Holocene Reef Accretion, Southwest Molokai, Hawaii Mary Engels

1. Holocene Reef Accretion, Southwest Molokai, Hawaii Mary Engels

2. Acknowledgements: - Chip Fletcher, Craig Glenn, Jane Schoonmaker - Chris Conger, John Rooney, Joe Reich - Family - Coastal Geology Group - SOEST - USGS, Mike Field, Curt Storlazzi and Eric Grossman - Khaled Bin Sultan Living Oceans Foundation - Hawaii Coral Reef Initiative

3. Overview: I. Introduction: Objectives and Strategy II. Modern Ecosystem Investigations i. Data collection: Methodology ii. Data Analysis: Substrate and coral types iii. Conclusions: Model of modern ecosystem zonation for SW Molokai III. Drill Core Investigations i. Data collection: Methodology ii. Data Analysis: Facies identification and distribution iii. Conclusions: Facies interpretation IV. Synthesis V. Conclusions

4. Objectives: • Exploratory investigation of the geologic history of the Molokai fringing reef system. • What is the spatial variability of the Molokai modern reef ecosystem? • What is the influence of Holocene sea level on the Molokai reef system?

5. LAAU POINT LONO HARBOR 0 mi 1 mi 0 km 1 km OVERVIEW OF THE SOUTHWEST SHORE OF MOLOKAI: HIKAUHI SITE HALE O LONO SITE HALE O LONO SITE: -High wave exposure -Sparse coral cover -Shore parallel ridge and runnel morphology HIKAUHI SITE -Medium wave exposure -Abundant coral cover -Shore normal spur and groove morphology

6. Strategy: Principle of Uniformitarianism: “the present is the key to the past” Application: Modern reef ecosystem zonation provides a model for understanding Holocene reef accretion.

7. Strategy: • Principle of Uniformitarianism: “the present is the key to the past” • Application: • Modern reef ecosystem zonation provides a model for • understanding Holocene reef accretion. • Survey and model modern ecosystem zonation (PRESENT)

8. Strategy: • Principle of Uniformitarianism: “the present is the key to the past” • Application: • Modern reef ecosystem zonation provides a model for • understanding Holocene reef accretion. • Survey and model modern ecosystem zonation (PRESENT) • Identification of lithofacies from drill cores (PAST)

9. Strategy: • Principle of Uniformitarianism: “the present is the key to the past” • Application: • Modern reef ecosystem zonation provides a model for • understanding Holocene reef accretion. • Survey and model modern ecosystem zonation (PRESENT) • Identification of lithofacies from drill cores (PAST) • Comparison of lithofacies and modern ecosystem model to determine depositional environments (PRESENT + PAST)

10. Strategy: • Principle of Uniformitarianism: “the present is the key to the past” • Application: • Modern reef ecosystem zonation provides a model for • understanding Holocene reef accretion. • Survey and model modern ecosystem zonation (PRESENT) • Identification of lithofacies from drill cores (PAST) • Comparison of lithofacies and modern ecosystem model to determine depositional environments (PRESENT + PAST) • Reconstruct paleoecosystem zonation from lithofacies distribution (PRESENT+PAST = RECORD)

11. Strategy:

12. Strategy:

13. Strategy:

14. Strategy:

15. Strategy:

16. Overview: I. Introduction: Objectives and Strategy II. Modern Ecosystem Investigations i. Data collection: Methodology ii. Data Analysis: Substrate and coral types iii. Conclusions: Model of modern ecosystem zonation for SW Molokai III. Drill Core Investigations i. Data collection: Methodology ii. Data Analysis: Facies identification and distribution iii. Conclusions: Facies interpretation IV. Synthesis V. Conclusion

17. Modern Ecosystem Investigations: Methodology 0 mi 1 mi 0 km 1 km HIKAUHI HALE O LONO • 10 m benthic surveys-Line Intercept Technique. • Recorded every change in substrate type. • Coincident (or nearly so) with drill cores. • 19 surveys from Hikauhi, 27 surveys from Hale O Lono

18. Modern Ecosystem Investigations: Data Analysis

19. Modern Ecosystem Investigations: Data Analysis

20. Modern Ecosystem Investigations: Results

21. Modern Ecosystem Investigations: Results Study Sites Modified from Storlazzi et al. (in press)

22. Modern Ecosystem Investigations: Results Study Sites Modified from Storlazzi et al. (in press)

23. Modern Ecosystem Investigations: Results Modified from Storlazzi et al. (in press)

24. Modern Ecosystem Investigations: Conclusions

25. Modern Ecosystem Investigations: Conclusions

26. Overview: I. Introduction: Objectives and Strategy II. Modern Ecosystem Investigations i. Data collection: Methodology ii. Data Analysis: Substrate and coral types iii. Conclusions: Model of modern ecosystem zonation for SW Molokai III. Drill Core Investigations i. Data collection: Methodology ii. Data Analysis: Facies identification and distribution iii. Conclusions: Facies interpretation IV. Synthesis V. Conclusions

27. Drill Core Investigations: Data Collection: Methodology • Shore normal transects • Water depth 4 m to 21 m • Where possible cores started on live coral. • 14 cores from Hikauhi • 10 cores from Hale O Lono. • Cores sub-sampled for radiocarbon dating, X-ray diffraction analysis and thin section analysis

28. Drill Core Investigations: Data Collection 157d 10’ 45” 157d 9’ 45” 21d 5’ 30” 157d 16’ 0” 157d 15’ 0” 21d 5’ 30” 21d 5’ 30” 21d 5’ 30” • 5.5 m • 8.5 m • 14.0 m • 17.7 m • 21.0 m 21d 4’ 45” 0 mi 0 mi 0.5 mi 0.5 mi 21d 4’ 30” 21d 4’ 45” 21d 4’ 30” 0 km 0 km 0.5 km 0.5 km 157d 16’ 0” 157d 15’ 0” 157d 10’ 45” 157d 9’ 45” Hale O Lono Hikauhi 4.0 m 5.5 m 6.1 m 9.1 m 9.8 m 10.7 m 12.8 m 14.3 m 18.3 m 19.8 m

29. Drill Core Investigations: Data Analysis Lithofacies (facies) A: Encrusting coral-algal bindstone B: Mixed skeletal rubble C: Massive coral framestone D: Unconsolidated floatstone E: Branching coral framestone

30. Drill Core Investigations: Data Analysis

31. Drill Core Investigations: Data Analysis A: Encrusting coral-algal bindstone High-Energy B: Mixed skeletal rubble High-Energy

32. Drill Core Investigations: Data Analysis A: Encrusting coral-algal bindstone High-Energy B: Mixed skeletal rubble High-Energy C: Massive coral framestone Mid-Energy

33. Drill Core Investigations: Data Analysis A: Encrusting coral-algal bindstone High-Energy B: Mixed skeletal rubble High-Energy C: Massive coral framestone Mid-Energy D: Unconsolidated floatstone Mid-Energy

34. Drill Core Investigations: Data Analysis A: Encrusting coral-algal bindstone High-Energy B: Mixed skeletal rubble High-Energy C: Massive coral framestone Mid-Energy D: Unconsolidated floatstone Mid-Energy E: Branching coral framestone Low-Energy

35. Drill Core Investigations: Data Analysis

36. Drill Core Investigations: Data Analysis 910 cal yr BP

37. Drill Core Investigations: Data Analysis

38. Drill Core Investigations: Data Analysis 4,812 cal yr BP

39. Drill Core Investigations: Conclusions • Decreasing age of reef toward shore • Distinct facies change between ~8,100 cal yr BP and ~7,900 cal yr BP • Youngest recorded age ~4,800 cal yr BP • Sequence is exposed, not buried under continued accretion

40. Drill Core Investigations: Conclusions • Decreasing age of reef toward shore • Distinct facies change between ~8,100 cal yr BP and ~7,900 cal yr BP • Youngest recorded age ~4,800 cal yr BP • Sequence is exposed, not buried under continued accretion

41. Drill Core Investigations: Conclusions • Possible causes: • Decreasing age of reef toward shore (long term, 8,000 years), • -Local relative sea-level rise (Hawaiian Islands): island • subsidence, localized oceanic thermal expansion • -Eustatic sea-level rise (Global):Glacial melting, thermal • warming, basin volume changes • Distinct facies change (short term, 200 years change ~8,100 cal yr BP): • -Rapid local relative sea-level rise (Hawaiian Islands): • island subsidence, localized oceanic thermal expansion • -Rapid eustatic sea-level rise (Global):Catastrophic Rise • Event III, 8.2 ka event

42. Drill Core Investigations: Conclusions

43. Drill Core Investigations: Conclusions Rapid sea-level rise

44. Drill Core Investigations: Conclusions Rapid sea-level rise

45. Drill Core Investigations: Conclusions Rapid sea-level rise

46. Drill Core Investigations: Conclusions Rapid sea-level rise

47. Drill Core Investigations: Conclusions • Decreasing age of reef toward shore • Distinct facies change between ~8,100 cal yr BP and ~7,900 cal yr BP • Youngest recorded age ~4,800 cal yr BP • Sequence is exposed, not buried under continued accretion

48. Drill Core Investigations: Conclusions • Possible causes: • Youngest age recorded, ~4,800 cal yr BP -Change in environmental conditions: change in El Nino, Southern Oscillation (ENSO) patterns, changes in wave shadowing (increasingly vertical topography), Penguin Bank • Sequence is exposed, not buried under continued accretion -Erosion -Changes in wave shadowing

49. Drill Core Investigations: Conclusions Modern Shoreline -10 m shoreline -20 m shoreline

50. Overview: I. Introduction: Objectives and Strategy II. Modern Ecosystem Investigations i. Data collection: Methodology ii. Data Analysis: Substrate and coral types iii. Conclusions: Model of modern ecosystem zonation for SW Molokai III. Drill Core Investigations i. Data collection: Methodology ii. Data Analysis: Facies identification and distribution iii. Conclusions: Facies interpretation IV. Synthesis V. Conclusions