By Will (guest blogger)
What will the earth be like in the future? This is quite a poignant question, one that many people want answered in no uncertain terms. A useful step in addressing such a question is to answer a similar one. What was earth’s climate like in the past?
We can collect evidence for changes in the earth’s climate from a variety of natural records. What one looks at is largely determined by when one wants to look, ice-cores, for example, provide an invaluable insight for the past 800,000 years. But for scientists hoping to see back as far as 50 million years, this required drilling sediment 4.5 km below the ocean surface.
Cores were collected during the Northern Summer using the specially fitted JOIDES Resolution. This ship is fitted with a pneumatic drilling apparatus, this allowed scientist and crew to drill and recover around 10 meters of core at a time. These individual cores are lifted on board the ship, where they were further cut into 1.5 meter sections before being catalogued and stored. On board was a team of thirty scientists who, working up to 12 hours at a time, collected and processed over 3 kilometres of such cores over the 2 month voyage.
The sediment cores were collected from J-Anomaly Ridge and South-East Newfoundland ridge off the coast of Newfoundland in the North Atlantic. These cores contain a record of earth’s climate variability from 34 to 56 million years ago. This includes an important time in Earth’s history when atmospheric CO2 was last as high as that predicted for the coming century based on human emissions.
So what can the records tell us? With careful dating and analysis we can identify changes in the climate and investigate how they may be causally related. Such as ice formation relating to declining atmospheric CO2, or, changes in oceanic circulation and the proliferation of whales. However there is still a large body of unanswered questions.
IODP Expedition 320/321, which sailed to the equatorial pacific in 2009, recovered evidence from the late Eocene of large variations in the carbonate compensation depth, the depth at which dissolution removes all carbonate shells. However we don’t fully understand what caused these variations and whether the record represents a global or regional shift.
This is why the scientist of Expedition 342 invested so much time and energy collecting new samples, and why so much more effort will be invested studying them. My honours project will consist of measuring the stable isotope composition of foraminifer, which are buried and preserved in oceanic sediments and can be easily recovered from sediment cores.
Foraminifera precipitate calcium carbonate from ocean water to form their shells. As they do this they record changes in the chemistry of the ocean water, such as variations in the isotopic composition. This composition changes because isotopes are partitioned through natural processes such as ice formation and photosynthesis. Thus by recovering the foraminifera from the sediment cores we can measure variations in their isotopic composition, which will provide insight to the changes in natural processes and climatic features that occurred.
We can view changes on many scales, examples of long term trends and shorter transient events were found in the equatorial Pacific, check out this record. The large body of international work focused on the North Atlantic cores from Expedition 342 will aid our understanding of these events and provide further insight into the drivers and sensitivity of climatic changes throughout Earth’s history.