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

5. OVERVIEW OF THE SOUTHWEST SHORE OF MOLOKAI: LONO HARBOR 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 HIKAUHI SITE HALE O LONO SITE LAAU POINT 0 km 0 mi 1 km 1 mi

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:

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  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 HIKAUHI HALE O LONO 0 km 0 mi 1 km 1 mi

18. Modern Ecosystem Investigations: Data Analysis

20. Modern Ecosystem Investigations: Results

21. Modified from Storlazzi et al. (in press) Study Sites

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

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

24. 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.  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 Drill Core Investigations: Data Collection: Methodology

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

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

35. Drill Core Investigations: Data Analysis

36. 910 cal yr BP

37. Drill Core Investigations: Data Analysis

38. 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. 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

51. Synthesis  Spatial variability of the Molokai modern reef ecosystem? Increasing wave energy, by depth changes and exposure to North Pacific swell, = decreased coral cover and a shift from delicate coral morphologies to robust coral morphologies

52. Synthesis  Influence of Holocene sea level on the SW Molokai reef system? -Early Holocene sea-level rise caused a landward migration of reef accretion centers. -Rapid sea-level rise between ~8,100 cal yr BP and ~7,900 cal yr BP changed depositional environments at Hale O Lono. -Stabilization of late Holocene sea level forced lateral progradation of reefs at Hikauhi  Spatial variability of the Molokai modern reef ecosystem? Increasing wave energy, by depth changes and exposure to North Pacific swell, = decreased coral cover and a shift from delicate coral morphologies to robust coral morphologies

53. 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

54. Drill Core Investigations:  Late Holocene accretion at Hikauhi has consisted of lateral progradation of the reef structure.  In the early Holocene at Hale O Lono, the reef back-stepped under rising sea levels which likely resulted from a combination of both local and global influences.  The distinct facies change at Hale O Lono between ~8,100 cal yr BP and ~7,900 cal yr BP is likely the result of rapid global sea-level rise, perhaps associated with CREIII or the 8.2 ka event.  Reef accretion at Hale O Lono terminated at ~4,800 cal yr BP due to changes in environmental conditions, possibly related to a reduction in wave shadowing by Laau Point or ENSO changes.  The transgressive sequence at Hale O Lono remains exposed, possibly due to a decrease in wave shadowing by Laau Point Conclusions: Modern Ecosystem Investigations:  On a small scale (by site), substrate and coral types change with depth.  On a large scale (western end of Molokai), substrate and coral types change with proximity to Laau Point, the refraction point for North Pacific swell.

55. Mahalo!