Radiocarbon dates, accumulation rates, d13C and July temperature of profiles obtained from Selwyn and Misaw Lake, subarctic Canada

The rapid warming of arctic regions during recent decades has been recorded by instrumental monitoring, but the natural climate variability in the past is still sparsely reconstructed across many areas. We have reconstructed past climate changes in subarctic west-central Canada. Stable carbon and oxygen isotope ratios (d13C, d18O) were derived from a single Sphagnum fuscum plant component; alpha-cellulose isolated from stems. Periods of warmer and cooler conditions identified in this region, described in terms of a "Mediaeval Climatic Anomaly" and "Little Ice Age" were registered in the temperature reconstruction based on the d13C record. Some conclusions could be drawn about wet/dry shifts during the same time interval from the d18O record, humification indices and the macrofossil analysis. The results were compared with other proxy data from the vicinity of the study area. The amplitude of the temperature change was similar to that in chironomid based reconstructions, showing c. 6.5 ±2.3 °C variability in July temperatures during the past 6.2 ka.

(Table 1) Mean temperatures in january and july, and total annual snowfall at Great Bear Lake and Great Slave Lake, Canada

The sensitivity of brightness temperature (T(B)) at 6.9, 10.7, and 18.7 GHz from Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) observations is investigated over five winter seasons (2002-2007) on Great Bear Lake and Great Slave Lake, Northwest Territories, Canada. The T(B) measurements are compared to ice thicknesses obtained with a previously validated thermodynamic lake ice model. Lake ice thickness is found to explain much of the increase of T(B) at 10.7 and 18.7 GHz. T(B) acquired at 18.7 GHz (V-pol) and 10.7 GHz (H-pol) shows the strongest relation with simulated lake ice thickness over the period of study (R**2 > 0.90). A comparison of the seasonal evolution of T(B) for a cold winter (2003-2004) and a warm winter (2005-2006) reveals that the relationship between T(B) and ice growth is stronger in the cold winter (2003-2004). Overall, this letter shows the high sensitivity of T(B) to ice growth and, thus, the potential of AMSR-E mid-frequency channels to estimate ice thickness on large northern lakes.