7-17 Arctica islandica shell Hg as a proxy for environmental Hg in the Gulf of Maine

Session: Undergraduate Research, Part I (Posters)

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Abstract:

Mercury (Hg) emissions to the environment, largely attributed to anthropogenic sources, have long posed a danger to terrestrial and marine ecosystems. Climate change makes the future of Hg cycling and uptake into marine food webs uncertain. Total Hg (THg) concentrations within absolutely-dated shells of the ocean clam Arctica islandica have potential as a high-resolution archive of past Hg concentrations in marine ecosystems.  This archive can inform understanding of how climate variability and anthropogenic climate change impact Hg cycling and entry into food webs. We first validated the reproducibility of Hg measurements within shell growth increments of A. islandica and assessed Hg concentrations in soft tissues of contemporary A. islandica specimens.  We then developed a sclerochronological Hg archive in A. islandica collected in the Gulf of Maine, spanning the years 1770-2024 CE.

Analysis of Hg in soft tissues of A islandica showed marked similarity in terms of both total Hg concentrations and distribution between tissues across co-eval samples. Shell Hg increased beginning around 1810 CE from ~2 ng/g to ~6 ng/g in the mid to late 19^th century. Concentrations declined over the period 1900-1940 CE to a minimum of about 1.3 ng/g, before increasing again and reaching a more recent peak of ~5 ng/g in the 1960s.  Since then, concentrations declined to about 1.1 ng/g and have remained relatively stable since the 1990s.  Overall, this pattern is consistent with the known history of anthropogenic Hg emissions, with the 19^th century peak likely related to gold and silver extraction and the 20^th century peak related to Hg release from coal combustion and industrial Hg use. We also highlight advances in methodological development of a sclerochronological Hg archive, particularly with respect to shell preparation for accurate Hg determination.  Future studies should investigate the impact of shell taphonomy on Hg concentrations, continue to expand sample depth, and incorporate additional fossil shells to extend the historical archive. 

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