阿塔卡马海沟深渊和非深渊站位的沉积脂肪酸对比研究

COMPARISON OF FATTY ACIDS IN SEDIMENTS FROM HADAL AND NON-HADAL SITES OF THE ATACAMA TRENCH

深渊海沟作为海洋的最深处,是最不被人了解的地球生态环境之一。有机质的输入、含量和活性对于维持深渊生态系统和深渊生物地球化学循环至关重要。本文利用脂肪酸生物标志物方法,研究了来自阿塔卡马海沟的4个沉积物柱状样(长度为15—35 cm),比较了水深2560—7770 m的深渊(A5,A10)和非深渊(A1,A9)站位的脂肪酸含量、来源和保存状况。本研究共检测到50种脂肪酸化合物,包括来自陆源有机质的长链饱和脂肪酸,来自海源浮游植物的短链饱和脂肪酸、单不饱和脂肪酸和多不饱和脂肪酸,以及来自细菌的甲基支链脂肪酸。总脂肪酸的平均含量在非深渊站位A1最高[(13.4±2.9)μg/g dws],而深渊站位A5最低[(5.4±2.2)μg/g dws],这可能与各站位的初级生产力和水深有关。在所有站位中,海源脂肪酸均处于主导地位(61.6%±9.2%),其比例显著高于陆源脂肪酸(33.6%±10.7%)和细菌脂肪酸(4.9%±2.3%),表明在阿塔卡马海沟沉积物中脂肪酸主要是海源有机质的贡献。在每个站位,随着沉积物深度的增大,陆源脂肪酸的比例均明显增加,而海源脂肪酸的比例则减少,该结果与脂肪酸指数FA-Index的结果一致,表明短链脂肪酸和不饱和脂肪酸相比于长链饱和脂肪酸更易被降解。最后,非深渊站位的脂肪酸含量随着深度的增加表现出明显的降低,展现出稳定沉积环境中典型的有机质成岩作用,而深渊站位的脂肪酸含量尽管出现波动,但随深度无明显的下降趋势,这可能归结于地震、浊流作用下形成的不稳定沉积环境,有助于有机质从非深渊区向深渊区的快速输入和埋藏。

The hadal trenches,as the deepest ocean realm,are one of the least explored habitats on the Earth.The input,abundance and bioavailability of organic matter play a key role in sustaining hadal ecosystem and hadal biogeochemical cycle.In this study,fatty acid(FA)biomarkers were used to investigate four sediment cores(15—35 cm long)from the Atacama Trench region(2560—7770 m)water depth),and FA concentration,source and distribution between hadal sites(A5,A10)and non-hadal sites(A1,A9)were compared.A total of 50 FA compounds were identified,including terrestrially derived long chain saturated FAs,marine plankton derived short chain saturated FAs,monounsaturated FAs and polyunsaturated FAs,and bacteria derived branched FAs.The concentration of total FAs was the highest at the non-hadal site A1[(13.4±2.9)μg/g dws],and the lowest at the hadal site A5[(5.4±2.2)μg/g dws],which was likely related to primary productivity and water depth at each site.The fractional abundance of marine derived FAs(61.6%±9.2%)is higher than that of terrestrial FAs(33.6%±10.7%)and bacterial FAs(4.9%±2.3%)at all sites,suggesting the predominance of marine organic carbon in the Atacama Trench region.In addition,downward profiles were shown with an increasing trend of terrestrial FAs at the expense of marine derived FAs in all cores,suggesting the selected degradation of short chain and unsaturated FAs from long chain and saturated FAs.In addition,the concentrations of total FAs at the non-hadal sites substantially decrease with increasing sediment depth,presenting a typical early diagenesis of organic matter under steady depositional conditions.However,such a trend was not observed at the hadal sites,suggesting that disturbed depositional conditions were likely due to earthquake-induced turbidity current that contributed to efficient transport of organic carbon from non-hadal to hadal environments and burial in the deepest ocean.