Award: OCE-1334252

The purpose of our research is to understand the processes responsible for the unusually high concentrations of methyl mercury (a neurotoxin) in fog. Members of our team have shown that fog-water contains many times more methyl mercury than does rain-water, and animals (including spiders and mountain lions) that live in foggy areas (redwood forests and maritime chaparral complexes) have greater body burdens of mercury than the same animals from non-foggy areas. With scientists from the California State University at Monterey Bay and the University of California at Santa Cruz, a fog-water sampling network was established from Big Sur to Eureka, California. We have also analyzed ground fog (or tule fog) from inland locations. We found that the fog from the ocean, close to shore, has the most methyl mercury. Our group at Moss Landing Marine Laboratories set to sea on four research cruises and sampled the coastal sea waters, fog, plankton and sediments between Southern California and Central Oregon to locate the source of this mercury. We found that the methyl mercury is concentrated more than 40 times at the very surface of the ocean in the surface microlayer, a film about as thick as a hair is wide. Bubbles bursting through this layer can carry mercury into both fog and sea-spray. We also found that dimethyl mercury (a gaseous precursor of monomethyl mercury), is formed at about 1,000 feet below the surface and escapes into the atmosphere from the oceans in certain upwelling regions known as mesoscale eddies (big, slow whirlpools offshore), coastal upwelling centers and the surf zone. Dimethyl mercury can be converted to monomethyl mercury in fog or on particles in the air. As coal-fired power plants continue to emit high levels of mercury into the atmosphere, the concentration of mercury in the oceans continues to rise. We have identified a mechanism by which this pollutant flows backwards, not from land to sea, but from sea back to land. Both the ocean and terrestrial ecosystems amplify the concentrations of this neurotoxin in top predator populations. We need further studies to understand the broader impacts to these systems and how to manage this impact. Our research helps us to understand how this complex system works. This work has been featured in several popular publications and web sites: http://www.popsci.com/mercury-observed-in-coastal-fog-off-california https://www.youtube.com/watch?v=C_mviqitVLw https://www.youtube.com/watch?v=5rtTuz8xA4I http://www.nsf.gov/mobile/discoveries/disc_summ.jsp?cntn_id=136056&org=NSF http://news.kusp.org/post/trace-amounts-mercury-fog http://ww2.kqed.org/science/2015/12/18/toxic-fog-mercury-showing-up-in-coastal-california-fog-banks/ http://www.citylab.com/weather/2016/01/theres-toxic-mercury-lurking-in-san-franciscos-fog/422664/ http://www.sfgate.com/bayarea/article/The-toxic-chemical-in-San-Francisco-s-fog-6734283.php Last Modified: 08/08/2016 Submitted by: Kenneth H Coale