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Marine Ecology Progress Series

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MEPS 387:97-108 (2009)  -  DOI: https://doi.org/10.3354/meps08075

Diel variability of heterotrophic bacterial production and underwater UV doses in the eastern South Pacific

France Van Wambeke1,*, Marc Tedetti1, Solange Duhamel1,2, Richard Sempéré1

1Laboratoire de Microbiologie, Géochimie et Ecologie Marines (LMGEM), CNRS, UMR 6117, Université de la Méditerranée, Campus de Luminy - Case 901, 13288 Marseille cedex 9, France
2Present address: C-MORE, Department of Oceanography, University of Hawaii, 1000 Pope Road, MSB205 Honolulu, Hawaii 96822, USA

ABSTRACT: Diel variability of heterotrophic bacterial production (BP) was investigated in the eastern South Pacific from October to December 2004. Three sites differing by their trophic status were studied: Marquesas Islands, the center (GYR) and the eastern South Pacific Gyre. By using a Lagrangian approach and high frequency measurements, an important increase (2- to 4-fold) in BP was observed at the 3 sites during the afternoon–sunset period within surface layers. To evaluate the impact of solar UV radiation on this variability, we determined, from in situ optical measurements, the mean UV-B (at 305 nm) and UV-A (at 380 nm) doses received within the mixed layer at a daily scale. At GYR, the doses were as high as 0.3 and 11 kJ m–2 nm–1 for the whole day, respectively due to high surface irradiances and very low light attenuations in the water column. The UV-B/UV-A tri-hourly dose ratios (Q) displayed substantial variations during the daytime, with highest values recorded during the periods 9:00 to 12:00 h or 12:00 to 15:00 h. The negative linear correlation observed between Q and BP in the surface waters of GYR suggests that changes in the balance between DNA damages and photorepairs (reflected by changes in the Q-ratio) could have a significant influence on the diel variability of BP in open oceans. However, assessing the effects of UV radiation on diel variability of BP through an in situ measurement approach, independently from other causes like availability of resources, is not so evident, even in these clearest waters of the world ocean.


KEY WORDS: Eastern South Pacific · Heterotrophic bacterial production · Diel variability · Ultraviolet radiation · UV-B and UV-A doses · Mixed layer · Leucine


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Cite this article as: Van Wambeke F, Tedetti M, Duhamel S, Sempéré R (2009) Diel variability of heterotrophic bacterial production and underwater UV doses in the eastern South Pacific. Mar Ecol Prog Ser 387:97-108. https://doi.org/10.3354/meps08075

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