Australia the plate-tectonic trampoline?

O’Leary et al (2013) have a paper in Nature Geosciences examining sea-level changes during the last-interglacial (stage 5e) using corals as sea-level indicators on the Western Australian coast. They show that between 127 and 119 kyr ago, eustatic sea level remained relatively stable at about 3–4 m above present sea level. However, stratigraphically younger fossil corals with U-series ages of 118±1.4 kyr are observed at elevations of up to 9.5 m above present mean sea level. They interpret this as indicating rapid sea-level rise caused by a catastrophic collapse of polar ice sheets. This work has obvious relevance to our greenhouse gas warmed future, as it suggests that the ice sheets are less stable than we might hope. Nine metres of sea-level rise would be catastrophically expensive to adapt to – goodbye Amsterdam, farewell New Orleans.

Rud Istvan, writing on Judith Curry’s blog, does not like this paper. Istvan rightly argues that tectonic activity needs to be taken into account, that earthquakes could raise or lower the land, making it appear that eustatic sea-level had changed. Not surprisingly the authors are aware of this. The authors show that the early 5e shoreline is approximately level along the entire Western Australia coastline, except for one sample. If there had been large vertical tectonic movement the palaeo-shoreline would not be flat.

a, The light blue lines represent the modern MSL datum, mean high high water (MHHW) and mean low low water (MLLW) levels. South Western Australia is characterized by a diurnal microtidal environment with a maximum tidal range of 1.2 m. b, Hatched bars represent the inner margin elevation of the modern shore platforms, which vary from −0.4 m below to +0.3 m above MSL (height of each bar represents the survey errors). c, Red bars represent palaeoMSL 119 kyr ago, calculated by adding/subtracting the offset of the modern shore platform from modern MSL to the observed elevation of the palaeoplatform (mean value = 2.5±0.5 m; the Cape Cuvier observation at +3.3 m, circled red bar, was excluded from the calculation). d, Blue bars represent GIA predictions (single run) of relative sea level 119 kyr ago, assuming that ice volumes during MIS 5e were the same as today (see Methods). The mean of numerous GIA simulations is −0.9±0.6 m (see text). e, GIA-corrected palaeoMSL for Western Australia (3.4±0.6) is the total vertical distance between the surveyed local palaeoMSL datum c and the Holocene equivalent 119-kyr-old shoreline (−0.9±0.6 m; d), measured from modern MSL.

O’Leary et al figure 1. a, The light blue lines represent the modern tidal datum.  b, Hatched bars represent the inner margin elevation of the modern shore platforms (height of each bar represents the survey errors). c, Red bars represent palaeoMSL 119 kyr ago, calculated by adding/subtracting the offset of the modern shore platform from modern MSL to the observed elevation of the palaeoplatform (mean value = 2.5±0.5 m; the Cape Cuvier observation at +3.3 m, circled red bar, was excluded). d, Blue bars represent GIA predictions (single run) of relative sea level 119 kyr ago, assuming that ice volumes during MIS 5e were the same as today. e, GIA-corrected palaeoMSL for Western Australia.

The authors write that the higher late last-interglacial shoreline is found across the southwest coast, but it is best represented along the 150-km-long Miocene Quobba Ridge, and it is here that all their dated corals are from. Istvar argues that an intra-plate earthquake analogous to the the 1811 New Madrid event could have displaced the shoreline on the Quobba Ridge. Istvar forgets the obvious. Firstly, this shoreline can be found across the region, not just in this one area. Secondly, if we invoke a large earthquake to lower the land at Quobba Ridge in the middle of 5e by 6m, this will disrupt the early 5e shoreline by 6m. As this shoreline is now approximately level, we need to invoke a second earthquake after stage 5e to raise the land back up again by 6m. What is Western Australia, a giant trampoline?

Why does Curry chose to host Istvan’s nonsense?

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About richard telford

Ecologist with interests in quantitative methods and palaeoenvironments
This entry was posted in Fake climate sceptics, Peer reviewed literature and tagged , , . Bookmark the permalink.

One Response to Australia the plate-tectonic trampoline?

  1. Eli Rabett says:

    FWIW Istvan steps right back into this in his comment on Hansen, et al.
    http://www.atmos-chem-phys-discuss.net/15/C5270/2015/acpd-15-C5270-2015.pdf

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