Geochemical proxies of North American freshwater routing during the Younger Dryas cold event

• Main Authors: Carlson, Anders E., Clark, Peter U., Haley, Brian A., Klinkhammer, Gary P., Simmons, Kathleen, Brook, Edward J., Meissner, Katrin J.
• Format: Article in Journal/Newspaper
• Language: English; unknown
• Published: The National Academy of Sciences of the USA
• Subjects: Canada; Lawrence River; Planktonic foraminifera
• Online Access: https://ir.library.oregonstate.edu/concern/articles/fx719p15g

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 (ΔMg/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 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 = 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 ≈0.06–0.12 Sverdrup, thus explaining the variability in the overturning circulation and climate during the Younger Dryas. Keywords: abrupt climate change, paleoclimate, Atlantic meridional overturning circulation