THE PROCESS APPROACH TO INTERPRETING GLACIAL VARVES

Glacial varves, like tree-rings, can provide annual temporal resolution and varve records are routinely used to reconstruct past environmental change. In most cases, varve thickness has been used as a proxy for up-valley glacier mass balance or summer air temperatures and varved lake records have been used to better constrain past climate variability (e.g. Kaufman et. al., 2012). Although the annual sedimentation cycle of summer silt and winter clay has been understood since the 1920s – calibrating a varve record with environmental conditions is often based on simplified assumptions, rather than on detailed process –oriented relationships.

The Svalbard REU has been studying sedimentation in pro-glacial Lake Linne’ located on the west coast of Spitsbergen, Svalbard . Since 2004, we have been monitoring various aspects of the Linne’ glacier-meltwater-lake system to better understand annual sedimentation in the lake and to calibrate varve thickness with the long term weather record of the last 100 years. Specifically, we have been monitoring sediment flux to the lake, (controlled by glacier mass balance, weather events and meltwater stream discharge) and in the lake we have been studying sediment distribution using sediment traps, temperature loggers (deployed throughout the lake and at various depths), Lake level, water turbidity and the timing of sedimentation. What we’ve learned is that varve sedimentation in Lake Linne’ is a complex process that is not easily related to summer temperature or glacier mass balance. One of the complicating factors is the 10 km meltwater stream that acts to store and release sediment during high discharge events associated with the nival melt and high rainfall events. Further, the water density interplay between the lake water and the meltwater stream controls sediment distribution processes in the lake resulting in transient under, inter or overflow conditions. As such, the varve record in Lake Linne’ appears to be more a hydrology proxy than solely an air temperature or glacier mass balance proxy.

The process approach to understanding geomorphic systems that Dusty Ritter promoted can often be time consuming and difficult, but it is the only way to truly understand the resulting deposits and landforms.