Summertime trends in pelagic biogeochemistry at the Porcupine Abyssal Plain study site in the northeast Atlantic

Stuart C. Painter, Michael I. Lucas, Mark C. Stinchcombe, Thomas S. Bibby, Alex J. Poulton

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

Measurements of nitrate and carbon uptake made in July 2006 in the Northeast Atlantic Ocean are evaluated with reference to the photophysiology of the attendant phytoplankton population. Over the 11-day observation period integrated chlorophyll concentrations and carbon fixation rates decreased by 76% and 60%, respectively. Integrated nitrate uptake decreased by 50% from initial to final rates but was generally less variable than carbon fixation and chlorophyll in the intervening period. Satellite derived estimates of surface chlorophyll concentrations reveal the uptake observations to be coincident with, and subsequent to, a peak in summer time production. Large reductions in diatom and dinoflagellate abundance were also seen at this time, with indications that increased grazing, due to an increase in ciliate abundance, was an important mechanism terminating summertime production in the NE Atlantic. Meanwhile, the presence of consistently low values of Fv/Fm (<0.3), particularly in surface waters, suggests that production occurs, or is inhibited, with suboptimal photochemical efficiency widespread amongst the phytoplankton population. Furthermore, the low values of Fv/Fm were not alleviated by day-to-day variability in macronutrient concentration. The timing of our observations places them within the seasonal period recognised for the widespread phenomena of carbon overconsumption, and we estimate C:N uptake ratios at this time could be as high as 13:1.

Original languageEnglish
Pages (from-to)1313-1323
Number of pages11
JournalDeep-Sea Research Part II: Topical Studies in Oceanography
Volume57
Issue number15
DOIs
Publication statusPublished - 1 Aug 2010

Keywords

  • Nitrate uptake
  • Northeast Atlantic Ocean
  • PAP site
  • Pelagic biogeochemistry
  • Photophysiology

ASJC Scopus subject areas

  • Oceanography

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