The opening of the Fram Strait and its influence on sediment transport, climate and ocean circulation between the Arctic Ocean and the North Atlantic

During a long period of its Cenozoic history, the Arctic Ocean was isolated from any global thermohaline circulation system. Thus, the opening and subsequent widening of the Fram Strait, the only deep-water connection between the Arctic and Atlantic oceans, was a fundamental tectonic process with extensive consequences for the global ocean circulation and paleoclimate evolution as well as for sedimentation processes in the adjacent ocean basins and along the continental margins.

In order to reconstruct both the development of the ocean circulation within and the glacial history of the Arctic-Atlantic gateway we interpreted sediment packages imaged in reflection seismic profiles together with updated stratigraphic information from existing Ocean Drilling Program (ODP) holes. Our new, high resolution seismic stratigraphy for the Molloy Basin (central Fram Strait) is based on a revised chronology for ODP Site 909 and on reprocessed seismic reflection data with now better resolution than in previous studies.

An improved core-log-seismic integration for ODP Site 909 and crossing seismic reflection profile AWI-20020300 was substantial in deriving the new seismic stratigraphy as well as characterizing the seismic units lithologically (Gruetzner et al., 2022). The core-seismic integration was combined with a revised magnetostratigraphy calibrated by new palynomorph bioevents which shifts previously used stratigraphies for ODP Site 909 (e.g. Myhre et al., 1995) to significantly younger ages in the time interval from c. 15 Ma to 3 Ma. The new stratigraphy implies that prominent maxima in coarse sand particles and kaolinite, often interpreted as evidence for ice rafting in the Fram Strait occur at c. 10.8 Ma, c. 3 Myr later as previously inferred. In the late Tortonian (< 7.5 Ma), sediment transport became current controlled, most probably through a western, recirculating branch of the West Spitsbergen Current. This current influence was strongly enhanced between c. 6.4 and 4.6 Ma and likely linked to the subsiding Hovgaard (Hovgård) Ridge and the widening of the AAG. Late Pliocene to Pleistocene seismic reflectors correlate with episodes of elevated ice-rafted detritus input related to major phases in Northern Hemisphere ice sheet growth such as the prominent glacial inception MIS M2 and the intensification of Northern Hemisphere glaciation starting at c. 2.7 Ma.

Tracing the most prominent reflectors in a dense net (~5800 km) of re-processed seismic profiles allowed us to extrapolate these events into the western Boreas Basin and towards the adjacent Northeast Greenland continental margin. Subsequently compilations of updated digital isochron and depth-to-horizon maps were used to map depocenter geometries of current controlled sediments and mass-transport deposits within the western part of the Arctic-Atlantic gateway.

 

References

Gruetzner, J., Matthiessen, J., Geissler, W.H., Gebhardt, A.C., Schreck, M. (2022). A revised core-seismic integration in the Molloy Basin (ODP Site 909): Implications for the history of ice rafting and ocean circulation in the Atlantic-Arctic gateway. Global and Planetary Change, 215, 103876.

Myhre, A. M., Thiede, J., Firth, J. V., Ahagon, N., Black, K. S., Bloemendal, J., et al. (1995). Site 909. Proceedings of the Ocean Drilling Program, Part A: Initial Reports, 151, 159-220.