sea level controls sedimentation and environments in coastal caves and sinkholes abstract quaternary climate and sea level research in coastal karst basins caves cenotes sinkholes blueholes etc generally focuses on analyzing isotopes in speleothems or associating cave elevations prior sea level highstands the sediments in coastal karst basins represent an overlooked source of climate and sea level information in the coastal zone but to accurately interpret these sediments first requires an understanding of the forcing mechanisms that emplace them in this study we hypothesize that coastal karst basins transition through vadose littoral anchialine and finally into submarine environments during sea level rise because groundwater and sea level oscillate in near synchrony in the coastal zone causing each environment to deposit a unique sedimentary facies to test this hypothesis the stratigraphy in twelve sediment cores from a bermudian underwater cave green bay cave was investigated and temporally constrained with twenty radiocarbon dates the results indicate that we recovered the first succession spanning the entire holocene from an underwater cave 13 ka to present the sediments were characterized with x radiography fossil remains bulk organic matter organic geochemistry 13corg c n and grain size analysis four distinct facies represent the four depositional environments i vadose facies 7 7 ka calcite rafts lithofacies ii littoral facies 7 7 to 7 3 ka calcite rafts and mud lithofacies iii anchialine facies 7 3 to 1 6 ka slackwater and diamict lithofacies and iv submarine facies

taphonomic differentiation of acropora palmata facies in cores from campeche bank reefs gulf of mexico a common assumption in the geological analysis of modern reefs is that coral community zonation seen on the surface should also be found in cores from the reef interior such assumptions not only underestimate the impact of tropical storms on reef facies development but have been difficult to test because of restrictions imposed by narrow diameter cores and poor recovery that assumption is tested here using large diameter cores recovered from a range of common zones across three campeche bank reefs it is found that cores from the reef front crest flat and rubble cay zones are similar in texture and coral composition making it impossible to recognize coral assemblages that reflect the surface zonation taphonomic signatures imparted by variations in encrustation bioerosion and cementation however produce distinct facies and delineate a clear depth zonation cores from the reef front zone 2 10 m depth are characterized by sections of acropora palmata cobble gravel interspersed with sections of in place but truncated a palmata stumps upper surfaces of truncated colonies are intensely bioeroded by traces of entobia isp and gastrochaenolites isp and encrusted by mm thick crustose corallines before colony regeneration and therefore indicate punctuated growth resulting from a hurricane induced cycle of destruction and regeneration cores from the reef crest flat 0 2 m depth are also characterized by sections of hurricane derived a palmata cobble gravels as well as in place a palmata colonies in contrast to the reef front however these cobble gravels are encrusted by cm thick crusts of intergrown coralline algae low relief homotrema and vermetids bored by traces of entobia isp and trypanites isp and coated by a dense peloidal micrite cement cores from the inter to supratidal rubble cay zone 0 5 m are only composed of a palmata cobble gravels and although clasts show evidence of subtidal encrustation and bioerosion these always represent processes that occurred before deposition on the cay instead these gravels are distinguished on the basis of their limited bioerosion and marine cements which exhibit fabrics formed in the intertidal zone these results confirm that hurricanes have a major influence on facies development in campeche bank reefs instead of reflecting the surface coral zonation each facies records a distinctive depth related set of taphonomic processes which reflect colonization alteration and stabilization following the production of new substrates by hurricanes

holocene sea level record on funafuti and potential impact of global warming on central pacific atolls geomorphic features inherited from the mid holocene glacio hydro isostatic sea level highstand that affected the central pacific region influence the susceptibility of atoll islets to potentially enhanced wave erosion associated with rise in sea level from global warming shoreline morphology on multiple islets of funafuti atoll in central tuvalu reflects a relative mid holocene sea level highstand 2 2 2 4 m above modern sea level typical islets are composed of unconsolidated post mid holocene sediment resting disconformably on cemented coral rubble formed beneath now emergent mid holocene reef flats exposed remnants of the lithified islet foundations serve as resistant buttresses protecting the flanks of atoll islets from wave attack islets lacking cemented mid holocene deposits as part of their internal structure are migratory sand cays with unstable shorelines any future sea level rise 0 75 m bringing high tide above the elevation of mid holocene low tide might trigger enhanced wave erosion of stable atoll islets by overtopping the indurated mid holocene reef platforms as analogous threshold relations are inferred for other central pacific atolls the risk of future inundation of island nations cannot be evaluated solely in terms of expected sea level rise with respect to gross islet elevations

high resolution stalagmite climate record from the yucatan peninsula spanning the maya terminal classic period the decline of the classic maya civilization was complex and geographically variable and occurred over a 150 year interval known as the terminal classic period tcp c e 800 950 paleoclimate studies based on lake sediments from the yucatan peninsula lowlands suggested that drought prevailed during the tcp and was likely an important factor in the disintegration of the classic maya civilization the lacustrine evidence for decades of severe drought in the yucatan peninsula however does not readily explain the long 150 year socio political decline of the classic maya civilization here we present a new absolute dated highresolution stalagmite 18o record from the northwest yucatan peninsula that provides a much more detailed picture of climate variability during the last 1500 years direct calibration between stalagmite 18o and rainfall amount offers the first quantitative estimation of rainfall variability during the terminal classic period our results show that eight severe droughts lasting from 3 to 18 years occurred during major depopulation events of classic maya city states during these droughts rainfall was reduced by 52 to 36 the number and short duration of the dry intervals help explain why the tcp collapse of the mayan civilization occurred over 150 years

post glacial evolution of the indo pacific warm pool and el nino southern oscillation recent research has revealed new insights into the temperature size and variability of the indo pacific warm pool ipwp and the nature of the el nino southern oscillation enso since the last glacial maximum lgm sea surface temperature sst reconstructions from foraminiferal mg ca alkenone and revised coral sr ca palaeothermometry agree that ssts in the ipwp during the lgm were similar to 3degreesc cooler than at present in the central portion of the ipwf the rapid post glacial rise in sst led the deglaciation by similar to 3000 years to produce near modern ssts by the early holocene in contrast further west and north post glacial shifts in ssts in the south china and sulu seas are synchronous with abrupt climate changes in the north atlantic new evidence for the nature of the little ice age in the tropics has been obtained from a 420 year record of coral sr ca and 6180 from the great barrier reef australia this indicates that ssts and salinity were higher in the 18th century than in the 20th century the results suggest that the tropical pacific played a role as a source region of water vapour during the global expansion of little ice age glaciers the onset of modern enso periodicities is identified by palaeo enso records throughout the tropical pacific region similar to 5000 years ago with an abrupt increase in enso magnitude similar to 3000 years ago individual enso events recorded by corals reveal that the precipitation response to el nino temperature anomalies was subdued in the mid holocene the apparent non linear onset of enso in the late holocene appears to reflect abruptly enhanced interaction between the southern oscillation and the pacific intertropical convergence zone comparisons of precipitation variability recorded by great barrier reef corals with enso indices for the last 350 years confirms that non stationarity of enso teleconnections is a natural characteristic of modern climate c 2003 elsevier ltd and inqua all rights reserved

rapid flooding of the sunda shelf a late glacial sea level record the increase in sea level from the last glacial maximum has been derived from a siliciclastic system on the tectonically stable sunda shelf in southeast asia the time from 21 to 14 thousand calendar years before the present has been poorly covered in other records the record generally confirms sea level reconstructions from coral reefs the rise of sea level during meltwater pulse 1a was as much as 16 meters within 300 years 14 6 to 14 3 thousand years ago

experimental fragmentation of gastropod shells by sediment compaction implications for interpreting drilling predation intensities in the fossil record abstract compaction is one of the taphonomic processes responsible for fragmenting invertebrate shells thereby removing them from the fossil record studies of drilling predation intensities in the fossil record depend on equal preservation of drilled and undrilled shells however predatory drill holes may weaken shells and these shells may be preferentially destroyed during compaction thus overprinting predation signals in the fossil record previous studies have experimentally compacted drilled and undrilled bivalve valves such experiments have not previously been performed with gastropod shells which may respond differently to compaction to test if drilled gastropod shells are preferentially removed by compaction 227 undrilled and 28 drilled olivella biplicata shells were subjected to compaction 70 602 n within a sediment column multiple shells were tested together but were given ample space so as not to rest on one another thereby avoiding forming point contacts many drilled and undrilled shells possessed aperture damage removed apices pinhole bores and spionid worm bores which in conjunction with shell size were hypothesized to lower compactional shell strength shell strength was assessed by using the frequency of shell failure binomial logistic regression models were utilized to identify the variables controlling shell failure three models were created each using the whole o biplicata sample each model used a unique and different definition of shell strength any damage breakage and obliteration

coral reefs of the turbid inner shelf of the great barrier reef australia an environmental and geomorphic perspective on their occurrence composition and growth investigations of the geomorphic and sedimentary context in which turbid zone reefs exist both in the modern and fossil reef record can inform key ecological debates regarding species tolerances and adaptability to elevated turbidity and sedimentation furthermore these investigations can address critical geological and palaeoecological questions surrounding longer term coral sediment interactions and reef growth histories here we review current knowledge about turbid zone reefs from the inner shelf regions of the great barrier reef gbr in australia to consider these issues and to evaluate reef growth in the period prior to and post european settlement we also consider the future prospects of these reefs under reported changing water quality regimes turbid zone reefs on the gbr are relatively well known compared to those in other reef regions they occur within 20 km of the mainland coast where reef development may be influenced by continual or episodic terrigenous sediment inputs fluctuating salinities 24 36 ppt and reduced water quality through increased nutrient and pollutant delivery from urban and agricultural runoff individually and in synergy these environmental conditions are widely viewed as unfavourable for sustained and vigorous coral reef growth and thus these reefs are widely perceived as marginal compared to clear water reef systems however recent research has revealed that this view is misleading and that in fact many turbid zone reefs in this region are resilient exhibit relatively high live coral cover 30 and have distinctive community assemblages dominated by fast growing acropora montipora and or sediment tolerant species turbinaria goniopora galaxea porites palaeoecological reconstructions based on the analysis of reef cores show that community assemblages are relatively stable at millennial timescales and that many reefs are actively accreting average 2 7 mm year where accommodation space is available despite recent anthropogenic pressures these turbid zone reefs challenge traditional views on the environmental conditions required for active reef growth but given their proximity to land and associated stresses current knowledge on these less well understood reefs should be synthesised to aid coastal management directives terrigenous sediments are a dominant influence on turbid zone reef occurrence composition and growth and therefore the assessment of their future prospects will require a detailed understanding of the sedimentary regimes under which they occur and of their differential response modes

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

diagenesis and sea level change lessons from moruroa french polynesia an inclined borehole through the margin of moruroa atoll french polynesia in which the ages of units are constrained by radiometric dates provides a unique opportunity to examine the relationship between sea level change and diagenetic history the oldest rocks encountered are dated at 355 840 yr bp and the overlying succession records five cycles of deposition and emergence culminating in the deposition of the holocene sequence successive intervals of emergence provided the driving force for diagenetic change promoting the through flow of chemically aggressive fresh waters that were at times either pervasive or confined within relatively isolated pathways on a millimetre to metre scale these locally varying flows and flow rates defined restricted zones characterized by differences in water chemistry and diagenetic signatures in contrast to some sequences elsewhere the upper part of the moruroa atoll succession is typified by alternations of intervals in which either several generations of cement growth are represented or only one or two cements are present three distinct diagenetic signatures can be recognized as follows i fresh water phreatic zones are reflected in neomorphism and the deposition of cements that occluded porosity thus preventing the deposition of later cements and conferring relative stability ii vadose zones are characterized by more complex diagenetic sequences reflecting multiple phases of dissolution and cement growth attesting to the relative duration of exposure and the conditions of ground water flow and iii deep in the core sequences reflect lowstand deposits that suffered sub sea diagenesis generating pores in which multi layered marine cements apparently formed at more frequent intervals than those subject to subaerial processes all cements appear to be of narrowly constrained ages these results highlight the contentious issue of whether the distributions of former diagenetic environments can be related to specific sea level stands and erosion surfaces it seems that in the moruroa core some cycles of sea level change are reflected in distinctive packages of diagenetic features that have not been overprinted by cement growths during later sea level stands

climate correlations between greenland and antarctica during the past 100 000 years the ice cores recovered from central greenland by the grip1 2 and gisp23 projects record 22 interstadial warm events during the part of the last glaciation spanning 20 105 kyr before present the ice core from vostok east antarctica records nine interstadials during this period4 5 here we explore links between greenland and antarctic climate during the last glaciation using a high resolution chronology derived by correlating oxygen isotope data for trapped o2 in the gisp2 and vostok cores we find that interstadials occurred in east antarctica whenever those in greenland lasted longer than 2 000 years our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between greenland and antarctica ice older than 115 kyr in the gisp2 core shows rapid variations in the 18o of o2 that have no counterpart in the vostok record the age depth relationship and thus the climate record in this part of the gisp2 core appears to be significantly disturbed

sequential evolution and diagenesis of pleistocene coral reefs south sinai egypt abstract the uplifted pleistocene coral reefs in south sinai represent two major depositional sequences they generally form two morphological terraces which locally are tilted and offset by still active faulting the major reef sequences are composed of several small scale sequences corals grew rapidly when accommodation space was created by eustatic sea level rise or fault block subsidence as the accommodation decreased coral rubble and siliciclastic sands prograded over reefal and lagoonal sediments thus creating a shallowing upward sequence terrigenous input was further stimulated by a more humid climate during interglacial times 230 th 234 u dating places the older reef cycle between 350 000 and 270 000 years b p which corresponds to the interglacial period of isotope stage 9 the younger reef cycle has been dated between 140 000 and 60 000 years b p isotope stage 5 an intermediate relic sequence found in only one outcrop can be attributed to isotope stage 7 correlation of the small scale sequences is difficult age dating is not precise enough and local tectonic activity in many cases overruled the smaller eustatic fluctuations the younger reef sequence commonly exhibits marine cements whereas the older sequence was exposed to freshwater dissolution and cementation an important feature is the locally pervasive dolomitization especially of the older reef oxygen and carbon isotope values suggest that the dolomite formed in a seawater dominated mixing zone multiple phases of dissolution cementation and dolomitization point to a very complex diagenetic history

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

holocene sea level changes in french polynesia abstract new data on holocene sea levels have been obtained in 28 atolls and 10 high islands in the society tuamotu gambier and austral islands in an area of the south pacific as wide as western europe sea level indicators are often very accurate 0 1 m and include exposed corals abandoned algal ridges and reef frameworks in growth position emerged tidal notches and skeletal reef conglomerates in which the position of the former low water level at the time of cementation has been determined by petrological analysis over 110 new samples have been dated by radiocarbon the overall pattern is that of a msl standstill at 0 8 1 0 m between 5000 and 1250 yr b p a set of radiocarbon dated samples covering the period 4500 1250 yr b p almost continuously is evidence that lasting msl drops could not ever have occurred below 0 7 m throughout this time the highest sea level peak about 1 0 m seems to have been reached between 2000 and 1500 yr b p since 1500 yr b p msl has been dropping gradually from about 1 0 m to the present position which has been reached only recently some islands show however a slightly different pattern the holocene emergence is smaller than average in moorea and tahiti and larger in rurutu makatea anaa and possibly hereheretue some data suggest also the possibility of a slight increase in the holocene emergence towards the south possible geodynamic isostatic oceanic and climatic causes of the sea level variations observed are discussed

geochemistry based coral palaeoclimate studies and the potential of non traditional non massive porites corals recent developments and future progression understanding the natural variability of the earth s climate system and accurately identifying potential anthropogenic influences requires long term geographically distributed records of key climate indicators such as temperature and precipitation that extend prior to the last 400 years of the holocene reef corals provide an excellent source of high resolution climate records and importantly represent the tropical marine environment where palaeoclimate data are urgently required recent decades have seen significant improvement in our understanding of coral biomineralisation the associated uptake of geochemical proxies and methods of identifying and understanding the effects of both early and late post depositional diagenetic alteration these processes all have significant implications for interpreting geochemical proxies relevant to palaeoclimatic reconstructions this paper reviews the current state of the art in terms of coral based palaeoclimate reconstructions and highlights a key remaining problem the majority of coral based palaeoclimate research has been derived from massive colonies of porites however massive porites are not globally abundant and may not provide material of a particular age of interest in those regions where they are present therefore there is great potential for alternate coral genera to act as complimentary climate archives while it remains critical to consider five key factors vital effects differential growth morphologies geochemical heterogeneity in the skeletal ultrastructure transfer equation selection and diagenetic screening of skeletal material in order to allow the highest level of accuracy in coral palaeoclimate reconstructions it is also important to develop alternate taxa for palaeoclimate studies in regions where porites colonies are absent or rare currently as many as nine genera other than porites have proven at least limited utility in palaeothermometry most of which are found in the atlantic caribbean region where massive porites do not exist even branching taxa such as acropora have significant potential to preserve environmental archives increasing this capability will greatly expand the number of potential geochemical archives available for longer term temporal records of palaeoclimate

holocene development of the belize barrier reef previously knowledge of the holocene development of the belize barrier reef bbr the largest reef system in the atlantic ocean was limited to one location carrie bow cay we present new data from 11 rotary drill cores taken at 9 locations and 36 radiometric ages that indicate that the bbr was established from 8 26 to 6 68 ky bp on pleistocene reef limestones presumably deposited during oxygen isotope stage 5 the nonsynchronous start of holocene reef growth was a consequence of variation in elevation of antecedent topography largely controlled by underlying nne trending structures from north to south pleistocene elevation decreases along these structural trends probably reflecting differential subsidence and variations in karst topography reef anatomy is characterized by three facies in order of decreasing abundance these facies are represented by corals mainly acropora palmata and members of the montastraea annularis group by unconsolidated sand and rubble and by well cemented coral grainstones rudstones holocene reef accumulation rates average 3 25 m ky the degree of reef consolidation is negatively correlated with holocene thicknesses indicating that slowly growing reefs are better cemented than fast growing ones we present a holocene sea level curve for belize based on 36 dates from this study and 33 dates from our previous studies in the area

the flickering switch of late pleistocene climate change polar ice contains a unique record of past climate variations previous greenland ice cores have documented relatively warm interstadial periods during the last glaciation and short centuryscale returns to colder conditions during the glacial to interglacial warming see for example ref 1 these climate features have also been observed to varying degrees in ocean sediment cores2 4 and terrestrial pollen and insect records5 7 here we report electrical conductivity measurements from a new greenland ice core which confirm these previous observations and also reveal a hitherto unrecognized mode of rapid climate variation fluctuations in ice conductivity on the scales of 5 20 years reflect rapid oscillations in the dust content of the atmosphere this flickering between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation

bathymetric zonation of modern microborers in dead coral substrates from new caledonia implications for paleodepth reconstructions in holocene corals abstract microboring endoliths were studied in dead modern corals collected at various depths and in growth position on la surprise atoll in new caledonia eight taxa of microborers were regularly observed three cyanobacteria hyella caespitosa mastigocoleus testarum and plectonema terebrans two chlorophytes ostreobium quekettii and phaeophila dendroides and three fungal forms dodgella priscus and two unidentified fungi the relative abundance of each taxon was determined in the modern corals throughout the studied sampling interval from 0 down to 40 m water depth this allowed us to propose for the first time a bathymetric model based on microendolith assemblages colonizing in situ hard substrates of corals in this model the occurrence of the cyanobacteria hyella and mastigocoleus indicates a bathymetric range from 0 down to a water depth of 3 and 6 m respectively the chlorophyta o quekettii associated with the cyanobacterium p terebrans and fungi is dominant from 10 to 40 m depth which is the lower limit of our sampling the distribution ranges of individual taxa observed in the dead coral substrates from new caledonia are much narrower than those reported in the literature for other substrates the bathymetric model based on distribution of microborers in modern corals was then applied to interpret the trace assemblages of microborers observed in holocene corals collected by drilling on two reef sites of new caledonia la surprise islet in the vicinity of the sampling sites of the modern corals and the barrier reef of bayes on the ne coast of grande terre the paleodepth interpretations performed at various levels along the cores allow identification of several shallowing upward sequences during the last 7000 years of reef growth in new caledonia differences in the thickness of these sequences between la surprise and bayes sites were interpreted as differences in the space available for accommodation between the two sites in turn related to the differential subsidence that affected new caledonia during holocene times the use of the microendolith trace assemblages in paleodepth reconstructions of holocene reefs from new caledonia allowed detection of relative sea level variations finer than those deduced from changes in coralgal assemblages

reef response to sea level and environmental changes during the last deglaciation integrated ocean drilling program expedition 310 tahiti sea level the last deglaciation is characterized by a rapid sea level rise and coeval abrupt environmental changes the barbados coral reef record suggests that this period has been punctuated by two brief intervals of accelerated melting meltwater pulses mwp occurring at 14 08 13 61 ka and 11 4 11 1 ka calendar years before present that are superimposed on a smooth and continuous rise of sea level although their timing magnitude and even existence have been debated those catastrophic sea level rises are thought to have induced distinct reef drowning events the reef response to sea level and environmental changes during the last deglacial sea level rise at tahiti is reconstructed based on a chronological sedimentological and paleobiological study of cores drilled through the relict reef features on the modern forereef slopes during the integrated ocean drilling program expedition 310 complemented by results on previous cores drilled through the papeete reef reefs accreted continuously between 16 and 10 ka mostly through aggradational processes at growth rates averaging 10 mm yr 1 no cessation of reef growth even temporary has been evidenced during this period at tahiti changes in the composition of coralgal assemblages coincide with abrupt variations in reef growth rates and characterize the response of the upward growing reef pile to nonmonotonous sea level rise and coeval environmental changes the sea level jump during mwp 1a 16 2 m of magnitude in 350 yr induced the retrogradation of shallow water coral assemblages gradual deepening and incipient reef drowning the tahiti reef record does not support the occurrence of an abrupt reef drowning event coinciding with a sea level pulse of 15 m and implies an apparent rise of 40 mm yr 1 during the time interval corresponding to mwp 1b at barbados

successive reef depositional events along the marquesas foreslopes french polynesia since 26 ka abstract bathymetric surveys of submarine platforms and terraces of the tropical marquesas archipelago french polynesia coupled with sedimentological and paleoecological analyses and radiometric dating of dredged rocks reveal the occurrence of several distinct intervals of reef deposition during the last deglacial sea level rise i e the last 26 000 yr or 26 ky five facies related to reef shallow water and deeper depositional zones have been identified on the basis of their respective biological assemblages facies 1 2 and 3 consist of in situ scleractinian corals mainly porites associated with thick crusts of coralline algae species hydrolithon onkodes h reinboldii lithophyllum pustulatum group and widespread vermetids and victoriellinid foraminifers these assemblages are typical of high energy shallow water reef settings i e upper forereef reef crest and outer reef flat and inner reef flat respectively facies 4 is characterized by the prevalence of halimeda plates mixed with debris of amphiroa and amphistegina spp these algae generally inhabit the inner parts of the reef flat and backreef zones but also the relatively protected deeper parts of outer reef slopes facies 5 is composed of large broken mollusc shells oysters embedded in fine grained sediments with significant numbers of deep living coralline algae mesophyllum sp and planktonic foraminifers locally mollusc shells are covered with microbialite crusts the replacement of shallower assemblages by deeper ones is interpreted as an upward deepening sequence identification of morphological and biological features combined with coral dating provide evidence of 4 reef generations rg between 26 and 9 ka now ranging from 138 to 58 m in depth 1 rg 0 from 26 to 19 ka in the 125 115 m depth interval 2 rg 1 from 18 to 15 ka between 110 and 95 m 3 rg 2 from 14 to 11 5 ka between 80 and 68 m and 4 rg 3 younger than 11 5 ka at around 55 to 60 m the first three units exhibit clear zonation from upper reef slope to reef flat their development was probably interrupted by abrupt rises in sea level and or drastic climate changes such a scenario is similar to observations reported in barbados and hawai i where rapid rises in sea level interpreted as reflecting major melting events of continental ice caused the drowning of reefs the younger unit refers to coral banks similar to those in modern marquesas environments the replacement of typical coral reefs by coral banks may reflect an increase el nino southern oscillation enso frequency and intensity inimical to reef development in the last 12 ka

coral reef records of quaternary changes in climate and sea level abstract although coral reefs have long been regarded as documenting climate change largely through its effects on sea level the temporal continuity and sensitivity to disturbance of their records appears to fall short of those provided by ice cores deep sea sediments and similar proxies the reasons for this anomaly relate principally to shifts in the loci of deposition the temporal windows in which accretion has been able to occur in a given place reflecting sea level at a particular height relative to the present datum are severely constrained where it has been possible coral growth and reef accretion have been and are sensitive to the signals provided by the environment in the form of changes in water depth temperature salinity nutrient supply turbidity and ph acidity concomitant with changes in sea level itself changes in these environmental parameters are directly or indirectly controlled by climate however because the responses of corals to stimuli are commonly site specific and the nature of the changes evoked so disparate it is likely that only major sea level cycles will provide evidence of a consistent global response in what has been a segmented record

accretion patterns in holocene tropical coral reefs do massive coral reefs in deeper water with slowly growing corals accrete faster than shallower branched coral reefs with rapidly growing corals it is a widely held concept that tropical coral reefs in shallower water with branched acroporid corals should accrete faster than those in deeper water dominated by massive corals results from a study of holocene development of the largest atlantic reef system including paleo waterdepth data challenge these concepts in belize barrier and atoll reefs reef accretion rates range from 0 46 to 7 50 m kyr and average 3 03 m kyr as measured along 33 dated reef sections interestingly accretion rates increase with increasing paleo waterdepth and sections dominated by massive corals accumulated even slightly faster than those with branched acroporids published data from some other reef locations reveal no significant trends when plotting reef accretion rate versus paleo waterdepth also indicating that the above mentioned concepts should be questioned massive corals apparently are more resistant and accrete in lower disturbance conditions in slightly deeper water 5 10 m and higher accomodation space available for sediment deposition as compared to shallow water 0 5 m branched acroporids which repeatedly get broken and leveled out during tropical cyclones

a new coral reef province in the gulf of carpentaria australia colonisation growth and submergence during the early holocene abstract multibeam sonar mapping drill cores and underwater video data have confirmed the existence of a previously unknown coral reef province in the gulf of carpentaria australia seven reefs comprised of coral limestone that support living corals have been mapped so far and as many as 50 other reefs may exist in the region u th ages show that reef growth commenced shortly after limestone pedestals were submerged by rising sea level around 10 5 kyr bp making them the oldest holocene reefs known in australia reef growth persisted for 2 0 kyr but it had ceased at most locations by 7 0 kyr bp measurements of reef growth rates 0 95 to 4 m kyr 1 indicate that the reefs were unable to keep pace with contemporaneous rapid sea level rise 10 m kyr 1 which is consistent with a give up reef growth history core samples from reef platforms demonstrate that pleistocene limestone is exposed at depths of 27 and 30 m below present mean sea level these depths represent regionally significant phases of reef growth during a prolonged sea level still stand we conclude that the reefs are therefore mostly relict features whose major phase of growth and development relates to an earlier pre holocene sea level still stand

hurricane induced sediment transport in open shelf tropical systems an example from st croix u s virgin islands hurricane hugo passed directly over st croix on 17 september 1989 sustained winds in excess of 110 knots gusts to 165 knots and waves 6 7 m in height accompanied the storm along the north coast wave height was lower ca 3 4 m due to the leeward position of the shelf in the deeper reefs at cane bay and salt river damage was confined primarily to the soft bodied benthic community e g sponges gorgonians coral damage was much less severe largely because of the buffering effects of the water column the greatest change observed after the storm was wholesale flushing of sand from shelf edge areas in salt river submarine canyon a minimum of 2 million kg of sediment were flushed into deeper water the transport rate associated with the storm was eleven orders of magnitude above that measured during fair weather and the volume of sediment that was removed from the canyon equalled roughly a century of normal sediment accumulation at cane bay 336 000 kg of sediment were flushed from a single channel with similar amounts removed from adjacent breaks in the shelf edge reef a current meter in salt river submarine canyon provided information on the timing and intensity of the oceanographic processes related to hurricane hugo as the storm approached waves piled water against the shoreface and in salt river bay as the storm passed over st croix the change in wind direction followed by a decrease in wave height triggered a release of water trapped in the bay and along the adjacent shoreline by waves earlier in the storm for a period of 4 6 hours net down canyon currents reaching 2 m s and oscillatory flows up to 4 m s occurred along the base of the western canyon wall removing up to 2 m of sand similar events were likely responsible for the wholesale removal of sand in eastern cane bay the paradoxical concurrence of wholesale sediment transport and low level reef damage is related to the protection from waves but not wind afforded by the north coast of st croix facing away from the direction of storm approach these observations and measurements provide our first opportunity to relate sediment export in such a high energy event to the physical processes that were responsible calculations based on post hugo measurements are in agreement with an earlier sediment budget for salt river canyon sediment export in cane bay exceeded the volume similarly predicted because such events are probably common on all exposed carbonate shelf margins storms like hurricane hugo are among the most important factors in the cycling of sediment through exposed open marine environments both now and in the geologic past the patterns of reef damage and sediment transport are much more complicated than previously envisioned and more thoughtful consideration of their variability and the processes responsible is essential to an understanding of the signature that will be left by major storms

use of in situ produced 10be in carbonate rich environments a first attempt we have determined the production rate of in situ produced 10be in calcite through measurements of 10be and 36cl concentrations in the same calcite samples and of 10be concentrations in depth profiles of flint from the same erosional surface this yields a 10be production rate in calcite of 37 9 6 0 at g yr at sea level and high latitude approximately sixfold higher than production in the coexisting flint we propose that this higher rate of production may be due to high production cross sections for c spallation by cosmic rays with energies below 50 mev these results also open the possibility of dating burial events in carbonate rich environments by differential radioactive decay of 10be and 36cl

event preservation in lagoonal reef systems paleontological data suggest that coral populations in the caribbean were consistently healthy for the past 2 3 k y beginning in the 1980s however disease outbreaks bleaching episodes hurricanes and other perturbations caused catastrophic coral mortality and regional turnover an alternative hypothesis based on historical sources posits that coral populations were already declining more than a century ago these hypotheses can be distinguished only if turnover events are reliably preserved in the holocene record of coral reefs push cores extracted from uncemented lagoonal reefs in belize showed that a direct hit by hurricane iris in 2001 did not disrupt the signature of the recent turnover event which entered the subfossil record essentially intact cores from lagoonal systems in several areas of the caribbean do not support the hypothesis that corals declined before the 1980s

response of reef coral communities to sea level rise a holocene model from mauritius western indian ocean the fringing reef at pointe au sable mauritius indian ocean was used to examine the effects of holocene sea level rise on coral growth this reef is about 1000 m wide and comprises a forereef slope 30 m maximum depth a narrow reef crest and a very shallow backreef 1 5 m maximum depth four major coral communities were recognized which developed within relatively narrow depth ranges a pachyseris oulophyllia community deeper than 20 m an acropora tabulate faviid community 20 6 m a robust branching acropora community less than 6 m and a pavona community less than 10m three high recovery cores show the holocene reef sequence is a maximum of 19 3 m thick and comprises four coral biofacies which are similar to counterparts identified in modern communities robust branching tabular branching robust branching domal and foliaceous coral facies a minimum sea level curve for the past 7500 years was constructed using distribution patterns of coral biofacies and radiocarbon dates from corals reconstruction of reef growth history indicates that both offshore and onshore reef zones were developing coevally aggrading at rates of 4 3 mm year 1 from 6900 years b p the reef caught up with sea level only after sea level stabilized changes in coral community and reef growth rates were driven principally by increasing water agitation due to the decrease in accommodation space based on the composition of the successive coral assemblages the reef appears to have grown through successive equilibrium stages

sea level changes and δ18o record for the past 34 000 yr from mayotte reef indian ocean new sea level and 18o curves for the past 34 000 yr based on uranium thorium chronology are proposed for the southwestern part of the indian ocean the archives include cores drilled from onshore coral reefs and submersed samples from foreslope corals of mayotte in the comoro islands the mayotte sea level curve shows a lowstand of 145 5 m below the present level during the last glacial maximum dated at 18 400 yr this lowstand is supported by the maximum18o enrichment in the coral colonies the residual signal 18o controlled by sea surface temperature changes indicates that surface waters 18 400 yr ago were approximately 5 c cooler than present the deglacial sea level rise is clearly recorded with a mean rate of about 1 7 cm yr 1between 18 400 and 10 000 yr ago the deglaciation phase is characterized by a strong18o depletion marked by two pulses related to meltwater discharges into the north atlantic ocean but also characterized by responses specific to the tropical indian ocean

holocene sea level change and hydro isostasy along the west coast of kyushu japan abstract mid to late holocene sea level variations have been obtained at sites along the west coast of kyushu japan sea level observations for this relatively stable area are very important for evaluating the crustal tilting associated with the hydro isostatic adjustment due to the last deglaciation and for examining the cause of underwater jomon sites submerged archeological sites during the jomon period of mid holocene typically observed in this region for these purposes we conducted systematic boring samplings at sites from goto island to tamana along the latitude of about 33 n then we performed diatom assemblage and pyrite sulfur analyses of these sediment samples and 14 c datings for intertidal shells in order to get the sea level variations for these sites observations at tsumizu faced to oomura bay with tidal range of 0 9 m show a sea level high stand of 1 m at about 5500 yr b p years before present followed by smoothly falling to the present level evidences for sea level oscillation of greater than 50 cm have not been found here relative sea levels at about 5000 yr b p are however 2 m at goto island 125 km west of tsumizu and 2 m at tamana 50 km east of tsumizu thus observations at sites along the traverse from goto island to tamana are indicative of crustal tilting of about 3 4 m for the distance of 175 km which seems to be consistent with the prediction caused by the hydro isostatic adjustment

seismic stratigraphy and development of the shelf edge reefs of the great barrier reef australia extensive shelf edge reefs sers and terraces are common along the seaward margin of the great barrier reef gbr we aim to better understand the architecture of the sers deposited during a poorly constrained period the last glacial maximum lgm and early postglacial a dense array of topas seismic lines was interpreted at hydrographers passage in the southern central gbr following a seismic stratigraphic approach ground truthed against integrated ocean drilling program expedition 325 iodp exp 325 sediment core data we interpreted two prominent sub bottom reflectors an upper r1 and a lower r2 that separate three seismic units according to our borehole to seismic correlation in a representative location r1 corresponds to a downward increase of impedance which is also reflected in lithological and diagenetical changes r2 is poorly constrained but likely also represents a lithological contrast seismic velocities were also estimated in the same borehole location for inter reef deposits and reef framework together with the geomorphic interpretation we reconstructed velocity maps for the study area leading to the generation of a 3d geomorphic model of the antecedent topography or substrate and volumetric calculations geomorphic and thickness trends suggest a strong relationship between the antecedent topography and the morphology of the sers the distribution of seismic facies identified in the dataset coupled to geomorphic trends and published sea level curves allowed us to reconstruct the lgm to postglacial depositional history of these deposits our interpretation suggests significant regressive reefal accumulations formed on top of a marine flooding surface represented by reflector r2 during the sea level fall to the lgm r1 is the distal equivalent of an unconformity previously identified in the gbr inner and mid shelf widely affected by subaerial exposure on top of which a postglacial transgressive mainly reefal unit 1 was deposited two zones are distinguished 1 a distal zone below 80 mbsl with thick deposits displaying fringing reef morphologies influenced by the late lgm fall and subsequent early postglacial rise in sea level and by the updip availability of substrate and 2 a proximal zone above 80 mbsl of enhanced vertical growth with unfilled lagoons resulting from the lack of lateral substrate and the rapid sea level rise our seismic stratigraphic model of the development of the sers sediment volumetrics and 3d reconstruction of the antecedent topography provides a foundation for future forward modeling stratigraphic studies

geomorphology of submerged reefs on the shelf edge of the great barrier reef the influence of oscillating pleistocene sea levels the submerged reefs on continental margins and surrounding oceanic islands are important archives of past climates eustatic sea level oscillations and oceanographic processes australia s north eastern submerged shelf edge reefs have previously been explored but all studies have been limited by either low resolution single beam profiles or by their limited spatial extent the aim of this study is to improve the understanding of the origin and development of submerged shelf edge reefs terraces and related features on the great barrier reef gbr and the influence of pleistocene sea level oscillations on their distribution and geomorphology we investigated the first large scale 1400 km2 3d bathymetry and acoustic backscatter dataset of four widely spaced sites located across ca 650 km along the shelf edge at ribbon reefs 1 5 noggin pass viper reef and hydrographers passage we provide a comprehensive description and systematic classification of the shelf edge features and constrain their spatial distribution and geomorphologic variability using a wide range of quantitative morphometrics fifteen features are defined four of which are the focus of this study including terraces pinnacles ridges and channels using modern reefs within the gbr for comparison we interpret these as fringing reefs patch and barrier reefs and tidal channels respectively the influence of gross shelf geomorphology and oceanographic factors driving the observed variability within and between sites is discussed in conjunction with mid late pleistocene sea level oscillations we observed two distinct types of reef growth characterised by the degree of development which we interpret as analogous to juvenile and mature modern reefs of the gbr juvenile reefs are very common and occur within each site at depths of less than 50 m to greater than 100 m they are defined as discontinuous peaked barrier reefs peaked patch reefs and fringing reefs mature reefs are less common and develop exclusively at a depth range of ca 50 70 m these reefs are defined as flat topped continuous barrier and double barrier reefs through a comparison with published mid late pleistocene sea level oscillations we note that the depth range of mature reefs is consistent with the depth of repeated low amplitude 20 m eustatic sea level oscillations and independent of the relative time spent at sea level we conclude that repeated low amplitude sea level rises provide the much needed accommodation space for vertical accretion that is not provided during stillstands without inducing reef drowning which can be caused by high amplitude sea level rise low amplitude sea level falls are also less detrimental than high amplitude falls in terms of habitat compression together the effects of enhanced reef accretion and limited habitat compression at depths of 50 70 m have lead to a concentrated net gain in vertical relief that is not observed elsewhere on the shelf edge

reef talus a popular misconception reef fronts have traditionally been regarded as comprising debris derived by contemporaneous erosion of the reef however evidence from wave transport indicates that on present day reefs the bulk of the debris generated in this way accumulates in the back reef area with only finer grained sediment carried off reef by retreating flows or by overwash nevertheless in contrast to this observation fore reef debris slopes are commonly considered characteristic of phanerozoic reefs this apparent error reflects the conflation of processes defining contemporary growth and accretion of the reef and the corresponding long term accretion of the carbonate platform on which it rests present day reefs are commonly although not exclusively additions to long lived carbonate platforms growth of the latter is intermittent and has been moderated by changes in sea level that for recent reefs have been on time scales of less than 100 ka during low sea level stands growth ceases or is translated downslope and earlier deposits are subject to lithification and subaerial erosion similar changes are applied on a larger scale to the aggrading growth of carbonate platforms but the bulk accretion of these includes quite different processes and reflects far longer timescales during low sea level stands the margins of platforms commonly become unstable with instability reflected in slope failure and in the shedding of blocks ranging from metres to kilometres in diameter associated with the generation of debris flows and turbidites it is argued that these are the materials that are commonly described as reef talus in ancient structures although their formation is largely independent of any contemporary reef growth difficulties arise where the reef and the platform are treated as a single functional entity it is important to recognize the conceptual distinction between them reef talus is a misleading description of the debris predominantly generated by platform erosion and slope failure

sea level changes in the holocene over the last 30 years the emphasis in studies of the recovery from low last glaciation sea levels has changed significantly the search for a eustatic sea level curve having global relevance has ended studies into the rheology of the earth s crust and recognition that the geoid has not remained stable over time have resulted in the recognition that there must have been regional differences in eustatic response to deglaciation as a part of this re appraisal there has been a growing appreciation that crustal isostatic response to the removal of the weight of ice sheets has been accompanied by a consequential hydro isostatic response particularly in the areas of the shelf seas in the later part of the post war period attention has additionally been focussed on the much greater potential for error over the whole field of palaeoenvironmental reconstruction in the holocene including not only errors in dating but also a large number of possible sources of errors in heighting as a result of this an increasing number of scientists are withholding judgement on the nature of sea level rise and more particularly on the problem of higher than present late holocene eustatic sea levels the problems outstanding in the early 1960s have not yet been resolved but the bases of uncertainty have changed

microatoll record for large century scale sea level fluctuations in the mid holocene coral microatolls have been long used as precise indicators of past sea level but their use for precise definition of detailed sea level fluctuations is still rare here we report twelve high precision thermal ionization mass spectrometric th 230 ages for twelve rims of five mid holocene microatolls from all emerged reef terrace at leizhou peninsula northern south china sea this is a tectonically stable area enabling lis to reconstruct both the timing and trajectory of local sea level fluctuations accurately the elevations of these microatoll rims and cores were accurately determined relative to the surface of modern livin microatolls at the same site the results indicate that the sea level during the period of 7050 6600 yr bp years before ad 1950 was about 171 to 219 cm above the present with at least four cycles of fluctuations over this 450 yr interval sea level fluctuated by 20 40 cm on century scales crown copyright c 2009 published by university of washington all rights reserved

quaternary atoll development new insights from the two dimensional stratigraphic forward modelling of mururoa island central pacific ocean knowledge about the quaternary evolution of mid ocean atolls comes mainly from drilling and field observations carried out on a number of pacific carbonate islands however little is known about the early to mid pleistocene atoll development history especially at margin and foreslope settings using previous field and subsurface data from mururoa atoll and a process based modelling software dionisos a two dimensional forward stratigraphic model of atoll development is proposed for the past 1 8 million years myr observational data from vertical to inclined coring seismic and bathymetric surveys indicate that from approximately 0 45 to 0 40 million years before present ma carbonate deposition at mururoa atoll resulted in a series of mostly prograding reef units the model is first constrained at the base by the shape and topography of the pre quaternary basement a number of sensitivity tests were performed to define the respective influence of variant parameters the best fit development scenario that accounts for the overall geometry and stratigraphic architecture of the quaternary sediment packages is obtained by using the sea level curve by miller et al 2005 uniform subsidence rate of 105 m myr 1 and carbonate production rates gradually increasing from 0 50 to 8 mm yr 1 between 1 80 ma and the present additional controlling parameters include subaerial erosion at a constant rate of 0 25 m kyr wave energy and sediment transport processes the stratigraphic forward model predicts a succession of three distinct types of carbonate systems that have developed since the earliest pleistocene toe of slope systems from 1 80 ma to about 0 80 ma open platform systems from 0 80 ma to 0 50 ma and framework reef systems from about 0 50 ma to the present the development of these different systems is most likely to be controlled by climate and changes in sea level cycles during the low amplitude 41 kyr cycle periods of the earliest pleistocene ambient conditions were not conducive to framework reef growth shallow water carbonate sedimentation was dominantly gravity driven operating along the platform foreslopes only during the mid pleistocene climate transition narrow open platform units have developed at the upper parts of the pre quaternary basement flanks with the onset of the high amplitude 100 kyr sea level modes and climate restoration reef frameworks started to be generated these models from mururoa agree with a number of previous studies suggesting that most of the true framework reefs were not initiated prior to 0 50 ma mururoa atoll is demonstrated to be a robust analogue for providing more realistic interpretations of the development history of pacific atolls further modelling with three dimensional dionisos could generate better predictions by taking into account hydrodynamic and transport parameters more accurately

coralgal composition of drowned carbonate platforms in the huon gulf papua new guinea implications for lowstand reef development and drowning abstract collision between the south bismarck plate and the northern edge of the australian plate has produced an actively subsiding foreland basin in the western huon gulf a series of drowned carbonate platforms and pinnacles are preserved on this margin due to a combination of this rapid subsidence and eustatic sea level changes over the last 450 ka we analyzed sedimentary and coralgal data from the platforms to better understand lowstand reef development and drowning in the huon gulf the recovered limestones are divided into five main sedimentary facies coral reef coralline foraminiferal nodule coralline foraminiferal crust halimeda and planktonic foraminiferal limestones based on a comparison with modern analogues in the indo pacific and elsewhere we identified coral reef deep fore reef slope deeper fore reef slope and pelagic hemipelagic paleoenvironmental settings an analysis of facies relationships and their paleoenvironmental meanings revealed lowstand corals reefs preserved at the top of the platforms that grew within 10 m of sea level two different coral assemblages were identified within this facies 1 a shallow high energy reef community characteristic of windward margins and limited to the deep platforms 1947 2121 2393 m and 2 another shallow community but indicative of more moderate lower energy reef conditions and limited to the middle 1113 1217 1612 m and shallow platforms 823 m the change from high to lower energy reef growth conditions suggests that oceanographic climatic conditions in the huon gulf have changed substantially through time primarily through the closure of the gulf as a result of tectonic rotation and uplift of the huon peninsula over the last 450 ka despite major environmental perturbations i e relative sea level and temperature changes the platforms and the shallow water coral reefs exposed at the top have been able to re establish themselves time and time again over the last 450 ka we also identified two different incipient drowning scenarios influenced by the rate of relative sea level rise more rapid drowning in the middle and deep platforms produced a thin veneer of coralline foraminiferal nodule and halimeda limestones over the shallow coral reef material while the slower drowning experienced by the shallowest platforms allowed thick coralline foraminiferal crust limestones to develop we recognize three main stages of platform development 1 initiation and growth characterized by shallow coral reef growth as the platforms grew close to sea level during the lowstands 2 incipient drowning marked by a shift to coralline foraminiferal nodule crust and halimeda limestones as the platforms began to drown during rapid eustatic sea level rise and continued subsidence and 3 the complete drowning of the platforms characterized by platform turn off increased bioerosion fe mn precipitation and pelagic hemipelagic sedimentation as the platform surfaces finally drop below the photic zone

high sea surface temperatures in tropical warm pools during the pliocene sea surface temperatures in the tropical oceans were thought to have remained stable during a period of warmth about five million years ago reconstructions of the sea surface temperature from the caribbean and pacific suggest that tropical temperatures have in fact changed in concert with global mean temperatures over the past five million years

wave set up on coral reefs 2 set up on reefs with various profiles abstract all available laboratory data for wave set up on two dimensional reef profiles of various shapes have been compared with data from an idealised horizontal reef with a steep reef face gourlay 1996 the data is generally well represented by a relationship between the relative set up parameter gh r t o and the submergence parameter g h r h r h o and the relative set up on reef profiles of natural form is found to be less than that observed on the idealised horizontal reef the important influences of reef rim slope and variable water depths on the reef top have been investigated and some methods for allowing for them are suggested comparison of data for irregular waves with that for regular waves has led to the development of a simple method for estimating the effects of wave groups upon the magnitude of the steady state mean wave set up gh r the results of the analyses are applied to the determination of wave set up and its effects at three specific coral reef sites

high precision u th dating of storm transported coral blocks on frankland islands northern great barrier reef australia abstract high energy storm transported coral blocks are widespread on the reef flats of the great barrier reef gbr australia and have the potential to be used as proxies for reconstructing past storm cyclone events prior to historical or instrumental records in this study samples from 42 individual transported coral blocks were collected from the inshore frankland islands northern gbr for high precision mc icpms u th dating with their surface mortality ages recording the timing of individual storms or cyclones responsible for their uplift from their original growth position the dated mortality ages were found to match well with known historical storm cyclone events in the last century with 80 of them falling within episodes of increased storm activity 1910 1915 1945 1950 1955 1960 1975 1990 1995 2000 ad captured by instrumental historic records confirming that transported coral blocks on inshore reefs can be used as proxies for past storm cyclone occurrences using this approach this study also identified 17 additional storm cyclone events that occurred before european settlement in the 1850s including three oldest events at 758 4 3 7 777 9 4 9 and 985 2 4 8 ad respectively our results despite still preliminary suggest that the storm cyclone activity in this region tends to broadly correlate with the positive modes of the pacific decadal oscillation pdo during the last millennium in addition there appears to be a decreasing age trend from the shore to the reef edge from 758 4 3 7 ad to 1988 3 1 6 ad which can be attributed to sea level fall and or reef island progradation over the last 2000 years

the age of water and ventilation timescales in a global ocean model abstract the age of water in the world ocean is studied using a passive age tracer introduced into a global ocean model additional information is derived from a transient dye tracer that tracks the time dependent spreading of surface waters into the model ocean interior of particular interest is the nature of ocean ventilation over the 10 100 yr timescale as well as the simulated age of deep and bottom water masses in the upper model levels young water is found to correspond with regions of convergence and downwelling in the surface ekman layer upwelling and convection are both shown to age the upper ocean by entraining older waters into the surface mixed layer in the deep model levels water age varies greatly between oceans with young water found in convectively active regions in the north atlantic and in the ross and weddell seas and old water found in the deep north pacific the oldest water mass mixture located at 2228 m depth in the western pacific ocean is dated at 1494 years made

evolution of ocean temperature and ice volume through the mid pleistocene climate transition earth s climate underwent a fundamental change between 1250 and 700 thousand years ago the mid pleistocene transition mpt when the dominant periodicity of climate cycles changed from 41 thousand to 100 thousand years in the absence of substantial change in orbital forcing over this time an increase occurred in the amplitude of change of deep ocean foraminiferal oxygen isotopic ratios traditionally interpreted as defining the main rhythm of ice ages although containing large effects of changes in deep ocean temperature we have separated the effects of decreasing temperature and increasing global ice volume on oxygen isotope ratios our results suggest that the mpt was initiated by an abrupt increase in antarctic ice volume 900 thousand years ago we see no evidence of a pattern of gradual cooling but near freezing temperatures occur at every glacial maximum

origins and development of holocene coral reefs a revisited model based on reef boreholes in the seychelles indian ocean until recently concepts of coral reef growth and accumulation have been predominantly based on a darwinian model in this the upwards and outwards growth of a reef core a coral framework takes place over a foreslope consisting of reef talus with the simultaneous filling of the back reef lagoon by reef derived debris the principal adaptations of this pattern relate to the influence of relative changes in sea level and commonly ignore oceanographic factors such as storm frequency and severity boreholes through the outer edge of a fringing reef in the seychelles western indian ocean reveal a record of holocene sediment accumulation first established approximately 8 ka ago faunal and floral associations show that growth of this body began in relatively deep water but that this shallowed to 5 m within 1 ka subsequent accumulation was of keep up style but as the rate of sea level rise slowed shoaling became more frequent and aggradation was limited by reducing accommodation space constructional facies are characterised either by massive corals including leptastrea porites and faviids or by branching corals typically acropora of the danai robusta group coral surfaces may be encrusted by red algae foraminifera and vermetids and are commonly bored by filamentous algae clionids and molluscs however detrital facies are volumetrically dominant and the paucity of a constructional framework requires a re evaluation of models of reef accretion new models relate the geometry of accretion to the interplay between extreme storm events and fairweather hydrodynamic conditions these suggest that a contiguous framework forms in areas of moderate fairweather energy without extreme storm events severe storms destroy the continuity of reef structures and generate increasing volumes of coarse detritus low storm severity coupled with low fairweather hydrodynamic energy may promote the accumulation of fine grained reef derived sediments that inhibit framework growth while ecology reflects year by year sea conditions lithology and structure are controlled by exceptional storms with the effects of changing sea level superimposed

coral reef response to quaternary sea level and environmental changes state of the science there is considerable uncertainty about future sea level projections due to the current poor understanding of the vulnerability and sensitivity of ice sheets to global warming fossil coral reefs represent a unique archive of sea level and associated environmental changes that extend far beyond instrumental records here recent advances in this field are summarized focusing on periods of earth history typified by rapid sea level rise and short term climate excursions sea level and reef response records from the last deglaciation and periods characterized by higher sea level stands and short term and low magnitude sea level oscillations such as the mid to late holocene and the last interglacial are synthesised special emphasis is given to understanding how coral reefs have responded to these changes in terms of reef development architecture and composition finally seven major challenges and future research directions are identified

paleohydraulics of the last outburst flood from glacial lake agassiz and the 8200 bp cold event abstract during the last deglaciation of north america huge proglacial lakes formed along the southern margin of the laurentide ice sheet the largest of these was glacial lake agassiz which formed about 11 7 14 c kyr and drained into hudson bay about 7 7 14 c kyr 8 45 cal kyr overflow from these lakes was variably directed to the mississippi st lawrence and mackenzie drainage systems and it is thought that switches in routing were accompanied by a response in ocean circulation that produced abrupt climate events when the ice dam across hudson bay finally was breached a massive flood drained lake agassiz which was routed through hudson strait to the labrador sea in terms of stored water volume the largest reservoir was associated with the kinojevis level of lake agassiz for this maximum filling the impounded water volume available to produce floods is estimated as 40 000 151 000 km 3 depending on the location of the ice margin and route used the timing of this rapid release of stored freshwater just precedes the early holocene cooling event at 8 2 cal kyr bp we use the spring hutter theory to simulate flood hydrographs for floods that originate in subglacial drainage conduits and find that flood magnitude and duration are 5 sv and 0 5 yr multiple fillings and floods are possible as are single floods having a complex multipulse structure modelling results suggest that the outburst flood from lake agassiz may have terminated before the lake surface elevation dropped to sea level and that the flood ended when a stable drainage channel was established connecting lake agassiz to the tyrrell sea

wave transformation on a coral reef wave transformation of regular waves was measured in a laboratory model of a fringing reef with a steep face and an outer reef top slope gradually decreasing in the landward direction data was obtained for various wave conditions and water levels a nonlinearity parameter fco g1 25ho 0 5t2 5 hc 1 75 based upon one proposed by swart and loubser 1979 is proposed as a suitable parameter for classifying wave transformation regimes on this reef in particular when fco 150 waves plunge on the reef edge and the amount of wave energy reaching a shore or structure is small 16 when fin co 100 waves spill on the reef top but the greater part of their energy is transmitted over the reef top the maximum values of the wave height to water depth ratio on the reef top were found to be consistent with nelson s analyses for laboratory and field data which indicate that the maximum stable wave height to depth ratio h d on a horizontal bottom never exceeds 0 55 for shallow water waves fc 500 the experimental data confirms that the maximum value of h d decreases when fc decreases but that it also increases when the bottom slope increases

revisiting the quaternary development history of the western new caledonian shelf system from ramp to barrier reef abstract the present paper is based on the study of a new core tenia 3 151 20 m long and revisitation of previous core data from the western new caledonian barrier reef based on variations in lithology and stable isotope signatures and the occurrence of unconformity surfaces the tenia 3 sequence is subdivided into ten units regarded as deposited during interglacial high sea levels five detrital and two framework facies are delineated using their biological and textural attributes including coral growth forms and assemblages these facies are interpreted as representative of outer to inner carbonate shelf ramp to barrier reef environments variations in the facies within each stratigraphic unit occur mainly as vertical transitions from lower energy and probably deeper to higher energy probably shallower settings the succession of depositional events is reconstructed using all available age criteria including lithostratigraphy magnetostratigraphy uranium series dating and nannofossil biostratigraphy shallow water coral communities appear to have been developed as soon as carbonate deposition started at around 1 2 million years ma but the initiation of typical coral reef tracts is likely to have occurred not prior to 0 40 million years during marine isotope stage mis 11 carbonate deposition previous to mis 11 is considered to have operated along an open shelf margin i e a ramp or non rimmed platform based on the re examination of the core dataset previously acquired from the new caledonian reefs the coral communities dominated by massive forms mainly poritids are assumed to have remained stable in composition over the past 1 4 ma similarly as indicated by a preliminary study of pollen assemblages in the core the composition of terrestrial flora dominated by podocarpaceae and araucariaceae has not apparently suffered significant change over the past 1 ma and reflects climate conditions cooler and drier than today mean subsidence rates are derived tentatively over the past 1 ma from the stratigraphic position at present reached by the top of depositional units mean rates of 0 08 mm yr 1 for the western new caledonian margin are consistent with past sea level estimates the quaternary depositional history of the new caledonian shelf margin appears to have been controlled by both the amplitude of sea level changes and by differing vertical tectonic movements comparison between the depositional shelf histories from western new caledonia north eastern australia southern belize and the ryukyu islands supports the assumption that coral populations over the early and mid pleistocene developed as non reefal communities along ramp systems not forming continuous outer shelf reef rims at a global scale quaternary reef rimmed platforms are likely to have initiated after the mid pleistocene climate transition from marine isotope stage 11 at about 0 4 ma

distinct relict fringing reefs in the northern shelf of the gulf of elat aqaba markers of quaternary eustatic and climatic episodes quaternary reef development and demise have been shown to correspond to worldwide sea level fluctuations and related environmental changes yet the mechanisms and rates affecting this relationship are not well resolved a set of high resolution seismic reflection and multibeam bathymetric data were interpreted six distinct systems of relict fringing reefs embedded within the sedimentary cover of the northern shelf of the gulf of elat aqaba were identified the two uppermost relict fringing reefs are also exposed on the sea floor in water depths of ca 20 m and ca 60 m along the north western corner of the northern gulf of elat aqaba and sub parallel to the current northern coast respectively two other relict fringing reefs are laterally correlated to each of the last two transgressive cycles and are inferred to have formed during decelerations in sea level rise during the last two deglaciations these reefs and the units to which they are laterally correlated portray a repeating stratigraphic pattern of reef development during deposition of seismically homogeneous sediment and an ensuing demise during deposition of heterogeneous sediment correlation of the reef stratigraphy with rates of late quaternary sea level rise and a sediment accumulation rate from one shelf core provide age estimations for the seismic stratigraphy two phases of fringing reef generation occurred during the last deglaciation since ca 18 ka the older reef probably developed between 12 8 ka and 11 5 ka at ca 60 m below present sea level and the younger reef after 8 4 to 8 0 ka at ca 20 m below present sea level these last two phases of reef generation are separated by a lobate seismic unit that is interpreted as fluvial deltaic deposits that backstepped across the shelf during the early holocene transgression results suggest that fringing reefs evolved along the northern shelf of the gulf of elat aqaba only during relative decelerations in sea level rise contemporaneous with low input of terrigenous sediment and probably during a period of aridity at present no fringing reef grows along the northern coast of the gulf of elat aqaba suggesting that these relatively arid periods may have been drier than recent the pattern of slowdown in sea level rise contemporaneous with conditions of increased aridity seems to have repeated during the last two sea level rises approximately at the same sea levels suggesting a common mechanism of short millennium scale phases of eustatic and climatic alteration during deglaciations

are catch up reefs an artefact of coring drill cores through modern coral reefs commonly show a time lag in reef initiation followed by a phase of rapid accretion to sea level from submerged foundations the so called catch up response but because of the difficulty of drilling in these environments core distribution is usually restricted to accessible areas that may not fully represent reef history especially if the reef initiated in patches or developed with a prograde or retrograde geometry as a consequence core data have the potential to give a misleading impression of reef development particularly with respect to the timing of initiation and response to sea level rise here we use computer models to simulate keep up reef development and from them quantify variations in the timing of reef initiation and accretion rate using mock cores taken through the completed simulations the results demonstrate that cores consistently underestimate the timing of reef initiation and overestimate the reef accretion rate so that statistically a core through a keep up reef will most likely produce a catch up pattern an initiation lag followed by a phase of rapid accretion to sea level this implies that catch up signatures may be an artefact of coring and that keep up reefs are significantly more common than previous core studies claim

numerical modeling of the growth and drowning of hawaiian coral reefs during the last two glacial cycles 0 250 kyr 1 drowned coral reefs on rapidly subsiding margins possess a unique archive of sea level and climate changes generally unavailable from stable or uplifting margins using available field observations and sedimentary radiometric age and numerical modeling data we propose a new model of submerged reef development around hawaii during the last two glacial cycles 250 kyr this model provides a quantitative predictive stratigraphy for the reefs that we argue if drilled will yield new information on sea level and climate changes as well as coral reef response over the last 250 kyr comparing the observational and numerical modeling data combined with sensitivity testing we present our best case scenario for the evolution of the drowned lowstand reefs now at 400 h2 and 150 m h1 we find that growth rates of 2 5 2 85 m kyr for the main shallow reef building facies a subsidence rate of 2 5 m kyr and a variable basement substrate configuration best explain the observational data modeling of the internal stratigraphic succession of the reefs shows that the number and thickness of shallow reef units as well as the frequency and duration of subaerial exposure and reef drowning events are sensitive to the frequency and amplitude of eustatic sea level variations but not the rate of subaerial erosion h2 and h1 initiated growth during stable eustatic sea level conditions during highstands circa 222 ka mis7 and circa 126 ka mis5e respectively both h2 and h1 have a long and complex growth history growing episodically for 90 kyr precessional 20 kyr and higher frequency suborbital eustatic sea level fluctuations dominate with each reef experiencing repeated but brief 5 10 kyr drowning and subaerial exposure producing a complex layer cake stratigraphy of shallow 0 30 m coral reef units separated by either subaerial exposure horizons or thin intermediate 30 60 m coralgal units final drowning of h2 and h1 occurs during the penultimate 133 134 ka and last deglaciation 12 14 ka these findings are consistent with available age data and qualitative predictions of previous studies around hawaii

deglacial meltwater pulse 1b and younger dryas sea levels revisited with boreholes at tahiti reconstructing sea level changes during the last deglaciation provides a way of understanding the ice dynamics that can perturb large continental ice sheets the resolution of the few sea level records covering the critical time interval between 14 000 and 9 000 calendar years before the present is still insufficient to draw conclusions about sea level changes associated with the younger dryas cold event and the meltwater pulse 1b mwp 1b we used the uranium thorium method to date shallow living corals from three new cores drilled onshore in the tahiti barrier reef no significant discontinuity can be detected in the sea level rise during the mwp 1b period the new tahiti sea level record shows that the sea level rise slowed down during the younger dryas before accelerating again during the holocene

the transient nature of the empty bucket model of reef sedimentation abstract the geometry of modern reefs has been likened to an empty bucket with the narrow reef rim comprising the container pail that encloses the water filled bucket while the analogy is valid the assumption that this constitutes a final geometry is not examples from the indian pacific and atlantic oceans individually and collectively demonstrate current filling of the lagoons by reef perimeter sand aprons since sea level only approximated its present position 3 to 6 ky ago it follows that the observed extent of modern highstand lagoon filling is minimal if the filling process was to continue unabated the result would be a flat topped bank but during the pleistocene low stands of sea level aborted the filling process extrapolating these relationships to the geologic record suggests that the empty bucket model of unfilled reef lagoon space is greatest during icehouse high frequency glacial fluctuations of sea level alternatively filled buckets in which cycle thickness approximates accommodation space are probably largely restricted to greenhouse time intervals the co occurrence of quaternary high amplitude frequency sea level changes with rapidly growing scleractinian corals probably enhanced the occurrence of empty bucket morphologies

sea level fingerprinting as a direct test for the source of global meltwater pulse ia the ice reservoir that served as the source for the meltwater pulse ia remains enigmatic and controversial we show that each of the melting scenarios that have been proposed for the event produces a distinct variation or fingerprint in the global distribution of meltwater we compare sea level fingerprints associated with various melting scenarios to existing sea level records from barbados and the sunda shelf and conclude that the southern laurentide ice sheet could not have been the sole source of the meltwater pulse whereas a substantial contribution from the antarctic ice sheet is consistent with these records

inhibition of reef framework by frequent disturbance examples from the arabian gulf south africa and the cayman islands abstract the environmental processes that prevent reef framework development in areas with a diverse and dense cover of coral were investigated in the southern arabian gulf dubai uae the southwestern indian ocean south africa and the central caribbean cayman islands bwi in dubai temperature anomalies predicted to recur every 10 15 yr cause repeated mass mortalities of acropora spp the dominant potential framebuilding species subsequent bioerosion of the dead coral skeletons renders them brittle and susceptible to fragmentation during winter storms as a consequence regrowth of the next generation of framebuilders which takes about 10 yr has to initiate on the original bedrock surface this cycle of mass mortality framework break down and regrowth inhibits in situ framework accumulation in south africa the formation of coral frameworks is prevented by annually recurring high wave energy events which stunt coral to such small sizes that no framework is built the situation is further aggravated by the fact that branching coral fragments which could serve as asexual propagules are washed off the reefs and lost in the cayman islands no coral framestones of in situ skeletons are formed in areas shallower than about 5 m in these areas coral frameworks formed by acropora palmata are removed by hurricanes broken up and deposited in the form of a rubble accumulation further inland on the island shelf thus although a coral deposit remains it is not an in situ grown framework however since the build ups in the upper 5 m are mostly made up by coral fragments such structures would likely be identified as reefs if encountered in a fossil outcrop situation these three models can help to explain the paleoecology of allochthonous peri reefal or non reefal coral deposits i e coral rudstones floatstones bindstones they also demonstrate that at least in recent coral systems species richness and high coral coverage alone need not necessarily translate into high in situ framebuilding potential

high precision u series ages of transported coral blocks on heron reef southern great barrier reef and storm activity during the past century transported coral blocks scattered on reef flats have previously been identified as useful proxies for past storm occurrences high precision tims u series dating and detailed field observations of 110 coral samples collected from 102 individual transported coral colonies coral blocks and 4 transported sections of reef matrix reef blocks from the northern side of heron reef southern great barrier reef indicate that 1 the youngest age of corals attached to reef blocks may represent the age of possible past storm occurrence providing a proxy for historical storm reconstruction 2 most ages of dated storm transported coral and reef blocks match well relatively with known cyclone and storm events further supporting that they are good indicators of past storm events and 3 age distribution and relative probability frequency analysis of the dated coral and reef blocks suggest that there have been eight broad periods of storm occurrence since 1900 ad 1904 1909 1914 1916 1935 1941 1945 1960 1965 1967 1976 1977 1983 1988 and 2001 2007 roughly showing decadal variations the coral based storm reconstruction therefore extended the database of past storm occurrences around heron reef area these findings suggest that coral reefs in the southern great barrier reef are frequently influenced by periods of high storm activity and show strong resilience to natural disturbances over the past century additionally our results show for the first time that the blue skeletal coral heliopora coerulea order helioporacae has u concentrations of only 0 12 to 0 30 ppm similar to 5 10 that of common reef building corals with white skeletons order scleractinia which may be a unique chemical signature of the only living species of the helioporidae family c 2012 elsevier b v all rights reserved

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

holocene sea level change and tectonic uplift deduced from raised reef terraces kikai jima ryukyu islands japan abstract kikai jima kikai island is surrounded by four holocene raised coral reef terraces which are thought to be an offlapping sequence of reef deposits caused by combined effects of seismic uplift and holocene sea level change many studies in this region have investigated holocene sea level changes and reef growth but there are relatively few in which reliable sea level indicators are given we have found that pocillopora verrucosa one of the most abundant coral species on the upper reef slopes of fringing reefs in the ryukyus has its peak abundance at a depth of 1 5 m therefore this species is considered ideal for the analysis of relative sea level change and can be used as a dipstick for the holocene reef deposits in this area based on the distribution of p verrucosa on the four holocene raised terraces we calculate relative paleo mean sea levels to be 10 8 11 1 and 8 5 8 9 m for terrace i 5 0 5 3 m for terrace ii 4 0 4 3 m for terrace iii and 1 9 2 5 m for terrace iv these results combined with hitherto known and newly measured radiometric dates 103 total clearly show that the four terraces formed in response to repeated seismic uplifts at 6 3 4 1 3 1 and 1 4 ka and that sea level was higher than present between 7 0 and 6 3 ka

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

geochronology of drowned hawaiian coral reefs abstract two deeply submerged coral reefs were sampled with the hurl submersible pisces v off the islands of hawaii and maui an ancient fringing reef at 950 m depth on the kohala slope of hawaii was observed from deep towed camera photographs and during submersible operations a second reef at 1650 m depth on the haleakala slope of maui was observed on side scan images deep towed camera photographs and during submersible observations ages of the two reefs were determined by electron spin resonance dating with a signal intensity for aragonitic coral at g 2 0007 used to ascertain the accumulated dose by the additive dose method uranium concentration was measured by neutron activation analysis the chronology of the reefs indicates that drowning coincided with periods of rapid global climate change at the termination of continental glaciation at approximately 250 ka and 340 ka the drowning events correlate with oxygen isotope stage boundaries 7 8 and 9 10 these data support models of reef drowning on subsiding volcanic edifices

sea level changes forced ice breakouts in the last glacial cycle new results from coral terraces abstract sea level cycles recorded by coral terraces at huon peninsula hp in papua new guinea match rapid climate changes that occurred between 30 000 and 65 000 years ago seen in greenland ice cores and marine sediments each cycle of 6000 7000 years ended with a sea level rise of 10 15 m lasting 1000 2000 years following a longer period of falling sea level precise dating shows that each rise corresponds to a heinrich episode of ice rafted detritus in north atlantic signalling massive ice outbreak from north america sea level may be the trigger that forced near synchronous breakouts of ice from north america and eastern greenland the hp sea level changes also correspond to similar cycles in benthic oxygen isotopes reported from the north atlantic which are too large to be explained entirely in terms of ice volumes jointly the sea level and isotope records suggest that the north atlantic deep ocean cooled as sea level fell and warmed as sea level rose in each 6000 year cycle

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

reef coralgal assemblages as recorders of paleobathymetry and sea level changes in the indo pacific province the coralgal framework within the outer reef margin of many indo pacific reefs exhibits three main shallow water communities the environmental significance of which can be inferred by comparison with their modern counterparts a community dominated by tabular acropora gr hyacinthus cytherea with branching pocillopora damicornis p eydouxi montipora digitata occasional domal faviids and mm thick crusts of the coralline algae lithophyllum and mesophyllum mainly typical of the 6 15 m paleodepth range a community including robust branching acropora gr danai robusta a humilis a digitifera and subordinate favia stelligera echinopora gemmacea associated to vermetid gastropods and thick coralline crusts of hydrolithon cf onkodes and neogoniolithon cf fosliei flourishing in depths less than 6 m in medium to high water energy settings a community composed of domal porites cf lutea and p cf lobata with occasional acropora gr danai robusta and cm thick crusts of coralline algae in sheltered habitats in depths less than 10 m these biological assemblages allow us to determine relationships between reef growth and paleobathymetry and consequently to reconstruct regional relative sea level curves high water energy reefal assemblages provide stronger evidence for reconstructing sea level curves than low energy buildups because they have generally been controlled by a keep up growth mode subsiding reef sites seem to be more reliable indicators of sea level variations because they usually present expanded reef sequences

mid late holocene sea level variability in eastern australia a re analysis of sea level data from eastern australia based on 115 calibrated c 14 ages is used to constrain the origin timing and magnitude of sea level change over the last 7000 years we demonstrate that the holocene sea level highstand of 1 0 1 5 m was reached 7000 cal yr bp and fell to its present position after 2000 yr bp these findings are in contrast to most previous studies that relied on smaller datasets and did not include the now common conversion of conventional c 14 ages to calendar years during this 5000 year period of high sea level growth hiatuses in oyster beds and tubeworms and lower elevations of coral microatolls are interpreted to represent short lived oscillations in sea level of up to 1 m during two intervals beginning c 4800 and 3000 cal yr bp the rates of sea level rise and fall 1 2 mm yr 1 during these centennial scale oscillations are comparable with current rates of sea level rise the origin of the oscillations is enigmatic but most likely the result of oceanographic and climatic changes including wind strengths ice ablation and melt water contributions of both greenland and antarctic ice sheets

the great barrier reef a 700 000 year diagenetic history a deep borehole through ribbon reef 5 in the great barrier reef off north eastern australia has identified a variety of cements including epitaxial radial prismatic and spherular aragonite together with blocky prismatic and fibrous calcite these cements are discontinuously arranged within the sequence that consists predominantly of grainstones but locally includes clotted muddy and filamentous textures that may be of microbial origin calcite cements vary in morphology with groups of crystals that include acute scalenohedral rhombohedral and flattened concordant terminations these show varying densities of inclusions that locally define growth zones and in some terminations divide in the manner of split crystals to form fibrous fringes morphological changes in calcite are inferred to reflect changes in water chemistry and crystal growth rates at the time of growth allied to their relationship to the palaeo water table and linked in turn to changes in sea level neomorphism and dissolution are widespread and variations in the severity of both imply response to the degree of undersaturation of pore waters that at times were probably balanced within very narrow limits a total of 10 depositional units are identified those units at the base of the borehole reflect deposition and diagenesis within a marine environment the influence of meteoric waters indicated by stable isotopes is first apparent at the top of unit 1 and in unit 2 184 to 155 m below sea floor petrographic evidence of vadose conditions appears at the tops of unit 3 131 to 99 m below sea floor units 4 to 8 all deposited under marine conditions provide isotopic evidence of meteoric or mixing zone waters and petrographic indicators of vadose conditions typically at the top of the units evidence indicates that in unit 5 the water table was mobile and units 6a 6b 7 and 8 all characterized by ultraviolet fluorescent cements are capped by sub aerial erosion surfaces unit 9 the holocene reflects the recent re establishment of marine conditions the extent of alteration of the entire sequence reflects the substantial and pervasive influence of meteoric waters this effect is interpreted as a result of a greater rainfall and river flow from the mainland during early and late stages of interstadial periods the study reflects progress in the ability to recognize the diagenetic signal generated by sea level change however whereas the isotopic results reflect the changing relationships between vadose and phreatic zones in groundwater systems beneath successive emergent surfaces their correspondence with petrographic features is expressed only weakly and commonly lacks the systematic sequential overprinting implied by the distribution of cathodoluminescent zones of cements in many ancient limestones

early diagenesis in pleistocene coral reefs southern sinai egypt response to tectonics sea level and climate the uplifted pleistocene terraces along the coast of southern sinai exhibit a well developed reef system formed during isotope stage 9 and a younger one formed during isotope stage 5 an intermediate reef corresponding to isotope stage 7 occurs only as an erosional relic in the study area the sediments comprise reefal framestones peri reefal facies coral rubble and siliciclastic dominated beach and aeolian facies the compositional and textural complexity of the sediments leads to a highly variable spatial distribution of diagenetic features however the geometric relationships and elemental analyses allow a reconstruction of the general diagenetic evolution during the major eustatic sea level highstand of isotope stage 9 the older reef was constructed and cemented with aragonite and high mg calcite climate was probably semiarid with some rainy periods which permitted the installation of ephemeral freshwater lenses especially during the minor sea level lowstand within isotope stage 9 in these lenses and during the subsequent major sea level lowstand some freshwater dissolution occurred the highstand during isotope stage 7 led to the construction of the intermediate reef in the older reef some high mg calcite precipitated at that time dolomite cement formed either in marine interstitial waters modified by some freshwater input or in a hypersaline context phreatic meteoric low mg calcite cement covers and partly replaces previous marine cements and dolomite but is still attributed to the major highstand of isotope stage 7 when freshwater lenses could develop during minor sea level lowstands the subsequent major sea level lowstand was dominated by an arid climate and only a little freshwater corrosion occurred the younger reef formed during the major highstand of isotope stage 5 aragonite and high mg calcite cements as well as some dolomite are common within the reef whereas freshwater cements are limited to beach and aeolian facies due to tectonic uplift only the lower part of the older reef was reflooded during isotope stage 5 and only some aragonite crystals precipitated on top of dolomite or low mg calcite the interrelationships between tectonics sea level variations of different orders and climatic changes thus had a profound impact on the diagenetic history of these reef systems

hurricane control on shelf edge reef architecture around grand cayman rimming the outer shelf of grand cayman is a submerged 87 km long shelf edge reef that rises to within 12 m of mean sea level it consists of an array of coral armoured buttresses aligned perpendicular to shore and separated by steep sided sediment floored canyons individual buttresses have a diverse coral dominated biota and consist of three architectural elements a shield like front wall colonized by platy corals a dome shaped crown colonized by head corals and a shoreward projecting spur covered by varying amounts of branching coral buttresses are commonly fronted by coral pinnacles that in some areas have amalgamated with buttress walls to produce pinnacle and arch structures as margin orientation changes shelf edge reef architecture shows systematic variations that are consistent with changes in fetch and height of hurricane waves along margins exposed to fully developed storm waves shelf edge reef buttresses are deep have large amplitudes and are dominated by robust head corals these characteristics are consistent with hurricane induced pruning of branching corals and the flushing of significant quantities of sand from buttress canyons by return flows along margins impacted by fetch limited storm waves reef buttresses are shallower have intermediate amplitudes and have a significantly higher proportion of branching corals these characteristics are consistent with less coral pruning and sand flushing by weaker hurricane waves along margins fully protected from storm waves the buttresses canyon architecture of the shelf edge reef breaks down producing a series of shallow undulating branching coral dominated ridges that merge laterally into an unbroken belt of coral these characteristics correspond with negligible amounts of pruning and flushing during hurricanes in addition to differences between margins local intra marginal changes in shelf edge reef architecture are consistent with changes in the angle of hurricane wave approach open sections of the shelf edge reef which face directly into storm waves are pruned of branching corals and the fragments swept back onto the shelf producing extensive spurs by contrast on more sheltered obliquely orientated sections storm waves sweep debris along and off shelf producing little or no spur development instead the debris shed seawards accumulates in front of the buttress walls and initiates the development of coral pinnacles over time repeated buttress pruning and canyon flushing during hurricanes not only controls reef architecture but may also influence accretion patterns vertical accretion is limited by the effective depth of storm wave fragmentation once this hurricane accretion threshold is reached the reef moves into a shedding phase and accretes laterally via pinnacle growth amalgamation and infilling consequently the reef steps out over its own debris in a kind of balancing act between lateral growth and slope failure a pattern widely recognized in ancient reefs

stratigraphy and chronology of late pleistocene reefs in the southern cook islands south pacific the makatea islands in the southern cook islands consist of a degraded volcanic core surrounded by emergent makatea limestones while much of this reefal limestone is of tertiary age the seawardmost reefs are late pleistocene last interglacial reefs oxygen isotope substage 5e identified by u series dating reach 12 2 m on atiu mean age of three samples 126 000 5000 yr b p 9 8 m on mitiaro mean age of five samples 119 000 3000 yr b p 10 0 12 7 m on mauke mean age of four samples 128 000 5000 4 000 yr b p and 14 5 20 0 m on mangaia mean age of four samples 115 000 7000 yr b p on atiu mauke and mitiaro a lower reef unit has been identified and is separated from the overlying substage 5e reef by a sharp discontinuity often with a crust of coralline algae u series dating from atiu and mauke indicates that this is a stage 7 reef formed in the penultimate interglaciation the makatea islands have emerged as a result of flexure of the lithosphere in response to loading by the pleistocene volcanic island of rarotonga isolated outcrops of makatea limestone on rarotonga reach 3 5 m and are probably of substage 5e age elastic and viscoelastic models of lithospheric flexure predict that much of the compensatory movement should occur shortly after the emplacement of the load however the age and elevation of late quaternary reefs on the southern cook islands where a pleistocene volcanic island has loaded relatively old ocean floor 80 myr indicate that differential uplift has been continuing over the last 250 000 yr

coral reefs and sea level change abstract coral reefs provide significant evidence for former sea level positions because of their geological preservation and suitability for dating interpretation of this evidence presumes an understanding of reef geomorphology modern reef organism distributions and environmental factors influencing them fossil reef terraces formed during the last interglacial marine oxygen isotope mis substage 5e 128 116 ka are prevalent on many tropical shorelines and there has been ongoing debate as to the height reached by sea level during that highstand observations from numerous last interglacial sites suggest that sea level was at least 3 m above present sea level implying less extensive icesheets than at present an elevation of 6 m has commonly been adopted when correcting tectonically active sites for uplift recent compilations suggest elevations up to 8 9 m but incorporate few observations from reefs where the last interglacial is found below sea level oscillation of sea level during mis 5e has been interpreted from several sites with recent studies inferring rapid rise of several metres at the end of the interglacial these interpretations are at the limits to the precision with which corals can currently be dated and their palaeo water depths inferred it is not surprising that constraining last interglacial sea level changes within uncertainties of less than 1 2 m remains controversial considering sea level variations recognised between reef sites in the holocene and observed geographical variation in isostatic or flexural adjustments fossil coral reefs on uplifting margins also provide clear evidence for mis substages 5c and 5a and those on huon peninsula indicate fluctuations related to heinrich events mis 3 interpretations show considerable variability between sites with still greater uncertainties about sea level timing and elevation during previous interglacials future study of extensive sequences of fossil reefs preserved on rapidly subsiding margins could address these uncertainties submerged reefs have already yielded important information about sea level rise during the last deglaciation coring around barbados and tahiti as well as on the huon peninsula has produced a broadly consistent picture of ice melt reflecting eustatic change since the last glacial maximum these studies have shown the sensitivity of reefs to rapid sea level rise associated with meltwater pulses with some reefs drowning while others back stepped integrated ocean drilling program iodp expeditions to tahiti and recently the great barrier reef extended these records but details of timing nature and impact of deglacial meltwater pulses remain elusive studies of holocene reefs have indicated different growth strategies some kept up with sea level while others caught up when sea level decelerated holocene sea level appears to have experienced a gradual rise up to present across the caribbean providing accommodation space for reefs to accrete vertically whereas in the indo pacific sea level has been near its present level since 7 ka with many reef flats emergent following a slight fall of sea level caused by ocean siphoning microatolls on reef flats provide perhaps the clearest evidence of past sea level position but in their absence novel biological or other sea level indicators are required to better constrain palaeo water depths there is an urgent need for further research from additional key reef locations not only to decipher processes driving past sea level change and its geographical variability but also to better understand how coral reefs will respond in the context of future sea level rise

continuous reef growth during the last 23 cal kyr bp in a tectonically active zone vanuatu southwest pacific abstract at urelapa island vanuatu sea level rise and a tectonic uplift of 3 mm yr 1 have controlled water depth and the colonization and reef development on a substrate from 23 until 6 cal kyr bp analysis of coralgal assemblages offers insights on the mode of reef growth and on water depth over the reef for the studied period those assemblages precisely dated by the 230 th 234 u method give valuable information on the rate and timing of sea level rise since the last glacial maximum the urelapa reef sequences are characterized by upwards replacement of reef frameworks which indicates changes in wave energy through time the sudden acceleration of sea level rise associated with meltwater pulse 1b at around 11 3 cal kyr bp is marked by a change in reef growth strategy from a keep up mode to a catch up mode we examine the delay in timing of the occurrence of suitable substrates the role of paleoceanographic factors and the influence of possible jumps in sea level

paleoceanographic reconstructions of surface ocean conditions in the greenland iceland and norwegian seas through the last 14 ka based on diatoms prior reconstructions of the last glacial maximum and the holocene did not include detailed paleoclimate data from the greenland iceland and norwegian gin seas which cover sensitive areas for oceanographic boundaries sea ice distribution and deep water formation in order to fill this gap we studied nine well dated sediment cores from this area and reconstructed the paleoceanographic conditions of the surface gin seas at 2000 year intervals since 13 400 bp based on the diatom record results show that a n s extending sea ice free corridor had opened along norway already at 13 400 bp indicating a northward flow of a branch of the north atlantic drift possibly caused by a change in the jet stream flow due to the decreased height of the north american ice sheet a major change of climatic conditions occurred over the gin seas as the insolation anomaly reached its maximum around 9000 bp when the sea ice cover and the oceanic fronts retreated to a northwesterly position along greenland and the ocean temperatures rose the first half of the holocene is recorded as the warmest period during the last 13 400 bp in the gin seas the duration of this climatic optimum decreased both toward the north and toward the margins of the area the second half of the holocene is characterized by a cooling trend in step with the decreasing insolation these results support the proposal of imbrie et al 1992 that the gin seas region acts as an initial responder to insolation changes

constraints on the duration and freshwater release of heinrich event 4 through isotope modelling heinrich events1 abrupt climate cooling events due to ice sheet instability that occurred during the last glacial period are recorded in sediment cores throughout the north atlantic ocean2 3 modelling studies have described likely physical mechanisms4 5 6 for these events but the quantitative characteristics of heinrich events are less well known here we use a climate model of intermediate complexity7 that explicitly calculates the distribution of oxygen isotopes in the oceans to simulate heinrich event 4 at about 40 000 yr ago we compare an ensemble of scenarios for this heinrich event with oxygen isotope data measured in foraminiferal calcite of a comprehensive set of sediment cores8 9 from this comparison we obtain a duration of 250 150 yr and an ice release of 2 1 m sea level equivalent for heinrich event 4 significantly reducing the uncertainties in both values compared to earlier estimates5 10 11 12 13 14 of up to 2 000 yr and 15 m of sea level equivalent ice release respectively our results indicate that the consequences of heinrich events may have been less severe than previously assumed at least with respect to greenland climate and sea level