MCA: Developing a Paleorecord of Hg in Long-Lived Mollusks from the Gulf of Maine

Grinnell College, Grinnell IA

Investigators

Abstract

Mercury (Hg) contamination is a serious environmental problem that affects ecosystems and human health, with most of human exposure coming from marine fish consumption. The impact of climate change and natural climate variability on the movement and bioaccumulation of Hg in marine ecosystems is not fully understood. Such understanding is vital to setting targets and assessing the progress of policy efforts to limit Hg contamination of marine ecosystems and human exposure. This research seeks to develop an approximately 1000-year record of Hg preserved in clam shells collected from the Gulf of Maine, one of the most rapidly warming regions of the world’s oceans. Like tree rings, clam shells possess layers that can be precisely dated and have potential to preserve highly resolved signals of past variation in Hg concentrations and accumulation by biota. Importantly, this Hg record can be paired with other kinds of climate proxy information preserved in the clam shells, giving detailed information about how marine Hg in this organism changes in response to a changing climate. This record will provide an especially useful dataset for calibrating and improving models for predicting the effects of policy and climate change on the recovery of marine ecosystems from centuries of Hg pollution. Other broader impacts include development of a new regional scientific partnership between researchers at a predominantly undergraduate institution (Grinnell College) and a large public research university (Iowa State University) and new opportunities for undergraduate research. Samples of the mollusk Arctica islandica will be collected from coastal locations in the Gulf of Maine and shell Hg concentrations compared to water, sediment, and biota concentrations of total Hg and methylmercury (MeHg). These comparisons will permit the researchers to evaluate whether shell Hg is a robust proxy of environmental Hg and MeHg bioaccumulation and to assess reproducibility of coeval shell samples. A master chronology of Hg in Gulf of Maine will then be constructed based on measuring shell Hg at high-resolution for an existing cross-dated A. islandica shell archive spanning the last millennium, a period which spans significant climatic and ocean circulation changes and large increases in Hg emissions from local and global sources. This record can be directly compared to existing and novel paleoclimate proxy records, including existing oxygen stable isotope records and newly measured trace-element records (Ba and Mn). Results of this work should permit determination of the sensitivity of Hg bioaccumulation to natural climate variability and evaluation of coupled biogeochemical-climate models used for predicting trajectory of future Hg in marine biota under various climate change scenarios. This project is jointly funded by the Division of Earth Sciences Geobiology and Low-Temperature Geochemistry Program, the Division of Ocean Sciences Marine Geology and Geophysics Program and the Established Program to Stimulate Competitive Research (EPSCoR). This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.