1 Living with the oceans. – A report on the state of the world's oceans

Ocean chemistry

How climate change alters ocean chemistry
> Massive emissions of carbon dioxide into the atmosphere have an impact on the chemical and biological processes in the ocean. The warming of ocean water could lead to a ­destabilization of solid methane deposits on the sea floor. Because of the excess CO2, the oceans are becoming more acidic. Scientists are making extensive measurements to determine how much of the humanmade CO2 is being absorbed by the oceans. Important clues are provided by looking at oxygen.

The oceans – the largest CO2-reservoir

> The oceans absorb substantial amounts of carbon dioxide, and thereby consume a large portion of this greenhouse gas, which is released by human activity. This does not mean, however, that the problem can be ignored, because this process takes centuries and cannot prevent the consequences of climate change. Furthermore, it cannot be predicted how the marine biosphere will react to the uptake of additional CO2.

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The consequences of ocean acidification

> Climate change not only leads to warming of the atmosphere and water, but also to an acidification of the oceans. It is not yet clear what the ultimate consequences of this will be for marine organisms and communities, as only a few species have been studied. Extensive long-term studies on a large variety of organisms and communities are needed to understand potential consequences of ocean acidification.

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Oxygen in the ocean

> Scientists have been routinely measuring oxygen concentrations in the ocean for more than a hundred years. With growing concerns about climate change, however, this parameter has suddenly become a hot topic. Dissolved oxygen in the ocean provides a sensitive early warning system for the trends that climate change is causing. A massive deployment of oxygen ­sensors is projected for the coming years, which will represent a renaissance of this parameter.

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Climate change impacts on methane hydrates

> Huge amounts of methane are stored around the world in the sea floor in the form of solid methane hydrates. These hydrates represent a large energy reserve for humanity. Climate warming, however, could cause the hydrates to destabilize. The methane, a potent greenhouse gas, would escape unused into the atmosphere and could even accelerate climate change.

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Material fluxes – getting the full picture

The chemical and geochemical processes in the ocean are complex. Explaining them in their entirety will be a challenge for decades. There is clear ­evidence of global changes, such as the decrease in oxygen levels and acidification in the oceans. So far, however, our knowledge is not sufficient to say with certainty or in detail what impact climate change will have and how it will affect various parameters in the future.
It is certain that disturbances caused by climate change can have very serious consequences, because the chemical and geochemical material fluxes amount to many billions of tons. The amount of methane hydrate bound up in the sea floor alone is gigantic. If it is released and the methane rises into the atmosphere, it will have a significant impact on the development of future climate. Investiga­tions of the chemical and geochemical processes are therefore of enormous importance if we want to learn what to expect and how humanity can respond to it.
Analyses of the CO2 cycle reveal how the CO2 reservoirs of the atmosphere, land biomass and ocean interact. The oceans are buffering increasing concentrations of atmospheric trace gases. But these processes and reaching a new CO2 equilibrium will take millennia. Natural processes therefore cannot keep up with the speed at which humans continue to discharge CO2 and other climate-relevant trace gases into the air. The only solution is to save energy and significantly reduce greenhouse gas emissions.