Cenozoic Arctic Ocean Climate History: Some Highlights from the Integrated Ocean Drilling Program Arctic Coring Expedition

With the Arctic Coring Expedition (ACEX) (the first Mission Specific Platform expedition within the Integrated Ocean Drilling Program) Expedition 302 in 2004, a new era in Arctic research began. For the first time, a scientific drilling expedition in the permanently ice-covered Arctic Ocean was carried out, penetrating 428. m of Quaternary, Neogene, Paleogene, and Campanian sediment on the crest of Lomonosov Ridge close to the North Pole between 87 and 88°N. By studying the unique ACEX sequence, a large number of scientific discoveries that describe previously unknown Arctic paleoenvironments were obtained during the last decade. Key results include subtropical warm conditions during the Paleocene-Eocene Thermal Maximum and the early-mid Eocene, an episodic freshening of Arctic surface waters in the Eocene, black shales and euxinic conditions in the Eocene Arctic Ocean, and an early onset of Arctic sea ice (Northern Hemisphere glaciation) in the middle Eocene. While these results from ACEX were unprecedented, key questions related to the climate history of the Arctic Ocean on its course from Greenhouse to Icehouse conditions during early Cenozoic times remain unanswered, in part because of poor core recovery, and in part because of the possible presence of a major mid-Cenozoic hiatus within the ACEX record. Furthermore, the ACEX sites remain the one and only drill holes in the entire central Arctic Ocean to date. In order to decipher the paleoclimatic and tectonic history of this unique and sensitive but still not well-known region on Earth, future scientific Arctic drilling is certainly needed.