Lecture 29: Millennial Changes in Other Lecture 29: Millennial Changes in Other RegionsRegions

Ch. 14

• Why is it difficult to correlate millennial oscillations in records from different regions?• Describe two kinds of evidence of millennial oscillations from North Atlantic sediments.

Millennial Changes in Other Regions

Ch. 14, p. 261-269

• What other regions show millennial oscillations like those in the North Atlantic and Greenland?

• What could explain the small size of millennial oscillations during the last 8000 years?

Detecting and Dating Millennial Oscillations in Regions Detecting and Dating Millennial Oscillations in Regions Other Than Greenland (Ice)Other Than Greenland (Ice)

Ideal proxy data for Ideal proxy data for millennial oscillationsmillennial oscillations

Revealed annual changesRevealed annual changesDated back to the last Dated back to the last glaciation and beyondglaciation and beyond

Uncertainties in dating Uncertainties in dating millennial oscillationsmillennial oscillations

1414C dating has errors of thousands of years, C dating has errors of thousands of years, thus difficulty in telling leads and lagsthus difficulty in telling leads and lags

Oscillations Recorded in North Atlantic SedimentsOscillations Recorded in North Atlantic SedimentsThe Atlantic Ocean is a good The Atlantic Ocean is a good place to detect millennial place to detect millennial changes.changes.

High deposition ratesHigh deposition ratesForaminifera and ice-rafted Foraminifera and ice-rafted debris stay in placedebris stay in place

More negative More negative δδ1818OO in Greenland ice core, in Greenland ice core, the colder air, the colder air, the colder ocean waterthe colder ocean water, the , the more icebergsmore icebergs, the more ice-rafted debris, , the more ice-rafted debris, and and the more polar planktonthe more polar plankton. .

ice-rafting eventsice-rafting events occurred when occurred when climate had been climate had been coolingcooling for several for several millennia, followed millennia, followed by by rapid warmingrapid warming. .

45°-50°N45°-50°N

Sources of ice-rafted debrisSources of ice-rafted debris Heinrich events:Heinrich events:

Millennial-scale North Atlantic Cycles?Millennial-scale North Atlantic Cycles?(Stochastic Resonance)(Stochastic Resonance)

1.1. 1500-yr “true” 1500-yr “true” cycle of minor ice cycle of minor ice rafting rafting (resonance = (resonance = cyclic behavior)cyclic behavior)

2.2. Gradual coolingGradual cooling 3.3. Reaching a Reaching a

thresholdthreshold4.4. Triggering a Triggering a

major ice rafting major ice rafting (n×1500, i.e., (n×1500, i.e., 3000, 4500, 6000, 3000, 4500, 6000, 7500, 9000; 7500, 9000; stochastic = stochastic = random)random)

Where Else Did Millennial Oscillations Occur?Where Else Did Millennial Oscillations Occur?

WorldwideWorldwide

N.H. Midlatitude Europe, Asia, USA, N.H. Midlatitude Europe, Asia, USA, N.H. Tropics, Equatorial AtlanticN.H. Tropics, Equatorial AtlanticSouth American AndesSouth American Andes

New Zealand, AntarcticaNew Zealand, Antarctica

Millennial Oscillations During the Last 8000 YearsMillennial Oscillations During the Last 8000 Years

Small fluctuations exist in the Greenland dust amount.Small fluctuations exist in the Greenland dust amount.

Millennial oscillations were evident when N.H. ice sheets were Millennial oscillations were evident when N.H. ice sheets were large.large.Millennial oscillations were small or absent during the interglacial.Millennial oscillations were small or absent during the interglacial.

No major episodes of ice rafting or plankton reductionNo major episodes of ice rafting or plankton reduction

The only large N.H. ice sheet left is the one in Greenland,The only large N.H. ice sheet left is the one in Greenland,from which a small number of icebergs can break off.from which a small number of icebergs can break off.

Advances and retreats of mountain glaciers.Advances and retreats of mountain glaciers.

• What initiates these oscillations?

• How are they transmitted to those parts of the climate system where they have been observed?

Causes of Millennial Changes

Ch. 14, p. 261-268

• Why are they stronger during glaciations than during interglaciations?

• Why would the climate system oscillate in such a way?

• H1. The natural oscillations inherent in the internal behavior of northern hemisphere ice sheets.

• H2. The result of internal interactions among several parts of the climate system.

• H3. A response to solar variations external to the climate system.

Processes Within Ice SheetsProcesses Within Ice Sheets

Ice sheets as a wholeIce sheets as a wholeVery slow response Very slow response Many thousands of yearsMany thousands of years

Ice sheets marginsIce sheets marginsFaster changes Faster changes

Thinner on lands underlying Thinner on lands underlying soft sediments or along the soft sediments or along the oceansoceans

Limitations:Limitations:

Heat from belowHeat from below

Depression of bedrockDepression of bedrockSea level change (10-Sea level change (10-15m)15m)

Affect only larger Affect only larger millennial oscillationsmillennial oscillations

Interactions Within the Climate SystemInteractions Within the Climate System

Key components of the climate Key components of the climate system: ice sheets, surface ocean, system: ice sheets, surface ocean, deep oceandeep ocean

Ice sheets Ice sheets meltwater runoff meltwater runoff salinity of surface ocean salinity of surface ocean formation of deep waterformation of deep water

Opposite Hemispheric Responses Caused by the Conveyor Opposite Hemispheric Responses Caused by the Conveyor BeltBelt

Conveyor belt strong: Conveyor belt strong: North Atlantic warm North Atlantic warm but southern but southern hemisphere coolhemisphere cool

When it is weak, the When it is weak, the temperature temperature responses are responses are reversed.reversed.

The bipolar seesaw The bipolar seesaw patternpattern

Causes External to the Climate System: Solar VariabilityCauses External to the Climate System: Solar Variability

1.1. Weaker magnetic field Weaker magnetic field weaker solar shielding weaker solar shielding more more bombardment by cosmic bombardment by cosmic particles particles faster production faster production of of 14C C

2.2. 420-year cycle; weak 2100-year 420-year cycle; weak 2100-year cycle cycle

3.3. No 1500-year cycleNo 1500-year cycle

Implications of Millennial Oscillations for Future ClimateImplications of Millennial Oscillations for Future Climate

Would natural Would natural oscillations cause oscillations cause climate to warm or to climate to warm or to

cool in future decades?cool in future decades?

How would How would Greenland and Greenland and Antarctic ice sheets Antarctic ice sheets melting affect melting affect climate?climate?