PAIS Subcommittee on Paleobathymetry & Paleotopography workshop

Held at PAIS conference, 2017, Trieste, Italy.

Aim: To provide updates on current palaeotopographic and palaeobathymetric work and discuss priorities for future reconstructions.

The overarching goals of the palaeobathymetric and palaeotopographic subcommittee of PAIS were introduced by Karsten Gohl (AWI). The workshop then received 6 brief talks on current work that is aimed at delivering gridded topographic products for use in palaeo ice sheet, climate and ocean models:

• Guy Paxman (Durham University): Guy outlined terrestrial reconstruction work in the Recovery region (Paxman et al., 2017, JGR: Earth Surface), The Wilkes Subglacial Basin, and the Gamburtsev Subglacial Highlands (Paxman et al., 2016, EPSL). Guy outlined his approach to quantifying erosion patterns and volumes and the load interactions these had with the lithosphere and with tectonics through time. The outcome of this work is that in a number of key sectors of East Antarctica, it should be possible to reconstruct palaeotopography broadly for the key time periods of ca.34 Ma (EOT), ca.14 Ma (Mid-Miocene), ca.5 Ma (Pliocene) amongst others. The model estimates of topography are constrained by current knowledge of offshore sediment volumes in the Weddell Sea (via Xiaoxia Huang), and in the Wilkes region (via German Leitchenkov).
• Xiaoxia Huang (formerly AWI, now University of Potsdam): Xiaoxia outlined her work to integrate seismic stratigraphic profiles and ODP drilling records in the Weddell Sea region. The key time-periods are also represented in this region (34, 14, 5 Ma). Sediment isopachs were calculated relating to the distribution of regionally traced units. Sediment thicknesses for the Weddell Sea were therefore presented with the advantage that they can provide volume estimates for eroded material during the key time periods. These data therefore form a key part of the ability to reconstruct palaeotopography in this region. Her work included a published study on modelling palaeo-ocean currents in the Weddell Sea for the Miocene, showing a large influence of the northward extent of the prograded continental shelf on the location and palaeo-climatic function of the Weddell Gyre.
• Isabel Sauermilch (University of Texas): Isabel outlined the palaeobathymetry of the Wilkes margin based on seismic stratigraphy tied by cores. A key finding is that for the Eocene there appears to have been relatively low rates of sediment deposition, thus raising the question of sediment starvation.
• Katharina Hochmuth (AWI): Katharina outlined her project to generate a circum-Antarctic analysis of marine sediment sequences by carefully re-examining existing regional work and new seismic-to-drill core correlation so that stratigraphic correlations can be made in a consistent manner. Currently, the stratigraphic work is nearing completion, with only the region offshore of the Wilkes Basin remaining as a data gap. Deriving circum-Antarctic palaeobathymetric grids for significant time slices is the next step.
• Alan Aitken (University of Western Australia): Alan provided a brief update to indicate that in the near future, basin modelling of the Aurora Subglacial Basin will be undertaken to investigate the interaction of erosion/sedimentation and basin evolution.
• Stewart Jamieson (Durham University): Stewart provided a brief reminder of how the original EOT (ca. 34 Ma) palaeotopography of Wilson et al. (2012) was generated and constrained. It was indicated that based on the more recent work (see talk summaries below) the EOT topography may be revisited. He also outlined the progress of a Late Cretaceous time-slice reconstruction which is being undertaken by Graeme Eagles at AWI.

Discussion focussed on 3 issues

• Are any other processes missing from the reconstructions, and what any additional products would be helpful to modellers? A clear indication was given that we are still tackling the appropriate time-slices and that these fit with where modellers wish to understand transitions in climate and ice sheet evolution. It was noted that a process that has hitherto been largely ignored is dynamic topography (i.e. mantle flow dynamics). This discussion is to be taken up further (by Jamieson and Paxman) with Jackie Austermann who may be able to give a better indication on scales of expected influence on topography, timescales of change, and, importantly, the ability to constrain change in the geologic past. Modellers in the room expressed an interest in having not only DEMs of reconstructed palaeotopography, but maps that are clear about where erosion has occurred and where deposition has occurred at each time-slice. Such products should be possible within the current framework of the reconstructions. Finally, a question was asked about whether, given we hope to provide reconstructions for a set of key time-slices, we could then provide intermediate topographies based upon interpolation between two time-slices. Such product should indeed be possible with the caviat that understanding rates of the various processes would ideally be fed into this and that currently, rates of change are not well constrained between the key time-slices. The initial option would be to use linear interpolation, with sophistication being added later should data become available in particular sectors.
• What are others research plans/where can contributions be made? Additional contributions in relation to the time between the EOT and the mid-Miocene were offered by Carlota Escutia and the IODP Leg 113 (Site 696) team for the region of the South Orkney microcontinent.
• What is the timeline (both in terms of demand from modellers and of deliverables from the palaeotopography team) for the next products? The timescales upon which products may be delivered are converging between the marine and terrestrial components. It is anticipated that by the time of the POLAR2018 conference, both components will be nearing completion of their current project components. At this time, a decision will be made about integrating these together in a continental-scale product. Guy Paxman may carry out the integration as the final stage of his PhD, but this is dependent upon progress from all parties. The group in the room seemed happy with the potential timeline and with the product objectives.

The group will meet again at the POLAR2018 Open Science Meeting in Davos and a workshop has already been scheduled.

Karsten Gohl (AWI, Germany) and Stewart Jamieson (Durham University, UK)