Relationship of Mn-carbonates in varved lake-sediments to catchment vegetation in Big Watab Lake, MN, USA
Relationship of Mn-carbonates in varved lake-sediments to catchment vegetation in Big Watab Lake, MN, USA
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DOI：
10.1023/a:1008169526577
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发表时间：
2000
影响因子：
2.1
通讯作者：
Lora R. Stevens;E. Ito;D. Olson
中科院分区：
文献类型：
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作者：
Lora R. Stevens;E. Ito;D. Olson
在美国明尼苏达州大瓦塔布湖的晚冰期各种沉积物中发现了锰碳酸盐。碳酸锰是自生的，并在同时代的外延磁方解石周围形成边缘。尽管这种碳酸盐在整个晚冰期序列中都有少量发现，但相当数量的碳酸锰主要与层状间隔有关。由于不同碳酸盐矿物之间可能存在同位素分馏的差异，大量碳酸盐样品的稳定同位素组成被用来代替沉积物中碳酸锰的相对含量。高δ~(18)O和低δ~(13)C值与富含锰碳酸盐有关。低δ~(18)O和高δ~(13)C值只与少量的锰碳酸盐有关。氧-18记录与基于花粉光谱的植被组合的波动相关，采用反向消去法建立多元回归模型。沉积档案与当地植被之间的联系被认为是森林成分在湖泊平流混合中的中介作用。在该模型中，森林封育期导致沉积物/水界面的分层良好的水柱缺氧，从而允许自生碳酸锰的形成。森林中的卤虫洞口允许风切变将氧气混合到深处，导致纹层的生物扰动，防止碳酸锰的形成。
Mn-carbonates are documented in the late-glacial varved sediments from Big Watab Lake, Minnesota, USA. The Mn-carbonate is authigenic and forms rims around contemporaneous epilimnetic calcite. Although such carbonates are found in minor amounts throughout the entire late-glacial sequence, significant quantities of Mn-carbonate are associated mainly with laminated intervals.Because of the suspected difference in isotopic fractionation between different carbonate minerals, the stable-isotopic compositions of bulk carbonate samples are used as a proxy for relative amounts of the Mn-carbonate in the sediment. High δ18O and low δ13C values are associated with abundant Mn-carbonates. Low δ18O and high δ13C values are associated with only minor concentrations of Mn-carbonates.The oxygen-18 record is correlated with fluctuations in the vegetation assemblage based on pollen spectra using a multiple regression model with backward elimination. The proposed link between the sedimentary archive and local vegetation is the mediation of advective mixing in the lake by forest composition. In this model, periods of forest closure resulted in a well-stratified water column that was anoxic at the sediment/water interface, permitting the formation of authigenic Mn-carbonates. Openings ofArtemisiain the forest allowed wind shear to mix oxygen to depth, causing bioturbation of the laminations and preventing the formation of Mn-carbonate.