Title: On the use of benthic foraminiferal δ <sup>13</sup> C in palaeoceanography: constraints from primary proxy relationships
Abstract: Abstract Recent findings are reviewed from observations in the field on the generation of the δ 13 C signal in shells of live (Rose Bengal stained) benthic foraminifera, and end up with implications for the interpretation of fossil signatures. The δ 13 C values of calcite tests of preferentially epifaunal foraminifera principally reflect the δ 13 C of dissolved inorganic carbon (DIC) of ambient seawater, whereas infaunal species record a porewater signal, both with an offset from equilibrium calcite. Species occupying the deepest average living depth in the sediment usually exhibit lowest δ 13 C test values, but δ 13 C values of conspecific specimens at a single site do not decrease with increasing subbottom depth and decreasing porewater δ 13 C DIC . Organic carbon fluxes to the sediment surface are generally reflected by infaunal species such that lowered δ 13 C values coincide with high fluxes, but even strictly epifaunal species may reflect seasonally pulsed phytodetritus supply by depleted test δ 13 C. In high-productivity environments, however, where dissolved oxygen and sedimentary carbonate contents are low, benthic foraminiferal tests show 13 C enrichment probably due to carbonate-ion undersaturation. Ontogenetic increase in δ 13 C values of certain infaunal species suggests a slow-down of metabolic rates during test growth and decreasing fractionation with age. At sites of active methane discharge δ 13 C values of infaunal species reflect low pore water δ 13 C DIC values, documenting active methane release in the sediment, whereas lowered δ 13 C values of strictly epifaunal species are most probably the result of incorporation of 13 C depleted methanotrophic biomass.
Publication Year: 2008
Publication Date: 2008-01-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 41
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