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Controls on Ph in Surface Waters of Northwestern European Shelf Seas

Controls on Ph in Surface Waters of Northwestern European Shelf Seas

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Open Access 3 emitted between Discussions ), thereby signifi- 2 2 Biogeosciences , D. C. E. Bakker 1 2 ) in this . The aim of 1 − , I. Brown 2 uptake or whether their capacity to absorb 944 943 2 , V. Kitidis , and E. P. Achterberg 1 4 concentrations, questions arise on whether are 2 , M. C. Mowlem , M. Ribas-Ribas 1 1,4 , T. Shi ering . About 27 % of the anthropogenic CO 3 ff is decreasing while waters reach higher dissolved inorganic carbon ( 2 This discussion paper is/has beenPlease under refer review to for the the corresponding journal final Biogeosciences paper (BG). in BG if available. University of Southampton, National Oceanography Centre, Southampton, Southampton Plymouth Marine Laboratory, Prospect Place, PlymouthSchool PL1 of 3DH, Environmental Sciences, UK UniversityNational of Oceanography East Centre, , Southampton , SO14 UK 3ZH, UK able to maintain theirCO current rate of CO processes simultaneously impacts the carbonate chemistry. 1 Introduction Oceans form an importantcantly sink bu of atmospheric carbon1959 and dioxide 2011 (CO has been takenincreasing up atmospheric by the CO oceans (Le Quéré et al., 2013). However with region. Riverine inputs(DOC) were levels evidenced in by thewith high Strait consequent of dissolved remineralisation processes Moyle organic andtion (northern carbon a described Irish reduction in 15 ) % pH. andthe of The high the DOC the spatial southern distribu- variability pH North of variance the Sea along surface water the pH full in transect. shelf seawaters This where study a range highlights of and ancillary data. The maintransect, processes and controlling their the relative pHThe importance, distribution study were along highlights the determined ship’s the usingon a impact the carbonate statistical of chemistry approach. biological dynamicscruise, activity, of temperature the the shelf biological and activity riverine surfacecruise formed water. inputs transect. For the this Variations summer in controlance chlorophyll of along and the the nutrients full pH explained transectIn distribution 29 and % contrast, along as the of the much temperature the as distribution pH 68 % explained vari- in ca. the 50 % northern of part the of pH the variation transect. in the We present here a highEuropean resolution shelf surface seas water in pH summer datasetat 2011. obtained This such in is a the the high first Northwest paper time spatial is that resolution to pH (10 investigate has measurementsh the been carbonate measured chemistry dynamics of the surface water using pH Abstract Controls on pH in surfacenorthwestern waters European of shelf seas V. M. C. Rérolle Biogeosciences Discuss., 11, 943–974, 2014 www.biogeosciences-discuss.net/11/943/2014/ doi:10.5194/bgd-11-943-2014 © Author(s) 2014. CC Attribution 3.0 License. G. A. Lee 1 SO14 3ZH, UK 2 3 4 Received: 20 December 2013 – Accepted: 23Correspondence December to: 2013 V. – M. Published: C. Rérolle 15 ([email protected]) JanuaryPublished 2014 by Copernicus Publications on behalf of the European Geosciences Union. 5 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2 ects ff concentra- shelf trans- ering e 2 ff ff ect pH depending ff -rich deep waters will T C data are widely reported 2 ) and partial pressure of CO CO T p aerosols will decrease seawater A depends on the role of biological 4 solubility (Mehrbach et al., 1973). freshwaters (Thomas et al., 2005; 2 to the deep North Atlantic (Thomas fluxes in coastal seas. Most of the 2 T ) in this shelf sea region. This paper T 2 SO 1 A C 2 − fluxes using and H ert, 1985). The oceanic carbonate system is 946 945 2 ff 3 and low T , total alkalinity ( C T C with export of 2 . 2 ects on the marine carbonate system and therefore, on the capacity ) due to their high biological activity resulting in a net o ff 1 and free protons and leads to an increase in pH, whereas respiration, − , and deposition of HNO T 2 ecting the carbonate system are usually occurring simultaneously, making C ff )) used to study the carbonate system. The main factors controlling the car- 2 (0.2 PgCyr 2 We present here a new dataset of surface water pH determined in the Northwest The carbonate chemistry in the and the has been The strong spatial and temporal variability in the surface water carbonate chemistry pH is one of the four variables ( CO p ture, , and data. The data interpretation is supported by lower resolution surface mer and autumn due(Gypens to et temperature al., 2011). increase and remineralisation of organicEuropean matter shelf seas inat summer a 2011. high It spatial is resolutionpresents the (10 a measurementsh first study of time theusing that carbonate pH pH chemistry and has dynamics ancillary been ofcesses data. measured the control We shelf pH and used sea their a surface relativealong waters statistical importance the ship’s in approach transect. explaining to We the explain investigate observed pH which pH dynamics variance pro- using solely underway pH, tempera- well studied and particularly(Thomas air-sea and CO Borges, 2012; Kitidisact as et a al., sink 2012). for atmospheric Theet CO al., North 2004). Sea Surface water has pH beenperature increases in decrease reported winter (winter) to and and spring/early biological summer due activity to (spring) tem- and then decreases in sum- has led to contradictingprocesses estimates a of air-seait CO challenging to understand and determinein the coastal main drivers seas. of This theresolution carbonate highlights to chemistry unravel the the need varioussystem. for processes datasets and their with consequences high for spatial the and carbonate temporal acidic. Localised upwelling atsignificantly shelf decrease breaks pH of while relatively simultaneously acidic nutrient enhancing primary supply productivity (Feely through etmospheric al., CO 2008). Finally, surface waterpH uptake (Doney et of al., anthropogenic 2007). at- on its composition: for example amines are basic while carboxyl- and keto-groups are (Frankignoulle et al., 1998). Organic matter itself may also directly a crease in pH. Howevercolumn an stratification increase and primary intion productivity temperature facilitates (Eppley, will export 1972). typically of Waterresults also column particulate in stratifica- enhance organic a matter water net increase outon in of pH. surface the Rivers water can surface pH. resultdischarge layer Riverine in and inputs in direct can hence the changes have North di inBorges Sea coastal and carbonate of chemistry Gypens, high through 2010;nutrient the supply Gypens by et rivers can al.,in stimulate an 2011), primary increase thereby productivity in in lowering pH, coastal pH. whereas waters, resulting Additionally, respiration of riverine organic matter will decrease pH discharges of river watercentration (Thomas of et al.,remineralisation 2005). and Photosynthesis calcification decreases leadfect the to the a con- carbonate decrease equilibrium inA constants pH. rise in Temperature and changes temperature CO triggers af- a shift in the marine carbonate system resulting in a de- port at depth toet al., the 2005; adjacent Chen and deepments Borges, are ocean 2009; dynamic, Thomas subject to et (shelfwith a al., contrasting sea range 2004). e of carbon However, coastal interacting pump) biological environ- of and (Borges coastal physical seas processes to absorb CO ( bonate chemistry in coastal water are biological activity, temperature changes and (soft tissue and carbonate)tions and in solubility the pump surface processescontrolled ocean in by (Volk altering and biological CO Ho andvariations. physical Shelf processes seas leading have to been recently seasonalCO recognized and as geographical a potentially significant sink of levels. The capacity of the oceans to sequester CO 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2 CO p , T A ), at a fre- T , T C 948 947 was used (Zhang and Byrne, 1996). The sea- scale), provided by the Scripps Institution of , with one-third coming from the snow-melt wa- 3 2 T K and with a precision of 1 mpH units. Three bottles 1 − research cruise D366 in northwest European shelf seas (see Discovery er (certified on the pH ff cients of Thymol Blue were determined after the cruise on the pH instrument ffi The current regime in the North Sea is dominated by an anti-clockwise current along for the salinity2013), and and a temperature reported ranges Thymol Blue observed p during the cruise (Rérolle et al., metric method from Claytonand Byrne, and 1993; Byrne Rérolle et usinget al., 2012). Thymol al. Details (2013). Blue of The the as pH instrumentquency pH are measurements of provided indicator were in made 10 (Clayton Rérolle measurementsh onof the Tris total pH pH scale bu Oceanography, (pH University of Sanof Diego the were cruise analysedcoe to at verify the the start, quality middle of and end the pH measurements. The indicator extinction 2.2.1 Underway measurements Surface water pHnected was to measured the continuously5 m ship’s with underway depth. an water The2011 automated supply automated and instrument which pH 7 con- has system July 2011. an was The operated intake pH continuously at measurements between approximately were 6 conducted June following the colori- the Skaggerak Strait areNorth an Sea important is fresh waterdeeper seasonally source layer stratified (Thomas to enabling et thetinuously net al., North. mixed 2004), export The throughout whereas the northern of year thereceives carbon except shallow the near and southern majority river of nutrient North outflow the (the Sea to riverine southern is fresh the North con- water Sea inputs2.2 to the North Data Sea). and Somme rivers inEms the and English rivers Channel, inthe and the North Sea southern the is North Thames, on Sea. theters , order The of of /, annual 300 freshwater km and river2000). input In and into addition, the the rest brackish from waters the of major the rivers adjacent (OSPAR Commission, discharged through study area is further influenced by important riverine freshwater inputs from the Norwegian Trench (OSPAR Commission, 2000). Tidal currents canresidual be current stronger than in the many areas and cause important mixing in the water column. The reach 700 m. The southerntowards North the Sea north is todepth shallower ca. towards than the 150 m. 50 shelf m The edgewith and with Celtic a increases the Sea shallow in Atlantic eastern and Ocean. depth parttrending the The (generally trough Irish English as less Sea deep Channel than as is 80 increase 250 semi-enclosed, mvia m. in deep), the The Irish and a Sea communicates to deeper with the north-south the northwest and thethe edges, to with the Atlantic southwest. lesser waters extent coming from mainly the from English Channel the and northwest leaving but along also the to Norwegian coast a via much the 2.1.1 Hydrography of the northwest EuropeanThe shelf northwest seas European shelf seastion are of typically the shallower deep thanthe Norwegian 250 m Trench Skagerrak with (Fig. northwards the 1) to excep- (Pingree the et open al., Atlantic 1978), Ocean. which In extends the from Skagerrak Strait depths 2.1 Cruise The data used in thisduring study the have RRS been collected betweencruise 6 June track 2011 in and 7 Fig.and July 1). 2011 pH) The were four determinedcarbonate parameters system at of and a the facilitating high2014). carbonate internal spatial data system resolution, quality ( thereby verification (Ribas-Ribas over-constraining et the al., (e.g. DOC). 2 Method water nutrient data, in addition to variables determined only at CTD sampling stations 5 5 25 15 20 10 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) + from ) and 2 − 3 4 K from Dick- 4 system with and fluorescence 1 2 a K ). C p . Calculations were using a VINDTA 3C data (Hunter, 1998). T ) were also collected T A T Live S A C value was available. The T and C T C until nutrient analysis (within ◦ C 0.001 pH units. An additional correc- ). Further details are presented in Ribas ± 0.05). The regions 4 and 11 were rela- to determine whether the data from the 2 S p < 950 949 ), conductivity and chlorophyll and nutrients were collected every two hours and T C from the ship’s intake to the pH instrument. T ◦ test, T ect) (see Rérolle et al., 2013 for more details). A ff t , data were used to calculate T T C C erent ( ff are not temperature dependent and can therefore be used to T ) was determined by automated Winkler titration with photometric 2 A samples were collected using standard protocols (Dickson et al., T and A ) were undertaken using a segmented flow auto-analyser (Skalar San T − C 4 4 and gases (0, 251.3 and 446.9 ppmv CO measurements were made using a PML-Dartcomm 0.004 pH units has been applied to the pH data to correct for an analysis T 2 + C 2 CO The Analyses of nitrate and nitrite (total oxidised nitrogen, TON), phosphate (PO Continuous seawater temperature ( p http://www.bodc.ac.uk/projects/uk/ukoa/data_inventories/cruise/d366/ ical and water(MANOVA) masses was performed characteristics with (Fig. pH, regions were 2). statistically A di tively multivariate small and analysis corresponded of tothe areas surface variance where by deep storm waterthe or had data shelf been from mixing. locally these No regions. brought to statistical analysis has been performed with endpoint detection (Carrittusing and a Carpenter, high temperature 1966). combustion technique Samples (Badr for et al., DOC2.3 2003). were analysed Study region The study area has been split into eleven regions which were defined by geograph- silicate (SiO following methods described by Kirkwoodcarbonate (1989). vials and Samples kept were refrigerated stored at12 approximately in h 4 25 after mL sampling). poly- 2.2.3 CTD parameters Dissolved oxygen (O 2007; Bakker and Lee, 2012)curic in chloride 250 solution, mL and glassinstrument subsequently bottles, analysed (Mintrop, poisoned for with 2004). a Measurementsmaterial saturated provided were mer- by calibrated the Scripps using Institution certified of Oceanography. reference ( calculate pH atA the linear in relationship situand between oceanic used pH temperature to and using calculate pHmagnitude temperature thermodynamic at of was relationships. in the situ derived correction temperaturetion from where was of this no about correction 0.002 perturbation due to thein inflexion the of absorption theThe cell light final (Schlieren triggered pH e by dataset the has density been lenses submitted created to the British Oceanographic Data Centre The pH data wereFor corrected this to purpose in situ themade temperature using pH using CO2SYS and the (PierrotMehrbach et et al., al. 2006), (1973), onson refitted the by (1990). total Dickson pH and scale Millero with (1987) and KHSO water temperature increased by 0.2 Discrete seawater samples for from the underway supply. Discreteevery water four samples hours for in salinitycrete order ( salinity to samples were calibrate analysed the using underway an Autosal conductivity salinometer measurements. (Guildline). Dis- (Chl) data were obtained(TSG) installed from on the the Sea-Bird ship’s underway Electronics supply. SBE452.2.2 ThermoSalinoGraph Discrete underway water samples a shower-head equilibrator, pre-equilibrator840) and an (Hardman-Mountford et infrared gas al.,dard analyser 2008), CO (LICOR, and LI- referenced againstRibas NOAA-certified et al. stan- (2014). 5 5 20 15 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | . − C 1 4 4 ◦ − 10 m , Chl, < T , SiO , − 3 4 S . 2 C). Lowest pH ◦ 0.3 erent inorganic car- , TON, PO and TON. The same ff ± ) showed an absolute T 2 − , 4 4 and hydrogen ions con- S CO p 12.5 2 T C = and Chl. And finally, stepwise CO T p , , Chl, SiO S T region10 (e.g. pH , ) to obtain a normal distribution and 2 S 10 , 2 CO varied between 0.1 and 5.34 µM with low- p − 952 951 4 4 and data varied between 220 and 436 µatm (Fig. 4). T A 2 , T CO C p . 2 CO p . ]. (1) + ® [H variations were controlled by temperature variations, biological activ- ) and lower temperatures (Tmean / 1 2 2 − variations during the cruise are shown in Fig. 4, and pH displayed a typ- 2 CO CO p p 1 CO p K 0 and TON which were obtained at a lower spatial resolution. K − 4 4 ≈ The pH- Surface seawater pH along the transect ranged between 7.995 and 8.210 (Fig. 3), A stepwise multi-linear regression to relate pH data to environmental parameters has In addition, multi-linear regressions have been performed to relate the pH data in T C hanced DOC concentrations (up toSea) 90 and µM compared presumably with associatedquent 65 enhanced µM decrease in organic in the pH. matter northern Surface pH respiration and North with a conse- ical anti-correlation with ity, calcification, gas exchangeCullison-Gray and et dilution al. processes (2011).centration (e.g. The can rain be relationship expressed fall) between as as illustrated in mean discrepancy between 0.004 and 0.009 pH units. with highest values in(up the northern to North 1.6 µgL Seavalues featuring were enhanced observed Chl in concentrations the central North Sea in a well-mixed water column with en- 10, whereas the lowestthe levels Skagerrak were (region observed 9). in the central North3.2 Sea (region 8) Distribution and of the carbonate chemistryA variables comprehensive quality checkbonate and variable datasets comparison can between bewas the found found in di between Ribas all Ribas datasets. eta Comparison al. pair of (2014). of measured A the pH carbonate good variables with agreement pH calculated from Skagerrak area (region 9).est TON and concentrations SiO observed innorthern the part Celtic of Sea thewere south observed transect in to (regions regions 8, 1,Highest (region 2 9 levels of and 3) and Chl 11. and were 10). Chl observed in levels Highest in varied the the nutrients between north 0.12 concentrations west and part 1.54 of µgL the transect regions 2 and gion 11). Highest temperaturestransect were observed in in the the Bay southernmost of part Biscay of (region the cruise 5), the southern North Sea (region 7) and the Mean values and standardand deviations per Chl regions are of presentedcruise surface transect in apart Table from 1. theest Salinity Skagerrak area varied were where observed between salinity in7) 33.2 the was Irish as and and Sea low the 35.8 (region as Skagerrak 1), 26.4. duringwith the area Low- the lowest southern (region temperatures North 9). observed Seacruise Temperature (region in varied around the between Ireland Irish 10.3 (regions and and the 1 17.1 Malin and Seas 2 at respectively) the and start south of to the the (re- SiO 3 Results and discussion 3.1 Non-carbonate data distributions the software Matlab first been performed with all thedeep) data using from the the following surface parameters: samplesstepwise DOC, of multi-linear CTD O regression stations has ( been performed again but without O each individual region with the underwaymulti-linear parameters regressions have been performed with the underway variables In order to perform statistical analysesformed on using the a data, all common thestandardised logarithm parameters (centred function have been (log to trans- 0tively and skewed, even scaled after to transformation. 1). The data Distributions analysis of has TON been was performed using strongly posi- 2.4 Statistical approach 5 5 25 15 20 10 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2 − 4 4 p < and CO erent − p ff 4 4 0.5987, indicated that = 2 , Chl, SiO T resulted in SiO , 2 S , the first and second , 2 2 K cient Rho ffi and 1 K with pH was statistically significant obtained in the northern part of the 2 S were found to explain 37 %, 24 % and R S and to determine how each process influences T ects of various environmental factors on the and T 954 953 ff A , T 2 , 2 and T C solubility and first dissociation constant for carbonic acid, or in the carbonate constants 2 T C ected by similar processes and this supports the hypothesis that ff the CO 1 K were a 62). The stepwise multi-linear regression with DOC, O 2 = and ) levels in the river discharges. Here, in the areas impacted by river discharges, n T 0 . An increase in C K 2 from the important agricultural and industrial activity inland. A positive correlation The large variability in water masses and environmental conditions sampled in the The impact of primary production on pH is highlighted by a positive correlation be- In the next sections, we consider the e T CO helped to untangle some of the key processes controlling the pH distribution in the C between pH and nutrients,can be and further a indications negativecoastal of waters. correlation riverine inputs with supplying dissolved high organic nutrient matter and DOCdynamic fluxes shelf to system constituted a clearchallenge challenge was for the that data the interpretation.sampling A samples further time had can been haveareas collected (Thomas a at and Borges, strong various 2012). times impact Nevertheless, the of on results of the surface the day. statistical water The approach pH, particularly in bloom of temperature on pH isThe evidenced impact by of a freshwater negativetween correlation inputs pH between by and these rivers salinity, variables. but(and is the evidenced sign by of enhanced thethe correlations correlation correlation will be- between depend pH on and the salinity total is alkalinity positive because the rivers are enriched in when the nutrient variablesbeing were explained. included, The resulting lowest inputs percentages 54 impacted were to the obtained pH 95 % distribution: inSea the of regions (regions Celtic the where 3, Sea, pH riverine 6 the variance Channel in- andtransect and 7 (region the respectively). 10) Southern The was North low duedirectly to evidenced by the a fact correlation that of the Chl impact concentration of with primary pHtween production (see pH below). was and not Chl, and a negative correlation between pH and nutrients. The impact regions, the two regressionsnant (with variables and being without linked nutrients topattern, data) the where resulted same mixing with processes. the Regions withpact 6 domi- on outflows to the from carbonate 8 rivers chemistry. showedbe Overall and a explained between di using 21 the only and Baltic salinity, 79 temperature % Sea and of had Chl. the a pH This variance was strong can significantly im- increased variability along the transect was mainly determined by biological activity. In most of the The statistical analysis, undertakenwhich using the the pH underway variance data, is indicates explained the by extent the to various forcing (Tables 2 and 3). The pH pH and O biological activity and remineralisation playedtransect. a The key same role in stepwise(18 the multi-linear %), pH regression DOC variations but along (15 %) without the cruise O and transect. Chl (11 %) explaining 44 %3.2.2 of the pH Underway data distribution for along the 11 the regions from the CTD stations along0.001, the full transect (correlationTON coe indicated that theand correlation explained of 72 % O of pH11 %, variance. respectively, O of the variance in pH. The strong correlation with O carbonate equilibrium constants, pH. pH control by environmental forcings 3.2.1 Surface data from CTD stationThe along pH the entire data transect was strongly correlated with dissolved oxygen for the surface samples respectively (Cullison-Gray etchanging al., the 2011). seawater Thisp carbonate relationship chemistry indicates will thatdissociation have constants processes opposite of carbonic impacts acidand on a respectively, will decrease pH result in in pH. and an increase in with 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2 to 2 ected ff (and pH) 2 . (2) 2 CO proportionally p erent stages of . The formation T variability in the ff T A 150O 2 A + CO P p ects on 16 ff N erent linear relationships ff 42 with µ specific growth rate, O T b · 175 a H = 106 but also increases C T C → + ect the carbonate chemistry in the bloom variability in the northern and central part of ff 956 955 2 18H + CO p to form organic matter (biological production) can O 2 2 , from Mehrbach et al. (1973) as refitted by Dickson 2 K 78H + − and 2 4 ect the carbonate equilibrium constants as detailed in the fol- 1 ff in the North Sea (Thomas et al., 2005) and the English Channel K 2 HPO + CO − 3 p levels than temperature increases. Similarly, Gypens and colleagues and chlorophyll concentration corresponding to the di 2 2 exchanges (months). Seawater pH may therefore have a memory of past CO 2 16NO CO p p + 2 erent regions. Biological processes were the dominant control over pH in regions 1, The impact of primary production on the pH distribution is evidenced by the posi- These observations are in agreement with previous studies investigating the controls ff Temperature changes a lowing expressions of explanation of 79 % ofbetween the pH pH and variance in temperature the intion region that regions primary (Table 1, 3). production 2, The was 3, positivein the 5, correlation dominant these parameter 7 regions. controlling and the The 10in pH provided positive distribution temperature a enhances correlation further the can primary indica- a be production and (µ related b constants; to Eppley, the 1972). fact that3.3.2 an increase Temperature exchanges. The anti-correlation betweenthat nutrients primary and production formed pH a reinforces majorample, control our in of observation pH region in 10 parts the ofcorrelation multi-linear the of study regression region. Chl with For with S, ex- T pHpH and over variance Chl S (Table highlighted and 2). the T, The strong but addition the regression of only TON described to 21 the % of regression the analysis resulted in an remineralisation processes will stronglywaters. For a example, Watson etbetween al. (1991) proposed three di development of the bloom:of the the “recent bloom and history the bloom”,chemistry “late the stage” changes “peak of in the stage” bloom. phytoplanktonair-sea This blooms CO is related occur to at theblooms fact shorter or that other timescales carbonate events (days) impacting than the carbonate chemistry faster than the air-sea CO therefore increases seawater pH. tive correlation between ChlIreland and (region pH 2) as (Fig.chlorophyll observed concentration in 5). as the However, pH the the Malin is stage Sea of not north-west the necessarily of phytoplankton directly bloom, correlated and to grazing the and to the ratio of carbon to nitrogen (Zeebe and Wolf-Gladrow, 2001). Biological production The nitrate uptake to formof organic organic nitrogen matter results therefore in not an only increase decreases in 3.3 pH dynamics 3.3.1 Primary production The photosynthetic uptake ofbe CO expressed as (Sarmiento and Gruber, 2006): 106CO inter-annual antagonism between biological and temperaturein e the English Channel andthe the competition Southern between Bight temperature ofby and riverine the biological nutrient North controls inputs Sea. can which They be stimulate also strongly biological show activity. a that on surface water (Gypens et al., 2011). Indeed, Thomaswas and the co-workers main observed driver that of biologicalthe the activity North seasonal Sea whereas temperaturesouthern variations part. were The driving fully the the mixed atmosphere, waters but of not the intermining southern spring region when were primary a productionobserved source was of in more CO important their in 3-D de- coupled biogeochemical-hydrodynamic model a seasonal and 2, 3, 5, 7the and Skagerrak 10. (region Temperature 9), was with8. dominant still River in an inputs the important seem central contribution tosouthern by North have biology North Sea a on Sea (region strong pH (region 8) impact in 7) region on and as pH well in as in the the Channel Celtic (region Sea 6) (region and 3). the di 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | and T 2 µM), C + ) and TON er capacity 1 ff − . (3) 2 S ciently pronounced ) and TON ( ffi 1 − 40 µmolkg + ( 0.000116 solubility (Zeebe and Wolf- T + C 2 ects on the carbonate chem- S ff . (4) 2 36 µmolkg S + ( 0.0118 T − C ) T 0.000118 958 957 + ) observed in these two regions, supports the S C) and enhanced T ◦ A 2 9.7944ln( − + 0.0184 − /T /T ciently high to balance the remineralisation processes. Pri- ffi 3670.7 + 1394.7 + . This could partly explain that the two regions 1 and 7 were sources of 62.008 T − 4.777 A = = ) ) 1 2 K K ( ( to the atmosphere. 2 10 10 4 µM) concentrations compared to surrounding waters. Higher nutrient concentra- An additional riverine impact, in our study area, is the lowering of the bu + log log to balance the acidity of the upwelled water. The second region waswas south brought of to the surfaceShetland partly passage Islands by (region the but advection 11) alsoIsles of area where by (Turrell, Atlantic 1992) deep intense (Fig. water water 8). tidal throughthe Indeed, mixing tidal the flow currents around is – are intensified constrained the inevidenced by Orkney the by topography area and (Pingree colder where et temperature Shetland al., ( ( 1978). This upwelled watertions was resulted in enhanced primary production but this was not su was likely mixed either byactivity. The strong mixing tidal of the mixing watergradients (Simpson column showed is and a evidenced Sharples, typical on stratified 2012) Fig. water 8b,and or column where a temperature storm the more profile temperature homogenised on temperature 15surface profile June on 2011 waters 23 with June 2011. higherand This mixing concentrations lower resulted of in pH, compared to observation made the previous week (Fig. 7c and d). Tidal and wind-driven(Huthnance, currents 1997). are These important currentsand in can includes the lead tidal northwest to upwellingSharples, European intense which 2012). shelf brings mixing These seas bottom of deepernutrients water the waters relative to water are to the column, typically surfacedepth. the more Acidified (Simpson surface acidic, waters and brought enriched waters to the in served due surface in by to two shelf remineralisation mixing regions processes duringsouthwest of have the of been organic - cruise. the The matter Lizard first at Peninsula region (UK) was (region to 4) the south (Fig. of 7a), Cornwall, where the water column due to low CO 3.3.4 Mixing 2012). The lower salinityhypothesis (and that lower the organic matter was derived from riverine inputs. ance of the twoEnhanced processes. levels Remineralisation of remineralisation wassolved were not organic infered measured matter from during (e.g. the DOC) ourmeasured high and in transect. concentrations low this of concentrations region of dis- duringthe particulate pH the organic variance cruise. matter along The the DOC(northern full distribution transect. part In could of two explain region areas, 15was the % 1) Strait of presumably and of southern not Moyle North in su mary the Sea Irish production (region Sea 7), in the thea primary southern consequence production of North a Sea fully mixed is water generally column limited and an by turbidity low (Simpson light and Sharples, levels as Riverine inputs potentially haveistry: two opposite the indirect addition e whereas the of addition nutrients ofineralisation organic enhances processes. carbon However, the may in result our primary in observations a production we decrease only (increase in note pH in the through resulting pH) rem- bal- Gladrow, 2001). The impact ofthe temperature Skagerrak on area the (region pH 9) distributioncoast (Fig. is relatively 6a evidenced and warm, here b). in lowTemperature In salinity distributions the deep waters explained trough of ca. alongure the the 50 6b % Norwegian Baltic shows of Sea the the anti-correlationas are between temperature pH discharged increased temperature (Fig. variation from and the 6a). pH in North with this Sea a into region. decrease3.3.3 the in Fig- Skagerrak pH Strait. Organic and inorganic river inputs: remineralisation An increase in temperature increasesin the a carbonate decrease equilibrium in constants and pH results (Hunter, 1998) (see Eq. 1) and CO and Millero (1987): 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2 in 2 , 2009. erent seasons. ff , 2011. 10.1016/j.dsr2.2009.01.001 960 959 fluxes in coastal regions. In order to quantify the 2 airs (Defra), the Natural Environment Research Council ff , 2010. 10.1016/j.marchem.2011.02.005 , 2005. We would like to thank Mark Stinchcombe for providing the nutrients and fluorescence and nutrients, enabled us to unravel the main processes a , Deep-Sea Res. Pt. II, 56, 578–590, doi: 10.4319/lo.2010.55.1.0346 10.1029/2005gl023053 2 Rasch, P. J.: Impact of anthropogenic atmospheric nitrogen and sulfur deposition on ocean Measurements, PICES special publication, 3, 2007. carbonic acid in seawater media, Deep-Sea Res., 34, 1733–1743, 1987. Johnson, K. S.: ApplicationsMar. of Chem., in 125, 82–90, situ doi: pH measurements for inorganic carbon calculations, CO concentration scale calibration of40, m-cresol 2115–2129, purple 1993. and at-sea results, Deep-Sea Res. Pt. I, and the Partial Pressure ofNational Carbon Dioxide, Oceanography Cruise Centre Report Southampton, D366/367 27–31, – 2012. 6 June–10 July 2011, strongly to eutrophicationdoi: than to ocean acidification,the Limnol. Oceanogr., coastal 55, ocean:doi: 346–353, diversity of ecosystems counts,of the Winkler Geophys. method for Res. determiningRes, dissolved 24, oxygen Lett., in 286–318, seawater; 1966. a 32, NASCO report, L14601, J. Mar. ocean: continental shelves as sinks and near-shore ecosystems as sources of atmospheric of dissolved organic nitrogenTrAC-Trend. Anal. Chem., in 22, natural 819–827, 2003. waters using high-temperature catalytic oxidation, Borges, A. V. and Gypens, N.: Carbonate chemistry in the coastal zone responds more Bakker, D. C. E. and Lee, G. A.: In situ Observations of Dissolved Inorganic Carbon, Alkalinity Badr, E. S. A., Achterberg, E. P., Tappin, A. D., Hill, S. J., and Braungardt, C. B.: Determination References Only datasets with aaccurate high estimates spatial of the and air-sea temporalmain CO controls coverage on will the allow carbonate chemistry usshould over be to an sampled annual obtain using time more the scale, the high same resolution transect pH approach during di between pH and otherment variables, with and previous infer studies,distribution the the along main the biological controlling cruise activity transect processes.temperature for formed and In this riverine the summer agree- inputs cruise. main balanced However, orduction. in control even some This dominated of regions the study the impact highlights of pH shelf primary the waters pro- strong where several variability processes ofThe simultaneously spatial the impact variability is the in particularly carbonate situ importantmixing chemistry. in conditions shelf providing in seas with a coastal rivers and relatively water column localised impact on the seawater carbonate chemistry. The high spatial and temporality, chlorophyll resolution of the pHcontrolling data the along with carbonate temperature,surface chemistry salin- waters. The dynamics statistical of approach allowed the us northwest to determine European the main shelf correlations sea 4 Conclusions Doney, S. C., Mahowald, N., Lima, I., Feely, R. A., Mackenzie, F. T., Lamarque, J.-F., and Dickson, A. G., Sabine, C. L., and Christian, J. R.: Guide to Best Practices for Ocean CO Dickson, A. and Millero, F.: A comparison of the equilibrium constants for the dissociation of Cullison-Gray, S. E., DeGrandpre, M. D., Moore, T. S., Martz, T. R., Friederich, G. E., and Chen, C.-T. A. and Borges, A. V.: Reconciling opposing views on carbon cycling inClayton, the T. and coastal Byrne, R.: Spectrophotometric seawater pH measurements: total hydrogen ion Borges, A. V., Delille, B., and Frankignoulle, M.:Carritt, Budgeting D. E. and sinks Carpenter, J.: and Comparison and sources evaluation of of currently employed modifications CO Programme, Contract Number PITN-GA-2009-237868.Ocean Acidification This Research work Programme (UKOA) is whichfor a was Environment, jointly contribution funded Food by to and the(NERC) the Department Rural and UK A the Departmentno. of NE/H017348/1. Energy and Climate Change (DECC) under grant agreement dissolved oxygen dataCurie used Initial in Training Network this (ITN) work. funded This by the work European was Commission supported Seventh Framework by SENSEnet, a Marie Acknowledgements. 5 5 30 25 20 10 15 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , 2 , 2004. 10.5194/essd-5- , 2012. 10.1016/j.aca.2013.05.008 , 2011. 10.1126/science.1095491 ects of vertical stability on phytoplankton dis- ff 962 961 , 2012. 10.1016/j.trac.2012.07.016 , 2012. , 2005. 10.1016/j.pocean.2010.11.004 é, G., Brown, J., and Dye, S.: An operational monitoring system to provide ff -related variables in the ocean, ICES J. Mar. Sci., 65, 1498–1503, 2008. 2 fluxes and seawater carbonate chemistry in the Southern North Sea, Prog. 10.1016/j.csr.2012.04.012 2 10.5194/bg-2-87-2005 , 2013. 10.1016/j.ecss.2012.02.016 Kattner, G., and87–96, Borges, doi: A. V.: The carbon budget of the North Sea, Biogeosciences, 2, from shelf sea pumping, Science, 304, 1005–1008, doi: Shelf Seas, Cambridge University Press, Cambridge, 424 pp., 2012. including biogeochemistry during the1–2, International doi: Polar Year, Estuar. Coast. Shelf S., 100, 165-2013 Bellerby, R. R. G. J.: Seawater-pHTrend. measurements Anal. for Chem., ocean-acidification observations, 40, TrAC- 146–157, doi: berg, E. P., and Tyrell,west T.: European Intercomparison shelf of seas, Biogeosciences carbonate Discuss., chemistry in determinations preparation, 2014. in2006. north- 153–162, 1997. Council for the Exploration of the Sea (ICES) CM,Fishwick, 100, J. 29, R., 1989. Harris, C.,sonal Martinez-Vicente, dynamics V., of Woodward, E. the M.42, carbonate S., 30–40, system and doi: in Smyth, the T. J.: western Sea- English Channel, Cont.Peters, Shelf G. Res., P., van derCiais, P.,Doney, Werf, S. C., G. Enright, R., C.,Kato, Friedlingstein, Ahlström, P.,Huntingford, E., C., A., Keeling, Jain, R. Andrew, A. F., K., R.pach, Klein Jourdain, M. M., Goldewijk, C., R., K., Bopp, Schwinger, Levis, L., J.,global S., Sitch, Canadell, Levy, S., carbon P., J. Stocker, Lomas, budget B. G., M., D., 1959–2011, Poulter, Viovy, N., B., Zaehle, Rau- S., Syst. and Sci. Zeng, Data, N.: The 5, 165–185, doi: 3S and 3C, Version2004. 2.0, MARine ANalytics and DAta (MARIANDA), Kiel, ,mission, 45 , pp., 149 pp., 2000. tributions in the summer on1978. the northwest European shelf, Deep-Sea Res., 25, 1011–1028, and Achterberg, E. P.: Development ofseawater a measurements, colorimetric Anal. microfluidic Chim. pH2013. sensor Acta, for 786, autonomous 124–131, doi: indicators of CO 45, 1919–1930, 1998. parent dissociation constants of carbonicOceanogr., 18, acid 897–907, in 1973. seawater at , Limnol. Théate, J.-M.: Carbon dioxide1998. emission from European estuaries, Science, 282, 434–436, of air-sea CO Oceanogr., 88, 59–77, doi: Hines, A., Moncoi 1972. upwelling of corrosive “acidified” water2008. onto the , Science, 320, 1490–1492, acidification and the inorganic2007. carbon system, P. Natl. Acad. Sci. USA, 104, 14580–14585, Kitidis, V., Hardman-Mountford, N. J., Litt, E., Brown, I., Cummings, D., Hartman, S., Hydes, D., Kirkwood, D.: Simultaneous Determination of Selected Nutrients in Sea Water, International Huthnance, J. M.: North Sea interaction with the North Atlantic ocean, Ocean Dynam., 49, Hunter, K. A.: The temperature dependence of pH in surface seawater, Deep-Sea Res. Pt. I, Gypens, N., Lacroix, G., Lancelot, C., and Borges, A. V.: Seasonal and inter-annualHardman-Mountford, N. variability J., Moore, G., Bakker, D. C. E., Watson, A. J., Schuster, U., Barciela, R., Frankignoulle, M., Abril, G., Borges, A., Bourge, I., Canon, C., Delille, B., Libert, E., and Feely, R. A., Sabine, C. L., Hernandez-Ayon, J. M., Ianson, D., and Hales, B.: Evidence for Eppley, R. W.: Temperature and phytoplankton growth in the sea, . B., 70, 1063–1085, Thomas, H., Bozec, Y., de Baar, H. J. W., Elkalay, K., Frankignoulle, M., Schiettecatte, L.-S., Thomas, H., Bozec, Y., Elkalay, K., and de Baar, H. J. W.: Enhanced open ocean storage of CO Thomas, H. and Borges, A. V.: Biogeochemistry of coastal seas and continental shelves – Rérolle, V., Floquet, C. F. A., Mowlem, M. C., Connelly, D. P., Achterberg, E. P., and Sarmiento, J. L. and Gruber, N.: Ocean Biogeochemical Dynamics, PrincetonSimpson, University Press, H. J. and Sharples, J.: Introduction to the Physical and Biological Oceanography of Pingree, R., Holligan, P., and Mardell, G.: The e Ribas Ribas, M., Rerolle, V. M. C., Bakker, D. C. E., Kitidis, V., Lee, G. A., Brown, I., Achter- Le Quéré, C., Andres, R. J., Boden, T., Conway, T., Houghton, R. A., House, J. I., Marland, G., OSPAR Commission: Quality Status Report 2000, Region II Greater North Sea, OSPAR Com- Rérolle, V. M. C., Floquet, C. F. A., Harris, A. J. K., Mowlem, M. C., Bellerby, R. R. G. J., Mintrop, L.: Versatile Instrument for the Determination of Titration Alkalinity, Manual for versions Mehrbach, C., Culberson, C. H., Hawley, J. E., and Pytkowicz, R. M.: Measurement of the ap- 5 5 30 25 20 25 10 20 30 15 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) 1 − ) (µgL 1 − ciencies in and Chl per Mean Chl Std Chl ffi − − 4 4 4 4 , SiO Std SiO − 3 4 − 4 4 Mean SiO − 3 4 , TON, PO T , Std PO S − 3 4 964 963 in Seawater: Equilibrium, Kinetics, Isotopes, Else- 2 changes, Cam. Contemp. Astrophy., 99–110, 1985. 2 Mean TON Std TON Mean PO T C) (µM) (µM) (µM) (µM) (µM) (µM) (µgL ◦ Std T C) ( ◦ Mean ( S ert, M.: Ocean carbon pumps-analysis of relative strengths and e ff Std S Mean values and standard deviations (Std) of situ conditions: absorbance and protonation1996. behavior of thymol blue, Mar. Chem., 52, 17–25, ocean-driven atmospheric CO variability in the sink for atmospheric1991. carbon dioxide in the North Atlantic, Nature, 350, 50–53, vier Science, 2001. to North Sea fish stock recruitment, ICES J. Mar. Sci., 49, 107–123, 1992. Region Mean 1234 34.115 35.14 0.236 35.24 0.237 35.38 11.06 0.148 35.65 11.34 0.069 35.09 0.60 13.63 0.1010 34.28 0.11 13.59 1.32 0.1111 34.86 0.40 14.55 3.15 0.44 30.88 0.94 14.09 0.10 35.25 0.14 0.59 14.99 0.63 35.31 2.09 1.15 0.29 13.68 0.16 0.80 1.71 0.65 14.69 0.01 0.90 12.50 0.00 0.26 1.07 0.24 10.95 0.92 1.24 0.17 0.21 0.31 0.64 0.18 0.06 0.10 0.74 0.55 0.06 1.58 3.89 0.10 0.08 0.03 0.10 0.06 0.06 0.06 0.71 0.07 1.51 0.04 0.54 0.04 2.00 0.04 0.03 1.12 0.06 0.03 0.58 0.33 0.05 0.93 1.06 0.08 0.64 1.97 0.03 0.05 0.92 1.56 0.04 0.54 0.30 0.42 0.24 0.59 0.15 0.44 0.41 0.20 1.61 0.11 1.34 0.39 0.24 0.33 0.43 0.07 0.10 0.38 0.29 0.20 0.31 0.44 0.27 0.20 0.09 0.30 0.63 0.16 0.43 0.05 0.07 0.41 0.04 regions. Table 1. Zhang, H. and Byrne, R. H.: Spectrophotometric pH measurements of surface seawater at in- Watson, A. J., Robinson, C., Robinson, J. E., le B. Williams, P. J., and Fasham, M.Zeebe, J. R.: R. Spatial E. and Wolf-Gladrow, D. A.: CO Volk, T. and Ho Turrell, W.: New hypotheses concerning the circulation of the northern North Sea and its relation 5 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | and − 4 4 0.009 0.030 − − 0.017 0.001 0.019 − − and Chl, SiO values express how T 2 , R 0.012 0.0010.011 0.005 0.002 S − − − and Chl parameters with the T , 0.019 0.012 0.004 0.025 S − − 0.006 0.006 0.003 0.003 0.010 0.009 0.002 0.018 − − − values express how much of the pH variance 2 0.005 966 965 R − 0.013 40.26 72.82 33.330.009 13.83 17.15 14.22 0.016 0.033 0.004 0.005 − 0.007 0.010 0.007 0.011 0.005 0.017 0.025 − 30.24− 42.82 68.49 − cients of each parameter used to describe pH. ffi 0.009 0.002 0.014 0.002 0.013 0.008 0.79 0.405.9145.62 36.65 12.12 0.37 28.85 0.58 37.26 31.81 35.50 0.41 54.67 29.06 30.06 0.21 16.41 6.53 50.99 0.65 19.99 73.01 0.63 8.55 6.11 0.25 0.94 0.94 0.54 0.61 0.81 0.61 0.78 0.74 0.79 36.22 59.74− 27.18 19.29 43.34 14.36 − − 4 4 4 4 2 2

InterceptS 8.080 8.107 8.112 8.111 8.078 8.080 8.094 8.111 8.161 Regions R1 R2 R3 R5T R6 R7 R8 R9 R10 R S T Chl 48.47 51.23 33.89 32.69 16.27 53.53 42.47 7.00 85.34 Chl 0.015 0.009 0.012 0.007 R S InterceptS 8.083 8.083 8.111 8.111 8.072 8.086 8.096 8.109 8.163 Regions R1 R2T ChlSiO R3TON 63.78 R5 26.37 R6T Chl 43.39 R7SiO 59.60 0.015 R8 0.015 40.40 R9 22.22 R10 0.007 25.16 0.022 36.13 49.66 0.022 TON

Results of the multi-linear regression analysis using

Results of the stepwise multi-linear regression analysis using

ffi cients coe ffi cients coe

cients of each parameter used to describe pH.

Equation ffi Equation % % much of the pH variance iscan explained be by attributed the regression. to Thedetails each component the parameter of equation is the coe pH expressed variance in that percentage. The second part of the table Table 3. Table 2. underway data divided into 11 regions. The is explained by theeach parameter regression. is The expressed component incoe of percentage. The the second pH part variance of that the table can details be the attributed equation to TON parameters with the underway data divided into 11 regions. The Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 968 967 ) characteristics. S − Map of the D366 cruise track (black line) with bathymetry contours (contour scale). The 11 regions indicated using colour coding and defined using geographical and water T Fig. 2. mass ( Fig. 1. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 970 969 and pH for the cruise D366 with the variables plotted 2 CO p in European shelf seas for the cruise D366 with colour bar T values. T Map of surface water pH Time series of sea surface Fig. 4. against Julian day. Fig. 3. indicating pH Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | the (A) map of sea surface salinity (A) 972 971 the northern North Sea (region 10). (B) sea surface pH and temperature plotted vs. Julian day for the Skagerrak (B) Impact of temperature on sea surface pH distribution. Observed sea surface pH and Chl concentrations plotted against Julian day for Fig. 5. Malin Sea (region 2) and Fig. 6. region. observed during the cruise D366limit in of the region Skagerrak 9. region (region 9). The dotted line shows the Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Chl, (B) sea surface temperatures (A) location of station 20 sampled (A) 974 973 depth profiles of temperature, DIC and TON at the two stations. TON concentrations, plotted against Julian day. The encircled part of the plots (B–D) (D) Impact of storm mixing on sea surface pH (region 4). Impact of tidal shelf mixing on sea surface pH (region 11). DIC and observed in region south of the(C) Orkney Islands. Time series plotsdenotes of sea data surface observed pH in and region 11. Fig. 7. on the 15Cornwall June (UK). 2011 (red) and station 30 sampled on the 30 June 2011 (green) south of Fig. 8.