The influence of labile and refractory C-org on benthic foraminifera: a laboratory mesocosm study

Karoliina A. Koho, A.M. Langezaal, Y.A. Van Lith, T.J. Kouwenhoven, G.J. Van Der Zwaan
2006 Anuário do Instituto de Geociências  
The vertical distribution of benthic foraminiferal communities is believed to be controlled by food supply (C org fluxes to the sea floor) and/or dissolved O 2 concentrations. However, the importance of quality or freshness of organic carbon has largely been neglected in previous studies. The C org flux to the deep sea sediment is already degraded, as remineralisation begins immediately at the sea surface and continues through the water column. The extent of the degradation depends on several
more » ... ctors including O 2 exposure time, water column length and sedimentation rate (Hedges & Keil, 1995, and references within. Marine Chemistry, 49: 81-115). Therefore, even in locations where C org concentrations are relatively high the nutritional value of organic matter may be low. This experiment is designed to explore whether benthic communities respond differently to varying qualities of organic matter. A phytoplankton bloom was simulated using the diatom species Thalassiosira pseudonana. A 'labile' component consisted of fresh freeze dried algae, while a 'refractory' part was prepared by salinity shock treatment of diatoms with UHQ water. This process causes rupture of the diatom cells and releases labile carbon as CO 2 . 39mg of either labile or refractory diatoms were added in the fed cores. In addition, blank (non-fed) cores were observed as a reference. The experiment was conducted under controlled laboratory conditions with stable oxygen concentrations. In total the experiment ran for eight weeks after the feeding. Sampling was carried out at four time intervals: at experiment set up, before feeding, at four weeks and at eight weeks after feeding. Two cores were also collected from the field site for background information. At each sampling time a replicate core was processed for foraminiferal studies. In addition, a core was sampled for geochemical analyses, including porewater and overlying water NO 3 -, NH 4 + and DOC concentrations and fluxes,
doi:10.11137/2006_1_463-464 fatcat:52jqw7hdfvetbbvvd5jpbe5oau