Abstract
Abstract. The bioavailability of organic matter in benthic deep-sea ecosystems, commonly used to define their trophic state, can greatly influence key ecological processes such as biomass production and nutrient cycling. Here, we assess the trophic state of deep-sea sediments from open slopes and canyons of the Catalan (NW Mediterranean) and Portuguese (NE Atlantic) continental margins, offshore east and west Iberia, respectively, by using a biomimetic approach based on enzymatic digestion of protein and carbohydrate pools. Patterns of sediment trophic state were analyzed in relation to increasing water depth, including repeated samplings over a 3 yr period in the Catalan margin. Two out of the three sampling periods occurred a few months after dense shelf water cascading events. The benthic deep-sea ecosystems investigated in this study were characterized by high amounts of bioavailable organic matter when compared to other deep-sea sediments. Bioavailable organic matter and its nutritional value were significantly higher in the Portuguese margin than in the Catalan margin, thus reflecting differences in primary productivity of surface waters reported for the two regions. Similarly, sediments of the Catalan margin were characterized by significantly higher food quantity and quality in spring, when the phytoplankton bloom occurs in surface waters, than in summer and autumn. Differences in the benthic trophic state of canyons against open slopes were more evident in the Portuguese than in the Catalan margin. In both continental margins, bioavailable organic C concentrations did not vary or increase with increasing water depth. Overall, our findings suggest that the intensity of primary production processes along with the lateral transfer of organic particles, even amplified by episodic events, can have a role in controlling the quantity and distribution of bioavailable organic detritus and its nutritional value along these continental margin ecosystems.
Highlights
Ocean ScienceContinental margins play a key role in the carbon budget and nutrient cycling on a global scale (Liu et al, 2010) and represent hot spots of biomass production and biodiversity (Rex et al, 2006; Danovaro et al, 2010; De Leo et al, 2010; McClain and Barry 2010)
Recent studies conducted on the Catalan margin reported that Cap de Creus canyon represents a preferential pathway of particle transport for the entire Gulf of Lion (Palanques et al, 2006) and that dense shelf water cascading (DSWC) events occurring during winter periods represent one of the main mechanisms of sediment export towards deeper waters (Canals et al, 2006; Sanchez-Vidal et al, 2008; Palanques et al, 2012)
No significant differences in hydrolyzed protein concentrations (HPRT) concentrations were generally observed between sediments of Cap de Creus canyon and those in the adjacent open slope (Table S2)
Summary
Continental margins play a key role in the carbon budget and nutrient cycling on a global scale (Liu et al, 2010) and represent hot spots of biomass production and biodiversity (Rex et al, 2006; Danovaro et al, 2010; De Leo et al, 2010; McClain and Barry 2010) They can reSproesleidnt eEithaerrtahsink for particulate matter of autochthonous origin (i.e. derived from biological productivity of surface waters and/or exported from the land), or a source of organic material fueling the deep ocean’s interior by lateral transport (Buscail and Germain, 1997; et al., 2B0a0u8e;rSaanndcDherzu-TfVfehildea1l9e9Ct8a;rlyC.,ao2n0sa0lps8;heMteaalr.s,es2o0n0e6t;aSl.a,m20p1e0re; Pusceddu et al, 2010). Identifying factors influencing the benthic trophic state (in terms of food quantity and quality) at different spatial and temporal scales is crucial for a better understanding of the functioning of continental margin ecosystems
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