Reconstruction of paleoclimate and loess provenance during the last glacial in Jersey using XRF analysis

Abstract: With our changing climate it becomes more vital to understand the processes that control climate change in order to better understand possible future shifts. By doing this, predictions can be made about future climates and better prepare us for them. Loess, a silt-sized aeolian sediment, makes up an important climate record of the Quaternary and can therefore be used to reconstruct past climate changes. Loess deposits can be found on the Channel Island Jersey, next to the North Atlantic where several major climate shifts occurred during the last glacial period. During warmer climate periods the sediment starts to undergo chemical weathering. This causes the parental materials elemental composition to change where some elements become enriched, and others are diminished. This project aims to understand how the climate changed during the late Quaternary on Jersey, as well as determining if there has been a change in the loess provenance, through analysis of the elemental composition of loess. Loess at La Motte on Jersey will be analysed using XRF (X-ray fluorescence), allowing constraint of its elemental composition. The elemental composition will be used to analyse how much the sediment has weathered, and in turn to infer what the climate was like during deposition. To do so, 79 samples from La Motte were dried, sieved, milled, and analysed with XRF. Weathering indexes such as CIW, CIA, CPA, PIA, and Index B are used to be able to constrain the weathering rates in the loess, as well as other ratios like Rb/Sr and Ba/Sr. Ratios of immobile elements Ti/Zr and Ti/Al are used to investigate loess provenance. The results indicate a stable climate in the oldest parts of the sequence, that gradually get colder and dryer, indicated by decreased weathering. Weathering rates then starts to increase meaning that the climate became warmer and wetter. The top part of the stratigraphy has likely been altered by humans and can therefore not be used to make assumptions regarding climate. As for the provenance of loess, many fluctuations occurred, indicating many changes in source which could be caused by several factors such as wind direction and melting of ice sheets causing sediment to be released.