Steig Research Group

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ResearcH

The polar ice sheets -- Greenland and Antarctica -- are the major focus of the Steig research group. How have the ice sheets changed in the past, why are they changing now, and how will they change in the future? Most of our work is highly interdisciplinary and involves close collaboration with colleagues at UW, across the US, and around the world.

Our primary observational tool is the ice itself – ice samples obtained by drilling cores into the ice sheet, which are brought back to our lab and analyzed. We use advanced techniques -- some developed ourselves -- for obtaining accurate measurements of the isotopic composition of the ice, which provides the key measurement of past climate variability and change. We've been involved with every major ice-coring program led by the National Science Foundation since the early 1990s. Our current work involves a series of papers on the South Pole ice core and planning the next major drilling project, at Hercules Dome, Antarctica.

In addition to developing records from ice cores, we make use of ice-sheet and climate models to help us to interpret what these records are telling us. Current work includes simulations of climate changes that are a consequence of the ice sheet change – how the topography of the ice sheet itself influences the climate – and how such changes would be manifested in paleoclimate data. An important current focus is the use of advanced data-assimilation techniques, in collaboration with our colleague Greg Hakim in Atmospheric Sciences, to develop better understanding of how ice sheet boundary conditions (precipitation, temperature, and ocean and atmospheric circulaiton have changed in the past.

Finally, we also use modern observations – from satellites, weather stations, etc. – as well as models, to understand why the ice sheets are changing now. Changes in the flow of circumpolar deepwater onto the Antarctic continental shelf -- from changing winds discovered in part from our ice core records -- may have increased in the last few decades, thanks anthropoenic CO2 emissions. You can read about more about this work, done in collaboration with colleagues at the British Antarctic Survey and Columbia University, at RealClimate.org

Further examples of our work, and highlights of our discoveries, can be found below and at our Publications page.  

Isotope geochemistry

The mainstay of our lab-based research is the measurement of isotopes of hydrogen and oxygen in ice cores. The isotopologues of water (H216O, H218O, HDO, and H217O) are the most important measurement of past climate from ice cores, providing a proxy for temperature and also telling us about atmospheric circulation changes, as well as (remarkably) conditions over the ocean where the water originally evaporated before being transported to the polar regions and precipitated as snow. The figure shows the absorption spectrum of infrared laser light as it passes through water vapor inside the measurement cell of one of our spectroscopy instruments.

Glacier geophysics 

Before we drill an ice core, we need to identify the best location, where the stratigraphy is undisturbed and where the ice flow is not too complex. We've been working for many years with our colleagues who have expertise in radio-echo sounding to map the ice in 3-D. The data collected are also useful after the ice core has been obtained and analyzed: for example, we need to know how much the ice has thinned to convert measurements of annual layer thickness into a record of snow-accumulation rate. Currently we're collaborating with Knut Christianson, TJ Fudge (both faculty in ESS) and Nick Holschuh (shortly joining the faculty at Amherst College) to pick the spot for dilling at Hercules Dome, Antarctica. The figure shows preliminary data from the most recent (2019-2020) field season, led by Knut.

Paleoclimate and ice-sheet modeling, and data-assimilation methods

We use numerical climate models and ice sheet models to help us understand fundamental processes, and to guide our interpretation of the modern and paleoclimate data. A particular goal is to investigate the impact that changes in the size of the Antarctic ice sheet would have on climate. This will help us eventually use our new ice-core record from Hercules Dome to constrain the size to the ice sheet in the past. We have also been heavily involved, in collaboration with Greg Hakim in Atmospheric Sciences, in the development of data-assimilation techniques to combinate paleoclimate data with ice and climate simulatios to provide statistically robust "state estimates" for the past. The figure shows the change in surface winds and temperature that would result from the collapse of the West Antarctic ice sheet.

Contemporary climate and ice-sheet change

A major focus of our work since the early 2000s has been the investigation of recent climate change in Antarctica, and its connection with the melting of the Antarctic ice sheet. The figure   illustrates the important context provided by our ice core records.  While modern weather station observations in Antarctica date ony to the year 1957, and direct measurements of what is happening to the ice sheet are even more recent (1990s), the record we've obtained from dozens of ice cores in West Antarctic climate goes back hundreds of years. A key result is that although the natural variability in Antarctica is large, recent decades are indeed different, and have probably been unique in the context of the last few millennia.