Bubbles of air in ice cores remember the pressure of the overlying air when they are trapped and thus could be used to monitor of the height of the ice sheet over time - but only if the processes during bubble trapping are fully understood.
Importance of the area of research concerned:
The demise of the Greenland and West Antarctic sheets has become an extremely high-risk scenario with an ever-increasing probability. Assigning likelihood of this scenario is challenging, requiring the prediction of ice sheet stability over centuries to millennia using complex numerical models. These model need to be ground-truthed with real world data, which at the absolute minimum span millennia. Data from the geologic past is thus our best test-bed for these model as it offers partial analogues for future changes in ice sheets. A useful target is the last deglaciation, the time period beginning at 18,000 years ago when changes in the earth’s orbit and increases in atmospheric CO2 drove the retreat of the West Antarctic Ice Sheet from its glacial to modern day configuration. What was the timing of the WAIS retreat during the last deglaciation? When was the modern grounding line established? What is the relationship between ice sheet retreat and ocean temperature? One under-utilized tool is the total amount of air trapped within an ice core sample (the “total air content”), which in principle acts as palaeo-barometer and thus a record of ice sheet elevation.
Project summary :
Total air content has recently been used as a crucial constraint in understanding the pattern of reconstructed temperature across the Antarctic ice sheet during the LGM (Buizert et al. 2021). Less work has been done looking at dynamic changes in total air content because there are secondary influences on total air content related to transient changes in firn processes (Eichler et al., 2016). To date, no theory has been able to account for all these secondary effects and thus an accurate reconstruction of ice sheet elevation through time remains elusive. The primary focus of this project is to investigate how ice sheet elevation can be deconvolved from the total air content signal.
What will the student do?:
The student will utilise a recently developed high-accuracy total air content system (Nehrhbass-Ahles et al., 2020, AGU Abstract) to collect new data from the suite of BAS ice cores from the ice rises and promontories that ring the West Antarctic sheet. The data collection will focus on the evolution of the West Antarctic ice sheet from the Last Glacial Period to the present, although other studies are possible depending on ice availability. To interpret the data the student will develop new numerical methods using a dynamic densification firn model to understand the processes during the air occlusion. Finally, the reconstructed histories will be compared to ice sheet model predictions (e.g. Kingslake et al., 2018) to derive a data and model consistent reconstruction of the West Antartic ice sheet elevation.
You can find out about applying for this project on the British Antarctic Survey (BAS) page.