the greenhouse effect, the oceans and climate change › ~brosenhe › oceanography › 13...the...

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EENS/EBIO 223 Prof. Rosenheim

Intro. Oceanography

The Greenhouse Effect, the Oceans and Climate Change


Intro. Oceanography

GreenhouseThe glass used for a greenhouse works as a selective transmission medium for different spectral frequencies, and its effect is to trap energy within the greenhouse, which heats both the plants and the ground inside it. Greenhouses thus work by utilizing electromagnetic radiation and preventing convection.


Intro. Oceanography

Greenhouse Effect

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Intro. Oceanography

Earth’s Atmospheric Greenhouse


Intro. Oceanography

Greenhouse Gases


Intro. Oceanography

Analysis of CO2• Non-dispersive infrared CO2 detector

– Uses IR light, shone through an optical cell and detected on the other side of the gas sample, to quantify CO2 concentration.

– It is an established and useful fact that CO2absorbs IR radiation.

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Intro. Oceanography

Greenhouse Gas Variability• Sources:

– Volcanoes• CO2, NOx

– Biomass burning• CO2 from forest fires, natural and otherwise

– Bacteria• CH4 in ocean sediments (perhaps thermogenic)

– Fossil fuel burning• CO2, Anthropogenic


Intro. Oceanography

Greenhouse Gas Variability

• In deep past (Phanerozoic), CO2concentration is very difficult to determine

• Most evidence points to relationship with volcanic cycles


Intro. Oceanography


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Intro. Oceanography

Greenhouse Gas Variability• Ice core record provides much more direct

CO2 measurement• 420,000 y of ice core records of ice age

cycles, related to CO2 concentrations


Intro. Oceanography

Glacial – Interglacial CO2 Variability• Temperature and CO2 concentration are

intimately related• Sometimes temperature leads CO2 and

vice versa.– Feedback

http://sitemaker.umich.edu/section2_group1/arctic_issues__permafrost


Intro. Oceanography

Milankovitch Cycles

• Milankovitch, a Serb physicist, had proposed orbital cycles

• 3 cycles– 100,000 y– 41,000 y – 19,000 and 23,000 y

• Published 1930, ignored

http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/climate.htm

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Intro. Oceanography

Insolation Variability of Eccentricity

• Insolation effects yield an incongruous response

• What was the cause?


Intro. Oceanography

The Thermohaline Circulation• Cooling of salty GSS waters• Formation of NADW• Cross-equatorial transport• Amplifier of orbital changes

http://www.pik-potsdam.de/~stefan/thc_fact_sheet.html

http://www.onr.navy.mil/Focus/ocean/motion/currents1.htm


Intro. Oceanography

Nonlinear-climate system

• Multiple factors to climate change– Albedo

• Ice cover• Exposed continental shelf• Sea ice

– Water vapor availability– Fresh water discharge into N. Atlantic

• All have feedbacks that can amplify orbital insolation changes

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Intro. Oceanography

Ocean Heat Content

• Heat content of the oceans:– Specific heat: 1cal·g-1·oC-1

– Volume: 1.37 x 109 km3

– Density: 1.028 g·mL-1

– Mass: 1.41 x 1024 g– 5.9 x 1024 cal (to inc. 1K)– 3.9 x 1026 cal (total)

• Heat content of atmosphere:– Specific heat: 0.24 cal·g-

1·oC-1

– Mass: 5 x 1018kg– 1.2 x 1021 cal (to inc. 1K)– 3.1 x 1023 cal (total)


Intro. Oceanography

Oceanic Heat Transport

• N. Atlantic, with current continental configuration, can effectively pull equatorial heat into high latitudes


Intro. Oceanography

Greenhous Feedbacks• Melting tundra, increased methane (+)• Warming oceans, melting sea ice, more

productivity (-)• More NADW formation, more CO2 flux into

deep ocean (+)

http://www.koshland-science-museum.org/exhibitgcc/historical02.jsp

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Intro. Oceanography

Paleo-Greenhouse Effect?• Does CO2 lead or lag glacial/interglacial

climate change?– Trigger is unknown, but strongest evidence

keys on orbital cycles– Melting ice and rising seas change seawater

chemistry and flow• CO2 degases

– Tundra melts• CO2 degases

http://www.koshland-science-museum.org/exhibitgcc/historical02.jsp


Intro. Oceanography

CO2 and the Oceans

The oceans can be both a source and sink of CO2

• CO2 Sink– Cooler oceans– High productivity– Expose continental shelf

• CO2 Sources– Warming deep ocean– Destabilize deep ocean


Intro. Oceanography


• Holocene (the period after the last glaciation) CO2levels paint a vivid picture of recent CO2 increases

• “Instantaneous” CO2increase

IPCC

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Intro. Oceanography

Greenhouse Gas Variability• Seasonal trends in CO2 persist due to

temperate forests and phytoplankton blooms


Intro. Oceanography

Sources for recent CO2 increase

• Humans.


Intro. Oceanography

Evidence for Human Sources

• Carbon isotope composition of the atmosphere

Direct Atmospheric Measurements

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Intro. Oceanography

Archived Proxy Records of Anthropogenic CO2


Intro. Oceanography

Earth’s Temperature Change• Average temperature of

Earth hasn’t climbed as fast as CO2 levels

• Our instrumental record is short (100 y), anything before that has a high uncertainty


Intro. Oceanography

Why isn’t the temperature increase proportional to the CO2 increase?

• 2 heat pumps – atmosphere and ocean• Oceans have more heat capacity than

atmosphere• Verifiable changes in ocean circulation

are the manifestation of this increased CO2.

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Intro. Oceanography

Ocean Heat Content


Intro. Oceanography

New Data from the Caribbean Sea

• Ocean climate change is not as straightforward as a global composite


Intro. Oceanography

New Data from the Caribbean Sea

• Climate change in the largest heat sink of our climate system is regionally complex.

30oN

0.5 1 1.5 2 2.5 3oC/century

15oN

90oW 60oWMann et al., 2004, global composite

Dep

th (m

)

0

400

200

Longitude80oW 70oW 60oW 50oW 20oW30oW40oW

Salinity (PSU)35.2 35.4 35.6 35.8 36.0 36.2 36.4 36.6 36.8 37.0

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Sclerosponges(Rosenheim et al., 2005)

B B’

B B’

a.

b.

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Intro. Oceanography

Geologic Carbon Cycle• How does the earth lower the CO2

concentration in the atmosphere?– Natural sinks of CO2

• Biomass burial• Formation of CaCO3• Tectonic burial/uplift of sediments


Intro. Oceanography

Biogenous Sediment

• CaCO3 is a CO2 sink


Intro. Oceanography

Tectonic Carbon Sinks

• Burial of CaCO3 sediments– Potential for volcanic evasion of CO2

• Uplift of sediments out of marine environment– Potential for weathering

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Intro. Oceanography

Oceans’ Roles in the Carbon Cycle• Dissolution of CO2• Calcification • Photosynthesis and metabolism• 50X atm. CO2 in oceans

http://www.visionlearning.com/library/module_viewer.php?mid=95


Intro. Oceanography

Carbon Sinks: Deep vs. Surface Ocean

• Surface ocean is site of carbon flux between ocean and atmosphere– Upwelling, ocean is a source– Downwelling, ocean is a sink– Productivity Pump

• Deep ocean - ~40X the carbon reservoir– Solubility Pump– CO2 is very soluble in the deepest parts of the

ocean


Intro. Oceanography

Surface Ocean Productivity Pump

• Biomass is created in photic zone• Biomass dies, and what is not recycled

(eaten) at the surface falls to the deep ocean

• Here most biomass is recycled (eaten). Small fraction of biomass is buried

• CaCO3 deposition is also biogenous

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Intro. Oceanography

Biomass Burial as Carbon Sink• Both marine (diatoms) and terrestrial

(plants)


Intro. Oceanography

Deep Ocean – Solubility Pump

• More CO2 can remain in solution at – Low temperature– High pressure

• Deep ocean fits these criteria and has a very large volume

All of our fossil fuels are about 1/10 of the deep ocean carbon content!


Intro. Oceanography

Anthropogenic Effects on Pumps

• Productivity Pump– Productivity pump may be diminished by ocean

acidification as CO2 increases in atmosphere• Solubility Pump

– As temperature rises, especially in surface oceans, CO2 dissolution becomes less efficient (g/L)

– But more overall CO2 will dissolve because more is available (total g)

• Net effect – decreasing pH (increasing acidity) of world oceans

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Intro. Oceanography

CO2 Sequestration

• How can WE get rid of CO2?– We need to control biomass accumulation

and burial, and/or ocean chemistry (for biogenous carbonate formation), and/or plate tectonics

– Or, we need to come up with alternatives that do not mimic known earth processes


Intro. Oceanography

Iron Seeding Projects

• Southern Ocean Iron (Fe) Experiment• Does iron fertilization lead to enhanced

carbon sequestration?• John Martin – “Give me a trainload of scrap iron and I’ll

give you another Ice Age.”http://www.mbari.org/expeditions/SOFeX2002/history&purpose.htm


Intro. Oceanography

Iron Seeding Projects

• Other projects – SOIREE, FeEx, SERIES

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Intro. Oceanography

Iron Seeding Outcome

• In most regions Fe is not the only limiting reagent for carbon sequestration

• In Southern Ocean, a diatom and phytoplankton bloom was persistent and was buried to deep water along an oceanic front

• It would be difficult to count on Fe seeding to sequester all of our carbon


Intro. Oceanography

What about changing sources?


Intro. Oceanography

Key Concepts

• Main sources and sinks of CO2• Oceans’ roles in the carbon cycle• Temperature change vs. CO2 increase

– Why the heterogeneity?• Carbon sequestration

– Fads, fables and facts• What can you do?

the greenhouse effect, the oceans and climate change › ~brosenhe › oceanography › 13...the...

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