Comment on “Relative sea-level records preserved in Holocene beach-ridge strandplains – An example from tropical northeastern Australia” by Brooke, B.P., Huang, Z., Nicholas, W.A., Oliver, T.S.N., Tamura, T., Woodroffe, C.D., Nichol, S.L
Refined records of Holocene sea level and coastal evolution are needed to forecast changes in the Anthropocene. Beach ridge strandplains and other prograded barriers preserve an exceptional (and relatively untapped) archive of past sea level within their stratigraphy. Extracting these records using high-resolution geophysics can unearth sea-level indicators with the potential to resolve small fluctuations over large spatial- and temporal-scales. Brooke et al. (2019) construct a sea-level curve from Cowley strandplain and performs interesting modelling/analyses; but does so based on the beach ridge topography. Unfortunately, this methodological approach contradicts a long-held understanding that it is not appropriate to use ridge morphology or sediment analysis from cores/augers/pits to indicate sea level. This sets a misleading precedent if perpetuated in future research and does so at a critical time when extracting sea-level reconstructions from prograded barriers is becoming more established. While the Brooke et al. (2019) curve appears to correlate with data from this region, it is not precisely clear how it was constructed. Particularly perplexing is the most recent half of the curve, starting with the peculiar location of the modern analogue below mean sea level. Simply adjusting the existing curve to zero on the y-axis removes it from the tenuous correlation. This comment paper uses the geophysical and topographic data published in Brooke et al. (2019), as well as the protocol referenced, to construct relative sea-level curves. The results accentuate the difference between the reconstructions from the berm stratigraphy and the ridge morphology. Furthermore, despite the nature of this analysis utilizing a derivative dataset, the berm heights demonstrate remarkable correlation with the modelled sea-level curve for the region as well as the more traditional sea-level indicators. Ultimately, this glimpse provides insight on the possible extent of information that lies buried not just at Cowley and the 30+ prograded barriers around Australia, but at 300+ sites worldwide.
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