Proglacial Lakes Control Glacier Geometry and Behavior During Recession

Abstract

Ice-contact proglacial lakes are generally absent from numerical model simulations of glacier evolution, and their effects on ice dynamics and on rates of deglaciation remain poorly quantified. Using the BISICLES ice flow model, we analyzed the effects of an ice-contact lake on the Pukaki Glacier, New Zealand, during recession from the Last Glacial Maximum. The ice-contact lake produced a maximum effect on grounding line recession >4 times further and on ice velocities up to 8 times faster, compared to simulations of a land-terminating glacier forced by the same climate. The lake contributed up to 82% of cumulative grounding line recession and 87% of ice velocity during the first 300 years of the simulations, but those values decreased to just 6% and 37%, respectively, after 5,000 years. Numerical models that ignore lake interactions will, therefore, misrepresent the rate of recession especially during the transition of a land-terminating to a lake-terminating environment. Plain Language Summary Lakes form at the margins of glaciers as meltwater accumulates against hillsides and behind ridges of glacier debris. Lakes at a glacier terminus are known to affect its behavior. However, glaciers terminating into such lakes are usually absent from computer simulations, and the effects of these lakes on the rates of deglaciation and on glacier behavior are poorly quantified. In this study, we tested the effect of a lake on glacier recession under two different scenarios; a land-terminating versus a lake-terminating glacier. We used an ice flow model called BISICLES and applied it to what was once the Pukaki Glacier in New Zealand during the end of the last ice age. We found that the presence of a lake caused the glacier to recede more than 4 times further and it accelerated ice flow by up to 8 times when compared to the same glacier that terminated on land under the same climate. Our simulated lake processes predominantly influenced the glacier over decades to centuries rather than over millennia. We suggest, therefore, that simulations of glacier evolution ignoring glacial lakes will likely misrepresent the timing and rate of recession, especially during the transition from a land-terminating to a lake-terminating environment. Recent observations, both field-based (e.g., Watson et al., 2020) and via satellite imagery (e.g., King et al., 2019), have highlighted the spatiotemporal frequency and magnitude of changes in glacial lakes and the associated glaciers that feed meltwater to them. However, field-based measurements are limited to

Toward Numerical Modeling of Interactions Between Ice-Marginal Proglacial Lakes and Glaciers

“…On a meso-scale, lake temperature affects subglacial hydrology (Carrivick et al, 2017;Stubblefield et al, 2019). On a macro scale (hundreds to thousands of meters) lake water temperature will affect the shape of the floating underside of a glacier and potentially also affect the shape of the entire terminus tongue (Sugiyama et al, 2019;Sutherland et al, 2020; Figure 2). Subglacial hydrology is affected by lake water temperature at all scales.…”

“…Representing the impact of short-lived (decadal) accelerations and decelerations of a glacier in response to ice-marginal lake effects (Sutherland et al, 2020) is difficult within a longer (millennial) glacier evolution model, and not least because those effects might not simply average out. Being able to perform long simulations over large spatial extents must contend with lake size being highly sensitive to the size and position of lake overspill channels, which are on a scale of 10-100 m.…”

“…Lake bathymetry, glacier bed topography, lake level and lake water temperature vary in space as well as through time. Multiple ice-marginal lakes will likely have differing elevations, which is quite different to conditions at a marine boundary and makes it difficult to adapt a marine ice sheet model for use with icemarginal lakes (Sutherland et al, 2020). Furthermore, individual lakes will have levels that vary with filling and draining.…”

“…FIGURE 2 | Visualization of outputs from BISICLES ice sheet model(Cornford et al, 2013) used bySutherland et al (2020) with starting condition of a glacier in equilibrium (A), then forced by climate only (B) and then by the same climate forcing with the addition of ice-marginal lake effects (C). The modeled lake-terminating glacier has a different terminus geometry and retreats further in the same period of time as the land-terminating glacier.…”

Understanding Complex Debris-Covered Glaciers: Concepts, Issues, and Research Directions

“…The evolution of many supraglacial lakes and ponds are governed by filling and draining cycles, and hydrological connectivity that are controlled by glacier surface and internal structures (Benn et al, 2001(Benn et al, , 2017Wessels et al, 2002;Miles et al, 2017). Studies also found that proglacial lakes also have a significant control on the glacier dynamics (Sutherland et al, 2020). These processes have only been studied on a handful of glaciers in the field, and there are still many processes and feedbacks that need to be investigated.…”