Mid-Piacenzian Variability of Nordic Seas Surface Circulation Linked to Terrestrial Climatic Change in Norway
|Author(s)||Panitz Sina1, de Schepper Stijn2, Salzmann Ulrich1, Bachem Paul E.2, Risebrobakken Bjorg2, Clotten Caroline2, Hocking Emma P.1|
|Affiliation(s)||1 : Northumbria Univ, Fac Engn & Environm, Dept Geog, Newcastle Upon Tyne, Tyne & Wear, England.
2 : Uni Res Climate, Bjerknes Ctr Climate Res, Bergen, Norway.
|Source||Paleoceanography (0883-8305) (Amer Geophysical Union), 2017-12 , Vol. 32 , N. 12 , P. 1336-1351|
|WOS© Times Cited||4|
|Keyword(s)||dinoflagellate cysts, Norwegian Atlantic Current, Arctic Front, northward heat transport, obliquity forcing, late Pliocene|
During the mid-Piacenzian, Nordic Seas sea surface temperatures (SSTs) were higher than today. While SSTs provide crucial climatic information, on their own they do not allow a reconstruction of potential underlying changes in water masses and currents. A new dinoflagellate cyst record for Ocean Drilling Program (ODP) Site 642 is presented to evaluate changes in northward heat transport via the Norwegian Atlantic Current (NwAC) between 3.320 and 3.137Ma. The record is compared with vegetation and SST reconstructions from Site 642 and SSTs from Iceland Sea ODP Site 907 to identify links between SSTs, ocean currents, and vegetation changes. The dinocyst record shows that strong Atlantic water influence via the NwAC corresponds to higher-than-present SSTs and cool temperate vegetation during Marine Isotope Stage (MIS) transition M2-M1 and KM5. Reduced Atlantic water inflow relative to the warm stages coincides with near-modern SSTs and boreal vegetation during MIS M2, KM6, and KM4-KM2. During most of the studied interval, a strong SST gradient between Sites 642 and 907 indicates the presence of a proto-Arctic Front (AF). An absent gradient during the first half of MIS KM6, due to reduced Atlantic water influence at Site 642 and warm, presumably Atlantic water reaching Site 907, is indicative of a weakened NwAC and East Greenland Current. We conclude that repeated changes in Atlantic water influence directly affect terrestrial climate and that an active NwAC is needed for an AF to develop. Obliquity forcing may have played a role, but the correlation is not consistent. Plain Language Summary At present, northward heat transport via the Norwegian Atlantic Current (NwAC) is a major reason for the mild climate in Norway. For the warmer-than-present late Pliocene (approximately 3.0-3.3Ma), it is unclear if changes in northward heat transport affected the Norwegian Sea and Scandinavian climate. We analyzed fossil dinoflagellate cysts in Ocean Drilling Program Hole 642B to reconstruct changes in the influence of the NwAC during the late Pliocene. We found that strong NwAC influence and changes in insolation are responsible for warmer-than-present climatic conditions in Norway. In contrast, reduced NwAC influence is associated with similar-to-present climatic conditions on land. These results highlight that changes in northward heat transport via the NwAC and insolation changes control late Pliocene climate changes in Norway.