Commentary: Biogeochemical analysis of ancient Pacific Cod bone suggests Hg bioaccumulation was linked to Paleo sea level rise and climate change

Citation: Kandasamy S and Weis P (2015) Commentary: Biogeochemical analysis of ancient Pacific Cod bone suggests Hg bioaccumulation was linked to Paleo sea level rise and climate change. Over the last 21,000 years, continuous and pulsed sea level rises from its glacial minimum of ∼120 m below the present sea level have affected the continental configuration of Earth's surface and thus land-sea interactions, materials exchanges and related biogeochemical processes. In this article, Murray and co-authors investigated total concentration of mercury (Hg) and stable carbon and nitrogen isotopes (δ 13 C and δ 15 N) in the bone collagen of archeologically recovered Pacific Cod (Gadus macrocephalus) and found high levels of total Hg in bones deposited during the early-mid Holocene interval. The authors suggested that the coastal flooding likely led to increased methylation of Hg in newly submerged terrestrial land and vegetation and thus high total Hg in bones. This study provides a clue that the coastal flooding due to future climate change may have the potential to enhance the amount of Hg significantly in marine food webs in the North Pacific region. Also of interest is the increase in methylmercury in receiving waters immediately following the flooding of previously dried wetlands, as occurred at the end of the last ice age on the continental shelves. It has been well-documented in the literature that flooding of wetlands leads to release of the sequestered methylmercury (and demonstrated experimentally by Porvari and Verta, 1995); the authors have acknowledged that this is the logical explanation to the higher levels they found in the older bones. It is unfortunate, however, that the authors chose muscle tissue to analyze in modern fish for comparison with the fossil bones. Nevertheless, an understanding of historical trends in contamination is always welcome. From stable isotopes point of view, it has been inferred based on increased carbon isotopic ratios since the mid-Holocene that shelf flooding due to sea level rise must have transferred the productivity regime from an oceanic to a shelf system. Furthermore, the authors suggested that the increase in δ 13 C may have resulted to increased phytoplankton growth rates or a change from pelagic to benthic foraging regime. δ 13 C-values in both pelagic and benthic planktons are ranging roughly from −18 to −21‰ and if one includes all suspended particles, surface sediments and ice algae investigated during both summer and winter seasons in north-central Bering Sea, …