M.L.I. Witt

Observational and modeling constraints on global anthropogenic enrichment of mercury.

Centuries of anthropogenic releases have resulted in a global legacy of mercury (Hg) contamination. Here we use a global model to quantify the impact of uncertainty in Hg atmospheric emissions and cycling on anthropogenic enrichment and discuss implications for future Hg levels. The plausibility of sensitivity simulations is evaluated against multiple independent lines of observation, including natural archives and direct measurements of present-day environmental Hg concentrations. It has been previously reported that pre-industrial enrichment recorded in sediment and peat disagree by more than a factor of 10. We find this difference is largely erroneous and caused by comparing peat and sediment against different reference time periods. After correcting this inconsistency, median enrichment in Hg accumulation since pre-industrial 1760 to 1880 is a factor of 4.3 for peat and 3.0 for sediment. Pre-industrial accumulation in peat and sediment is a factor of ∼ 5 greater than the precolonial era (3000 BC to 1550 AD). Model scenarios that omit atmospheric emissions of Hg from early mining are inconsistent with observational constraints on the present-day atmospheric, oceanic, and soil Hg reservoirs, as well as the magnitude of enrichment in archives. Future reductions in anthropogenic emissions will initiate a decline in atmospheric concentrations within 1 year, but stabilization of subsurface and deep ocean Hg levels requires aggressive controls. These findings are robust to the ranges of uncertainty in past emissions and Hg cycling.

Multi-Decadal Decline of Mercury in the North Atlantic Atmosphere Explained by Changing Subsurface Seawater Concentrations

decline of 0.046 0.010 ng m 3 a 1 (2.5% a 1 )o ver the NA (steeper than at Northern Hemispheric land sites) but no significant decline over the SA. Surface water Hg 0 measurements in the NA show a decline of 5.7% a 1 since 1999, and limited subsurface ocean data show an 80% decline from 1980 to present. We use a coupled global atmosphere-ocean model to show that the decline in NA atmospheric concentrations can be explained by decreasing oceanic evasion from the NA driven by declining subsurface water Hg concentrations. We speculate that this large historical decline of Hg in the NA Ocean could have been caused by decreasing Hg inputs from rivers and wastewater and by changes in the oxidant chemistry of the atmospheric marine boundary layer. Citation: Soerensen, A. L., D. J. Jacob, D.G.Streets, M.L.I.Witt, R. Ebinghaus,R.P.Mason, M.Andersson, and E. M. Sunderland (2012), Multi-decadal decline of mercury in the North Atlantic atmosphere explained by changing subsurface seawater concentrations, Geophys. Res. Lett., 39, L21810, doi:10.1029/ 2012GL053736.

A total volatile inventory for Masaya Volcano, Nicaragua

NERC project “Magma dynamics at persistently degassing basaltic volcanoes: A novel approach to linking volcanic gases and magmatic volatiles within a physical model” (NE/F004222/1 and NE/F005342/1).