Carbon content and C : N ratio of transparent exopolymeric particles (TEP)produced by bubbling exudates of diatoms

The carbon content of transparent exopolymeric particles (TEP) was measured in the laboratory in particles produced by bubbling exudates of the diatom Thalassiosira weissflogii, grown under nitrogen non-limited conditions (N: P = 7). The carbon content of these particles (TEP-C) appears to vary as a function of their size according to TEP-C = 0.25 x 10(-6) r(2.55) (mu g C T EP-1), where r is the equivalent spherical radius of the TEP, article (Fun) . This relationship implies that TEP are fractal aggregates having a fracta l dimension D = 2.55. When this value was applied to historical TEP size sp ectra from a coastal area (Kattegat, Denmark), TEP carbon concentration in the surface mixed layer was on the order of 230 +/- 150 mu g C l(-1). This is high relative to other sources of particulate organic carbon (e.g. phyto plankton) and depending on TEP turnover rates, suggests that TEP is an impo rtant pathway for dissolved organic carbon in coastal seas. The carbon to n itrogen ratio of TEP was measured from particles formed by bubbling exudate s of the diatoms T. weissflogii, Skeletonema costatum, Chaetoceros neograci le and C. affinis. Each of these diatom species was grown under various N:P ratios, from N-non-limited to N-limited conditions. While the C:N ratio of the diatom cells grown under N-limited conditions was high (C:N greater th an or equal to 14), the TEP aggregates formed by coagulation of the extrace llular release produced by these cells exhibited a C:N ratio relatively con stant (C:N = 7.3 +/- 2.6) and apparently independent from that of the cells .