Climate trajectories for 1960-2009: north Southern Hemisphere ocean

The file contains maps of climate trajectories derived from the velocity of climate change for 1960-2009 for the northern part of the Southern Hemisphere ocean. Methods follow: Velocity-derived trajectories to indicate global regions susceptible to effects of geographical limits to climate-driven distribution shifts. Climate trajectories are paths that points on an isotherm will travel over specific periods, integrating spatially variable speeds and directions of climate velocity along the way to show effects that static velocity maps cannot. Geographical limits to trajectories, either barriers such as coasts and mountains or lack of connections to cooler or warmer environments, suggest limits to climatic niche shifts and, by inference, local species persistence or replacement from warmer environments. Velocity fields were derived for 1960-2009 for land and ocean surface temperatures7 on a 1º grid, allowing inference at a global scale, but sacrificing small-scale detail. We categorized types of trajectory behaviour using trajectory length and the percentages of trajectories starting in, ending in and passing through cells. Short trajectories indicated non- or slow-moving thermal niches. Cells were classed as relative climate sinks if a high proportion of trajectories terminated there. Absolute climate sinks were also distinguished: coastal climate sinks where trajectories were blocked by coasts, and internal climate sinks where velocities in neighbouring cells converged. Cells were classed as climate sources if no trajectories ended there. Thereafter, cells with a high proportion of trajectories passing through were classed as corridors. Divergence cells were identified as those where fewer trajectories ended than started in that cell, and convergence cells if the opposite were true. Uncertainty evaluated by bootstrap resampling of annual average temperature maps gave a likely (>66% consistency) designation of types for 59% of ocean and 72% of land cells. Consistency was 90%) was achieved for 40% of land and 26% of ocean cells, mainly sources, coastal sinks and low velocity areas .

本数据集文件包含基于1960-2009年南半球北部海域气候变化速率生成的气候轨迹（climate trajectories）图谱。其研究方法遵循：以速率衍生轨迹标识易受气候驱动分布迁移地理限制效应影响的全球区域。气候轨迹指等温线（isotherm）上的点位在特定时段内的移动路径，整合了沿途气候变化速率的空间可变速度与方向，以此呈现静态速率图谱无法展现的效应。轨迹的地理限制因素包括海岸、山脉等屏障，或是无法连通至更冷或更暖环境的区域，这些因素预示着气候生态位（climatic niche）迁移的限制，并可据此推断本地物种的存续情况，或是被来自更温暖环境的物种所替代。研究基于1°网格（1º grid）的陆地与海洋表面温度数据[7]，生成了1960-2009年的速率场，可支持全球尺度的推断，但牺牲了小尺度细节。我们通过轨迹长度以及轨迹的起始、终止和途经单元格占比，对轨迹行为类型进行了分类。短轨迹代表热生态位未发生移动或移动缓慢。若大量轨迹终止于某单元格，则将该单元格归类为相对气候汇。此外还区分了绝对气候汇：一类是被海岸阻断轨迹的海岸气候汇，另一类是相邻单元格速率汇聚形成的内部气候汇。若某单元格无轨迹终止，则将其归类为气候源。随后，将有大量轨迹途经的单元格归类为廊道。发散单元格指轨迹终止数少于起始数的单元格，汇聚单元格则反之。通过对年平均温度图谱进行bootstrap重采样（bootstrap resampling）来评估不确定性，结果显示，59%的海洋单元格与72%的陆地单元格可获得大概率（一致性>66%）的类型判定。另有40%的陆地单元格与26%的海洋单元格可达到90%以上的一致性，这类单元格主要为气候源、海岸气候汇与低速区域。