Initial shipboard observations of the recovered sediments indicate that the major ice sheets surrounding the North Atlantic have been unstable during most glacial intervals over at least the last million years. Because of the possible effect of low-salinity meltwater on North Atlantic circulation, the signals of ice sheet instability are an important factor in understanding the effect global warming will have on the modern oceanic circulation.
“This is the first time that we have been able to recover continuous, high-resolution records of ice sheet instability over the last few million years in the North Atlantic - or anywhere for that matter,” says Jim Channell, co-chief scientist of the expedition from the University of Florida. “Considering the role of major ice sheet dynamics in abrupt climate change in the last 100,000 years, it is important to know if, and when, ice sheet instability occurred further back in time,” adds Toki Sato, co-chief scientist from Akita University in Japan.
For this expedition, the third of the Integrated Ocean Drilling Program, 30 geoscientists from Japan, the United States, Canada, the United Kingdom, Germany, Switzerland, Denmark, France and China staffed the ship. The ship is uniquely equipped to recover continuous sediment records from the deep ocean, and the targets for this expedition were sites where the sediments contain high-resolution archives of climate change over the last few million years. Six sites were drilled, to a depth of several hundred meters below seafloor, at locations off Newfoundland, off the southern tip of Greenland, and in the central Atlantic.
The expedition was designed to determine the history of the three large ice sheets that have had a dominating effect on North Atlantic climate over the last few million years. Melt (instability) events of the major ice sheets leave their mark in the sediments as detrital layers composed mainly of ice-rafted debris, and as meltwater events detectable in the chemical composition of microfossils that lived in the surface waters. These detrital layers originally were detected in young (<100,000 year old) sediments from the Central Atlantic and were termed “Heinrich events” after the German geologist who first recognized them. One of the objectives of this expedition was to determine the history of ice sheet instability further back in time, and to record this instability at locations close to the ice-sheets themselves, at the mouth of the Labrador Sea. This is the first time that such high-resolution (high sedimentation rate) records have been recovered from these critical regions of the North Atlantic, and the sedimentary records will provide unprecedented resolution in monitoring the instability of the major North Atlantic ice sheets.
Although scientists will continue to examine the cores for many years, Mitch Malone from Texas A&M University notes, “It already is clear that a very unique archive of climate change has been recovered, which provides hitherto unavailable resolution of changes in surface and deep-water conditions and ice sheet instability during a range of glacial and interglacial conditions since the intensification of northern hemisphere glaciation about 2.7 million years ago. The results from research on these sediments will drive North Atlantic climate studies for years to come.”
The JOIDES Resolution's next project is an expedition to study the formation of oceanic core complexes.