3J-05 Proposed acidification indicators for the Baltic Sea

3J-05 Proposed acidification indicators for the Baltic Sea Bo Gustafsson Gregor Rehder Jacob Carstensen

2 Proposed acidification indicators for the Baltic Sea Introductory Thoughts MSFD Proton activity (or concentration) is per se the most direct acidification indicator Basically governed by the inorganic carbon system Carbon as eutrophication key variable Nixon et al., 1995 Carbon is the most direct link between productivity and O 2 - consumption MSFD, Annex III (Indicative lists of characteristics, pressures and impacts), table I, physical and chemical features: Profiles of ph and pco 2 or similar information to measure marine acidification ph = - log a H+ ph T = -log ([H + ] + [HSO 4- ]). Eutrophication: An increase in the rate of supply of organic matter to an ecosystem 106CO 2 + 16NO 3 - + HPO 4 2- + 122H 2 O + 18 H + (CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 ) + 138O 2

pco 2 : +1.6 µatm yr -1 CO 2 H 2 CO 3 H + + HCO 3 HCO 3 Ca 2+ + CO 3 2 Ω = Ca2+ [CO 3 2 ] K L ph T : -0.0016 yr -1 Weathering CaCO 3 Biogenic calcification 3 From Doney et al., 2009 2 Strict linkage relies on constant alkalinity

Carbon dioxide system C T Method readily established, very few measurements in the Baltic Sea No brackish water limitations A T Measured since a century, large improvement of data quality in the last 25 years Baltic Sea: Non negligible contribution from organic alkalinity, trends on decadal scale 4 pco 2 Mainly surface water applications Not included in HELCOM monitoring manual, but established SOPs (SOCAT) No brackish water limitations ph Inherent problem in potentiometric measurements Spectrophotometry so far only state-of-the-art method for open ocean conditions In HELCOM monitoring as side parameter

From global to local 5

A T - Alkalinity Trends in the Baltic Introduction of reference materials! 1995-2014 Rate: +3.4 µmol kg -1 yr -1 Relative Change: +5% Comp. North Atlantic: +0.1% 6 From Müller et al., 2016 A T -increase - mitigates acidificiation through CO 2 -uptake! - Increases potential CO 2 - uptake

pco 2 15 year time line 15 years of pco 2 measurements on VOS Finnmaid (and Finnpartner) long-term joined effort of Alg@line and Integrated understanding recently published in a Springer monograph Baltic (2008-15) Slope (µatm yr 1 ) 4.6-6.1 1.62 P-value <0.01 <0.01 BATS (1983-2011) 7 From Schneider and Müller 2018 R 2 0.007-0.023 0.16

pco 2 Productivity assessment Independent of C/N/P stoichiometry incp ( C z F t) 0.8 T eff F AS CO 2 exchange with the atmosphere; AS Z eff effective penetration depth; Δt considered time intervall; Calculated net carbon production in the different basins during the spring bloom for 2009. Schneider and Müller, 2018 8

ph ph Proposed acidification indicators for the Baltic Sea ph Obstacles Methods used so far not suitable for long-term analysis Difficult to separate any true signal from methodological problems Re-calibration not possible 8.4 8.2 8.0 7.8 Gotland Basin, Baltic Sea 7.6 1950 1960 1970 1980 1990 2000 2010 2020 8.4 8.2 Søren Sørensen Carlsberg Laboratorien Kopenhagen, 1909 Potentia Hydrogenii Bornholm Basin, Baltic Sea 8.0 9 ph-time series BY 15 (SMHI data) Glas electrode Monthly cruises Only at monitoring stations ------------------------------------------------------ 1995-2015 to detectable trend 7.8 1950 1960 1970 1980 1990 2000 2010 2020

ph recent progress Large variablility calls for high spatiotemporal resolution Until now lack of reference materials for S<20 Strong, instrumentdepending salinity dependence of ph-electrodes No user-friendly instrument for brackish waters Considerable progress made within BONUS PINBAL 10

BONUS INTEGRAL A BONUS Blue Baltic Research Project BONUS INTEGRAL Integrated carbon and TracE Gas monitoring for the baltic sea Funded 07/2017 06/2020 8 partners, 5 nations, 2.1 Mio Key Theme 5.1 Developing and improving the scientific basis for integrated monitoring programmes for continuous assessment of ecological status and human pressures 5.2 Developing and testing innovative in situ, remote sensing and laboratory techniques

Overarching ideas: BONUS INTEGRAL A BONUS Blue Baltic Research Project Use of the (extended) ICOS network for biogeochemical monitoring of the Baltic Sea, in combination to existing monitoring programs Improved ASE-parameterizations for the Baltic Sea Provide best experimentally based seasonal concentration charts for carbon dioxide, methane, and nitrous oxide Full integration of carbon system into high resolution physical biogeochemical model Advice for countries with upcoming ICOS infrastructure Model-ouput based recommendations on effective biogeochemical monitoring

14 Proposed acidification indicators for the Baltic Sea Summary and Discussion points Inorganic carbon system parameters as the primary tool to assess acidification Also allowing important insights on eutrophication and the link between net productivity and deep water oxygen demand Methods (almost) readily developed Methods allow an important bridge in the spatio-temporal coverage between discrete (monitoring cruises) and entire system (remote sensing / modelling) approaches Major advantage for ecosystem assessment in a world with MULTIPE DRIVERS

Vision Improved Assessment (Monitoring) of the Baltic Sea biogeochemistry through continuous CO 2 and GHG-observations on a basin wide scale Carbon system parameters as best indicator for Eutrophicaton Acidification Non-CO 2 GHG flux as ecosystem health indicator High spatiotemporal resolution bears potential to detect trends and gradual changes A Baltic Sea marine GHG measurement network Potential for extension and remote sensing based extrapolation 16

PUBLICATIONS 2016-2018 Müller, J.D., Schneider, B. and Rehder, G., (2016). Long-term alkalinity trends in the Baltic Sea and their implications for CO 2 -induced acidification. Limnol. & Oceanogr., 61: 1984-2002. Bakker, D.C.E., Pfeil, B., Landa, C.S., Metzl, N., Brien,... Schneider, B.... and Xu, S., (2016). A multi-decade record of high-quality fco 2 data in version 3 of the Surface Ocean CO2 Atlas (SOCAT). Earth System Science Data, 8(2): 383-413. Le Quéré, C., Moriarty, R., Andrew, R.M., Canadell, J.G., Sitch,... Rehder, G.,.. and Zeng, N., (2016). Global Carbon Budget 2015. Earth System Science Data, 7(2): 349-396. Müller, J.D., Schneider, B., Aßmann, S. and Rehder, G., (2018). Spectrophotometric ph measurements in the presence of dissolved organic matter and hydrogen sulfide. Limnology and Oceanography: Methods, 16: 68-82. Le Quéré, C., Andrew, R.M., Friedlingstein, P., Sitch, S., Pongratz,...Rehder,G.,.. and Zhu, D., (2018). Global Carbon Budget 2017. Earth System Science Data, 10(1): 405-448. Schneider, B. and Müller, J.D., (2018). Biogeochemical Transformations in the Baltic Sea - Observations Through Carbon Dioxide Glasses. Springer Oceanographie. Springer. submitted Müller, J.D., Bastkowski, F., Sander, B., Seitz, S., Turner, D.R., Dickson, A.G. and Rehder, G., submitted. Metrology for ph measurements in brackish waters part 1: Extending electrochemical pht measurements of TRIS buffers to salinities 5 20. Frontiers in Mar. Biogeochemistry. Müller, J.D. and Rehder, G., submitted. Metrology of ph measurements in brackish waters part 2: Experimental characterization of purified meta-cresol Purple for spectrophotometric pht measurements. Frontiers in Mar. Biogeochemistry.