Distribution of glycerol ether lipids in the oxygen minimum zone of the Eastern Tropical North Pacific Ocean

The distributions of microbial glycerol ether lipids in suspended particulate matter in the oxygen minimum zone (OMZ) of the Eastern Tropical North Pacific Ocean (ETNP) were investigated. Nine groups of glycerol ether core lipids were detected and quantified: isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) (iso-GDGTs), isoprenoid glycerol dialkanol diethers (iso-GDDs) and hydroxylated isoprenoid GDGTs and GDDs (OH-GDGTs and OH-GDDs) of archaeal origin; branched glycerol dialkyl glycerol tetraethers (br-GDGTs) of bacterial origin and overly branched GDGTs (OB-GDGTs), sparsely branched GDGTs (SB-GDGTs), hybrid isoprenoid/branched GDGTs (IB-GDGTs) and a tentatively assigned H-shaped GDGT (H-1020) of unknown biological origin. The archaeal iso-GDGTs were the most abundant core lipids (89% of total), followed by iso-GDDs (4%), br-GDGTs (2%) and OH-GDGTs (1%). Archaeal intact polar GDGTs (IP GDGTs), including both mono- and diglycosidic iso-GDGTs, had depth profiles similar to OH-GDGTs and OH-GDDs, with a maximum concentration in the upper OMZ and secondary peaks in the mid and lower OMZ, suggesting similar but multiple planktonic sources. Core lipids of iso-GDGTs and other glycerol ethers showed deviating concentration profiles compared with IP GDGTs and OH-GDGTs and were most abundant in the mid OMZ. This is the first report of OH-GDDs, OB-GDGTs, SB-GDGTs, IB-GDGTs and H-1020 in the marine water column and the distribution patterns of these “orphan lipids” suggest that anaerobic planktonic microbes are their main source.