abrupt climate change paleoceanography presentation 6/15/2015 by beth hart ?

Abrupt Climate Change

Paleoceanography Presentation

04/18/23

By Beth Hart

?

Abrupt Climate Cycles

Lockwood, J.G., 2001, Abrupt and sudden climatic transitions and fluctuations: a review, International Journal of Climatology, 21: 1153-1179.

Abrupt Climate Cycles

Ivanochko, T.S.,et al., 2005, Variations in tropical convection as an amplifier of global climate change at the millennial scale, Earth and Planetary Science Letters, 235: 302-314.

The end of the present interglacial: how and when?

Broecker, W.S., 1998, The end of the present interglacial: how and when?, Quaternary Science Reviews, 17: 689-694.

Three Questions:

1. Were previous intervals of peak interglaciation terminated by abrupt climate change?

2. How close are we to the end of the present interval of peak interglaciation?

3. Will the ongoing buildup of greenhouse gases alter the natural sequence of events?

Were previous intervals of peak interglaciation terminated by abrupt climate change?


How do interglacials end?

Figure 14-20(Ruddiman text)



•Decreased insolation

•No evidence of renewed ice growth



Evidence of abrupt change:• European pollen records

(Woillard, 1978)• N. pachyderma forminifera go

“gang-buster” (McManus, 1996)

How close are we to the end of the present interval of peak interglaciation?


Estimate the length of previous interglacials. • 18O records for benthic foraminifera • Warmth lasted ~11kyr (one half precession

cycle)• Terminations occur at N.H. insolation peaks

and last ~11kyr

Length of present interglacial (11.5kyr – 17kyr)

• After Heinrich event #1 (17kyr)• Beginning of Bölling warm interval (14.5kyr)• Younger Dryas within glacial period

(11.5kyr)


Lockwood, J.G., 2001, Abrupt and sudden climatic transitions and fluctuations: a review, International Journal of Climatology, 21: 1153-1179.



If analogous to Eemian: Ice cap growth should precedeSea level fall has not begunInterglacial will last more than several

kyrs

If analogous to stage 11: Driven by precession Interglacial much longer

From Broecker and Stocker (2006)


From Ruddiman (2005)

Will the ongoing buildup of greenhouse gases alter the natural sequence of events?


THC – potential mode for abrupt climate switch

• Weakened NADW formation during glacial periods

• Requires the addition of fresh water (change in density) in North Atlantic

• Interglacials end due to release of fresh water from melting of newly formed ice caps

• Ice growth prior to end of Eemian warm conditions



What about greenhouse gases?

• Cause a premature transition from between modes

• Retard growth of ice sheets

No new ice sheets => no fresh water to North

Atlantic => no reorganization of THC

• Greenhouse gas buildup could be enough to trigger an alteration of THC

Conclusions


Where do we go from here?

1. Monitor present-day deep water formation

2. Learn where and how deep water forms

3. Determine if THC reorganizations (induced by greenhouse gas) would cause climatic cooling

AND…….

We’re still in an interglacial cycle!

(Even in Ohio)

Surprised, anyone?


Tzedakis, C., 2003, Timing and duration of Last Interglacial conditions in Europe: a chronicle of a changing chronology, Quaternary Science Reviews, 22: 763-768.

Timing and duration of Last Interglacial conditions in Europe: a chronicle of a

changing chronology

1. The Last Interglacial

2. Current interpretation

3. Remaining issues

Figure 15-6c(Ruddiman text)


The Last Interglacial:

Why study the Last Interglacial?• Most recent period with similar interglacial

conditions• Minimal anthropogenic effects

Uncertainties• Lack precise absolute timescales and

stratigraphic markers• Correlation of terrestrial evidence with

changes in ice volume and sea level• Timing and response of environment to the

end of interglacial periods



The First Steps:• Shackleton (1969) – Eemian equivalent to MIS

5eLast Interglacial lasts ½ precessional cycle (not

½ eccentricity cycle)

• Agreed with Muller (1974) terrestrial evidence from Germany

Involved annual laminations and extrapolation of sedimentation rates

• No absolute dates

• Assumption of synchronous boundaries

Marine timescales assigned to terrestrial records



Piecing it together:• Many scientists attempted to correlate marine

timescales to terrestrial records.

• Terrestrial interglacial period extended into MIS 5d

• Evidence provided a range of times for Last Interglacial duration (11kyr – 23kyr)

• Neither upper nor lower boundaries were coincident between marine and terrestrial records

• Diachroneity between northern and southern European terrestrial records


Current Interpretation:

128ka – sea level at present height

127ka – peak insolation

126ka – full interglacial

120ka – decrease of temperatures due to orbital changes; sea-ice and tundra expand

~Increased albedo~

115ka – end interglacial in northern Europe

110ka – end interglacial in southern Europe


Remaining Issues:

Timing and nature of Heinrich event 11• Deglaciation complete by 128ka• What is the cause of postulated ice-

rafting event at 127ka?

Replication of marine patterns with other margins

• Is there a lagged SST and arboreal response everywhere?

• Is response geographically dependent?Large diachroneity in Europe• When does glaciation begin in

intermediate areas?



Piecing it together:

Tzedakis, et al., 1997• Glacial-to-interglacial transitions used as tie

pointsTransitions represent rapid eventsVegetation response without significant delay

• Interglacial endpoints not fixedLacked evidence of abrupt elimination of

vegetationCreated effect of terrestrial interglacials

extending after marine glacial conditions began

• Observed that forest (terrestrial interglacial) period extended into MID 5d (marine stadial period)



Piecing it together:

Kukla, et al., 1997• Grande Pile pollen record with fixed beginning of

Last Interglacial (MIS 6/5) and Pleniglacial (MIS 5/4)

• Inferred duration of Last Interglacial (23 kyr)

• Terrestrial interglacial extends into MIS 5d and concludes with major IRD

• MIS 5e to 5d transition occurs before IRD and polar foraminifera N. pachyderma (McManus, et al., 1994)

abrupt climate change paleoceanography presentation 6/15/2015 by beth hart ?

Documents

kyr slide

interglacials end

evidence of abrupt change

quaternary science reviews

precession interglacial

abrupt climate cycles

ruddiman text slide

kyr younger dryas