From Bedrock to Sediments: Insights on the Ross Sea Ice-Flow Dynamics Inferred from Detrital Data

The Ross Sea received about one third of the Antarctic ice. It is a crucial area to investigate the ice dynamics during the Cenozoic as it records the evolution of both the East Antarctic Ice Sheet (EAIS) and West Antarctic Ice Sheet (WAIS), whose variations are a direct response to climate change. Reconstructions of the ice flow models are mainly based on multi-proxy provenance analysis of glacigenic sediments but so far, a well-established model is not existing. There are still disputes of the different ice contribution between the EAIS and the WAIS, and the ice confluence in the Ross Sea. Thus, the main target of this study is to provide new inputs to build a robust model of Ross Sea ice flow during the Cenozoic. This work is based on 48 samples collected across the Ross Sea and analyzed by apatite fission track (AFT) dating. More in detail, a first set of 16 samples is from the drilling core CIROS-2, whose stratigraphic range is from early Pliocene to Quaternary. A second group of 32 samples derives from 18 post-Late Glacial Maximum (LGM) piston cores drilled across the Ross Sea. The obtained fission-track data have been modelled with statistical tools (among them, the Multidimensional Scaling) and finally interpreted in terms of thermal evolution by the HeFTy software. The AFT age data of CIROS-2 samples show a large range of ages but most of the grains fit well with two main age components at 24-42 Ma and 43-70 Ma whereas the other components are not regularly distributed through the well. This pattern indicates a mixture of provenance from different areas along the Transantarctic Mountains (TAM). Furthermore, it suggests glacial expansion over the McMurdo Sound during the Pliocene, and periodically ice invading and retreating in Pleistocene. The data of post-LGM piston cores samples also show a large range of individual grain ages. The lack of systematic trends across the Ross Sea indicates the presence of multiple sources with a complex and differentiated erosional history. The presence of apatites younger than 21 Ma, clearly of volcanic origin, such as ages older than 230 Ma represent a significant signature for a source related to evolution of East Antarctica. Moreover, thermal modelling and the presence of apatites with cooling ages of about 30-40 Ma reveal a main exhumation phase of the TAM during the Oligocene associated to the last phases of the West Antarctic Rift System. The spatial distribution of key marker apatites (e.g. younger than 21 Ma or older than 230 Ma) allows to identify the Central High as a major ice-flow divide. West of the Central High, the ice flow is from East Antarctica, with general northwards trend but with local flows from outlet glaciers, especially during ice sheet retreat phases. East of the Central High, sediments derived mainly by West Antarctica, with only minor contributions from the southernmost portion of the TAM and the lack of any significant input from the inner Marie Byrd Land. As a whole, this work supports the idea of a WAIS-dominated ice flow model during the early Pliocene, an EAIS-dominated ice flow model during the late Pleistocene and an EAIS-WAIS balanced ice flow model during the Last Glacial Maximum.