Ocean acidification may mitigate negative effects of warming on carbon burial potential in subtidal unvegetated estuarine sediments

• Published in: Limnology and Oceanography
• Main Authors: Simone, Michelle N., Schulz, Kai G., Eyre, Bradley D., Oakes, Joanne M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2021
• Subjects: Ocean acidification
• Online Access: http://dx.doi.org/10.1002/lno.11796; https://onlinelibrary.wiley.com/doi/pdf/10.1002/lno.11796; https://onlinelibrary.wiley.com/doi/full-xml/10.1002/lno.11796; https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.1002/lno.11796

Abstract Estuarine sediments make an important contribution to the global carbon cycle, but we do not know how this will change under a future climate, which is expected to have lower pH oceans and frequent high‐temperature days. Six combinations of warming and partial pressures of CO 2 ( p CO 2 ) were chosen to investigate the combined and individual effects of short‐term pressures on the diel metabolic response of shallow unvegetated sediments ex‐situ. Whereas warming significantly increased respiration, making sediments more heterotrophic, high‐ p CO 2 increased net primary productivity, resulting in less heterotrophic sediments. As a result, warming decreased the carbon burial potential of estuarine sediments and high‐ p CO 2 had the opposite effect. High‐ p CO 2 mitigates the negative effects of warming on benthic metabolism under the combined scenario, with carbon burial similar to that expected under high‐ p CO 2 conditions alone. Climate scenarios also changed the diurnal p CO 2 variation, with ranges increasing by 33% with warming, and almost doubling under high‐ p CO 2 conditions. An additive response in p CO 2 variability was observed under the combined scenario, increasing to 2.3× the current diel‐ p CO 2 range, highlighting the reduced buffering capacity of the water associated with a high CO 2 climate. Future carbon burial and export under increased frequencies of unseasonably warm days projected for mid and end of century (30% and 50% of days‐per‐year, respectively) were estimated with and without ocean acidification. By 2100, warming alone could decrease annual estuarine sediment burial potential by 25%. However, ocean acidification could mitigate the negative effects of more frequent high‐temperature days and increase carbon burial potential over current conditions by ~18%.