Revisiting four scientific debates in ocean acidification research

Abstract

Abstract. In recent years, ocean acidification has gained continuously increasing attention from scientists and a number of stakeholders and has raised serious concerns about its effects on marine organisms and ecosystems. With the increase in interest, funding resources, and the number of scientific investigations focusing on this environmental problem, increasing amounts of data and results have been produced, and a progressively growing and more rigorous understanding of this problem has begun to develop. Nevertheless, there are still a number of scientific debates, and in some cases misconceptions, that keep reoccurring at a number of forums in various contexts. In this article, we revisit four of these topics that we think require further thoughtful consideration including: (1) surface seawater CO 2 chemistry in shallow water coastal areas, (2) experimental manipulation of marine systems using CO 2 gas or by acid addition, (3) net versus gross calcification and dissolution, and (4) CaCO 3 mineral dissolution and seawater buffering. As a summation of these topics, we emphasize that: (1) many coastal environments experience seawater pCO 2 that is significantly higher than expected from equilibrium with the atmosphere and is strongly linked to biological processes; (2) addition of acid, base or CO 2 gas to seawater can all be useful techniques to manipulate seawater chemistry in ocean acidification experiments; (3) estimates of calcification or CaCO 3 dissolution based on present techniques are measuring the net of gross calcification and dissolution; and (4) dissolution of metastable carbonate mineral phases will not produce sufficient alkalinity to buffer the pH and carbonate saturation state of shallow water environments on timescales of decades to hundreds of years to the extent that any potential negative effects on marine calcifiers will be avoided.

Towards a meaningful assessment of marine ecological impacts in life cycle assessment (LCA)

“…mussels, oysters, corals, coralline algae) reside in shallow water coastal environments. In addition, in many coastal regions, seawater pCO 2 is already significantly higher, and pH lower, than expected from CO 2 equilibrium partitioning between the atmosphere and the open ocean, in part due to biological processes (Andersson and MacKenzie, 2012).…”

“…Among the main reasons for this are morphological differences leading to differences in species sensitivity (Kroeker et al, 2010;Pandolfi et al, 2011;Fabry, 2008;Kroeker et al, 2011), and the potential effect of ocean acidification on a variety of physiological processes, including calcification, acid-base (metabolic) physiology, and photosynthesis, which are correlated to different components of the carbonate system. (Hofmann and Todgham, 2009;Doney et al, 2009;Kleypas and Yates, 2009;Pörtner, 2008;Veron, 2011;Andersson and MacKenzie, 2012). Moreover, differences in experimental conditions may lead to variable responses (Pandolfi et al, 2011;Fabry, 2008).…”

“…A major limitation of ocean-carbon cycle models is that coastal regions are presently not well represented (Andersson and MacKenzie, 2012). Coastal environments are characterized by much larger fluctuations in seawater carbonate chemistry than the open ocean, due to tidal dynamics, coastal upwelling, and major fluvial inputs (Andersson and MacKenzie, 2012), and evaporation and precipitation in shallow tropical basins (Hu et al, 2015).…”

“…While it is apparent that changing seawater chemistry will have serious negative consequences for most marine calcifiers, a strong (mechanistic) cause-effect understanding of how changes in ocean carbonate chemistry affect organism fitness and survival, which (physiological) response variables are most sensitive and which dissolved inorganic carbon specie(s) are most important to marine organisms is yet lacking (Pörtner, 2008;Andersson and MacKenzie, 2012). Additionally, potential trade-offs among calcification and other physiological responses, and the interaction between calcification and photosynthesis, are currently poorly understood (Hofmann and Todgham, 2009;Ries et al, 2009).…”

Free-ocean CO<sub>2</sub> enrichment (FOCE) systems: present status and future developments

“…The natural range and variability of pH conditions experienced by the organisms may effectively have profound consequences on their physiology (e.g., Price et al, 2012). Many nearshore environments are exposed to large diurnal fluctuations in pH associated with daytime and nighttime changes in the intensity of photosynthesis/respiration and/or calcification/dissolution, as well as water advection owing to tidal cycles and changes in winds (Andersson and Mackenzie, 2012). Note, however, that alternative treatments such as constant pH or abrupt changes may be required for particular experimental questions.…”