Effects of divide migration on ice-core records at Summit, Greenland with Ed Waddington, TJ Fudge, and the Centre for Ice and Climate (Copenhagen)

Transients in accumulation and in ice flow can drive ice-divide migration. However, it is likely that dynamical changes initiated near the ice-sheet margin control ice-divide position. Interior ice responds to modern marginal changes, and larger margin changes (e.g. during glacial interglacial transitions) likely led to a larger interior response. We investigate how flux perturbations that drive ice-divide migrations on hundreds to thousands of year timescales can affect the thinning function, which alters the depth-age scale, the ice-temperature profile, and the modeled ice-core accumulation history at ice-core sites on the divide or on the flank of the divide. For this study we use a 2.5-D (flowband) ice-flow model that sufficiently captures the broad-scale behavior of ice-sheet interiors, including ice-divide migration. Since we do not know the actual migration history of ice divides, we explore the response of interior ice to plausible changes in accumulation and flow on various timescales to assess the degree to which upstream effects may need to be considered in order to characterize ice-sheet history at an ice-core site.

In particular, the divide position in Central Greenland near the Greenland Ice Core Project (GRIP) and the Greenland Ice Sheet Project Two (GISP2) ice-core sites may not have been stable, and for this reason we evaluate migration scentarios for an ice sheet with a modern state similar to Central Greenland. This site is distinct because of the two deep ice cores within 30 km of each other, one approximately on the modern divide and one approximately 30 km west on the flank of the modern divide. We are investigating how an offset in these ice-core records over a specific time period may be due to a past episode of divide migration.