INTERPRETATION OF METEORIC 10 BE IN MARGINAL ICE-BOUND SEDIMENT OF - - PowerPoint PPT Presentation

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INTERPRETATION OF METEORIC 10 BE IN MARGINAL ICE-BOUND SEDIMENT OF - - PowerPoint PPT Presentation

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INTERPRETATION OF METEORIC 10 BE IN MARGINAL ICE-BOUND SEDIMENT OF THE GREENLAND ICE SHEET, WEST GREENLAND Joseph Graly Thesis Defense Outline of Presentation Project Motivation and Concept Glaciological Background Meteoric 10 Be

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INTERPRETATION OF METEORIC 10BE IN MARGINAL ICE-BOUND SEDIMENT OF THE GREENLAND ICE SHEET, WEST GREENLAND

Joseph Graly

Thesis Defense

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Outline of Presentation

  • Project Motivation and Concept
  • Glaciological Background
  • Meteoric 10Be and Atmospheric Processes
  • Meteoric 10Be in Soils
  • West Greenland Results
  • Interpretation of Greenland Glacial History
  • Conclusions
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Past Performance Predicts Future Results?

Climate models for the Arctic for the present, last interglacial period (116- 130 ka before present) and 2100 (form Overpeck et. al., 2006) The temperatures modelled for Greenland are similar in the last Interglacial period and 2100

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Meteoric 10Be as a Tracer

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Map of Greenland showing modern glacier flowlines (from Zwally and others, 2001) Locations of our three western Greenland field sites and central Greenland ice cores are shown The yellow lines indicate plausible source areas for rock and sediment delivered to the western Greenland sites

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Six models of Eemian ice sheet retreat from the published literature. Approximate locations of

  • ur field sites at

Kangerlussuaq (K), Ilulissat (L), and Upernavik (U) are marked. Models agree on substantial retreat at southern latitudes and more moderate retreat at northern latitudes

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Data from Britanja and van de Wal, 2008

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North Atlantic Glacial Erosion Rates

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Typical Subglacial Processes

According to Alley and others, 1997

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Modern Sediment Transport Rate

Based on a model by W.L. Wang

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Meteoric 10Be and Atmospheric Processes

  • What controls the distribution of meteoric

10Be in Earth’s atmosphere?

  • Can the long-term meteoric 10Be

deposition rate be predicted at a given site?

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Meteoric 10Be deposition predicted by precipitation

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Meteoric 10Be deposition predicted by latitude

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Meteoric 10Be deposition in Polar Regions

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Long-term Record: Marine Sediment

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Long-term Record: Soils

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Long-term Record: Greenland Ice Sheet

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Meteoric 10Be in Soils

  • How is meteoric 10Be typically distributed

in soils?

  • Can the effects of erosion of meteoric 10Be

bearing sediment be modeled from a typical depth distribution?

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Existing work on meteoric 10Be in soils

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Typical Distribution with Depth

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Declining Profile Shapes: Eroding Hillslopes

Profiles from Contra Costa, California McKean et al, 1993

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Declining Profile Shapes: Young Surfaces

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Development of max accumulation zone

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Maximum predictive of total inventory

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Topsoil Meteoric

10Be Concentration

Predictive of Total Inventory

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West Greenland Results and Interpretation

  • Which sites were sampled and what

meteoric 10Be measurements were made?

  • What can be inferred about the erosion

and interglacial exposure of West Greenland?

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Kangerlussuaq: Isunnguata Sermia Glacier

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Kangerlussuaq: Dead Ice Zone

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Ilulissat: Sermeq Avannarleq Glacier

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Upernavik: Transect

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Upernavik: Nunatak

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West Greenland Meteoric 10Be Results

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Estimate of Meteoric 10Be Inventory

Soil Ages

Upernavik: 60-122 ka Ilulissat: 39-78 ka Kangerlussuaq: 9-18 ka

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Erosion model: Top 150 cm

Pre-Glacial Inventory: N=q(1-E·α·(N/q)β)/( λ(1-e-λt)) Interglacial Inventory: N=(q/λ)(1-e-λt) Inventory Lost to Glacial Erosion: NL=z·q·α·(N/q)β

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Erosion Model: Deep Erosion

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Glacial Sediment Transport Lag

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Development of Modern 10Be Inventory

Years before present

Data from Britanja and van de Wal, 2008

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Valid Erosion Exposure Interpretations

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Glacial Erosion Rates Reconsidered

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Interglacial Exposure Reconsidered

Data from Britanja and van de Wal, 2008

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Conclusions

  • Long-term meteoric 10Be deposition rate is

moderately predictable from precipitation and latitude

  • Meteoric 10Be depth distribution is

moderately predictable from total soil meteoric 10Be inventory

  • Pre-Quaternary regolith under Greenland’s

Main Dome has not completely eroded, with glacial erosion rates < 5 m/My

  • Greenland’s Southern Dome has

experienced substantial interglacial exposure

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Acknowledgements

  • National Science Foundation
  • CH2M HILL Polar Services (Kangerlussuaq)
  • Lawrence Livermore National Laboratory
  • Greenland Cosmochronology Project Team
  • Fellow geology grad students, family, and

friends

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Thanks for Listening… Any Questions?

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Upernavik Transect Experimental Results, Iverson and Souchez, 1996

West Greenland Stable Isotope Results

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West Greenland Stable Isotope Results

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Distribution Controlled by Soil Properties?

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Grain Size Effect

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Comparable Mobile Cations

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CEC, Organic Carbon, and pH

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Meteoric 10Be deposition predicted by latitude