Holocene sea level history and reef development in Hawaii and the equatorial Pacific OceanEric E. GrossmanDepartment of Geology and GeophysicsPh.D. Committee

Chip Fletcher (chair)Richard Grigg (outside member)Fred MackenzieBrian PoppGordon Tribble

The Coastal HuiDaily positive supportLaborious underwaterassistanceData processing savvyMultispectral imageryACKNOWLEDGMENTSChris CongerJodi HarneyGeoff GarrisonClark ShermanJohn RooneyKimball MillikanPaul JohnsonBruce AppelgateJames FosterEbitari IsounVideo footageThomas GorgasWave spectra analysesJerome Aucan

Chip FletcherA Special Thanksto

Who held on during the storm

My lovely fianc Jodi

Mama MiaArlene HambletDEDICATION

IntroductionControls on reef accretionHolocene sea level in the PacificPeltier (1996), Grossman et al. (1998)Holocene reef development on OahuMethodsStudy AreaResults Modern community structureGrossman et al. (in review) Holocene reef developmentGrossman and Fletcher (in review)ConclusionsOUTLINE

Subsidence Theory(Darwin, 1842)Moorea,TahitiGlacial Control Theory (Daly, 1915)Sea level

karstKarst Theory and the role of antecedent topography (MacNeil, 1954; Purdy, 1974)

Controls on accretionModified after Hubbard (1988)

Blanchon Holocene sea levelAcropora palmatacorals track sea levelin the Caribbean( 5-6m)Absence = Drowning during catastrophic rise events (CREs)Reef accretion histories record sea-level behavior coral community composition and zonation important proxy data

ICE-5GPacific deglacialsea-level history

distinct from Caribbean middle Holocene highstand +1-3 mUncertainties no proven biotic indicators of sea level role of wave energy? reef initiation time limited (single) analyses

Hawaiidifferential island tectonics and wave energyVariable relative sea-level histories Wave base limits accommodation space Variable effect on each island through time

OAHUHanauma BayKailuaEmerged fossil reef (>125 ka) (Stearns 1970; Muhs and Szabo, 1994)Submerged fossil reef (~210 ka) (Sherman et al. 1999)Holocene reef (

Hanauma Reef(Easton and Olson, 1976)Shallow volcanic basement (

Hawaii sl - hanAccommodation space +2-3 m above reef(Montaggioni, 1988)Hanauma Reef(Easton and Olson, 1976)Hawaii sea levelincluding +1.75 mhighstand at 3500 yr BP(Stearns, 1978; Grossman and Fletcher, 1998)

Hawaii sl - egdataKailua Reef(this study)Windward reef accretion history is distinct from wave-sheltered Hanauma Bay.Accommodation space +2-3 m above reef(Montaggioni, 1988)Hawaii sea levelincluding +1.75 mhighstand at 3500 yr BP(Stearns, 1978; Grossman and Fletcher, 1998)Hanauma Reef(Easton and Olson, 1976)

Purpose Analyze structure and zonation of modern reef community in a wave-exposed setting Characterize internal composition and developmental history of a windward fringing reef Assess the relative roles of sea-level history, wave energy and antecedent topography on reef accretion and resulting architecture Move away from fair-weather studies and models of reef development

Bathymetric mappingSubstrate mappingDrill coringWave spectra measurementsMETHODS

BathymetricmappingLIDAR (0-40 m)~0.1 m vertical1 m lateralSingle beam (channel)~0.01 m vertical~0.1 m along track 6.5 m line spaceNOS (>40 m)2-3 m vertical?~30 m lateral

Substrate mappingSubstrate types recordedalong 30 m transects at60 sites (-3 to -20 m depth)using Line Intercept MethodQuantifies percent cover,colony counts, size, growth form, and diversity

Drill CoringX-Ray of coral skeleton

Drill Coring

Drill system in operationCourtesy of Thomas Gorgas

Wave heights and periods collected with directional Waverider buoys and pressure sensorsMokulua Isls.http://www.cdip.eduData available at Scripps web site:with Jerome Aucan

KawainuiChannelSTUDY AREA

WindwardSoutheast OahuDrownedpaleochannel of Kawainui StreamLarge sand-filedkarst features incentral back reef

Kailua ReefMapping sitesKawainuiChannelNorthCentralSouthBack reef (

KawainuiChannelNorthCentralSouth32 coresCore lengths0.5 to 18 mRecovery76%, all cores84%, 12 primary coresReplicatescross-checkrecovered lithologieswater depths-3 to -20 mKailua Reef Drill sites

Broad shelf0 to -14 mNorthNarrow, gradual slopeCentralHummocky, shallowSouthVery broad, smoothlow slopeKailua Reef Bathymetry

innerH

Trade swellN&NWswellKawainuiChannelKailua Reef Wave climate

Central fore reef (looking landward)Multispectral scanner imagery draped on bathymetry

Flythrough

Modern reef community structureGrossman, Fletcher, and Harney (in review)Variations in wave-related stress and antecedent topography govern the unique zonation and growth form response of reef building coralsUnderstanding community structure and controls enables interpretation of fossil communities and paleoenvironmentsImportance:Ecotypes

Wave shoaling produces distinct niches

Cover and diversity

Species and form

Species and form

fore reef1-16 to -18 mFOV=4 m12-18 mFOV=5 m2

Platy to encrustingEcotypes are more sensitive of environment than species alone2-10 mFOV=2.5 m112Porites lobata, Montipora capitata, M. patulaPlasticity leads to higher diversity due to the added capacity to withstand stress

Wt_mean depth

Colony agesReef sub-communities maintained at different stages of development by wave-related stress and disturbanceModerate stress and disturbance leads to high diversity and greater age (K5, K4)Disturbancegoverns successionColony Age = size / growth rateGrowth rate = 1 cm/yr (Grigg, 1982)Persistent stressshapes compositionHigh stress and excessive disturbance (waves and sediment abrasion) clears substrate and resets succession (K1)Century-scale turnover

Modern community structure summaryEcotypes are more sensitive indicators of environmentsthan species alone.Variations in wave-related stress over a complex topography produce distinct cor-algal communities undergoing different rates of succession within a single reef system.Plasticity enables species to adapt to different levels of wave-related stress thereby increasing cover and diversity.

Holocene reef developmentGrossman and Fletcher (in review)Accommodation space for reef accretion may be strongly modulated through time by wave energy and its interaction with complex antecedent topographyImportance:Distinct styles of architectural development and accretion occur within a single reef systemImportant implications for interpreting sea level

Kailua reefsurface

Internal Biolithofaciesin the 32 drill coresBranching coral rudstoneEncrusting cor-algal bindstoneMixed-skeletal rudstone/ grainstoneMassive coral framestoneBranching coral framestoneMudstone/wackestoneDepositionalenergyHighLow

Branching coral rudstone faciesStrongly lithified rubble derived from fore reefCommon in upper sections of central platform coresMiddle to late Holocene

Encrusting bindstone faciesStrongly bound encrusting coral and coralline algaeModerate to high bioerosion, rhodoliths presentCommon in upper sections of all coresIndicative of wave-swept platform communities

Mixed-skeletal rudstone/grainstone faciesStrongly cemented fragments of all reef sedimentsCommon in north central back reef and Flat Isl. CoreRepresents beach, high energy nearshoreMiddle to late Holocene and pre-Holocene

Massive coral framestone faciesIn situ Porites lobataModerate bioerosionCommon in lower sections of central platform coresFramework builder in depths of -10 to -14 mEarly to middle Holocene

Branching framestone faciesIn situ Porites compressaBioerosion present but rareOccurs in basal sections of seaward and southern coresRepresents deep (12-20 m) fore reef environmentEarly Holocene

Mudstone faciesWell-lithified mudOccurs as infills in inter and intra-skeletal cavitiesIndicative of low energy or cryptic environmentPre-Holocene

Reef UnitsHolocene ReefOriginal skeletal mineralogy (Aragonite and Mg-calcite)Marine cementationHolocene ages (125,000 yr BP)Order of magnitude increase in stabilization to calciteDissolution and entire loss of molluscs in addition to coralsMultiple episodes of meteoric phreatic and vadose diagenesisMIS 7 ages or older

Holocene cementsAragonite cement rareInter-skeletal cavities in Holocene coral

Holocene cementsMassive peloidal micriteMost abundant cement in Holocene reefLaminae suggest calm environmentCommon of branching coral framestone facies

Holocene cementsMg-calcite cementsGrain coatings, void linings, isopachous rim cementsin all Holocene facies

Diagenesis of Pre-Holocene reefMultiple generations ofsubaerial diagenesis(pre-MIS 5e)Drusy calcite sparReplace and occlude primary inter- and intra- skeletal porosityIndicative of subaerial exposure and alteration in meteoric phreatic zoneCommon of MIS 5e reef

Diagenesis of Pre-Holocene reefMultiple generations ofsubaerial diagenesis(pre-MIS 5e)Moldic porosityEntire loss of mollusc fragments by dissolutionUbiquitous in pre-MIS 5e reef

Diagenesis of Pre-Holocene reefMultiple generations ofsubaerial diagenesis(pre-MIS 5e)Sparry calcite and whisker cementsInfills of gastropod moldsWhisker cements indicate alteration in vadose zoneCommon of pre-MIS 5e reef

Diagenesis of Pre-Holocene reefMultiple generations of marine and subaerial exposureSubaerial - Initial dissolution of massive coral creates vugMarine - Micrite cements partly infill vugMarine - Second generation cementation of aragonite needle cements penetrate existing micriteSubaerial - All components converted (stabilized) to calciteMultiple generations ofsubaerial diagenesis(pre-MIS 5e)

Kailua Reef drill sites

Mole%Mg-calciteSD of Mg-calciteDeterminations=0.15 mole %Mg-calcite

LandwardandseawardtransectsKawainuiChannelNorthCentralSouth

Landward cores

Seaward cores

Start-up reefInitiation at 7900 yr BPEncrusting coral onash-rich sandsTerrigenous soil in coral skeleton (arrows)shows continuity ofcolony across fracture7 sequences of start-upover the course of at least500 years and 3.5 m ofaccretion

Seaward cores

Accretion Histories

flood5Kailua Bay today

flood10

flood95

flood9

flood85

flood8

flood75

flood7

flood65

flood6

flood55

flood5

Rates plot

3D fig S plat

3D north plat

Holocene reef developmentsummaryAntecedent low topography of drowned stream valley providedaccommodation space below wave scour but only until reef caught upwith sea-level rise ~5000 yr BP.

Reef structure maintained at depth of 10-15 m by moderate wave exposure.

Wave sheltering enabled continued development in north central reef; strong cementation required to lithify rubble transported from fore reef.

Rubble, sediment, and coralline algae important components of reef core.

Holocene reef has mimicked antecedent topography of meandering stream,despite infilling of central channel-valley.

CONCLUSIONSDynamic interaction between wave shoaling and complex antecedent topography produces distinctly different reef communities and architectural responses within a single reef system.Inter-reef variability of accretion histories has important implications for sea-level studies necessitating detailed investigation of site-specific processes and responses.

CONCLUSIONSHolocene reefs on Oahu exist in a limited depth environment provided by antecedent low topography below wave scour and in settings sheltered from long period wave impact.Isolated modern and Holocene reef communities on Oahu exist in a geologic window of vulnerability to human impacts.

FUTURE DIRECTIONSQuantify wave forcing at the sediment-water interface to determine annual mean and maximum and episodic extreme stress that shape structure and reset development history.Refine ecotype depth distribution to account for wave-exposure and stress.Test the hypothesis that wave energyand antecedent topography controlreef development along a gradient in wave exposure. Research in wave-exposed areas offers the capacity to understand changes in wave regime owing to climate.

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