Climate Science Speaker
Monday, February 23, 2015
David McGee, MIT, Department of Earth, Atmospheric &
Planetary Sciences
Title: Drivers and impacts of changes in North African
dust emissions of the last 53,000 years
Abstract: North Africa is the world’s largest source of mineral dust to the atmosphere, exporting hundreds of
teragrams of dust over the tropical North Atlantic each year. These dust emissions sensitively track changes in
regional winds and precipitation on timescales ranging from the seasonal cycle to glacial-interglacial variations,
and reconstructions of past dust deposition in marine sediments provide foundational records of North African
climate over the last 5 million years. Beyond its role as a passive recorder, African dust also actively impacts
regional climate through direct and indirect radiative effects, and in the modern climate appears to significantly
amplify decadal-scale climate changes. Dust also is an important driver of surface ocean productivity in the
subtropical North Atlantic, supplying iron necessary for nitrogen fixation.
In this talk I will explore both the interpretation and the potential radiative and biogeochemical impacts of past
changes in African dust emissions. I will begin by presenting new quantitative records of African dust deposition
in the North Atlantic that document high-amplitude, abrupt changes in dust deposition that track past changes
in North Atlantic SSTs and summer insolation over the last 35,000 years. Additionally, a new record from the
Bahamas provides the first constraints on past changes in long-range African dust transport. We find that
African dust is likely to have played a substantial role in reinforcing past climate changes. Dust-related radiative
effects may help to explain why climate models often fail to reproduce the magnitude of changes in the West
African monsoon documented by pollen and lake level records, and, in combination with vegetation feedbacks,
may predispose the monsoon to abrupt transitions. Finally, I will present preliminary data testing whether past
changes in dust deposition were accompanied by changes in nitrogen fixation in the western subtropical North
Atlantic.
Bio: David McGee’s research focuses on building and interpreting records of past changes in atmospheric
circulation and hydrology from natural archives, including lake deposits, stalagmites and ocean sediments.
David’s graduate studies were conducted at Tulane University (Masters) and Columbia University (Ph.D.),
followed by postdoctoral research at the University of Minnesota as a NOAA Climate and Global Change
Fellow. He has been an assistant professor at MIT since 2012.
All talks will be held in Kline Geology Laboratory
Auditorium, Room 123 at 2 pm