Linking ventilation changes in the thermocline with surface outcrop variations

了解海洋对全球变暖的反应，包括海水从表面更新（通风）的变化，对未来的气候预测很重要。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）是内部氧气浓度变化的主要原因。正如在全球变暖条件下所预期的那样，通气减少的标志是氧气库存的减少。然而，年代际波动等自然变率可以掩盖气候趋势；为了充分区分趋势和周期，需要长期数据记录。这项研究将使用现有数据，包括过去几十年来在北太平洋收集的Argo剖面浮标、船舶调查和卫星衍生的表面密度。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错误陈述。该小组结合了卫星海洋学和海洋水文学两名研究人员的专门知识。本科生暑期实习生将被纳入该项目，并在这些领域进行培训，以促进地球科学教育。这两个pi也在公立学校和太平洋科学中心积极参与研究生咨询和推广活动。这项研究的结果将纳入这种推广活动，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的反馈。如果达到阈值，北太平洋氧气浓度下降可能成为海洋生物的压力源。所使用的数据方法也可转移到其他海洋盆地。该项目将重点关注北太平洋温跃层，在那里已经观察到世界上一些海洋中最大的氧气变化。这些变化被描述为在一个小的下降趋势之上的双年代际循环，在北太平洋西北部的混合层中露头的地下等平线上最强。据推测，等斜露头位置和面积的变化，包括露头的完全停止，是下游观测到的地下氧变化的原因。Argo数据将与卫星海面数据和海洋内部数据相结合，这些数据来自持续重复的水文剖面、时间序列站和新兴的生物Argo剖面浮标（带有O2传感器），以检查过去~40年来北太平洋表面密度的记录，并结合向温跃层的水输送和海洋内部O2的变化。该研究将侧重于季节到年代际变化和长期趋势。具体目标是(1)计算北太平洋西北部海面密度和等环流露头面积变化，(2)估计每年从露头到温跃层的俯冲速率和氧通量，以及(3)将北太平洋西北部的俯冲与东北部下游的氧变化联系起来。假设北太平洋西北部的地表密度表现出与地下氧相似的年代际循环（以及下降趋势），并且北太平洋东部内陆（温跃层）的氧变化与北太平洋西北部的地表密度/俯冲率变化具有几年的滞后关系。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。

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.