Late Miocene and Pliocene dinoflagellate cysts, acritarchs and terrestrial palynomorphs from ODP Hole 642B, Vøring Plateau, Norwegian Sea

The globally warm climate of the early Pliocene gradually cooled from 4 million years ago, synchronous with decreasing atmospheric CO2 concentrations. In contrast, palaeoceanographic records indicate that the Nordic Seas cooled during the earliest Pliocene, before global cooling. However, a lack of knowledge regarding the precise timing of Nordic Seas cooling has limited our understanding of the governing mechanisms. Here, using marine palynology, we show that cooling in the Nordic Seas was coincident with the first trans-Arctic migration of cool-water Pacific mollusks around 4.5 million years ago, and followed by the development of a modern-like Nordic Seas surface circulation. Nordic Seas cooling precedes global cooling by 500,000 years; as such, we propose that reconfiguration of the Bering Strait and Central American Seaway triggered the development of a modern circulation in the Nordic Seas, which is essential for North Atlantic Deep Water formation and a precursor for more widespread Greenland glaciation in the late Pliocene.

Organic carbon and oxidation in waters of the Norwegian Sea and Northeast Atlantic

Average total organic carbon concentration in the Norwegian Sea waters varies from 1.93 mg C/liter at depth of 10 m to 1.25 mg C/liter at depth of 2000 m, which is close to average values previously calculated from determinations made by the Marine Hydrophysical Institute at 19 stations in the Atlantic Ocean. The average carbon concentration in waters of the Northeast Atlantic adjacent to the Norwegian Sea is somewhat lower. Particulate carbon concentration, as determined by precipitation with aluminum hydroxide, is measured in tens of µg C/liter, that is few percent of total carbon concentration.

Dinocyst datum events of several holes in the Norwegian-Greenland Sea

The presence of abundant age-diagnostic dinoflagellate cysts in Ocean Drilling Program (ODP) Hole 913B (Leg 151), Deep Sea Drilling Project Hole 338 (Leg 38) and ODP Hole 643A (Leg 104) has enabled the development of a new biostratigraphy for the Eocene-Oligocene interval in the Norwegian-Greenland Sea. This development is important because the calcareous microfossils usually used for biostratigraphy in this age interval are generally absent in high latitude sediments as a result of dissolution. In parallel with this biostratigraphic analysis, we developed a magnetic reversal stratigraphy for these Norwegian-Greenland Sea sequences. This has allowed independent age determination and has enabled the dinocyst biostratigraphy to be firmly tied into the global geomagnetic polarity timescale (GPTS). The relatively high resolution of this study has enabled identification of dinoflagellate cyst assemblages that have affinities with those from the North Sea and the North Atlantic, which allows regional correlation. Correlation of each site with the GPTS has also allowed comparison of the stratigraphic record preserved in each drill-hole. Hole 913B is the most complete and is the best-preserved record of the Eocene and Oligocene in the Northern Hemisphere high latitudes, and can serve as a reference section for palaeoenvironmental reconstructions of this age interval.