Cenozoic Arctic Gateway Paleoclimate Variability: Indications from Changes in Coarse-Fraction Composition

Abstract

Coarse-fraction sediment (>63 µm) studies for Leg 151 Sites 908 and 909 have enabled us to reconstruct the paleoclimate since the early Miocene (18.0 Ma) of the Fram Strait, in order to better understand this gateway between the North Atlantic and the Arctic Ocean. Study of the grain-size distribution patterns (subfractions 63-125 µm, 125-250 µm, 250-500 µm, 500-1000 µm, and >IOOO µm plus the coarse-component composition) suggests possible seasonal ice-rafting starting as early as 14.0 Ma. Also shown is a clear signal of ice-rafting events between 10.8 and 8.6 Ma, 7.2 and 6.8 Ma, 6.3 and 5.5 Ma, and since 5.0 Ma. Evidence indicates that the initiation of the East Greenland Current took place at 10.8 Ma and is related to the reorganization and shutdown of deep-water connections in the Middle and Central American Seaways during the latest middle to late Miocene. During the Pliocene-Pleistocene, the polar front moved over Site 908, covering the area with sea ice and pack ice during the Pleistocene (between 1.9 and 1.2 Ma). The West Spitsbergen Current episodically reached the Fram Strait during the Pliocene-Pleistocene, suggesting that the Norwegian Sea was never completely covered by sea ice and pack ice in that era.

Batiacasphaera bergenensis and Lavradosphaera elongata — New dinoflagellate cyst and acritarch species from the Miocene of the Iceland Sea (ODP Hole 907A)

“…Furthermore, the record of ice-rafted debris (IRD) at other high latitude sites close to Greenland (e.g. Schaeffer and Spiegler, 1986;Fronval and Jansen, 1996;Wolf-Welling et al, 1996;Helland and Holmes, 1997) suggests the establishment of small-scale glaciations on Greenland large enough to reach sea level at around this time. However, based on the stratigraphic occurrence at Site 907 it is difficult to assess the detailed paleoecological affinities of B. bergenensis sp.…”

The Cenozoic western Svalbard margin: sediment geometry and sedimentary processes in an area of ultraslow oceanic spreading

“…Based on mineralogical data from ODP sites 908 and 909 in the Fram Strait (Fig. 1), Wolf-Welling et al (1996) suggested that the West Spitsbergen Current reached the Fram Strait episodically during Plio-Pleistocene (between 1.9 and 1.2 Ma). Thus, this influx of water masses along west Svalbard could have created environments for contourites to develop (Fig.…”

Development of the Western Boundary Undercurrent at Eirik Drift related to changing climate since the early Miocene

“…Unfortunately, only few details of the exact extent of sea ice are known for this period. A local glaciation at Svalbard is thought to have yielded a general strengthening of NHG at $ 6.9 Ma (Winkler et al, 2002) and an enhanced sea-ice extent at the Greenland Sea between $ 7.5 and 6.2 Ma (Wolf-Welling et al, 1996). The enhanced sea-ice extent would easily have resulted in a shift of the NCW formation area south towards the Norwegian Sea (Fig.…”