Publication Date:
2016-10-25
Description:
The Younger Dryas cold interval represents a time when much of the
Northern Hemisphere cooled from �12.9 to 11.5 kiloyears B.P. The
cause of this event, which has long been viewed as the canonical
example of abrupt climate change, was initially attributed to the
routing of freshwater to the St. Lawrence River with an attendant
reduction in Atlantic meridional overturning circulation. However,
this mechanism has recently been questioned because current proxies
and dating techniques have been unable to confirm that eastward
routing with an increase in freshwater flux occurred during the
Younger Dryas. Here we use new geochemical proxies (�Mg/Ca,
U/Ca, and 87Sr/86Sr) measured in planktonic foraminifera at the
mouth of the St. Lawrence estuary as tracers of freshwater sources to
further evaluate this question. Our proxies, combined with planktonic
�18Oseawater and �13C, confirm that routing of runoff from western
Canada to the St. Lawrence River occurred at the start of the Younger
Dryas, with an attendant increase in freshwater flux of 0.06 +- 0.02
Sverdrup (1 Sverdrup = 106 m3s-1). This base discharge increase is
sufficient to have reduced Atlantic meridional overturning circulation
and caused the Younger Dryas cold interval. In addition, our data
indicate subsequent fluctuations in the freshwater flux to the St.
Lawrence River of ~0.06–0.12 Sverdrup, thus explaining the variability
in the overturning circulation and climate during the Younger
Dryas.
Type:
Article
,
PeerReviewed
Format:
text
DOI:
10.1073/pnas.0611313104
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