Hydrochemical dynamics on sub-Antarctic Marion Island

• Main Author: Stowe, Michael-James
• Other Authors: Eckardt, Frank, Nel, Werner
• Format: Master Thesis
• Language: English
• Published: Department of Environmental and Geographical Science 2017
• Subjects: Landscape and Climate Interactions; Antarc*; Antarctic; Marion Island
• Online Access: http://hdl.handle.net/11427/25445

Although sub-Antarctic maritime environments are some of the most sensitive regions to climate change, investigations into isotopic and hydrochemical dynamics on sub-Antarctic islands are limited. To address this, the Soft Plume River on sub-Antarctic Marion Island was sampled daily along an altitudinal gradient during an intense high-resolution 16-day field campaign in April/May 2015. Samples were analysed for stable isotopes (δ²H and δ¹⁸O) and major ions (Ca²⁺, Mg²⁺, K⁺, Na⁺, Cl⁻ , SO4²⁻, NO³⁻). In addition, stream water physicochemistry (pH, water temperature, dissolved oxygen and total dissolved solids) was monitored in situ at a single site in the stream at 5 minute resolution for the duration of the field campaign. Monthly precipitation δ²H and δ¹⁸O had mean values of -27.51‰ and -4.67‰ respectively. Stream water δ²H and δ¹⁸O values were significantly different to that of precipitation, with values ranging from -48.0‰ to -33.6‰ and from -7.6‰ to -5.6‰, respectively. Major ion concentrations were dominated by Na⁺ and Cl⁻, reflecting the overwhelming influence of the surrounding ocean on the island's stream water chemistry. This finding is consistent with previous studies on Marion Island and other maritime sub-Antarctic islands. Temporal variability in stream chemistry was assessed through daily sampling. Findings show that variation was predominantly controlled by precipitation. Following high precipitation amounts low stream water δ²H and δ¹⁸O values were recorded. This was likely the result of the "amount effect". Similarly, a decrease in ion concentrations was also observed following high rainfall amounts. This was because of stream dilution. Sampling along the stream revealed that variation in δ²H and δ¹⁸O and most major ions was largest at the highest site. This pattern is likely the result of an altitudinal precipitation gradient, with higher amounts of precipitation falling at the highest altitude site. High-frequency monitoring of stream water physicochemistry revealed the presence of diel ...