Warm, warmer, hot! Antarctic crustal radiogenic heat production.

Jacqueline Halpin1, Alex Burton-Johnson2, Sally Watson1, Joanne Whittaker1, Tobias Staal1, Anya Reading1, Alessandro Maritati1

1Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia, 2British Antarctic Survey, Cambridge, United Kingdom

The geothermal heat flux (GHF) to the base of the Antarctic ice sheet is inherently difficult to measure, yet accurate estimates are necessary to better understand cryosphere dynamics. GHF includes heat supplied to the lithosphere from the convective mantle and radiogenic heat generated within the lithosphere from the decay of heat producing elements (HPEs), mainly Thorium (Th), Uranium (U) and Potassium (K). Through differentiation processes, HPEs are preferentially concentrated into the dominantly felsic rocks of the upper continental crust. The distribution of HPEs is therefore heterogeneous at a range of scales, and fundamentally tied to the geological evolution of the crust in space and time.


Current GHF models of the Antarctic continent based on geophysical properties use idealised crustal parameters that do not reflect the inherent geological heterogeneity. For example, recent studies have shown that radiogenic heat production values for Antarctic granites and gneisses can be significantly enriched (>10-15, and up to 65 micro watts per metre cubed) compared to average crustal values that are used across the entire continent in existing Antarctic GHF models (~ 1-2 micro watts per metre cubed). Regional ice sheet models have shown that localised regions of such high HPE-enriched crust can impact the organisation of ice flow, particularly in slow-flowing regions, underscoring the need for improved knowledge of both the magnitude and spatial variability of radiogenic heat production in Antarctic crust.


Here we assess the range in heat production values from diverse lithologies across outcrops and moraines in Antarctica using a compilation of previously published and new geochemical analyses. We explore variations with lithology, age and between geological terranes. Our analysis demonstrates significant spatial variability in heat production that will need to be integrated with deeper lithospheric structure and heat flow constraints to improve GHF models of the Antarctic continent.

Improved models of Antarctic geothermal temperatures and crustal heat flux: constraints from geochemistry and Curie depth analysis

Matthew Gard1, Derrick Hasterok1

1University Of Adelaide, Adelaide, Australia

In this study, we develop a new model for heat flux and crustal temperatures for the Antarctic continent utilising new geophysical and geochemical constraints. Crustal heat flux directly influences ice sheet stability, glacial dynamics and basal melting. However, the geothermal input into the base of the ice sheets is poorly constrained due to the logistical difficulty and high expense of obtaining direct measurements through the ice sheets. Thus we require robust indirect estimates by utilising proxies.  Past studies focus on seismic velocity estimates of temperature, but this method is limited to mantle temperatures, which constrain mantle contributions to crustal heat loss.  However, seismic models have poor sensitivity to the crustal radiogenic contribution to the crustal heat loss. Radiogenic heat generation can contribute anywhere from 30-80% of the total crustal heat loss, and therefore must be considered as part of any geothermal model. In this study, we improve estimates of crustal heat generation by employing empirical estimators applied to geophysical datasets.  The empirical estimators are calibrated to geochemical estimates of heat production made on Antarctic rock samples and from formerly adjacent continental terranes determined by tectonic reconstructions. We combine this radiogenic model with crustal temperatures constrained though Curie depth analysis.  Curie depth estimates computed from the equivalent dipole method are achieved by utilising a new lithospheric magnetic model derived from SWARM and CHAMP satellites. This improved lithospheric magnetic model is much higher resolution than previous Curie depth studies. Our estimates of temperature and crustal heat flux into the base of the Antarctic ice sheet represent an improvement over previous models, allowing for more realistic models of ice sheet dynamics.


Taking the temperature of Antarctica with satellites

Folker Pappa1, Giovanni Macelloni3, Michael Kern2, Fausto Ferraccioli4, Jörg Ebbing1

1Kiel University, Germany, 2ESA-ESTEC, Netherlands, 3IFAC-CNR, Italy, 4British Antarctic Survey, , UK

Different methods have been applied in recent years to quantify the thermal structure of Antarctica. Estimates are often derived from modelling of satellite data or seismological models, or based on a combination of these. Here, we present results from the ESA Support to Science Elements GOCE+Antarctica and CryoSMOS.


An interesting, novel and complimentary observation to the estimates mainly derived on geophysical data reflecting the Solid Earth, is the geothermal heat flux as established by analysis of data from the SMOS (Soil Moisture and Ocean Salinity) satellite mission. In the CryoSMOS study, it was shown that the L-band brightness temperature (TB) observations over Antarctica could mainly be attributed to the ice-sheet temperature profile variability. Error assessment showed that the geothermal heat flux, as resulting from the inversion against the ice temperature profiles from SMOS, is in the range of ±20 mW/m2. The difference is huge with respect to its implications on ice-sheet conditions.


We compare these results to a 3D lithospheric model based on the integration of satellite gradient gravity data and seismological models as established in the GOCE+Antarctica study.  Differences of more than 10 km in crustal thickness estimates are observed. Such huge differences have strong implications for the characteristics of the crust itself and the underlying mantle in terms of density, temperature and composition. To isostatically compensate the differences in Moho depth, the composition and thermal thickness of the lithospheric mantle is adjusted. In both cases, the observables are equally well explained, but the models significantly differ in the heat flow for the coastal region (differences >20 mW/m2).


The different satellite derived estimates differ significantly from heat-flow estimates based on magnetic satellite data and we discuss how to reconcile the different observations by modelling the crustal thermal properties.

Inferring geothermal heat flux from englacial temperatures in East Antarctica

Syed Abdul Salam1, Jacqueline Halpin1, Felicity Graham1, Jason Roberts2

1Institute for Marine and Antarctic Studies, Hobart, Australia, 2CRC-Antarctic Climate & Ecosystems, Hobart, Australia

Geothermal heat flux (GHF) supplied to the base of the Antarctic ice sheet strongly controls its internal temperature distribution. GHF is, therefore, a critical thermal boundary condition in ice sheet modeling directly influencing the deformability of ice and ice-flow velocities. Accurate and high-resolution GHF measurements are necessary to reliably predict ice sheet evolution and future climate change. But, GHF datasets used in ice sheet models are poorly constrained by actual measurements. Here, we use englacial temperature measurements to estimate GHF for key regions in East Antarctica. The attenuation rate of radar reflections is greatly affected by the temperature within the ice sheet and its chemical properties. Spectral analysis of the radar reflectors through the ice sheet will be employed to constrain radar attenuation, which will then be used as a proxy for ice temperature. The GHF can be inferred from the gradient of englacial temperatures and thickness of the ice. Here we will describe the different methods used to extract the attenuation of reflections from radar datasets, which will enable us to map englacial temperature distributions and produce high-resolution GHF estimates.



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