Geochemical fingerprints of glacially eroded bedrock from West Antarctica: Detrital thermochronology, radiogenic isotope systematics and trace element geochemistry in Late Holocene glacial-marine sediments

Abstract

2018). Geochemical ngerprints of glacially eroded bedrock from West Antarctica: Detrital thermochronology, radiogenic isotope systematics and trace element geochemistry in Late Holocene glacial-marine sediments. Earth-Science Reviews, 182 pp. 204-232.For guidance on citations see FAQs. fingerprints of glacially eroded bedrock from West Antarctica: Detrital thermochronology, radiogenic isotope systematics and trace element geochemistry in Late Holocene glacial-marine sediments. AbstractGeochemical provenance studies of glacial-marine sediments provide a powerful approach to describe subglacial geology, sediment transport pathways, and past ice sheet dynamics. The marinebased West Antarctic Ice Sheet (WAIS) is considered highly vulnerable to ocean warming and sea level rise that is likely to cause its rapid and irreversible retreat. Studies of its past response to climate change are hence essential for projecting its future behaviour. The application of radiogenic and trace element provenance studies for past ice sheet reconstructions requires surveying the geographic variability of geochemical compositions of glaciomarine sediments. In this study, we characterize the provenance of the detrital fraction of 67 Late Holocene marine sediment samples collected off the Pacific margin of West Antarctica (60°W to 160°W), including 40 Ar/ 39 Ar ages of individual hornblende and biotite grains (>150μm), as well as Sr and Nd isotope and trace element composition of the fine-grained (<63μm) sediment fraction. Overall, this approach allows differentiating West Antarctica into five source regions: the Antarctic Peninsula, Bellingshausen Sea, Amundsen Sea, Wrigley Gulf-Hobbs Coast and Sulzberger Bay. Minor geochemical variability is found within each individual sector due to local variability in onland geology. 40 Ar/ 39 Ar ages of icebergrafted hornblende and biotite grains record primarily Carboniferous to Lates Quaternary ages (~0 to 380 Ma), with a notable age peak of ~100 Ma, associated with plutonic intrusions or deformation events during the mid-Cretaceous. Permian-Jurassic 40 Ar/ 39 Ar ages are widespread in the Amundsen Sea sector, marking episodes of large-volume magmatism along the long-lived continental margin.Metasedimentary rocks and Late Cenozoic alkali basalts in West Antarctica cannot be detected using detrital hornblende and biotite 40 Ar/ 39 Ar ages due to the absence or small grain-size (i.e. <150μm) of these minerals in such rocks. These sources can however be readily recognized by their fine-grained geochemical composition. In addition, geographic trends in the provenance from proximal to distal sites provide insights into major sediment transport pathways. While the transport of fine-grained detritus follows bathymetric cross-shelf troughs, the distribution of iceberg-rafted grains shows

A circumpolar dust conveyor in the glacial Southern Ocean

“…Likewise, northwards penetrating turbidity flows are unable to supply significant amounts of lithogenic fine fraction material to the mid-latitude South Pacific 34 . Accordingly, the zonal diversity of Nd-Sr isotope compositions of West Antarctic shelf sediments 50 is not reflected in our LGM fine fraction data (Fig. 2 ).…”

“…a Overview of potential source area compositions in the Southern Hemisphere. West Antarctic and Ross Sea shelf data obtained from < 63 µm fractions 50 , 96 . SB: Sulzberger Bay.…”

Ross Sea West Antarctic Ice Sheet History

“…Climate snapshots near magnetic reversals will be targeted (e.g., the M2 glacial in Figure F4) because these events can be traced to more continuous records from the continental rise (Site U1524) and global sea level records. Sediment provenance studies (clast/sand petrology, mineral thermochronology, and radiogenic isotope analysis) at Sites U1521 and U1522 will enable understanding of the changes in the origin of sediments (e.g., local ice caps versus ice sheet expansion and provenance from East versus West Antarctic sources) ( Figure F7) (Licht et al, 2005(Licht et al, , 2014Talarico et al, 2012;Cook et al, 2013;Perotti et al, 2017;Simões Pereira et al, 2018). As with all objectives, data integration with modeling studies will be undertaken ( Figure F4) (Golledge et al, 2012;Wilson et al, 2013;DeConto and Pollard, 2016;Gasson et al, 2016;Colleoni et al, 2018b).…”

The geochemical and mineralogical fingerprint of West Antarctica's weak underbelly: Pine Island and Thwaites glaciers

“…Sites of seafloor surface sediments analysed in this study are shown as different symbols, and numbers correspond to descriptions provided in Table 1. Additional sites mentioned in the text are from Simões Pereira et al (2018) A major hurdle in identifying ice-sheet collapse in the proxy record of marine sediment cores recovered from the West Antarctic margin is our limited understanding of how exactly such a collapse might be expressed in the sediments (Hillenbrand et al, 2009). A powerful way in which to study past ice dynamics and presence/absence of an eroding ice sheet is to examine the mineralogical and geochemical provenance of the marine sediments deposited at the periphery of the ice sheet (for a recent review see Licht and Hemming, 2017).…”