Modelled seabed response to possible climate change scenarios over the next 50 years in the Australian Northwest - Low Energy scenario datasets with Sedsim input files and output files

Using data from ocean forecast models, field observations and seabed sampling we ran a numerical sediment transport model to estimate the Australian Shelf seabed evolution under three climate change scenarios. This data collection is for the Low Energy climate change scenario of: \n lowest rainfall,\n lowest sediment load,\n lowest outflow, and\n El-Niño year oceanographic conditions,\n no sea level rise in next 50 years.\n\nIn this study, the interaction of seabed sediment types and hydrodynamic forces in the northwestern region has been investigated using a state-of-the-art numerical model, Sedsim. The simulation area for this collection covers the northwest Australia continental shelf and abyssal basins which include Houtman Abrolhos, the Northwest Shelf, Shark Bay, Ningaloo reef and part of the Timor Sea.\n\nThe model uses the known grain-size distribution of the present-day seabed based on a comprehensive analysis of currently available seabed data Information available from this data source includes grainsize, mud content, rock exposure, and estimates of critical seabed shear stress. This sediment layer is incorporated in the latest high-resolution (0.0025°) seabed bathymetry obtained from the Australian National Oceans Office (NOO). The seabed topography and present-day sediment layer are represented by a 566 (columns) by 550 (rows) grid with a spatial resolution of 2.1 km. The environmental forcing factors considered in the present model are sediment-laden river flows and turbidity currents, waves, tides, wind-driven currents, sea level change, submarine slope failure and carbonate sediment production.\nLineage: Long-term seabed change is the cumulative result of dynamic forcing and sediment responses. The environmental forces integrated in the model are:\n sediment-laden river flows,\n temperature and salinity variations,\n waves and tides regimes,\n wind-driven currents,\n ocean geostrophic currents,\n sea-level changes,\n submarine slope failures and turbidity currents.\n\nThe Defence Oceanographic Data Centre has provided the wind climate in a monthly form. The data consist of mean and maximum wind speed and simultaneous wind direction when maximum speed occurred. The original wind data cover the time period from July 1999 to May 2004 at a resolution of 0.25°.\nCSIRO WAM wave model has been used to define wave condition around the Australian Shelf. The data are six-hourly predictions of significant wave height, period and mean wave direction, gridded at 0.1° spatial resolution, for the period of March 1997 to February 2002.\nThe National Tidal Centre has provided the tidal range and depth-averaged tidal current speed (5 minutes resolution). In addition, bottom current fields simulated by the Ocean Forecasting Australia Model (0.1° spatial resolution) are used as input into the sediment-transport model. High-frequency water movement caused by wave and tides are the major factors affecting the seabed sediment availability to long-term and large scale transport although the net sediment movement by waves and tides may be negligible, at least in deep water.\nIn the model, seabed mobility index (ratio between the total and critical Shields parameter (induced by wave, tidal current and wind-driven current)) serves as the major indicator of the level of intensity and frequency of seabed sediment available for movement. Modification of the mobility index formulation integrates effects of reef, algae and mangroves on sediment transport and mobility. The mobility index is calculated under the condition of monthly mean and extreme climate.\nThe Australian Shelf has been divided in nine regions. This data collection is for the Northwestern and Western regions. Depending on the area, several meshes have been used with cell size ranging between 2000 and 2400 metres. The construction of an existing seabed deposit layer is mainly based on the comprehensive sediment database auSEABED. The data collected are mostly retrieved from grabbed samples and bottom photographs. Based on this compilation the mean sediment grain size, the rock membership, the gravel and carbonates content have been estimated. Very little data is available to determine the thickness of loose sediment. The main reason being that the thinness of the sediment veneer covering the hard ground makes gravity coring almost impossible. Thus initial seabed loose sediment thickness is built on available data and according to simple rules for depth and rock membership.\nFor the Australian Shelf simulation, 131 major river and inlet systems have been identified and evaluated in terms of their annual sediment carrying capacity. Mean annual river discharge and sediment yield have been mainly extracted from the OzEstuaries database and converted into discharge rates and sediment concentration.

利用海洋预报模型、现场观测及海床采样数据，我们运行了数值泥沙输运模型，以估算三种气候变化情景下澳大利亚大陆架海床的演化过程。本数据集对应低能气候变化情景，具体包括：
最低降雨量、
最低泥沙负荷、
最低流出量、
厄尔尼诺（El-Niño）年海洋学条件、
未来50年无海平面上升。

本研究采用先进的数值模型Sedsim，探究了西北地区海床沉积物类型与水动力之间的相互作用。本数据集的模拟区域涵盖澳大利亚西北部大陆架及深海盆地，包括豪特曼·阿布洛霍斯群岛（Houtman Abrolhos）、西北大陆架、鲨鱼湾（Shark Bay）、宁加洛礁（Ningaloo Reef）及帝汶海（Timor Sea）部分区域。

模型基于现有海床数据的综合分析，采用了现今海床的已知粒度分布；该数据源包含粒度、泥含量、岩石出露情况及临界海床剪切应力的估算值。该沉积物层被整合到澳大利亚国家海洋局（Australian National Oceans Office，NOO）提供的最新高分辨率（0.0025°）海床测深数据中。海床地形与现今沉积物层通过566列×550行的网格表示，空间分辨率为2.1千米。模型考虑的环境动力因素包括含沙河流径流与浊流、波浪、潮汐、风生流、海平面变化、海底滑坡及碳酸盐沉积作用。
谱系（Lineage）：长期海床变化是动力强迫与沉积物响应的累积结果。模型中整合的环境动力包括：
含沙河流径流、
温度与盐度变化、
波浪与潮汐系统、
风生流、
海洋地转流、
海平面变化、
海底滑坡与浊流。

国防海洋学数据中心（Defence Oceanographic Data Centre）提供了月尺度的风气候数据，包括平均风速、最大风速及最大风速出现时的同步风向。原始风数据覆盖1999年7月至2004年5月，分辨率为0.25°。
CSIRO WAM波浪模型被用于确定澳大利亚大陆架周边的波浪条件。数据为1997年3月至2002年2月期间的六小时一次预测结果，包括有效波高、周期及平均波向，空间分辨率为0.1°。
国家潮汐中心（National Tidal Centre）提供了潮差及垂向平均潮流速度数据（分辨率5分钟）。此外，澳大利亚海洋预报模型（Ocean Forecasting Australia Model，分辨率0.1°）模拟的底层流场被用作泥沙输运模型的输入。波浪与潮汐引发的高频水体运动是影响海床沉积物可参与长期、大规模输运的主要因素，尽管波浪与潮汐导致的净泥沙运动可能可忽略不计（至少在深水区如此）。
模型中，海床活动性指数（seabed mobility index，即总希尔兹参数（Shields parameter）与临界希尔兹参数的比值，由波浪、潮流及风生流共同诱导）是表征海床沉积物可运动强度与频率水平的主要指标。活动性指数公式的修正整合了珊瑚礁、藻类及红树林对泥沙输运与活动性的影响。活动性指数在月平均及极端气候条件下计算。
澳大利亚大陆架被划分为九个区域，本数据集针对西北及西部地区。根据区域不同，采用了多个网格，单元格大小介于2000至2400米之间。现有海床沉积层的构建主要基于综合沉积物数据库auSEABED。所收集的数据大多来自抓斗采样与海底照片；基于此汇编，估算了平均沉积物粒度、岩石归属、砾石及碳酸盐含量。可用于确定松散沉积物厚度的数据极少，主要原因是覆盖硬底的沉积物表层（veneer）较薄，使得重力取芯几乎无法实现。因此，初始海床松散沉积物厚度基于现有数据，并根据深度与岩石归属的简单规则构建。
在澳大利亚大陆架模拟中，识别并评估了131个主要河流与河口系统的年输沙能力。年均河流流量与输沙量主要从OzEstuaries数据库提取，并转换为流量速率与泥沙浓度。