David C. Heroy and John B. Anderson Rice University, Houston, TX

1. Ice Sheet Extent, Paleo-Ice Streams and Glacial Retreat History of Antarctic Peninsula during the Last Glacial Maximum (LGM) David C. Heroy and John B. Anderson Rice University, Houston, TX

2. Thickness of ice removed since the LGM (Nakada et al., 2000) • Large ice mass in Peninsula • Large disagreement between these models

3. Scientific Questions: • 1. What was the configuration of the ice sheet during the LGM? • 2. What geologic evidence is there for paleo-ice streams? • 3. What are the geologic controls of ice streams? • 4. What is the nature and timing of ice sheet retreat? (BAS, 2000)

4. Previous work (Clapperton and Sugden, 1982; Kennedy and Anderson, 1989; Harden et al., 1992; Pope and Anderson 1992; Pudsey et al., 1994; Banfield and Anderson, 1995; Larter and Vanneste, 1995; Bart and Anderson, 1996; Shevenell et al., 1996; Canals et al., 2000; Domack et al, 2001) (Anderson 1999) • Maximum extent of grounded ice based on core and seismic data • Mid-shelf grounding line during the LGM

5. Previous work (Wellner et al., 2001)

6. Methods • Collected multibeam swath bathymetry, sediment cores (jumbo and standard piston, kasten, smith-mac), seismic (airgun and chirp), sidescan aboard the Nathaniel B. Palmer, 2002 • Build on existing seismic and core data bases • Carbon-14 (AMS) dating

7. Data Set (multibeam, high resolution seismic, cores) PD 88-8

8. Geologic controls of ice stream behavior? PD88-8 (crystalline bedrock) (accretionary sediments) Two way travel time (seconds) 10 km Anderson et al (1990)

9. Results • Mega-scale glacial lineations: • Identified in at least 6 locations around the Peninsula • Crest-to-crest distances of ~ 300-650 m • Similar morphology and size to lineations found in Ross Sea, Amundsen Sea, Bellingshausen Sea • Form on the prograding wedge of sedimentary deposits without exception PD 88-8

10. Indicate rapid ice flow by deformation of sediments along paleo-ice stream • Thin sediment cover (1-2 m, approx) suggests these MSGL are relatively young • Preliminary sediment core analysis and C-14 dating support this conclusion PD 88-8

11. Anvers Trough

12. Biscoe Trough

13. Biscoe South

14. Marguerite Trough

15. Mega-scale glacial lineations Weddell Margin (northern)

16. Weddell Margin (southern)

17. Other geomorphic features and their relation to bedrock?

18. Smith Trough Boyd Strait Grooves Bedrock drumlins 0 10 km Canals et al (2000) North Anvers Trough • Inner shelf geomorphic features • Bedrock drumlins and grooves • Crest to crest distances of 1-5 km • Timing of formation is unconstrained

19. KC-26 Age dating? KC-26 Glacial marine Transitional glacial-marine 12,810 14C yr BP - 14,880 14C yr BP - Mottled stiff and soft diamicton • These MSGL were formed during the LGM • The ice pulled back before 14,880 14C yr • > 2000 yr before Palmer Deep 12,250 14C yr (Domack et al., 2001)

20. Minimum estimate of pullback of ice at the LGM

21. ? ? • At least six, possibly eight, paleo-ice streams have been identified • Ice was grounded at or near (<10 km) the shelf break around most of the Peninsula

22. Conclusions 1) Ice was grounded at or near the shelf break around most of the Peninsula. 2) At least 6, possibly 8, paleo-ice streams have been identified surrounding the Peninsula. 3) MSGL are covered with minimal (1-2 m) Holocene drape, suggesting these features relatively young. Initial core analysis and carbon-14 dating suggests these features are were formed during the LGM. 4) Preliminary carbon-14 dating suggests gradual retreat, with the initial pullback sometime before 14,880 14C yr BP from the outer shelf, and by 12,250 14C yr BP from the inner shelf at Palmer Deep. 5) Future work in this area will include continued dating and examination of geomorphic features.

23. Thank you

25. Line-sourced gullies • Found in three troughs concomitant with mega-scale glacial lineations. • Probably formed by ice grounded at the shelf break. • Timing of their formation is unconstrained. Anvers Trough gullies