Dynamic variability of dissolved Pb and Pb isotope composition from the US North Atlantic GEOTRACES transect
Dynamic variability of dissolved Pb and Pb isotope composition from the US North Atlantic GEOTRACES transect
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DOI：
10.1016/j.dsr2.2014.11.011
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发表时间：
2015-06-01
影响因子：
3
通讯作者：
Smethie, William
中科院分区：
文献类型：
--
作者：
Noble, Abigail E.;Echegoyen-Sanz, Yolanda;Smethie, William
本文研究了美国北大西洋样带GEOTRACES GA03的溶解铅浓度和同位素组成分布。海洋中的铅主要来自人为来源，在1975年至1995年期间北美和欧洲逐步停止使用烷基铅汽油之后，流入北大西洋的铅通量一直在稳步减少。对近30年反复观测的3个站点的溶解Pb剖面的汇编显示，尽管在北大西洋环流中心的通风时间尺度比西部边界长，但仍观察到浓度高于60 pmol/kg的升高，但表层和热模态的浓度急剧下降。这些监测站的稳定铅同位素的演变表明，20世纪80年代初地表水中主要的类似北美的成分在后来几年转向了更类似欧洲的成分。百慕大大西洋时间序列站（BATS）最近的浅层特征显示，在欧洲完全淘汰含铅汽油后，铅-206/铅-207比率出现了更高的趋势，这可能是因为最近沉积的铅受工业和焚烧铅的影响比对残余烷基含铅汽油的影响更大。在地表水中，在盆地中部和欧洲海岸也发现了欧洲影响更突出的趋势，与地表溶解铅浓度较高相一致。在TAG热液柱中观察到人为Pb的清除，但尚不清楚热液流体浸出的玄武岩Pb是否对深水有重大贡献。在上层水柱中，沿样带的许多站点显示Pb浓度在100 m深度处达到最大值，与典型的欧洲排放源的低Pb-206/Pb-207同位素特征相一致。虽然美国的Pb矿石历史上倾向于携带Pb-206/Pb-207特征> 1.17 (Hurst, 2002)，但在该特征中观测到的地下特征低至1.1563 in (206) Pb /(207) Pb。这一特征似乎在咸水亚热带水下（STUW）中向西传播，从北大西洋副热带环流中东部通风，在那里观察到最低的地表同位素Pb-206/Pb-207比率。在西部边界，不同年龄的深水团具有不同的同位素比值，对应于它们各自的通气时间。最后，东缘底部水的低Pb-206/Pb-207特征表明，可能有一些来自欧洲的人为铅从最近的海底表面沉积物中被动员起来。(C) 2014 Elsevier Ltd.版权所有。
This study presents dissolved Pb concentration and isotopic composition distributions from GEOTRACES GA03, the U.S. North Atlantic Transect. Pb in the ocean is primarily derived from anthropogenic sources and Pb fluxes into the North Atlantic Ocean have been steadily decreasing following the phase-out of alkyl leaded gasoline usage in North America and Europe between 1975 and 1995. A compilation of dissolved Pb profiles from three stations occupied repeatedly during the last three decades reveals a dramatic decrease in concentrations within the surface layers and the thermodine maxima, although elevated concentrations greater than 60 pmol/kg are still observed in the center of the North Atlantic gyre where ventilation timescales are longer than at the western boundary. The evolution of stable Pb isotopes at these stations shows a shift from dominantly North American-like composition in surface waters in the early 1980s towards a more European-like composition in later years. The most recent shallow signatures at the Bermuda Atlantic Time Series station (BATS) show an even more recent trend returning to higher Pb-206/Pb-207 ratios after the completed phase-out of leaded gasoline in Europe, presumably because recently deposited Pb is more strongly influenced by industrial and incineration Pb than by residual alkyl leaded gasoline utilization. In surface waters, trends toward a more prominent European influence are also found in the middle of the basin and toward the European coast, coincident with higher concentrations of surface dissolved Pb. Scavenging of anthropogenic Pb is observed within the TAG hydrothermal plume, and it is unclear if there is any significant contribution to deep water by basaltic Pb leached by hydrothermal fluids. In the upper water column, many stations along the transect show Pb concentration maxima at 100 m depth, coincident with a low Pb-206/Pb-207 isotopic signature that is typical of European emission sources. Although Pb ores from the United States historically tend to carry Pb-206/Pb-207 signatures > 1.17 (Hurst, 2002), subsurface signatures as low as 1.1563 in (206)pb/(207)pb were observed in this feature. This signature appears to be carried westward within saline Subtropical Underwater (STUW), that ventilates from the Central Eastern part of the North Atlantic Subtropical Gyre where the lowest surface isotope Pb-206/Pb-207 ratios are observed. Along the western boundary, deep water masses of different ages carry distinct isotope ratios corresponding to their respective times of ventilation. Finally, a low Pb-206/Pb-207 signature in bottom water along the Eastern margin suggests that there may be some mobilization of European-derived anthropogenic Pb from recent surface deposits on the ocean floor. (C) 2014 Elsevier Ltd. All rights reserved.