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

[摘要] The Arctic Ocean is considered the most vulnerable ecosystem to oceanacidification, and large-scale assessments of pH and the saturation state foraragonite (Ω_arag) have led to the notion that the Arctic Oceanis already close to a corrosive state. In high-latitude coastal waters theregulation of pH and Ω_arag is, however, far more complex thanoffshore because increased biological activity and input of glacial meltwateraffect pH. Effects of ocean acidification on calcifiers and non-calcifyingphototrophs occupying coastal habitats cannot be derived from extrapolationof current and forecasted offshore conditions, but theyrequire an understanding of the regimesof pH and Ω_arag in their coastal habitats. To increaseknowledge of the natural variability in pH in the Arctic coastal zone andspecifically to test the influence of benthic vegetated habitats, wequantified pH variability in a Greenland fjord in a nested-scale approach. Asensor array logging pH, O₂, PAR, temperature and salinity was appliedon spatial scales ranging from kilometre scale across the horizontalextension of the fjord; to 100 m scale vertically in the fjord, 10–100 mscale between subtidal habitats with and without kelp forests and betweenvegetated tidal pools and adjacent vegetated shores; and to centimetre tometre scale within kelp forests and millimetre scale across diffusiveboundary layers of macrophyte tissue. In addition, we assessed the temporalvariability in pH on diurnal and seasonal scales. Based on pH measurementscombined with point samples of total alkalinity, dissolved inorganic carbonand relationships to salinity, we also estimated variability in Ω_arag. Results show variability in pH and Ω_arag of upto 0.2–0.3 units at several scales, i.e. along the horizontal and verticalextension of the fjord, between seasons and on a diel basis in benthichabitats and within 1 m³ of kelp forest. Vegetated intertidal poolsexhibited extreme diel pH variability of > 1.5 units and macrophytediffusive boundary layers a pH range of up to 0.8 units. Overall, pelagic andbenthic metabolism was an important driver of pH and Ω_aragproducing mosaics of variability fromlow levels in the dark to peak levels at high irradiance generally appearingfavourable for calcification. We suggest that productive coastal environmentsmay form niches of high pH in a future acidified Arctic Ocean.

[学科分类] 地球化学与岩石