Seafloor pockmarks on the South Westland margin of the South Island/Te Waipounamu, Aotearoa New Zealand

Enclosed depressions, termed pockmarks, are widespread seafloor morphologies, commonly associated with fluid seepage. This study provides the first detailed documentation of pockmarks offshore the South Westland margin of the South Island/Te Waipounamu, Aotearoa New Zealand. Pockmarks are identified from multibeam bathymetry (25-m grid) through manual and semi-automated selection in water depths of 100-2600 m. Pockmarks are most concentrated at 400-850 m water depth on continental slope areas between submarine canyons. A continuum of pockmark morphologies includes - (1) large (>0.5 km(2) area) and irregularly shaped pockmarks above partially infilled channels; (2) small and circular pockmarks (similar to 100-200 m diameter; similar to 0.008-0.03 km(2) area) occurring between canyons; and (3) elongated and intermediate size pockmarks, generally oriented along-slope and often occurring above buried sediment waves. Elongated pockmarks appear to have been modified by near-seafloor oceanographic and/or turbidity current flows. Pockmark features occur across many locations around Aotearoa, including both the eastern and western margins. Some similar pockmark morphologies are identified in these different tectonic, sedimentary, and oceanographic settings, suggesting that there may be some similarity in formative mechanisms, but clear mechanisms leading to their formation remain enigmatic.

Automated summary

This study provides the first detailed documentation of pockmarks offshore the South Westland margin of the South Island/Te Waipounamu, Aotearoa New Zealand. The pockmarks are most concentrated at 400-850 m water depth on the continental slope areas and exhibit a range of morphologies that may be influenced by oceanographic and turbidity current flows. Similar pockmark morphologies occur in different tectonic, sedimentary, and oceanographic settings, suggesting potential similarities in their formative mechanisms.