Holocene lake sediments in West Greenland and their palaeoclimatic and palaeoecological implications

Abstract

There is considerable interest both from social and environmental perspectives as to the possible effects of future climate changes. This interest, which focuses on the time scales and rates of change of future climatic variability, has led to an increased recognition of the importance of studies of palaeoclimates and their ecological impacts (Street-Perrot & Roberts, 1994). General circulation models (GCMs) suggest that the Arctic will be especially sensitive to increased atmospheric temperatures (the ‘greenhouse effect’). Such predictions or forecasts of future climatic scenarios are the primary role for GCMs in the debate about future global climate change (Henderson-Sellers, 1994), but it is also possible to use GCMs to model past-climate changes (Henderson-Sellers, 1990; Street-Perrot & Roberts, 1994). GCM hindcasts of past climate have the advantage that the predictions can be independently validated against palaeoclimate data derived from a variety of proxy sources, e.g. ice cores, peats, marine and lake sediments (Street-Perrot & Roberts, 1994; Anderson, 1995). Arctic lake sediments are an important natural archive of past changes in climate, but they also record the impact of these climatic changes on the local biota and environment (Smol et al., 1991). Lake sediment records can be used to provide the necessary baseline information against which future anthropogenic changes can be evaluated (Anderson, 1993). Such baseline conditions are often difficult to determine from contemporary data as the monitoring programmes are initiated after change has already occurred. Arctic lakes and their catchment areas have two other important aspects which make them ideally suited to detailed, quantitative palaeoecological and palaeoclimatic approaches: they have a relatively simple biological structure, and anthropogenic impacts on the catchment areas are so small they can be effectively discounted. Because the shallow lakes are often fishless, the effects of higher trophic levels (the trophic cascade) on the lower trophic levels (primary producers, e.g. algae and phototrophic bacteria) can also be discounted. This has the implication that the majority of the limnological changes recorded in the lake sediments represent climate-driven catchment-lake interactions. It is possible therefore, to evaluate the effect of past-climate changes, such as the Holocene thermal maximum, on the lake biota. Importantly, independent estimates of past-climate can be derived from GCMs or from the ice-core records (Johnsen et al., 1995). In contrast to most other regions of the globe that are experiencing increasing temperatures, West Greenland and the Baffin Bay region have seen decreasing temperatures during recent decades. Studies of lake sediments that are widespread in West Greenland can provide information about the temporal and spatial climatic variability since the last ice age.