the greenhouse effect, the oceans and climate changebrosenhe/oceanography/13_oceans... · the...
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EENS/EBIO 223 Prof. Rosenheim
Intro. Oceanography
The Greenhouse Effect, the Oceans and Climate Change
EENS/EBIO 223 Prof. Rosenheim
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.
EENS/EBIO 223 Prof. Rosenheim
Intro. Oceanography
Greenhouse Effect
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EENS/EBIO 223 Prof. Rosenheim
Intro. Oceanography
Earth’s Atmospheric Greenhouse
EENS/EBIO 223 Prof. Rosenheim
Intro. Oceanography
Greenhouse Gases
EENS/EBIO 223 Prof. Rosenheim
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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EENS/EBIO 223 Prof. Rosenheim
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
EENS/EBIO 223 Prof. Rosenheim
Intro. Oceanography
Greenhouse Gas Variability
• In deep past (Phanerozoic), CO2concentration is very difficult to determine
• Most evidence points to relationship with volcanic cycles
EENS/EBIO 223 Prof. Rosenheim
Intro. Oceanography
Greenhouse Gas Variability
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EENS/EBIO 223 Prof. Rosenheim
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
EENS/EBIO 223 Prof. Rosenheim
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
EENS/EBIO 223 Prof. Rosenheim
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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EENS/EBIO 223 Prof. Rosenheim
Intro. Oceanography
Insolation Variability of Eccentricity
• Insolation effects yield an incongruous response
• What was the cause?
EENS/EBIO 223 Prof. Rosenheim
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
EENS/EBIO 223 Prof. Rosenheim
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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EENS/EBIO 223 Prof. Rosenheim
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)
EENS/EBIO 223 Prof. Rosenheim
Intro. Oceanography
Oceanic Heat Transport
• N. Atlantic, with current continental configuration, can effectively pull equatorial heat into high latitudes
EENS/EBIO 223 Prof. Rosenheim
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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EENS/EBIO 223 Prof. Rosenheim
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
EENS/EBIO 223 Prof. Rosenheim
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
EENS/EBIO 223 Prof. Rosenheim
Intro. Oceanography
Greenhouse Gas Variability
• Holocene (the period after the last glaciation) CO2levels paint a vivid picture of recent CO2 increases
• “Instantaneous” CO2increase
IPCC
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EENS/EBIO 223 Prof. Rosenheim
Intro. Oceanography
Greenhouse Gas Variability• Seasonal trends in CO2 persist due to
temperate forests and phytoplankton blooms
EENS/EBIO 223 Prof. Rosenheim
Intro. Oceanography
Sources for recent CO2 increase
• Humans.
EENS/EBIO 223 Prof. Rosenheim
Intro. Oceanography
Evidence for Human Sources
• Carbon isotope composition of the atmosphere
Direct Atmospheric Measurements
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EENS/EBIO 223 Prof. Rosenheim
Intro. Oceanography
Archived Proxy Records of Anthropogenic CO2
EENS/EBIO 223 Prof. Rosenheim
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
EENS/EBIO 223 Prof. Rosenheim
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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EENS/EBIO 223 Prof. Rosenheim
Intro. Oceanography
Ocean Heat Content
EENS/EBIO 223 Prof. Rosenheim
Intro. Oceanography
New Data from the Caribbean Sea
• Ocean climate change is not as straightforward as a global composite
EENS/EBIO 223 Prof. Rosenheim
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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EENS/EBIO 223 Prof. Rosenheim
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
EENS/EBIO 223 Prof. Rosenheim
Intro. Oceanography
Biogenous Sediment
• CaCO3 is a CO2 sink
EENS/EBIO 223 Prof. Rosenheim
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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EENS/EBIO 223 Prof. Rosenheim
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
EENS/EBIO 223 Prof. Rosenheim
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
EENS/EBIO 223 Prof. Rosenheim
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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EENS/EBIO 223 Prof. Rosenheim
Intro. Oceanography
Biomass Burial as Carbon Sink• Both marine (diatoms) and terrestrial
(plants)
EENS/EBIO 223 Prof. Rosenheim
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!
EENS/EBIO 223 Prof. Rosenheim
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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EENS/EBIO 223 Prof. Rosenheim
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
EENS/EBIO 223 Prof. Rosenheim
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
EENS/EBIO 223 Prof. Rosenheim
Intro. Oceanography
Iron Seeding Projects
• Other projects – SOIREE, FeEx, SERIES
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EENS/EBIO 223 Prof. Rosenheim
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
EENS/EBIO 223 Prof. Rosenheim
Intro. Oceanography
What about changing sources?
EENS/EBIO 223 Prof. Rosenheim
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?