Assimilating glaciological and geochronological data into ice-flow models to constrain the deglaciation of Beardmore Glacier, Transantarctic Mountains

Abstract:

Geochronological data can provide constraints on the maximum ice thickness at the Last Glacial Maximum (LGM), the timing of deglaciation, and the Holocene thinning history of TransAntarctic Mountain (TAM) outlet glaciers. While the amount of data and our understanding of ice evolution across the TAM has increased, this critical spatial and temporal information about ice extent is sparsely distributed relative to the longitudinal scale of these glaciers. We assimilate geochronological data in a new glacier modeling workflow to address: What was the ice-thickness history along the glacier length, and what was the timing of the drawdown near the grounding line? Was ice evolution near the grounding line synchronous (or asynchronous) with evolution upstream near the head of the glacier? The approach we have developed can be applied where sufficient geochronological and glaciological data exist at the same glacier, which is the case for multiple TAM outlets. If data constraining past surface elevation are available near the modern grounding zone then they can be used as direct constraints on lower-glacier deglaciation, and data far from the modern grounding zone make it possible to more robustly evaluate deglaciation hypotheses. Here we present an application to Beardmore Glacier, where there is a record of ice-surface elevation from ~20 ka to present, and strong constraints on Holocene deglaciation. The data from the site nearest the Beardmore grounding line provide a time-varying ice-thickness boundary condition for our flowband model, while the data from the up-glacier site are used to calibrate model parameters. Since model-parameter values may be poorly known we discuss our approach to evaluate the bed topography and modern ice state from multiple data sets and gridded data products, as well as to design a modeling strategy that deals with uncertainties in initial conditions and boundary conditions by seeking a suite of solutions.