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

2. 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?

3. 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, 2001 2 hours

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

5. 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

6. 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): 465 443 412 395 380 340 320 313 305 Iz = Io e-Kz ap(λ) = 2.3 ODf() C / V ß () (Bricaud & Stramski, 1990) Chla Photosynthetic pigments MAA’s UV VIS

7. Material and Methods: CDOM analysis 0.2 µm MilliQ as blank Double-beam Spectrophotometer: Absorbance spectra (DO) range = 250-700 nm; Scan speed = 120 nm/sec Spectral slopes: S 275-295 and S 350-400 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)

8. 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 -0.3352-0.2616-0.2361-0.1623-0.0818-0.0625-0.094194.35410.0828 428.17-0.4689-0.3524-0.3200-0.2299-0.1321-0.1052-0.137162.8560.069 505.92-0.4697-0.3412-0.3057-0.2061-0.0997-0.0702-0.095470.8190.073 582.59-0.4767-0.3588-0.3249-0.2327-0.1340-0.1072-0.144860.5970.063 655.71-0.4495-0.3203-0.2853-0.1908-0.0904-0.0627-0.085069.3930.064 741-0.4578-0.3321-0.2995-0.2131-0.1236-0.0327-0.132259.4660.069 823.5-0.6567-0.3983-0.3642-0.2727-0.1001-0.1452-0.183373.7430.060 972.51-0.5037-0.3728-0.2870-0.2408-0.1353-0.1071-0.134366.6490.069 * From CTD data Values in the table are average in time

9. ACIDIFICATION INCREASES UV TRANSPARENCY?

10. Results: aCDOM spectras VERY LOW COEFFICIENTS, no differences

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

12. Results: Photobleaching kinetics Means CDOM (m -1 ) 428.17 (µatm)505.91 (µatm)582.59 (µatm)655.71 (µatm)741 (µatm)823.49 (µatm)972.52 (µatm) a4650.02740.04570.02470.04610.04110.05100.0396 a4430.03760.04970.02990.04900.04150.04670.0538 a4120.04120.05590.03550.05920.04670.05300.0559 a3950.04810.06320.04010.06740.05460.05860.0607 a3800.05480.06550.04440.07370.06190.06740.0643 a3400.09190.12040.08920.12110.11280.10260.1017 a3300.11140.13980.10790.14020.13090.12340.1201 a3200.14560.17370.13850.17800.16750.15760.1510 a3130.17840.20730.17470.21680.20330.19440.1798 a3050.23310.26290.22670.27370.25890.25140.2326 S(275-295)-0.0446-0.0422-0.0451-0.0421-0.0426-0.0415-0.0435 kb 320 (d -1 )-0.0164-0.0654-0.0535-0.0385-0.03190.0052-0.0551 Half life 320 (d) 42.168810.590612.951918.003921.744012.5846 Duplication time 320 (d)193.5823 Chla 428.17 (µatm)505.91 (µatm)582.59 (µatm)655.71 (µatm)741 (µatm)823.49 (µatm)972.52 (µatm) 0.0690.0730.0630.0640.0690.060.069

13. 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 ) 428.170.0040.003 0.002 0.008 505.920.004 0.003 0.002 0.0030.0020.009 582.590.003 0.002 0.0030.0020.009 655.710.0020.001 0.0020.001 0.002 0.009 7410.003 0.002 0.008 823.50.0030.002 0.009 972.510.002 0.0010.002 0.009

14. 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 2 675305313320330340380395440465 428.170.1240.0530.0280.0620.1050.0470.0180.0420.1250.052 505.920.1270.0520.0290.0660.1120.0460.0210.0500.1230.049 582.590.1490.0460.0180.0600.1410.0420.0130.0450.1990.055 655.710.1390.0240.0110.0600.1360.0250.0090.0550.2360.038 7410.1200.0380.0220.0630.1030.0350.0150.0470.1250.040 823.50.1480.0420.0150.0560.1510.0350.0100.0460.2190.046 972.510.1310.0350.0160.0600.1380.0320.0100.0480.2190.046 ap( )/Chla

15. 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

16. MANY THANKS TO EVERYBODY