Publication Abstract

Seasonal variability of inorganic and organic nitrogen in the North Sea.

Suratman, S, Jickells, T, Weston, K., Fernand, L.*

Sampling of the central region of the NorthSea was carried out to study the spatial and seasonalchanges of dissolved and particulate organic C (DOCand POC, respectively). The surface waters werecollected during four cruises over a year (Autumn2004–Summer 2005). DOC and POC concentrationswere measured using high temperature catalytic oxidationmethods. The surface water concentrations ofDOC and POC were spatially and temporally variable.There were significantly different concentrations ofDOC and POC between the inshore and offshorewaters in winter and summer only, with no clear trendin autumn and spring. Highest mean concentrations ofDOC were measured in spring with lower and similarmean concentrations for other seasons. POC showed aclear seasonal cycle throughout the year with highestsurface mean concentrations found in autumn andspring, but lowest in winter and summer. The DOCdistributions during autumn and spring were stronglycorrelated with chlorophyll suggesting extracellularrelease from phytoplankton was an important DOCsource during these two seasons. The lower concentrationsof DOC in summer were probably due to theheterotrophic uptake of labile DOC. The seasonalchanges in the C:N molar ratios of surface DOM(dissolved organic matter) resulted in higher meanC:N molar ratios in spring and lower ratios in winter.These high ratios may indicate nutrient limitation ofheterotrophic uptake immediately after the springbloom. There is limited data available for DOCcyclingin these productive shelf seas and these results showthat DOC is a major component of the C cycle withpartial decoupling of the DOC and DON cycling in thecentral North Sea during the spring bloom.

Reference:

Suratman, S, Jickells, T, Weston, K., Fernand, L.* (2010) Seasonal variability of inorganic and organic nitrogen in the North Sea. Hydrobiologia 610, 1, 83-98