I am interested in Quaternary paleoclimate research and understanding natural climate change. In this regard, I focus on geochronology and glacial geomorphology. I want to understand when and why glaciers and ice sheets expanded and contracted or thickened and thinned in the past. This sort of firm geologic data of past change is crucial to understanding the climate system and what future changes we can expect in a warming world.
I measure the concentration of cosmogenic nuclides such as 10Be, 26Al, 36Cl, 21Ne and 14C that have accumulated in Earth surface sediments. Doing so enables me to answer a range of questions regarding both paleoclimate and Earth surface processes. For example, you will see in the brief project descriptions below, I have been able to determine the timing of major advances of the Patagonian Ice Sheet throughout the Pleistocene, the rate at which the Patagonian landscape is eroding and lowering through time, and the amount and timing of thinning of the Antarctic Ice Sheet in the Weddell Sea region. My research is interdisciplinary; it involves collaborations with geologists, geomorphologists, palaeoecologists and glacial modelers, and I have been fortunate enough to work with several accomplished collaborators in their respective fields. My research activities focus on two regions, Antarctica and southern South America. A brief description of some of these projects can be found below.Check out our blog detailing our current (November 2012) Ellsworth Mountains Blue-ice project
Predicting the future of the Antarctic Ice Sheet in a warming world is one of the key challenges facing geoscientists today. The models used for this purpose must be able to reconstruct past changes in the ice sheet before confidence can be gained in their future predictions. Well-dated geologic evidence of changes in the thickness of the Antarctic Ice Sheet during and following the Last Glacial Maximum (LGM) is a powerful way to constrain and validate such models. These projects aim to provide such data in a relatively unknown part of Antarctica, the Weddell Sea embayment.
The Shackleton Range is critically located to gain insight on both the East and West Antarctic Ice Sheets, which coalesce to form the Filchner Ice Shelf to its west. The range is bounded to its north and south by the East Antarctic Slessor and Recovery glaciers. To record the thinning history of Slessor Glacier, we obtained 10Be and 26Al surface exposure ages from erratics deposited on the flanks of three presently ice-free mountains in the range.
Our key finding is that, unlike most glaciers in Antarctica which thickened during the LGM and thinned subsequently, the Slessor Glacier was no thicker than today during the LGM and perhaps for even longer. We attribute this surprising behaviour to the presence of the deep Thiel Trough beneath the Filchner Ice Shelf, which has restricted seaward migration of the grounding line of Slessor Glacier. Because the Bailey, Recovery, Support Force and Foundation Glaciers also follow the Thiel Trough, we predict that their grounding-lines were similarly affected and thus there has been limited change in the thickness of the ice sheet across a major portion of the Weddell Sea embayment since the LGM. Our findings highlight the importance of topography on the dynamics of ice streams, constrain the volume changes and Antarctica's contribution to sea level fluctuations, explain anomalies in measurements of glacio-isostatic adjustment and affect the interpretation of remote sensing of present ice mass changes.
The manuscript presenting these data can be found [here (soon!)]; a further manuscript discussing the long-term evolution of the Shackleton Range will soon be available.
This project follows the same 'mountain dip-stick' approach used in the Shackleton Range to constrain past changes in thickness of the Antarctic Ice Sheet around the Pensacola Mountains. The range is situated between the East and West Antarctic Ice Sheets and is bounded by the Foundation and Support Force Glaciers which flow northward into the Ronne-Filchner Ice Shelf. Samples collected by the PI, Professor Mike Bentley, are currently being processed in Edinburgh's Cosmogenic Nuclide Laboratory.
Blue-ice moraines exist in many parts of Antarctica. We believe they are formed by wind erosion and ablation of the ice sheet in the lee of a break in an escarpment, where strong katabatic winds are focused after descending from the interior of the ice sheet. The accelerated erosion in these zones steepens the ice surface profile toward the escarpment, thus causing compressive flow in this direction. The moraines therefore act like terminal moraines, despite their location on the lateral margins of the glacier. Preliminary exposure dating of material in an around these areas in the Heritage Range suggest that these moraines have survived intact for several glacial cycles. If so, the existence of these moraines tells us of the stability of the ice sheet. We believe their survival indicates that the West Antarctic Ice Sheet did not collapse during the last interglacial period, as is often suggested.
The manuscript describing this hypothesis is available [here].
I am involved with a group from Heidelberg University, Germany, who are mapping the glacial geomorphology of the Altiplano in southern Peru. I have been working to develop the chronology of these moraines using surface exposure methods. Having sampled these glacial boulders, I am now measuring 36Cl concentrations in feldspars mineral separates to obtain their surface exposure ages.
My PhD work focused on developing the glacial chronology in this valley. The preserved moraines and outwash terraces reflect major expansions of the Patagonian Ice Sheet over the past one million years. The deposits, even those known to be older than one million years, are well preserved owing to the semi-arid climate and fortuitous drainage reversals during interglacial periods. During my PhD I focused my efforts in particular on dating these rare, well preserved pre-LGM glacial surfaces.
In doing so, I compared exposure ages from moraine boulders, moraine cobbles, and outwash terrace cobbles deposited during the same glacial events. I found that surface cobbles on stable outwash terraces gave exposure ages that were older and more reliable than exposure ages from moraine boulders/cobbles. The younger moraine ages are caused by degradation and hence renewal of moraine surfaces through time. This pattern is consistent for all pre-LGM events that I investigated. What surprised me was the long-term stability of these outwash terrace surfaces. For example, I obtained 10Be and 26Al exposure ages of ~1.2 Ma from the outermost and oldest Gorra de Poivre outwash terrace, which is the local expression of the Greatest Patagonian Glaciation, the most extensive advance in Patagonia and one that has been dated elsewhere by 40Ar/39Ar methods at ~1.1 Ma; thus, my exposure ages which directly date the surface, and the 40Ar/39Ar ages which bracket its age, are in close agreement. I obtained additional exposure ages indicating later advances occurred during marine isotope stages (MIS) ~16 (Caracoles ice limit), MIS 8 (Hatcher ice limit) and MIS 2 (Río Blanco ice limit). My findings suggest that, by expanding this approach to other regions in Patagonia, it should be possible to develop the first comprehensive, directly dated long-term glacial chronology in the Southern Hemisphere; this would give rare insight into the development of terrestrial climate in southern South America alongside the global climate record as evident in marine and ice-cores.
I am working with Jake Boex, a PhD student from Exeter, to obtain the first constraints on the past thickness of the former Patagonian Ice Sheet east of the present-day North Patagonian Icefield. This outlet glacier occupied the Chacabuco valley and ultimately terminated east of Lago Pueyrredón. We sampled erratics from the summits and flanks of peaks south of the valley to determine their exposure ages and the timing and rate of thinning and retreat.
Ice cores provide a record of changes in dust flux to Antarctica, which is thought to reflect changes in atmospheric circulation and environmental conditions in dust source areas. Isotopic tracers suggest that South America is the dominant source of the dust, but it is unclear what led to the variable deposition of dust at concentrations 20–50 times higher than present in glacial-aged ice. In this project we characterized the age and composition of Patagonian glacial outwash sediments, to assess the relationship between the Antarctic dust record from Dome C and Patagonian glacial fluctuations for the past 80,000 years. We show that dust peaks in Antarctica coincide with periods in Patagonia when rivers of glacial meltwater deposited sediment directly onto easily mobilized outwash plains. No dust peaks were noted when the glaciers instead terminated directly into pro-glacial lakes. We thus propose that the variable sediment supply resulting from Patagonian glacial fluctuations may have acted as an on/off switch for Antarctic dust deposition. At the last glacial termination, Patagonian glaciers quickly retreated into lakes, which may help explain why the deglacial decline in Antarctic dust concentrations preceded the main phase of warming, sea-level rise and reduction in Southern Hemisphere sea-ice extent.
The manuscript can be found [here].
I was involved in the field sampling of trachite lava flows from the Payun Matru volcanic complex in Argentina. This work was part of the international CRONUS-EU project which aimed to improve the accuracy of cosmogenic-nuclide production rates and systematics. Three lava flows were sampled to obtain production rates for cosmogenic-nuclides over a 1,500 meter altitude range. The results will soon be published by Dr. Tibor Dunai and other collaborators.
For my MSc in GIS, I used a 3D glaciological model to reconstruct the Patagonian Ice Sheet in central Patagonia. After establishing a modelled ice sheet that closely matched the known configuration of the LGM ice sheet in the region, I then modified the bed topography to assess the modelled glaciers sensitivity to such changes. Some of the results can be found [here] and [here].
Prof. David Sugden; Prof. Tibor Dunai; Dr. Nicholas Hulton; Dr. Mike Kaplan; Dr. Christoph Schnabel; Dr. Finlay Stuart; Dr. Chris Fogwill; Dr. Jorge Rabassa; Dr. Andrea Coronato; Dr. Oscar Martinez; Dr. Bob McCulloch; Dr. Mark Naylor; Dr. Sheng Xu; Dr. Alun Hubbard; Prof. Mike Bentley; Dr. Bertil Maechtle; Prof. Neil Glasser; Prof. Stewart Freeman and others.
Quaternary Science Reviews
Journal of Maps.
The figure showing the oblique view of the Weddell Sea area are from the USGS-Terra-web. The bathymetry data is from (Makinson and Nicholls, 1999). The photos below are from the Lago Pueyrredón valley, Argentina.