EVIDENCE FOR INCREASED LATE GLACIAL AEOLIAN ACTIVITY FROM KYLEN LAKE, MINNESOTA

Abrupt climate changes during the last glacial termination (18,000 to 11,000 years before present) are hypothesized to be driven by changes in atmospheric circulation. Changes in atmospheric wind patterns are not well recognized in the North American mid-continent outside of large aeolian deposits. Lake sediments offer a complementary archive. Several lake sediment studies from northern Minnesota, USA report zones with high percentages of non-local pollen. This suggests an increase in aeolian activity. For example, Birks (1981) described such a unit in Kylen Lake, Minnesota (47.33⁰ N, -91.80⁰ W), a small lake located in the Toimi drumlin field.

Here, I present grain size analysis from Kylen Lake to examine a wind-blown contribution to the sediment. The bottom 2.3 meters of the Kylen record are deglacial sediments overlain by an interesting fine-grained unit. Below the non-local pollen level mean grain size is 10-20 mm with standard deviation of 5 mm. In the non-local pollen, the mean decreases to 2 mm with a decreased standard deviation of 3 mm indicating a better sorted fine grain sediment. Above the non-local pollen mean increases to 15 mm with standard deviation near 10 mm. Fine silt and clay particles are finer than typical proximal aeolian sands and loess (>20 mm) suggesting long distance transport. The shift to fine grain particles, in concert with the pollen is interpreted to be a unit of non-local aeolian sediment. If supported by strontium isotopes, which are used to track sediment provenance from a distal source, the presence of a dominant aeolian signature can corroborate mid-continent loess records. This previously untapped archive can uncover insights into late glacial wind patterns.