Collaborative Research: Probing the Earth System in Patagonia: Crustal motion in relation to tectonics, earth structure, the hydrological cycle and climate change

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).In this work we explore the elastic and viscoelastic responses of the solid earth related to climate induced surface load changes. The climate changes and associated loads occur at time scales ranging from annual hydrological cycles at one extreme to ice sheet evolution (over the past 20,000 years) at the other. Our geographical focus is Patagonia, which currently possesses the largest body of ice in the southern hemisphere outside of Antarctica. The Patagonian Ice Fields are known to be rapidly wasting, e.g. faster than those in Alaska in percentage terms, and there is growing evidence this ice loss is accelerating. Our primary approach to this earth system science project is through crustal motion geodesy and regional geophysics, including elastic and viscoelastic modeling of several overlapping phenomena. One task in our study is using the earth as a ?bathroom scale? to weigh annual and inter-annual changes in ice mass using Earth?s instantaneous elastic response to surface load changes. This approach will be calibrated and validated by relating annual or seasonal patterns of loading (the cause) with in-phase seasonal oscillations of adjacent bedrock (the effect). Having calibrated our ?weighing machine? in this way, we will be able to very quickly detect and analyze any abrupt changes in long term rates of ice gain or loss. We will use our results to test all predictions for postglacial rebound (PGR) in Patagonia. The results obtained here will also provide essential ?PGR correction? calibration information to scientists using gravity data from the Gravity Recovery and Climate Experiment (GRACE) satellite project, and enable GRACE to make the first direct observations of mass transfer between the ice sheets and the oceans. The results from Patagonia will also provide useful input to the POLENET project?s measurements of the effects of climate change, which is a project of tremendous societal importance. It is widely understood that there is serious danger that the W. Antarctic or Greenland ice sheets could collapse, or break up, and become icebergs in the ocean. This would raise sea level over the short time, much shorter than that necessary to melt the ice, during which this break up occurred. The rise in sea level associated with such a collapse would seriously damage the global economy and degrade the social infrastructure supporting hundreds of millions of people by inundating large swaths of densely inhabited coastal areas worldwide. While it may be too late to reverse global warming before sea level rise becomes seriously problematic, it is crucial to assess both the possible severity of sea level rise, and the amount of time that governments have to respond to, or mitigate developments they may be powerless to prevent. This project demonstrates the role in which solid earth sciences can contribute to modern climate change research; its broadest impact is likely to be a better metrology of mass transfer between ice sheets and the oceans at the global scale.In this work we explore relations between the solid earth and climate. These earth processes include tectonics, subsurface rheological structure, and elastic and viscoelastic loading responses. The climate contribution ranges over time scales encompassing annual hydrological cycles at one extreme to ice sheet evolution and Holocene climate change (at a minimum) at the other. Our geographical focus is Patagonia, which possesses the largest body of ice currently found in the southern hemisphere outside of Antarctica. These ice bodies are rapidly wasting, e.g. faster than the Alaskan ice fields in percentage terms, and there is growing evidence this ice loss is accelerating. Our primary approach to this earth system science project is through crustal motion geodesy (using both campaign and continuous GPS measurements and precise, scientific, GPS processing tools) and regional geophysics, including elastic and viscoelastic modeling of various physical phenomena overlapping in time and space. One task in our study for example is to ?weigh? annual and inter-annual changes in ice mass using Earth?s instantaneous elastic response to surface load changes. This approach will be calibrated and validated by relating annual or seasonal patterns of loading (the cause) with in-phase seasonal oscillations of adjacent bedrock (the effect). Having calibrated our ?weighing machine? in this way, we will be able to very quickly detect and analyze any abrupt changes in long term rates of ice gain or loss that may occur. We will use our results and all available information about ice mass oscillations and secular trends from glaciology to test all available predictions for postglacial rebound (PGR) in Patagonia. The results obtained here will also provide essential ?PGR correction? calibration information for proper analysis of gravity data from the Gravity Recovery and Climate Experiment (GRACE). The PGR correction will enable GRACE to make the first direct observations of mass transfer between the ice sheets and the oceans. The advantages of pursuing this agenda in Patagonia, over Antarctica and Greenland, include: the ?convenient? scale of the ice fields, the very pronounced tectonic gradients already documented there, the far easier access to bedrock surrounding the ice fields, the less expensive logistics, and a far denser and far more easily managed geodetic infrastructure. The results from Patagonia will also provide useful input to the POLENET project?s measurements of the effects of climate change, which is of tremendous societal importance. It is widely understood there is serious danger the W. Antarctic or Greenland ice sheets could collapse. This would seriously damage the global economy and degrade the social infrastructure supporting hundreds of millions of people by inundating large swaths of densely inhabited coastal areas worldwide. While it may be too late to reverse global warming before sea level rise becomes seriously problematic, it is crucial to assess both the possible severity of sea level rise, and the amount of time that governments have to respond to, or mitigate developments that they may be powerless to prevent. This project demonstrates the role in which solid earth sciences can contribute to modern climate change research; its broadest impact is likely to be a better metrology of mass transfer between ice sheets and the oceans at the global scale.