长江口及邻近海域沉积物中四醚脂类的来源及其对底层溶解氧指示作用探究

Source of tetraether lipids in sediments of the ChangjiangRiver Estuary and adjacent sea: Indication of bottom waterdissolved oxygen

甘油二烷基甘油四醚(glycerol dialkyl glycerol tetraethers,GDGTs)作为一种重要的膜脂化合物,广泛存在于海洋水体和沉积物中。基于GDGTs对温度的敏感性,TEX86(TetraEther indeX of tetraethers consisting of 86 carbons)指标被广泛用于海洋古温度重建。然而,研究表明GDGTs母源生物古菌也会受到环境中溶解氧(DO)变化的影响,进而影响其膜脂组成,但边缘海DO对GDGTs组成的影响仍不清楚。本文研究了夏季长江口及其邻近海域颗粒物与表层沉积物中GDGTs的含量与组成,探讨了表层沉积物中GDGTs的来源及其组成对底层DO的响应。结果表明,长江口及其邻近海域颗粒物GDGTs的含量随水深的增加而增加,同时表层沉积物中的GDGT-2/GDGT-3和GDGT-0/Cren比值均与底层颗粒物相近,表明沉积物中GDGTs主要来源于底层颗粒物的沉降输入。进一步对受陆源有机质输入影响较小的站位研究发现有机质来源BIT(Branched and Isoprenoid Tetractter)指标<0.2。研究发现,随着底层DO的降低,表层沉积物中GDGT-0/Cren比值与底层DO具有较好的正相关性(R2=0.57,P<0.01),提示GDGT-0/Cren具有指示夏季长江口及邻近海域底层DO变化的潜力。未来还需结合颗粒物与表层沉积物中古菌生物群落和完整极性GDGTs的分析,进一步阐明GDGTs指示DO的机制及适用性。

Glycerol dialkyl glycerol tetraethers(GDGTs),membrane lipids of archaea and certain bacteria,are widely distributed in marine water columns and sediments.Due to the temperature sensitivity of GDGTs,TEX86(TetraEther indeX of tetraethers comprising 86 carbons)is widely used in marine paleotemperature reconstruction.However,some evidences suggest that dissolved oxygen(DO)could also play an important role in determining GDGTs distributions in cultured archaeal strains,but how GDGTs composition in marginal sea surface sediments respond to DO levels has remained unclear.The composition of GDGTs both in particulate matters and surface sediments in the Changjiang River Estuary and adjacent sea area in summer were investigated in this study,to identify the source of GDGTs in sediments and trace the responses of sedimentary GDGTs to bottom DO.This result showed that concentration of GDGTs in particulate matters increased with depth,and both the ratios of GDGT-2/GDGT-3 and GDGT-0/Cren in particulate matters of bottom layer were similar with those in surface sediments,suggesting that the main source of sedimentary GDGTs are from the deposition of bottom particulate matter.Further studies found that after excluding stations that were heavily affected by terrestrial factors(BIT>0.2,the relative abundance of branched GDGTs and crenarchaeol),the relationships between GDGT-0/Cren and bottom DO(R2=0.57,P<0.01)showed significant positive correlation.This result suggests that GDGT-0/Cren can be potentially used to indicate the changes of bottom DO in the studied area.Further studies should be conducted by combining analysis of archaea communities with intact polar GDGTs to elucidate the driving mechanisms and applicability of GDGTs for DO indicating.