Early Pliocene diatom record from the ANDRILL Mc Murdo Ice Shelf Core AND-1 with correlation to other sites within the Mc Murdo Sound and Ross Sea region

The ANDRILL AND-1 Core recovered from beneath the Ross Ice Shelf between Ross and White islands in Mc Murdo Sound, Antarctica contains a spectacular continental shelf marine record of the Pliocene. Alternating diamictite and diatom-rich sediments were deposited at this site throughout the Pliocene; this punctuated style of deposition and preservation reflecting the highly glacially influenced nature of deposition in this area. One time interval specifically, the early Pliocene, is represented by an extended diatomaceous unit almost 100m in thickness. This contiguous unit has frequent IRD within as well as varying amounts of volcanogenic material. The age of this early Pliocene unit has been constrained through the diatom assemblage present and magnetostratigraphy. Other sites from the Mc Murdo Sound area and Ross Sea have also recovered early Pliocene material but not in such breadth and completeness. The exact amount of time represented in this interval in the AND-1 core is uncertain but the species present in the assemblage would suggest an estimated time span from 4.2-4.9 Ma. The unit is bounded at its base by an erosional surface and there are three possible erosional surfaces in the upper 15 m but apart from this it appears this unit represents a period of uninterrupted sedimentation dominated by biogenic material. Across the sound in Taylor Valley, several land-based drill cores have been recovered with parts of this interval in each. The Dry Valleys Drilling Project Holes 10 and 11 contain thin intervals (2-20m) of diatomaceous-rich sediment from the early Pliocene. The very base of the CIROS-2 core, which was drilled from the sea ice in from of Ferrar Valley, also contains material from this time interval. Further out, in the Eastern Ross Sea, Deep Sea Drilling Project Hole 271 penetrated early Pliocene sediments, though core recovery was poor. The diatom data from the AND-1 material as well as the other sites mentioned suggest that for what now appears to be an extended period of time in the early Pliocene, the Ross Sea experienced minimal sea ice cover and was a highly productive region for diatoms. This record provides an important constraint on Antarctic climate and ice sheet history during a critical interval in global climate.