14 DAY TRIAL // A new study conducted by Christina Ravelo, professor of ocean sciences at the University of California, Santa Cruz, and co-chief scientist Kozo Takahashi of Kyushu University, Japan, concluded that during the Earth's last warm period, the Bering Sea was ice-free and full of life.
The two scientists led a nine-week expedition of the Integrated Ocean Drilling Program (IODP) to the Bering Sea last summer aboard the research vessel JOIDES Resolution.
They drilled down 700 meters through rock and sludge and collected sediments deposited 3.5 to 4.5 million years ago, during the Pliocene Warm Period, which prove that the region was ice-free all year then, and the biological productivity was very high.
Just like it is happening nowadays, during the Pliocene Warm Period there was a more rapid warming at the poles, compared to other places on Earth.
After analyzing the sediments Ravelo's team concluded that the average sea surface temperatures in the Bering Sea were at least 5 degrees Celsius higher than today, while the average global temperatures were only 3 degrees warmer than today.
Also, throughout the past five million years, in the Bering Sea there was a great biodiversity, and the findings in the sediments confirm it.
The researchers found fossils of plankton – like diatoms, which means that there was a very resistant ecosystem, that persisted from the start of the Pliocene Warm Period until today.
They also found deep-water organisms that would have needed far more oxygen than the sea water has today, which according to Ravelo implies that the mixing of water layers in the Bering Sea was higher than it is now.
“We usually think of the ocean as being more stratified during warm periods, with less vertical movement in the water column.
“If the ocean was actually overturning more during a period when it was warmer than today, then we may need to change our thinking about ocean circulation.
Ravelo added that the “evidence from the Pliocene Warm Period is relevant to studies of current climate change because it was the last time in our Earth's history when global temperatures were higher than today.”
Today, it is only during the summer that the Bering Sea is ice-free, but it is important to know what was life during the Pliocene Warm Period, because this “should benefit the scientists today who are sorting out how ocean circulation and conditions at the poles change as the Earth warms.”
Christina Ravelo presented the new findings at the fall meeting of the American Geophysical Union (AGU) in San Francisco.