Comparison of bacterial carbon production estimates from dilution and <scp>³H</scp>‐leucine methods across a strong gradient in ocean productivity

The uptake of 3H-labeled leucine into proteins, a widely used method for estimating bacterial carbon production (BCP), is suggested to underestimate or overestimate growth in the open ocean by factor 40 uncertainty. Meanwhile, an alternative BCP approach, dilution method, has untested concerns about potential overestimation from dissolved substrates released filtration. We compared BCPDil and BCPLeu estimates three cruises across broad trophic gradient, offshore oligotrophy coastal upwelling, California Current Ecosystem. Our initial analyses based on midday microscopical size priori assumptions conversions relationships revealed mean two-fold difference (BCPDil higher), but no systematic bias between low high productivity stations. both demonstrated strong with bacteria cell abundance. Reanalysis results, involving different carbon-biovolume relationship informed forward angle light scatter flow cytometry as relative index, that are fully compatible, 1 : fit 5 fg C cell−1. Based these results considering strengths methods, combined use techniques provide mutually supportive constraints biomass production.