Seismic Ocean Thermometry

越来越多的温室气体滞留在地球上的能量中，超过90%被海洋吸收。监测由此产生的海洋变暖仍然是一个具有挑战性的采样问题，尽管观测系统在过去二十年中有了巨大的改进。该项目将通过从重复自然地震产生的声波中推断大尺度和深海温度变化来补充现有的观测结果。这些波在整个海洋盆地中传播，它们传播时间的变化反映了它们沿途遇到的平均海洋温度的变化。初步的工作表明，将要使用的地震海洋测温法限制了赤道东印度洋2900公里长剖面的平均温度变化，精度为0.007 K。这个最初的海洋温度测量地震的例子将被扩展成一种广泛适用的方法，可以收集每年成千上万次浅层海底地震产生的海洋变暖的一些丰富信息。这个项目将有助于了解海洋的热量吸收和向深海的运输速度，这是驱动气候变化的因素。测量和了解热吸收的模式及其在表层和深海之间的分配，对于改善对未来几十年和几个世纪气候轨迹的预测至关重要。此外，海洋变暖对海平面上升有重要贡献，并对区域海平面上升的吸收模式有显著影响。地震测温方法有可能大大增强现有的观测系统，并且它可以以非常低的成本运行。此外，该项目将通过一名博士后学者和一名研究生的支持，为新一代科学家的发展做出贡献。利用2005年至2016年期间的数据，对赤道东印度洋2900公里长的剖面进行了地震海洋测温的初步应用，确定了12个月、6个月和大约10天的时间尺度上的温度波动，并推断出了明显超过先前估计的年代际变暖趋势。拟议的工作将改进目前地震海洋测温的初步方法，并将改进对大尺度深海温度变化和趋势的限制。该项目将把这种方法应用到两个新的区域：南大洋和亚热带西北太平洋。南大洋很有趣，因为以前的数据覆盖范围特别稀疏，估计的趋势很大，而且SOFAR通道向海面扩展。西北太平洋很有趣，因为它表现出强烈的年代际变化，并与黑潮系统一起拥有一个强大的锋面和一个高能涡流场。因此，这两个区域是理想的测试平台，既可以改进方法，又可以发现有趣的信号。另一个进步将是使用水听器而不是地震站的数据。这将提高灵敏度，从而允许使用更丰富的小地震，并将允许观察不同频率的旅行时间变化，从中推断有关温度变化的深度结构信息。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Of the energy trapped on Earth by increasingly abundant greenhouse gases, over ninety percent is absorbed by the ocean. Monitoring the resulting ocean warming remains a challenging sampling problem, despite drastic improvements of the observing system over the past two decades. This project will complement the existing observations by inferring largescale and deep ocean temperature changes from sound waves that are generated by repeating natural earthquakes. These waves propagate across entire ocean basins, and changes in their travel time reflect changes in the average ocean temperature they encounter along their paths. Preliminary work has shown that the seismic ocean thermometry to be used constrains temperature changes averaged over a 2900 km long section in the equatorial East Indian Ocean with an accuracy of 0.007 K. This initial example of seismic ocean thermometry would be expanded into a broadly applicable method that harvests some of the abundant information on ocean warming that is generated every year by tens of thousands of shallow submarine earthquakes. This project will contribute to understanding of the ocean’s heat uptake and rate of transport to the deep ocean, that drives climate change. Measuring and understanding the patterns of heat uptake and its partitioning between the surface and deep ocean is crucial for improving projections of the climate’s trajectory in the coming decades and centuries. Furthermore, ocean warming contributes substantially to sea level rise, and the patterns of uptake imprint on regional sea level rise. The method of seismic thermometry has the potential to substantially enhance the existing observing system, and it could be operated at very low cost. In addition, the project will contribute to the development of the new generation of scientists through the support of a post-doctoral scholar and a graduate student.Preliminary application of the seismic ocean thermometry over a 2900 km long section in the equatorial East Indian Ocean using data from the period 2005 to 2016 identified temperature fluctuations on time scales of 12 months, 6 months, and about 10 days and inferred a decadal warming trend that significantly exceeds previous estimates. The proposed work would improve the currently preliminary methodology of seismic ocean thermometry, and it would provide improved constraints on the temperature variability and trends of the largescale deep ocean. The project will apply the method to two new regions: the Southern Ocean and the subtropical Northwest Pacific. The Southern Ocean is interesting because previous data coverage is particularly sparse, estimated trends are large, and the SOFAR channel expands towards the surface. The Northwest Pacific is interesting because it displays strong decadal variability and with the Kuroshio current system hosts a strong front and an energetic eddy field. These two regions are therefore ideal test beds, both to improve the methodology and to uncover interesting signals. Another advance will be to use hydrophone rather than seismic station data. This will improve the sensitivity and thus allow use of more abundant small earthquakes, and will allow observation of travel time changes at different frequencies, from which to infer information on the depth structure of the associated temperature changes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.