An assessment of variability in the influx of cosmic dust during the Holocene and the potential effect on iron concentrations in the Southern Ocean.

Metadata record for data from AAS (ASAC) project 3132.Public This research will determine variability in the influx and mineralogy of cosmic dust to the Southern Ocean during the Holocene from peat bog cores. Cosmic dust contains significant quantities of soluble iron, a micronutrient required for photosynthesis. Therefore, variations in the deposition of cosmic dust could significantly affect primary production in the Southern Ocean. This may also play an important role in global climate due to its influence on carbon dioxide draw-down from, and emission of volatile sulphur compounds to, the atmosphere.The download file contain a csv spreadsheet of carbon dating from geochemical peat cores collected from Green Gorge on Macquarie Island.Project objectives:This project will sample peat bogs on Macquarie Island to:1. Quantify and develop a high-temporal resolution record of the variability in cosmic dust deposition during the Holocene;2. Determine the mineralogy and quantify the solubility of iron contained in the cosmic dust;Iron is a micronutrient required for photosynthetic reactions within chloroplasts. Martin [1990] proposed that many oceanic phytoplankton, especially those in the high nutrient - low chlorophyll (HNLC) regions of the world's oceans (such as the Southern Ocean) were limited by the availability of iron. Martin et al. [1991] demonstrated that nanomolar increases in dissolved iron stimulated phytoplankton blooms in the North and Equatorial Pacific and Southern Oceans. Several large-scale field experiments (see de Baar et al [2005] for a summary) demonstrated that the addition of iron stimulated phytoplankton productivity significantly. Eleven further experiments have confirmed these results in many other regions [Boyd, et al., 2007] and models of the cellular processes by which iron fertilisation stimulates phytoplankton blooms are now available [Fasham, et al., 2006]. The response of phytoplankton to iron fertilisation has attracted much research effort because phytoplankton blooms increase the draw-down of carbon from the atmosphere and ultimately export a fraction to the deep ocean where it is stored as particulate organic carbon [Watson, et al., 2000] and hence may play an important role in climate.Cosmic and terrestrial dust can both contain significant quantities of soluble, bio-available iron [Fung, et al., 2000; Plane, 2003]. The potential for iron contained in aeolian terrestrial dust to affect climate was recently assessed by Kohfeld et al. [2005], who concluded that dust-induced iron-fertilisation of ocean ecosystems might account for 30 - 50 ppm of atmospheric CO2 draw-down during the last glacial period. Satellite data provide support for these hypotheses at the regional scales at which terrestrial dust deposition events occur [Cropp, et al., 2003; Gabric, et al., 2002]. The influx of cosmic dust to the oceans could be significantly different to terrestrial dust inputs as it is likely to be uniformly distributed around the globe [Johnson, 2001], vary on longer time scales (although this is not well understood [Winckler and Fischer, 2006]), and is expected to be of finer particle-size and contrasting mineralogy [Plane, 2003].Ice cores provide excellent long-term records of terrestrial and cosmic dust deposition, however, cores from ombrotrophic peat bogs, that receive their inputs exclusively from the atmosphere, can provide high temporal resolution records of cosmic and terrestrial dust during the Holocene [Cortizas and Gayoso, 2002]. Data from ice cores in Greenland and ocean sediment cores in the tropical Pacific have revealed variations in cosmic dust influx between glacial and inter-glacial periods, with increases in cosmic dust influx associated with cooler temperatures [Dalai, et al., 2006; Gabrielli, et al., 2004; Karner, et al., 2003]. Johnson [2001] calculated that the current background cosmic dust deposition of about 40,000 tonnes per annum delivered 30-300% of the aeolian iron flux due to terrestrial dust and about 20% of the upwelled iron flux in the Southern Ocean. Ombrotrophic peatlands, such as those found on Macquarie Island, which receive inputs of material solely from the atmosphere, provide especially useful records of cosmic dust deposition over the Holocene.Taken from the 2009-2010 Progress Report:Progress against objectives:Peat core samples were collected on Macquarie Island in April 2010. These samples will be analysed over the coming year.

本数据集为AAS (ASAC) 3132号公开项目的元数据记录。本研究将通过泥炭沼泽岩芯，解析全新世时期沉降至南大洋的宇宙尘埃的通量变化与矿物学特征。宇宙尘埃中含有大量可溶性铁——一种光合作用所需的微量营养素，因此宇宙尘埃沉降的变化可能显著影响南大洋的初级生产力。这一过程还可能通过影响大气二氧化碳吸收与挥发性硫化物排放，对全球气候产生重要作用。
本次提供的下载文件包含一份CSV电子表格，数据取自麦夸里岛绿谷（Green Gorge）采集的地球化学泥炭岩芯的放射性碳定年结果。

项目目标：
本项目将对麦夸里岛的泥炭沼泽开展取样工作，以实现以下目标：
1. 量化并建立全新世时期宇宙尘埃沉降变化的高时间分辨率记录；
2. 测定宇宙尘埃的矿物学特征，并量化其中铁的可溶性。

铁是叶绿体中光合反应所需的微量营养素。马丁（Martin）[1990]提出，全球海洋中诸多浮游植物，尤其是南大洋等高营养盐低叶绿素（HNLC, high nutrient - low chlorophyll）区域的浮游植物，其生长受铁可用性的限制。马丁等人（Martin et al.）[1991]证实，溶解态铁的纳摩尔级浓度提升即可刺激北太平洋、赤道太平洋与南大洋的浮游植物水华爆发。多项大型现场实验（详见德巴尔等人[de Baar et al., 2005]的综述）表明，添加铁可显著提升浮游植物生产力。另有11项后续实验在全球诸多区域验证了这一结论[Boyd et al., 2007]，而阐释铁施肥如何促进浮游植物水华的细胞过程模型也已问世[Fasham et al., 2006]。浮游植物对铁施肥的响应受到广泛研究关注，原因在于浮游植物水华可提升大气碳吸收量，并最终将部分碳以颗粒有机碳的形式封存至深海[Watson et al., 2000]，因此这一过程可能对气候发挥重要作用。

宇宙尘埃与陆源尘埃均含有大量可溶性、可被生物利用的铁[Fung et al., 2000; Plane, 2003]。科菲尔德等人（Kohfeld et al.）[2005]近期评估了风成陆源尘埃中铁对气候的潜在影响，其结论认为，尘埃诱导的海洋生态系统铁施肥效应，可能解释末次冰期大气二氧化碳浓度下降30~50 ppm的现象。卫星数据在陆源尘埃沉降发生的区域尺度上为这一假说提供了支持[Cropp et al., 2003; Gabric et al., 2002]。宇宙尘埃向海洋的沉降通量可能与陆源尘埃存在显著差异：宇宙尘埃在全球的分布更均匀[Johnson, 2001]，其变化的时间尺度更长（尽管相关机制尚未完全明晰[Winckler and Fischer, 2006]），且预期具有更细的粒径与不同的矿物学特征[Plane, 2003]。

冰芯可提供优质的陆源与宇宙尘埃沉降长期记录，但仅接收大气沉降物的贫营养泥炭沼泽（ombrotrophic peat bogs）岩芯，则可提供全新世时期宇宙尘埃与陆源尘埃沉降的高时间分辨率记录[Cortizas and Gayoso, 2002]。格陵兰冰芯与热带太平洋海洋沉积岩芯的数据显示，冰期与间冰期的宇宙尘埃通量存在差异，宇宙尘埃通量的提升与气温降低相关[Dalai et al., 2006; Gabrielli et al., 2004; Karner et al., 2003]。约翰逊（Johnson）[2001]测算得出，当前宇宙尘埃的背景沉降通量约为每年4万吨，其贡献的铁通量相当于陆源风成铁通量的30%~300%，约占南大洋上升流铁通量的20%。仅接收大气沉降物的泥炭地（如麦夸里岛的泥炭地），可为全新世时期的宇宙尘埃沉降提供极具价值的记录。

摘录自2009-2010年度进展报告：
目标完成进度：2010年4月，研究团队已在麦夸里岛采集泥炭岩芯样本。相关分析工作将在未来一年内完成。