Multi-frequency observations of seawater carbonate chemistry on the central coast of the western Antarctic Peninsula

Abstract

Assessments of benthic coastal seawater carbonate chemistry in Antarctica are sparse. The studies have generally been short in duration, during the austral spring/summer, under sea ice, or offshore in ice-free water. Herein we present multi-frequency measurements for seawater collected from the shallow coastal benthos on a weekly schedule over one year (May 2012–May 2013), daily schedule over three months (March–May 2013) and semidiurnal schedule over five weeks (March–April 2013). A notable pH increase (max pH = 8.62) occurred in the late austral spring/summer (November–December 2012), coinciding with sea-ice break-out and subsequent increase in primary productivity. We detected semidiurnal variation in seawater pH with a maximum variation of 0.13 pH units during the day and 0.11 pH units during the night. Daily variation in pH is likely related to biological activity, consistent with previous research. We calculated the variation in dissolved inorganic carbon (DIC) over each seawater measurement frequency, focusing on the primary DIC drivers in the Palmer Station region. From this, we estimated net biological activity and found it accounts for the greatest variations in DIC. Our seasonal data suggest that this coastal region tends to act as a carbon dioxide source during austral winter months and as a strong sink during the summer. These data characterize present-day seawater carbonate chemistry and the extent to which these measures vary over multiple time scales. This information will inform future experiments designed to evaluate the vulnerability of coastal benthic Antarctic marine organisms to ocean acidification.

• Antarctica
• aragonite
• calcite
• pH
• seawater chemistry
• total alkalinity

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Acknowledgements

The authors gratefully acknowledge the science and logistics support staff of Antarctic Support Contract for their invaluable help and support. We thank Janice O'Reilly and Caroline Lipke for their assistance with on-site seawater sample collection during the austral winter of 2012 and the austral summer of 2012/13, respectively. On-site sample collections and analyses were aided by the efforts of Margaret Amsler and Kevin Scriber. Thanks are due to Margaret Amsler and two anonymous reviewers whose constructive feedback enhanced and improved this manuscript. Annual data for Palmer Station regional sea ice and chl a concentrations were obtained from the Palmer LTER Data Repository supported by the Office of Polar Programs (National Science Foundation grants ANT-0823101, OPP-9011927, OPP-9632763 and OPP-0217282). The present study was supported by National Science Foundation grant ANT-1041022 awarded to JBM, CDA and RAA. Additional support was provided by the Department of Biology at the University of Alabama at Birmingham.

Notes

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