A wet strawman: A response to Ward et al.

Abstract

Ward et al. (2022) assert in their desktop study that we are "mistaken" in our interpretation of the artifacts at the Cape Bruguières Channel (CBC), Flying Foam Passage (FF), and Dolphin Island (DI) sites as evidence of cultural activity on a pre-inundation land surface (Benjamin et al., 2020 [CBC and FF]; Dortch et al., 2019 [DI]) and that we have failed to take account of local hydrodynamic processes that could have displaced artifacts and moved them over much greater distances than we thought possible. They argue two key points in support: (1) that "these sites are in the intertidal zone" (p. 783) and (2) that "many or all artefacts are likely to have been reworked" (p. 783). | SUPPORTING DATA SETSWard et al. have relied on a hydrodynamic model with a parent 2500 m grid and a smaller nested 500 m grid (Ward et al. supplementary information). From this, they have derived modeled current movements at peak ebb and flood tides and generated a range of hypotheses of possible artifact movement in response to these current flows. They do not model currents at the seabed nor provide a justification for their bed roughness value of 0.0002 m. The smaller 500 m grid is almost five times larger than the width of the CBC reported in Benjamin et al., so there is no way this model could accurately represent current speeds in CBC, yet they still incorporate a grid cell over this site and model the current speed. The DI site reported in Dortch et al. is located within a shallow embayment on the eastern side of the FF and is not even captured in their grid. Large reef areas across the northern archipelago (immediately adjacent to CBC) are also completely unsurveyed. Nevertheless, this area is incorporated into the grid mesh. In their supplementary information, they also refer to RPS data with measured cyclonic current speeds that exceed 2 m/s on the North West Shelf. They do not provide a location for this measurement. Given that the North West Shelf covers an area of over 200,000 km 2 with tidal ranges of more than 10 m in the north, we question how this value is even remotely relevant to the Murujuga sites. It is axiomatic in geoarchaeological studies of underwater archaeological sites that the local conditions most relevant to archaeological site formation and deformation processes can vary over distances of as little as 10 s or 100 s of meters. The model proposed by Ward et al. is too coarse to be useful in contradicting our LETTER TO THE EDITORS

Bathymetric LiDAR and Semi‐Automated Feature Extraction Assist Underwater Archaeological Surveys

“…Even more importantly, archaeological deposits can survive with reasonable horizontal integrity in at least some cases, including low‐energy conditions such as those found in Apalachee Bay, making spatial interpretations within such deposits more sound (Benjamin et al. 2022; Cook Hale et al. 2022; cf.…”

“…Depending on marine conditions (depths above or below wave base or storm wave base, sedimentation rates, tectonic effects, etc. ), such sites may or may not be stable-a topic of current debate (Benjamin et al 2022;Cook Hale et al 2022;Ward et al 2022).…”

“…), such sites may or may not be stable—a topic of current debate (Benjamin et al. 2022; Cook Hale et al. 2022; Ward et al.…”

Correction: Aboriginal artefacts on the continental shelf reveal ancient drowned cultural landscapes in northwest Australia

“…In ‘A wet strawman: A response to Ward et al’ published in Geoarchaeology [ 3 ] the authors have reiterated the interpretations of the minimum ages of the two sites published in PLOS ONE and reviewed why these interpretations remain in place. From Benjamin et al ([ 3 ], pg 3) the authors conclude, “It may well be that we will never achieve 100% certainty about the status of artifacts that are surface finds without means of direct and independent radiometric dating… On the presently available evidence, we reject Ward et al’s critique and stand by our original interpretations until such time as new and relevant evidence is forthcoming to further confirm or refute them”. This interpretation is further reinforced by additional field investigations in 2022 and the authors have interpreted the available evidence to rule out any hypotheses arguing for wholesale secondary deposition.…”

“…In 2019, the Deep History of Sea Country (DHSC) Project team found and published two submerged archaeological sites in Murujuga (Dampier Archipelago) Western Australia [ 1 ]. Following publication in 2020, a further discussion has ensued and was published in the journal Geoarchaeology by Ward et al [ 2 ], with a subsequent response to their critique published by Benjamin et al [ 3 ]. This coincided with the project team returning to Murujuga in 2022 to collect further field data and to confirm the nature and context of the two underwater archaeological sites located in the shallow coastal waters of the continental shelf ([ 4 ] in press).…”