Effects of warming and CO 2 enrichment on O 2 consumption, porewater oxygenation and pH of subtidal silt sediment
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Aquatic Sciences
RESEARCH ARTICLE
Effects of warming and CO2 enrichment on O2 consumption, porewater oxygenation and pH of subtidal silt sediment Kay Vopel1 · Bonnie Laverock1 · Craig Cary2 · Conrad A. Pilditch2 Received: 2 March 2020 / Accepted: 19 October 2020 © Springer Nature Switzerland AG 2020
Abstract We investigated the effects of seawater warming and C O2 enrichment on the microbial community metabolism (using O 2 consumption as a proxy) in subtidal silt sediment. Intact sediment cores, without large dwelling infauna, were incubated for 24 days at 12 (in situ) and 18 °C to confirm the expected temperature response. We then enriched the seawater overlying a subset of cold and warm-incubated cores with C O2 (+ ΔpCO2: 253–396 µatm) for 16 days and measured the metabolic response. Warming increased the depth-integrated volume-specific O 2 consumption (Rvol), the maximum in the volumespecific O2 consumption at the bottom of the oxic zone (Rvol,bmax) and the volume-specific net O 2 production (Pn,vol), and decreased the O2 penetration depth (O2-pd) and the depth of Rvol,bmax (depthbmax). Benthic photosynthesis oscillated the pH in the upper 2 mm of the sediment. C O2 enrichment of the warm seawater did not alter this oscillation but shifted the pH profile towards acidity; the effect was greatest at the surface and decreased to a depth of 12 mm. Confoundment rendered the CO2 treatment of the cold seawater inconclusive. In warm seawater, we found no statistically clear effect of C O2 enrichment on Rvol, Rvol,bmax, Pn,vol, O2-pd, or depthbmax and therefore suspect that this perturbation did not alter the microbial community metabolism. This confirms the conclusion from experiments with other, contrasting types of sediment. Keywords Climate change · Ocean acidification · Coastal sediment · Sediment O2 consumption · Porewater pH and oxygenation
Introduction Because aquatic microbial communities play critical roles in governing Earth’s carbon cycle including feedbacks from Earth System perturbations, knowledge of their responses to warming and CO2 enrichment is important (Falkowski et al. 2008; Dutta and Dutta 2016; Boetius 2019). The microbial response to warming can affect the metabolic balance of open ocean and coastal ecosystems generating a positive feedback (Cox et al. 2000; Yvon-Durocher et al. 2010), Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00027-020-00765-5) contains supplementary material, which is available to authorized users. * Kay Vopel [email protected] 1
School of Science, Auckland University of Technology, Private Bag 92006, Auckland, New Zealand
School of Science, University of Waikato, Private Bag 3105, Hamilton, New Zealand
2
but the responses of such communities to CO2 enrichment, or warming combined with CO2 enrichment, are less well known. CO2 enrichment resulting from the absorption of atmospheric CO2 by the ocean alters the speciation of dissolved inorganic carbon (DIC): the dissociation of
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