Seismic Ocean Thermometry

地球上越来越多的温室气体所捕获的能量中，超过90%被海洋吸收。尽管观测系统在过去二十年中有了很大的改进，但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。该项目将补充现有的观测，从自然地震重复产生的声波推断大规模深海温度变化。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着路径遇到的平均海洋温度的变化。初步工作表明，将使用的地震海洋测温法将赤道东印度洋2 900公里长的区域的平均温度变化限制在0.007 K的精度。这一地震海洋测温的初步实例将扩大为一种广泛适用的方法，收集每年成千上万次浅层海底地震产生的海洋变暖的丰富信息。该项目将有助于了解海洋的热量吸收和向深海输送的速度，这是气候变化的驱动力。测量和了解热量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，海洋变暖在很大程度上导致海平面上升，而吸收模式对区域海平面上升产生影响。地震测温法有可能大大加强现有的观测系统，而且可以以很低的成本运作。此外，该项目还将通过一名博士后学者和一名研究生的支持，为培养新一代科学家做出贡献。使用2005年至2016年期间的数据，在赤道东印度洋2900公里长的剖面上初步应用地震海洋测温法，确定了12个月、6个月、大约10天，并推断出一个十年变暖趋势，大大超过以前的估计。拟议的工作将改进目前初步的地震海洋测温方法，并将对大规模深海的温度变化和趋势提供更好的限制。该项目将把这一方法应用于两个新的区域：南大洋和西北太平洋亚热带区域。南大洋是有趣的，因为以前的数据覆盖范围特别稀疏，估计的趋势很大，SOFAR通道向表面扩展。西北太平洋是一个有趣的区域，因为它显示出很强的年代际变化，并且黑潮流系统拥有一个强大的锋和一个充满活力的涡旋场。因此，这两个区域是理想的测试平台，既可以改进方法，也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，并将允许观测不同频率的旅行时间变化，从中推断相关温度变化的深度结构信息。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.