Tracing sediment source within a glaciated landscape: new observations from detrital thermochronology and Raman spectroscopy in the Southern Alps of New Zealand

The erosion of mountain landscapes is the greatest source of terrestrial sediment to global ocean basins and a critical part of the global carbon cycle regulating Earth’s climate over geologically relevant timescales. In particular, the expansion of mountain glaciers may accelerate bedrock erosion and rapidly increase the flux of terrestrial sediment from source areas. However, the mechanisms by which glaciation augments sediment flux are complex, and understanding them requires further research. Our research adopts a novel approach to determine the source of sediment in rivers exiting a glaciated landscape, combining detrital zircon fission-track “tracer” thermochronology and Raman spectroscopy of carbonaceous material (RSCM). Our research focuses on the Southern Alps of New Zealand as a model landscape with well-constrained lithology and a predictable exhumation gradient. In 5 west-draining transverse river catchments, we test the hypothesis that modern sediment is preferentially derived from glaciated, high-elevation areas of the catchment. Our 5 rivers span a range of glacial coverage, allowing us to further test the hypothesis that glacially-sourced sediment increases with the degree of glaciation in the catchment. Our preliminary results suggest that sediment is not exclusively derived from glaciated areas of the catchment, but may instead reflect additional deglaciated source areas affected by landsliding, possibly induced by seismicity along the Alpine Fault. Our research demonstrates a powerful and novel approach to tracing sediment sources within an individual catchment area and highlights complex interrelationships between mountain glaciation and changes in the magnitude and sources of sediment fluxes.