Patterns of reef coral calcification in an upwelling zone (Oman)

热带浅水珊瑚礁中珊瑚的骨骼钙化受到全球海洋表面温度(SST)上升、海洋pH下降和人为富营养化的日益威胁。除了少数养殖实验外，从自然环境来看，单一的应激因素，如高SST、低pH或富营养化对珊瑚净钙化的贡献尚不清楚。阿曼珊瑚礁是研究未来珊瑚礁骨骼钙化环境控制的天然实验室，因为人为干扰可以忽略不计，阿拉伯海上升流带(低SST，低pH)和阿曼湾(高SST，高pH)之间存在明显的环境应力空间梯度。在DFG资助的一个正在进行的项目中，我们研究了阿曼珊瑚(Porites)的骨骼钙化模式。根据我们的数据，受阿拉伯海夏季上升流影响的珊瑚由于海水pH值低而减少了骨骼体积密度，但由于高营养物质可获得性而增加了伸展速率。另一方面，来自阿曼湾的珊瑚由于文石过饱和度高，伸展不明显，密度较高。它们受到保护，不会漂白，因为它们在夏天受益于来自上升流带的冷水细丝。这些发现支持了预测上升流区域代表未来和过去暖期珊瑚礁避难所的假设。该项目成功的重要原因是采样方法的改进和珊瑚内部年龄模型的校准，这使我们第一次能够区分不同(亚)季节应力对整体钙化平衡的影响。然而，由于阿曼当局许可的意外后勤问题、美因茨大学的实验室改装以及由于科罗纳大流行而导致的实验室设施全面关闭，该项目的延误使我们落后了一年的计划。在正在进行的项目中出现的新的研究问题和延误导致我们提交了一份续签提案。在额外的工作时间内，我们将完成对我们现有材料的所有计划分析，并遵循三个额外的研究目标：(1)对选定的珊瑚(230Th/U)进行测年，以便更好地记录上升流的高频变化；(2)重建钙化流体的碳酸盐化学(B/Ca-δ10B)，以便更好地了解内部调节机制与外部海水对钙化性能的影响；以及(3)从项目期间安装的环境测井站(pH、SST)中提取短岩心，以便校准替代数据和钙化记录。

Skeletal calcification of corals in tropical shallow-water coral reefs is increasingly threatened by globally rising sea surface temperatures (SST), lowering of ocean pH, and anthropogenic eutrophication. Except for few culture experiments, the contribution of a single stressor such as high SST, low pH or eutrophy to net calcification of reef corals is not known from the natural environment. The coral reefs of Oman are a natural laboratory to the study of environmental controls on skeletal calcification of future reefs because anthropogenic disturbances are negligible and pronounced spatial gradients of environmental stresses exists between the Arabian Sea upwelling-zone (low SST, low pH) and the Gulf of Oman (high SST, high pH).In an ongoing project funded by the DFG we studied patterns of skeletal calcification of corals (Porites) from Oman. According to our data, corals affected by summer upwelling of the Arabian Sea have diminished skeletal bulk density due to low seawater pH, but enhanced extension rate due to high nutrient availability. On the other hand, corals from the Gulf of Oman have high density because of high aragonite super-saturation and inconspicuous extension. They are protected from bleaching because they benefit during summer from cool-water filaments derived from the upwelling zone. The findings support hypotheses predicting regions of upwelling to represent refuges for coral reefs during future and past warm periods. Important for the success of the project were improvements of the sampling method and calibration of coral-internal age models that allow us for the first time to separate the effects of different (sub-) seasonal stresses on the overall calcification balance. However, delays of the project through unexpected logistical problems with permits by Omani authorities, a laboratory conversion at Mainz University and the general shutdown of laboratory facilities due to the Corona pandemic brought us one year behind schedule. New research questions that came up during the ongoing project and the delays led us to submit a renewal proposal. Within the additional work time, we will complete all planned analytics of the materials already available to us and follow three additional research aims: (1) dating of selected corals (230Th/U) for an even better documentation of high-frequency variations of upwelling, (2) reconstructing the carbonate chemistry of the calcification fluid (B/Ca-δ10B) in order to better understand internal regulation mechanisms vs. external seawater effects on calcification performance, and (3) extracting short cores from massive Porites at an environmental logging station (pH, SST) installed during the project for calibration purposes of proxy data and calcification records.