Composition and sources of sedimentary organic matter in the deep Eastern Mediterranean Sea

Abstract

International audienceSurface sediments collected from deep slopes and basins (1018–4087 m depth) of the oligotrophic Eastern Mediterranean Sea have been analysed for bulk elemental and isotopic composition of organic carbon, total nitrogen and selected lipid biomarkers, jointly with grain size distribution and other geochemical proxies. The distribution and sources of sedimentary organic matter (OM) have been subsequently assessed and general environmental variables, such as water depth and currents, have been examined as causative factors of deep-sea sediment characteristics. Lithogenic and biogenic carbonates are the dominant sedimentary fractions, while both bulk and molecular organic tracers reflect a mixed contribution from autochthonous and allochthonous sources for the sedimentary OM, as indicated by relatively degraded marine OM, terrestrial plant waxes and anthropogenic OM including degraded petroleum by-products, respectively. Wide regional variations have been observed amongst the studied proxies, which reflect the multiple factors controlling sedimentation in the deep Eastern Mediterranean Sea. Our findings highlight the role of deep Eastern Mediterranean basins as depocentres of organic-rich fine-grained sediments (mean 5.4 ± 2.4 μm), with OM accumulation and burial due to aggregation mechanisms and hydrodynamic sorting. A multi-proxy approach is hired to investigate the biogeochemical composition of sediment samples, which sheds new light on the sources and transport mechanisms along with the impact of preservation vs. diagenetic processes on the composition of sedimentary OM in the deep basins of the oligotrophic Eastern Mediterranean Sea

Transient hydrodynamic effects influence organic carbon signatures in marine sediments

“…Previous studies indicate alkenones, which are more recalcitrant to oxidation 20 , 26 , 70 , occur in association with sedimentary particles of <6 μm (refs. 71 , 72 ), but less-recalcitrant GDGTs 66 , 69 are associated with sedimentary particles of 6–32 μm (ref. 73 ).…”

Atmospheric and Oceanographic Forcing Impact Particle Flux Composition and Carbon Sequestration in the Eastern Mediterranean Sea: A Three-Year Time-Series Study in the Deep Ierapetra Basin

“…Its seasonal variability is correlated with an average threemonth lag between maximum negative wind stress curl caused by the Etesians and maximum negative current vorticity linked to the anticyclone (Amitai et al, 2010). The Ierapetra anticyclone entraps water masses exiting from the Cretan straits enhancing the downward fluxes/transport of particulate matter and nutrientdepleted waters with important implications on the biogeochemical functioning of the area (Lampadariou et al, 2009;Pedrosa-Pàmies et al, 2015). The Ierapetra anticyclone also presents interannual variability in intensity and positioning.…”

“…Moreover, in order to evaluate the benthic-pelagic linkages in the study area, the time series data of sinking particles flux are being discussed along with the corresponding biogeochemical parameters and lipid compounds/indices data previously reported by Pedrosa-Pàmies et al (2015) for surface sediment samples (undisturbed top 0-1 cm) collected from January 2007 to June 2012 in the NW Levantine Sea (Figure 1, Supplementary Table S1). The sedimentation rate in the deep EMS is in the order of 0.003 cm y −1 (Van Santvoort et al, 1996).…”

“…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).…”

Climate action requires new accounting guidance and governance frameworks to manage carbon in shelf seas

“…However, we still do not know what fraction of the accumulating organic matter, herewith termed as particulate organic carbon (POC), is derived from each of the potential sources listed above. Wide regional variations in the composition of the accumulating sediment are to be expected due to multiple and divergent organic matter sources [3][4][5] . Information is lacking also on the amount of organic carbon produced that becomes ultimately buried in shelf sea sediments.…”