Will ocean acidification affect marine microbes?

Abstract

The pH of the surface ocean is changing as a result of increases in atmospheric carbon dioxide (CO2), and there are concerns about potential impacts of lower pH and associated alterations in seawater carbonate chemistry on the biogeochemical processes in the ocean. However, it is important to place these changes within the context of pH in the present-day ocean, which is not constant; it varies systematically with season, depth and along productivity gradients. Yet this natural variability in pH has rarely been considered in assessments of the effect of ocean acidification on marine microbes. Surface pH can change as a consequence of microbial utilization and production of carbon dioxide, and to a lesser extent other microbially mediated processes such as nitrification. Useful comparisons can be made with microbes in other aquatic environments that readily accommodate very large and rapid pH change. For example, in many freshwater lakes, pH changes that are orders of magnitude greater than those projected for the twenty second century oceans can occur over periods of hours. Marine and freshwater assemblages have always experienced variable pH conditions. Therefore, an appropriate null hypothesis may be, until evidence is obtained to the contrary, that major biogeochemical processes in the oceans other than calcification will not be fundamentally different under future higher CO2/lower pH conditions.

Global declines in oceanic nitrification rates as a consequence of ocean acidification

“…The oceans' response to acidification will not be uniform: Different regions (35,45) and different depths (37) already exhibit different trends, and the activities of microbes and other organisms may accelerate or modulate these trends (9,37,45). Keeping spatial and temporal variability and the limited duration of our experiments in mind, it is nevertheless instructive to use our results to estimate the potential overall impact of acidification on marine nitrification and associated nitrogen cycle processes.…”

“…Temporal variability in pH and spatial variability with depth or across different regions-e.g., between upwelling regions and midocean gyres-could in principle be used to examine pH effects on nitrification without direct manipulation of pH (9). However, few measurements of ammonia oxidation rates have been made, and they typically display irregular patterns in space and time (12,(38)(39)(40).…”

“…This more than twofold increase in surface ocean hydrogen ion concentrations [H + ] will be accompanied by increasing CO 2 partial pressures (pCO 2 ), increasing bicarbonate ion concentrations [HCO 3 − ], decreasing carbonate ion concentrations [CO 3 2− ], and multiple shifts in trace metal and nutrient chemistry (2)(3)(4). Predicting the responses of marine organisms, ecosystems, and biogeochemical processes to these fundamental changes in ocean chemistry is consequently a major scientific challenge (5)(6)(7)(8)(9). Although marine bacteria and archaea constitute the majority of biomass in the sea, sustain a large percentage of global primary production, and govern biogeochemical cycling of carbon and nitrogen (10), we lack a clear understanding of how they will react to ocean acidification (9,11).…”

“…Predicting the responses of marine organisms, ecosystems, and biogeochemical processes to these fundamental changes in ocean chemistry is consequently a major scientific challenge (5)(6)(7)(8)(9). Although marine bacteria and archaea constitute the majority of biomass in the sea, sustain a large percentage of global primary production, and govern biogeochemical cycling of carbon and nitrogen (10), we lack a clear understanding of how they will react to ocean acidification (9,11).…”

Effects of Elevated Carbon Dioxide and Salinity on the Microbial Diversity in Lithifying Microbial Mats

“…The Earth's climate has naturally fluctuated over its 4.6 billion year history [1], however, it is the recent, rapid change in climate that has been cause for concern, as it is unclear how these anthropogenic changes will impact the taxonomic and functional diversity of many lithifying microbial ecosystems [2]. Of the various components of climate change, the accumulation of fossil-fuel derived carbon dioxide (CO 2 ) in the atmosphere and the subsequent uptake by the world's oceans has been of particular concern, as the global carbon cycle is closely linked to the biogeochemical cycling of nutrients and may impact the microbes that mediate these cycles [3][4][5].…”