ABSTRACT: Multiple abrupt shifts in the early-Holocene climate of Western Canada.

CGRG Bibliography of Canadian Geomorphology
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Abstract

Occurrences of abrupt climate change during the Holocene, including the widely documented oscillation at 8200 years before present (8.2 kyr BP), are widely attributed to changes in the North Atlantic thermohaline circulation. Additional mechanisms, such as interactions between atmospheric circulation, ice-sheet dynamics, and the possible influence of solar irradiance, have been proposed to explain abrupt climatic events during the Holocene, but evidence remains elusive. We present a lake-sediment record from interior British Columbia to evaluate Holocene climatic variability and potential drivers. Changes in the abundance of biogenic silica (BSi) and oxygen-isotope composition of diatom opal (d18Odiatom) reveal four abrupt climatic shifts in the early Holocene. The largest two of these events occurred at 9.3 kyr BP and 8.5 kyr BP, the latter of which was coeval with a major collapse of the Laurentide ice sheet. The record also reveals a cooling at 8.2 kyr BP that is distinct from the 8.5 kyr BP event and comparable to several short-lived late-Holocene events. Both BSi and d18Odiatom¬ are strongly correlated with solar-irradiance indices, but these correlations are opposite in sign to that expected from direct solar forcing and become weak after 8 kyr BP. In contrast with the North Atlantic-forced events, the abrupt and persistent climate changes of the early Holocene probably resulted from the influence of solar irradiance variability on the strength of the glacial anticyclone, and sudden losses of ice and proglacial lake extent, causing a shift of the meridional structure of atmospheric circulation.

Bibliography of Canadian Geomorphology