Cenozoic ice‐rafting history of the central Arctic Ocean: Terrigenous sands on the Lomonosov Ridge

Abstract

[1] The Cenozoic ice-rafted debris (IRD) history of the central Arctic is reconstructed utilizing the terrigenous coarse sand fraction in IODP 302 cores from 0 to 273 meters composite depth. This HoloceneÀmiddle Eocene quantitative record of terrigenous sand accumulation on the Lomonosov Ridge, along with qualitative information on grain texture and composition, confirms the interpretation that ice initiation (sea ice and glacial ice) occurred $46 Ma in the Arctic, and provides a long-term pattern of Arctic ice expansion and decay since the middle Eocene. IRD mass accumulation rates range from 0 to 0.13 g/cm 2 /ka in the middle Eocene and from 0 to 0.36 g/cm 2 /ka in the Neogene. IRD mass accumulation rate (MAR) maxima in the Miocene and Pliocene cooccur with either glacial initiation or intensification in the sub-Arctic. The 46.25 Ma IRD onset in the central Arctic slightly precedes the earliest evidence of ice in the Antarctic, and compares in timing with a >1000 ppm decrease in atmospheric concentrations of CO 2 . The decline of pCO 2 in the middle Eocene may have driven both poles across the temperature threshold that enabled the nucleation of glaciers on land and partial freezing of the surface Arctic Ocean, especially during times of low insolation.

Expanding the Cenozoic paleoceanographic record in the Central Arctic Ocean: IODP Expedition 302 Synthesis

“…In a study of the ACEX coarse fraction, St. John [100] confirmed the initial interpretation of early occurrence of IRD in the ACEX record [19,41] (Figure 5). This study cleary demonstrated that the coarse fraction is IRD and not other types of primary sedimentation, e.g.…”

“…In terms of sea-ice circulation conditions, the ACEX provenance results show a dominant Russian source for the IRD that extends from the present back to the middle Eocene [100], suggesting that the modern two-component sea-ice circulation system (Transpolar Drift and Beaufort Gyre) has been a persistent feature since this time.…”

“…In the Neogene, the onset of a perennial sea-ice pack in the Arctic Ocean has been suggested, using different analytical approaches, to have occurred sometime between 15 Ma and 13 Ma [100,[102][103][104]. This spans the time of major growth of the East Antarctic ice sheet [105] and may point to a paleoclimatic teleconnection between the two poles during the middle Miocene [105,106].…”

New insights on Arctic Quaternary climate variability from palaeo-records and numerical modelling

“…Studies of this sediment sequence provide the first glimpses of the long term Cenozoic history of Arctic Ocean sea ice. IRD first appears in the ACEX core at w46 Ma, in the middle Eocene, implying that ice, glacial or sea ice, rafted this material to the Ridge from this time onwards (St John, 2008). That sea ice appeared in the central Arctic in the early Eocene was subsequently supported by findings of sea ice-dependent fossil diatoms (Synedropsis spp.)…”

Plio-Pleistocene trends in ice rafted debris on the Lomonosov Ridge

“…Speculations on how these processes may be linked are derived from modern patterns of circulation and sea ice stability, and how circulation patterns would be predicted to change through the Plio-Pleistocene. (St. John, 2008), C. Occurrence of drop stones (> 5 mm diameter) and sand lenses from visual core descriptions (Backman et al, 2006), D. Core recovery (black ¼ total recovery; grey ¼ disturbed). E. 10 Be/ 9 Be derived age model for the last 6.5 Myr.…”