Submitted on June 6, 2007
Accepted on September 11, 2007
Mixed-Layer Deepening During Heinrich Events: A Multi-Planktonic Foraminiferal 
18O Approach
Harunur Rashid 1* and Edward A. Boyle 2
1 College of Marine Science, University of South Florida, 140 7th Avenue South, St. Petersburg, FL 33701, USA.; Department of Earth & Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
2 Department of Earth & Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
* To whom correspondence should be addressed.
Harunur Rashid , E-mail: hrashid{at}marine.usf.edu
Proxies from Greenland ice cores and North Atlantic marine sediment cores document repeated extreme climate swings of a few decades to millennia, including Heinrich massive ice-rafting events (HEs). We have found similar oxygen isotope from 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 upper water column. This implies that the surface mixed layer was deeper during HEs. Similar deepening can be seen in a published dataset from 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 intensifies vertical mixing of meltwater from ice-rafting in the upper ocean.
