Development and evaluation of a diatom-conductivity model from lakes in West Greenland

1. The area around Kangerlussuaq (Sondre Stromfjord; West Greenland, 67degreesN 51degreesW) contains thousands of lakes ranging from coastal, dilute (conductivity < 30 muS cm(-1) ) oligotrophic systems to subsaline (similar to4000 muS cm(-1) ), closed basin lakes close to the ice sheet margin. In closed basins, salinity (or conductivity) is often a proxy for effective moisture, and thus palaeorecords of lake conductivity can provide valuable palaeoclimatic data. Little or nothing is known about the recent history of these lakes and hence it is difficult to evaluate how they will respond to effects of future changes. 2. Over 100 lakes have been sampled (1996-2000) between the ice sheet and the outer coast for a variety of water chemical and limnological variables. Surface sediments were taken from a subset of 40 lakes and analysed for diatoms. Diatom responses to 28 environmental variables were analysed by multivariate ordination techniques and indicate that the main gradient is highly correlated to conductivity (explaining similar to12% of species variance). Despite the relatively short gradient (24-4072 muS cm(-1) ), diatom assemblages exhibit a clear response to conductivity. The most saline lakes do not contain a true saline flora. 3. We developed a range of weighted averaging (WA) and weighted-averaging partial least squares (WA-PLS) models from this training data set and found two component WA-PLS models performed best. The effects of data transformation and omission of dissolution susceptible species (Diatoma spp.) on model performance were also examined. The error statistics for the preferred WA-PLS (2) model (r (2) (jack) =0.88, root mean square error of prediction (RMSEP)=0.217 log muS cm(-1) ) compare well with other published models. 4. A (210) Pb-dated short core from a meromictic, subsaline lake (Braya So; location 67degreesN, 51degreesW, max. depth 23 m; conductivity 2600 muS cm(-1) ) was analysed for diatoms. Diatom preservation is poor and some taxa (e.g. Diatoma spp.) are badly corroded. Lake water conductivity was reconstructed using WA-PLS models. Diatom-inferred conductivity ranges from 1800 to 4400 muS cm(-1) over the last 600 years (extrapolated (210) Pb chronology). 5. The Kangerlussuaq area of West Greenland is an important area for palaeoclimatic research, located as it is between the Greenland ice sheet (ice core records) and the Davis Straits to the west. The development of a statistically robust transfer function for diatoms and conductivity will enable the reconstruction of conductivity from the many subsaline lakes around the head of the fjord and, hence, regional estimates of changing palaeoprecipitation.