Experimental evaluation of the hypothesis that dilution limits DOC utilization in the deep ocean

The dilution hypothesis was tested by adding different concentrations of ambient DOC obtained by solid phase extraction to deep seawater samples. Microbial growth and consumption of DOC were assessed by flow cytometry, HTCO measurements of DOC and oxygen consumption measurements in 14 experiments using water collected from deep water masses of the Atlantic and Pacific Oceans.There are two kinds of experiments 14 (A-N) where prokaryotic growth was evaluated under increasing concentrations of ambient DOC and 2 additional experiments (O and P) where DOC composition and the utilization of different compounds was evaluated by means of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). A utilization index for each compound was derived from the FT-ICR-MS fingerprints, showing whether the relative signal for each compound remained stable (refractory or not used), decreased (was consumed) or increased (was produced). Detailed information on conditions and procedures can be found in the article. Enquiries can be sent to Jesús M. Arrieta at txetxu[at]mail.com.