Instrumentationcean Acidi? cation (OA) has long been accepted pressure, nor the natural spatial and temporal variation of pH as an equally troublesome companion of Global and dissolved CO2 in their native habitats. Warming. Studies have not only exposed impend- The measurement of OA is historically complex and the cor-Oing problems, but have given scientists an insight rect determination of at least two parameters is necessary to into the complexities behind achieving a comprehensive under- obtain a valid description of the whole carbonate system and standing of the overall bionetwork response to this worldwide hence correctly interpret organism responses (9). Although problem. However, are investigators equipped well enough to dissolved CO2 is relative to the pH and partial pressure of deliver precise robust data critically needed for global ocean- CO2 (pCO2), due to previous dif? culties with pCO2 resolu-atmospheric models, allowing attribution of changes to both tion and disputes in pH measurement protocols, total alkalinity anthropogenic and natural causes? This article discusses the (AT) and dissolved inorganic carbon (CT) were the favoured considerations which need to be made while studying the im- parameters for ocean carbonate calculations (9). However, pacts of OA, on both an ecological and technological level. now that technology has developed allowing for more robust measurements of small-scale pCO2 and stable pH readings, From the Beginning there is debate on what parameters offer the least uncertainty. Since the Industrial Revolution, the mean ocean surface This has resulted in dif? culties with comparability of data, acidity is estimated to have increased by 25-30% (1, 2), and an assortment of the four parameters being measured in equivalent to a drop of 0.1pH, roughly 100 times faster than various experiments (9). Therefore, not only an appreciation any change in acidity known within the last 20 million years. of ecological variables is required but also standardisations in Predictions suggest an increase by a further 150-200%, repre- methods for measuring OA across the scienti? c community. senting an additional drop of 0.3pH, by the end of this century (2, 3, 4). Global unease as to the consequences of altering Freshwater Systemsthis ancient balance has seen OA become one of the fastest Acidi? cation of freshwater was a problem that was ? rst growing areas of research in marine sciences over the last few identi? ed in Scandinavia during the early 1970s. Freshwater decades. In 2011, Andersson & Mackenzie (5) documented a ecosystems typically have a neutral pH, but inconsistencies Google internet search for OA as generating around 605,000 can occur between acidic or alkaline (10), depending on fac-results; a replica search this week generated just under 3.2 tors such as rainfall and buffering capacity. The acidity of million, demonstrating the dramatic surge of international in- freshwater lakes and streams is predominantly determined by terest from both the Public, Government and Scienti? c com- the soil and rock types of an area, since 90% of the water en-munities. tering these systems has passed through the ground (11). Biota Although the speci? c effects of warming, acidi? cation and within these systems can be in? uenced directly by changes in changes in circulation will vary across ocean basins, it is clear water quality during both short acidic episodes and longer-that there will be multiple impacts on ocean and coastal eco- term sustained periods of acidi? cation as well as indirectly, by systems throughout the world(6). For aquatic ecosystems, the alterations to the balance of acid-sensitive and acid-tolerant consequences of long-term exposure to rising carbon dioxide organisms at different trophic levels (12). (CO2) concentrations are still poorly understood (7) and while Although species living in environments that naturally ex-the detection of direct effects (physiological) is readily achiev- perience signi? cant variation in pH and/or pCO2 may be more able, it will not necessarily shed light on the principal drivers tolerant of anthropogenic acidi? cation (10), the combined ef-which will be key in shaping future communities (8). Effects fects of both the chemical and biological alterations can ad-on individual species are likely to cascade throughout the entire versely impact biogeochemical processes (12). Therefore, it’s ecosystem, in? uencing species interactions, food web dynam- important to recognise the mechanisms which can cause both ics, migration patterns and the overall bionetworks resiliency natural and anthropogenic ? uctuations, and how the local to-(6). The complications in studying ecosystem-level impacts, pography in? uences the deviations. include yielding not only “unexpected results” but also some of the strongest ecological responses (i.e. phase-shifts) which Marine Systemsare often unanticipated as the impact of one component (e.g. Similarly to freshwater, local topography and biological OA) on another (e.g. kelp decline), requires knowledge of a activities can cause pCO2 and pH ? uctuations in marine en-third species (e.g. kelp-competitors) or mediating factors (e.g. vironments. A change in the balance between the respiratory interactions among stressors) (8). The real problem therefore, CO2 production and photosynthetic CO2 consumption of ma-is understanding the combined effects of additional stressors rine reef organisms, can cause substantial pH gradients on a (i.e. global warming effects) which happen in line with ris- diel cycle, which may be more prominent in shallow water ing acidity. Laboratory experiments can offer insight into how reefs where there is restricted exchange with the open ocean synergistic effects of added stressors determines alterations of (10). As these temporary variations seem to occur regularly, marine communities in high CO2 conditions, however, this it might not simply be the range over which pH varies that is doesn’t take into account adaptations and shifts in competitive important for tolerance to acidi? cation, but also the duration. March 201446 MTRMTR #2 (34-49).indd 46 MTR #2 (34-49).indd 46 2/21/2014 11:13:53 AM2/21/2014 11:13:53 AM