Geochemical proxies of North American freshwater routing during the Younger Dryas cold event
Geochemical proxies of North American freshwater routing during the Younger Dryas cold event
Date
2006-12-19
Authors
Carlson, Anders E.
Clark, Peter U.
Haley, Brian A.
Klinkhammer, Gary P.
Simmons, Kathleen
Brook, Edward J.
Meissner, Katrin J.
Clark, Peter U.
Haley, Brian A.
Klinkhammer, Gary P.
Simmons, Kathleen
Brook, Edward J.
Meissner, Katrin J.
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Abstract
The Younger Dryas cold interval represents a time when much of the Northern
Hemisphere cooled from ~12.9 to 11.5 kiloyears before present. 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 (ΔMg/Ca, U/Ca & 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 δ18Oseawater and δ13C, 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 (Sv) = 106 m3 s-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 to 0.12 Sv, thus
explaining the variability in the overturning circulation and climate during the Younger
Dryas.
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Author Posting. © The Authors, 2006. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences 104 (2007): 6556-6561, doi:10.1073/pnas.0611313104.