The Pliocene record in the central Arctic Ocean

Abstract

Pliocene sediment from the central Arctic Ocean was reported first some 25 years ago. Although the basis of the Pliocene age was tenuous, none of the data subsequently presented have invalidated the original Pliocene age report. New data confirm the earliest report as well as establish the presence of older Miocene sediment. The Pliocene sediment recovered from the central Arctic Ocean to-date includes only 2–3 m of silty lutite consisting largely of illite, kaolinite, and chlorite, with lesser amounts of expandable clays, abundant Fe-Mn micronodules, but few fossils. The Pliocene age is based on extrapolation of sedimentation rates from paleomagnetic boundaries, arenaceous foraminifera, and 87Sr/ 86Sr isotope ratios obtained from Fe-Mn micronodules and compared to established seawater 87Sr/ 86Sr isotope ratios for this time. Notably absent in all except the upper part of the central Arctic Ocean Pliocene sediment is coarser-grained glacially ice-rafted debris (IRD) or any indication of measurable surface water productivity. Early interpretations of the Arctic Ocean record included the concept that sea ice was present during the Pliocene, and that the ice-cover existed more or less continually to the present. Late Cenozoic warming events that may have temporarily removed all or part of the Arctic Ocean's ice were thought to be restricted to the Pleistocene. More recently, published data suggest that the Pliocene Arctic Ocean was a warmer, perhaps ice-free ocean. General Circulation Modeling experiments with all or parts of the Arctic ice-cover removed are cited in support of Pliocene data generated primarily from the Arctic Ocean's margins that have suggested a warmer ocean. While there is important evidence for a warmer Pliocene Earth, the data to support significant warming in the central Arctic Ocean remains ambiguous. Reevaluation of part of the data used to support supposed Pliocene warming intervals on the Arctic Ocean's margins suggests that at least some of the implied Pliocene warming events may have actually occurred during the Pleistocene. The central Arctic Ocean's Pliocene record studied to date indicates only that the ocean had very low surface water productivity and extremely low sedimentation rates, both consistent with the presence of an ice-cover. There is little evidence of organic activity of any kind. However, the sum of the data obtained is equivocal concerning the affect of a warmer Earth on the central Arctic Ocean and the presence or absence of sea ice.