WorldWide Drilling Resource

58 OCTOBER 2016 WorldWide Drilling Resource ® The North Pole Hasn’t Always Been Covered in Ice Adapted from a Information by the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research An international team of scientists led by the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) have opened a new window into the climate history of the Arctic Ocean. Using unique sediment samples from the Lomonosov Ridge, the researchers discovered 6-10 million years ago the central Arctic was completely ice free during summer. In spring, autumn, and winter, however, the ocean was covered by sea ice of variable extent. The new findings from the Arctic region provide new benchmarks for global climate reconstructions and modeling. Researchers recovered the samples during a Polarstern expedition in the summer of 2014. Professor Dr. Rüdiger Stein, AWI geologist, ex- pedition leader, and lead author of the study, explained, "The Arctic sea ice is a very critical and sensitive component in the global climate sys- tem. It is therefore important to better understand the processes con- trolling present and past changes in sea ice. In this context, one of our expedition’s aims was to recover long sediment cores from the central Arctic, that can be used to reconstruct the history of the ocean's sea ice cover throughout the past 50 million years. Until recently, only a very few cores representing such old sediments were available, and, thus, our knowledge of the Arctic climate and sea ice cover several millions of [years] ago is still very limited." The scientists found an ideal place for recovering the sediment cores on the western slope of the Lomonosov Ridge, a large undersea mountain range in the central Arctic. "This slope must have experienced gigantic recurring landslides in the past, which resulted in the exhuma- tion of...ancient sediment and rock formations. We were also surprised about the widespread occurrence of these slide scars, which extend over a length of more than [180 miles], almost from the North Pole to the southern end of the ridge on the Siberian side," stated Dr. Stein. Stein and his team took 18 sediment cores from this narrow area on Lomonosov Ridge onboard the Polarstern research vessel. Although the recovered cores were only about 13-25 feet long, one of them turned out to be precisely one of those cli- mate archives the scientists had been looking for. "With the help of certain microfossils, so-called dinoflagellates, we were able to unambiguously establish that the lower part of this core consists of approximately 6-8 million-year-old sediments, thereby tracing its geological history back to the late Miocene Epoch [23 million to 5.3 million years ago]," he said. Some scientists were of the opinion the central Arctic Ocean was covered with dense sea ice year-round 6-10 million years ago - roughly to the same extent as today. The new research findings contradict this assumption. The data clearly indi- cates the North Pole and the entire central Arctic Ocean was ice free in the summer 6-10 million years ago. The new findings of the Arctic Ocean climate history reconstructed from sediment data, are further corroborated by climate simulations, as was shown by the AWI modelers who participated in the study. This only applies, however, if we assume a relatively high carbon dioxide content in the atmosphere of 450 ppm (parts per million). If the climate models were run using a significantly lower carbon dioxide con- tent of about 280 ppm, as some studies suggest for the late Miocene, then an ice free Arctic cannot be simulated. Whether the carbon dioxide content was indeed relatively high or whether the sensitivity of the model was too weak to simulate the magnitude of high-latitude warming in a warmer than modern climate, is currently subject to further international research. One of the primary goals is to improve the predictive capacity of climate models. Once climate models are capable of reliably repro- ducing surface-water temperature and sea ice cover of earlier periods, we will be able to improve the climate models for a better prediction of future climate change and sea ice conditions in the central Arctic Ocean. Despite the outstanding results and the accompanying euphoria, the participating scientists agree this was merely the first step and other important steps must follow. "While our new sediment cores give us an undreamt of initial insight into the early climate history of the Arctic, these climate records are still very incomplete. In order to fully unravel the great mystery of Arctic climate history over the past 20-60 million years, we need much longer, continuous sediment sequences, which can only be obtained by drilling. An Arctic drilling expedition is planned for 2018 in the Lomonosov Ridge study area, and it will be carried out as part of the international drilling programme IODP (International Ocean Discovery Program). The preliminary investigations carried out by our Polarstern expedition have played a significant role in selecting the precise drilling locations," concluded Dr. Stein, who will be one of the expedition leaders of the IODP campaign in 2018. Polarstern expedition leader Rüdiger Stein (blue hat) and his team are posing next to the box core. Photos courtesy of Alfred Wegener Institute / Audun Tholfsen, UoB. Dr. Stein and his team sampling the valuable sediment core in the lab onboard the research ship Polarstern.