Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 12, 4895-4911, 2015
https://doi.org/10.5194/bg-12-4895-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
19 Aug 2015
Macroalgae contribute to nested mosaics of pH variability in a subarctic fjord
D. Krause-Jensen1,2, C. M. Duarte3,4, I. E. Hendriks5, L. Meire6,7,8, M. E. Blicher6, N. Marbà5, and M. K. Sejr1,2 1Arctic Research Centre, Bioscience, Aarhus University, C.F. Møllers Allé 8, 8000 Århus C, Denmark
2Department of Bioscience, Aarhus University, Vejlsøvej 25, 8600 Silkeborg, Denmark
3Red Sea Research Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
4Faculty of Biosciences, Fisheries and Economics, University of Tromsø, Tromsø, Norway
5Department of Global Change Research, IMEDEA (CSIC-UIB) Instituto Mediterráneo de Estudios Avanzados, Miquel Marqués 21, 07190 Esporles, Spain
6Greenland Climate Research Centre, Greenland Institute of Natural Resources, Kivioq 2, Box 570, 3900 Nuuk, Greenland
7Marine Biology Laboratory, University of Ghent (UGent), Krijgslaan 281 (S8), 9000 Ghent, Belgium
8Royal Netherlands Institute of Sea Research (NIOZ), Department of Ecosystem Studies, Korringaweg 7, 4401 NT, Yerseke, the Netherlands
Abstract. The Arctic Ocean is considered the most vulnerable ecosystem to ocean acidification, and large-scale assessments of pH and the saturation state for aragonite (Ωarag) have led to the notion that the Arctic Ocean is already close to a corrosive state. In high-latitude coastal waters the regulation of pH and Ωarag is, however, far more complex than offshore because increased biological activity and input of glacial meltwater affect pH. Effects of ocean acidification on calcifiers and non-calcifying phototrophs occupying coastal habitats cannot be derived from extrapolation of current and forecasted offshore conditions, but they require an understanding of the regimes of pH and Ωarag in their coastal habitats. To increase knowledge of the natural variability in pH in the Arctic coastal zone and specifically to test the influence of benthic vegetated habitats, we quantified pH variability in a Greenland fjord in a nested-scale approach. A sensor array logging pH, O2, PAR, temperature and salinity was applied on spatial scales ranging from kilometre scale across the horizontal extension of the fjord; to 100 m scale vertically in the fjord, 10–100 m scale between subtidal habitats with and without kelp forests and between vegetated tidal pools and adjacent vegetated shores; and to centimetre to metre scale within kelp forests and millimetre scale across diffusive boundary layers of macrophyte tissue. In addition, we assessed the temporal variability in pH on diurnal and seasonal scales. Based on pH measurements combined with point samples of total alkalinity, dissolved inorganic carbon and relationships to salinity, we also estimated variability in Ωarag. Results show variability in pH and Ωarag of up to 0.2–0.3 units at several scales, i.e. along the horizontal and vertical extension of the fjord, between seasons and on a diel basis in benthic habitats and within 1 m3 of kelp forest. Vegetated intertidal pools exhibited extreme diel pH variability of > 1.5 units and macrophyte diffusive boundary layers a pH range of up to 0.8 units. Overall, pelagic and benthic metabolism was an important driver of pH and Ωarag producing mosaics of variability from low levels in the dark to peak levels at high irradiance generally appearing favourable for calcification. We suggest that productive coastal environments may form niches of high pH in a future acidified Arctic Ocean.

Citation: Krause-Jensen, D., Duarte, C. M., Hendriks, I. E., Meire, L., Blicher, M. E., Marbà, N., and Sejr, M. K.: Macroalgae contribute to nested mosaics of pH variability in a subarctic fjord, Biogeosciences, 12, 4895-4911, https://doi.org/10.5194/bg-12-4895-2015, 2015.
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Short summary
The Arctic Ocean is considered the most vulnerable ecosystem to ocean acidification (OA), but very little information is available on natural variability of pH in the Arctic coastal zone. We report pH variability at various scales in a Greenland fjord. Variability ranged up to 0.2-0.3 pH units horizontally and vertically in the fjord, between seasons and on diel basis in kelp forests and was extreme in tidal pools. Overall, primary producers played a fundamental role in producing mosaics of pH.
The Arctic Ocean is considered the most vulnerable ecosystem to ocean acidification (OA), but...
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