Download Primary science goal: map geothermal heat flux under an ice sheet

Icebase: A proposed suborbital
survey to map geothermal heat
flux under an ice sheet
Michael Purucker
SGT at Planetary Geodynamics Lab, Goddard Space Flight
Center/NASA, Greenbelt, USA
Team members include: Connerney, Blakely, Bracken, Nowicki, Le, Sabaka,
Bonalsky, Kuang, Ravat, Ritz, Bouligand, Vaughan, Gaina, McEnroe, Tyler,
Nelson + Danish team
Outline

Motivation: Magnetic fields as ‘tracers’ of processes active in the
lithosphere of a planet or moon. Rheology, tectonics, subduction,
igneous processes and impact (Earth, Moon, Mars, Mercury)

Primary science goal: map geothermal heat flux under an ice
sheet.
Relevance: response of ice sheet to climate forcing, search for
oldest ice.
Isolating the geothermal heat flux:
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–
–
–
–
–
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Unmodeled external fields
Induced vs remanent magnetism
Varying magnetic susceptibility and thickness
Magnetizations below Moho
Heat production within the crust, mantle, thermal conductivity
Designing the survey and instrument suite. Why Global Hawk?
What else could the survey accomplish?
Taipei: 19 Nov 2012
Focus and Physics
This talk will examine
Earth’s magnetic field
complex, concentrating
on fields of internal
origin.
Taipei: 19 Nov 2012
NASA
Planetary magnetic power spectra

Purucker, 2012
Taipei: 19 Nov 2012
The Earth: a satellite view of its magnetic lithosphere
Maus et
al., 2010
Taipei: 19 Nov 2012
Integrated satellite and ground views of
Earth’s magnetic lithosphere
WDMAM
Taipei: 19 Nov 2012
Earth: rheology
Purucker and
Whaler, in
preparation
Taipei: 19 Nov 2012
Why sub-orbital?

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Sub-orbital missions at altitudes comparable to
crustal thickness ‘image’ the upper and lower
crust with comparable sensitivity. In contrast,
aeromagnetic surveys are overwhelmingly
dominated by the upper crust, and satellite
surveys are unable to distinguish between the
upper and lower crust.
Sub-orbital missions at higher, mesospheric (8090 km) altitudes, ‘image’ a poorly understood
region important for an understanding of space
climate, and it’s impact on atmospheric climate.
Taipei: 19 Nov 2012
Why the Global Hawk?
Taipei: 19 Nov 2012
Survey and Instrument suite
12 km flight line separations, 200 km
tie lines, base stations,
compensation maneuvers
 Vector & total field magnetometers,
dual frequency GPS, star camera
 Team: GSFC, USGS, DTU, Grenoble,
Trondheim

Taipei: 19 Nov 2012
Isolating the geothermal heat flux

Starting point: 3SMAC starting thermal and compositional
model.

3SMAC modified in an iterative fashion with magnetic
observations until the magnetic field predicted by the model
matches the observed magnetic field to some Delta.
Thermal model: 1-D, heat conducttion, steady state,
constant thermal conductivity, simple model for radioactive
heat production in the crust.
Input: CHAMP high degree crustal field solution (Deg 120)
Validation: Western North America, India, Australia, High
Antarctic heat flux corresponds to active volcanism
Other processes in action:




–
–
–
–
–
Unmodeled external fields
Induced vs remanent magnetism
Varying magnetic susceptibility and thickness
Magnetizations below Moho
Heat production within the crust, mantle, thermal conductivity
Taipei: 19 Nov 2012
Heat flux map: Antarctica
Taipei: 19 Nov 2012
Purucker and Fox Maule, 2010
Heat flux map-Greenland
Taipei: 19 Nov 2012
Basal boundary condition
Taipei: 19 Nov 2012
Hagdorn et al.,2006
What else could the survey
accomplish-1?

Mapping of time variable magnetic
fields associated with oceanic, core,
crustal, ionospheric, and
magnetospheric sources through the
use of exact repeat surveys under
Swarm.
Taipei: 19 Nov 2012
Motional Induction

Magnetic field range produced by ocean flow
estimated from monthly averages (Jan-Dec, 2001).
Taipei: 19 Nov 2012
Serpent,
2009
What else could the survey
accomplish-2?

In areas where heat flux can not be
isolated, the magnetic maps could
be used for
– Tectonics
– Igneous processes
– Identification of impacts
– Resource assessment
Taipei: 19 Nov 2012
Earth: subduction-1
Purucker and
Clark, 2011
Serpent, 2009
Taipei: 19 Nov 2012
Earth: subduction-2
Serpent, 2009
Purucker
and Clark,
2011
Taipei: 19 Nov 2012
Earth: igneous processes
Western Australia
Purucker and Whaler, 2006
Taipei: 19 Nov 2012
Earth: impact
2013 IAGA Mtg
On outer ring
Spray et al. 2004
Purucker and Whaler, 2006
Taipei: 19 Nov 2012
Basin development
Siberia
Purucker and Whaler, 2006
Potsdam: 12 Dec 2011
Summary
A
knowledge of magnetic fields at suborbital (20
km) altitudes would help answer questions about
the lithosphere, and specifically heat flux under
ice sheets. It is also expected to add to our
knowledge of the global hydrologic cycle, and
the processes producing time-variable magnetic
fields of core, crustal, ionospheric, and
magnetospheric sources.
Taipei: 19 Nov 2012