Inferring trace element inputs to North Pacific surface waters from Alaskan and Asian dust

了解海洋中的化学循环的一个重要部分是了解向海洋输送元素和营养物质或从海洋中移除元素和营养物质的过程。大气可能是雨水和尘埃物质的重要来源。在海洋的某些部分，来自灰尘(可能还有雨水)的铁等元素的输入可以在刺激浮游植物生长方面发挥重要作用，浮游植物是海洋食物链的基础。这项研究将涉及收集和分析北太平洋次北极两个地点过滤后的空气样本，为期两年，目的是了解阿拉斯加和亚洲尘埃以及化石燃料燃烧对海洋表面的金属输入。建议的尘埃时间序列观测和分析将提供洞察力，有助于解释2018年美国地理跟踪太平洋子午线考察的观测结果。这个项目将支持一名研究生两年的时间，并将作为他或她的博士研究的基础。研究人员将从两个非常适合捕捉亚北极北太平洋表层水域的大气尘埃样本中收集大气尘埃样本。一个在阿留申群岛的北侧，第二个是阿拉斯加湾北部的一个岛屿(米德尔顿岛)，在搁架的断裂处。将在米德尔顿岛使用自动抽样系统全年进行抽样，而在有针对性的已知季节性事件期间，将在两个地点每个地点进行为期一个月的大量抽样。这些将有助于推断和描述来自亚洲沙尘和阿拉斯加沙尘的输入，已知沙尘主要出现在春季，而阿拉斯加沙尘主要出现在秋季。来自大型活动的样本将提供给GEOTRACES研究界进行分析。HYSPLIT模型将被用来模拟尘埃的传输和沉积，以便与观测结果进行比较。以前的工作证明，阿拉斯加和亚洲的尘埃通量存在很大的年际变化，而火山灰的输入更是多变的。考虑到粉尘来源的季节性、年际和空间变异性，以及铁和其他微量元素和同位素在地表水中的短暂停留时间，粉尘和化石燃料燃烧的沉积历史及其地球化学特征，将有助于更全面地区分各种输入，而不是单一研究巡航所可能做到的。我们将收集和分析各种大小的颗粒，以推断包含每种金属的颗粒大小范围。将对20多种元素进行分析，包括铁、铝、稀土元素、铅、锶和钕的同位素(最能区分粉尘来源终端成员的示踪剂)，以及包括钒和银在内的金属，以推断化石燃料燃烧的贡献。将确定天然放射性核素铅-210和铍-7在空气中的活动及其沉积通量，以将尘埃中的元素浓度转换为对地表水的通量估计。实验将评估不同有机配体对铁和其他金属在表层海水中的溶解度的控制，不同尺寸组分的相对溶解度，以及粉尘和化石燃料衍生金属的相对溶解度。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。

An important part of understanding chemical cycling in the ocean is understanding the processes that deliver elements and nutrients to or remove them from the oceans. The atmosphere can be an important source of material from rain and from dust. In some parts of the oceans, input of elements such as iron from dust (and possibly rain) can play an important role in stimulating the growth of phytoplankton, the base of the marine food chain. This study will involve collection and analysis of a two-year time-series of filtered air samples from two locations in the subarctic North Pacific, aimed at understanding the inputs of metals to the ocean surface from Alaskan and Asian dust and from fossil fuel combustion. The dust time series observations and analyses proposed will provide insight that will aid the interpretation of observations from the 2018 U.S. GEOTRACES Pacific Meridional Transect expedition. This project will support a graduate student for two years and will be the basis of his or her Ph.D. research.The investigators will collect atmospheric dust samples from two land-based locations well suited to capture the flux to surface waters of the subarctic North Pacific. One is on the northern side of the Aleutian chain, and the second is an island to the northeast (Middleton Island), at the shelf break, in the northern Gulf of Alaska. Sampling will be carried out year round at Middleton Island using an automated sampling system, while high-volume sampling will be carried out for one month at each of the two locations during targeted known seasonal events. These will help infer and characterize inputs from Asian dust, known to occur primarily in the spring, and from Alaskan dust, known to occur primarily in the autumn. Samples from large events will be made available to the GEOTRACES research community for analyses. The HYSPLIT model will be used to simulate dust transport and deposition, for comparison to observations. Previous work documents substantial interannual variability in dust fluxes from Alaska and from Asia, and volcanic ash input is even more variable. Given the seasonality and interannual and spatial variability of the dust sources, and the short residence time of Fe and other trace elements and isotopes in surface waters, this history of deposition from dust and fossil fuel combustion, and its geochemical characterization, will help to distinguish the various inputs more comprehensively than is possible with a single research cruise.
A variety of size fractions will be collected and analyzed to infer the particle size range that contains each of the metals. Analyses will be carried out on over twenty elements, including Fe, Al, the REE, the isotopes of Pb, Sr and Nd (the tracers that best distinguish the dust source end members), and metals including V and Ag to infer contributions from fossil fuel combustion. Activities in air of the natural radionuclides lead-210 and beryllium-7, and their depositional fluxes, will be determined to convert elemental concentrations in dust into flux estimates to surface waters. Experiments will evaluate the control of different organic ligands on the solubility of iron and other metals in surface seawater, the relative solubility of different size fractions, and the relative solubility of dust- versus fossil fuel-derived metals.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.