Icebase: A proposed suborbital Icebase: A proposed suborbital survey to map geothermal heat survey to map geothermal heat

flux under an ice sheetflux 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

Taipei: 19 Nov 2012

OutlineOutline 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:– 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?

Focus and PhysicsFocus and Physics

Taipei: 19 Nov 2012

This talk will examine Earth’s magnetic field complex, concentrating on fields of internal origin.

NASA

Taipei: 19 Nov 2012

Planetary magnetic power spectraPlanetary magnetic power spectra

Purucker, 2012

The Earth: a satellite view of its magnetic lithosphereThe Earth: a satellite view of its magnetic lithosphere

Taipei: 19 Nov 2012

Maus et al., 2010

Integrated satellite and ground views of Integrated satellite and ground views of Earth’s magnetic lithosphereEarth’s magnetic lithosphere

Taipei: 19 Nov 2012

WDMAM

Earth: rheologyEarth: rheology

Taipei: 19 Nov 2012

Purucker and Whaler, in preparation

Why sub-orbital?Why sub-orbital?

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 (80-90 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?Why the Global Hawk?

Taipei: 19 Nov 2012

Survey and Instrument suiteSurvey 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 fluxIsolating 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: AntarcticaHeat flux map: Antarctica

Taipei: 19 Nov 2012Purucker and Fox Maule, 2010

Heat flux map-GreenlandHeat flux map-Greenland

Taipei: 19 Nov 2012

Basal boundary conditionBasal boundary condition

Taipei: 19 Nov 2012 Hagdorn et al.,2006

What else could the survey What else could the survey accomplish-1?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 InductionMotional Induction

Taipei: 19 Nov 2012

Magnetic field range produced by ocean flow estimated from monthly averages (Jan-Dec, 2001).

Serpent, 2009

What else could the survey What else could the survey accomplish-2?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-1Earth: subduction-1

Taipei: 19 Nov 2012

Purucker and Clark, 2011

Serpent, 2009

Earth: subduction-2Earth: subduction-2

Taipei: 19 Nov 2012

Purucker and Clark, 2011

Serpent, 2009

Taipei: 19 Nov 2012

Earth: igneous processesEarth: igneous processes

Western Australia

Purucker and Whaler, 2006

Taipei: 19 Nov 2012

Earth: impactEarth: impact

Purucker and Whaler, 2006

Spray et al. 2004

2013 IAGA MtgOn outer ring

Potsdam: 12 Dec 2011

Basin developmentBasin development

Siberia

Purucker and Whaler, 2006

SummarySummary

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