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Near-shore Antarctic pH variability has implications for the design of ocean acidification experiments

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ABSTRACT

Understanding how declining seawater pH caused by anthropogenic carbon emissions, or ocean acidification, impacts Southern Ocean biota is limited by a paucity of pH time-series. Here, we present the first high-frequency in-situ pH time-series in near-shore Antarctica from spring to winter under annual sea ice. Observations from autonomous pH sensors revealed a seasonal increase of 0.3 pH units. The summer season was marked by an increase in temporal pH variability relative to spring and early winter, matching coastal pH variability observed at lower latitudes. Using our data, simulations of ocean acidification show a future period of deleterious wintertime pH levels potentially expanding to 7–11 months annually by 2100. Given the presence of (sub)seasonal pH variability, Antarctica marine species have an existing physiological tolerance of temporal pH change that may influence adaptation to future acidification. Yet, pH-induced ecosystem changes remain difficult to characterize in the absence of sufficient physiological data on present-day tolerances. It is therefore essential to incorporate natural and projected temporal pH variability in the design of experiments intended to study ocean acidification biology.

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Annual changes in pH and aragonite saturation state ranges.Projections of yearly changes in pH and aragonite saturation state, Ωarag, in McMurdo Sound, Antarctica, using a disequilibrium (a, c) and equilibrium (b, d) scenario. Annual range in pH increases and Ωarag decreases with future acidification. End-century maximum pH and Ωarag remain above acidification thresholds of pH 7.9 and Ωarag of 1. Projections are based on field data collected in 2011–2013 (circle). January and June monthly means represent mid-summer and winter conditions, respectively. The overall mean represent mean values from spring into winter conditions. Onset of aragonite undersaturation (triangles) is marked for each parameter and additionally for November monthly mean conditions.
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f5: Annual changes in pH and aragonite saturation state ranges.Projections of yearly changes in pH and aragonite saturation state, Ωarag, in McMurdo Sound, Antarctica, using a disequilibrium (a, c) and equilibrium (b, d) scenario. Annual range in pH increases and Ωarag decreases with future acidification. End-century maximum pH and Ωarag remain above acidification thresholds of pH 7.9 and Ωarag of 1. Projections are based on field data collected in 2011–2013 (circle). January and June monthly means represent mid-summer and winter conditions, respectively. The overall mean represent mean values from spring into winter conditions. Onset of aragonite undersaturation (triangles) is marked for each parameter and additionally for November monthly mean conditions.

Mentions: McMurdo Sound regional ocean acidification trajectories were made using averaged pH observations from 2011–2013 and forced with the Representative Concentration Pathway 8.5 (RCP8.5) CO2 emission scenario23. Due to the potential offset in pH measurements associated with use of unpurified m-cresol dye (~0.03 pH units, see Methods), our results may slightly overestimate acidification trends. The equilibrium scenario12, which represents an increase in seawater pCO2 that tracks atmospheric levels, predicted more extreme acidification than the disequilibrium scenario12, which represents a 65% reduced CO2 uptake due to seasonal ice cover (Fig. 4, 5).


Near-shore Antarctic pH variability has implications for the design of ocean acidification experiments
Annual changes in pH and aragonite saturation state ranges.Projections of yearly changes in pH and aragonite saturation state, Ωarag, in McMurdo Sound, Antarctica, using a disequilibrium (a, c) and equilibrium (b, d) scenario. Annual range in pH increases and Ωarag decreases with future acidification. End-century maximum pH and Ωarag remain above acidification thresholds of pH 7.9 and Ωarag of 1. Projections are based on field data collected in 2011–2013 (circle). January and June monthly means represent mid-summer and winter conditions, respectively. The overall mean represent mean values from spring into winter conditions. Onset of aragonite undersaturation (triangles) is marked for each parameter and additionally for November monthly mean conditions.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4488960&req=5

f5: Annual changes in pH and aragonite saturation state ranges.Projections of yearly changes in pH and aragonite saturation state, Ωarag, in McMurdo Sound, Antarctica, using a disequilibrium (a, c) and equilibrium (b, d) scenario. Annual range in pH increases and Ωarag decreases with future acidification. End-century maximum pH and Ωarag remain above acidification thresholds of pH 7.9 and Ωarag of 1. Projections are based on field data collected in 2011–2013 (circle). January and June monthly means represent mid-summer and winter conditions, respectively. The overall mean represent mean values from spring into winter conditions. Onset of aragonite undersaturation (triangles) is marked for each parameter and additionally for November monthly mean conditions.
Mentions: McMurdo Sound regional ocean acidification trajectories were made using averaged pH observations from 2011–2013 and forced with the Representative Concentration Pathway 8.5 (RCP8.5) CO2 emission scenario23. Due to the potential offset in pH measurements associated with use of unpurified m-cresol dye (~0.03 pH units, see Methods), our results may slightly overestimate acidification trends. The equilibrium scenario12, which represents an increase in seawater pCO2 that tracks atmospheric levels, predicted more extreme acidification than the disequilibrium scenario12, which represents a 65% reduced CO2 uptake due to seasonal ice cover (Fig. 4, 5).

View Article: PubMed Central - PubMed

ABSTRACT

Understanding how declining seawater pH caused by anthropogenic carbon emissions, or ocean acidification, impacts Southern Ocean biota is limited by a paucity of pH time-series. Here, we present the first high-frequency in-situ pH time-series in near-shore Antarctica from spring to winter under annual sea ice. Observations from autonomous pH sensors revealed a seasonal increase of 0.3 pH units. The summer season was marked by an increase in temporal pH variability relative to spring and early winter, matching coastal pH variability observed at lower latitudes. Using our data, simulations of ocean acidification show a future period of deleterious wintertime pH levels potentially expanding to 7–11 months annually by 2100. Given the presence of (sub)seasonal pH variability, Antarctica marine species have an existing physiological tolerance of temporal pH change that may influence adaptation to future acidification. Yet, pH-induced ecosystem changes remain difficult to characterize in the absence of sufficient physiological data on present-day tolerances. It is therefore essential to incorporate natural and projected temporal pH variability in the design of experiments intended to study ocean acidification biology.

No MeSH data available.


Related in: MedlinePlus