Precise chronological control of glacier advances through time are an important tool for reconstructing local and regional equilibrium line altitudes (ELAs) and for identifying climate trends on centennial to millennial time scales (Young et al., 2015). Glacier margin chronologies are typically built by dating the stabilization of glacial moraines or the formation of geomorphic features on the landscape using surface exposure dating methods (lichenometry, cosmogenic exposure dating, etc.). In general, on Baffin Island, glaciers reached their largest Holocene extents during the Little Ice Age, often overrunning previous advances, meaning only the Little Ice Age advance is preserved (Davis, 1985). However, the highlands of southern Baffin Island are often mantled by thin, cold-based ice that is now retreating and exposing preserved ancient landscapes complete with in situ plants (Miller et al., 2013). We take advantage of these conditions at Divide Ice Cap on Cumberland Peninsula (Figure 1) to reconstruct the spatial and temporal history of ice extent over the last ~1000 years. A transect of 10 radiocarbon ages of in situ dead plants that were killed by the advancing ice range from 910 +28/-39 CE at the 2015 ice margin to 1780 +111/-165 CE at the local trimline ~200 m away. The current ice margin lies at the bottom of a small saddle and the transect continues up the opposing south-facing hill to the trimline (Figure 1). These conditions mean that an advancing ice margin up this south-facing slope is more representative of the elevation of ice in the saddle than horizontal extent.
Four samples collected near the ice margin with dates between 900 and 1050 CE are seemingly out of order given their position with respect to the modern ice margin (Figure 2). However, it is possible that they each faithfully record smaller advances of a fluctuating ice cap early in the first millennium. Moving farther from the ice margin, radiocarbon ages become progressively younger with increasing distance (and elevation) from the 2015 ice margin (Figure 2). Overall, these data show and advancing ice margin and the expansion of the Divide Ice Cap from ~1000 CE towards its local maxima during the late 18th century. Aerial photography show the ice margin retracted to ~13 m below the trimline, but still ~40 m above the 2015 ice margin (Figure 2). It should be noted that since our data suggest the preservation of multiple advances, it is possible our chronology is incomplete, and only dating of additional in situ plants within the transect will expose additional ice margin advances.
We will also employ a simple 2D finite element numerical model to simulate the steady state ELA for both the 2015 ice margin and local trimline to determine the minimum ELA change and infer the cooling required to expand the ice margin to it’s local trimline between ~1000 and ~1800 CE (Kessler et al., 2006). This cooling is a minimum value, and it is likely that ELA fluctuations were of higher magnitude and frequency. Preliminary model outputs indicate a strong gradient in mass balance with respect to aspect. We hope to produce one of the first chronologies of late Holocene cryosphere expansion on Cumberland Peninsula and assign approximate ELA fluctuations and climate trends during the same time period.