Skip to main content

Comminution dating of glacio-marine sediments in Antarctica and the Southern Ocean

Final Report Summary - COMANT (Comminution dating of glacio-marine sediments in Antarctica and the Southern Ocean)

A novel approach termed “comminution dating” was pursued in Antarctic subglacial erosion products during the Late Quaternary, and enables to determine spatial and temporal changes in the transport time of fine clastic sediments in Antarctica and the Southern Ocean. The transport time for this material varies on various time scales, from glacial-interglacial to sub-millenial, and is related to the combined impact of the flux of iceberg discharge into the ocean and ocean current fluxes. The processes that control comminution ages are controlled by climate, and on longer timescales by tectonics. Thus, it is also related to the relative contribution of the Antarctic Ice Sheet (AIS) to global sea level changes. This study focused on U-series disequilibrium in terrigenous material, which was explored as a measure of weathering and transport time. The time elapsed since the initial grinding of the bedrock by glacial abrasion that produces rock flour, including the transport process and age of deposition, defines the “comminution age” of the sediment, and is determined by the relative degree of 234U-depletion of the samples.

Efforts have focused on the reintegration of the proponent into his new position at the Hebrew University of Jerusalem, Israel (HUJI) and the Interuniversity Institute (IUI) for Marine Science. The researcher has established a completely new, state of the art, clean chemical lab. In addition, the researcher established a strong working group that has included, over the course of this study, a full time technician, three postdocs, five graduate students, and several undergraduate research assistants. Several new local and international collaborations were established, including with groups in the USA, UK and Germany. The researcher is involved in teaching courses at both HUJI and IUI.

Research efforts included extensive experiments geared towards establishing a robust working protocol and acquirement of samples from the designated study regions. Similarly, sample sets from the Amundsen Sea and the Howe – Achernar Mountains located in the Ross Sea embayment, in collaboration with colleagues from the USA and UK. The researcher is further involved in a joint effort with an international group of scientists in an NSF-funded project to study the deglacial ice dynamics in the Weddell Sea embayment using sediment provenance. Accordingly, the CIG award has facilitated both the integration of the researcher in a new faculty position in Israel, as well as a wide range network of active international collaborations.

Scientifically, the results provide the first systematic and wide-scale study of comminution ages in the Southern Ocean and Antarctica. One of the outcomes of this project was expansion of exploring U isotope fractionation to other regions (e.g. Red Sea), mediums (atmospheric dust, ocean floor phosphorites), and other isotopes (e.g. 238U-235U fractionation). As such, this study will also greatly enhance the provenance tracer data set in this region. Additional constraints on the connection between continental weathering and the evolution of marine (234U/238U) activity ratios are important in the context of U-Th dating of marine sediments and the ability to identify the effects of diagenesis in the sediments. Further indirect impacts of this study will be to expand the possibilities of dating continental deposits and to better understand fundamental aspects of sedimentology, glaciology and landscape evolution.