Late Neogene Paleoclimates and Paleoceanography in the Iceland-Norwegian Sea: Evidence from the Iceland and Vøring Plateaus

Abstract

Continuous late Neogene sediment sections from Site 907 on the Iceland Plateau and Sites 642, 643, and 644 on the V0ring Plateau were studied using stable isotope stratigraphy and sedimentological methods. Paleoclimatic and paleoceanographic changes have been placed in a time framework by using paleomagnetic reversals, biostratigraphic events, and isotope stratigraphic events as chronostratigraphic tools. The results show a general cooling of the Iceland-Norwegian Sea deep waters during the last 12 m.y., with major cooling events ~ll.O Ma and 6.4 Ma. At the V0ring Plateau, the oldest pulses of glacial icerafted debris (IRD) date to -12.6 Ma, indicating that glaciers reached sea level as early as the middle Miocene. The records of ice-borne deposits document a gradual intensification of glaciation from 7.2 to 6.0 Ma, which reflects the onset of small-scale glaciation in the Northern Hemisphere. The onset of large-scale Northern Hemisphere glaciation is dated at 2.75 Ma at the V0ring Plateau and 2.90 Ma at the Iceland Plateau, possibly reflecting different timing of growth of large-scale ice sheets in Greenland and Scandinavia. The middle Pleistocene climate shift (-0.9 Ma) is documented in both stable isotope stratigraphy and IRD deposition. The changes indicate a shift toward more extensive glacials of longer duration and the initiation of warmer interglacials with enhanced influx of Atlantic waters and ventilated deep waters. Within the Brunhes, deep-water formation apparently peaks during times of general climate deterioration and is not a linear response to global ice volume and sea-surface temperature. A general increase in planktonic 6 13 C -400 ka may reflect decreased global deep-sea carbonate preservation associated with the middle Brunhes climate transition.

Expansion of subarctic water masses in the North Atlantic and Pacific oceans and implications for mid‐Pleistocene ice sheet growth

“…There is evidence, nevertheless, for advance of the Scandinavian ice sheet at around 1.1 Ma [Sejrup et al, 2000] and significant increases in IRD in the North Atlantic and Nordic Seas after 1.0 Ma [Fronval and Jansen, 1996;Ruddiman et al, 1986]. Mean global ice volume, however, underwent a later stepwise increase during the intense glacial cooling of MIS 22 (0.9 Ma), the proposed onset of the MPT [Mudelsee and Schulz, 1997].…”

Pleistocene sea-surface temperature evolution: Early cooling, delayed glacial intensification, and implications for the mid-Pleistocene climate transition

“…Enhanced ice-rafting to the Nordic Seas and north Atlantic resumes after 1.0 Ma (Fronval and Jansen, 1996;Ruddiman et al, 1986), and after 0.9 Ma from the Alaskan and Greenland ice-sheets (Sancetta and Silvestri, 1986). Thus, early Pleistocene icesheet advance by the northern hemisphere ice sheets is followed by some delay until repeated and extensive glaciations characterize the later Pleistocene.…”

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

“…2 and 3). The range top might be related to the glacial inception in the Iceland Sea as depicted by the onset of predominantly siliciclastic deposition, the occurrence of the first drop stone, and the lowest occurrence of the coldwater acritarch Decahedrella martinheadii between 11 and 10 Ma at ODP Site 907 (Shipboard Scientific Party, 1995;Fronval and Jansen, 1996;. Furthermore, the record of ice-rafted debris (IRD) at other high latitude sites close to Greenland (e.g.…”

“…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.…”

“…Despite their importance, detailed reconstructions of paleoenvironmental changes that occurred across this period are still seriously hampered by insufficient temporal control on marine sedimentary sequences, primarily due to the rare occurrence of traditionally used calcareous microfossils in these deposits (e.g. Fronval and Jansen, 1996;Matthiessen et al, 2009a). In consequence, organicwalled dinoflagellate cysts (dinocysts) and acritarchs gained increased attention owing to their relatively high abundance and diversity in this realm.…”