The Scotia Sea Magnetic Susceptibility Record: Coupling of the Deep Ocean and Atmosphere?

Abstract:

Magnetic susceptibility (k) records from Scotia Sea deep water contourites are remarkably similar to atmospheric dust flux records in East Antarctic ice cores, suggesting Scotia Sea contourite evolution and atmospheric dust transport are responding to common forcing mechanisms. Glacial-marine k records reflect the interplay of lithogenic sediment provenance, biological productivity, sediment transport processes, and post-depositional diagenesis. Here we explore the origin of the Scotia Sea k record via a rock magnetic study across the MIS 6 to MIS 5 transition at IODP Expedition 382 Site U1537. We analyzed bulk sediment and grain size separates to understand magnetic signatures of iceberg rafted debris (IBRD), sortable silt, and eolian input. MIS6 consists of a silty-clay rich diatomaceous mud with high k and multidomain titanomagnetite. Deglaciation is characterized by a silty-clay that is IBRD-rich but with low k. This unit has a greater proportion of high coercivity minerals such as hematite or goethite. Grain size specific measurements will be used to determine if this signal resides in the IBRD, silt, or clay fraction, the latter of which may represent glacial flour. MIS5e consists of diatomaceous ooze in which k is uniformly low and IBRD decreases after deglaciation. The clay mass fraction, where eolian input resides, is > 0.5 in all three lithologies and has the weakest k signal, and is therefore not the main carrier of the bulk k signal. Scotia Sea k also does not correlate with the sand mass fraction or with gravel abundance determined from x-rays. The absence of k peaks in IBRD-rich intervals across all lithologies reflects the weakly magnetic lithogenic detritus supplied by Weddell Sea Embayment (WSE) ice streams, such as sandstone, quartzite, phyllite and schist observed in lateral moraines adjacent to eastern WSE ice streams. The Scotia Sea k signal exhibits the closest correspondence with the medium silt and fine silt fractions, suggesting that sediment transport related to nepheloid layers and bottom currents exert a strong control on k. Rock magnetic signatures and iron oxide mineralogy in the sediment will be compared with terrestrial till and bedrock from the WSE glacigenic sediment in South America to identify the sediment sources and environmental processes responsible for the k signal.