Seismic Ocean Thermometry

越来越多的温室气体困在地球上的能量中，超过90%被海洋吸收。监测由此导致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20年里有了巨大的改进。该项目将通过从重复的自然地震产生的声波推断大范围和深海海洋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，它们旅行时间的变化反映了它们在传播路径上遇到的平均海洋温度的变化。初步工作表明，将要使用的地震海洋测温系统能够以0.007 K的精度约束赤道东印度洋2900公里长区域的平均温度变化。这个地震海洋测温系统的最初例子将扩展为一种广泛适用的方法，它可以获取每年数以万计的浅层海底地震所产生的一些关于海洋变暖的丰富信息。该项目将有助于理解海洋的热量吸收和向深海的输送速度，这是气候变化的驱动因素。测量和了解海洋表面和深海之间的热量吸收模式及其分配，对于改进对未来几十年和几个世纪气候轨迹的预测至关重要。此外，海洋变暖在很大程度上促进了海平面上升，吸收的模式对区域海平面上升产生了影响。地震测温方法有可能大大增强现有的观测系统，而且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，促进新一代科学家的发展。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，发现了12个月、6个月和大约10天的时间尺度上的温度波动，并推断出显著超过先前估计的十年变暖趋势。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异性和趋势的制约。该项目将把这种方法应用于两个新的区域：南大洋和亚热带西北太平洋。南大洋之所以有趣，是因为之前的数据覆盖范围特别稀疏，估计的趋势很大，而且遥远的海峡向海面延伸。西北太平洋很有趣，因为它表现出很强的年代际变化，并且与黑潮洋流系统一起拥有一个强大的锋面和一个能量涡流场。因此，这两个地区是理想的试验台，既可以改进方法，也可以发现有趣的信号。另一项进步将是使用水听器而不是地震台数据。这将提高敏感性，从而允许使用更多的小地震，并将允许观察不同频率的旅行时间变化，从中推断有关相关温度变化的深度结构的信息。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.