[1] Total organic carbon (TOC) was measured in the midlatitudes of the northeast Atlantic in 2000-2001 during the Programme Océan Multidisciplinaire Méso Echelle (POMME). In spring, mixed layer depth (MLD) was positively correlated with the north latitude, while the surface TOC and chlorophyll-a (Chl a) were negatively correlated with it. It indicates the northward propagation of TOC accumulation along the onset of spring bloom, which was triggered by shoaling of MLD from the south. Surface TOC was highest in summer, though surface Chl a was lowest. Surface TOC was significantly correlated with surface Chl a during winter and spring but not during summer or fall, indicating the minor influence of total phytoplankton biomass on surface TOC distribution in the oligotrophic season. High surface TOC in summer and fall was related with shallow MLD, which could hold fresh TOC near the surface. Downward TOC flux from the surface to below the seasonal thermocline was estimated for the processes of winter convection (F c ), turbulent diffusion (F d ) and sinking flux (F p ). The sum of these fluxes accounts for 6-75% of annual new production. To our knowledge, this is the first estimation based on the simultaneous measurement of F c , F d , F p , and annual new production.
Carbon-normalized yields of amino acids in size-fractionated seawater samples and bacterial cultures were used in a novel application to estimate the carbon content of heterotrophic marine bacteria. The estimated carbon content (6.3 ± 1.6 fg C cell ) of open ocean bacteria derived using this approach was lower than most values estimated in previous studies. Based on these values, living heterotrophic bacteria accounted for 6.8 ± 1.1% of suspended particulate organic carbon (POC) in surface waters at Stn ALOHA in the North Pacific gyre. Living cyanobacteria accounted for 13.3 ± 2.2% of suspended POC in surface waters. Carbon-normalized yields of muramic acid, D-alanine and D-glutamic acid, unique biomarkers of bacteria, were used to estimate that bacterial detritus accounted for 4.3 ± 2.9% of suspended POC in surface waters. The relative contribution of bacterial detritus to suspended POC increased dramatically with increasing depth, indicating that some components of bacterial detritus are resistant to decomposition in the deep ocean. The total living and detrital bacterial contribution to suspended POC in surface waters was ~25%.
KEY WORDS: Bacterial carbon content · Bacterial detritus · Bacterial biomarkers · Suspended particulate organic carbonResale or republication not permitted without written consent of the publisher
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