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Research: Research


Silty ice, sediment, and bedrock from the base of ice cores offer a unique view into the landscapes below ice sheets and contain information about past times when Greenland or Antarctica were ice-free. 

We published an article in the Proceedings of the National Academy of Sciences (PNAS) about the long-lost sediment from the Camp Century ice core. We report the discovery of fossil tundra plants and biomolecules from from ancient ecosystems when NW Greenland was ice-free: once in the Early Pleistocene and again in the last million years. The latter ice-free event coincides with similar findings from the bedrock core from GISP2. The main implication of our findings: the Greenland Ice Sheet survived most Pleistocene interglacial periods, but it melted beyond some climate threshold without human influence. Click here to see the reporting from international news outlets about our study.

As part of an international collaborative team (36 scientists from 22 institutions), I am coordinating a full analysis of the entire Camp Century subglacial sediment archive. Our goals are to better understand the depositional history of the sediment, reconstruct paleoclimate conditions and paleoecosystems conditions during ice-free events, and better characterize the sub-glacial geology of northwest Greenland. 



About 7 million years ago, glaciers on Greenland grew large enough to reach the ocean. Since this time, the ice sheet has eroded the Greenland landscape and exported sediment to the ocean, either by directly depositing diamict onto the continental shelf or releasing plumes of fine sediment and icebergs further out to sea.

Since the Greenland Ice Sheet presently covers and significantly eroded the landscape, offshore sediments offer one of the only ways to understand the long-term history of the ice sheet. By analyzing these sediments with many different techniques we can understand patterns of erosion near the surface (cosmogenic nuclides), at the crustal scale (thermochronometry), and the types of vegetation (biomarkers) that covered Greenland during past ice-free times.

We published a paper in Geophysical Research Letters outlining our approach, and continue to work on additional marine cores from around Greenland. I am sailing on IODP Expedition 400: Glaciated NW Greenland Margin in the summer of 2023 to apply this approach to sediments collected from Baffin Bay and Melville Bugt.



98% of Antarctica is encased in glacier ice and holds ~60 m of potential sea level rise. In order to understand the fate of Antarctica as the climate system warms, records of past changes in the thickness and extent of the Antarctic ice sheets are invaluable. The McMurdo Sound region is a unique ice-free oasis where such records are found.

During my PhD, I embarked to the ice-free volcanic islands and peninsulas of McMurdo Sound, Antarctica, where marine ice sheets in the Ross Sea expanded and contracted repeatedly over the past several million years. During these episodes of glaciation, the ice sheet transported rocks and sediment sourced from deep in the Antarctic interior, leaving behind "bath tub rings" that outline the former geometry of the ice sheet.  Along the margins of the former ice sheet, algae thrived in meltwater streams that drained into small ponds, and were buried. Radiocarbon ages of the algae provide a timeframe when ice was present. In an ideal world, cosmogenic nuclide exposure ages of boulder left behind by the ice sheet would tell us how long ago ice retreated from these positions, but in practice, reveal more information about erosional history of the Transantarctic Mountains.

I published a paper in GSA Bulletin focused on the extent during the local Last Glacial Maximum and continue to work on the Pleistocene history of ice sheet behavior in the Ross Sea.

From Christ & Bierman, 2020, GSA Bulletin


As the earth moved out of the last ice age, the present interglacial period, the Holocene, began about 12,000 years ago. All of human civilization has flourished within this short time, and in only the last ~200 years humans began to fundamentally alter the climate system by burning fossil fuels and releasing greenhouse gases into the atmosphere at exponential rates.

The polar regions are rapidly responding to climate change, and it is important to place these environmental changes in the context of the prior several thousand years during the Late Holocene. This topic first fascinated me as an undergraduate at Hamilton College, where I investigated how the Antarctic Peninsula responded to Late Holocene climate variability and anthropogenic climate change. We found that regional climate cooled for the last ~4000 years, resulting in greater sea ice coverage and culminating in the advance of tidewater glaciers and expansion of small ice shelves in the western Antarctic Peninsula during the Little Ice Age between ~800-130 years ago. We published papers about a couple of west Antarctic Peninsula fjords - Barilari Bay (GSA Bulletin) and Bigo Bay (Quaternary Science Reviews) 

During my PhD, I collected an ice core from an ice-covered lake in McMurdo Sound, and advised an undergraduate thesis that examined how Late Holocene climate variability and teleconnections directly influenced local hydroclimate. We published the results in Antarctic Science.

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Techniques I use to do science


Cosmogenic nuclides extraction

Quartz purification

Malvern Particle Sizer


Radiocarbon sample preparation

ICP/MS Analysis

Water stable isotopes


Geologic Mapping
Cosmogenic nuclide sampling
Sedimentology & stratigraphy descriptions
Core logging
Groundwater monitoring well installation & sampling
Surface water sampling for VOCs, metals
Soil sampling


ArcGIS Pro & ArcMap


Image analysis

Research: List
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