Is the deep vertical export related to surface biotic and abiotic processes ?

1. IMBER IMBIZO II meeting, Heraklion, Greece, 11/10/2010 Gaby Gorsky, Lars Stemmann, Lionel Guidi, Marc Picheral, Hervé Claustre, Louis Legendre and Pieter Vandromme Is the deep vertical export related to surface biotic and abioticprocesses? Laboratoire d’Océanographie de Villefranche-sur-mer

2. Summary • Background • UVP methodology • Data available • Linking particles size to fluxes • Linking fluxes to surface autotrophic communities composition • Importance of mesoscale physical processes and lateral advection • Perspectives (zooplankton processes) • Conclusion

3. Background • We have tried to evaluate the connectivity between the different main types of surface ecosystems and the deep export • Since the stratification may affect the surface ecosystem that could be a link between stratification and characteristics of the deep export.

4. Background Conditions within the mixed layer (community composition, physical processes) are important parameters that influence the export ! The mixed layer depth in the ArabianSea, subtropical North Pacific and subpolar North pacific showing high variability

5. Background UVP4 MUVP (mini UVP): nextgeneration Miniaturization are underway to adapt the UVP on gliders and profilingfloats UVP5, last generation Methodology used : In situ particles counter and imaging system ! • Different generation of UVP • Measure particles and images from a certain size UVP5 30 kg 3000m

6. Location of data + TARA 2000 profiles since 1991 The different symbols indicate different versions of the UVP

7. µg m d-1 mm mm Fractal dimension Guidi et al. (2008a) From abundance to mass and flux Flux mg m-2 d-1 Abundance nbr m-3 f(size) Dry Weight mg m-3 f(size) 100 m 1000 m - k: Measure of the export efficiency Alldredge & Gotschalk (1988) Estimation of the mass from the size Estimation of the sinking rate from the size Using calibration from literature (mostly surface)

8. Estimation of the Flux from size distribution m d-1 mg m-2 d-1 Best fit for A and b mg # m-3 Guidi et al. (2008a) No depth effect Fractal dimension: ~2.3 Error of ~30% in A, ~20% in b Guidi et al. (2008b) Can we convert size to mass and flux? Worldwide R² = 0.70 • From size to flux (minimization) Biosope

9. Relating phytoplanktoin photophysiological properties to community structure The trophic status of the environment is globally correlated with the community structure of the autotrophic plankton : globally: more microphytoplankton means more productivity Figure 2 from Uitz et al. 2008

10. Flux (mg m-2 d-1) Ze 3000 depth Flux (mg m-2 d-1) Ze 30 10 depth 2 Primary producer community and aggregate export • Mass flux and phytoplankton • (from pigments) • Export efficiency and phytoplankton k mg m-2 d-1 Eutrophic region Oligotrophic region R²=0.27 k = 0.9 k = 0.2 Guidi et al. 2009

11. Particle size and phytoplankotn Link between surface communities and export Guidi et al., 2009

12. Conceptual scheme Guidi et al. 2009 • But : • Physical processes and heterogeneity • Impact of zooplankton (some groups could feed directly on picophytoplankton) If stratification leads to globally more oligotrophy (left) then flux will be reduced and bacterial degradation would dominate. Nevertheless, we should take into consideration the spatial heterogeneity of dynamic physical processes that may influence the mass vertical or oblique transport of particulate matter. Than a given biological production may fuel distant ecosystems. (Guidi et al. 2008)

13. LATERAL EXPORT AND COASTAL PRODUCTION TRANSPORT OFFSHORE • Oligotrophic zone could be enriched by lateral advection • mesoscale eddy field produces submesoscale features that mediate POC export via surface frontogenesis

14. LATERAL EXPORT AND COASTAL PRODUCTION TRANSPORT OFFSHORE Lateral advection is related in part to physical structure such as isopycnes but also to the agregation, dispersion, reagregation processes. Then it will be necessary to know the structure of the planktonic ecosystem from end to end. abundance of large particulate matter in the South Pacific gyre. The discontinuity is due to a subtropical frontal zone L. Guidi et al.: Aggregates distribution in the South-Eastern Pacific, Biogeosciences, 5, 2008

15. Heterogeneous vertical export • Dynamic hydrological (eddies, filaments, gyres, currents) may upwell nutrients and stimulate the primary and secondary production. • The vertical export of PM can be heterogenous, averaging over large scales may give underestimated values: • According to Garcon et al. (2001) Mesoscale physical dynamics govern the major time/space scales of bulk biological variability (biomass, production and export). Mesoscale eddies seem to have a strong impact on the ecosystem structure and functioning

16. Heterogeneous vertical export NE Atlantic B) A) Guidi et al., 2007 Equatorial Pacific C) Depending on the mesoscale structures, the vertical export of PM can be spatially heterogeneous Gorsky et al., 2001

17. Aggregates and mesoscale structures A, B filaments, currents, C, D eddies, • Anticyclonic eddies and filaments show nutrient injection that enhance new production • Eddies transport and concentrate particles from coastal origin into the open ocean (Australia) E) Fernandez et al. 2005 Gorsky et al., 2002 Stemmann et al., 2008

18. Aggregation by zooplankton Zooplankton processes of aggregation contribute to the vertical export.. For example appendicularians filter picophytoplankton but are not on biogeochemistry models. It may be possible to model the distribution of some species from the potential food source distribution and hence their potential contribution to the geochemical processes Oikopleura spp. Ocean-wide seasonal distributions of potentially dominant appendicularian species predicted by our model using MODIS satellite seasonal mean sea surface temperature and chl a, compared to in situ data (dots) from the literature. Blue: Oikopleura dioica. Green: O. longicauda. Brown: O. fusiformis. Orange: O. rufescens However, a better estimation could be obtained by the end to end approach. Lombard et al.: New multispecies appendicularian model. MEPS 398: 109–125, 2010

19. End to End plankton community structure in March 2010 Villefranche sur mer, France 200 0.02 0.2 2 20 >2000 We are conducting now end to end studies in order to include the whole planktonic system. It is important to take into consideration the ecosystem as whole and sample it at once. SIZE µm Viruses Pico-autotrophs Nanoplankton Microplankton Mesozooplankton Pico-heterotrophs Invertedmicroscopy Flow Cytometry Flowcam Zooscan Methods Zooprocess Zooprocess Zooprocess Software + UVP in TARA

20. Conclusion • It is possible to estimate a large part of the variance (~70%) of fluxes with the composition of autotrophs in surface waters, and to estimate the fluxes (and exponent of Martin curves) with particles size distribution. • The IMBIZO workshop in 2008 (Burd et al. 2010) underlined that an • imbalance exists between organic carbon sources and sinks in the dark ocean. Among other features • the estimates of metabolic activity in the dark ocean exceed the influx of organic substrates. • two sources are poorly quantified: lateral advection of particles and the population of slowly settling particles

21. Conclusion • Here we are suggesting that • the vertical export due to the mesoscale physical processes, • the lateral export due to large scale physical processes and • the ecosystem structure • can be responsible of a heterogenous vertical export. • New technologies are needed for high resolution data acquisition on large scales (MUVP) together with an understanding of how the predicted stratification will affect these mesoscales features !