WHAT CAN WE LEARN FROM SUB-ANUALLY RESOLVED WEST ANTARCTIC ICE CORE SULFATE? Daniel A. Dixon, P. A. Mayewski, S. Kaspari, S. Sneed, M. Handley ACKNOWLEDGEMENTS: Office of Polar Programs, National Science Foundation, 109th Air National Guard, Ice Core Drilling Services, Raytheon Polar Services.

OVERVIEW ●Sixteen sub-annually dated ice cores from West Antarctica are used to examine the spatial and temporal distribution of sulfate for the last 200 years. ●The ice cores are dated using seasonal signals and well- known volcanic events. ●The sulfate is separated into its sea salt (ss) and excess (xs)SO4 components and the mean values are plotted vs. site elevation, distance from open water, and accumulation rate. ●Mean annual concentrations of ssSO4 are plotted vs. time. ●A robust spline is applied to the mean annual xsSO4 record and the smoothed series is plotted vs. time. ●The robust spline residuals are filtered to identify global- scale volcanic signals. ●The volcanic signals are examined using raw xsSO4 data.

INTERNATIONAL ITASE TRAVERSES FOR THE PERIOD U.S.ITASE TRAVERSES

ICE CORE LOCATIONS Map created using the RAMP DEM (Liu and others, 2001).

DATING THE CORES USING ANNUAL SIGNALS IN THE MAJOR ION TIMESERIES Ice core m depth Ion concentrations in parts per billion.

THE 1815 TAMBORA VOLCANIC ERUPTION IN xsSO4 ION CONCENTRATION TIMESERIES All concentrations in parts per billion.

SPATIAL VARIABILITY OF MEAN ssSO4 and xsSO4 CONCENTRATIONS ( )

EOF OF ANNUAL ssSO4 CONCENTRATIONS

EOF OF ANNUAL xsSO4 CONCENTRATIONS

TEMPORAL VARIABILITY OF ANNUAL ssSO4 CONCENTRATIONS IN ppb (dark line = 5-yr. run. av.)

ROBUST SPLINE SMOOTHED ANNUAL xsSO4 CONCENTRATIONS (in ppb)

ICE CORE LOCATIONS Map created using the RAMP DEM (Liu and others, 2001).

FILTERED POSITIVE RESIDUALS FROM ROBUST SPLINE SMOOTHED ANNUAL xsSO4 CONCENTRATIONS (in ppb)

THE 1963 AGUNG ERUPTION AS SEEN IN RAW xsSO4 CONCENTRATION DATA (in ppb) NO CLEAR VOLCANIC SIGNAL

THE 1991 PINATUBO ERUPTION AS SEEN IN RAW xsSO4 CONCENTRATION DATA (in ppb) NO CLEAR VOLCANIC SIGNAL

CONCLUSIONS ●West Antarctic ice core data indicate that there are two distinct transport sources for West Antarctic sulfate: lower troposphere for regions below 1000m and mid- upper troposphere/stratosphere for areas above 1000m. ●There is no compelling evidence for anthropogenic impact on the Antarctic sulfur budget. ●These data indicate that some kind of climate transition occurs over Central West Antarctica at around ●Global-scale volcanic eruptions appear as significant peaks in the robust spline residual xsSO4 records from sites located above 1000m elevation but do not appear in the residual records from sites located below 1000m.

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