Miocene to Quaternary Paleoceanography in the Northern North Atlantic: Variability in Carbonate and Biogenic Opal Accumulation

Abstract

Based on accumulation rates of the bulk sediment and some pelagic components (carbonate, total organic carbon, and biogenic opal fractions) major changes in the paleoceanography of the northern North Atlantic from Miocene to Recent are discussed. Interactions of various processes could have created a stepwise evolution of cold climates in the northern hemisphere. Prominent events were the onset of deep water export across the Greenland-Scotland Ridge with the first significant overflow across the Iceland-Scotland segment occurring most probably between 13 – 11 Ma and at about 7 Ma across the Denmark Strait. Oscillations of sea-level around the critical sill depth in the early phases of the subsidence may have influenced the oceanic circulation in the North Atlantic as well as in the Norwegian-Greenland Sea. Furthermore the potential of the Norwegian-Greenland Sea to form and export dense deep water, increased the meridionality in the northern hemisphere. During 10.2 – 9.3, 8.7 – 8.2, 5.8 – 5.4 and 4.8 – 3.2 Ma representing times of increased water mass exchange to the central North Atlantic, carbonate deposition occurred. On the other hand, higher opal accumulation rates and decreased water mass exchange (9.3 – 8.7 and 5.4 – 4.8 Ma) may be correlated with sea-level oscillations around the critical sill depth of the Greenland-Scotland Ridge. The build-up of northern hemisphere cooling can probably traced back to late Miocene times with modest ice-rafted debris input. A significant stepwise increase of northern hemisphere cooling occurred around 4 Ma and finally resulted in the first large extension of sea ice and ice-rafting in the entire North Atlantic at ca. 2.6 Ma.