Ocean Acidification

Water in its three ambient phases plays the central thermodynamic role in the terrestrial climate system. Clouds control Earth’s radiation balance, atmospheric water vapour is the strongest ‘greenhouse’ gas, and non-equilibrium relative humidity at the air–sea interface drives evaporation and latent heat export from the ocean. On climatic time scales, melting ice caps and regional deviations of the hydrological cycle result in changes of seawater salinity, which in turn may modify the global circulation of the oceans and their ability to store heat and to buffer anthropogenically produced carbon dioxide. In this paper, together with three companion articles, we examine the climatologically relevant quantities ocean salinity, seawater pH and atmospheric relative humidity, noting fundamental deficiencies in the definitions of those key observables, and their lack of secure foundation on the International System of Units, the SI. The metrological histories of those three quantities are reviewed, problems with their current definitions and measurement practices are analysed, and options for future improvements are discussed in conjunction with the recent seawater standard TEOS-10. It is concluded that the International Bureau of Weights and Measures, BIPM, in cooperation with the International Association for the Properties of Water and Steam, IAPWS, along with other international organizations and institutions, can make significant contributions by developing and recommending state-of-the-art solutions for these long standing metrological problems in climatology.

Continue reading ‘Metrological challenges for measurements of key climatological observables: oceanic salinity and pH, and atmospheric humidity. Part 1: overview’

Water dissolves many substances with which it comes into contact, leading to a variety of aqueous solutions ranging from simple and dilute to complex and highly concentrated. Of the multiple chemical species present in these solutions, the hydrogen ion, H+, stands out in importance due to its relevance to a variety of chemical reactions and equilibria that take place in aquatic systems. This importance, and the fact that its presence can be assessed by reliable and inexpensive procedures, are the reasons why pH is perhaps the most measured chemical parameter. In this paper, while examining climatologically relevant ocean pH, we note fundamental problems in the definition of this key observable, and its lack of secure foundation on the International System of Units, the SI. The metrological history of seawater pH is reviewed, difficulties arising from its current definition and measurement practices are analysed, and options for future improvements are discussed in conjunction with the recent TEOS-10 seawater standard. It is concluded that the International Bureau of Weights and Measures (BIPM), in cooperation with the International Association for the Properties of Water and Steam (IAPWS), along with other international organisations and institutions, can make significant contributions by developing and recommending state-of-the-art solutions for these long standing metrological problems.

Continue reading ‘Metrological challenges for measurements of key climatological observables. Part 3: seawater pH’

Acidification research has exploded in recent years, however, experiments testing effects of co-cycling hypoxia and pH on ecological and physiological processes are rare, despite the pervasiveness and potential importance of co-varying fluctuations in these parameters. Co-cycling dissolved oxygen (DO) and pH are difficult to precisely control, as gases used for manipulation influence both parameters. We successfully developed a LabVIEW™-based system capable of monitoring and controlling co-varying DO and pH in raw seawater flow-through aquaria. Using feedback from Oxyguard DO probes and Honeywell ion sensitive field effect transistor Durafet pH sensors, our system controls ratios of nitrogen, oxygen, carbon dioxide, atmospheric air, and CO2-stripped air within a total gas flow rate through mass flow controllers, to achieve target co-cycling DO and pH values in five treatments. Our system performed well in two long-term experiments investigating effects of diel-cycling hypoxia and pH on eastern oyster (Crassostrea virginica) feeding, growth, fecundity, Perkinsus sp. (Dermo) infection dynamics and immune response. In our 2013 adult oyster experiment, the severe low DO treatment averaged only 0.04 mg L−1 higher than the 0.50 mg L−1 target, and the moderate hypoxia averaged only 0.05 mg L−1 higher than the 1.30 mg L−1 target over 48 d of cycles. Mean pH for the hypercapnia plateau was within 0.02 above the 7.00 target. In our 2013 spat experiment, daily minimum DO in the severe and moderate hypoxia treatments were both within 0.06 mg L−1 of the 0.50 and 1.3 mg L−1 targets, respectively; hypercapnia plateau pH values were within 0.01 of our 7.00 target.

Continue reading ‘An automated monitoring and control system for flow-through co-cycling hypoxia and pH experiments’