Younger Dryas Period/ CO2-climate feedbacks Chapter 14—Part 3 Younger Dryas Period/ CO2-climate feedbacks

CO2 Variations Bubbles in ice cores provide samples of ancient air. These samples tell us that CO2 levels track the changes in temperature

CO2 T CH4 http://www.pbs.org/wgbh/warming/stories/

Temperature and CO2 change together http://www.env.leeds.ac.uk/envi2150/lecture6/lecture6.html

CO2 Variations Bubbles in ice cores provide samples of ancient air. These samples tell us that CO2 levels track the changes in temperature This suggests CO2 can amplify climate change that is initiated by orbital variations. How?

Weathering Volcanism The Weathering Cycle is TOO SLOW! The weathering cycle operates over millions of years Glacial climate changes take place over thousands of years Weathering CaSiO3 + CO2 CaCO3 + SiO2 Volcanism

The Biological Pump (marine organic carbon cycle) transfer of CO2 to the deep ocean: North Atlantic Pacific Ocean Transfer of carbon Deep water

surface water Photosynthesis CO2 + H2O  CH2O + O2 sinking particles Respiration CH2O + O2  CO2 + H2O deep water

Changes in the Biological Pump: Atmospheric CO2 can decrease if more CO2 is stored in deep waters

Changes in the Biological Pump: Atmospheric CO2 can decrease if more CO2 is stored in deep waters. This could be due to: 1) slower deep ocean circulation

Changes in the Biological Pump: Atmospheric CO2 can decrease with more storage of CO2 in deep waters. This could be due to: 1) slower deep ocean circulation or 2) greater photosynthesis in surface waters

Changes in the Biological Pump: Atmospheric CO2 can decrease with more storage of CO2 in deep waters. This could be due to: 1) slower deep ocean circulation or 2) greater photosynthesis in surface waters More nutrients to the ocean? Limiting nutrients: N, P, and Fe

Redfield Ratios These are the ratios of different elements in living organisms Element Relative # of atoms C 106 N 15 P 1 Fe 0.01-0.1

Nitrogen in organisms Amino acids (shown at left) are the building blocks of proteins Nitrogen is part of the amino (NH2) group Diagram from Wikipedia

Phosphorus in organisms Phosphorus is a key component of nucleic acids, i.e., DNA and RNA Nucleic acids also contain nitrogen http://www.isof.cnr.it/ppage/capob/synth.html

Iron in organisms Iron is used as part of various catalysts There evidently is some iron in chlorophyll, but not much (main metal atom is Mg) But, iron is required for the synthesis of chlorophyll http://chaitanya1.wordpress.com/2007/07/09/strawberries/

Possible glacial-interglacial CO2/climate feedback loops Broecker’s “shelf hypothesis” (P) Martin’s “iron hypothesis” (Fe) “Coral reef hypothesis” (carbonate saturation state)

Broecker’s “Shelf” hypothesis Interglacial sea level -Weathering releases P from rocks -Some of this P accumulates in sediments on the shelves P-rich sediments Glacial sea level When sea level falls, P-rich sediments on the continental shelves are washed into the deep ocean, raising productivity

The Shelf Hypothesis Feedback Loop Start here Atm. CO2 Surf. Temp. Ts Continental Ice Sheets (+) Sea Level Biological Pump P to ocean Shelf exposure  Positive feedback loop!

Martin’s “Iron hypothesis” Iron is a limiting nutrient in parts of the ocean, especially the southern oceans near Antarctica Iron is supplied to the oceans by windblown dust from the continents Wind strength increases when the climate becomes glacial because the poles cool more than does the equator Saharan dust plume

Iron Fertilization Feedback Loop Start here Atm. CO2 Surf. Temp. Ts Equator to pole Temp. gradient (+) Iron in Dust to Ocean Wind Speeds Biological Pump  Positive feedback loop!

Coral Reef Hypothesis Interglacial sea level Coral (CaCO3) CaCO3 + CO2 + H2O  Ca++ + 2 HCO3 Glacial sea level Reefs form when sea level goes up  CO2 goes up Reefs weather and dissolve when sea level goes down  CO2 goes down

Coral reef feedback loop Start here Surf. temp Ts Continental glaciers Sea level (+) Atmospheric CO2 Surface ocean CO2 Reef formation  Positive feedback loop!

So, there are several positive feedback loops that may cause atmospheric CO2 to go up and down in concert with the glacial-interglacial cycles Some combination of these feedback loops, combined with changes in ocean circulation, is probably responsible for the CO2 fluctuations seen in the Vostok ice core

Younger Dryas Period Towards the end of the last Ice Age, climate warmed, then suddenly cooled again for almost 1000 yrs The evidence comes from the reappearance of the Dryas flower in the Alps, which flourishes in glacial climates Image from Wikkipedia

Younger Dryas Period Temperatures come from O and H isotopes in ice cores High 18O (or high D/H)  warmer temperatures Younger Dryas

The Atlantic Conveyor Did the oceanic thermohaline circulation shut down during the Younger Dryas Period?

Atlantic Conveyor Shutdown As the Laurentide ice sheet retreated, melt water was diverted from the Mississippi River to the St. Lawrence River North Atlantic ocean became capped with freshwater  not dense enough to sink  thermohaline circulation shut down for ~1000 yrs Could this happen again as a result of global warming?