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.
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
