NSFGEO-NERC: Impacts of sea ice melt and anthropogenic emmisions on biogenic sulfur aerosol as measured in a central Greenland ice core

冰芯观测的甲烷磺酸（MSA）被用作过去海洋生物生产力的代表，因为MSA仅来自海洋浮游植物排放的二甲基硫化物（DMS）的氧化。使用MSA作为生物源生产力的代理依赖于假设MSA与二氧化硫（SO2）的分支比在DMS氧化过程中保持恒定。然而，近800年来格陵兰冰芯对MSA和生物源硫酸盐的观测表明，MSA与生物源硫酸盐的比值（MSA/bioSO4）并没有保持不变。我们假设MSA最近的趋势是由氧化剂丰度（例如NOx）的变化驱动的，这些变化导致DMS氧化过程中MSA的产率降低而SO2的产率增加。我们建议在格陵兰的Summit钻取覆盖近30年积雪的浅冰芯，测量离子和MSA浓度以及硫酸盐的硫同位素。过去30年将涵盖北美和欧洲的人为氮氧化物排放量开始下降的时间（在20世纪90年代中期之后）。与我们目前记录的从公元1200年到2006年的数据相比，这将增加16年的数据。我们假设，由于北美和欧洲的氮氧化物排放减少，从20世纪90年代中期到现在，MSA/生物so4比率继续增加。为了协助数据解释，我们将利用全球化学运输模型GEOS-Chem来量化不同氧化剂在DMS氧化中的作用，因为这些氧化剂由于人为排放而发生了变化。除了从工业化前存档的冰中选择离散样本外，我们还将以亚季节分辨率测量硫酸盐同位素在过去30年的积雪积累。我们假设，由于北极变暖导致海冰融化提前，DMS排放在今年比工业化前更早达到峰值。自工业化前以来以季节分辨率测量生物源性硫酸盐将使我们能够研究北极气候变化导致的北极生物源性硫气溶胶的季节性变化。这是美国和英国的pi之间的合作项目，该项目的英国部分将由NERC提供支持。

Ice-core observations of methane sulfonic acid (MSA) are used as a proxy for past oceanic biogenic productivity because MSA originates solely from the oxidation of dimethyl sulfide (DMS) emitted by ocean phytoplankton. The use of MSA as a proxy for biogenic productivity relies on the assumption that the branching ratio of production of MSA versus sulfur dioxide (SO2) from DMS oxidation remains constant over time. However, recent Greenland ice-core observations of MSA and biogenic sulfate over the last 800 years show that the ratio of MSA-to-biogenic sulfate (MSA/bioSO4) has not remained constant.We hypothesize that recent trends in MSA are driven by changes in oxidant abundances (e.g., NOx) that lead to a reduced yield of MSA and increased yield of SO2 during oxidation of DMS.We propose to drill shallow ice cores at Summit, Greenland covering the last 30 years of snow accumulation and measure ion and MSA concentrations and sulfur isotopes of sulfate. The last 30 years will cover the time when anthropogenic NOx emissions from North America and Europe began to decline (after the mid-1990s). This will yield an additional 16 years of data compared to our current record extending from 1200 C.E. through 2006.We hypothesize that the MSA/bioSO4 ratio continues to increase from the mid-1990s to the present day due to decreases in NOx emissions in North America and Europe.To assist data interpretation, we will utilize a global chemical transport model GEOS-Chem in order to quantify the role of different oxidants on DMS oxidation as these oxidants have changed due to anthropogenic emissions. We will measure sulfate isotopes at sub-seasonal resolution over the last 30 years of snow accumulation from the proposed shallow ice cores in addition to select, discrete samples from archived ice in the preindustrial.We hypothesize that DMS emissions peak earlier in in the year today than in the preindustrial due to the earlier sea-ice melt resulting from Arctic warming.Measuring biogenic sulfate at seasonal resolution since the preindustrial will allow us to investigate changes in the seasonality of biogenic sulfur aerosol in the Arctic resulting from changes in Arctic climate. This is a collaborative project between PIs in the US and the UK, and the UK part of the project will be supported by NERC.