Spatial and seasonal changes of dissolved and particulate organic C in the North Sea |
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Authors: | Suhaimi Suratman Keith Weston Tim Jickells Liam Fernand |
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Institution: | (1) Environmental Research Group (ERG), Department of Chemical Sciences, University Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu, Malaysia;(2) Laboratory for Global Marine and Atmospheric Chemistry (LGMAC), School of Environmental Sciences, University of East Anglia, NR4 7TJ Norwich, Norfolk, UK;(3) Centre for Environment, Fisheries and Aquaculture Science (CEFAS), Pakefield Road, NR33 0HT Lowestoft, Suffolk, UK |
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Abstract: | Sampling of the central region of the North Sea was carried out to study the spatial and seasonal changes of dissolved and
particulate organic C (DOC and POC, respectively). The surface waters were collected during four cruises over a year (Autumn
2004–Summer 2005). DOC and POC concentrations were measured using high temperature catalytic oxidation methods. The surface
water concentrations of DOC and POC were spatially and temporally variable. There were significantly different concentrations
of DOC and POC between the inshore and offshore waters in winter and summer only, with no clear trend in autumn and spring.
Highest mean concentrations of DOC were measured in spring with lower and similar mean concentrations for other seasons. POC
showed a clear seasonal cycle throughout the year with highest surface mean concentrations found in autumn and spring, but
lowest in winter and summer. The DOC distributions during autumn and spring were strongly correlated with chlorophyll suggesting
extracellular release from phytoplankton was an important DOC source during these two seasons. The lower concentrations of
DOC in summer were probably due to the heterotrophic uptake of labile DOC. The seasonal changes in the C:N molar ratios of
surface DOM (dissolved organic matter) resulted in higher mean C:N molar ratios in spring and lower ratios in winter. These
high ratios may indicate nutrient limitation of heterotrophic uptake immediately after the spring bloom. There is limited
data available for DOC cycling in these productive shelf seas and these results show that DOC is a major component of the
C cycle with partial decoupling of the DOC and DON cycling in the central North Sea during the spring bloom.
Handling editor: Luigi Naselli-Flores |
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Keywords: | Dissolved and particulate organic carbon Spatial Seasonal changes C:N molar ratio North Sea |
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