Environmental control on phytoplankton size-fractionated primary production in the tropical and subtropical Atlantic, Indian and Pacific oceans The 45 th International Liège Colloquium. Liège (Belgium), May 2013 M. Huete-Ortega, P. Cerme ñ o, A. Fernández, B. Fernández-Castro, N. González, D. López-Sandoval, B. Mouriño-Carballido, C. Sobrino and E. Mara ñó n

Phytoplankton size structure… Ecosystems dominated by small phytoplankton: Organic matter is recycled into the microbial loop Ecosystems dominated by large phytoplantkon: Organic matter transferred towards higher trophic levels or to the deep ocean Barber & Hiscock 2006 Global Biog. Cycles …influences the organization of the pelagic trophic chain and plays an important role in the global carbon cycle

Phytoplankton cell size affected by: Light availability Nutrients availability Grazing pressure Water-column dynamism (turbulence, stratification…) Which environmental factors are more important in determining the phytoplankton community size structure at global scales?

The oceanic circunnavegation Malaspina Expedition sampling stations between Dec 2010 and July 2011 Source: M. Fuster Truyol, IMEDEA

The oceanic circunnavegation Malaspina Expedition 2010 Sampling at 5 depths (Surface, 50% PAR, 20% PAR, 7% PAR, 1%PAR) Incubations on deck following the 14 C method (3 clear, 1 dark bottles). Dawn-Sunset incubations. Size-fractionated primary production estimated at Surface, 20%PAR, 1%PAR: micro- (>20 µm ESD), nano- (20-2 µm ESD) and pico-phytoplankton (2-0.2 µm ESD) Total primary production estimated at 50%PAR and 7%PAR

Depth-integrated total primary production (mgC m -2 h -1 ) Integrated total PP ranged 7-70 mgC m -2 h -1 in the subtropical and tropical Atlantic, Indian and Pacific Oceans with higher values towards the coast and in the areas influenced by equatorial upwellings.

Microphytoplankton primary production (mgC m -3 h -1 ) Atlantic Ocean SNEW W E Indian Ocean WEEW Pacific Ocean SNWE

Nanophytoplankton primary production (mgC m -3 h -1 ) Atlantic Ocean SNEW W E Indian Ocean WEEW Pacific Ocean SNWE

Picophytoplankton primary production (mgC m -3 h -1 ) Pacific Ocean Atlantic Ocean SNEW W E Indian Ocean WEEW SNWE

% contribution of picophytoplankton PP to total Indian Ocean WEEW Pacific Ocean SNWE Atlantic Ocean SNEW W E

Variability of N diffusive fluxes, stability and mld

Influence of physical variables on phytoplankton PP N diffusive fluxesBrunt-Vaisala freq.Mixed layer depth Surface total PP -0.03(0.865)0.36 (0.000)-0.38 (0.000) 20%PAR total PP 0.19 (0.199)0.36 (0.000)-0.14 (0.120) 1%PAR total PP 0.23 (0.117)-0.14 (0.137)0.10 (0.260) Integrated total PP 0.04 (0.805)0.34 (0.000)-0.22 (0.013) Integrated Micro PP -0,02 (0.906)-0.04 (0.671)0.04 (0.646) Integrated Nano PP (0.674)0.18 (0.050)-0.25 (0.006) Integrated Pico PP 0.13 (0.367)0.35 (0.000)-0.20 (0.031) N diffusive fluxesBrunt-Vaisala freq.Mixed layer depth % Micro PP surface (0.598)-0.15 (0.107)0.17 (0.066) % Nano PP surface 0.01 (0.941)-0.26 (0.004)-0.11 (0.256) % Pico PP surface 0.11 (0.439)0.31 (0.001)0.02 (0.797) % Micro PP 20%PAR (0.725)0.03 (0.761)0.01 (0.935) % Nano PP 20%PAR (0.109)-0.25 (0.008)-0.08 (0.425) % Pico PP 20%PAR 0.32 (0.035)0.25 (0.008)0.04 (0.664) % Micro PP 1%PAR 0.42 (0.003)-0.01 (0.888)0.04 (0.691) % Nano PP 1%PAR 0.10 (0.496)0.11 (0.221)-0.17 (0.072) % Pico PP 1%PAR (0.047)-0.07 (0.459)0.14 (0.133)

Conclusions and future work Similar patterns for size-fracionated PP were found in the subtropical and tropical oceans, being the picophytoplankton the size class with higher primary production rates. The contribution of microphytoplankton to total PP increased in the stations closer to the coast or under the influence of equatorial upwellings. Integrated total PP was in general around 10 mgC m -2 h -1 in the subtropical and tropical oceans, except in those stations under the influence of equatorial upwellings or close to the coast. Water column stability, N diffusive fluxes and mixed layer depth showed a size-differential relationship with phytoplankton PP that also varied with the sampling depth. Future work: 1) futher analysis about the influence (linear regression) of physical variables on the phytoplankton size-fractionated PP including their combined effect (multiple linear regression and rda analysis); and 2) to explore this relationship by biogeochemical provinces.

Acknowledgements Thanks to all the people that contributed to the succesful development of the Malaspina 2010 Expedition, including the captain and crew of the RV Hespérides and the members of the UTM technical staff Ortega/

Pearson correlations by biogeochemical provinces N diffusive fluxesColumn stabilityMixed layer depth Surface total PP 0.39 (0.208)0.43 (0.123)0.04 (0.906) 20%PAR total PP 0.24 (0.460)0.74 (0.003)-0.04 (0.885) 1%PAR total PP 0.10 (0.766)-0.08 (0.786)-0.04(0.893) Integrated total PP (0.913)0.66 (0.011)-0.19 (0.523) Integrated Micro PP 0.27 (0.401)0.11 (0.971)0.51 (0.063) Integrated Nano PP (0.650)0.66 (0.010)-0.30 (0.299) Integrated Pico PP 0.06 (0.855)0.69 (0.006)-0.14 (0.637) N diffusive fluxesColumn stabilityMixed layer depth % Micro PP surface 0.22 (0.493)-0.57 (0.035)0.60 (0.023) % Nano PP surface (0.141)0.13 (0.650)-0.39 (0.172) % Pico PP surface 0.46 (0.132)0.10 (0.747)0.20 (0.493) % Micro PP 20%PAR 0.63 (0.027)0.12 (0.692)0.25 (0.393) % Nano PP 20%PAR (0.164)0.25 (0.388)-0.41 (0.144) % Pico PP 20%PAR (0.996)-0.36 (0.203)0.25 (0.399) % Micro PP 1%PAR 0.69 (0.013)-0.16 (0.582)-0.00 (0.991) % Nano PP 1%PAR 0.14 (0.672)0.48 (0.081)-0.08 (0.795) % Pico PP 1%PAR (0.171)-0.28 (0.332)0.09 (0.756)

Variability of each size class contribution with PP