Geomorphic and habitat mapping of submarine canyons of the Australian continental margin

Submarine canyons influence oceanographic processes, sediment transport, productivity and benthic biodiversity from the continental shelf to the slope and beyond. The relative influence of an individual canyon on these processes will, in part, be determined by its form, shape and position on the continental margin. Based on the latest bathymetry data for the Australian margin, we have mapped 753 submarine canyons and derived a large number of geomorphic metrics based on canyon form, shape and position. In this presentation we highlight key results, which show that these canyon metrics describe a wide variety of canyon form and physical complexity that is consistent with the geological evolution of the Australian margin and the local influence of geological and geomorphological processes. Thus, Australian submarine canyons cluster in the east, southeast, west and southwest where the margin is steepest and continental shelf is narrow. Subsequently, we used 22 environmental variables (including many of the geomorphic metrics) as surrogates to derive estimates of habitat potential for these submarine canyons. Our analysis shows that the high geomorphic and oceanographic diversity of Australian submarine canyons creates a multitude of potential habitat types, notably for benthic infaunal and epifaunal communities. Canyons with particularly high benthic habitat potential are located mainly offshore of the Great Barrier Reef and the New South Wales coast, on the eastern margin of Tasmania and Bass Strait, and on the southern Australian margin. Many of these canyons have complex bottom topography, are likely to have high primary and secondary production, and have less potential for sediment disturbance due to bottom current. Canyons that incise the shelf tend to score higher in habitat potential than those confined to the slope. This habitat potential is exemplified by Perth Canyon, a large shelf-incising canyon on the southwest Australian margin, which we present in this talk as a case study. High-resolution (20m) multibeam sonar data for the canyon reveals the geomorphic complexity characterised by escarpments, transverse ridges, large-scale mass movements and active bedform fields. This geodiversity and the interaction of the Perth Canyon with regional oceanographic currents (the Leeuwin Current and Undercurrent) provide highly diverse habitats for benthic fauna such as deep-sea corals and sponges and a variety of pelagic fauna including cetaceans (e.g., Australian pygmy blue whales, minke whales, sharks and tunas).

Abstract submitted to/presented at the 2018 International Network for Submarine Canyon Investigation and Scientific Exchange (INCISE) Symposium (https://www.incisenet.org/)

海底峡谷（submarine canyons）会影响从大陆架到陆坡乃至更远区域的海洋学过程、沉积物输运、初级生产力以及底栖生物多样性。单个峡谷对上述过程的相对影响，在一定程度上取决于其在大陆边缘的形态、几何特征与空间位置。基于澳大利亚大陆边缘的最新水深地形测深数据，我们共绘制了753处海底峡谷的分布图，并基于峡谷的形态、几何特征与空间位置提取了大量地貌指标（geomorphic metrics）。本次报告中，我们将重点展示核心研究成果：上述峡谷指标能够反映出多样的峡谷形态与物理复杂性，且该特征与澳大利亚大陆边缘的地质演化过程，以及当地地质与地貌过程的影响相契合。因此，澳大利亚海底峡谷集中分布于大陆边缘最为陡峭、大陆架最为狭窄的东部、东南部、西部与西南部海域。随后，我们以22项环境变量（包含多数上述地貌指标）作为替代变量，估算了这些海底峡谷的栖息地潜力。分析结果表明，澳大利亚海底峡谷极高的地貌与海洋学多样性，造就了丰富多样的潜在栖息地类型，尤其适配底内与底上生物群落的生存需求。栖息地潜力极高的峡谷主要分布于大堡礁（Great Barrier Reef）与新南威尔士州沿岸外海、塔斯马尼亚岛东部边缘与巴斯海峡，以及澳大利亚南部大陆边缘。此类峡谷多数具备复杂的海底地形，大概率拥有较高的初级与次级生产力，且受底层海流影响引发的沉积物扰动风险较低。切穿大陆架的峡谷，其栖息地潜力评分通常高于仅局限于陆坡的峡谷。珀斯峡谷（Perth Canyon）便是此类栖息地潜力的典型代表：它是澳大利亚西南缘一处规模宏大的切架型海底峡谷，本次报告将其作为案例进行展示。该峡谷的20米分辨率高分辨率多波束声呐（multibeam sonar）数据显示，其地貌复杂性体现为崖壁、横向脊、大规模块体运动与活跃底形场等特征。这种地貌多样性，加上珀斯峡谷与区域海洋流系——勒温海流（Leeuwin Current）及其底层流——的相互作用，为深海珊瑚、海绵等底栖动物，以及包括澳大利亚侏儒蓝鲸、小须鲸、鲨鱼与金枪鱼在内的多种远洋动物提供了高度多样的栖息环境。本摘要已提交并将在2018年国际海底峡谷调查与科学交流网络（International Network for Submarine Canyon Investigation and Scientific Exchange, INCISE）研讨会（https://www.incisenet.org/）上展示。