Aquatic Ecosystem Variability and Climate Change – A Palaeoecological Perspective - Climate Change Impacts on Freshwater Ecosystems - page 25

SFL49.1 SFL35.1 SFL17.1 SFL6.1 SFL6.1 NAUJG1.1

20 24 18 22 26 15 20 25 10 12 14 12 16 20 38 34

Loss on ignition (%)

Figure 2.5 Lithostratigraphic correlation of smoothed loss on ignition curves from the
uppermost (50-100 cm) sediments in six West Greenland lakes plotted against sediment
core depth. Note inverted scale for NAUJG1.1. (Redrawn from Willemse & Tornqvist
1999.)

small, probably not more than 1°C-2°C, significantly less than the increases in
temperature projected for the future over the next 100 years by climate models.
Temperature effects on lake ecosystems over the Holocene can be obscured by
independent changes in catchment and lake processes (cf. Anderson et al .
2008). It is difficult, consequently, to identify significant events or changes in
palaeolimnological records that can be unambiguously attributed to past changes
in temperature. The best evidence comes from remote sites where the confounding
impact of human activity is least. In such regions, sediment records often show
cyclical changes in organic matter concentration that can be interpreted as
temperature-driven changes in lake productivity (e.g. Willemse & Tornqvist
1999; Battarbee et al . 2001). The Willemse and Tornqvist study examined the
loss-on-ignition (LOI) record for six lakes in the Kangerlussuaq region of
Greenland in a transect away from the margin of the West Greenland ice sheet.
The results (Fig. 2.5) showed striking time-parallel variations between sites,
indicating that the variability was controlled not by local factors but by a regional
forcing mechanism matching the d 18 O-based temperature records from the GRIP
and GISP ice cores nearby. The authors argued that the quasi-cyclical variability
in organic matter concentration reflected a temperature-controlled variation in
the length of the ice-cover period, increased light penetration and enhanced
production during the longer growing season, an interpretation reinforced by the
correspondence between the LOI and the abundance of Chara stems preserved in