Diverse origins of "soil marker" bacteriohopanepolyols in marine oxygen deficient zones

Bacteriohopanepolyols (BHPs) that are commonly associated with soil and peat environments ("soil marker" BHPs), were analyzed along redox gradients in marine oxygen deficient zones (ODZs). The latter included suspended particulate organic matter (POM) from two fjords on Vancouver Island (Canada) and the Black Sea, as well as sinking POM collected in sediment trap time-series deployed in the Cariaco Basin. Our results show that the so-called "soil marker" BHPs occur in all ODZ settings. They have distributions that are best explained by in situ chemotrophic production within the chemocline and in anoxic/ euxinic waters, rather than exclusive supply from soils. In particular, adenosylhopane, adenosylhopanetype 2 and 2Me-adenosylhopane-type 2, appear to be produced within a common biogeochemical niche in the water column, irrespective of setting. On the other hand, 2Me-adenosylhopane, adenosylhopanetype 3 and 2Me-adenosylhopane-type 3 may be supplied partly from the continent, as they are also abundant in surface water suspended POM on Vancouver Island and accumulate almost exclusively in the shallower (upper chemocline) trap in the Cariaco Basin. However, their water column suspended POM distributions and time-series sinking POM fluxes also indicate additional chemotrophic sources that have spatially and temporally diverse origins. Our study suggests that caution is warranted when using "soil marker" BHPs and their associated soil input proxies in ODZ settings, as the diverse microbial community in these settings produces BHP signatures similar to those found in soils. (C) 2020 Elsevier Ltd. All rights reserved.