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Ocean acidification: the other CO2 problemOcean acidification: the other CO2 problem

Andreas J. AnderssonScripps Institution of

Oceanography

Andreas J. AnderssonScripps Institution of

OceanographyOceanography

Photo: Alex Venn

Number of Ocean Acidification publications over time

Gattuso and Hansson, 2011

• What is ocean acidification?

• What is the evidence for ocean acidification?

• How will the acid-base balance of the ocean change in the future?

• Why are we concerned about ocean acidification?

• How and what do we know about the future consequences of OA to marine ecosystems?

• What are the implications to humans from ocean acidification?

• How can ocean acidification be prevented?

Fate of Anthropogenic CO2 Emissions (2000-2008)

Le Quéré et al. 2009, Nature Geoscience; Canadell et al. 2007, PNAS, updated

1.4 PgC y-1

+7.7 PgC y-1

3.0 PgC y-1

29%

4.1 PgC y-1

45%

26%2.3 PgC y-1

What is ocean acidification?

1. CO2 (g) atm. → CO2 (g) sw.

2. CO2+ H2O → H2CO3

3. H2CO3 → H+ + HCO3-

4. H++ CO32- → HCO3

-

CO2

CO2

N. Bates, BIOS

What is the evidence for ocean acidification?

What is the evidence for ocean acidification?

IPCC 2007

How will the acid-base balance of the ocean change in the future?

1980 2000 2020 2040 2060 2080 2100

pH reduction by 0.3-04 units by 2100 ~ 100-150% increase in acidity

Joos et al. 2011

Why are we concerned about ocean acidification?

• Seawater acid-base balance important in regulating biological and chemical processes, e.g.:– Function of enzyme and proteins– Chemical reaction rates– Availability of nutrients and trace metals

• CO32- is an essential building block for marine

organisms depositing skeletons or shells made of CaCO3– Less building material equals slower growth, weaker structures

(similar to osteoporosis in humans) and increased vulnerability to environmental stress in general

Winners and losers

Alex Venn

http://www.noaanews.noaa.gov

How and what do we know about the future consequences of OA to marine ecosystems?

• Geologic record• Experimental manipulations• Natural high CO2 environments• Model simulations

Geologic record

Paleocene-Eocene Thermal Maximum (55 Mya)-Rapid increase in temperature (5-9 ºC)-Rapid increase increase in CO2 and OA-Extinction of forams, coral reefs declined

Cooper et al. 2008

Photo: Hannes Grobe, AWI

Experimental manipulations

Credit: Chris Langdon

Photo: Kim Yates

Natural high CO2 environments

Hall-Spencer et al. 2008

Fabricius et al. 2011

• Change microbial processes and biogeochemical cycles

• Affect marine organisms: positive, negative or no effect– different effect on different life stages

• Changes in community structure, food web dynamics, and biodiversity– coral reefs transition to net erosion

Based on current evidence: what do we know about the effects of OA to marine ecosystems?

To what extent and at what rate will these changes occur?

What are the implications to humans from ocean acidification?

• Food security• Economic impacts

– Fisheries– Tourism

• Coastal protection– Erosion– Storms, hurricanes– Tsunamis

Hypothesized future transition of coral reefs

Hoegh-Guldberg et al. 2008

How can ocean acidification be slowed down or prevented?

• Reduce atmospheric CO2 emissions

• Increase buffer capacity of seawater

– Natural feedback to ocean acidification: CaCO3sediment dissolution and weathering

– Proposals to add limestone (CaCO3) to ocean

What about geoengineering solutions?

Potential strategy but could also create more risk (e.g., AMS, Royal Society)

• Solar Radiation Management (SRM) – do not address OA– Sulfur dioxide– Space shades• Carbon Dioxide Removal (CDR) – Carbon Capture and Storage– Ocean fertilization– Forestation

At research stage and largely unproven, limited analysis of practicality, cost and benefits, and environmental consequences