Ocean Acidification: The Other CO\u3csub\u3e2\u3c/sub\u3e Problem?

Rising atmospheric carbon dioxide (CO2), primarily from human fossil fuel combustion, reduces ocean pH and causes wholesale shifts in seawater carbonate chemistry. The process of ocean acidification is well documented in field data, and the rate will accelerate over this century unless future CO2 emissions are curbed dramatically. Acidification alters seawater chemical speciation and biogeochemical cycles of many elements and compounds. One well-known effect is the lowering of calcium carbonate saturation states, which impacts shell-forming marine organisms from plankton to benthic molluscs, echinoderms, and corals. Many calcifying species exhibit reduced calcification and growth rates in laboratory experiments under high-CO2 conditions. Ocean acidification also causes an increase in carbon fixation rates in some photosynthetic organisms (both calcifying and noncalcifying). The potential for marine organisms to adapt to increasing CO2 and broader implications for ocean ecosystems are not well known; both are high priorities for future research. Although ocean pH has varied in the geological past, paleo-events may be only imperfect analogs to current conditions. Republished with permission from 1 Ann. Rev. Mar. Sci. 169 (2009)

A global atlas of potential thermal refugia for coral reefs generated by internal gravity waves

Coral reefs are highly threatened by ocean warming and the majority are likely to be lost in less than three decades. A first step in maximizing reef conservation through this period is to identify where coral reefs are more likely to survive rising ocean temperatures, such as locations that experience lower temperatures than surrounding regions, high temperature variability, and high food supply. Such conditions are often the result of naturally occurring internal gravity waves (IGWs), oscillatory subsurface disturbances that can entrain cooler and/or nutrient-rich subsurface waters and cause high frequency temperature fluctuations. These features usually remain undetected because they occur subsurface and at spatial scales of O(1 km) and smaller. To shed light on where IGWs are likely to impact temperature conditions within coral reef regions, we present an analysis of data from the LLC4320, a massive high resolution (1/48˚; < 2.5 km) numerical global ocean simulation. The results highlight strong regional differences in the incidence of IGW-induced temperature variability. The analysis also reveals that thermal refugia are limited to depths where high temperature variability coincides with the actual reef depth and may not persist year-round. Assuming 10-m depth as the nominal reef depth, reef regions likely to benefit from IGW-induced cooling occur in SE Asia and the Coral Triangle, the Galápagos, along the Pacific shelf of Central America, and isolated locations worldwide. Such refugia are rare within the Atlantic reef sector. An interactive global atlas showing the results of this study has been made freely available online at https://ncar.github.io/coral-viz/

Ocean Acidification: Summary for Policymakers

Third Symposium on the Ocean in a High-CO2 Worl

Ozeanversauerung: Zusammenfassung für Entscheidungsträger

Third Symposium on the Ocean in a High-CO2 Worl

El cambio climático y los ecosistemas marinos tropicales: una revisión con énfasis en los arrecifes de coral

Climate change is usually associated with warming and weather extremes that impact the human environment and terrestrial systems, but it also has profound effects on the ocean, which is probably the most unique, life-supporting feature of planet Earth. The most direct consequence of rising CO2 concentration in the atmosphere is “ocean acidification,” a term that refers to the lowering of seawater pH, but encompasses a suite of chemical changes that affect marine organisms from shell formation, to reproduction, physiology, and behavior. The oceans are also warming in pace with the atmosphere, and in fact store the vast majority of the additional heat generated by rising CO2 and other greenhouse gases in the atmosphere. This warming is causing the more mobile marine species to redistribute poleward and deeper, and is causing high mortality in more sessile species such as those that build and habituate coral reefs. But warming is also leading to a decrease in dissolved oxygen in the oceans. For tropical marine ecosystems, the combination of ocean acidification, warming, and deoxygenation will continue to impact marine ecosystems in the future. The extent of these impacts depends on which energy pathway society follows, and our abilities to reduce other stressors and assist the rate at which species can adapt and migrate to more suitable environments.El cambio climático generalmente está asociado con el calentamiento y las condiciones climáticas extremas que impactan el ambiente humano y los sistemas terrestres, pero también tiene profundos efectos en el océano, que es probablemente la característica más importante del planeta Tierra para mantener la vida. La consecuencia más directa del aumento de la concentración de CO2 en la atmósfera es la “acidificación del océano”, que se refiere a la disminución del pH del agua de mar, pero abarca un conjunto de cambios químicos que afectan a los organismos marinos desde la formación de conchas hasta la reproducción, fisiología y comportamiento. Los océanos también se están calentando como la atmósfera, y de hecho almacenan la gran mayoría del calor adicional generado por el aumento de CO2 y otros gases de efecto invernadero en la atmósfera. Este calentamiento está causando que las especies marinas más móviles se redistribuyan hacia los polos y a más profundidad, y está causando una alta mortalidad en especies más sésiles, como las que construyen y habitúan los arrecifes de coral. Pero el calentamiento también está conduciendo a una disminución del oxígeno disuelto en los océanos. Para los ecosistemas marinos tropicales, la combinación de acidificación, calentamiento y desoxigenación de los océanos continuará afectando los ecosistemas marinos en el futuro. El alcance de estos impactos depende de la ruta energética que siga la sociedad y de nuestra capacidad para reducir otros factores estresantes y ayudar a la velocidad a la que las especies pueden adaptarse y migrar a entornos más adecuados

Coral Reefs & Global Climate Change: Potential Contributions of Climate Change to Stresses on Coral Reef Ecosystems

Outlines the likely impacts of climate change over the next century to coral reef systems both in U.S. waters and around the world

Coral reefs modify their seawater carbon chemistry - case study from a barrier reef (Moorea, French Polynesia)

Changes in the carbonate chemistry of coral reef waters are driven by carbon fluxes from two sources: concentrations of CO2 in the atmospheric and source water, and the primary production/respiration and calcification/dissolution of the benthic community. Recent model analyses have shown that, depending on the composition of the reef community, the air-sea flux of CO2 driven by benthic community processes can exceed that due to increases in atmospheric CO2 (ocean acidification). We field test this model and examine the role of three key members of benthic reef communities in modifying the chemistry of the ocean source water: corals, macroalgae, and sand. Building on data from previous carbon flux studies along a reef-flat transect in Moorea (French Polynesia), we illustrate that the drawdown of total dissolved inorganic carbon (C-T) due to photosynthesis and calcification of reef communities can exceed the draw down of total alkalinity (A(T)) due to calcification of corals and calcifying algae, leading to a net increase in aragonite saturation state (Omega(a)). We use the model to test how changes in atmospheric CO2 forcing and benthic community structure affect the overall calcification rates on the reef flat. Results show that between the preindustrial period and 1992, ocean acidification caused reef flat calcification rates to decline by an estimated 15%, but loss of coral cover caused calcification rates to decline by at least three times that amount. The results also show that the upstream-downstream patterns of carbonate chemistry were affected by the spatial patterns of benthic community structure. Changes in the ratio of photosynthesis to calcification can thus partially compensate for ocean acidification, at least on shallow reef flats. With no change in benthic community structure, however, ocean acidification depressed net calcification of the reef flat consistent with findings of previous studies

Environmental Limits to Coral Reef Development: Where Do We Draw the Line?

SYNOPSIS. Understanding how reefs vary over the present ranges of environmental conditions is key to understanding how coral reefs will adapt to a changing environment. Global environmental data of temperature, salinity, light, carbonate saturation state, and nutrients were recently compiled for nearly 1,000 reef locations. These data were statistically analyzed to (1) re-define environmental limits over which reefs exist today, (2) identify “marginal” reefs; i.e., those that exist near or beyond “normal” environmental limits of reef distribution, and (3) broadly classify reefs based on these major environmental variables. Temperature and salinity limits to coral reefs, as determined by this analysis, are very near those determined by previous researchers; but precise nutrient levels that could be considered limiting to coral reefs were not obvious at the scale of this analysis. However, in contrast to many previous studies that invoke low temperature as the reef-limiting factor at higher latitudes, this study indicates that reduced aragonite saturation and light penetration, both of which covary with temperature, may also be limiting. Identification of “marginal” reef environments, and a new classification of reefs based on suites of environmental conditions, provide an improved global perspective toward predicting how reefs will respond to changing environmental conditions