The Pliocene sediment in the central Arctic Ocean includes 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 of any kind. The Pliocene age is based on extrapolation of sedimentation rates from paleomagnetic boundaries, arenaceous foraminifera with a known Pliocene range, 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 the central Arctic Ocean Pliocene sediment is coarser-grained ice-rafted debris (IRD) or any indication of measurable surface water productivity.
Early interpretations of the Arctic Ocean Pliocene record included the concept that sea-ice was present during this time, and that ice-cover existed more or less continually to the present. 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 have suggested that the Pliocene Arctic Ocean was a warmer, perhaps ice-free ocean. GCM modeling experiments with all or parts of the Arctic ice-cover removed were thought to be supported by the Pliocene data generated primarily from the Arctic ocean's margins.
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 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 are more likely of Pleistocene age. The central Arctic Ocean's Pliocene record studied to date indicates only that the ocean had very low surface water productivity, extremely low sedimentation rates, and that there is little evidence of much organic activity, all of which is equivocal concerning the presence or absence of sea-ice.