Geochemical Characterization of Prince William Sound and Copper River Sediments: A Proxy Development to Assess Climate-Driven Variations in a High-Resolution Sedimentary Record

Williams Joshua R, Galveston TX

Investigators

Abstract

As part of a two-year postdoctoral research fellowship, this project focuses on determining the elemental composition of Prince William Sound (PWS) and Copper River sediments by analyzing a time-series throughout varying environmental conditions. These data will be used to interpret preserved sedimentary signatures contained within cores whose record extends into the last century, the period for which relatively robust instrumental records of discharge, climate, and oceanographic conditions exist. Ultimately, it is hoped the results of this research will allow high-resolution characterization of climatic drivers over the last several millennia. This knowledge will further understanding of how this system has responded in the past, and may provide crucial predictive information concerning future climate variations. Additionally, a key outreach component for this study is the development of a teaching curriculum to be used by underserved populations within rural Alaska who have limited access to science education or current research. The program will aim to further student understanding of how scientists use sediment cores to identify climate trends in PWS and the northern Pacific Ocean, and the subsequent impact on fisheries distribution, subsistence, and commercial harvests. This project will be conducted under the mentorship of Dr. Steven A. Kuehl at the Virginia Institute of Marine Science. The PWS is a sensitive sub-arctic region where rapidly changing climate patterns strongly alter hydrological and oceanographic conditions in ways that have profound ecological and economical implications. This research seeks to exploit the potential for a high-resolution environmental record contained within PWS sediment, which may allow us to understand changing river sediment dispersal and/or climate-driven oceanographic patterns throughout the Holocene. Previous X-ray Fluorescence (XRF) analyses reveal that PWS sediment cores contain geochemical and sedimentological signatures that can potentially resolve varying source input. Elemental ratios (e.g. Sr/Mn, Zn/S, K/Ca) may provide a basis for differentiating Chugach/northern PWS derived sediment loads from those of the upper Copper River. However, there is a paucity of information on compositional variations within the major drainage basins, and understanding seasonal variability influenced by changing provenance/ freshwater sources (e.g., snow melt, glacial melt, and rainfall, Chugach vs. Wrangell Range) in Copper River discharge is critical for the development of environmental proxy records. Once constrained, these proxies have the potential to resolve climatic oscillations on sub-annual to decadal timescales. Therefore, this project focuses on collecting a high-resolution time-series of representative samples of PWS and Copper River basin sediments with the aim to confidently constrain elemental variations observed in sediment core XRF records. Elemental composition of suspended sediment concentrations will be determined using Inductively Coupled Plasma Mass Spectrometry (ICPMS). Samples will also be analyzed for cosmogenic 7Be to test the hypothesis that the ubiquitously used tracer for recent fluvial sedimentation may be problematic in high latitude settings during spring discharge/ glacial melt.