Attribution of climate change in the subtropical North Atlantic Ocean: exploiting tritium-helium data and adjoint sensitivity analyses

北大西洋在气候系统中的运作方式存在不确定性，包括其热量含量和有机物的生物输出，这最终会影响海洋从大气中吸收多余碳的方式。例如，在过去50年里，北大西洋副热带的热含量有所增加，这与上层温跃层水（18至24摄氏度）和冷温跃层水（4至10摄氏度）的体积增加有关，但其他邻近温度等级则有所减少。该提案旨在通过分析沿盆地36N和25W的氚-氦观测，了解亚热带北大西洋在气候系统中的运作方式。推断出的氚氦年龄提供了水最后一次与大气接触所经过时间的测量。氚氦年龄的测量将用于理解：通风如何控制北大西洋副热带热含量的观测变化2. 利用氚氦年龄法通过氧利用率间接诊断出有机物的输出速率。数据信号的可靠性将通过与环流模型及其伴随模型相比较来评估。气候变化的敏感性、有机物的输出和营养物质的循环，将通过使用相同的模式及其伴随物来理解，从而有效地识别外部强迫和模式物理变化的影响。

There is uncertainity in how the North Atlantic operates in the climate system in terms of its heat content and biological export of organic matter, which ultimately affects how the ocean uptakes excess carbon from the atmosphere. For example, over the last 50 years, there has been an increase in heat content in the subtropical North Atlantic, associated with an increase in volume of both upper thermocline water (18 to 24C) and cold thermocline waters (4 to 10C), but a decrease in other neighbouring temperature classes. This proposal aims to understand how the subtropical North Atlantic operates in the climate system by analysing tritium-helium observations along 36N and 25W across the basin. The inferred tritium-helium age provides a measure of the elapsed time since the water was last in contact with the atmosphere. The measurements of tritium-helium age will be used to understand: 1. How ventilation controls the observed changes in heat content in the subtropical North Atlantic; 2. To identify the rate of export of organic matter which is diagnosed indirectly from the rate of oxygen utilisation using the tritium-helium age. The reliability of the data signals will be assessed by comparying with a circulation model and its adjoint. The sensitivity of the climate change, the export of organic matter and cycling of nutrients, will then be understood by using the same model and its adjoint, which efficiently identifies the effect of changes in external forcing and model physics.