Deep-sea pre-glacial to glacial sedimentation in the Weddell Sea and southern Scotia Sea from a cross-basin seismic transect

摘要

Identification of the pre-glacial, transitional and full glacial components in the deep-sea sedimentary record is necessary to understand the ice sheet development of Antarctica and to build circum-Antarctic sediment thickness grids for palaeotopography/-bathymetry reconstructions, which constrain palaeoclimate models. A 3300 km long Weddell Sea to Scotia Sea multichannel seismic reflection data transect was constructed to define the first basin-wide seismostratigraphy and to identify the pre-glacial to glacial components. Seven main seismic units were mapped: Of these, WS-S1, WS-S2 and WS-S3 comprise the inferred Cretaceous-Palaeocene pre-glacial regime (>27 Ma in our age model), WS-S4 the Eocene-Oligocene transitional regime (27-11 Ma) and WS-S5, WS-S6, WS-S7 the Miocene-Pleistocene full glacial climate regime (11-1 Ma). Sparse borehole data from ODP Leg 113 and SHALDRIL constrain the ages of the upper three seismic units and seafloor spreading magnetic anomalies compiled from literature constrain the basement ages in the presented age model. The new horizons and stratigraphy often contradict local studies and show an increase in age from southeast to the northwest. The up to 1130 m thick pre-glacial seismic units form a mound in the central Weddell Sea basin and in conjunction with the eroded flank geometry, allow the interpretation of a Cretaceous proto-Weddell Gyre bottom current. The base reflector of the transitional seismic unit has a model age of 26.6-15.5 Ma from southeast to northwest, suggesting similar southeast to northwest initial ice sheet propagation to the outer shelf. We interpret an Eocene East Antarctic Ice Sheet expansion, Oligocene grounding of the West Antarctic Ice Sheet and Early Miocene grounding of the Antarctic Peninsula Ice Sheet. The transitional regime sedimentation rates in the central and northwestern Weddell Sea (6-10 cm/ky) are higher than in the pre-glacial (1-3 cm/ky) and full glacial regimes (4-8 cm/ky). The pre-glacial to glacial rates are highest in the Jane- and Powell Basins (10-12 cm/ky). Total sediment volume in the Weddell Sea deep-sea basin is estimated at 3.3-3.9 10~6 km~3.