Thallium dynamics in the southern North Sea

摘要

In open ocean waters thallium (Tl) belongs to the group of conservative elements, even though deviations from this trend have been observed in NW German coastal waters. Here, we report on tidal, seasonal and spatial dynamics of Tl along with Mo and Mn in the water column of a backbarrier tidal flat close to the island of Spiekeroog, the Jade system (Inner Jade and Jade Bay) and the adjacent offshore region. Dissolved thallium (Tl-diss) displays strong tidal and seasonal variations (similar to 25-60 pM) unrelated to salinity. In all study areas, Tl-diss clearly deviates from conservative behavior. In general, Tl-diss is low during low tide (with a loss of up to 50%) and inversely related to Mn-diss, except in summer. The tidal Tl variations as well as the loss of Tl in the water column may be due to Tl removal from pore waters in reducing sediments and drainage of Tl-free but Mn-rich pore waters into the water column during low tide. The negative Tl anomaly can be traced offshore for more than 40 km to the island of Helgoland.