“…Bulk geochemical proxies, such as the stable isotopic composition of organic carbon (δ 13 C), and lipid biomarkers have been widely used as indices of sources and transformation processes of organic matter in marine systems (Meyers, 1994;Wakeham, 1995;Volkman and Tanoue, 2002;Goñi et al, 2003;Hu et al, 2006;Pedrosa-Pàmies et al, 2013;Quirós-Collazos et al, 2017), as well as to assess the biogeochemical dynamics controlling the export of POC to the deep sea (Goutx et al, 2000;Wakeham et al, 2002;Conte et al, 2003;Pedrosa-Pàmies et al, 2018De Bar et al, 2019). While there have been several investigations on the δ 13 C signature of sinking particles in the Mediterranean Sea (Kerhervé et al, 2001;Turchetto et al, 2012;Pasqual et al, 2015;Theodosi et al, 2019) but also on the molecular composition of POC particulate fluxes in the western Mediterranean Sea, both in the upper mesopelagic layers (100-300 m depth) (e.g., Tolosa et al, 2005;Goutx et al, 2007;Marty et al, 2009;Méjanelle and Dachs, 2009) and the deep sea (Marchand et al, 2005;Wakeham et al, 2009), little is known about the POC molecular composition of the EMS particle fluxes (Tsapakis et al, 2006;Theodosi et al, 2013) and deep-sea floor (Gogou and Stephanou, 2004;Parinos et al, 2013a;Pedrosa-Pàmies et al, 2015).…”