The 8200calyr BP cooling event in eastern North America and the utility of midge analysis for Holocene temperature reconstructions [An article from: Quaternary Science Reviews]

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Description:
Between about 8400 and 8000calyr BP two sites from the White Mountains of eastern North America record loss-on-ignition (LOI) reductions in the organic content of lake sediment. At Speck Pond LOI values reach a near-Holocene minimum of 35% whereas at Surplus Pond LOI values are maintained near 35% for about 100calyr. We interpret this change in LOI as a response to the 8200calyr BP cooling event known to occur throughout the circum-North Atlantic region. Detailed midge (including Chironomidae, Chaoboridae, and Ceratopogonidae) analyses were used to measure changes in summer surface-water temperatures from about 8800 to 8000calyr BP at both sites. Midge-inferred temperatures are highly variable at Speck Pond (ranging from 12.2^oC to 16.7^oC) whereas a ''no-analogue'' situation persists at Surplus Pond with inferred temperatures near 30^oC. These results bring into question the usefulness of midges as a climate proxy to infer relatively brief, small-magnitude Holocene climatic events such as the 8200calyr BP cooling event.