Description: Elevated and/or spatially variable geothermal heat flux (GHF) is suspected to affect basal conditions of ice sheets, i.e. basal melting and subglacial hydrology. Thermomechanical models demonstrate the influential boundary condition of geothermal heat flux for (paleo) ice sheet stability. Due to a complex tectonic and magmatic history of West Antarctica, the region is suspected to exhibit strong heterogeneous geothermal heat flux variations [e.g. Schroeder et al., 2014; Fisher et al., 2015]. Although the maximum ice extent has retreated from the shelf since the last glacial maximum, the trends of offshore GHF patterns and the overall order of magnitude are hypothetically related to those areas onshore where the West Antarctic Ice Sheet (WAIS) rests on geologically related structures. High-resolution GHF will aid the understanding of the paleo-retreat of the ice sheet in this sector. The problem with testing these possibilities is that direct observations of GHF in Antarctica are so sparse that it is accounted for the greatest source of uncertainty in ice sheet studies for the continent [Larour et al., 2012]. This presentation builds on our previous studies in which we discussed geothermal heat flux based on 26 in-situ temperature measurements that were conducted in 2010 in the Amundsen Sea Embayment (ASE) in West Antarctica. We found, that the shallow (3 m) in-situ temperature measurements were likely influenced by inter-annual bottom-water temperature variability, leading to GHF estimates biased towards lower values (mean = 33 mWm-²). In contrast, our numerical models of geothermal heat fluxes, based on Depth-to-the-Bottom-of-the-Magnetic-Source estimates, suggest that GHF spatially varies from 68 to 110 mWm-². During RV Polarstern expedition PS104 in early 2017 we collected additional 28 in-situ temperature measurements in marine sediments (up to 11 m probe depth) for deriving geothermal heat flux in the ASE, which will overall improve the spatial coverage of this region. We present GHF results of this novel data set and discuss challenges of measuring in-situ temperatures for GHF in the Amundsen Sea Embayment.

Description: The West Antarctic Rift System is one of the least understood rift systems on earth, but displays a unique coupled relationship between tectonic processes and ice sheet dynamics. Geothermal heat flux is a poorly constrained parameter in Antarctica and suspected to affect basal conditions of ice sheets, i.e., basal melting and subglacial hydrology. Thermomechanical models demonstrate the influential boundary condition of geothermal heat flux for (paleo-)ice sheet stability. Young, continental rift systems are regions with significantly elevated geothermal heat flux, because the transient thermal perturbation to the lithosphere caused by rifting requires ~100 Ma to reach long-term thermal equilibrium. We discuss airborne, high-resolution magnetic anomaly data from the Amundsen Sea sector to provide additional insight into deeper crustal structures related to the West Antarctic Rift System in the Amundsen Sea sector. Using depth-to-the-bottom of the magnetic source (DBMS) estimates, we reveal spatial changes at the bottom of the igneous crust and the thickness of the magnetic layer, which can be further incorporated into tectonic interpretations and which is used to derive geothermal heat flux, supplemented by heat flux derived from measured temperature gradients in shelf sediments. We relate the distribution of geothermal heat flux to paleo and present ice sheet flow conditions.

Description: Elevated and/or spatially variable geothermal heat flux (GHF) is suspected to affect basal conditions of ice sheets, i.e. basal melting and subglacial hydrology. Thermomechanical models demonstrate the influential boundary condition of geothermal heat flux for (paleo) ice sheet stability. Due to a complex tectonic and magmatic history of West Antarctica, the region is suspected to exhibit strong heterogeneous geothermal heat flux variations [e.g. Schroeder et al., 2014; Fisher et al., 2015]. Although the maximum ice extent has retreated from the shelf since the last glacial maximum, the trends of offshore GHF patterns and the overall order of magnitude are hypothetically related to those areas onshore where the West Antarctic Ice Sheet (WAIS) rests on geologically related structures. High-resolution GHF will aid the understanding of the paleo-retreat of the ice sheet in this sector. The problem with testing these possibilities is that direct observations of GHF in Antarctica are so sparse that it is accounted for the greatest source of uncertainty in ice sheet studies for the continent [Larour et al., 2012]. This presentation builds on our previous studies in which we discussed geothermal heat flux based on 26 in-situ temperature measurements that were conducted in 2010 in the Amundsen Sea Embayment (ASE) in West Antarctica. We found, that the shallow (3 m) in-situ temperature measurements were likely influenced by inter-annual bottom-water temperature variability, leading to GHF estimates biased towards lower values (mean = 33 mWm-²). In contrast, our numerical models of geothermal heat fluxes, based on Depth-to-the-Bottom-of-the-Magnetic-Source estimates, suggest that GHF spatially varies from 68 to 110 mWm-². During RV Polarstern expedition PS104 in early 2017 we collected additional 28 in-situ temperature measurements in marine sediments (up to 11 m probe depth) for deriving geothermal heat flux in the ASE, which will overall improve the spatial coverage of this region. We present GHF results of this novel data set and discuss challenges of measuring in-situ temperatures for GHF in the Amundsen Sea Embayment.

Description: Due to a complex tectonic and magmatic history of West Antarctica, the region is suspected to exhibit strong heterogeneous geothermal heat flux variations. Although the maximum ice extent has retreated from the shelf since the last glacial maximum, the trends of offshore GHF patterns and the overall order of magnitude are hypothetically related to those areas onshore where the West Antarctic Ice Sheet (WAIS) rests on geologically related structures. High-resolution GHF will aid the understanding of the paleo-retreat of the ice sheet in the Amundsen Sea Sector. This presentation builds on our previous studies in which we discussed geothermal heat flux based on 26 in-situ temperature measurements that were conducted in 2010 in the Amundsen Sea Embayment (ASE) in West Antarctica. We found, that the shallow (3 m) in-situ temperature measurements were likely influenced by inter-annual bottom-water temperature variability, leading to GHF estimates biased towards lower values (mean = 33 mWm-²). During RV Polarstern expedition PS104 in early 2017 we collected additional 28 in-situ temperature measurements in marine sediments (11 m) for deriving geothermal heat flux in the ASE, which will overall improve the spatial coverage of this region. Furthermore, we monitored the vertical temperature profile of the water column at these stations, which allows to map Circumpolar Deep Water (CDW) distributions across the inner Pine Island Shelf with greater detail.

Description: The West Antarctic Rift System (WARS) provides a key component to Antarctica's tectonic evolution. The system's expansion is thought to progress from the Ross Sea to the Bellingshausen Sea and Amundsen Sea, where smaller rift arms seem to spread more diffusely. The rift troughs provide pathways for major ice streams, thus, their dynamics might directly be coupled to tectonic-morphological constraints. To-gether with regional crustal uplift (e.g. Marie Byrd Land), a common process in conti-nental rift systems, this has widely shaped the West Antarctic landscape during the Neogene. In the Amundsen Sea Embayment (ASE), a key sector of the West Antarctic Ice Sheet (WAIS), rapid changes have occurred over recent decades. The adjacent Pine Island Glacier and Thwaites Glacier, two outlets from a large drainage basin in the centre of the WAIS, exhibit highest increase in flow velocity in all of Antarctica. A large fraction of the WAIS is discharged into the embayment here. However, various models have been developed on the crustal architecture and tectonic history of this region, based on recent geophysical surveys, but any possible WARS activity re-mains uncertain. To investigate the possible effects of rifting history from the WARS on the ASE ice sheet dynamics, we use Curie Point Depth (CPD) estimates. They are based on air-borne-magnetic anomaly data and provide an additional insight into the deeper cru-stal properties. The CPD estimates image the depth of the deepest magnetic layer, hence the bottom depth of the igneous crust. For our estimates we assume a Curie temperature of 580°C at this depth. The well-established centroid method is used to calculate 30 CPDs in area windows of 200 x 200 km each with 50% overlapping the magnetic anomaly grid. We find that shallow CPDs and, therefore, higher geothermal gradients coincide with the location of previously postulated rift arms on the ASE shelf. Our in-situ tempera-ture measurements and derived geothermal heat flow provide a further geophysical data-set to investigate the extend of any crustal thinning and possible rift arms into the Amundsen Sea Embayment. The crustal thickness is an important contributor to the observed regional-scale geothermal heat flux variations and provides a geo-physical proxy for thermal status of crust and upper mantle.

Description: The West Antarctic Rift System (WARS) is one of the largest continental rifts globally, but its lateral extent, distribution of local rifts, timing of rifting phases, and mantle processes are still largely enigmatic. It has been presumed that the rift and its crustal extensional processes have widely controlled the history and development of West Antarctic glaciation with an ice sheet of which most is presently based at sub-marine level and which is, therefore, likely to be highly sensitive to ocean warming. While the western domain of the WARS in the Ross Sea has been studied in some detail, only recently have various geophysical and geochemical/thermochronological analyses revealed indications for its eastern extent in the Amundsen Sea and Bellingshausen Sea sectors of the South Pacific realm. The current model, based on these studies and additional data, suggests that the WARS activity included tectonic translateral, transtensional and extensional processes from the Amundsen Sea Embayment to the Bellingshausen Sea region of the southern Antarctic Peninsula. We present the range of existing hypotheses regarding the extent of the eastern WARS as well as published and yet unpublished data that support a conceptual WARS model for the eastern West Antarctica with implications for glacial onset and developments.