Linking ventilation changes in the thermocline with surface outcrop variations

将温跃层的通风变化与地表露头变化联系起来

• 批准号: 1851149
• 负责人: Sabine Mecking
• 金额: $ 38.69万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-04-15 至 2023-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1851149&HistoricalAwards=false
• 关键词: Linking; ventilation; changes; thermocline; surface

Understanding the response of the ocean to global warming, including changes in the renewal of ocean waters from the surface (ventilation), is important for future climate predictions. Oxygen distributions in the ocean thermocline are an effective way to infer changes in ventilation because physical processes (ventilation and circulation) that supply oxygen are primarily responsible for changes in interior oxygen concentrations. Reduced ventilation, as expected under global warming conditions, is signified by a reduction in oxygen inventories. However, natural variability such as decadal oscillations can obscure climatic trends; long-term data records are needed to fully distinguish between trends and cycles. This study will use available data, including Argo profiling floats, ship-based surveys, and satellite-derived surface densities, collected in the North Pacific over the past decades. This study is unique in that it examines physical mechanisms of ocean interior oxygen variability using a data-only approach, overcoming biases and misrepresentations possible with ocean models and reanalysis products. The team combines the expertise of two researchers in satellite oceanography and ocean hydrography respectively. Undergraduate summer interns will be incorporated into the project and trained in these fields with the goal of fostering geoscience education. Both PIs are also active in graduate student advising and outreach activities in public schools and at the Pacific Science Center. Results from this research will be included into such outreach, raising public awareness about the changing ocean environment. Monitoring ocean ventilation is important because a reduction in ventilation reduces the ocean ability to take up anthropogenic CO2 with important feedbacks to the global climate system. Declining North Pacific O2 concentrations may become stressors for marine organisms if threshold values are reached. The data methods used are transferrable to other ocean basins as well.This project will focus on the North Pacific thermocline, where some of the world ocean's largest oxygen variations have been observed. These variations, described as bidecadal cycles on top of a small declining trend, are strongest on subsurface isopycnals that outcrop into the mixed layer the northwestern North Pacific. It has been hypothesized that changes in the isopycnal outcrop positions and area, including complete cessation of outcrop, are the cause for the subsurface oxygen changes observed downstream. Argo data will be combined with satellite sea surface data and ocean interior data from continued repeat hydrography sections, time series stations, and also emerging bio-Argo profiling floats (with O2 sensors) to examine records of North Pacific surface density over the past ~40 years, in combination with water transfer into the thermocline and ocean interior O2 variability. The study will focus on seasonal to decadal variability and long-term trends. Specific objectives are (1) computing sea surface density and isopycnal outcrop area variability in the northwestern North Pacific, (2) estimating annual subduction rates and O2 fluxes from the outcrops into the thermocline, and (3) linking subduction in the northwestern North Pacific to downstream oxygen variability in the northeast. It is hypothesized that surface densities in the northwestern North Pacific exhibit decadal cycles similar to subsurface oxygen (as well as a declining trend) and that oxygen variations in the eastern North Pacific interior (thermocline) are correlated with surface density/subduction rate variations in the northwestern North Pacific with a few year lag.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.

了解海洋对全球变暖的反应，包括地表海水更新（通风）的变化，对于未来的气候预测非常重要。海洋温跃层中的氧气分布是推断通风变化的有效方法，因为供应氧气的物理过程（通风和循环）主要负责内部氧气浓度的变化。正如在全球变暖条件下所预期的那样，通风量的减少表现为氧气库存的减少。然而，年代际振荡等自然变化可能会掩盖气候趋势；需要长期数据记录才能充分区分趋势和周期。这项研究将使用过去几十年在北太平洋收集的现有数据，包括 Argo 剖面浮标、船基调查和卫星表面密度。这项研究的独特之处在于，它使用纯数据方法研究了海洋内部氧气变化的物理机制，克服了海洋模型和再分析产品可能存在的偏差和误传。该团队结合了卫星海洋学和海洋水文学两位研究人员的专业知识。本科生暑期实习生将被纳入该项目并接受这些领域的培训，以促进地球科学教育。两位 PI 还积极参与公立学校和太平洋科学中心的研究生咨询和外展活动。这项研究的结果将纳入此类宣传活动中，以提高公众对不断变化的海洋环境的认识。监测海洋通风非常重要，因为通风的减少会降低海洋吸收人为二氧化碳的能力，并对全球气候系统产生重要反馈。如果达到阈值，北太平洋氧气浓度下降可能会对海洋生物造成压力。使用的数据方法也可以转移到其他海洋盆地。该项目将重点关注北太平洋温跃层，在那里观察到了世界海洋中一些最大的氧气变化。这些变化被描述为在小幅下降趋势之上的二十年循环，在北太平洋西北部的混合层中露头的地下等重岩上最为强烈。据推测，等密度露头位置和面积的变化，包括露头的完全停止，是下游观察到的地下氧变化的原因。 Argo 数据将与来自连续重复水文剖面、时间序列站以及新兴生物 Argo 剖面浮标（带有 O2 传感器）的卫星海面数据和海洋内部数据相结合，以检查过去约 40 年北太平洋表面密度的记录。年，结合水转移到温跃层和海洋内部氧气的变化。该研究将重点关注季节性到十年间的变化和长期趋势。具体目标是 (1) 计算北太平洋西北部的海面密度和等密度露头面积变化，(2) 估计年俯冲率和从露头进入温跃层的 O2 通量，以及 (3) 将北太平洋西北部的俯冲与东北部下游的氧气变化。据推测，北太平洋西北部的表面密度表现出类似于地下氧气的年代际循环（以及下降趋势），并且北太平洋东部内陆（温跃层）的氧气变化与北太平洋内部的表面密度/俯冲率变化相关。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。