Macroalgae contribute to nested mosaics of pH variability in a subarctic fjord

• Published in: Biogeosciences
• Main Authors: Krause-Jensen, D., Duarte, Carlos M., Hendriks, I. E., Meire, L., Blicher, M. E., Marbà, N., Sejr, M. K.
• Other Authors: King Abdullah University of Science and Technology (KAUST), Biological and Environmental Sciences and Engineering (BESE) Division, Marine Science Program, Red Sea Research Center (RSRC), Arctic Research Centre, Bioscience, Aarhus University, C.F. Møllers Allé 8, 8000 Århus C, Denmark, Department of Bioscience, Aarhus University, Vejlsøvej 25, 8600 Silkeborg, Denmark, Faculty of Biosciences, Fisheries and Economics, University of Tromsø, Tromsø, Norway, Department of Global Change Research, IMEDEA (CSIC-UIB) Instituto Mediterráneo de Estudios Avanzados, Miquel Marqués 21, 07190 Esporles, Spain, Greenland Climate Research Centre, Greenland Institute of Natural Resources, Kivioq 2, Box 570, 3900 Nuuk, Greenland, Marine Biology Laboratory, University of Ghent (UGent), Krijgslaan 281 (S8), 9000 Ghent, Belgium, Royal Netherlands Institute of Sea Research (NIOZ), Department of Ecosystem Studies, Korringaweg 7, 4401 NT, Yerseke, the Netherlands
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus GmbH 2015
• Subjects: Arctic; Arctic Ocean; Greenland; Ocean acidification; Subarctic
• Online Access: http://hdl.handle.net/10754/577018; https://doi.org/10.5194/bg-12-4895-2015; https://doi.org/10.5194/bgd-12-4907-2015

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 ...