Comment on: “The spatial extent of the Deep Western Boundary Current into the Bounty Trough: new evidence from parasound sub-bottom profiling” by Horn and Uenzelmann-Neben

Abstract

Horn and Uenzelmann-Neben (2016) have described computing power spectra from sediment profiler data collected over the Bounty Trough from which they inferred Milankovic cycles. Sediment profiler records are routinely acquired on research vessels, so the method presented is interesting if it can help to resolve different influences on sediment deposits from such data. A significant concern, however, is that attenuation dominates the amplitude variation in profiler data, distorting power spectra computed over the sediment age intervals of interest. In the case of the Bounty Trough data shown, attenuation appears to have strongly varied amplitudes over the depth range commensurate with the first 41 ky Milankovic cycle, so the article’s result is less certain than claimed. Attenuation rates can vary spatially (both along track and with depth) so evaluating cycles will not be straightforward without ground truth from boreholes, which potentially diminishes the utility of remote-sensing data. Nevertheless, while not separating attenuation and reflectivity unequivocally, alternative displays of such data as explained below can help to suggest the relative importance of attenuation and reflectivity on amplitude variations.