Chronology of Greenland Scotland Ridge overflow: What do we really know?

As a sill constricting the exchange of deep water masses between the Nordic Seas and the North Atlantic, which forms an essential part of the Atlantic Meridional Overturning Circulation, the dynamic height of the Greenland Scotland Ridge and thus its overflow have an important influence on global climate. Several DSDP, ODP, and IODP sites have been drilled in the North Atlantic to shed light on the overflow and climate development. Reconstructions of bathymetry and sediment thickness have been put forward as well as calculations of the potential temperature of the conduit feeding the Iceland plume. The available studies have been screened to construct a conceptual model for the evolution of the palaeo-circulation in the North Atlantic and identify possible weaknesses in our knowledge. Details, e.g., timing and location, about the onset of the overflow are unknown, and especially the Paleogene development remains enigmatic. The database for this period is inadequate, and covers only small areas. The discussion centres on the earliest traces of the overflow leading to formation of sediment drifts in the eastern North Atlantic. More data provide a better base to reconstruct variations for the Neogene overflow, but also appears insufficient for in-depth analyses in time and space. Sediment drifts in the Iceland Basin indicate a first Iceland Faroe Ridge overflow for the early Miocene. Denmark Strait overflow appears to have started in mid-Miocene times, but evidence for this still is sparse. Grids of high-resolution seismic reflection data across all sediment drifts and all limbs of the Greenland Scotland Ridge combined with deeper drill sites targeting the complete sedimentary column down to basement are needed to fully understand the chronology of the Greenland Scotland Ridge overflow and its detailed impact on climate