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

Abstract

Abstract. Nitrogen (N) and phosphorus (P) availability, in addition to other macro-and micronutrients, determine the strength of the ocean's carbon (C) uptake, and variation in the N : P ratio of inorganic nutrient pools is key to phytoplankton growth. A similarity between C : N : P ratios in the plankton biomass and deep-water nutrients was observed by Alfred C. Redfield around 80 years ago and suggested that biological processes in the surface ocean controlled deepocean chemistry. Recent studies have emphasized the role of inorganic N : P ratios in governing biogeochemical processes, particularly the C : N : P ratio in suspended particulate organic matter (POM), with somewhat less attention given to exported POM and dissolved organic matter (DOM). Herein, we extend the discussion on ecosystem C : N : P stoichiometry but also examine temporal variation in stoichiometric relationships. We have analyzed elemental stoichiometry in the suspended POM and total (POM + DOM) organic-matter (TOM) pools in the upper 100 m and in the exported POM and subeuphotic zone (100-500 m) inorganic nutrient pools from the monthly data collected at the Bermuda Atlantic Time-series Study (BATS) site located in the western part of the North Atlantic Ocean. C : N and N : P ratios in TOM were at least twice those in the POM, while C : P ratios were up to 5 times higher in TOM compared to those in the POM. Observed C : N ratios in suspended POM were approximately equal to the canonical Redfield ratio (C : N : P = 106 : 16 : 1), while N : P and C : P ratios in the same pool were more than twice the Redfield ratio. Average N : P ratios in the subsurface inorganic nutrient pool were ∼ 26 : 1, squarely between the suspended POM ratio and the Redfield ratio. We have further linked variation in elemental stoichiometry to that of phytoplankton cell abundance observed at the BATS site. Findings from this study suggest that elemental ratios vary with depth in the euphotic zone, mainly due to different growth rates of cyanobacterial cells. We have also examined the role of the Arctic Oscillation on temporal patterns in C : N : P stoichiometry. This study strengthens our understanding of the variability in elemental stoichiometry in different organic-matter pools and should improve biogeochemical models by constraining the range of non-Redfield stoichiometry and the net relative flow of elements between pools.

Lateral Transport of N‐Rich Dissolved Organic Matter Strengthens Phosphorus Deficiency in Western Subtropical North Atlantic

“…The inorganic nutrients released form the mineralization of high N:P dissolved organic matter should accumulate at ratios higher that the Redfield value and contribute to the development of high N:P ratios (Hansell et al, ). The TON:TOP ratios found in the surface of NASW (231:1 ± 70) and the EDW waters (Figure h) exceed data of previous studies from the western subtropical Atlantic that report values of about 60–90:1 (Ammerman et al, ; Singh et al, ; Wu et al, ), while those found below the EDW and in the SSNA region (TON:TOP ≈ 50:1) agree. We think that a combination of all the previously stated factors: sedimentation of diazotrophs, sedimentation of N‐rich organic matter resulting from preferential surface P remineralization, and the horizontal transport and mineralization of high N:P dissolved organic matter within the EDW, converges to produce the high dissolved inorganic N:P ratios of the subsurface NASW.…”

Stoichiometry of Prochlorococcus, Synechococcus, and small eukaryotic populations in the western North Atlantic Ocean

“…). The higher Q C : Q N ratio in autotrophic biomass could significantly increase estimates of C export from the euphotic zone (Teng et al ., ; Singh et al ., ) and potentially help resolve C budgets in the ocean (Burd et al ., ). Additionally, a simple mass balance would imply that the remainder of particles making up organic matter in the North Atlantic Ocean must be relatively enriched in N. Presumably, this would be primarily due to heterotrophic bacterial cells, which potentially have a lower range of stoichiometric ratios (minimum Q C : Q N = 4) in marine systems (Gundersen et al ., ).…”

A reevaluation of the magnitude and impacts of anthropogenic atmospheric nitrogen inputs on the ocean

“…The oceanic residence times of N and phosphorus (P) are therefore quite distinctly different, despite their close ocean scale coupling as is evident from the Redfield ratio. This coupling is due to large‐scale thermohaline water mixing that smooths out the effects of the different internal ocean biogeochemical N and P cycling [ Martiny et al ., ; Singh et al ., ; Weber and Deutsch , ]…”