Enhanced acidification of global coral reefs driven by regional biogeochemical feedbacks

Abstract

Physical uptake of anthropogenic CO 2 is the dominant driver of ocean acidification (OA) in the open ocean. Due to expected decreases in calcification and increased dissolution of CaCO 3 framework, coral reefs are thought to be highly susceptible to OA. However, biogeochemical processes can influence the pCO 2 and pH of coastal ecosystems on diel and seasonal time scales, potentially modifying the long-term effects of increasing atmospheric CO 2 . By compiling data from the literature and removing the effects of short-term variability, we show that the average pCO 2 of coral reefs throughout the globe has increased 3.5-fold faster than in the open ocean over the past 20 years. This rapid increase in pCO 2 has the potential to enhance the acidification and predicted effects of OA on coral reef ecosystems. A simple model demonstrates that potential drivers of elevated pCO 2 include additional anthropogenic disturbances beyond increasing global atmospheric CO 2 such as enhanced nutrient and organic matter inputs.

Benthic coral reef calcium carbonate dissolution in an acidifying ocean

“…83), which together could enhance CaCO 3 sediment dissolution. Similarly, increased bleaching-induced stress and respiration due to climate change 84 may also increase the pCO 2 of coral reef waters, most likely due to the release of high amounts of organic matter 85 .…”

Twenty Years of Marine Carbon Cycle Observations at Devils Hole Bermuda Provide Insights into Seasonal Hypoxia, Coral Reef Calcification, and Ocean Acidification

“…Complicating our understanding are the interactions and feedbacks between coral biogeochemical processes (i.e., calcification, production, respiration, dissolution) and CO 2 -carbonate chemistry over different spatial (e.g., patch reef, reef tract, whole reef) and temporal time-scales (e.g., diurnal, seasonal to decadal; Bates et al, 2010;Andersson et al, 2014;Cyronak et al, 2014). These factors include the following: (1) water circulation of the reef system (e.g., Falter et al, 2012Falter et al, , 2013Comeau et al, 2014c); (2) habitat complexity, community dynamics and variable responses between coral species (e.g., Bates et al, 2010;Kroeker et al, 2013a,b,c;Fabricius et al, 2014;Comeau et al, 2014b;Hendricks et al, 2015) (3) corals modifying internal and external CO 2 -carbonate chemistry (e.g., Anthony et al, 2011;Jokiel, 2011aJokiel, ,b, 2013Kleypas et al, 2011); (4) variability of reef CO 2 from diurnal time-scales (e.g., Ohde and van Woesik, 1999;Jokiel et al, 2014;Comeau et al, 2014a;Koweek et al, 2015) to longer time-scales (e.g., Shamberger et al, 2011;Edmunds et al, 2012;Gray et al, 2012;Shamberger et al, 2011;Shaw et al, 2012;Albright et al, 2013); and, (5) coral reef environments with naturally lower pH such as CO 2 seeps (Crook et al, 2011(Crook et al, , 2013Shamberger et al, 2014).…”

Nitrous oxide and methane dynamics in a coral reef lagoon driven by pore water exchange: Insights from automated high‐frequency observations

“…While coral reef carbon dioxide dynamics have been relatively well studied [Cyronak et al, 2014b], less attention has been given to the dynamics and drivers of other major greenhouse gases such as methane and nitrous oxide. Most previous studies of greenhouse gases other than carbon dioxide focused on methane diagenesis in coral reef pore waters [Falter and Sansone, 2000].…”