Tropical Pacific and South Atlantic Teleconnections in Antarctic Coastal Ice Core

1. Tropical Pacific – high latitude South Atlantic teleconnections as seen in the d18O variability in an Antarctic Coastal Ice Core CONCLUSIONS D. Divine (1, 2), E. Isaksson (1), M. Kaczmarska (1), F. Godliebsen (1,2), H. Oerter (3), E. Schlosser (4), S.J. Johnsen (5), M. van den Broeke (6), R.S.W. van de Wal (6) (1) Norwegian Polar Institute, N-9296 Tromsø, Norway. (2) Department of Statistics, University of Tromsø, Tromsø, Norway (3) AWI, Bremerhaven, Germany (4) Institute of Meteorology and Geophysics, Univ. of Innsbruck, Germany (5) The Niels Bohr Institute, Department of Geophysics, University of Copenhagen, Denmark (6) Institute for Marine and Atmospheric Research, Utrecht University, The Netherlands Acknowledgements Thanks to all participants of NARE 2000/01 and others who helped with these drilling projects Financial support came from The Norwegian Research Council and EU EPICA-MIS.

2. Since about 1920there appears to have been a regional trend of significant increase in d18O and a decrease in accumulation in the coastal area of Dronning Maud Land

3. • • S100 The Norwegian Antarctic Program Troll M150 • NARE 1996/97 • • NARE 2000/01 • Nor-US IPY traverse 2007-09

4. Why bother with coastal ice core records? • High annual accumulation makes dating more reliable • Cores can be calibrated to the existing instrumental records • Cores can provide ”more local” climate records • Cores have the possibility to provide a sea ice proxy

5. What are the δ18O ice core records represent: SAT or something else?

6. A regional decreasing trend of the accumulation during the 1900s Kaczmarska and others, 2004

7. Core S100 * Site information S100 50 m asl T10 = – 17.5C Acc = 28 cm weq Core depth = 100 m Annual dating with DEP, ECM and d18O stratigraphy

8. Sizer* analyses of trends in S100 There is a significant increasingtrend in d18O between about 1925-1975 There is a significant decreasing trend in accumulation from about 1920 30 Smoothing window (years) 10 Smoothing window (years) 3 Year (AD) Year (AD) SiZer color coding purple – no significant trend blue – significant increase red – significant decrease *Chaudhuri, P., and Marron, J.S., 1999. SiZer for Exploration of Structures in Curves.J. Am. Stat. Ass., 94 (447), 806-823.

9. MTM (multi taper method)* analysis of the annual δ18O series in the S100 core QB= quasi –biannual QQ=quasi-quadrennial QD= quasi-decadal QBD=quasi-bidecadal QB, QQ – typical ENSO-scale variabilities These four components are representing 40% of the total variability What is the driving force of the QBD variation? black line=QD+QBD, grey line=QB+QQ *Thomson, 1982; Percival and Walden, 2000. SSA-MTM toolkit provided by Ghil et al. 2002.

10. .. and for another core B04* * black line=QD+QBD, grey line=QB+QQ *Schlosser, E., and H. Oerter, 2002. Shallow firn cores from Neumayer, Ekströmisen, Antarctica: a comparison of accumulation rates and stable-isotope ratios. Annals of Glaciology, 35, 91–96.

11. Composite maps (max-min δ18O ) for mean summer (DJF) SST and winter-spring (SON) SLP • Stacked δ18O record based on 8 ice cores , • 1955-1999 (black) • SON SLP anomalies • at Novolazarevskaya station (grey) Composite difference of DJF SST (shown in colors) and SON SLP (contours) anomalies for the period 1980-1999 between years with positive and negative annual mean anomalies of d18O in the stacked DML ice core record Increased SLP in SON (late winter-early spring) less isotopically ”cold” precipitation

12. Tropical Pacific – a pacemaker for δ18O variations in coastal DML precipitation? TNI index = Trans-Niño Second component of ENSO variability – variations in SST gradient across the Pacific S100 and TNI QBD modes are in anti-phase - position of the center of TC affects theteleconnection to the DML (at least at decadalscales) No straightforward SAT- δ18O link due to a substantial bias in seasonal accumulation driven by the existing teleconnections to Tropical Pacific

13. Summary • Variability in the δ18O records on typical ENSO scales but with substantially amplified bidecadal mode • The positive trend in the δ18O records in DML is due to warming of the central Pacific (more negative TNI) • A western displacement of the TC center causesmore frequent winter “blocking” → less isotopically “cold” precipitation which is in line with the negative accumulation trend • DML δ18O signal is substantially biased by accumulation

14. The mechanism of teleconnections is still debatable and may include- displacement of the atmospheric Rossby wave train [Turner, 2004]- modification of circulation cells [Yuan, 2004]- modulation of coupling between ENSO-PSA and SAM modes [Fogt&Bromwich, 2006] Finally Are the δ18O records from coastal DML then useful at all? Hopefully…. The inferred link between the tropical Pacific variability and S100 δ18Ois used to reconstruct a 260-year long series of the smoothed Trans-Nino index (TNI) representative of the second mode of the tropical ENSO variability in SST. Work in progress by Dmitry Divine

15. Next Norwegian focus:Fimbul Ice Shelf – Top to Bottom Due to its location the Fimbul Ice Shelf is exposed to warm water and therefore very vulnerable to any changes. A joint oceanography and glaciology effort will try to establish the status of this ice shelf