Data for: Increasing hypoxia on global coral reefs under ocean warming

Ocean deoxygenation is predicted to threaten marine ecosystems globally. However, current and future oxygen concentrations and the occurrence of hypoxic events on coral reefs remain underexplored. Here, using autonomous sensor data to explore oxygen variability and hypoxia exposure at 32 representative reef sites, we reveal that hypoxia is already pervasive on many reefs. 84% of reefs experienced weak to moderate (≤153 to ≤92 μmol O2 kg-1) hypoxia and 13% experienced severe (≤61 μmol O2 kg-1) hypoxia. Under different climate change scenarios based on 4 Shared Socioeconomic Pathways (SSPs), we show that projected ocean warming and deoxygenation will increase the duration, intensity, and severity of hypoxia, with more than 94% and 31% of reefs experiencing weak to moderate and severe hypoxia, respectively, by 2100 under SSP5-8.5. This projected oxygen loss could have negative consequences for coral reef taxa due to the key role of oxygen in organism functioning and fitness.

Methods
As described in the Methods section of the accompanying manuscript and the Supplementary Information by Pezner et al.:

Sensor and deployment information

The majority of dissolved oxygen data presented in the current study (25 of 32 sites) were recorded by SeapHOx or Sea-Bird Scientific CTD sensor packages with Aanderaa oxygen optodes (Table S1). The remaining oxygen datasets were recorded by Idronaut CTD and oxygen sensor packages (Dongsha 1 and Dongsha 2), Sea-Bird SBE19 Plus CTD and SBE 43 oxygen sensor packages (Baker, Jarvis, Palmyra 3, and Tutuila), or Sea-Bird Scientific CTD and PME miniDOT sensor packages (Taiping 1). Detailed site and deployment information can be found in the Supplementary Information Extended Methods section. For each location, different instrument deployment sites are represented by numbers (e.g., Dongsha 1 and Dongsha 2), or a combination of letters and numbers where letters represent either different depths at the same site (e.g., Bocas 1a, 1b, 1c, and 1d) or different deployments at the same site over time (e.g., Crocker 1a, 1b, and 1c). 

Calibrations and conversions of datasets

All sensors were calibrated by the manufacturer or according to the manufacturer’s instructions by the user as noted in previous publications. If applicable, salinity corrections were implemented according to the manufacturer’s specifications and analog measurements were converted from voltages to concentrations. Data were assessed for quality and erroneous data points (defined as missing values or values that exceeded the measurement range of the instrument), which were flagged and excluded from any subsequent analyses. Deployment data were restricted to measurements in seawater based on salinity values to exclude extraneous data points collected during instrument transport, initial deployment, or recovery (exposure to air). Density calculations using the Gibbs Seawater Toolbox functions in RStudio were used to convert all oxygen concentration units to μmol O2 kg-1. See Supplementary Information Extended Methods (and Table S8) for an assessment and discussion on the potential errors and uncertainty of the oxygen measurements. All data and relevant code (https://github.com/apezner/GlobalReefOxygen) files are available for download online and may be used with proper attribution.

海洋脱氧（Ocean deoxygenation）预计将对全球海洋生态系统构成威胁。然而，当前珊瑚礁海域的氧浓度现状、未来变化趋势以及低氧事件的发生情况仍未得到充分研究。本研究利用自主传感器数据，对32个典型珊瑚礁站点的氧浓度变化与低氧暴露情况展开分析，结果显示低氧现象已在众多珊瑚礁中广泛存在：84%的珊瑚礁经历过轻度至中度低氧（≤153至≤92 μmol O₂ kg⁻¹），13%的珊瑚礁经历过重度低氧（≤61 μmol O₂ kg⁻¹）。基于4种共享社会经济路径（Shared Socioeconomic Pathways, SSPs）构建的不同气候变化情景下，研究表明预估的海洋增温和海洋脱氧将加剧低氧事件的持续时长、强度与严重程度：在SSP5-8.5情景下，至2100年将有超过94%和31%的珊瑚礁分别经历轻度至中度低氧与重度低氧。由于氧气对生物机能与生存适应性具有关键作用，上述预估的氧含量损失将对珊瑚礁类群产生负面影响。

研究方法
如Pezner等人所著的附属论文方法章节与补充材料所述：

传感器与布放信息
本研究中绝大多数溶解氧数据（32个站点中的25个）由搭载安德拉光学溶解氧传感器（Aanderaa oxygen optodes）的SeapHOx或海鸟科学（Sea-Bird Scientific）温盐深仪（CTD）传感器组记录（详见表S1）。剩余的氧数据集分别由以下设备记录：Idronaut CTD与氧传感器组（东沙1号、东沙2号）、海鸟SBE19 Plus CTD与SBE 43氧传感器组（贝克岛、贾维斯岛、帕尔米拉3号、图图伊拉岛），以及海鸟科学CTD与PME miniDOT传感器组（太平1号）。详细的站点与布放信息可参见补充材料扩展方法章节。对于每个采样区域，不同的仪器布放站点以数字标识（如东沙1号、东沙2号），或由字母与数字组合标识：字母代表同一站点的不同深度（如博卡斯1a、1b、1c、1d），或是同一站点随时间开展的不同布放任务（如克罗克1a、1b、1c）。

数据集的校准与转换
所有传感器均由制造商完成校准，或如既往发表文献所述由用户按照制造商的操作指南完成校准。若适用，将按照制造商的规范进行盐度校正，并将模拟测量值从电压转换为浓度。研究人员对数据开展质量评估，标记并剔除异常数据点（定义为缺失值或超出仪器测量量程的值），且不将其纳入后续任何分析。基于盐度值将布放数据限定为海水环境中的测量值，以排除仪器运输、初始布放或回收过程中（暴露于空气时）采集的无关数据点。利用RStudio中的吉布海水工具箱（Gibbs Seawater Toolbox）函数进行密度计算，将所有氧浓度单位转换为μmol O₂ kg⁻¹。关于氧测量的潜在误差与不确定性的评估与讨论，详见补充材料扩展方法章节（及表S8）。所有数据与相关代码（https://github.com/apezner/GlobalReefOxygen）均可在线下载，引用时请注明原作者。