Collaborative Research: Estimation of particle aggregation and disaggregation rates from the inversion of chemical tracer data

海洋中的生物碳泵是将大气中的CO2有效地从海洋表层输送到深海，从而从大气中去除CO2的重要过程。这种运输是在多步骤过程中进行的。首先，浮游植物在阳光照射的海洋表面沃茨进行光合作用，吸收大气中的二氧化碳并将其固定为颗粒有机碳。浮游植物中所含的一部分有机碳被包装成更大的集群（聚集体），可以沉入深海。这些聚集体下沉得越深，其中所含的碳从大气中移除的时间就越长。集料下沉的深度随时间和空间变化很大，难以预测。一般来说，较大的聚集体下沉得更快，因此比较小的颗粒下沉得更深。促进聚集成较大颗粒的过程应增强生物泵，而促进有机碳的解聚（颗粒簇的分解）和再生（分解）的过程应降低生物泵的强度和效率。因此，颗粒聚集和解聚速率对于理解生物泵的可变性至关重要，但很难直接测量。该项目将使用化学示踪剂和建模方法来量化这些重要过程的速率。研究人员将把这种方法应用于各种海洋环境，并首次大规模量化海洋上层500米的这些速率。作为该项目的一部分，他们将与CalTeach计划对接，该计划是加州大学的科学和数学计划，旨在将大学科学，数学和工程专业纳入K-12教室。这些CalTeach实习生中的许多人后来成为加州的K-12科学教师。两名本科生在加州大学加州，圣克鲁斯（UCSC）的CalTeach计划注册将作为实验室助理参与，并开发一个实践教学模块的碳循环和生物泵的K-12教室。圣克鲁斯的加州大学和伍兹霍尔海洋研究所的科学家提议，通过反演三种化学示踪剂的观测结果，即钍-234、成岩颗粒和分布在小的悬浮颗粒和大的下沉颗粒之间的颗粒有机碳，来估计中层的颗粒聚集和解聚速率。钍的同位素长期以来一直被用来估计粒子动力学过程的速率，因为它们已知的源函数和粒子反应行为。以前的工作表明，成岩颗粒作为一种惰性，被动示踪剂的颗粒动力学。研究人员将把钍和成石颗粒的测量与POC的测量结合起来，以估计各种海洋环境中颗粒的聚集和解聚率。从化学示踪剂数据反演推导出的颗粒循环速率的估计提供了一个重要的定量约束，从其他方法得出的速率可以进行比较。这项工作的主要目标是估计EXPORTS和GEOTRACES考察的每个站点与示踪剂数据最一致的深度变化（分解）聚集率。这项工作还将产生不同深度的POC矿化率和颗粒沉降率的估计。该奖项反映了NSF的法定使命，并已被认为是值得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的支持。

The biological carbon pump in the ocean is an important process by which atmospheric carbon dioxide (CO2) is effectively transported from the surface ocean to the deep ocean, and thereby removing CO2 from the atmosphere. This transport occurs in a multi-step process. First, phytoplankton carry out photosynthesis in the surface, sunlit waters of the ocean, taking up atmospheric CO2 and fixing it into particulate organic carbon. A portion of the organic carbon contained in the phytoplankton is packaged into larger clusters (aggregates) that can sink to the deep ocean. The deeper these aggregates sink, the longer the carbon contained in them is removed from the atmosphere. The depth to which aggregates sink varies greatly over time and space and are difficult to predict. In general, larger aggregates sink more quickly, and thus more deeply, than smaller particles. Processes that promote aggregation to larger particles should enhance the biological pump, and processes that promote disaggregation (breakdown of particle clusters) and regeneration (decomposition) of the organic carbon should decrease the strength and efficiency of the biological pump. Particle aggregation and disaggregation rates are thus crucial to understanding the variability of the biological pump, but are very difficult to measure directly. This project will use chemical tracers and a modeling approach to quantify the rates of these important processes. The investigators will apply the approach to a variety of oceanic environments and provide the first large-scale effort to quantify these rates in the upper 500 meters of the ocean. As part of this project, they will interface with the CalTeach program, which is a University of California Science and Math Initiative to place university science, math, and engineering majors in K-12 classrooms. Many of these CalTeach interns go on to become K-12 science teachers in California. Two undergraduate students enrolled in the CalTeach program at the University of California, Santa Cruz (UCSC) will participate as laboratory assistants and develop a hands-on teaching module on the carbon cycle and biological pump for K-12 classrooms. Scientists from the University of California at Santa Cruz and Woods Hole Oceanographic Institution propose to estimate the rates of particle aggregation and disaggregation in the mesopelagic zone through the inversion of observations of three chemical tracers, namely thorium (Th)-234, lithogenic particles, and particulate organic carbon (POC) distributed between small, suspended particles and large, sinking particles. The isotopes of Th have long been used to estimate rates of particle dynamics processes because of their known source function and particle-reactive behavior. Previous work has shown that lithogenic particles act as an inert, passive tracer of particle dynamics. The investigators will couple thorium and lithogenic particle measurements to measurements of POC to estimate particle aggregation and disaggregation rates from a wide range of oceanographic environments. Estimates of particle cycling rates deduced from the inversion of chemical tracer data provide a crucial quantitative constraint to which rates derived from other approaches can be compared. The main objective of this work is to estimate depth- varying (dis-) aggregation rates at each station of the EXPORTS and GEOTRACES cruises that are most consistent with the tracer data. This work will also produce depth-varying estimates of POC remineralization rates and particle sinking rates.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.