm/yr, with ~0.75 mm/yr now attributable to the net transfer of water mass from the melting of Greenland’s grounded ice. One hypothesis for the increase in ice sheet mass loss is that the subsurface waters circulating above its continental shelf have warmed, leading to increased submarine melt rates at the ice-ocean interface of its marine-terminating glaciers. While in situ temperature and satellite sea surface height (SSH) data in the basins adjacent to the ice sheet indicate warming over the past two decades, few hydrographic data exist on the shelf to test the hypothesis. Our goal is an improved understanding of sea surface height and ocean heat variability on the Greenland shelf, its relationship to hydrographic and atmospheric variability, and the implications for past and future ocean-ice sheet interaction and sea level rise through the development of new techniques to analyze satellite ocean surface topography data.

To this end, we will investigate the past two and half decades of sea surface height and ocean heat content on Greenland’s shelf using remote sensing data including altimetry, atmospheric reanalyses, in situ hydrography data, and numerical ocean modelling. We propose the following activities:

  1. Characterize SSH variability on Greenland’s continental shelf. SSH data for this activity will come from a set of satellite altimeters. Removal of the tide signal from SSH will be performed using a new tide model using new high-resolution shelf bathymetry from NASA Oceans Melting Greenland (OMG) mission. Following a period of cross-evaluation, analysis, and reprocessing, these coastal altimetry data will be combined to produce a consolidated SSH around the Greenland shelf from 1992-present.
  2. Estimate the magnitudes and drivers of steric and non-steric SSH variations around the Greenland shelf from 1992-present using SSH data and numerical coupled sea ice-ocean models from the Estimating the Circulation and Climate of the Ocean (ECCO) consortium. As part of this analysis. We will use the ocean models to precisely diagnose how the fluxes of heat, salt, and mass from the atmosphere and ocean cause these density and mass changes as function of space and time.
  3. Quantify the extent to which SSH and temperature variations on the shelf can be explained using the adjoint of our ocean model in conjunction with anomalies from (a) in situ and remotely sensed ocean and atmosphere data and (b) the full ocean state reconstructed in ECCO ocean syntheses. Data for this task include ocean surface topography, in situ temperature and salinity (from OMG, Argo, and others), and atmospheric forcing. An important result of this activity will be the determination of whether the existing ocean observation system as it has evolved from 1990 to present provides enough information to reconstruct ocean temperature changes on Greenland’s shelf. If the present ocean observation system is inadequate for the task we will determine how it would need to be augmented to achieve this objective.

By combining our ocean heat content reconstructions with ice sheet measurements from OMG and other NASA missions, including ICESat-1, Operation Ice Bridge, and the forthcoming ICESat-2, we will be able to link changes of Greenland’s marine-terminating glaciers to ocean temperature changes on their neighboring shelves. Our study will also pave the way for future monitoring of ocean thermal forcing of the Greenland Ice Sheet using altimetric data from the upcoming SWOT, Sentinel-3, and Jason-CS missions.



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