Spring bloom carbon to nitrogen ratio of net community production in the temperate N. Atlantic

• Published in: Deep Sea Research Part I: Oceanographic Research Papers
• Main Author: Koeve, Wolfgang
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2004
• Subjects: North Atlantic; Northeast Atlantic; Subarctic
• Online Access: https://oceanrep.geomar.de/id/eprint/13633/; https://oceanrep.geomar.de/id/eprint/13633/1/koeve.pdf; https://doi.org/10.1016/j.dsr.2004.07.002

The carbon to nitrogen ratio of net community production, (C:N)NCP, during the spring phytoplankton bloom in the temperate northeast Atlantic is estimated from a re-analysis of published data from the North Atlantic Bloom Experiment (NABE, 1989) and a north–south transect along 20°W carried out in 1996. The average seasonally integrated cumulative (C:N)NCP ratio between winter mixing and the end of the diatom bloom ranges between 5.9±0.4 (1996 study) and 6.9±0.9 (NABE) and is not significantly different (p>0.1) from the ‘Redfield’-C:N ratio. The instantaneous ΔDIC:ΔNO3 ratio, uncorrected for CO2 air–sea exchange and CaCO3 production, during the diatom bloom is 8.0±0.9, which is significantly (p<0.01) lower than previous estimates (9.9±0.7) drawn from the same data sets. This difference reflects regional variation in pre-formed winter total CO2 and nitrate concentrations, which is corrected for in the data analysis presented here. The instantaneous (C:N)NCP, including air–sea exchange and CaCO3 production correction during the diatom bloom is 7.3±0.7. DIC and nitrate changes between winter pre-formed values and observations early during the NABE diatom bloom study indicate a lower instantaneous ΔDIC:ΔNO3 of 3.7–5.9, and an elevated NO3:Si(OH)4 uptake ratio of about 2.9 early in the growth season. Following the diatom bloom, a second bloom, dominated by non-siliceous phytoplankton, takes up carbon and nitrate largely in Redfield proportion; the cumulative (C:N)NCP ratio integrated until nitrate depletion ranges from 7.2±0.9 (NABE) to 7.9±0.6 (1996 study). It is concluded that significantly elevated cumulative (C:N)NCP in the temperate and subarctic Northeast Atlantic, which have been reported elsewhere, generate from carbon overconsumption during summer, not from spring bloom new production. Consequences for carbon export into the deep ocean are discussed.