Long-Term Changes in Global Sea Level Craig S. Fulthorpe University of Texas Institute for Geophysics John A. and Katherine G. Jackson School of Geosciences.

Long-Term Changes in Global Long-Term Changes in Global Sea LevelSea Level

Craig S. FulthorpeCraig S. Fulthorpe University of Texas Institute for GeophysicsUniversity of Texas Institute for Geophysics

John A. and Katherine G. Jackson School of GeosciencesJohn A. and Katherine G. Jackson School of Geosciences

Public Policy ForumPublic Policy Forum10 March 201010 March 2010

Growth and decay of continental ice Growth and decay of continental ice sheets has been the primary cause of sheets has been the primary cause of large sea-level changes (e.g., ~120 m large sea-level changes (e.g., ~120 m lower at last glacial maximum) for at lower at last glacial maximum) for at least the last 40 million yearsleast the last 40 million years

Causes and Effects of Global Sea-Level ChangeCauses and Effects of Global Sea-Level Change

Miller et al. (2005)

Total potential sea-level rise cause by Total potential sea-level rise cause by melting of onshore ice sheets is ~70 m.melting of onshore ice sheets is ~70 m.

• All of Antarctica: ~57-60 m (IPCC)All of Antarctica: ~57-60 m (IPCC)

• West Antarctic Ice Sheet West Antarctic Ice Sheet alone: up to ~7 malone: up to ~7 m

• Greenland: ~7 mGreenland: ~7 m

Principal methods for estimating long-term changes in sea-level:Principal methods for estimating long-term changes in sea-level:

1)1) Oxygen isotopic record from deep-sea sedimentsOxygen isotopic record from deep-sea sediments

2)2) Continental margin sedimentary sequencesContinental margin sedimentary sequences

Record from >40 scientific ocean drilling sites Record from >40 scientific ocean drilling sites (Zachos et al., 2001)(Zachos et al., 2001)

1. Oxygen Isotopic Record of Ice Volume and Temperature1. Oxygen Isotopic Record of Ice Volume and Temperature

• DSDP/ODP/IODP drilling of pelagic sediments DSDP/ODP/IODP drilling of pelagic sediments has revolutionized climate studies by providing has revolutionized climate studies by providing long-term oxygen isotopic records.long-term oxygen isotopic records.

• High-frequency (40 ky – 100 ky), orbitally forced High-frequency (40 ky – 100 ky), orbitally forced climate change is modulated by long-term climate change is modulated by long-term changes in plate motion, oceanic gateways and changes in plate motion, oceanic gateways and atmospheric COatmospheric CO22. .

Abrupt EventsAbrupt Events

• PETM (55 Ma): 5-6°C rise in deep-sea PETM (55 Ma): 5-6°C rise in deep-sea temperature in <10 ky (release of methane from temperature in <10 ky (release of methane from marine gas hydrates?)marine gas hydrates?)

• Cooling events: Oi-1 (34 Ma), Mi-1 (23 Ma)Cooling events: Oi-1 (34 Ma), Mi-1 (23 Ma)

Climate, and sea level, do not always Climate, and sea level, do not always respond linearly to forcingrespond linearly to forcing

Schweitzer and Thompson (1996); USGS Open-File Report 96-000Schweitzer and Thompson (1996); USGS Open-File Report 96-000

After Lisiecki and Raymo (2005). Figure by R. Rohde, Global Warming Art project.After Lisiecki and Raymo (2005). Figure by R. Rohde, Global Warming Art project.

Early Pliocene Warm PeriodEarly Pliocene Warm Period• No Northern Hemisphere No Northern Hemisphere ice, periodic (40 ky) collapse ice, periodic (40 ky) collapse of West Antarctic Ice Sheet.of West Antarctic Ice Sheet.

• 7-10 m sea-level 7-10 m sea-level equivalent.equivalent.

• COCO22 similar to present, but: similar to present, but:

• ~3°C warmer (IPCC ~3°C warmer (IPCC estimate this would estimate this would require a doubling of COrequire a doubling of CO22) )

• Sea level ~25 m higher.Sea level ~25 m higher.

• So climate and sea level So climate and sea level were more sensitive to COwere more sensitive to CO22 variation than today.variation than today.

• Provides a glimpse of the Provides a glimpse of the future Earth system.future Earth system.

2. Estimating Sea-Level Change Using2. Estimating Sea-Level Change UsingContinental Margin Drilling TransectsContinental Margin Drilling Transects

Expedition 317: Expedition 317: Canterbury Basin, Canterbury Basin, New ZealandNew Zealand

• Targets the environment directly affected by sea-level changeTargets the environment directly affected by sea-level change

• Thick early Thick early Pliocene sectionPliocene section

Figure by A. Droxler, Figure by A. Droxler, Rice UniversityRice University

Stratigraphic signature of the Neogene Stratigraphic signature of the Neogene (Bartek et al., 1991)(Bartek et al., 1991)

1) Late Oligocene-early Miocene aggradation, backstepping and partial drowning 1) Late Oligocene-early Miocene aggradation, backstepping and partial drowning 2) Late early Miocene-early middle Miocene vertical growth or aggradation 2) Late early Miocene-early middle Miocene vertical growth or aggradation 3) Earliest middle Miocene downward shift of deposition 3) Earliest middle Miocene downward shift of deposition 4) Late middle Miocene systematic lateral growth (progradation) 4) Late middle Miocene systematic lateral growth (progradation) 5) Late Miocene-early Pliocene re-flooding and aggradation 5) Late Miocene-early Pliocene re-flooding and aggradation

Climatic and Global Sea-Level RecordsClimatic and Global Sea-Level Records

• The geologic record provides an opportunity to quantify the timing, amplitudes, The geologic record provides an opportunity to quantify the timing, amplitudes, rates, mechanisms/controls, and effects of global sea-level change.rates, mechanisms/controls, and effects of global sea-level change.

• This record can tell us:This record can tell us:

• How the earth system has operated during past abrupt climate changes and How the earth system has operated during past abrupt climate changes and under past conditions of extreme climate forcing.under past conditions of extreme climate forcing.

• The potential sea-level response (rates and amplitudes) to elevated COThe potential sea-level response (rates and amplitudes) to elevated CO22 levels. levels.

• Improved understanding of the long-term record of global sea-level change:Improved understanding of the long-term record of global sea-level change:

• Enables critical evaluation of computer model predictions. Enables critical evaluation of computer model predictions.

• Improves our ability to predict the societal impact of future sea-level change Improves our ability to predict the societal impact of future sea-level change and allow us to better assess the contribution of greenhouse gases.and allow us to better assess the contribution of greenhouse gases.

Importance of Studying Past Sea-Level ChangeImportance of Studying Past Sea-Level Change

craig@ig.utexas.educraig@ig.utexas.eduwww.ig.utexas.eduwww.ig.utexas.edu