Typhoon- and earthquake-enhanced concentration and inventory of dissolved and particulate trace metals along two submarine canyons off southwestern Taiwan

Abstract

The influence of typhoon and earthquake events on the distributions of dissolved and particulate trace metals (Al, Fe, Mn, Cd, Cu, Pb, Zn) is evaluated along the Gaoping Canyon and Fangliao Canyon in a tectonically active margin off southwestern Taiwan. The Fangliao Canyon was mightily struck by a large Pingtung Earthquake (ML 7.0) in winter when terrestrial inputs were insignificant. This large earthquake clearly enhanced the concentration and inventory of total suspended matter (TSM), dissolved and particulate metals by 2–5 fold in Fangliao Canyon and nearby Gaoping Canyon, as compared to those in normal winter conditions. The Gaoping Canyon is typically inundated with massive amounts of terrestrial materials during summer typhoons from the mountainous Gaoping River. Strong contrast of particle and metal distributions can be found between summer and winter and between typhoon and regular summer periods in the Gaoping Canyon, which was apparently caused by various strengths of river inputs followed by sediment resuspension and lateral advection at intermediate and near-bottom depths along the canyon. The water-column and canyon-wide inventories of TSM, dissolved and particulate metals increased up to 2-fold higher during the post-typhoon period than during the rainy period in summer in the Gaoping Canyon. After extreme events, most metals tend to increase their release into the dissolved phase through the increase of TSM concentration. In addition to huge river inputs during typhoon, both typhoon and earthquake induce energetic sea conditions that cause sediment resuspension and enhance the concentration and inventory of particles and metals in submarine canyons.