Holocene climate driving spatially variable mercury input to an Arctic fjord environment

Abstract

Mercury (Hg) is a globally distributed pollutant, affecting the Arctic through ocean and atmospheric circulation, coastal erosion, and riverine export from continents. We employ Hg stable isotopes and geochemical proxies to evaluate how climatic variation over the Holocene has influenced Hg sources in Arctic fjord environments. Hg isotopes measured in four sediment cores from western Svalbard are compared to gather insights into spatiotemporal variability of Hg sources and depositional history. Compared to other pre-industrial marine sediments, which are primarily influenced by wet deposition (precipitation) and terrestrial runoff, Hg sourced from bedrock erosion and Hg bound to particulate organic matter (pHg) transported by Atlantic Ocean currents are the dominant Hg sources to the Svalbard fjords. The temporal profiles of these two Hg sources vary spatially, with Kongsfjorden showing greater bedrock-Hg around 12.6 ka BP, while Woodfjorden and Dicksonfjorden exhibit higher influences at 8 ka and 4 ka BP, respectively. Despite these temporal differences, colder periods are generally dominated by Hg sourced from bedrock, whereas warmer periods are characterized by the contribution of pHg. In modern times, global anthropogenic activities have widespread Hg influences, whereas regional activities such as coal mining have little Hg influence. Our study highlights the importance of regional environmental setting and the global rise in anthropogenic activities in determining the spatiotemporal variation in Hg sources in Arctic over the Holocene. The findings provide insights into complex interactions between climate change and the Hg cycle in an Arctic fjord ecosystem.