The branched glycerol dialkyl glycerol tetraethers (brGDGTs) can be produced in situ under methanotrophic/hypoxic conditions in lakes. However, the effect of dynamic methanotrophic activities in the widely-distributed seafloor methane seeps on brGDGTs distributions in global continent margins remains enigmatic. In this study, we firstly report the occurrence of in situ produced brGDGTs in cold seep environments, based on the analysis of tetraether lipid distributions in the authigenic carbonates collected from the northern section of the Okinawa Trough (OT). The abundance ratio of isoGDGTs to brGDGTs (R_i/b) was much lower in the authigenic carbonates (0.94 to 2.25) than in the adjacent normal marine sediments (>10) and suspended particulate matter (>60) in the East China Sea (ECS). Such significant higher bacterial branched GDGTs ratios in the authigenic carbonates indicate its additional sources besides terrestrial and/or water column inputs. Specifically, the brGDGT (Ia), brGDGT (IIa) and brGDGT (IIa’) appear to form in situ in cold seeps, and are influenced by the methane flux significantly as indicated by the fractional abundances of GDGTs along the transect of pipes, network analysis, and correlations between Methane Index (MI) and brGDGTs. Our study highlights that the distributions of seafloor methane seeps could impact the bacterial tetraether lipid distributions in ocean, which would hamper the universal application of brGDGT-based proxies for terrigenous organic carbon tracing and paleoclimate reconstruction in marine environments.

支链甘油二烷基甘油四醚（brGDGTs）可以在甲烷的富营养/低氧条件下原位产生。但是，在分布广泛的海底甲烷渗漏中动态甲烷营养活动对全球大陆边缘brGDGTs分布的影响仍然是未知的。在这项研究中，我们首先分析了从冲绳海槽（OT）北部收集的自生碳酸盐中的四醚脂质分布，分析了在冷渗流环境中原位产生的brGDGT的发生。isoGDGT与brGDGT的丰度比（R _{i / b}自生碳酸盐（0.94至2.25）比东海（ECS）相邻的正常海洋沉积物（> 10）和悬浮颗粒物（> 60）低得多。自生碳酸盐中如此显着较高的细菌支链GDGTs比值表明，除了陆地和/或水柱输入之外，它还具有其他来源。具体而言，brGDGT（Ia），brGDGT（IIa）和brGDGT（IIa'）似乎是原位形成的GDGTs沿管道横断面的分数丰度，网络分析以及甲烷指数（MI）和brGDGTs之间的相关性表明，甲烷在冷渗流中受到甲烷通量的影响很大。我们的研究强调，海底甲烷渗漏的分布可能会影响海洋中细菌四醚脂质的分布，这会阻碍基于brGDGT的代理在海洋环境中进行陆源有机碳追踪和古气候重建的普遍应用。