Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 7 2 2010 10.5194/bg-7-657-2010 http://www.biogeosciences.net/7/657/2010/ http://www.biogeosciences.net/7/657/2010/bg-7-657-2010.html http://www.biogeosciences.net/7/657/2010/bg-7-657-2010.pdf 657 669 2010-02-16 Effects of an iron-light co-limitation on the elemental composition (Si, C, N) of the marine diatoms <I>Thalassiosira oceanica</I> and <I>Ditylum brightwellii</I> E. Bucciarelli eva.bucciarelli@univ-brest.fr P. Pondaven G. Sarthou Université Européenne de Bretagne, France Université de Brest, CNRS, IRD, UMR 6539 LEMAR, IUEM; Technopôle Brest Iroise, Place Nicolas Copernic, 29280 Plouzané, France We examined the effect of iron (Fe) and Fe-light (Fe-L) co-limitation on cellular silica (BSi), carbon (C) and nitrogen (N) in two marine diatoms, the small oceanic diatom <I>Thalassiosira oceanica</I> and the large coastal species <I>Ditylum brightwellii</I>. We showed that C and N per cell tend to decrease with increasing Fe limitation (i.e. decreasing growth rate), both under high light (HL) and low light (LL). We observed an increase (<I>T. oceanica</I>, LL), no change (<I>T. oceanica</I>, HL) and a decrease (<I>D. brightwellii</I>, HL and LL) in BSi per cell with increasing degree of limitation. The comparison with literature data showed that the trend in C and N per cell for other Fe limited diatoms was similar to ours. Interspecific differences in C and N quotas of Fe limited diatoms observed in the literature seem thus to be mostly due to variations in cell volume. On the contrary, there was no global trend in BSi per cell or per cell volume, which suggests that other interspecific differences than Fe-induced variations in cell volume influence the degree of silicification. 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