Composition, age, and provenance of organic matter in NW African dust over the Atlantic Ocean
Composition, age, and provenance of organic matter in NW African dust over the Atlantic Ocean
复制标题
DOI：
10.1029/2001gc000269
复制
发表时间：
2002-08
期刊：
影响因子：
3.7
通讯作者：
T. Eglinton;G. Eglinton;L. Dupont;E. Sholkovitz;D. Montluçon;C. Reddy
中科院分区：
文献类型：
--
作者：
T. Eglinton;G. Eglinton;L. Dupont;E. Sholkovitz;D. Montluçon;C. Reddy
1992/1993年冬、春两季在非洲西北部（18°N，22°W）东北大西洋海域的气象浮标上沉积的风成尘为详细评价其地球化学特征和物源提供了充足的资料。对样品进行显微镜检查和批量、元素、同位素、黑碳和分子（木质素、脂质）分析。大量的元素组成和有机碳（OC）含量（1.02%干重）确定了尘埃的起源为大陆上地壳，是典型的来自西非的尘埃。这些数据雅阁记录撒哈拉和萨赫勒地区尘埃云过境的大量卫星图像（例如，NASA TOMS气溶胶指数）。显微镜检查显示，来自植被火灾的木炭状颗粒（“黑碳”（BC））是最丰富的形态独特的有机成分。加速器质谱（AMS）14 C分析产生了1260 ± 40年的大OC和2070 ± 35年的BC的常规14 C年龄。结合相应的稳定碳同位素组成（δ 13 C，分别为-18.9和-15.1 ‰），这些结果表明存在生物质和燃烧残留物，这些残留物主要来自全新世晚期积累在土壤中的C4植被。分子水平的测量也与这种情况一致。例如，降尘样品中的木质素衍生酚表明被子植物草型组织的重要贡献。木质素性质的改变表明其作为残留物储存在土壤中。溶剂可提取的（脂质）成分包括一个显着的叶蜡型成分的分子和稳定的碳同位素组成类似于在该地区的海洋表层沉积物中观察到的。碳氢化合物部分含有一些柴油型污染物，但正构烷烃（C23-C33）保持显著的奇/偶分布，δ 13 C范围为−26.7至−28.5‰。偶数碳数的正链烷醇（C22-C32）的碳同位素年龄为647 ± 150年，δ 13 C值介于−23.9 ‰至−30.4‰之间。长链正链烷酸（C22-C32）的δ 13 C值范围为−22.6至−27.4‰。这些蜡显然是来自当代C3和C4植被和剥蚀的土壤和干燥的湖泊沉积物中晚全新世的混合信号。这种分子方法显示出作为大陆古环境评估工具的希望，特别是在过去的植被覆盖，区域干旱和风系统。
Eolian dust deposited on a meteorology buoy over the boreal winter and spring of 1992/1993 in the Northeast Atlantic off Northwest Africa (18°N, 22°W) afforded sufficient material for detailed assessment of its biogeochemical characteristics and provenance. The sample was subjected to microscopic examination and bulk, elemental, isotopic, black carbon, and molecular (lignin, lipid) analyses. The bulk elemental composition and organic carbon (OC) content (1.02% dry weight) establishes the dust's origin as continental upper crust and is typical of dusts that emanate from West Africa. These data are in accord with the extensive satellite imagery documenting the transit of dust clouds from the Sahara and Sahel regions (e.g., NASA TOMS aerosol index). Microscopic examination reveals that charcoal‐like particles from vegetation fires (“black carbon” (BC)) are the most abundant morphologically distinct organic components. Accelerator mass spectrometry (AMS) 14C analysis yields conventional 14C ages for bulk OC of 1260 ± 40 years and BC of 2070 ± 35 years. Taken together with corresponding stable carbon isotopic compositions (δ13C, −18.9 and −15.1‰, respectively), these results suggest the presence of biomass and burning residues derived from predominantly C4 vegetation that accumulated in soils over the late Holocene. Molecular‐level measurements are also consistent with this scenario. For example, lignin‐derived phenols in the dustfall sample indicate a significant contribution of angiosperm grass‐type tissue. The altered nature of the lignin suggests storage as residues in soils. Solvent extractable (lipid) constituents include a marked leaf wax type component with a molecular and stable carbon isotopic composition similar to those observed in surface marine sediments in this region. The hydrocarbon fraction contained some diesel‐type contamination but the n‐alkanes (C23–C33) retained a prominent odd/even distribution, with δ13C ranging from −26.7 to −28.5‰. The suite of even carbon numbered n‐alkanols (C22–C32) is 14C dated at 647 ± 150 years, with δ13C values ranging from −23.9 to −30.4‰. The long‐chain n‐alkanoic acids (C22–C32) exhibited δ13C values ranging from −22.6 to −27.4‰. These waxes are evidently a mixed signal derived from contemporary C3 and C4 vegetation and from ablated soils and desiccated lake sediments of middle to late Holocene age. This molecular approach shows promise as a tool for continental paleoenvironmental assessment, particularly with respect to past vegetation cover, regional aridity, and wind systems.