TRACE ELEMENT FLUXES FROM A HIGH-LATITUDE ISLAND ARC WATERSHED

The chemical weathering of high-latitude volcanic arc watersheds is not well understood on a global scale. The elemental contributions resulting from weathering of volcanic arcs can be significant because these arcs are typically composed of young, reactive deposits and the potential enhancement of weathering through geothermal activity which increases temperature and acidity. The Aleutian volcanic arc is one of the largest on Earth, yet understanding of its contributions to the global weathering cycle is lacking. Akutan Volcano is located in the east-central part of the Aleutian arc. It is covered by a seasonal snow pack and average annual temperature is around 4.5^oC and average annual rainfall is close to 190 cm.

The Hot Springs Bay Valley (HSBV) located on the northeast side of the volcano and island hosts one of the larger drainages on the island. It is characterized by one major drainage that receives input of geothermal waters along the lower reaches before entering the ocean. The hot springs emanating at the surface range in temperature between 55-100 ^oC. Water samples were collected from sites upstream and downstream of each major hot spring and from each hot spring. Major cations, anions, trace elements and water stable isotopes were measured for each water sample. Trace elements in the hot springs are one to two orders or magnitude higher than in the stream water. For example, As in hot springs waters ranges from 451 µg/L to 1,700 µg/L whereas the stream water has 10 µg/L to 208 µg/L. Similar patterns are found for Ni, Mo, Sb, Fe, and Mn, indicating that the flux of trace elements in this drainage is directly related to the high temperature weathering processes and/or direct sources of geothermal activity. The δ¹⁸O and δD values for waters in the HSBV drainage indicate that the most upstream water is meteoric and most of the hot springs waters indicate an increase in δ¹⁸O with constant δD indicative of water-rock interaction in geothermal settings. Based on the discharge measurements from the furthest downstream site and the As concentration in the lower reaches the As flux for this drainage is approximately 1.1 kg/day. This work indicates that high temperature weathering and geothermal activity are important contributors to trace element flux from the Aleutian volcanic arc to the near-shore ocean environment.