Seasonal variation in aragonite saturation in surface waters of Puget Sound – a pilot study

Gregory Pelletier,Mindy Roberts,Simone R Alin,Mya Keyzers,Jody W Deming,Lisa A Miller

doi:10.1525/elementa.270

Abstract

A pilot study of sampling, using monthly marine flights over spatially distributed stations, was conducted with the aim to characterize the carbonate system in Puget Sound over a full year-long period. Surface waters of Puget Sound were found to be under-saturated with respect to aragonite during October–March, and super-saturated during April–September. Highest pCO2 and lowest pH occurred during the corrosive October–March period. Lowest pCO2 and highest pH occurred during the super-saturated April–September period. The monthly variations in pCO2, pH, and aragonite saturation state closely followed the variations in monthly average chlorophyll a. Super-saturated conditions during April–September are likely strongly influenced by photosynthetic uptake of CO2 during the phytoplankton growing season. The relationship between phytoplankton production, the carbonate system, and aragonite saturation state suggests that long-term trends in eutrophication processes may contribute to trends in ocean acidification in Puget Sound.

Highlights

In recent years, a significant body of research has shown that increases in atmospheric CO2 concentrations are causing ocean acidification (OA) via ocean uptake of the excess CO2
The present study aims to explore the monthly variation in the carbonate system and aragonite saturation state in the surface waters of Puget Sound, by sampling a spatially distributed set of stations over a full year-long period
Summary statistics for observed temperature, salinity, and carbonate system variables were compared with published averages by Feely et al (2010) (Table 3)

Summary

Introduction

A significant body of research has shown that increases in atmospheric CO2 concentrations are causing ocean acidification (OA) via ocean uptake of the excess CO2. OA decreases the saturation state of calcium carbonate. A decrease in the saturation state of calcium carbonate has been suggested as a potential negative impact on the health of some organisms (e.g., Bednaršek et al, 2012; Waldbusser et al, 2015a). Aragonite is a metastable form of calcium carbonate that naturally occurs in the shells of many mollusk species. Aragonite has relatively rapid dissolution kinetics, and may become undersaturated in the open ocean by the year 2050 if present trends in OA continue (Orr et al, 2005). The aragonite saturation state in the surface waters of the ocean is changing rapidly with OA as a result of human activities that increase global atmospheric CO2 (Feely et al, 2008). Aragonite under-saturation is likely to affect aragonite-shelled organisms (e.g., Hunt et al, 2008; Bednaršek et al, 2012)

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Conclusion