C : N : P stoichiometry at the Bermuda Atlantic Time-series Study station in the North Atlantic Ocean

[摘要] Nitrogen (N) and phosphorus (P)availability, in addition to other macro- and micronutrients, determine thestrength of the ocean's carbon (C) uptake, and variation in the N : P ratioof inorganic nutrient pools is key to phytoplankton growth. A similaritybetween C : N : P ratios in the plankton biomass and deep-water nutrientswas observed by Alfred C. Redfield around 80 years ago and suggested thatbiological processes in the surface ocean controlled deep-ocean chemistry.Recent studies have emphasized the role of inorganic N : P ratios ingoverning biogeochemical processes, particularly the C : N : P ratio insuspended particulate organic matter (POM), with somewhat less attentiongiven to exported POM and dissolved organic matter (DOM). Herein, we extendthe discussion on ecosystem C : N : P stoichiometry but also examinetemporal variation in stoichiometric relationships. We have analyzedelemental stoichiometry in the suspended POM and total (POM + DOM) organic-matter (TOM) pools in the upper 100 m and in the exported POM andsubeuphotic zone (100–500 m) inorganic nutrient pools from the monthlydata collected at the Bermuda Atlantic Time-series Study (BATS) site locatedin the western part of the North Atlantic Ocean. C : N and N : P ratiosin TOM were at least twice those in the POM, while C : P ratios were upto 5 times higher in TOM compared to those in the POM. Observed C : Nratios in suspended POM were approximately equal to the canonical Redfield ratio (C : N : P = 106 : 16 : 1), while N : P and C : Pratios in the same pool were more than twice the Redfield ratio. AverageN : P ratios in the subsurface inorganic nutrient pool were ~ 26 : 1,squarely between the suspended POM ratio and the Redfield ratio. We havefurther linked variation in elemental stoichiometry to that ofphytoplankton cell abundance observed at the BATS site. Findings from thisstudy suggest that elemental ratios vary with depth in the euphotic zone,mainly due to different growth rates of cyanobacterial cells. We have alsoexamined the role of the Arctic Oscillation on temporal patterns in C : N : Pstoichiometry. This study strengthens our understanding of the variability in elemental stoichiometry in different organic-matter pools and should improvebiogeochemical models by constraining the range of non-Redfield stoichiometryand the net relative flow of elements between pools.

[学科分类] 地球化学与岩石