The Cenozoic palaeoenvironment of the Arctic Ocean

Abstract

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 >400 m 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 ∼14 Myr, we find sedimentation rates of 1-2 cm 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 (∼3.2 Myr ago) and East Antarctic ice (∼14 Myr ago). We find evidence for the first occurrence of ice-rafted debris in the middle Eocene epoch (∼45 Myr ago), some 35 Myr earlier than previously thought; fresh surface waters were present at ∼49 Myr ago, before the onset of ice-rafted debris. Also, the temperatures of surface waters during the Palaeocene/Eocene thermal maximum (∼55 Myr 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. © 2006 Nature Publishing Group

Seismic velocities within the sedimentary succession of the Canada Basin and southern Alpha-Mendeleev Ridge, Arctic Ocean: evidence for accelerated porosity reduction?

“…There is little variation between any of the five subregional velocitydepth models over this range. Likewise, borehole sonic velocities from Lomonosov Ridge collected during Expedition 302 of the Integrated Ocean Drilling Program (Moran et al 2006) are all slower than 1.8 km s −1 and are from depths shallower than 0.2 km.…”

“…Mudie & Blasco 1985). The only scientific boreholes, drilled in 2004 during Expedition 302 of the Integrated Ocean Drilling Program, are located on the Lomonosov Ridge more than 1000 km to the north of central Canada Basin (Moran et al 2006). Over 500 industry wells have been drilled along the Arctic Alaska and Beaufort-Mackenzie margins , but these penetrate mainly nearshore successions that are unlikely to be present in the deep-water basin.…”

Anoxia and high primary production in the Paleogene central Arctic Ocean: First detailed records from Lomonosov Ridge

“…From this early ''Greenhouse'' time interval continuous central Arctic Ocean sedimentary records, allowing a development of chronologic sequences of climate and environmental change through Cenozoic times and a comparison with global climate records, however, were missing prior to the Integrated Ocean Drilling Program (IODP) Expedition 302 (Arctic Ocean Coring Expedition -ACEX) [Backman et al, 2006;Moran et al, 2006]. For the central Arctic Ocean in only four short cores obtained by gravity coring from drifting ice flows on the Alpha Ridge (Figure 1), some older pre-Neogene organiccarbon-rich sediments representing isolated, discontinuous fragments of the Late Cretaceous/Early Cenozoic climate history and depositional environment, have been recovered [Jackson et al, 1985;Clark et al, 1986].…”

Spatial and temporal Arctic Ocean depositional regimes: a key to the evolution of ice drift and current patterns

“…The Lomonosov Ridge was the target for the Integrated Ocean Drilling Program (IODP) Expedition 302 (the Arctic Coring Expedition; ACEX). Approximately 428 m of sediment draping the ridge, encompassing the past 56 Ma, were cored near 88 N during ACEX (Moran et al, 2006). The recovered Neogene sediment is characterized by oxygenated silty mud with numerous thin sand lenses and dropstones and indicates a generally persistent mode of glaciomarine deposition since about 17.5 Ma .…”