On the coherence of organic carbon flux and benthic foraminiferal biomass

Benthic foraminiferal biomass values from the literature are compared with annual flux rates of organic carbon to the sea floor. A data set of 212 loc ations is compiled from 2m to 9300m water depth, covering the Arctic, Atlan tic, Indian, and Pacific Oceans. Annual flux rates nearly cover 3 orders of magnitude (0.3g to > 100g C-org m(-2)), and foraminiferal biomass covers m ore than 5 orders of magnitude (0.01 mg to >4 g C-org m(-2)). In shallow wa ters no coherence is observed due to randomly distributed biomass values sp anning 4 orders of magnitude. Flux rates and biomass values are correlated (r = 0,7, p < 0.001) at water depth below 1000m, but within a broad range o f variability (about factor 4 from the regression line). Annual fluctuation s of foraminiferal biomass values are reported by several authors within a factor of 5 to more than 10, corroborating these ranges of variability as n atural. In addition, broad deviations were observed to result from methodol ogical errors or spatial gradients. In the deep sea, annual flux rates of organic carbon range from 0.3 to 5 g m(-2). The gradient in mean foraminiferal biomass (C-org) is steeper, decre asing from 0.002 to 0.3 g m-2. A decrease of annual flux rates by a factor of about 10 produces a decrease in mean foraminiferal biomass by a factor o f more than 100. As a result, the potential nutritional supply per biomass unit or individual is gradually improved by up to a factor of 10 for most o ligotrophic environments. This may be considered an adaptation to lowered e fficiency of food gathering and increasing amounts of biodegraded matter. F rom the calculations presented, an annual turnover of foraminiferal biomass can be estimated within 1 to 2 years.