Ocean Acidification source -

Key Ideas Purpose of carbon How/Why are we adding extra to the oceans? What is the impact of acidification on ocean life How nitrogen and phosphorus get into water systems Eutrophication, hypoxia and dead zones

Simplified Carbon Cycle

Keeling Curve

Credit: Richard A. Feely, Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, USA, with atmospheric data from Pieter Tans and seawater data from David Karl. Adapted from Feely (2008) in Levinson and Lawrimore (eds), Bull. Am. Meteorol. Soc, 89(7): S58.

How acidic are the oceans? The oceans are not, in fact, acidic, but slightly basic. Acidity is measured using the pH scale, where 7.0 is defined as neutral, with higher levels called "basic" and lower levels called "acidic". Historical global mean seawater values are approximately 8.16 on this scale, making them slightly basic. To put this in perspective, pure water has a pH of 7.0 (neutral), whereas household bleach has a pH of 12 (highly basic) and battery acid has a pH of zero (highly acidic). However, even a small change in pH may lead to large changes in ocean chemistry and ecosystem functioning. Over the past 300 million years, global mean ocean pH values have probably never been more than 0.6 units lower than today (6). Ocean ecosystems have thus evolved over time in a very stable pH environment, and it is unknown if they can adapt to such large and rapid changes. Figure reproduced from the Pew Charitable Trust Policy Brief "Carbon Dioxide and Our Ocean Legacy", by Feely, Sabine, and Fa

Rising CO2 is changing the chemistry of the oceans

Coral Bleaching Unbleached coralBleached coral CaCO 3 → CaO + CO 2

Foraminifera Laboratory experiments show that calcification rates of many marine calcifyers, like certain corals, foraminifera, coccolithophores and shellfish, reduce under more acidic (high CO2) conditions. Currently, the average pH of the world’s oceans is about 8.1, which is already about 0.1 units lower compared to pre- industrial times and corresponds to an increase in acidity of 30%. Model calculations show that by the end of the 21st century pH levels will have dropped another 0.4 units under a business as usual scenario and possibly even 0.7 units lower than pre- industrial values by the year Due to the logarithmic nature of the pH scale this corresponds to three (0.5 units) and five (0.7 units) fold increase of H+ ions compared to the pre- industrial situation. These changes are probably larger than any pH change in the past 300 million years because of the extreme speed at which it takes place. The ability of species to adapt to their changing environment might therefore be limited.

Exit Card 1.What is eutrophication and what does it cause? 2.Name two problems caused by algae growth (algae is a producer…. That is a good thing, right?) 3.Why nitrogen & phosphorus ( and not carbon or sulfur)?