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- Title
The trophic and metabolic pathways of foraminifera in the Arabian Sea: evidence from cellular stable isotopes.
- Authors
Jeffreys, R. M.; Fisher, E. H.; Gooday, A. J.; Larkin, K. E.; Wolff, G. A.; Billett, S. M.
- Abstract
The Arabian Sea is a region of elevated productivity with the highest globally recorded fluxes of particulate organic matter (POM) to the deep ocean, providing an abundant food source for fauna at the seafloor. However, benthic communities are also strongly influenced by an intense oxygen minimum zone (OMZ), which impinges on the continental slope at bathyal depths. We compared the trophic ecology of foraminifera on the Oman and Pakistan margins of the Arabian Sea (140-3185 m water depth). Organic carbon concentrations of surficial sediments were higher on the Oman margin (3.32 ± 1.4%) compared to the Pakistan margin (2.45 ± 1.1 %) and sedimentary organic matter (SOM) quality estimated from the Hydrogen Index was also higher on the Oman margin (300-400mgHC(mgTOC)-1) compared to the Pakistan margin (< 250mgHC(mgTOC)-1). δ13 C and δ15 N values of sediments were similar on both margins (-20 and 8‰, respectively). Stable isotope analysis (SIA) showed that foraminiferal cells had a wide range of δ13C values (-25.5 to -11.5‰), implying that they utilise multiple food sources; indeed δ13 C values varied between depths, foraminiferal types and between the two margins. Foraminifera had broad ranges in δ15 N values (-7.8 to 27.3‰). The enriched values suggest that some species may store nitrate to utilise in respiration; this was most notable on the Pakistan margin. Depleted foraminiferal δ15 N values were identified on both margins, particularly the Oman margin, and may reflect feeding on chemosynthetic bacteria. We suggest that differences in productivity regimes between the two margins may be responsible for the differences observed in foraminiferal isotopic composition. In addition, at the time of sampling, whole jellyfish carcasses (Crambionella orsini) and a carpet of jelly detritus were observed across the Oman margin transect. Associated chemosynthetic bacteria may have provided an organic-rich food source for foraminifera at these sites. Our data suggest that foraminifera in OMZ settings can utilise a variety of food sources and metabolic pathways to meet their energetic demands.
- Subjects
ARABIAN Sea; FORAMINIFERA; STABLE isotopes; ORGANIC compounds; OCEAN bottom; SUBMARINE topography
- Publication
Biogeosciences Discussions, 2014, Vol 11, Issue 12, p18145
- ISSN
1810-6277
- Publication type
Article
- DOI
10.5194/bgd-11-18145-2014