interpretation of meteoric be in marginal ice-bound ... presentation gra… · interpretation of...
TRANSCRIPT
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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
our 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 ProcessesAccording to Alley and others, 1997
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Modern Sediment Transport RateBased 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