RESULTS FROM MESOCOSMS EXPERIMENT STARESO 2012: TRANSPARENT EXOPOLIMERIC PARTICLES AND OPTICAL PROPERTIES 15th January 2013 Meeting MedSeA, Villefranche Sur Mer Francesca Iuculano Susana Agustí

Introduction: TEPs & Biological pump efficiency in high CO 2 world HYPOTHESIS: high pCO 2, high PP, higher ER, increase in TEP pool and size, higher export, sink of CO 2, higher microbial hotspot (From Dogsa et al., 2005) NEGATIVE FEEDBACKS (Engel 2004; Mari, 2008) for BIOLOGICAL PUMP VS NO pH EFFECT ON TEP PRODUCTION (Egge, 2009, Passow 2011) (From Arrigo, 2007) pH alters exo-polisaccaride structure POSITIVE FEEDBACKS?

Materials & methods: TEPs estimates FILTRATION (Vol 500 mL) duplicates for each treatment, every 2 days Into policarbonate filters of 0.4 µm and 2r = 25mm 1 mL staining Alcian Blue working solution (prefiltered by 0.2µm) EXTRACTION in 5 mL [H 2 SO 4 ] 80% blanks Absorbance at = 787 nm CTEP = (a sample - a blank) V -1 *F Spectrophometrically, following Passow & Alldredge (1995) Units: Xanthan Gum solution equivalent (µg Eq L -1 ) Microscopic enumeration VS colorimetric method NDR: Detection limit 2.2 µg; variation coefficient 13% Carbon content TEP = 0.75*TEP colour (µg XG eq L -1 ) from Engel and Passow, hours

Results: Transparent Exopolimeric Particles NO SIGNIFICANT pCO 2 EFFECTS IN TEP PRODUCTION TROUGHT TIME AND TREATMENTS VERY LOW CONCENTRATIONS

Introduction: UV LIGHT ABSORPTION Increase UV => Photobleaching, higher UV transmission, lower CDOM (optically active pool in UV) PHOTOCHEMICAL TRANSFORMATION OF DOM and of its BIOVAILABILITY (L vs HMW compounds) HYPOTHESIS: +pCO2?? + PHOTOBLEACHING? (From Zepp et al, 2007) (From Orellana and Verdugo, 2003) No studies for marine ecosystems on photo-reactivity: only 1 for CDOM (Rochelle Newall, 2004), assess NO pH IMPACT on CDOM concentrations

Underwater UV penetration Materials & methods: LIGHT ABSORPTION RADIOMETER PUV-2500/2510 (Biospherical instrument) ABSORPTION COEFFICIENT OF TOTAL (BIOGENEOUS) PARTICULATE MATTER (phytoplankton + detritus): Vol = 3L filtered into Whatman GF/F 25mm, every 2 days Absorbance spectras (DO) by double-beam spectrofotometer from 280 to 750 nm, 1nm interval (nm): Iz = Io e-Kz ap(λ) = 2.3 ODf() C / V ß () (Bricaud & Stramski, 1990) Chla Photosynthetic pigments MAA’s UV VIS

Material and Methods: CDOM analysis 0.2 µm MilliQ as blank Double-beam Spectrophotometer: Absorbance spectra (DO) range = nm; Scan speed = 120 nm/sec Spectral slopes: S and S by standard linear regression and RATIO (SR) as proxy of source and type of CDOM and DOM MW (Helms et al., 2008) Sampling, every 2 days in 100 mL glass flasks a 305 = UVB ref (Setlow,1974) 320 = UVA ref (Nelson&Siegel, 2002) 443 = CDOM satelites ref And other of radiometer (395,380,340,313) NB: in oligotrophic water we work at the very detection limit of the instrument! 10 cm quartz cuvettes NET photobleaching coefficients rates expressed in time, Kb (320) Kb (443) and determined by equation: K (d -1 ) = ln (a n /a 0 ) / t Positive K values indicate photo-humification process (thus we calculate duplication time) whereas negative values indicate photobleaching (thus we calculated half life time)

Results: RADIOMETER Unfortunately, no possible relationships between light extinction coefficient and cdom (only day 9) Steeper slope, lower UV penetration pCO 2 K 305K 313K320k340k380k395PARPAR*Chla* OUT * From CTD data Values in the table are average in time

ACIDIFICATION INCREASES UV TRANSPARENCY?

Results: aCDOM spectras VERY LOW COEFFICIENTS, no differences

Results: Photoreactivity of organic matter Means for each treatments through Exp time No significant differences SPECTRAL SLOPE Very low cdom abs coefficients

Results: Photobleaching kinetics Means CDOM (m -1 ) (µatm) (µatm) (µatm) (µatm)741 (µatm) (µatm) (µatm) a a a a a a a a a a S( ) kb 320 (d -1 ) Half life 320 (d) Duplication time 320 (d) Chla (µatm) (µatm) (µatm) (µatm)741 (µatm) (µatm) (µatm)

Results: PARTICLES LIGHT ABSORPTION pCO 2 Ap 305 (m -1 ) Ap 313 (m -1 ) Ap 320 (m -1 ) Ap 330 (m -1 ) Ap 340 (m -1 ) Ap 380 (m -1 ) Ap 395 (m -1 ) Ap 412 (m -1 ) Ap 440 (m -1 ) Ap 465 (m -1 )

General discussion: Environmental conditions during the summer in the Mediterranean ecosystem investigated: strong nutrient limitation; very low Chl a values, limiting PP NO pCO 2 impact in TEP production between mesocosms, in accordance with no effects in POC concentrations, B-glucosidase activity, bacterial abundance and production, metabolic rates, Synechococcus..coccolitophorides? TEPs produced under nutrient deficiency may become recalcitrant to bacterial utilization No alteration of CDOM as function of pH, no shifts in its bio-availability. ACIDIFICATION DO NOT INCREASE Photobleaching rates, but affect in some ways the half life time of this bio-optically active pool of DOM. No variation in particles light absorption in relation to very low Chla and phytoplankton biomass. pCO ap( )/Chla

Conclusions: This is the first OA mesocosm experiment conducted in such very oligotrophic conditions: DYNAMICS OF TEPS ARE NOT SENSITIVE TO ACIDIFICATION NO SIGNIFICANT CHANGES IN UV LIGHT TRANSMISSION (not enough datas), CDOM ABSORPTION PROPERTIES, SPECTRAL SLOPE AND PHOTOBLEACHING. Optical datas need to be further investigated (to calculate the contribution of phyto vs detritus to absorption particles

MANY THANKS TO EVERYBODY