Reconciling geological and radioglaciological context for heat flow in West Antarctica

Duncan Young1, Enrica Quartini1, Donald Blankenship1

1University of Texas Institute for Geophysics, Austin, United States

West Antarctica hosts the large West Antarctic Rift System (WARS), a region of continental extension which has formed during several stages of rift reactivation from the Cretaceous through the Cenozoic.

 

Subglacial volcanic activity has been documented along the Executive Committee Range in Marie Byrd Land, where a swarm of deep long-period earthquakes was registered in 2010 and 2011 by the POLENET seismic network.  Recent modeling has also evaluated the sensitivity of the West Antarctic Ice Sheet to hotspots; however, these results have not been evaluated in the context of basal conditions and crustal geology.

 

Here we analyze magnetic anomalies collected during recent aerogeophysical expeditions over Thwaites Glacier (THW), Pine Island Glacier (PI), and eastern Marie Byrd Land (MBL), in order to evaluate the distribution of potential hotspots in the region. We identify three different regions with distinct magnetic character and correlate each one of them to specific stages of tectonic and magmatic activity in WARS.  Our interpretation supports both the hypothesis that MBL was tectonically and magmatically reactivated multiple times during the Cretaceous and that a hotspot was emplaced there later in the Cenozoic, therefore pointing to a hotter MBL compared to THW and PI.

 

We also evaluate the basal conditions in the interior flank of Marie Byrd Land, in the context of basal reflectivity, specularity, and subglacial water routing.  We find a region of high specularity (indicative of elevated subglacial water) along the flank of Marie Byrd Land.  We evaluate whether this water formed in place, or routed out of the Marie Byrd Land dome.

 

We place these observations in the context of the now well surveyed larger scale structure of the West Antarctic Rift System, and the crustal gradients observed by POLENET.

 

Constraints on the geothermal heat flow of Antarctica and surrounding oceans from new seismic structure models

Douglas A. Wiens1, Weisen Shen1, Andrew Lloyd1, Andrew Nyblade2, Richard Aster3, Terry Wilson4

1Washington University In St Louis, Saint Louis, USA, 2Penn State University, University Park, USA, 3Colorado State University, Fort Collins, USA, 4Ohio State University, Columbus, USA

Geothermal heat flow has a major effect on ice sheet dynamics, but there are few direct measurements of Antarctic heat flow. Previous studies have estimated the geothermal heat flow of Antarctica from seismic structure models, but these efforts have had very limited resolution due to poor seismic station coverage. We have recently constructed two new seismic structure models of Antarctica using complementary methodologies that incorporate data collected from more than 200 temporary broadband seismic stations deployed across Antarctica over the last 15 years. One model seeks to obtain the highest possible resolution within the upper 200 km depth in the well-instrumented region of central and West Antarctica using a joint inversion of Rayleigh wave velocities and receiver functions (Shen et al., submitted). We obtain an estimate of the geothermal heat flux via a Bayesian inversion of Rayleigh wave observations for thermal structure using relationships between seismic velocity and temperature (see Weisen Shen presentation). The second seismic structure model is an adjoint full-waveform inversion for mantle structure beneath the entire continent and surrounding oceans, extending down to mantle transition zone depths (Lloyd et al., in prep). This model allows for lithospheric thickness to be mapped across the entire Antarctic plate, and for corresponding implications for geothermal heat flow to be made. Very thin or absent lithosphere along the Ross Sea Coast from Northern Victoria Land to the Southern Transantarctic Mountains, along the Amundsen coast and continental shelf, and beneath the Antarctic Peninsula suggest the likelihood of higher geothermal heat flow in these locations. Although most of East Antarctica shows thick, cold lithosphere, we also find younger or tectonically modified thinner lithosphere beneath portions of Dronning Maude Land and the Lambert Graben, suggesting the possibility of somewhat higher mantle contributions to heat flux in these areas.

 

Elevated sub-ice thermal flux mapping using magnetotellurics considering the U.S. Great Basin as an analog

Phil Wannamaker1, Graham Hill2, John Stodt3, Virginie Maris1, Yasuo Ogawa4, Kate Selway5

1University Of Utah/Energy & Geoscience Institute, Salt Lake City, United States, 2University of Canterbury, Gateway Antarctica, Christchurch, New Zealand, 3Numeric Resources LLC, Salt Lake City, United States, 4Tokyo Institute of Technology, Volcanic Fluid Research Center, Tokyo, Japan, 5Macquarie University, Earth and Planetary Sciences, Sydney, Australia

Bedrock heat flux of Marie Byrd Land and much of the West Antarctic Ice Sheet has been conjectured to significantly exceed the global average of ~85 mWm-2, e.g. 100-200 mWm-2 or more, with implications for ice sheet stability. Advective affects may complicate shallow heat flow measurements and so deeper-seeking geophysical techniques may have a greater role in estimating crustal thermal state. The actively extensional U.S. Great Basin province has been considered a partial tectonic analog to West Antarctica although extension rates in the latter are generally much less. The magnetotelluric (MT) geophysical method has been widely applied in the Great Basin to understand province-scale down to geothermal prospect-scale thermal structure using electrical resistivity as a proxy. There, widespread zones of crustal magmatic underplating and fluid release over broad areas correlate with surface heat flow and volcanic occurrences, with depth to top of low resistivity approximating an isotherm. Spatially concentrated low-resistivity upwellings imply local upward convection and commonly connect into known high-temperature geothermal resource areas exhibiting magmatic-origin fluid fluxes. This has been the basis of significant recent research into greenfield reconnaissance for blind, high-enthalpy geothermal systems. Similar low-resistivity structures correlating with analogous magmatic and convective processes in West Antarctica have been revealed in recently published MT field campaigning there. Appropriately designed surveys have potential to constrain the magnitude and spatial variation of crustal geotherms including local hotter zones that could provide particularly high thermal input to the overlying ice sheets.

Temperature gradients and geothermal fluxes in deep boreholes drilled through the Antarctic Ice Sheet: a review

Pavel Talalay1, Laurent Augustin2, Ryan Bay3, Gary Clow4,5, Jialin Hong1, Roger LeB.  Hooke6, Eric Lefebvre7, Alexey Markov1, Hideaki Motoyama8, P. Buford Price3, Catherine Ritz7, Herbert Ueda9

1Polar Research Center, Jilin University, Changchun, China, 2Division Technique de l’INSU, CNRS, La Seyne sur Mer, France, 3Department of Physics, University of California, Berkeley, USA, 4U.S. Geological Survey, Lakewood, USA, 5Institute of Arctic and Alpine Research, University of Colorado Boulder, Boulder, USA, 6School of Earth and Climate Sciences and Climate Change Institute, Bryand Global Sciences Center, University of Maine, Orono, USA, 7Université Grenoble Alpes, CNRS, IGE, Grenoble, France, 8National Institute of Polar Research, Tokyo, Japan, 9U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, USA

The temperature of the Antarctic ice sheet and the temperature gradient at its base have been directly measured only a few times, although extensive thermodynamic modeling has been used to interpolate among measurements. During the last five decades, deep drilling projects at seven sites – Byrd, Dome C, South Pole, Kohnen, Dome F, Vostok, WAIS Divide – have succeeded in reaching to, or nearly to, the bedrock in inland locations in Antarctica. The Byrd and Kohnen holes encountered water at the base of the ice sheet and water welled up into the holes. The borehole at Vostok penetrated to subglacial Lake Vostok at 3769.3 m, and here water rose from the lake to a height of more than 340 m. Measured temperature profiles in five of the boreholes (Vostok, Dome C, Kohnen, Dome F, South Pole) increase nearly linearly with depth as expected in locations with minimal accumulation and hence small vertical velocities. Vertical advection is much greater at the locations of the Byrd and WAIS Divide boreholes in West Antarctica and there the upper part of the ice sheet is nearly isothermal, but at depth the temperature gradient is nearly the same as at the other sites. Temperature gradients at the bed are 2.2-2.5 C/100 m at Dome C, Dome F and Vostok, and significantly higher – 3.04 C/100 m – at Kohnen. Measured temperature gradients at Dome C, Kohnen, and Dome F correspond to conductive heat fluxes between 51.1–62.7 mW m-2, while at Vostok, at the boundary between the ice and the lake water, the flux is only 46.1 mW m-2. To estimate the geothermal flux from the sub-ice temperature gradients, however, one also needs to account energy used to melt ice at the base.

 

Towards a multi-domain lithospheric model of East Antarctica.

Tobias Staal1,2, Anya Reading1,3, Jacqueline  Halpin1, Joanne Whittaker1

1University of Tasmania / Institute for Marine and Antarctic Studies, Hobart, Australia, 2University of Tasmania / Earth Sciences, Hobart, Australia, Hobart, Australia, 3University of Tasmania / Mathematics and Physics, Hobart, Australia

The knowledge of the lithospheric structure of East Antarctica is very limited and as a consequence we cannot produce accurate and precise maps of the subglacial geothermal heat flux density. Seismic tomography studies and potential field data can be used to derive lithosphere structure, but the resolution is relatively low, and the smoothed models don’t reflect the amalgamation of lithospheric terranes that formed the continent.

 

We combine geophysical constraints with geological knowledge from the sparse outcrops and known geology from Gondwanan neighbours in a plate reconstruction framework to attempt a regionalization of East Antarctica. We use Bayesian inference to suggest the most probable boundaries by using a multivariate prior constrained by available geophysical datasets. The boundaries form a segmentation of the Antarctic lithosphere and can be weighted with probabilistic significance and location. Our implementation allows sequential improvement as updated and refined seismic tomography and potential field data compilations.  Likewise, a more consistent approach to adding mapped geological information adds further robust constraints.

 

The result is presented as a first draft of a multi-domain tessellated terrane map of the East Antarctic lithosphere. We believe that this approach will be useful in estimating both basal lithosphere and crustal contributions to heat flux. The approach provides a stepping stone towards more refined models in an evolving framework.

Thermal structure and heat flow of central and West Antarctica estimated from seismic data

Weisen Shen1,2, Douglas Wiens2, Richard Aster3, Andrew Nyblade4, Terry Wilson5

1Stony Brook University, Stony Brook, United States, 2Washington University in St Louis, St Louis, United States, 3Colorado State University, Fort Collins, United States, 4Penn State University, University Park, United States, 5Ohio State University, Columbus, United States

Investigating the thermal state of the Antarctic lithosphere plays an important role for understanding the history and future of the West Antarctic Ice Sheet (WAIS), at least from two perspectives: 1) Surface heat flow imposes a key boundary condition for ice sheet dynamics modeling; 2) Mantle viscosity and lithospheric thickness are important parameters for glacial isostatic adjustment calculation. However, because of its remoteness and lack of direct measurements, the lithosphere’s thermal state is not completely understood. Here we discuss a most recent effort that produces a thermal model for the Antarctic lithosphere using the seismic data collected in the past two decades.

By processing over 15-year seismic data recorded across Antarctica, we obtain a seismic velocity model for the crust and uppermost mantle from a Bayesian Monte Carlo inversion of Rayleigh waves from earthquakes, ambient noise, and receiver functions. After fixing crustal thickness, we further invert the seismic data for thermal structure employing experimental results relating mantle shear velocity variations to temperature, with a range of acceptable crustal heat generation values as prior constraints. We solve for the best fitting conductive geotherm through a thermodynamic inversion, thus providing estimates of surface heat flow and the thermal lithospheric thickness. The resulting seismic and thermal models reveal a highly heterogeneous mantle lithospheric thermal structure. In particular, thinner lithosphere and higher estimated geothermal heat flow (70-100 mW/m2) are found beneath the West Antarctic Rift system, Marie Byrd Land, Ellsworth-Whitmore Mountains, and southern Transantarctic Mountains, while the East Antarctica has lower heat flow (40-60mW/m2). Notably, an anomalously thin lithosphere with high surface heat flow is identified in the vicinity of the Thwaites Glacier, indicating a mantle source that may facilitate the future instability of the WAIS in that area.

 

Ice flow modeling and geothermal heat flux

Helene Seroussi1

1Jet Propulsion Lab, United States

Conditions at the base of ice sheets are critical to understand ice motion and the future evolution of the ice sheets but remain largely unknown due to the lack of direct measurements. These conditions are influenced by the underlying crust and mantle, including the presence of mantle plumes, which translate into high geothermal heat flux at the interface between ice and the underlying bedrock.

 

In this presentation, we will discuss the impact of geothermal heat flux on ice sheet dynamics, and how uncertainties in such measurements affect ice flow simulations and ice sheet future contribution to sea level rise. Ice flow models are also limited by uncertainties in many other model inputs, including geometry, boundary conditions and ice properties, so we examine how uncertainties in other model inputs compare to uncertainties in geothermal heat flux. Finally, we will consider the possibilities of using ice flow models to infer poorly known ice sheet basal properties, including sliding and geothermal heat flux, and the observations required to better constrain such parameters.

 

This work was performed at the California Institute of Technology’s Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration, Cryospheric Sciences and Sea Level Science Team Programs.

Observationally Constraining Geothermal Heat Flux Using Ice Penetrating Radar

Dustin Schroeder1, Winnie  Chu1

1Stanford University, Stanford, United States

Geothermal heat flux exerts a fundamental control on the behavior, stability, and evolution of ice sheets. However, this basal boundary is also exceedingly difficult and costly to measure directly. Geophysical remote sensing technique provides a cheap and effective way to constrain the distribution of geothermal heat that is critical for the initialization and spin-ups of predictive ice sheet models. Airborne ice penetrating radar sounding can provide observations of englacial and subglacial conditions at the catchment- to continent-scale. Specifically, the character and strength of radar bed echoes encode information about the thermal and hydrologic state of the ice sheet and its bed. While on an echo-by-echo basis, this information is highly non-unique, on a regional basis advanced radar processing approaches can disambiguate englacial- and subglacial-genic signals. However, even high-fidelity basal condition mapping does not directly map geothermal heat flux .  This requires careful and creative application of hydrological, geologic, and glaciological assumptions and information to the parameter estimation problem.  However, despite these considerable challenges, we will demonstrate how to combine radar sounding data with subglacial hydrologic and thermo-mechanical models to place meaningful observational constraints geothermal heat flux in a range of glaciological settings. We present a range of promising applications and problems for these approaches as well as their underlying assumptions, enabling conditions, and inherent limitations.

Combining interpolated and locally observed contributions to heat flow models

Anya Reading1, Tobias Staal1, Jacqueline Halpin1, Joanne Whittaker1

1Institute for Marine and Antarctic Studies, University Of Tasmania, Hobart, Australia

The spatial variation of heat supplied to ice sheets is an important input model parameter in ice sheet models.  Continental models of heat flow (usually referred to in the cryosphere research community as heat flux density, abbreviated to heat flux) may be calculated using seismic wavespeed tomography maps or by inference from other geophysical observables.  These broadscale maps are interpolated, smoothed representations.  Upper crustal models, in contrast, are generated directly from measuring the heat production of dominant or particularly radiogenic lithologies.

 

In this contribution, we combine interpolated and locally observed contributions to heat flow models with a focus on East Antarctica, including the continental interior which is covered by ice of several kilometres thickness.  We review alternative approaches to combining low resolution information on the deeper lithosphere with broad spatial coverage, and high resolution information with very limited spatial coverage relating to the present day upper crust.  Providing effective estimates of the heat supplied by the upper crust is an important research goal due to the significance of small pockets of elevated heat flow on ice sheet models.  Alternative approaches inform future probabilistic solid Earth constraints for ice sheet models.

Constraining basal heat flux in eastern Antarctica using new heat flow data from the Coompana Province, Nullarbor Plain, southern Australia

Alicia Pollett1, Betina Bendall2, Tom Raimondo1, Martin Hand3

1School of Natural and Built Environments, University Of South Australia, Adelaide, Australia, 2Energy and Resources Division, Department of Premier and Cabinet, Adelaide, Australia, 3Geology and Geophysics, School of Physical Sciences, University of Adelaide, Adelaide, Australia

A critical parameter in accurately modelling Antarctic ice sheet behaviour is basal heat flux, which has a significant impact on ice viscosity and melt generation. Currently, this input is poorly constrained due to the logistical and financial challenges of obtaining boreholes that intersect basement rocks blanketed by thick ice cover. Consequently, we have pursued an alternative approach that employs heat flow measurements from analogous rock units in the Coompana Province of southern Australia, representing the geological counterparts of those beneath the Totten Glacier in eastern Antarctica. The Coompana Province is underlain largely by Mesoproterozoic granitic and gneissic rocks characteristic of the Musgrave orogenic system, observed to project into Wilkes and Queen Mary Land. Facilitated by mineral exploration drilling as part of the PACE Program undertaken by the Geological Survey of South Australia and Geoscience Australia, we have compiled 10 new continuous temperature logs from this previously uncharacterised region. Drill core samples have also enabled an accompanying dataset of thermal conductivity values to be obtained. Preliminary calculations indicate heat flow estimates in the range 52–62 mWm-², equivalent to global continental averages. All values are slightly lower than the single heat flow measurement of 72 mWm-² obtained from Law Dome located on the conjugate margin of eastern Antarctica, and appreciably lower than the average of ~80 mWm-² for Proterozoic terranes of the central Australian heat flow province. Combined with existing data from adjacent parts of southern Australia, this provides the first regional heat flow characterisation of geological provinces previously contiguous with eastern Antarctica, allowing a more robust evaluation of the contribution of anomalous basal heat flux to ice sheet instability.

 

About conferences.com.au

conferences.com.au provides delegate registration, website and app solutions, and financial management for conferences, conventions and scientific meetings.

Contact Us

Please contact the team at conferences.com.au with any questions regarding the conference.
© 2017 - 2020 Conference Design Pty Ltd. conferences.com.au is a division of Conference Design Pty Ltd.