Sterenes in suspended particulate matter in the eastern tropical North Pacific

Abstract

Particulate matter in the oceans is operationally partitioned into two pools. Large (≳ 32 µm) particles, such as zooplankton faecal pellets and marine snow, sink rapidly and dominate the vertical flux of organic matter in the oceans1–4. These relatively rare particles, usually collected in sediment traps, sink at rates of tens to hundreds of metres per day5–8 leading to a significant flux of labile particulate organic matter from sites of production in the euphotic and mesopelagic zones to the deep ocean9–14. Finer (≲ 2 µm) suspended material, on the other hand, dominates the standing stock of particulate matter1. Sinking rates of only a few metres per day for small particles result in long residence times in the water column during which major transformations of the suspended organic matter may occur. Source and transformation processes involving particulate organic matter in seawater and Recent sediments may be traced by studying various classes of specific organic marker compounds, including the steroids9,11,15–18. We report here the apparent production of sterenes (steroidal alkenes) on suspended particulate matter within the oxygen minimum zone in the equatorial Pacific Ocean off central Mexico; this provides further evidence of the importance of water column processes on early stages of the transformation of biogenic sterols to the steranes present in mature sediments.