Upwelling and bleaching on the Great Barrier Reef (MTSRF Project 2.5i.2)

As part of MTSRF Task 2.5i.2, a range of indices were investigated to quantify upwelling on the central Great Barrier Reef (GBR), Australia. These indices are necessary for exploring environmental and biological relationships in areas where upwelling may be sporadic and less intense, especially along western boundary currents such as the East Australian Current. 'Upwelling days' (the number of days of upwelling, inferred from erratic downward temperature spikes) and diurnal variation in subsurface temperature (max-min, 20m depth) were found to be the best metrics to describe the duration and intensity of upwelling events, respectively. These were used to examine key characteristics of shelf-break upwelling in the central GBR. Temperature logger data (20m) were used to derive 'upwelling days' and the local mean summer temperatures (Dec - Feb) and NOAA AVHRR Pathfinder data were used to derive regional SSTs.
To investigate the best metrics to quantify upwelling and to explore relationships between these metrics, SST and coral bleaching.
Exploration of upwelling indices was done using hierarchical classification trees. Linear regression analysis was used to explore relationships between upwelling and SST and coral bleaching events, especially 1998 and 2002.Coordinates of the temperature logger sites are:Magnetic Island (Florence Bay): LATITUDE -19.12248, LONGITUDE 146.88155Kelso Reef: LATITUDE -18.44701, LONGITUDE 146.98907Myrmidon Reef: LATITUDE -18.25673, LONGITUDE 147.38104

作为MTSRF项目2.5i.2子任务的一部分，本研究针对澳大利亚中部大堡礁（Great Barrier Reef, GBR）的上升流量化问题，开展了一系列指标的筛选与探究工作。对于上升流偶发且强度较弱的海域（尤其是东澳大利亚海流这类西边界流区域），这些指标是探究环境与生物关联关系的必要工具。
研究发现，“上升流天数（Upwelling days）”——即通过不稳定的温度负峰值推断得到的上升流持续天数——与20米深度次表层温度的日变化（即最大-最小温差），分别被确定为描述上升流事件持续时长与强度的最优量化指标。上述两项指标被用于探究中部大堡礁陆架坡折带上升流的关键特征。本研究采用20米水深温度记录仪数据计算上升流天数，同时利用局地夏季（12月至次年2月）平均海表温度（Sea Surface Temperature, SST）以及NOAA AVHRR Pathfinder卫星数据集计算区域海表温度。

本研究的核心目标为筛选最优上升流量化指标，并探究该类指标与海表温度、珊瑚白化事件之间的关联关系。其中，上升流指标的筛选采用层级分类树方法完成；线性回归分析则被用于探究上升流与海表温度、珊瑚白化事件（尤其是1998年与2002年的白化事件）之间的关联。

各温度记录仪布设点位的坐标如下：
磁岛（弗洛伦斯湾）：纬度-19.12248，经度146.88155
凯尔索礁（Kelso Reef）：纬度-18.44701，经度146.98907
米尔米登礁（Myrmidon Reef）：纬度-18.25673，经度147.38104