INVESTIGATION OF HYDROTHERMAL ACTIVITY AT DECEPTION ISLAND, ANTARCTICA

The influence of hydrothermal activity on water, temperature, salinity, and chemistry (dissolved silica and Ca/Mg ratios) was investigated in Port Foster, the submerged caldera of Deception Island, an active volcano located in the Bransfield Strait near the Antarctic Peninsula. The work reported here is part of a larger project aimed at determining how hydrothermal exchange between water inside Port Foster and the young volcanic rocks that make up the island land mass is affecting the local and regional seawater chemistry. Thermal anomalies in beach interstitial water obtained from peripheral coves in Port Foster were as high as 99⁰C in May/June and 57⁰C in November. Salinity ranged from 5-34 psu. These thermal anomalies dissipated within 1 m during May/June. In November, we observed a thermal anomaly of 7-15⁰C in surface waters, which persisted as a thin surface layer from the shoreline to about 20-30 m offshore. Dissolved silica was up to 6 times higher and Ca/Mg molar ratios were 5 to 100 times higher in peripheral coves than in the middle of the bay and out in the Drake Passage. Ca/Mg molar ratios were 2 times higher than normal seawater in samples taken in the Bransfield Strait, south of Deception Island. Samples from the Bransfield Strait north of Deception Island have Ca/Mg molar ratios near that of normal seawater. We suggest that there are seasonal differences in the influence of hydrothermal activity on the temperature and chemical composition of the seawater in hydrothermal coves at Deception Island. During the early winter when ground water flux is limited by freezing, any thermal anomaly produced by venting of hot water dissipates within one meter. However, during the late spring, high groundwater flow from melting glaciers delivers hydrothermally heated water into the peripheral coves. In addition, these data suggest that outflow from the bay at Deception Island is carried southward along the Bransfield Strait.