Hg0 trends in the North and South Atlantic Marine Boundary Layer: the importance of the subsurface ocean mercury reservoir

Transcription

1 Hg trends in the North and South Atlantic Marine Boundary Layer: the importance of the subsurface ocean mercury reservoir ICHMET Anne Laerke Soerensen Daniel J. Jacob, Robert Mason, Melanie Witt, Ralf Ebinghaus4, David Streets5, Maria Anderson6, Elsie Sunderland Harvard University University of Connecticut University of Oxford 4 Helmholtz-Zentrum Geesthacht, Institute of Coastal Research 5 Argonne National Laboratory 6 ESSIQ AB

2 Introduction :8 Atmospheric emissions Natural emissions ~9 Mg/y Anthropogenic emissions ~ Mg/y Re-emissions ~5 Mg/y

3 Introduction :8 [Cole et al. ] Atmospheric TGM (Hg +Hg II ) trends.5 ng/m /y.9 ng/m /y Hg (ng m - ). ng/m /y 996 Hg (ng m - ). ng/m /y.4 ng/m /y.5 ng/m /y 996 Hg (ng m - ) 996 [Cole et al. ] [Slemr et al. ]

4 Cruise observations 4:8 cruises in the Northern Hemisphere 5 cruises in the Southern Hemisphere 97s 99s s 6 o N o N Mace Head Cruise references: Temme et al. [] Mason et al. [998] Lamborg et al. [999] Mason et al. [] Laurier and Mason [7] Aspmo et al. [6] Andersson et al. [8] Mason et al. [9] Sommar et al. [] Soerensen et al. [] Kuss et al. [] M. Witt (manuscript in preparation, ) R. Ebinghaus (unpublished data, ) Latitude o o S 6 o S Cape Point 75 o o o o W 45 W 5 W 5 E [Soerensen et al. (in press] doi:.9/gl576

5 Cruise observations 5:8 Atmospheric Hg cruise observations Hg, ng m - 6 o N o N Mace Head North Atlantic Latitude o Hg, ng m - o S Cape Point South Atlantic Year Cruises Trend (cruises) MaceHead/Cape Point 6 o S 75 o o o o W 45 W 5 W 5 E [Soerensen et al. (in press] doi:.9/gl576

6 Cruise observations 6:8 Atmospheric Hg cruise observations Hg, ng m - Significant decrease -.46±. ng m - a - (p <., n = 8).5% a - North Atlantic North Atlantic > other NH sites (.-.5) Hg, ng m - South Atlantic Year Cruises Trend (cruises) MaceHead/Cape Point Not significant decrease -.±. ng m - a - (p =.6, n = ) South Atlantic < Cape Point (.5)

7 Cruise observations 7:8 Atmospheric Hg cruise observations Changes in anthropogenic emissions?? Hg, ng m -.8 ng/m North Atlantic AMAP/UNEP (Wilson et al., ) Hg, ng m - South Atlantic Year Cruises Trend (cruises) MaceHead/Cape Point Streets et al. () 99 8

8 Cruise observations 8:8 Atmospheric Hg cruise observations Changes in anthropogenic emissions?? Hg, ng m -.8 ng/m North Atlantic Hg, ng m - South Atlantic Year Cruises Trend (cruises) MaceHead/Cape Point [Wilson et al. ]

9 Model simulations 9:8 GEOS-Chem global -D chemical transport model Assimilated meteorology from NASA Goddard Earth Observing System (GEOS)!!! Horizontal resolution 4 o x5 o, 48 vertical layers Atmospheric Hg, Hg II and HgP [Selin et al. 7] Br is the atmospheric oxidant of Hg [Holmes et al. ] Associated surface ocean model representing Hg, Hg II and HgP [Soerensen et al. ]

10 Model simulations :8 Changes in anthropogenic emissions???? Hg, ng m - North Atlantic ng/m -. to. ng/m Hg, ng m - South Atlantic Cruises Trend (cruises) MaceHead/Cape Point Streets inventory Wilson inventory Subsurface changes

11 Overview :8 Atmospheric emissions Natural emissions ~9 Mg/y Anthropogenic emissions ~ Mg/y Re-emissions ~5 Mg/y

12 Subsurface Hg :8 Declining subsurface ocean HgT (5- m) in the North Atlantic.78±.4.95±.59 6.±.5 6 o N Mace Head o N Latitude o [pm] o S Cape Point [Mason et al. ] 6 o S 75 o o o o W 45 W 5 W 5 E

13 Model simulation :8 GEOS-Chem global -D chemical transport model subsurface water [Soerensen et al. ] Horizontal resolution 4 o x5 o

14 Model simulation 4:8 GEOS-Chem global -D chemical transport model 5 m 5 m [Soerensen et al. ] [Montegut et al. 4] Meters Oct 5th Nov 5th Dec 5th.. Mean monthly mixed layer depth No variation between years Extrapolation between mean monthly depths allows for change with each timestep

15 Model simulation 5:8 GEOS-Chem subsurface concentrations (pm) based on observations presented in: Sunderland & Mason 7, Sunderland et al. 9, Mason et al..6 pm. pm 5. pm (99).95 pm ().78 pm (8). pm.8 pm.8 pm. pm.9 pm

16 Model simulation 6:8 Atmospheric Hg cruise observations Hg, ng m - North Atlantic Surface air Hg Decrease between between 5. pm and.78 pm subsurface concentration 9 o N 6 o N o N driven by subsurface North Atlantic trends o o S Hg, ng m - 6 o S 9 o S 8 o o W 6 o W o 6 o E o E 8 o South Atlantic Year ng m - a - Cruises Trend (cruises) MaceHead/Cape Point Streets inventory Wilson inventory Subsurface changes [Soerensen et al. (in press] doi:.9/gl576

17 Rivers as a source 7:8

18 Summary Atmospheric Hg decline most pronounced in the Northern Hemisphere Changes in North Atlantic subsurface Hg concentration explain the decline We hypothesize that the decline is caused by changes in anthropogenic sources We need information of rivers as a source of Hg to the ocean Acknowledgement NSF Chemical Oceanography Electric Power Research Institute Team-Hg (Harvard)