Matthew O'Regan

The Cenozoic palaeoenvironment of the Arctic Ocean

The history of the Arctic Ocean during the Cenozoic era (0–65 million years ago) is largely unknown from direct evidence. Here we present a Cenozoic palaeoceanographic record constructed from >400u2009m of sediment core from a recent drilling expedition to the Lomonosov ridge in the Arctic Ocean. Our record shows a palaeoenvironmental transition from a warm ‘greenhouse’ world, during the late Palaeocene and early Eocene epochs, to a colder ‘icehouse’ world influenced by sea ice and icebergs from the middle Eocene epoch to the present. For the most recent ∼14u2009Myr, we find sedimentation rates of 1–2u2009cm per thousand years, in stark contrast to the substantially lower rates proposed in earlier studies; this record of the Neogene reveals cooling of the Arctic that was synchronous with the expansion of Greenland ice (∼3.2u2009Myr ago) and East Antarctic ice (∼14u2009Myr ago). We find evidence for the first occurrence of ice-rafted debris in the middle Eocene epoch (∼45u2009Myr ago), some 35u2009Myr earlier than previously thought; fresh surface waters were present at ∼49u2009Myr ago, before the onset of ice-rafted debris. Also, the temperatures of surface waters during the Palaeocene/Eocene thermal maximum (∼55u2009Myr ago) appear to have been substantially warmer than previously estimated. The revised timing of the earliest Arctic cooling events coincides with those from Antarctica, supporting arguments for bipolar symmetry in climate change.

Late Cenozoic Paleoceanography of the Central Arctic Ocean

The Arctic Ocean is the smallest and perhaps least accessible of the worlds oceans. It occupies only 26% of the global ocean area, and less than 10% of its volume [1]. However, it exerts a disproportionately large influence on the global climate system through a complex set of positive and negative feedback mechanisms directly or indirectly related to terrestrial ice and snow cover and sea ice. Increasingly, the northern high latitude cryosphere is seen as an exceptionally fragile part of the global climate system, a fact exemplified by observed reductions in sea ice extent during the past decades [2]. The paleoceanographic evolution of the Arctic Ocean can provide important insights into the physical forcing mechanisms that affect the form, intensity and permanence of ice in the high Arctic, and its sensitivity to these mechanisms in vastly different climate states of the past. However, marine records capturing the late Cenozoic paleoceanography of the Arctic are limited – most notably because only a single deep borehole exists from the central parts of this Ocean. This paper reviews the principal late Cenozoic (Neogene/Quaternary) results from the Arctic Coring Expedition to the Lomonosov Ridge and in light of recent data and observations on modern sea ice, outlines emerging questions related to three main themes: 1) the establishment of the modern Arctic Ocean and the opening of the Fram Strait 2) the inception of perennial sea ice 3) The Quaternary intensification of Northern Hemisphere glaciations.