Using the past to inform the future: the role of palaeoglaciology

The study of glaciers and ice sheets has traditionally been split into three communities: those conducting observational research of the present day cryosphere; those developing theory and models to simulate cryospheric processes; and those who use the palaeo record to interpret glaciations of the past. Isolation of these three branches of glaciology can hinder both improved understanding of physical glacial processes and improved interpretations of the palaeo record. In a recently published paper (Greenwood et al., in press) my colleagues and I reviewed the current state of knowledge of one aspect of glaciology (ice sheet hydrology) from the perspectives of these three research communities. The paper further discussed key questions and uncertainties in understanding of the glacial hydrological system, leading to conclusions including: that the traditional bi-modal view of subglacial hydrology is challenged by both modern observations and palaeo interpretations; that we do not fully understand the extent to which different landforms represent different drainage modes or are different expressions of one drainage mode; and that the geomorphic imprint of the multitude of frequencies and magnitudes (figure 1) of drainage events remains poorly understood. These conclusions highlight only some of the many research challenges for the glaciological community which cross-disciplinary cooperation could help to tackle.

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Figure 1. Peak discharge circles, scaled by area. The peak discharge of the Glacial Lake Missoula floods is 340000 times greater than the Adventure Trench drainage; like comparing the Amazon River with a small brook. From Greenwood et al. (in press).

 

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Figure 2. Glacial lineations visible on the sea floor: A) rat tails c. 200 m long; B) drumlins c. 1-2 km long; C) mega scale glacial lineations c. 10-20 km long; D) lineations of cross-cutting directionality (pink and blue).

Our understanding of physical glaciological processes, and controls on the stability, dynamics and retreat of ice sheets must continue to improved if we are to better predict ice sheet sea level contribution in response to future climatic change. Accessing the proglacial and subglacial environments of ice sheets to observe processes first-hand is, however, very much restricted due to both logistical and safety constraints. Furthermore, despite the advent of remote sensing, observational records from present-day ice sheets are short (up to tens of years) in comparison to glacial cycles (thousands of years). The glacial landform record, a footprint of previous glaciations left behind on both present day land and the sea floor, provides a window into these environments, and a great deal of insight into the processes operating beneath past ice sheets. Mapping and analysis of glacial landforms can reveal a significant amount of information, including the direction and speed of ice flow, the topology of the subglacial hydrological system, the retreat pattern of the ice sheet margin, and the extent of iceberg calving activity. As an example figure 2 illustrates some of the multitude of forms of glacial lineations, from which both direction and relative speed of ice flow can be interpreted.

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Figure 3. Flow path of the Bothnian Sea ice stream inferred from glacial lineations. Longer lineations depicted in green, shorter lineations in red. From Greenwood et al. (2015).

Marine-terminating catchments are the source of much of the mass loss from the Greenland and Antarctic ice sheets, sensitive to changes in both climate and in the ocean. It is thus particularly important to better understand controls on marine ice sheet instability if we are to predict the effect of future atmospheric and environmental change. Recent work in the Gulf of Bothnia region of the past Fennoscandian Ice Sheet gives a unique insight to the dynamics, retreat pattern, and processes operating under a marine-terminating ice stream during the last deglaciation. In addition to ongoing modelling work and data analyses, mapping of glacial lineations allowed us to identify the onset of fast ice flow from the north-east Swedish coast (Greenwood et al., 2015; figure 3). Relating bedform length to relative ice flow speed (Stokes & Clark, 2002), the ice stream width was constrained by a sharp transition between relatively short and relatively long lineations visible on both present day land and the sea floor. Aside from an improved understanding of ice dynamics and retreat in this region of the Fennoscandian Ice Sheet, this research offers a unique perspective on marine-terminating ice stream catchments. The broad, shallow, low salinity setting of the Gulf of Bothnia contrasts with the topographically-constrained continental shelf settings typical of studies of present-day marine outlet glaciers. Palaeoglaciological study can thus improve our understanding of the multitude of responses exhibited by ice sheets, in a range of geographical settings, to external forcings.

In concert with palaeo proxies for reconstructing past climates and environments, glacial landforms can provide a record of long-term response to changing conditions. The study of ice sheets of the past can thus offer important insights to ice sheet response in the future. There is a real danger of isolation between glaciological research groupings, leading to disconnects in understanding of processes important for predicting the future response of present day ice sheets to a warming climate. Fostering cross-disciplinary research is imperative if the true diversity of processes and controls exhibited by contemporary ice sheets are to be understood; using the past to inform the present, and vice versa.

 

Greenwood, S.L., Clason, C.C., Mikko, H., Nyberg, J., Peterson, G. & Smith, C.A., (2015), Integrated use of LiDAR and multibeam bathymetry reveals onset of ice streaming in the northern Bothnian Sea, GFF, DOI:10.1080/11035897.2015.1055513

Greenwood, S.L., Clason, C.C., Helanow, C. & Margold, M., (in press), Theoretical, contemporary observational and palaeo perspectives on ice sheet hydrology: processes and products, Earth-Science Reviews, doi:10.1016/j.earscirev.2016.01.010

Stokes, C.R. & Clark, C.D., (2002), Are long subglacial bedforms indicative of fast ice flow?, Boreas, 31 (3), 239–249, doi:10.1080/030094802760260355

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