Circulation changes on Antarctic Peninsula from ice cores Liz Thomas 1, Gareth Marshall 1 Joe McConnell 2 & Paul Dennis 3 1.British Antarctic Survey 2.Desert Research Institute 3.University of East Anglia

BAS Core locations Beethoven –1991 – 1948 Berkner –948 m (completed 2004) Dolmen Island – Dyer Plateau –D –D James Ross Island –365 m (completed 2008) Gomez – James Ross Island Faraday Rothera Dolman Island Dyer Plateau (1&2) Gomez Berkner Island Beethoven

Drill site Medium depth ice core drilled to a depth of 136 meters with an electromechanical, 104 mm diameter drill Encompasses the period between 1855 – 2006 (150 years) Ground penetrating radar (GPR) used to asses accumulation variability Gomez ice core (73.59°S, 70.36°W, 1400 m a.s.l)

Site selection Strong SAM signal from reanalysis data High accumulation site –High resolution records Increased elevation ( ), thought to be due to greater snowfall –satellite altimeter data –[Davis et al., 2005; Wingham et al., 2006]. Correlation between SAM and precipitation from ECMWF

Methods Continuous Flow Analysis with Trace Elements-Dual The annual accumulation record was derived using two methods: –winter-winter value determined from the minima of hydrogen peroxide (H 2 O 2 ) –summer-summer value based on maxima in non-sea salt sulphate (nssS) Estimated uncertainty in the dating is ±1 year from 1855 to 1875 and <<1 year from 1875 to 2006

Gomez Accumulation record Annual thicknesses converted to water equivalents corrected for thinning assuming a linear strain rate Doubling of accumulation: the mean for was 0.49 m weq y -1 while that for was 1.10 m weq y -1 Most rapid increase in recent period, following a slight reduction in the 1970s Annual snowfall at the Gomez site (dashed) and decadal average (solid) Elizabeth R. Thomas., G., J, Marshall., Joseph R. McConnell, (2008), A doubling in accumulation in the western Antarctic Peninsula since 1850, Geophysical Research Letters, 35

Atmospheric circulation Two principal spatial patterns related to known modes of atmospheric circulation variability 1.SAM –strong negative correlations over the Antarctic continent with ring of positive correlations to the north (exception of the south-east Pacific) Correlation map of Gomez accumulation vs. 500 hPa geopotential height,

Atmospheric circulation Correlation, SAM and the Gomez accumulation record is % of the increase in snowfall ( ) due to positive trend in the annual SAM Correlation map of Gomez accumulation vs. 500 hPa geopotential height,

Relationship with ENSO No significant relationship over the entire period Some periods when significant (<10% level) positive correlation with the SOI: El Niño = less accumulation But also periods when negative correlations exist Running 21-year correlations between Gomez accumulation and the Southern Oscillation Index

Marine signal Large marine input –Average Na + ( ) 39 ppb Increase in sea salts since 1950’s Changes in sea salt ratio’s –increased continental input? Is changing atmospheric circulation affecting the marine signal?

Back trajectories BADC ( Daily release over 5 days Location, height, temperature To help identify source of chemical and isotope signal in ice core Combined with satellite data to identify individual storm events 2 weeks of back trajectory data from Gomez site (Jan 2004)

Isotopes Isotope (  18 O) record Compared with 18 months surface temp from AWS (r 2 = 0.89) In combination with other chemistry and a mean seasonal cycle of precipitation, aim is to derive seasonal time series Back-trajectory analysis to try to understand intra-annual variability Isotope record from Gomez approx bi-weekly resolution

Conclusions The Gomez ice core reveals a doubling of accumulation over the past 150 years –change is restricted to the central and southern Antarctic Peninsula The SAM is a major driver of accumulation variability in the region. –Gomez accumulation provides a good proxy of the SAM –next step to compare with 150 year SAM reconstructions No consistent ENSO signal in SW Peninsula accumulation (similar to West Antarctica) Gomez core will allow us to derive a temperature record in the southwestern peninsula since 1850 and several other proxy records at a sub-seasonal timescale Back trajectories used to identify source of ins in ice core –Help answer questions relating to sea ice effect on temperature