Coral reef response to global sea-level change during the previous interglacial period Karen Vyverberg, University of Florida Belinda Dechnik | Andrea Dutton Jody Webster | Dan Zwartz
Searching for evidence of past sea-level change …
Sedimentary evidence in fossil coral reefs • Shifts in coral communities • Unconformities • Freshwater exposure
The Last Interglacial (LIG) period: 129,000 – 116,000 years ago • Relatively abundant sea-level records • Warmer temperatures – especially at the poles • Global sea level higher than today
Sea-level Oscillations • Abrupt changes in global mean sea level (GMSL)
Reconstructing Sea Level Elevation Elevation
Time Reconstructing Sea Level Elevation Elevation
Time Elevation Elevation
Time LIG Sea Level Reconstructions
Bahamas W. Australia Bahamas Global Mediterranean • Corals • Corals • Corals • Corals • d18O Pl. Forams • Beach deposits Good agreement that: • LIG SL peaked 6-9 m above present day SL One global ice • Significant Antarctic contribution volume history • Up to 3.5 m from Greenland • ~ 1 m from mountain glaciers and thermal expansion The multi-proxy approach: Using fossil corals from the LIG (125,000 years ago) to reconstruct a global sea level curve
Field Work Analytical Work
• Outcrop Description • X-Ray Diffraction (XRD) • Stratigraphy • Degree of aragonite • Coralgal preservation Assemblages/Facies • Thin Sections • Elevation Surveying INFORMS • Cement type and • Sampling generation • Drill cores or • Stable Isotopes hammer • U/Th Dating Multiple spatial scales of observation yield information about stratigraphic and paleoenvironmental changes Narrowing the paleo-water depth estimate Narrowing the paleo-water depth estimate
Coral Assemblage Key Components Palaeoenvironmental Interpretation Assemblage A Massive/sub-massive and encrusting Shallow water reef environment; subtidal Goniastrea sp. (G. minuta; G. aspera; sandy reef flats at 0-2 m depth (Taylor, Goniastrea ( ) G. retiformis). G. retiformis is most 1968), and especially in the intertidal common. zone (Veron, 1986).
Assemblage B Massive/sub-massive Favites sp. and Broad paleo-depth; Stylophora sp. may Favia sp. Stylophora sp. and limit to environment to protected lagoons Stylophora (Faviid/ ) massive/sub-massive Cyphastrea sp. and lower reef slopes (Veron, 1986), but are common. Rare massive Platygyra Lewis (1969) observed Stylophora sp. in sp. and Porites sp. 1-2 m water depth on the reef crest. Favia sp. are also common in the reef crest/reef front in as low as 1-2 m depth (Taylor, 1968). Assemblage C Encrusting plates of Siderastrea sp. Shallow reef environment or sandy and Pavona sp. with less common lagoon; subtidal reef flat at 1-2 m low tide Siderastrea/Pavona ( ) platy Favites sp. and Millepora sp. water depth (Taylor, 1968 and Veron, 1986). Assemblage D Encrusting Porites sp. and Faviids Reef edge/reef front community in <6m with extensive coralline algae. water depth (Taylor, 1968). (Porites/Faviid) Reef Units in Outcrop
Reef Framework
Transition Layer
Reef Framework Assemblage A Intertidal/ 0-2 m
Transition Layer Assemblage B 1-2 m water depth Reef Framework Outcrop Architecture
Reef Framework
Transition Layer
Reef Framework
Transition Layer
Reef Framework Timing of transitions
Reef Framework
Transition Layer Reef Framework
Transition Layer Elevation Elevation Reef Framework N Time
Curieuse La Digue
Assemblage B + 6.6 m Shallow Corals + 5.9 m 125.1 ±0.4 ka 125.8 ±0.5 ka Rubble Rubble
• Upper timing bound on rubble Assemblage B Shallow Corals • Concurrent with a global drop in sea level (Dutton et al., QSR 2015) Summary Three episodes of reef growth punctuated by two interruptions
At least one sea-level oscillation; concurrent with a global drop
Sea level was unstable during the LIG
Ice sheets may behave dynamically in future warm T’s
Acknowledgements P. Samson at PetroSeychelles |Seychelles National Parks Authority Ministry of Environment and Energy |Seychelles Bureau of Standards δ18O vs δ13C of La Digue Hand-Samples and Cores
14.00 Micrite Location of sampled cements at 7.52 m above 12.00 MLWS in Core C from Site 7. CEMENTS Large Pendant Large Pendant Cement Cement 1st Gen Cement 10.00 2nd Gen Cement
Second 8.00 Generation CORAL-DWELLING BARNACLES
6.00 First Fossil Trevathana sp. Generation Modern Trevathana sp.
4.00 Fossil Host Coral of VPDB) vs Trevathana sp. ‰ C (
13 2.00 REEFBUILDERS δ Coralline Algae Corals 0.00
-2.00
-4.00
-6.00 -12.00 -10.00 -8.00 -6.00 -4.00 -2.00 0.00 2.00 δ18O (‰ vs VPDB) δ18O vs δ13C of La Digue Hand-Samples and Cores
14.00 Micrite Location of sampled cements at 7.52 m above 12.00 MLWS in Core C from Site 7. CEMENTS Large Pendant Large Pendant Cement Cement 1st Gen Cement 10.00 2nd Gen Cement
Second 8.00 Generation CORAL-DWELLING BARNACLES
6.00 First Fossil Trevathana sp. Generation Modern Trevathana sp.
4.00 Fossil Host Coral of VPDB) vs Trevathana sp. ‰ C (
13 2.00 REEFBUILDERS δ Coralline Algae Corals 0.00
-2.00
-4.00
-6.00 -12.00 -10.00 -8.00 -6.00 -4.00 -2.00 0.00 2.00 δ18O (‰ vs VPDB) Chen et al., 1991 Thompson et al., 2011