EVALUATING SOUTHERN PATAGONIA GLACIAL OUTWASH AS A POTENTIAL DRIVER OF SCOTIA SEA MAGNETIC SUSCEPTIBILITY VARIATIONS

Magnetic susceptibility (k) profiles from Scotia Sea deep water contourites are remarkably similar to Late Pleistocene atmospheric dust flux records in East Antarctic ice cores, suggesting Scotia Sea contourite evolution and atmospheric dust transport are responding to common forcing mechanisms. An unresolved question is what proportion of Scotia Sea sediment is comprised of dust. Models of annually averaged dust deposition flux using particle densities of 2.5 g/cc and particle sizes finer than 20 µm yield a plume originating over southern South American and extending over the western Scotia Sea. Scotia Sea k signals are carried by titanomagnetite residing in the fine and medium silt fractions. With a density of ~ 5.5 g/cc, titanomagnetite is more challenging to entrain and transport via wind. This study develops magnetic provenance tracers of southern Patagonia glacial outwash with the goal of evaluating to what extent these grains contribute to Scotia Sea k profiles. We analyzed glacial sediment from the southern shore of the Strait of Magellan where a moraine dated at approximately 20,000 yr BP transitions into an outwash plain. We analyzed the magnetic properties of bulk sediment and grain size separates. The glacial outwash sediment has roughly even proportions of sand, coarse silt, fine silt and clay (20-25 wt%), but a low medium silt content (~ 10 wt%). The coarse silt and sand fractions are magnetically enriched relative to the bulk sample, while the medium silt, fine silt, and clay fractions are magnetically depleted. With the exception of the clay fraction, the outwash grain size fractions are magnetically coarser-grained than Scotia Sea sediment and display multidomain (MD) hysteresis parameters and MD first-order reversal curves. The outwash clay fraction is magnetically finer than glacial (silty-clay) and interglacial (biosiliceous oozes) units from the Scotia Sea, and are comparable to deglacial units. Outwash silt fractions contain euhedral Fe-Cr-Al-Ti-Mg spinels. The cation substitution for Fe and slight oxidation is likely responsible for the range of Curie temperatures observed between ~465-600 ˚C. Magnetic and geochemical properties of the southern Patagonia glacial outwash are being integrated into rock-magnetic and mineralogic fingerprints that will be used to assess if Fe-Ti oxide grains in the Scotia Sea can be matched to this source area.