The Bottom of the Arctic Ocean Tells Scientists What the Climate Was Like Millions of Years Ago

How can scientists go back in time, millions of years, to see what the earth was like? A time machine? You could think of it that way. Except these time machines pull up cylinders of ice or of  sediment—particles of rocks, sand, shells, and anything that has settled—from the bottom of a lake, or an ocean.  
    Two scientists from the US Geologic Survey, Laura Gemery and Thomas Cronin, spent two months this summer in the Arctic Ocean, surrounded by nothing but open water, ice, a polar bear, and a walrus or two. They spent their tour on an ice breaker—the only kind of ship that can get through Arctic sea ice—pulling up sediment cores. It’s hard work. Heavy work. Sometimes it’s really cold work. It can still get down to -20° C considering the wind chill factor, in August and September!
    Why do they do it? Laura and Tom are paleoclimatologists. They study climate—weather conditions for long periods of time—in ancient times. The sediment cores they pull up hold a record of what the earth was like hundreds, thousands, even millions and millions of years ago. Laura says that if we can learn what has happened on the earth through history, we’ll be better able to predict the climate of the future. When we know how climate may change, we can be prepared to respond to similar conditions.
    Think about temperature, for an example. The temperature of the Arctic Ocean has changed over history.  It has been as warm as 18 - 23° C (64-73° F). At that time, 55 million years ago, there were crocodiles in the Arctic Ocean. The level of the ocean was much higher.  That means that during that period, which scientists call the Paleocene-Eocene Thermal Maximum (PETM), the ocean was much higher than it is today. The areas where cities like New York, Miami, Norfolk, San Francisco, San Diego lie today, were all under water. Lots of water. Other times, however, the temperature has been colder, the ice in the Arctic was very thick, and the level of the ocean has been much lower. The towns I mentioned above, would be totally safe and dry like they are now.
    How do scientists get the cores? Corers are pushed into the sediment using gravity and weights. Each one of the cores can recover many meters of sediment. Since sediment collects at different rates during different times, these cores can represent tens, hundreds, thousands or millions of years. As the core barrels reach farther and farther down, they reach further down in history. Right now, scientists have sediment records back millions of years.
    Laura says that they take the cores, which can be hard, like packed mud, or soft, like pudding, and cut them in half lengthwise.  Then they have two “D” shaped lengths. One of the “D” shaped lengths of each core is stored as a permanent record. Scientists sample the other “D” shaped half. On this last trip, Laura took samples every 35 cm to see if they contained microfossils.  She was looking for small crustaceans with two shells which are called ostracodes. She was also looking for foramnifera, organisms made up of a single cell. Ostracodes and foramnifera have shells that can be preserved, or become fossils when the conditions are right. Laura washed the samples through a sieve to remove very fine grains of sediment and separate the ostracodes and foramnifera.
    So what do ostracodes and foramnifera shells tell Laura? Since there are many different species of ostracodes and foramnifera, let’s say Laura finds an ostracodes species that can only survive in water temperature between 20° C and 30° C. Now she has a very good idea—she can infer—that the water temperature at the time the sediment was laid down was in that same range. Since each species of ostracodes and foramnifera have different needs to survive, Laura can use them to predict certain environmental conditions such as the temperature of the water at the time the sediment was laid down. But Laura is not happy with just using the little foramnifera or ostracodes to peg a temperature to a period.  She and colleagues use other methods to support their findings. The information they collect is put into a database that allows scientists to know what the climate was like at a specific place in the Arctic, at a specific time in history.
    Temperature is not the only information sediment cores show us. Scientists also use the foramnifera and ostracode shells and the fossils of other organisms to determine how much salt there was in the ocean, how productive the oceans were (how much sea life there was) and how the currents in the ocean moved.
    Who will use this? We can put together the temperature, salinity, and water current information with information we have about changing sea levels. Suppose you are an admiral in charge of a naval base in Norfolk, Virginia. You need to know what will happen to sea level in the future so you can prepare to move your ships. Building new docks takes many, many years. Or suppose you’re a fisherman. How will species in the Arctic change as the temperature warms, or salinity—the amount of salt in the water—changes? Or if you are the mayor of a town on the coast. You need to know what will happen to your town if sea levels rise.
    We know that air and ocean temperatures in the Arctic and around the world are rising. We know that sea levels are rising. We know that ice is melting from glaciers (land ice) and there is not as much ice in the Arctic as there was before. Having the data that Laura and Tom compiled, along with many other scientists, will help us prepare to adjust to how our environment will change.
    Do you think that when you’re old enough you’ll be willing to spend a couple of months in the Arctic, like Laura, to collect data to help us all be even more prepared as our climate changes?