Source, settling and degradation of branched glycerol dialkyl glycerol tetraethers in the marine water column
Source, settling and degradation of branched glycerol dialkyl glycerol tetraethers in the marine water column
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DOI：
10.1016/j.gca.2016.07.014
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发表时间：
2016-10
影响因子：
5
通讯作者：
Masanobu Yamamoto;A. Shimamoto;T. Fukuhara;Yuichiro Tanaka
中科院分区：
文献类型：
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作者：
Masanobu Yamamoto;A. Shimamoto;T. Fukuhara;Yuichiro Tanaka
支链甘油二烷基甘油四醚（支链GDGT）通常存在于远源海洋沉积物中。然而，它们在水体中的存在、来源和输送过程尚不完全清楚。1997年11月至1999年8月，在39°N，147°E的西北太平洋中纬度海域，研究了分支GDGT沉降颗粒和下垫面沉积物中的通量的季节和深度变化。它们的环化和甲基化程度几乎是恒定的，与碱性土壤的环化和甲基化程度有一定的相似性。这表明，西风运输分支GDGT通过大气从亚洲大陆的研究地点。1999年分支GDGT的下沉通量高于1998年，这可能反映了亚洲沙尘响应厄尔尼诺-南方涛动的迁移路径的变化。不同深度分支GDGT浓度的同步变化意味着分支GDGT快速垂直输送到深水，下沉速度超过260 m d−1。分支GDGT的下沉通量随深度的增加而减小，但减小的速率远小于其他化合物。在水-沉积物界面上，支链GDGT的保存效率为3.5-6.4%，远高于类异戊二烯GDGT和其他化合物的保存效率（1.0-1.3%）。支化和类异戊二烯四醚（BIT）指数值与迄今为止的任何其他研究相比非常低（即<0.0015）。BIT值在表层沉积物中的5倍高于那些在下沉颗粒，这是由于优先保存的分支GDGT在好氧环境。
Branched glycerol dialkyl glycerol tetraethers (branched GDGTs) are commonly found in distal marine sediments. However, their presence in the water column, source and delivery process are not fully understood. In this study, we examined seasonal and depth variation in the flux of branched GDGTs in sinking particles and underlying sediment at 39°N, 147°E in the mid-latitude NW Pacific from November 1997 to August 1999.Branched GDGTs showed synchronous variation in their sinking flux at different depths, and the variation was similar to that of lithogenic material of eolian dust origin. Their degrees of cyclization and methylation were nearly constant and bear some resemblance to those of alkaline soils. This suggests that westerly winds transport branched GDGTs to the study site via the atmosphere from continental Asia. The sinking flux of branched GDGTs was higher in 1999 than in 1998, presumably reflecting changes in the migration path of Asian dust in response to the El Niño-Southern Oscillation.Synchronous variation in branched GDGT concentrations at different depths implies rapid vertical transport of branched GDGTs to deep water with a sinking velocity exceeding 260 m d−1. The sinking flux of the branched GDGTs decreased with increasing depth, but the rate of decrease was much smaller than those of other compounds. The preservation efficiency of branched GDGTs was 3.5–6.4% of surface inputs at the water–sediment interface, which is much higher than those of isoprenoid GDGTs (1.0–1.3%) and other compounds. The branched and isoprenoid tetraether (BIT) index values were extremely low (i.e. <0.0015) in comparison with any other studies so far. The BIT values in the surface sediment were five times higher than those in sinking particles, which is attributed to the preferential preservation of branched GDGTs in oxic environments.