Elevated pCO2 from late summer coastal upwellings in the western Baltic Sea enhances vegetative growth in the brown algae Fucus serratus: a laboratory assessment

The brown algae Fucus serratus is one of the major meadow forming algae of the Western Baltic Sea nearshore ecosystem. At the end of summer, those meadows are exposed to local upwelling suddenly increasing the pCO2 and DIC up to 2500 µatm and 2250 µmol/kg resp., for period of days to weeks. This study investigates the growth response of summer's vegetative Fucus serratus to elevated pCO2 (1350 and 4080 µatm) during a 40 days laboratory incubation. After 10 days, increases of growth rates of 20 % and 47 % of the control were observed in the 1350 and 4080 µatm pCO2 treatments respectively. Beyond 20 days, the growth rates collapsed in all treatments due to nutrients shortage, as demonstrated by high C:N ratios (95:1) and low N tissue content (0.04 % of dry weight). The collapse occurs faster at higher pCO2. On day 30, growth rates were reduced by 40 % and 100 % relative to the control at 1350 and 4080 µatm respectively. These results are consistent with a fertilizing effect of elevated pCO2 on Fucus serratus presumably linked to the transition from active HCO3- to passive CO2(aq) uptake. This positive effect is limited by nutrients resources, low seawater dissolved inorganic N and P and shortage of the nutrients reserves accumulated over the previous autumn and winter.

(Figure 3d) Export production reconstruction based on planktonic foraminiferal sampled in surface sediments

To reconstruct Export Productivity (Pexp), 27 taxonomic categories of the planktonic foraminifera census data were used with the modern analog technique SIMMAX 28 (Pflaumann et al., 1996, doi:10.1029/95PA01743; 2003, doi:10.1029/2002PA000774). To the 26 taxonomic groups widely used and listed in Kucera et al. (2005, doi:10.1016/j.quascirev.2004.07.014), Turborotalita humilis was added in our calibration as it is associated with the PCC source region (Meggers et al., 2002, doi:10.1016/S0967-0645(02)00103-0). The modern analog file is based on the Iberian margin database (Salgueiro et al., 2008, doi:10.1016/j.marmicro.2007.09.003) combined with the North Atlantic surface samples used by the MARGO project (Kucera et al., 2005). This results in a total of 999 analogs for Pexp. Modern oceanic primary productivity (PP) is obtained for each site by averaging 12 monthly primary productivity values for a 8-year period (1978-1986) that were estimated from satellite color data (CZCS) and gridded at 0.5° latitude - longitude fields (Antoine et al., 1996, doi:10.1029/95GB02832). Export Productivity (Pexp) was calculated from the PP values following the empirical relationship Pexp = PP**2/400 for primary production below 200 gC/m**2/yr, and Pexp = PP/2 for primary production above 200 gC/m2/yr (Eppley and Peterson, 1979, doi:10.1038/282677a0; Sarnthein et al., 1988, doi:10.1029/PA003i003p00361). The residuals gives the differences between satellite based Pexp and foraminiferal Pexp.