Auto- and heterotrophic microbial activity (biomass production and respiration) were investigated in a cyclonic eddy that formed off Mauritania along the ∼ 900 km zonal corridor between Mauritania and the Cabo Verde islands in the eastern Tropical North Atlantic during the M156 cruise on the RV Meteor from July 3rd to August 1st 2019. The dataset includes measured and calculated data over the epipelagic layer (0-200 m depth) of 25 stations with 14 of them inside or in the vicinity of a cyclonic eddy. Temperature, salinity, and oxygen were obtained from a Seabird 911 plus CTD system equipped with two independently working sets of temperature–conductivity–oxygen. Seawater samples were collected using 10 L Niskin bottles attached to the CTD Rosette. Ammonium was analysed based on Solórzano (1969, https://doi.org/10.4319/lo.1969.14.5.0799) and nitrate, nitrite, phosphate and silicate were measured photometrically with continuous-flow analysis on an auto-analyser based on Hansen and Koroleff, (1999, https://doi.org/10.1002/9783527613984.ch10). To estimate the fraction of semi-labile dissolved organic carbon, we determined high-molecular-weight (>1 kDa) dissolved combined carbohydrates (dCCHO) based on Engel and Händel (2011, https://doi.org/10.1093/plankt/fbq122) and dissolved hydrolysable amino acids (dHAA) based on Lindroth and Mopper (1979, https://https://doi.org/10.1021/ac50047a019) and Dittmar et al, (2009). The analysis of DCCHO detected 11 monomers: and the dHAA analysis classified 13 monomers. The calculations for the carbon content of dCCHO and dHAA were based on carbon atoms contained in the identified monomers. The sum of dCCHO and dHAA carbon content is referred to as SL-DOC. Chlorophyll a was measured from photometric analysis based on Evans et al, (1987). Heterotrophic bacteria, photosynthetic bacteria (Prochlorococcus and Synechococcus), and autotrophic pico and nanoplankton (<20 μm) abundances were measured by flow cytometry. We converted the cell abundance of the different autotrophic pico- and nanoplankton populations into biomass based on Hernández-Hernández et al. (2020, https://doi.org/10.3389/fmars.2020.00667). Extracellular release rates, dissolved-, particulate- and total- primary production rates were determined from 14C incorporation according to Nielsen (1952, https://doi.org/10.1093/icesjms/18.2.117) and Gargas (1975). Community respiration was obtained from optode-based method from incubations by measuring changes in dissolved oxygen over 24–36 h. Bacterial biomass production rates were measured through the incorporation of labelled leucine (3H) using the microcentrifuge method (Kirchman et al., 1985, https://doi.org/10.1128/aem.49.3.599-607.1985; Smith and Azam, 1992, ). Community respiration and bacterial biomass production were converted to rates at 22°C using equations from Regaudie-De-Gioux and Duarte (2012, https://doi.org/10.1029/2010GB003907) and from López-Urrutia and Morán (2007, https://doi.org/10.1890/06-1641) respectively. Community respiration rates were converted to bacteria respiration rates based on Aranguren-Gassis et al, (2012, https://doi.org/10.3354/meps09707). Bacteria carbon demand and growth efficiency were calculated from bacterial production and respiration rates. Dittmar, T., Cherrier, J., and Ludwichowski, K. U.: The analysis of amino acids in seawater, in: Practical guidelines for the analysis of seawater, edited by: Wurl, O., 67–78, CRC Press, Boca Raton, ISBN: 978-1-4200-7306-5, 2009. Evans, C. A., O'Reily, J. E., and Thomas, J. P.: A handbook for measurement of Chl a and primary production, College Station, TX, Texas A and M University, ISBN:9780948277078, 0948277076, 1987. Gargas, E.: A Manual for Phytoplankton Primary Production Studies in the Baltic, The Baltic Marine Biologists, 2, 88 pp. Ed. Gargas E. (Hørsholm, Denmark: Water Quality Institute), 1975. Smith, D. and Azam, F.: A simple, economical method for measuring bacterial protein synthesis rates in seawater using, Mar. Microb. Food Webs, 6, 107–114, 1992.
