reef response to global sea-level change during the previous interglacial period Karen Vyverberg, University of Belinda Dechnik | Andrea Dutton Jody Webster | Dan Zwartz

Searching for evidence of past sea-level change …

Sedimentary evidence in 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 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 • 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