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 locations is compiled from 2m to 9300m water depth, covering the Arctic, Atlantic, 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 more than 5 orders of magnitude (0.01 mg to >4 g C(org) m(-2)). In shallow waters no coherence is observed due to randomly distributed biomass values spanning 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 of variability (about factor 4 from the regression line). Annual fluctuations of foraminiferal biomass values are reported by several authors within a factor of 5 to more than 10, corroborating these ranges of variability as natural. In addition, broad deviations were observed to result from methodological 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, decreasing 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 of 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 oligotrophic environments. This may be considered an adaptation to lowered efficiency of food gathering and increasing amounts of biodegraded matter. From the calculations presented, an annual turnover of foraminiferal biomass can be estimated within 1 to 2 years.