Living deep-sea benthic foraminifera from the Cap de Creus Canyon (western Mediterranean): faunal-geochemical interactions.
Contreras Rosales, L.A.
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Currently, the Cap de Creus canyon experiences dense water cascading (DSWC) events with seasonal frequency and decadal peaks in intensity. These events transport suspended organic particles which could potentially sustain higher biological productivity inside the canyon in comparison to the adjacent slope. To investigate this, Rose Bengal stained samples were collected along a depth transect over the Cap de Creus Canyon and its adjacent slope. Benthic foraminifera were studied in the top 5 cm of sediment, and faunal abundances and assemblages were compared against geochemical data. Results indicate that the decrease of food quality (Chl a/Phaeo ratio), with increasing water depth, is the main factor determining the distribution of foraminifera species both in canyon and slope environments. The decrease of food quantity (CPE concentration), which appears to be somewhat higher in the canyon than open slope environments at equivalent water depths, represents the second most important factor. However, as the contrast with the slope is largest in the canyon head and the upper canyon, the DSWC seem to influence mostly these settings. Thus, eutrophic conditions were only found at the canyon head, dominated by the species Ammoscalaria pseudospiralis, Cibicides ungerianus, Cassidulina laevigata, and Bolivina spathulata. Mesotrophic environments occurred in the shallow open slope and around the middle canyon section. Assemblages were dominated by Uvigerina mediterranea, Bigenerina nodosaria, Bolivina spathulata and Eponides pusillus. Chrithionina cf. mamilla was abundant inside the canyon probably profiting from currents activity. The canyon sites at these water depths were also abundant in arborescent and tubular foraminiferal fragments, (especially Saccorhiza ramosa and Dendrophrya sp.). Oligotrophic environments occurred in the deepest canyon and slope areas and were dominated by Ammolagena clavata, Glomospira charoides and an unidentified single-chambered “agglutinated dome” species. E. pusillus was also abundant in these environments probably profiting from the hemipelagic rain of particles from the early spring phytoplankton bloom. Our results are in good agreement with previous studies of foraminifera from submarine canyons and deep-sea environments; however, our data highlight that submarine canyons are complex systems, each modified by a number of local processes that are specific for the setting.