Toward an assessment of ocean acidification in the Adriatic sea and its impact on the biogeochemistry of marine carbonate system

The increase of CO2 amount in the atmosphere has created great concern: it will in all probability result in changes in temperature, precipitation and/or their seasonal amplitudes with consequences not only on sea level rise but also on chemical equilibrium of the CO2 system in seawater, mainly reducing pH and carbonate ion concentration (Ocean Acidification). The process is now well documented in field data from all around the world. However is not sufficiently witnessed in the Mediterreranean Sea, due to the scarcity of good quality data. On this concern, results for the Adriatic Sea are presented: from experimental measures of pH and total alkalinity, two seasonal pictures of pH and carbonate system parameters have been drawn. In addition, a pH decrease of 0.063 pHT units with related chemistry changes has been inferred in the North Adriatic Dense Water (NAdDW) over the two last decades. These results, although preliminary, merit attention as confirm that N. A. sea has been affected by OA, being sensitive to the climate forcing. Potential impacts of OA are several and should be assessed, as many might even exacerbate hyopoxia/anoxia events, already affecting the area. OA might also affetc the food web, as the carbonate reduction has the potential to alter the distribution and abundance of marine organisms that use calcium carbonate to build their shells or skeletons (corals, plankton) and the organisms that depend on them for survival (fishes, marine mammals)

New observations of CO2 - induced acidification in the northern Adriatic Sea.

In the Mediterranean area the North Adriatic is one of the most suitable sites for studying the response of marine pH to increased atmospheric CO2 levels because of its shallow depth and being exposed to strong cold winds during winter. During VECTOR VECSES 1 cruise (15 to 19 February 2008), pH and total alkalinity (AT) were measured over the North Adriatic basin. These data were compared with that collected during ASCOP 2 cruise (30 April to 8 May 1983), 25 years before. During ASCOP 2 cruise pH was determined at 25 ?C using a potentiometric method in NBS scale (pHNBS) while during VECSES 1 cruise it was measured by the spectrophotometric method (precision ? 0.003) and the results expressed on "total scale" at 25?C (pHT). To allow a comparison the pHNBS values were converted into the total scale and the reliability of the conversion was checked. Comparable North Adriatic dense water bodies were identified according to T, S and AOU data from both the datasets and the carbonate system parameters were compared. Results at 25?C showed an acidification of -0.063 pHT units from 1983 and 2008 and a decrease in carbonate ion concentration (-19.6Qmol kg-1), whereas total alcalinity (+ 74 Qmol kg-1), dissolved inorganic carbon (+ 110 Qmol kg-1) and CO2 (+ 108 Q atm) exhibited a net increase over the same period. The drivers of these changes were analyzed and the increase in atmospheric CO2 concentration was identified as the main forcing that determined the acidification observed. It would correspond to an acidification rate of -0.0025 pH units/year, that is of the same order of magnitude of the rate measured in other oceanic regions. This study, even if it was based on the comparison of only two datasets spanning 25 years is the first published work (Luchetta et al., Chem. and Ecol., 2010, vol. 26, 1-17) assessing the ocean acidification process in the Mediterranean region and one of the few based on the analysis of experimental data

Carbonate chemistry dynamics and saturation states of calcium carbonate in the surface waters of the Adriatic Sea

The amount of high quality measured carbonate system properties (pH, TA, TCO2, fCO2) is so scarce in the Mediterranean Sea that is almost impossible to have any precise idea of their distribution throughout this semi-enclosed sea (Touratier & Goyet, 2010). The carbon chemistry is even more poorly known in the Adriatic Sea, although this basin is affected by the gradual process of ocean acidification (OA), at least in the northern part (Luchetta A. et al. 2010), receives the runoff of several rivers and hosts sites of dense water formation by two different mechanisms (bottom convection on the shallow shelf in the northern sub-basin and open sea deep convection in the southern sub-basin). This contribute presents the results of two cruises along the Adriatic Sea, in 2008, that investigated the carbonate chemistry dynamics of surface seawaters (pHT, TA and derived parameters as TCO2, fCO2, CO3=, HCO3-) and the saturation states with respect to aragonite (Ar) and calcite (Ca). The two campaigns were conducted under very different seasonal conditions: characteristic of wintry season in February, as shown by the low sea surface temperature (8?C<SST<14?C) and the high quite homogeneous density (29.15<<29.45) all along the basin, except on the western slope affected by river runoff, and conditions characteristic of late summer in October, as shown by the warm SST (17 ?C <SST<21 ?C) and the higher density stratification (26.5<<29.4) all along the basin. Surface waters exhibited large spatial and temporal variations in pHT (7.945<pH<8.100) and TA (2620 ?m/KgSW <TA< 2750 ?m/KgSW) at 25 ?C, as well as large variations at in situ temperature in fCO2 (230 ?atm< fCO2< 415 ?atm), TCO2 (2275 ?m/KgSW <TCO2<2450 ?m/KgSW), HCO3- (2075 ?m/KgSW< HCO3- < 2250 ?m/KgSW) and CO3= (195 ?m/KgSW < CO3=<265 ?m/KgSW ), depending on the main drivers (physical pump, biological processes, river runoff). The average in situ values of pHT, TCO2, CO3=, Ca and Ar exhibited by Adriatic surface waters in the two seasons have been compared to those of other oceanic regions (Feely et al. 2009), they show that Adriatic Sea contains the highest amount of dissolved inorganic carbon, thus assessing that Adriatic marine system is able to absorb significant amounts of atmospheric CO2. In the end, the computed saturation states of calcium carbonate are presented as an interesting example of impacts of OA; actually such parameters have been shown to control the impacts of OA on many marine calcifying organisms. Ca and Ar largely vary (4.75<Ca<6.45; 3.1<Ar<3.9) in space, within the same cruise, and in time, between the two seasons, in dependence of the major drivers. However their values, being well above the limit (=1)under which calcium carbonate dissolves, indicate a good environmental status for surface waters of the Adriatic Sea

Distributions of pHT, total alkalinity and CO2 fugacity in the Adriatic Sea during the SESAME campaigns, winter and late summer 2008. CIESM

pH experimental data of good quality are still scarce in the Mediterranean as in the Adriatic Sea. Here are presented the results of two repeated surveys at basin scale, conducted within SESAME project, showing significant longitudinal and seasonal variabilities of the pH and other carbonate system parameters

Seasonal cycles of pH and carbonate system parameters in the southern Adriatic Sea during one year of VECTOR project

Within the VECTOR project (activity 8.1.2) the pH and other physical chemical parameters were acquired as seasonal time series from September 2007 to June 2008, at the AM1 station (in the centre of the Southern Adriatic Pit). The pH was measured by the spectrophotometric method (precision ? 0.003) and the results expressed on "total scale" at 25?C (pHT@25?C). In a few seasons also the total alkalinity (AT) was measured by potentiometric titration at 25?C (precision ? 3 Qmol/kg) and the results were checked against sea water certified as reference material (by dr. A.G. Dickson). The other derived parameters of the carbonate system (pCO2, DIC, lAr, lCa) were computed from pH, TA, salinity, temperature, SiO2, PO4 according to Lewis and Wallace 98. The pH seasonal variability was the highest in the upper layer (0-100 m), as clearly recognizable in fig 1a, b being the pH value mainly driven by biology during the productive seasons (from spring to late summer) or by mixing with deeper waters and exchange processes with atmosphere in winter. In the deeper layers (intermediate and bottom) the seasonal variability was lower but not negligible, probably driven by remineralization processes of dissolved and particulate organic matter locally produced, as suggested by Apparent Oxygen Utilization (AOU) and nitrate seasonal variabilities (fig. 1c, d, e, f). Generally, the highest differences of physical and biogeochemical properties can be observed in both the upper (0-100m ) and the intermediate (100-800 m) layers in September and June whereas during wintry season (January and February) variabilities were much lower. Through early to late summer season, the nutrients pH and dissolved inorganic carbon (TCO2) all suggest that both layers are strongly affected by biology (quite active primary production in the upper layer although in general the region has to be considered oligotrophic, and remineralisation processes in the intermediate layer). As confirmed by the good correlation with AOU and fluorescence. The vertical variabilities of such parameters are large, representing the 28 %, 0.4 %, -115 % of the total amount. Narrower changes can be observed passing from the intermediate to the bottom layer (800 - bottom) in January, February and June. A good correlation between changes of nutrients, pH, carbonate system and AOU is still observed, indicating the significant contribution of remineralisation processes to the final values. The physical and biogeochemical differences between the intermediate and the bottom layer further suggest that water masses of different origin filled these two layers. The persistence of inter layers variability through the year might suggest the absence of any abrupt change in the circulation scheme. The three forms of carbon dioxide in seawater (TCO2 aq, HCO3 -, CO3 = ) and the saturation states of calcite and aragonite were computed, from the experimental measures of pH and total alkalinity (reported in table 1) along the water column, in February June and October 2008. Values at surface show to be higher than the surface values of other oceanic regions, this is due to the higher alkalinity of the Mediterranean Sea, thus confirming peculiar characteristics of the carbonate system and the good saturation states of the Med Sea and southern Adriatic sea in particular

Role of meteorological, hydrological and biogeochemical forcings on carbonate system variability at PALOMA station (Gulf of Trieste)

The Gulf of Trieste is the Northernmost area of the Adriatic Sea and, as other shallow shelf areas, is more influenced by exchanges with the atmosphere than deep seas. Hence, it is thought to be highly sensitive to the effects due to the increase of CO2 dissolved in seawater induced by global atmospheric CO2 increase. The most concerning consequence of CO2 dissolution in marine waters is the decrease of pH: a process commonly referred to as "ocean acidification". On the other hand, the dynamics of carbonate system in this coastal zone are also influenced by the variability of oceanographic conditions, mainly induced by meteorological and hydrological forcings, and by production and regeneration processes. We present preliminary results of a monitoring activity started in January 2008, addressed to a better comprehension of the effects of meteorological forcings and biogeochemical processes on the carbonate system and pH in the Gulf of Trieste. Real-time meteorological data, hydrological and biogeochemical monthly sampling were collected in the site of the mast PALOMA, located in the centre of the gulf (25 m of depth). During 2008, the highest values of pHT, (spectrophotometric method, Total scale, 25?C), were measured in the upper layer during summer (pHT=8.120), as a result of a event of production. A strong thermohaline stratification of the water column occurred from June to beginning of August, when remineralization processes in the deeper waters (AOU>142.87 &#956;M -O2) released CO2 (fCO2=1044 &#956;atm) and caused a decrease of pHT (7.648). This process was probably interrupted by one unusually storm event with strong wind (up to 163 km/h) that occurred on 08/08/2008, since in September the water column appeared well ventilated. Total alkalinity (TA) concentrations were modulated both by river inputs and by biogeochemical processes, as the remineralization of organic nitrogen coupled to ammonia production, which determined the maximum values of TA in August and November (up to 2693 &#956;mol/kg)

Carbonate system dynamics in the Gulf of Trieste (North Adriatic Sea)

We present first results of a study started in January 2008 and focused on the analysis of the variability of carbonate system in the Gulf of Trieste (N. Adriatic Sea). Total alkalinity, pH, and mayor physical and biogeochemical parameters were measured at PALOMA station (centre of the Gulf). We evidenced the role of direct inorganic carbon riverine inputs, sea water temperature and production / regeneration processes as mayor drivers of the observed carbonate system variability during the studied period

Integrated management of coastal hypoxia in the Northern Adriatic Sea: the case study of the Province of Rimini

An integrated monitoring network aimed at the management and mitigation of environmental and socio-economic costs of hypoxia was developed for the coastal zone of Rimini (Emilia Romagna - Italy). This area was chosen for the presence of high anthropogenic pressure (416,000 equivalent inhabitants and tourist summer peak of up to 973,110), industrial and agricultural activities, as well as maritime traffic and nutrient river discharges (about 600 ty&#1048576;1 of N and 300 ty&#1048576;1 of P in 2002). EMMA monitoring network was planned by linking scientific knowledge on hypoxia phenomenon with in situ experimental investigations. Its integration with existing environmental monitoring, available facilities and data resources was considered in order to increase the cost effectiveness of the project. The structure of EMMA monitoring network was based on four main components: - an instrumental monitoring network of the coastal zone, by means of an automated remote station coupled by traditional sampling at fixed stations, to provide a set of high resolution environmental data; - a 3-D numerical model (ROMS) implemented to perform hydrological simulations and forecast of hypoxia in the area of interest; - a Local Information Centre (LIC) devoted to the acquisition and exchange of data and model results among network components; - a Decision Supporting System to bring scientific aspects of hypoxia phenomena into management requirements of local institutions and socio-economic operators

The carbonate system in the Gulf of Trieste: a two years time series at PALOMA station

In the framework of VECTOR project (activity 6.2.2), pH, Total Alkalinity (AT) and physical/chemical parameters were acquired on a monthly basis since January 2008, in the water column at the PALOMA site (Advanced Oceanic Laboratory PlatforM for the Adriatic sea, Gulf of Trieste, 25m depth ). The pH was measured by the spectrophotometric method (precision ? 0.003) and the results expressed on "total scale" at 25?C (pHT@25?C). AT was measured by potentiometric titration at 25?C (precision ? 3 Qmol/kg) and the results were checked against sea water certified as reference material. The other parameters of the carbonate system (pCO2, DIC, CO3 =, lAr, lCa) were computed from pH, AT, salinity, temperature, SiO2, PO4. To our knowledge this is the first time series of these parameters collected in the North Adriatic Sea. These data allowed an initial identification of roles played by biological ad physical factors in controlling the carbonate system dynamics and the pH annual cycle. During the stratified period (April to September), CO2 uptake by primary producers in the upper layer (DO sat > 100 %, Fig 1) determined the highest annual values of pHT@25?C in both years (Fig 1). By contrast, remineralization processes generally prevailed in the deeper waters undersaturated of oxygen (DO down to 48%, Fig 1) and the minima annual values of pHT@25?C were reached. From January to March of both years the water column was homogeneous and cold, reaching the lowest annual temperatures (down to 8.8 ?C). The pHT@25?C values were generally low and constant and the oxygen saturation was around 100 %. These characteristics indicated that biological processes were playing a minor role in determining the observed values of pHT@25?C while physical factors as temperature induced CO2 solubilization were more important. AT concentrations (median value 2633 Qmol/kg) were higher than in open Mediterranean sea (~ 2600 Qmol/Kg ) due to the inflow of rivers with a carbonatic drainage basin. AT variability was mainly modulated by riverine inputs with variable AT concentrations and by the occurrence of strong remineralization processes in the bottom layer (Aug.- Nov. 2008, up to 2658 Qmol/kg, S=37.5) as shown by the relationship with AOU. The seasonal evolution of in situ pCO2 was deeply influenced by the variations of temperature that modulated not only CO2 solubility but also the chemical equilibria between carbonate species. Despite the production processes in the upper water column during summer, pCO2 values were higher than 400 Qatm on the whole water column, from July to December 2008 and from August to October 2009. During these months the Gulf of Trieste was thus acting as a potential CO2 source. In contrast, from January to June of both years, pCO2 values were always lower than 400 Qatm and the Gulf was a CO2 sink (up to -19.0 mmol C m-2 d-1, on 14 Jan 2009) especially during high wind events. An exception to this trend were the high pCO2 value (up to 606 Qatm) observed in April 2009 and May 2008, in surface low salinity waters (S down to 27.6 psu), which were ascribed to the ventilation of CO2 from supersaturated riverine waters

Biogeochemical properties of Adriatic dense waters

Distribution and characteristics of dense waters in the Adriatic Sea were monitored during their formation in winter 2008, and later, in autumn at the end of the seasonal stratification period in the Adriatic Sea. Different types of dense waters were identified on the basis of their physical features. In order to characterised their biogeochemical properties dissolved oxygen, nutrient, and particulate organic matter (chlorophyll a, particulate organic carbon, particulate nitrogen and phosphorus) were analysed