The Arctic Ocean and its sedimentary record

Reconstructing paleoenvironmental conditions of the high northern latitudes


Contact: Christian März, W15-2-236, (0441) 7983627, cmaerz@icbm.de

The Arctic, despite being one of the coldest regions on Earth, is currently a hot topic. On one hand, it is a region where the phenomenon of „global warming“ is more evident than anywhere else. The disappearence of summer sea ice, the melting of the Greenland ice sheet, the fate of the ice- and cold-adapted ecosystems are subjects of vivid debates - not only in science, but also in politics. On the other hand, the Arctic region gets more and more into the focus of economic interest, be it transportation and logistics, or exploration for oil, gas and ore deposits. The melting of the ice on sea and land uncovers seaways like the Northwest Passage, offering a shortcut for trade ships between Europe and Asia, and opens new opportunities for exploitation of metal and hydrocarbon reservoirs so far inaccessible. All in all, we are facing fundamental environmental changes around the North Pole. However, one fundamental question arises: Are these climatic changes really so unique, or have similar changes occurred before? Has an ice-covered Arctic Ocean rather been an exception than the rule during Earth history? Answers to these and other questions can be deciphered from the sediments deposited at the bottom of the Arctic Ocean. We try to extract relevant information from these environmental archives by using inorganic geochemical proxies.

Currently, our research focuses on three Arctic regions: The long-term history of the Arctic Ocean, from the Late Cretaceous (the age of the dinosaurs) until today, is studied on a 420 m long sediment record recovered from the Central Arctic Lomonosov Ridge, a submarine mountain range. It was recovered during Expedition 302 of the Integrated Ocean Drilling Program (IODP), the so-called Arctic Coring Expedition (ACEX), and is unprecedented in its length and age. We try to reconstruct the development of the Arctic region of the last 80 million years via analyses of major and trace element contents within the different sediment units. As far as we know to date, the Arctic was a warm, subtropical region for many million years, completely different from its modern chilly appearance. The Arctic Ocean was, even more extreme than today, enclosed by land masses, leading to strong stratification of the water column and anoxic conditions similar to the modern Black Sea. Because it was ice-free, algal productivity in the surface water was very high, which sustained water column anoxia and promoted organic matter accumulation on the sea floor. This situation changed fundamentally when the only deep-water connection between the Arctic and the Atlantic Oceans (the Fram Strait) opened around 18 million years ago. Only since then, the Arctic water masses are well ventilated. The history of the more recent development of this cold ventilated Arctic Ocean, and its geochemical expression in the sediments, is another topic of our research. We recovered several sediment cores of up to 9 m length from the remote East Siberian Sea and the Mendeleev Ridge during Polarstern Expedition ARKIII/3, and sampled pore waters and sediments. Our main objective is to unravel the development of chocolate-brown, very manganese-rich layers that are ubiquitous in Arctic sediments, and put them into a paleoenvironmental context. In detail, we would like to know if these layers are primary recorders of climatic changes in the Arctic realm, or if they formed (or were at least altered) during degradation of organic matter within the sediments (early diagenesis). For this purpose, we are analyzing major and trace elements in the sediments and the pore waters. An upcoming topic regarding the Arctic region will be related to the Pliocene to Pleistocene history of the Bering Sea, which is situated between Siberia and Alaska. During IODP Expedition 323, several up to 750 m long records were recovered from seven drill sites, recording the sedimentation and climate history of this marginal Arctic basin connecting the Arctic and the Pacific Ocean. We are mostly interested in reconstructing a) the paleoproductivity and nutrient inventory of the basin, which is currently amongst the most productive ocean regions worldwide; b) the stratification and redox history of the water column and its relation to the North Pacific; and c) the connection between the Arctic and Pacific Oceans via the shallow Bering Strait, which is highly sensitive to sea level fluctuations.