Mixed-Layer Deepening During Heinrich Events: A Multi-Planktonic Foraminiferal 
18O Approach
Harunur Rashid1,2* and
Edward A. Boyle2
Proxies from Greenland ice cores and North Atlantic marine sediment cores document repeated extreme climate swings of a few decades to millennia during the last glacial cycle, including periods of intense ice rafting called Heinrich events (HEs). We have found similar oxygen isotope variations recorded in mixed-layer–and thermocline-dwelling planktonic foraminifera during HEs 0, 1, and 4, suggesting that three foraminiferal taxa calcified their shells at similar temperatures in a homogenized upperwater column. This implies that the surface mixed layer was deeper during HEs. Similar deepening occurred on the northern margin of the ice-rafted–debris belt, implying that these deep mixed layers during HEs were widespread in the region. We suggest that an increase in storminess during HEs intensified the vertical mixing of meltwater from ice rafting in the upper ocean.
1 College of Marine Science, University of South Florida, 140 7th Avenue South, St. Petersburg, FL 33701, USA.
2 Department of Earth and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
* To whom correspondence should be addressed. E-mail: hrashid{at}marine.usf.edu
