u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

synchroneity of meltwater pulse 1a and the bolling warming new evidence from the south china sea a twofold decrease in long chain n alcane n nonacosane concentrations in a downcore record from the northern south china sea indicates a rapid drop in the supply of terrigenous organic matter to the open south china sea during the last deglaciation paralleled by an equally rapid increase in sea surface temperatures corresponding with the bolling warming at 14 7 ka the sudden drop in terrigenous organic matter delivery to this marginal basin is interpreted to reflect a short term response of local rivers to rapid sea level rise strongly implying that the bolling warming and the onset of meltwater pulse mwp 1a are synchronous this phase relation contrasts with the widely cited onset of this mwp 1a ca 14 ka and implies that previous studies postulating a weakening of deep water formation in the north atlantic due to massive meltwater discharge during mwp 1a need to be reevaluated

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

post glacial sea level rise from a coral record at huon peninsula papua new guinea dating of coral reef terraces can provide a record of changes in sea level which should be pronounced during the transition between glacial and interglacial periods cores drilled from coral reefs at barbados in the equatorial west atlantic1have revealed the sea level changes that occurred during the younger dry as event at the end of the last glacial maximum 11 000 yr bp it has not been known however whether pacific coral reefs can grow at a rate sufficient to keep up with the rise in sea level during such a transition here we report results obtained from a 52 m drill core from the post glacial reef at huon peninsula papua new guinea spanning the interval from 7 000 to 11 000 14c yr bp which show that coral growth kept pace while the relative sea level rose by 50m although the tectonic environment is very different from that at barbados the two records compare well when corrections are made for local tectonic uplift showing that sea level rise was similar at both locations the rate of rise was greatest between 9 000 and 10 00014c yr bp corresponding to the time of the younger dryas

diagenesis and geochemistry of porites corals from papua new guinea implications for paleoclimate reconstruction coral proxy records of sea surface temperature sst and hydrological balance have become important tools in the field of tropical paleoclimatology however coral aragonite is subject to post depositional diagenetic alteration in both the marine and vadose environments to understand the impact of diagenesis on coral climate proxies two mid holocene porites corals from raised reefs on muschu island papua new guinea were analysed for sr ca 18 o and 13 c along transects from 100 aragonite to 100 calcite thin section analysis showed a characteristic vadose zone diagenetic sequence beginning with leaching of primary aragonite and fine calcite overgrowths transitional to calcite void filling and neomorphic fabric selective replacement of the coral skeleton average calcite sr ca and 18 o values were lower than those for coral aragonite decreasing from 0 0088 to 0 0021 and 5 2 to 8 1 respectively the relatively low sr ca of the secondary calcite reflects the sr ca of dissolving phases and the large difference between aragonite and calcite sr ca partition coefficients the decrease in 18 o of calcite relative to coral aragonite is a function of the 18 o of precipitation carbon isotope ratios in secondary calcite are variable though generally lower relative to aragonite ranging from 2 5 to 10 4 the variability of 13 c in secondary calcite reflects the amount of soil co 2 contributing 13 c depleted carbon to the precipitating fluids diagenesis has a greater impact on sr ca than on 18 o the calcite compositions reported here convert to sst anomalies of 115 c and 14 c respectively based on calcite sr ca compositions in this study and in the literature the sensitivity of coral sr ca sst to vadose zone calcite diagenesis is 1 1 to 1 5 c per percent calcite in contrast the rate of change in coral 18 o sst is relatively small 0 2 to 0 2 c per percent calcite we show that large shifts in 18 o reported for mid holocene and last interglacial corals with warmer than present sr ca ssts cannot be caused by calcite diagenesis low level calcite diagenesis can be detected through x ray diffraction techniques thin section analysis and high spatial resolution sampling of the coral skeleton and thus should not impede the production of accurate coral paleoclimate reconstructions copyright 2003 elsevier science ltd

constraints on the dynamics of mantle plumes from uplift of the hawaiian islands the v0 2 mm yr uplift of hawaiian islands lanai and molokai and hawaiian swell topography pose important constraints on the structure and dynamics of mantle plumes we have formulated 3 d models of mantle convection to investigate the effects of plume plate interactions on surface vertical motions and swell topography in our models the controlling parameters are plume radius excess plume temperature and upper mantle viscosity we have found that swell height and swell width constraints limit the radius of the hawaiian plume to be smaller than 70 km the additional constraint from the uplift at lanai requires excess plume temperature to be greater than 400 k if excess plume temperature is 400 k models with plume radius between 50 and 70 km and upper mantle viscosity between 10 20 and 3u10 20 pa s satisfy all the constraints our results indicate that mantle plume in the upper mantle may be significantly hotter than previously suggested this has important implications for mantle convection and mantle melting in addition to constraining plume dynamics our models also provide a mechanism to produce the observed uplift at lanai and molokai that has never been satisfactorily explained before 9 2002 elsevier science b v all rights reserved

morphology of fore reef slopes and terraces takapoto atoll tuamotu archipelago french polynesia central pacific the tectonic sea level and coral growth control abstract a dataset of 41 bathymetric profiles detected by satelline imagery and echo sounding to a maximum depth of 38 m along the fore reef slopes of takapoto atoll tuamotu plateau french polynesia central pacific were qualitatively and quantitatively analyzed in order to identify the main geomorphological features in addition scuba diving investigations from a selected site resulted in defining coral composition and cover rate six distinct fore reef sectors were morphologically differentiated on the basis of seaward extension and slope gradient only the north end and a restricted area of the mid south east side extend seawards over an average distance of 150 m with a relatively low gradient 23 38 most of the outer slope areas are narrow 10 m high outer reef crest like reliefs 0 5 m 1 5 m high pinnacles 2 m 17 m high coral heads

the impact of the mid pleistocene transition on the composition of submerged reefs of the maui nui complex hawaii the submarine reef terraces l1 l12 of the maui nui complex mnc the islands of lanai molokai maui and kahoolawe in hawaii provide a unique opportunity to investigate the impact of climate and sea level change on coral reef growth by examining changes in reef development through the mid pleistocene transition 900 800 ka we present an analysis of the biological and sedimentary composition of the reefs that builds directly on recently published chronological and morphological data we define nine distinct limestone facies and place them in a spatial and stratigraphic context within 12 reef terraces using rov and submersible observations these include oolitic two coral reef two coralline algal nodule algal crust hemi pelagic mud bioclastic and peloidal mud facies these facies characterise environments from high energy shallow water coral reef crests to low energy non reefal deep water settings combining the bottom observations and sedimentary facies data we report a shift in the observed sedimentary facies across the submerged reefs of the mnc from dominant shallow coral reef facies on the deep reefs to coralline algae dominated exposed outcrop morphology on the shallower reefs we argue that this shift is a reflection of the change in period and amplitude of glacioeustatic sea level cycles 41 kyr and 60 70 m to 100 kyr and 120 m during the mid pleistocene transition mpt 800 ka coupled with a slowing in the subsidence rate of the complex the growth of stratigraphically thick coral reef units on the deep pre mpt reefs was due to the rapid subsidence of the substrate and the shorter smaller amplitude sea level cycles allowing re occupation and coral growth on successive cycle low stands longer larger amplitude sea level cycles after the mpt combined with greater vertical stability at this time produced conditions conducive to deep water coralline algae growth which veneered the shallower terraces additionally we compare reef development both within the mnc and between the mnc and hawaii finally we suggest that climatic forcings such as sea surface temperature and oceanographic currents may also have influenced the distribution of coral species within the sample suite e g the disappearance of the acropora genus from the maui nui complex in the middle pleistocene

deglacial sea level record from tahiti corals and the timing of global meltwater discharge the timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets1 and their effects on the earth s surface2 3 moreover the disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans which probably disturbed the ocean s thermohaline circulation and hence global climate4 7 sea level increases bear witness to the melting of continental ice sheets but only two such records from barbados8 9 and new guinea10 11 corals have been accurately dated but these corals overlie active subduction zones where tectonic movements are large and often discontinuous especially in new guinea so the apparent sea level records may be contaminated by a complex tectonic component here we date fossil corals from tahiti which is far from plate boundaries and thus is likely to be tectonically relatively stable and remote from the locations of large former ice sheets the resulting record indicates a large sea level jump shortly before 13 800 calendar years bp which corresponds to meltwater pulse 1a in the barbados coral records8 9 the timing of this event is more accurately constrained in the tahiti record revealing that the meltwater pulse coincides with a short and intense climate cooling event12 15 that followed the initiation of the bolling allerod warm period12 16 but preceded the younger dryas cold event by about 1 000 years

timing of meltwater pulse 1a and climate responses to meltwater injections the temporal relationship between meltwater pulse 1a mwp 1a and the climate history of the last deglaciation remains a subject of debate by combining the greenland ice core project d18o ice core record on the new greenland ice core chronology 2005 timescale with the u th dated barbados coral record we conclusively derive that mwp 1a did not coincide with the sharp bolling warming but instead with the abrupt cooling of the older dryas to evaluate whether there is a relationship between meltwater injections north atlantic deep water nadw formation and climate change we present a high resolution record of nadw flow intensity from eirik drift through the last deglaciation it indicates only a relatively minor 200 year weakening of nadw flow coincident with mwp 1a our compilation of records also indicates that during heinrich event 1 and the younger dryas there were no discernible sea level rises and yet these periods were characterized by intense nadw slowdowns shutdowns clearly deepwater formation and climate are not simply controlled by the magnitude or rate of meltwater addition instead our results emphasize that the location of meltwater pulses may be more important with nadw formation being particularly sensitive to surface freshening in the arctic nordic seas

age of tilted reefs hawaii submerged carbonate reefs are preserved as a series of submarine terraces between molokai and hawaii along a 200 km span of the southeastern hawaiian ridge limestones from two of the terraces have been sampled from submersibles and dated radiometrically at 13 and 120 ka recognition that the terraces are tilted permits assignment of about a dozen terraces from 150 to 1300 m depth to eight general reef platforms these reefs were drowned by the combined effects of island subsidence and sea level rise at the end of successive glacial stages from 13 to 647 ka the platforms are tilted 5 m km southeast toward the locus of volcanic loading centered on the island of hawaii the end of the active period of volcanic shield building is represented on each nonactive volcano by a submerged change in slope dating of this slope change by reference to the dated reefs provides independent evidence that shield building ended at about the same time that the volcano changed from eruption of tholeiitic to alkalic basalt the variation in depth of the dated tilted reefs along the ridge indicates that the end of subsidence follows the end of shield building by about one half million years the present northwest margin of major subsidence probably crosses southeast maui during the last half million years the rate of southeast migration of the beginning of both subsidence and of tholeiitic volcanism does not appear to have increased however the rate of southeast migration of the end of both subsidence and of tholeiitic volcanism has apparently increased this shortening of the life history of the younger volcanoes implies an increase in eruption rates

a new model of holocene reef initiation and growth in response to sea level rise on the southern great barrier reef the fossil record provides valuable data for improving our understanding of both past and future reef resilience and vulnerability to environmental change the spatial and temporal pattern of the initiation of the holocene great barrier reef presents a case study of reef response to rapid sea level rise past studies have been limited by the lack of well dated and closely spaced reef core transects and have not closely examined the composition of the reef building communities through time this study presents 80 new high precision u sbnd th and 5 radiocarbon ages from twelve new cores located along three transects across different geomorphic and hydrodynamic settings of one tree reef southern great barrier reef to document three distinct stages of holocene reef development in unprecedented detail temporal constraints on changing paleoecological assemblages of coral coralline algae and associated biota revealed three distinct phases of reef development consisting of 1 a fast shallow and clear water reef initiation from 8 2 until 8 ka 2 a shift to slower deeper and more turbid water reef growth from 8 to 7 ka and 3 a return to shallow and rapid branching coral growth in clear water conditions as the reef catches up to sea level a minimum lag prior to reef initiation of 700 years was identified which differs in length depending on reef environment and pleistocene substrate height in this new model reef growth initiated on the topographically lower leeward margin and patch reef prior to the start of windward margin development contrary to the traditional reef growth model while there was a shift to conditions less favorable for reef growth at 8 ka this did not prevent the slow accretion of more sediment tolerant coral communities the majority of the reef reached sea level by 6 ka this new conceptual model of holocene reef growth provides new constraints on changes in paleoenvironment that controlled reef community composition and growth trajectories through sea level rise following inundation

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

sea level constraints on the amplitude and source distribution of meltwater pulse 1a sea level rose rapidly during meltwater pulse 1a about 14 500 years ago a reassessment of sea level rise and isostatic adjustment suggests sea level rose roughly 8 to 15 m in total with 0 to 10 m derived from the antarctic ice sheets

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

land motion estimates from gps at tide gauges a geophysical evaluation summary space geodesy applications have mainly been limited to horizontal deformations due to a number of restrictions on the vertical component accuracy monitoring vertical land motion is nonetheless of crucial interest in observations of long term sea level change or postglacial rebound measurements here we present a global vertical velocity field obtained with more than 200 permanent gps stations most of them colocated with tide gauges tgs we used a state of the art homogeneous processing strategy to ensure that the reference frame was stable throughout the observation period of almost 10 yr we associate realistic uncertainties to our vertical rates taking into account the time correlation noise in the time series the results are compared with two independent geophysical vertical velocity fields 1 vertical velocity estimates using long term tg records and 2 postglacial model predictions from the ice 5g vm2 adjustment the quantitative agreement of the gps vertical velocities with the internal estimates of vertical displacements using the tg record is very good with a mean difference of 0 13 1 64 mm yr 1 on more than 100 sites for 84 per cent of the gps stations considered the vertical velocity is confirmed by the tg estimate to within 2 mm yr 1 the overall agreement with the glacial isostatic adjustment gia model is good with discrepancy patterns related either to a local misfit of the model or to active tectonics for 72 per cent of the sites considered the predictions of the gia model agree with the gps results to within two standard deviations most of the gps velocities showing discrepancies with respect to the predictions of the gia model are however consistent with previously published space geodesy results we in turn confirm the value of 1 8 0 5 mm yr 1 for the 20th century average global sea level rise and conclude that gps is now a robust tool for vertical land motion monitoring which is accurate at least at 1 mm yr 1

images of diagenetic textures in porites corals from papua new guinea and indonesia diagenesis is now recognized as a potentially major source of error in paleoclimatic reconstructions from fossil and modern coral geochemical records key to avoiding spurious results caused by diagenesis is thorough screening of coral material prior to geochemical analysis in this data brief we present color images from thin sections of fossil and modern porites corals and demonstrate the effectiveness of thin sections in detecting low levels of diagenesis the images presented here cover a range of coral preservation levels from pristine aragonite to 100 calcite we particularly focus on samples containing around 1 diagenetic material a level known to create artifacts in key climate parameters such as sea surface temperature and close to the detection limits of other screening methods such as x ray diffraction xrd a qualitative scheme is also presented to rate the degree of diagenesis in a coral where xrd results are not available or where secondary aragonite is present overall this collection of images is designed as a starting point in combination with other techniques to assist in identifying and screening corals for diagenesis

meltwater pulse 1a from antarctica as a trigger of the bolling allerod warm interval meltwater pulse 1a mwp 1a was a prominent feature of the last deglaciation which led to a sea level rise of 20 meters in less than 500 years concurrent with mwp 1a was the onset of the bolling allerod interstadial event 14 600 years before the present which marked the termination of the last glacial period previous studies have been unable to reconcile a warm northern hemisphere with mwp 1a originating from the laurentide or fennoscandian ice sheets with the use of a climate model of intermediate complexity we demonstrate that with mwp 1a originating from the antarctic ice sheet consistent with recent sea level fingerprinting inferences the strength of north atlantic deep water nadw formation increases thereby warming the north atlantic region and providing an explanation for the onset of the bolling allerod warm interval the established mode of active nadw formation is then able to respond to subsequent freshwater forcing from the laurentide and fennoscandian ice sheets setting the stage for the younger dryas cold period the melting of continental ice sheets during the last deglaciation provided a freshwater source to the ocean that affected global sea level and the strength of the thermohaline circulation an exceptionally large melting event inferred from far field relative sea level records occurred

hydrocarbon geochemistry of the puget sound region ii sedimentary diterpenoid steroid and triterpenoid hydrocarbons cyclic components of the aliphatic hydrocarbon mixtures extracted from puget sound sediment cores include a suite of c19 and c20 diterpenoid hydrocarbons of which fichtelite sandaracopimaradiene and isopimaradiene have been identified although apparently also derived from vascular plants these diterpenoid hydrocarbons have relative abundances distinctly different from the co existing plant wax n alkane suite five c27 c28 and c29 diasteranes and four c29 c30 and c31 17 h 21 h hopanes occur in relatively constant proportion as components of a highly weathered fossil hydrocarbon assemblage these chromatographically resolved cycloalkanes along with the strongly covarying unresolved complex mixture have been introduced to puget sound sediments from adjacent urban centres at increasing levels over the last 100 yr in the absence of any major oil spill naturally occurring triterpenoid hydrocarbons including hop 22 29 ene diploptene are also present a new group of c30 polyenes has been detected which contains compounds apparently structurally related to a co existing bicyclic c25 diene and to c20 and c25 acyclic multibranched hydrocarbons described in a previous paper barrick et al 1980

morphology and evolution of drowned carbonate terraces during the last two interglacial cycles off hilo ne hawaii abstract the eastern side of hawaii island is a rapidly subsiding margin dominated by drowned carbonate platforms we present detailed bathymetric and backscatter data remotely operated vehicle and submersible observations sedimentological and 14c accelerator mass spectrometry and u th age data from seven submerged terraces h7 h2a d h1a b in water depths between 1100 and 25 m off hilo north eastern hawaii the main carbonate deposits on these terraces are coral deposits rhodolith beds coralline algal mounds crusts pavements and tabular sheets we identified five previously described sedimentary shallow to deep water facies and one new facies type that are consistent with reef drowning on a rapidly subsiding margin we used palaeobathymetric data derived from the sedimentary facies age versus depth relationships and published sea level curves to estimate a uniform long term subsidence rate of 2 80 0 36 m ky for the eastern side of hawaii over the last 150 ky terrace h7 developed about 380 ka based on data from the western side of the island active coral growth on terrace h2d occurred during the marine isotope stage mis 6 to 5 transition and the terrace drowned during the peak of mis 5e when sea level rose faster than reefs could grow favoured by the gentle platform gradient reefs established progressively landwards with a backstepping pattern during mis 5e to form the terraces h2c and h2b 122 ka final turn off of shallow water carbonate production on terraces h2b d coincided with the relative sea level rise of the interstadial mis 5a bathymetry and submersible data suggest that carbonate sediments on terraces h2a and h1b were deposited over an antecedent topography of local lava deltas emplaced during rising sea levels at ca 85 and 65 ka while terrace h1a established on lava delta substrates of the mauna loa volcano ca 11 ka we conclude that the initiation growth and drowning of coral reef terraces off hilo differ in some ways from the pattern observed in the submerged terraces in the western side of hawaii and that the platform evolution off hilo is more strongly influenced by emplacement of offshore lava flows

reef drowning during the last deglaciation evidence for catastrophic sea level rise and ice sheet collapse elevations and ages of drowned acropora palmata reefs from the caribbean atlantic region document three catastrophic metre scale sea level rise events during the last deglaciation these catastrophic rises were synchronous with 1 collapse of the laurentide and antarctic ice sheets 2 dramatic reorganization of ocean atmosphere circulation and 3 releases of huge volumes of subglacial and proglacial meltwater this correlation suggests that release of stored meltwater periodically destabilized ice sheets causing them to collapse and send huge fleets of icebergs into the atlantic massive inputs of ice not only produced catastrophic sea level rise drowning reefs and destabilizing other ice sheets but also rapidly reduced the elevation of the laurentide ice sheet flipping atmospheric circulation patterns and forcing warm equatorial waters into the frigid north atlantic such dramatic evidence of catastrophic climate and sea level change during deglaciation has potentially disastrous implications for the future especially as the stability of remaining ice sheets such as in west antarctica is in question

geochemistry of halogens in the milk river aquifer alberta canada abstract analytical data are presented for cl br and i on a regional scale for the milk river aquifer the three halides show strikingly similar spatial distributions and are highly correlated concentrations are low in the freshwater portions of the aquifer but increase by as much as two orders of magnitude along the margins however halide ratios reach nearly constant values moving down gradient suggesting the dominance of a common subsurface source for these ions ratios of cl i and cl br are less than those of seawater and fit an origin derived from the diagenesis of organic matter in the sediments halide ratios rule out leakage and or diffusion from the underlying colorado group as a major influence on the chemistry the favored hypothesis is altered connate seawater diffusing from low permeability units within the milk river formation as the primary source of salts this hypothesis of an internal source has important implications for solute sources in other aquifers affected by saline waters because it does not require the importation of a distant fluid the129i i ratio has a meteoric value in groundwater collected near the recharge area but ratios for downflow waters are only 8 70 of this value due to the 16 ma half life of129i these data indicate that most of the increase in dissolved i cannot derive from concentration of a meteoric source by ion filtration but must have a subsurface origin concentrations of129i producedin situ by spontaneous fission of238u attain measurable levels only in the oldest waters sampled ages 105a in which it may account for nearly 90 of the total dissolved129i concentration water ages based upon36cl cl data range up to 2 ma if uncorrected for any dilution by subsurface sources of dead cl if one assumes that the subsurface contributions of cl contribute at least 90 of total cl in the distal portion then the36cl based ages are reduced to 1ma somewhat greater than those estimated by hydrodynamic modeling

collapse of the north american ice saddle 14 500 years ago caused widespread cooling and reduced ocean overturning circulation collapse of ice sheets can cause significant sea level rise and widespread climate change we examine the climatic response to meltwater generated by the collapse of the cordilleran laurentide ice saddle north america 14 5 thousand years ago ka using a high resolution drainage model coupled to an ocean atmosphere vegetation general circulation model equivalent to 7 26 m global mean sea level rise in 340 years the meltwater caused a 6 sverdrup weakening of atlantic meridional overturning circulation amoc and widespread northern hemisphere cooling of 1 5 c the greatest cooling is in the atlantic sector high latitudes during boreal winter by 5 10 c but there is also strong summer warming of 1 3 c over eastern north america following recent suggestions that the saddle collapse was triggered by the bolling warming event at 14 7 14 5 ka we conclude that this robust submillennial mechanism may have initiated the end of the warming and or the older dryas cooling through a forced amoc weakening

rates of iodine remineralization in terrigenous near shore sediments much of the sedimentary geochemistry of iodine has been surmised from analyses of solid phase distributions without direct documentation of reactions or reaction rates it is shown here that the anoxic production rate of dissolved i in nearshore terrigenous sediments decreases rapidly below the sediment water interface and is strongly temperature controlled an apparent activation energy of 19 3 kcal mole comparable to that found for other microbially mediated reactions describes the temperature dependence of release production of dissolved iodide is zeroth order with respect to natural ranges of pore water concentrations and apparently first order with respect to a reactive i component in the solid phase first order reaction coefficients in sediments from mud bay south carolina and long island sound connecticut u s a are strongly depth dependent varying from 6 9 yr in the top few centimeters to an average of 0 011 yr over the upper 70 cm about 90 of the dissolved i flux comes from the top 10 cm with estimated values of 15 and 29 moles m2 day at 22 23 c in mud bay and long island sound respectively the i c net release ratio of decomposing material changes rapidly below the sediment surface when temperature corrections are made i remineralization rates from nearshore sediments below the bioturbated zone appear to be similar to those observed in deep water sediments underlying oxygenated waters

crustal subsidence rate off hawaii determined from 234u 238u ages of drowned coral reefs a series of submerged coral reefs off northwestern hawaii was formed during largely glacial intervals when the rate of local sea level rise was less than the maximum upward growth rate of the reefs mass spectrometric sup 234 u sup 238 u ages for samples from six such reefs range from 17 to 475 ka and indicate that this part of the hawaiian ridge has been subsiding at a roughly uniform rate of 2 6 mm yr for the past 475 ka the sup 234 u sup 238 u ages are in general agreement with model ages of reef drowning based on estimates of paleo sea level stands derived from oxygen isotope ratios of deep sea sediments but there are disagreements in detail the high attainable precision plus minus 10 ka or better on samples younger than approximately 800 ka large applicable age range relative robustness against open system behavior and ease of analysis for this technique hold great promise for future applications of dating of 50 1 000 ka coral

determination of source ages and migration patterns of brines from the u s gulf coast basin using 129i abstract the long lived cosmogenic and fissiogenic isotope 129i has been applied to the study of source ages and migration patterns of oil field brines from the u s gulf coast basin 129 i i ratios were measured in sixty samples of saline formation water from depths of 660 4503 m in several oil fields in southeast texas south central louisiana and offshore louisiana comparisons between measured ratios and the decay curve for surface hydrospheric 129i result in minimum source ages much older than present host formation ages indicating vertical migration of brine from older deeper sources conservative corrections for a fissiogenic component due to spontaneous fission of 238u in the subsurface result in the following median source ages iberia field 55 ma port barre field 53 ma and eugene island blocks 316 and 330 55 ma pointing to wilcox group shales as source formations mesozoic sources cannot be ruled out due to the uncertainties in estimating the fissiogenic component some of the ratios measured in texas gulf coast brines show evidence of a greater fissiogenic component which indicates that the brines have resided in formations with locally high u concentrations

palaeoenvironmental records from fossil corals the effects of submarine diagenesis on temperature and climate estimates the geochemistry of coral skeletons may reflect seawater conditions at the time of deposition and the analysis of fossil skeletons offers a method to reconstruct past climate however the precipitation of cements in the primary coral skeleton during diagenesis may significantly affect bulk skeletal geochemistry we used secondary ion mass spectrometry sims to measure sr mg b u and ba concentrations in primary coral aragonite and aragonite and calcite cements in fossil porites corals from submerged reefs around the hawaiian islands cement and primary coral geochemistry were significantly different in all corals we estimate the effects of cement inclusion on climate estimates from drilled coral samples which combine cements and primary coral aragonite secondary 1 calcite or not vert similar2 aragonite cement contamination significantly affects sr ca sst estimates by 1 c and 0 4 to 0 9 c respectively cement inclusion also significantly affects mg ca b ca and u ca sst estimates in some corals x ray diffraction xrd will not detect secondary aragonite cements and significant calcite contamination may be below the limit of detection not vert similar1 of the technique thorough petrographic examination of fossils is therefore essential to confirm that they are pristine before bulk drilled samples are analysed to confirm that the geochemistry of the original coral structures is not affected by the precipitation of cements in adjacent pore spaces we analysed the primary coral aragonite in cemented and uncemented areas of the skeleton sr ca b ca and u ca of primary coral aragonite is not affected by the presence of cements in adjacent interskeletal pore spaces i e the coral structures maintain their original composition and selective sims analysis of these structures offers a route to the reconstruction of accurate ssts from altered coral skeletons however mg ca and ba ca of primary coral aragonite are significantly higher in parts of skeletons infilled with high mg calcite cement we hypothesise this reflects cement infilling of intraskeletal pore spaces in the primary coral structure

mechanical models of the 1975 kalapana hawaii earthquake and tsunami abstract our objective is to produce a mechanically realistic model for the 1975 kalapana event that explains the overall deformation and geological evolution of the south flank of kilauea and reproduces most known earthquake and tsunami observations to do this we present a new structural interpretation of geological data from kilauea along with modeling of the tsunami using recent seismic analyses in so doing we hypothesize an offshore north facing normal fault that we call the kalapana fault because of its limited onshore expression near kalapana we argue that several different interpretations of seismic data are simultaneously true each coinciding with a specific geological structure we perform a direct numerical simulation of the 1975 kalapana tsunami and we report results for the near field and the far field simultaneously our interpretation of geological structures provides sufficient constraints to derive three tsunami sources the kalapana fault a slump and a thrust fault these three tsunami sources are mechanically coupled according to our model of kilauea evolution although their contributions to tsunami generation remain relatively distinct slump displacement predicts a small shear stress beneath kilauea volcano we find that our geological interpretation and tsunami sources are sufficiently robust to reproduce almost all tsunami observations repeated earthquakes like the 1975 kalapana event will produce extension and subsidence in the upper flank of kilauea as well as compression and uplift of the toe region accompanied by limited slump movement these deformations appear to stabilize kilauea and make catastrophic failure of the volcano flank less likely at this time

the influence of humic substances on the geochemistry of iodine in nearshore and hemipelagic marine sediments iodine is characteristically enriched at the surface of hemipelagic and nearshore sediments deposited under oxygenated conditions in such sediments bulk i corg ratios usually decrease with depth to values which are characteristic of anoxic sediments reflecting a preferential release of i during early diagenesis there is some debate as to whether sedimentary i is associated with the iron oxyhydroxide phase or with the organic fraction and whether the decrease in i corg with depth is due to the dissolution of the iron oxyhydroxides or the decomposition of labile organic matter it is shown that in a surficial hemipelagic sediment sample and in a nearshore sediment core i is mainly associated with the organic fraction and moreover that humic substances are involved in the surficial iodine enrichment laboratory experiments on the uptake and release of i by and from sedimentary humic substances also suggest a mechanism whereby humic materials reduce iodate at the sediment water interface to an electrophilic i species which further reacts with the organic matter to produce iodinated organic molecules during burial this excess i could be displaced from the organic matrix by nucleophiles such as sulphide ions or thiosulphate thus providing a possible explanation for the decrease in i corg ratio with depth observed in many nearshore and hemipelagic sediments

abrupt bolling warming and ice saddle collapse contributions to the meltwater pulse 1a rapid sea level rise elucidating the source s of meltwater pulse 1a the largest rapid sea level rise caused by ice melt 14 18 m in less than 340 years 14 600 years ago is important for understanding mechanisms of rapid ice melt and the links with abrupt climate change here we quantify how much and by what mechanisms the north american ice sheet could have contributed to meltwater pulse 1a by driving an ice sheet model with two transient climate simulations of the last 21 000 years ice sheet perturbed physics ensembles were run to account for model uncertainties constraining ice extent and volume with reconstructions of 21 000 years ago to present we determine that the north american ice sheet produced 3 4 m global mean sea level rise in 340 years due to the abrupt bolling warming but this response is amplified to 5 6 m when it triggers the ice sheet saddle collapse

the 40ar 39ar dating of core recovered by the hawaii scientific drilling project phase 2 hilo hawaii 1 the hawaii scientific drilling project phase 2 hsdp 2 recovered core from a 3 1 km thick section through the eastern flanks of mauna loa and mauna kea volcanoes we report results of 40ar 39ar incremental heating by broad beam infrared laser of 16 basaltic groundmass samples and 1 plagioclase separate mostly from k poor tholeiites the tholeiites generally have mean radiogenic 40ar enrichments of 1 3 and some contain excess 40ar however isochron ages of glass poor samples preserve stratigraphic order in all cases a 246 m thick sequence of mauna loa tholeiitic lavas yields an isochron age of 122 86 kyr all errors 2 at its base beneath the mauna loa overlap sequence lie mauna kea s postshield and shield sequences a postshield alkalic lava yields an age of 236 16 kyr in agreement with an age of 240 14 kyr for a geochemically correlative flow in the nearby hsdp 1 core hole where more complete dating of the postshield sequence shows it to have accumulated at 0 9 0 4 m kyr from about 330 to 200 ka mauna kea s shield consists of subaerial tholeiitic flows to a depth of 1079 m below sea level then shallow submarine flows hyaloclastites pillow lavas and minor intrusions to core bottom at 3098 m most subaerial tholeiitic flows fail to form isochrons however a sample at 984 m yields an age of 370 180 kyr consistent with ages from similar levels in hsdp 1 submarine tholeiites including shallow marine vitrophyres clasts from hyaloclastites and pillow lavas were analyzed however only pillow lava cores from 2243 2614 and 2789 m yield reliable ages of 482 67 560 150 and 683 82 kyr respectively a linear fit to ages for shield samples defines a mean accumulation rate of 8 6 3 1 m kyr and extrapolates to 635 kyr at core bottom alternatively a model relating mauna kea s growth to transport across the hawaiian hot spot that predicts downward accelerating accumulation rates that reach 20 m kyr at core bottom depaolo and stolper 1996 is also consistent with all reliable ages except the deepest

isostatic consequences of giant landslides on the hawaiian ridge giant landslides like melting glaciers lead to a redistribution of mass which will have isostatic consequences three dimensional numerical modeling experiments were devised to examine how this mass redistribution affects the isostatic flexural curve a debris avalanche of 10 40 of pre slide oahu is required to account for the 1200 5000 km3 nuuanu deposit while only 1 of pre slide hawaii island is necessary to generate the 200 800 km3 alika i and ii avalanche deposits trials were run using 25 30 and 40 km elastic plate thicknesses t e the island uplift resulting from the nuuanu slide was calculated to be 23 m and 109 m for 10 and 40 volume slides respectively both using t e 25 km a rebound of 10 m and 49 m was calculated for the same volumes respectively using t e 40 km a greater amount of uplift is expressed direct lyover the failed flank causing the edifice to tilt away from the calved off portion the landslide deposit depresses the plate several meters beneath the debris field itself smaller slides e g alika i and ii do not produce as much flexural response with 17 m and 7 m uplift for t e 25 and 40 km respectively the effects of slow moving intact slumps where the failed blocks remain relatively close to the island pedestal were examined for the case of the hilina slump making up approximately 10 of the hawaii island edifice perhaps more significant than the uplift for the hilina slump comparable to that for the 10 nuuanu debris avalanche is the 114 m and 56 m of downwarp beneath its massive slumped foot t e 25 and 40 km respectively the landslide rebound process in the case of a relatively large landslide should be considered as an added component to the evolutionary course of oceanic islands

dominant influence of volcanic loading on vertical motions of the hawaiian islands abstract rates of island vertical motion above intra plate hotspots record the processes that arise from interactions between lithospheric plates and mantle plumes to assess the contribution of mantle and lithospheric processes to surface motion above the hawaiian hotspot we compare simple models of lithospheric deformation to vertical motion rates measured from dated paleoshorelines and tide gauge records in the hawaiian islands our analysis shows that observed uplift and subsidence rates mainly record the flexural response of the lithosphere to volcanic loads the effective elastic plate thickness that best fits the spatial distribution of subsidence and uplift rates is 40 km consistent with previous estimates based on total vertical deflection because volcanic loading dominates the vertical motion signal hawaiian islands appear to follow a predictable trajectory of vertical motion when they reside within one flexural half wavelength of the active volcanic center islands initially subside at rapid and decreasing rates in the first 1 myr following their construction uplift relatively slowly 1 2 5 myr following their construction and eventually subside again but at slow rates within 5 myr of their construction this observed pattern of uplift and subsidence is consistent with the pattern of vertical motion predicted to result from volcanic loading at the hawaiian hotspot lithospheric migration over the long wavelength topographic swell associated with the hawaiian hotspot has a comparatively minor influence on island uplift and subsidence its contribution to island vertical motion is not readily observed in our data with the possible exception of some uplift observed in the past 500 kyr on o ahu that might correspond to non steady state behavior of the hawaiian plume

129i in gulf of mexico waters abstract nuclear weaponry and power generation have released far more 129 i onto the earth s surface than was formerly present the effects of this release are clearly visible in the waters of the gulf of mexico far from the major sources new 129 i is found down to at least 500 m and probably to 1000 m surface values are approximately 60 times the pre nuclear era levels the 129 i penetration depth of 470 m agrees well with that determined from bomb fallout isotopes 3 h and 14 c during the 1970s and 1980s in the gulf of mexico and in the western north atlantic at similar latitudes the observed levels exceed amounts expected from globally distributed nuclear test fallout the observed surplus must come primarily from spent fuel reprocessing plants in the eastern north atlantic followed by rapid circulation of the north atlantic gyre and subsequent delivery into the caribbean sea and thence into the gulf of mexico airborne transport also appears significant

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

dynamic surface topography a new interpretation based upon mantle flow models derived from seismic tomography the very long wavelength i e in the degree range l 1 8 dynamic topography at the earth s surface estimated by isostatic reduction of the observed topography is shown to be in good agreement with the topography predicted by a model of viscous flow in the mantle this flow model was previously derived by independent consideration of the observed nonhydrostatic geoid and is based upon a recent model of large scale seismic shear velocity heterogeneity in the mantle our estimate and prediction of the long wavelength dynamic surface topography reveals significant depressions 2 3 km of the continental shields relative to their hydrostatic reference positions

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

ice sheet and solid earth influences on far field sea level histories previous predictions of sea level change subsequent to the last glacial maximum show significant systematic discrepancies between observations at tahiti huon peninsula and sunda shelf during lateglacial time 14 000 to 9000 calibrated years before the present we demonstrate that a model of glacial isostatic adjustment characterized by both a high viscosity lower mantle 4 1022 pa s and a large contribution from the antarctic ice sheet to meltwater pulse ia 15 meters eustatic equivalent resolves these discrepancies this result supports arguments that an early and rapid antarctic deglaciation contributed to a sequence of climatic events that ended the most recent glacial period of the current ice age

critical depth for the survival of coral islands effects on the hawaiian archipelago coral islands drown when sea level rise exceeds the maximum potential of coral reefs to grow upward about 10 millimeters per year during the holocene transgression 18 000 years ago to present sea levels rose at rates of up to 10 to 20 millimeters per year and most coral island reefs situated deeper than a critical depth of30 to 40 meters below present day sea level drowned coral islands that did not drown during the holocene transgression apparently all developed on antecedent foundations shallower than critical depth during low stands in sea level during the pleistocene these islands were elevated and subject to subaerial erosion today in the hawaiian archipelago the depth of drowned banks is inversely related to summit area smaller banks are progressively deeper evidently because of erosional truncation during low sea level stands bank summit area may therefore be an important factor determining the failure or success of coral islands

drowned reefs as indicators of the rate of subsidence of the island of hawaii a major submerged terrace whose seaward edge is at about 150 m depth was investigated in 1983 during 10 dives with the hawaii undersea research laboratory hurl submersible makali i off kealakekua bay hawaii the seaward termination of the terrace is a steep wall of reef limestone that extends from 150 to 250 m below sea level three samples of limestone collected from the reef face at depths of 204 219 m yield a weighted average 14 c age of 13 250 s d 380 years before present the 150 m terrace as well as two deeper terraces off northwestern hawaii at depths of 390 pm 50 m and 580 pm 40 m apparently were formed by the interaction of glacioeustatic sea level changes and island subsidence the best fit of depth age and subsidence data indicates that the northwestern coast of hawaii has subsided at an absolute rate of 1 8 to 3 mm yr and that the rate of subsidence has generally increased over the past 0 3 m y each reef terrace grew intermittently for nearly 0 1 m y the 150 m reef ter

a large drop in atmospheric 14c 12c and reduced melting in the younger dryas documented with 230th ages of corals paired carbon 14 14 c and thorium 230 230 th ages were determined on fossil corals from the huon peninsula papua new guinea the ages were used to calibrate part of the 14 c time scale and to estimate rates of sea level rise during the last deglaciation an abrupt offset between the 14 c and 230 th ages suggests that the atmospheric 14 c 12 c ratio dropped by 15 percent during the latter part of and after the younger dryas yd this prominent drop coincides with greatly reduced rates of sea level rise reduction of melting because of cooler conditions during the yd may have caused an increase in the rate of ocean ventilation which caused the atmospheric 14 c 12 c ratio to fall the record of sea level rise also shows that globally averaged rates of melting were relatively high at the beginning of the yd thus these measurements satisfy one of the conditions required by the hypothesis that the diversion of meltwater from the mississippi to the st lawrence river triggered the yd event

coastal erosion rates of lava deltas around oceanic islands abstract rates of coastal erosion are needed for planning purposes and to improve understanding of how the shelves of islands develop ultimately becoming submerged banks near shore submarine platforms created by erosion of lava deltas of known age provide an opportunity to quantify erosion rates and to investigate how those rates vary between different types and ages of lava flows as well as how they vary with wave climate we have compiled data on deltas formed during historical and holocene eruptions age 6 ka from both a and p hoehoe lava flows and from diverse localities azores and hawaiian islands and ascension island near shore platforms were interpreted from multibeam sonar bathymetric light detection and ranging lidar and historical sounding data from them we estimated time averaged shoreline retreat rates from the seaward distances between the modern coastlines and the submarine platform edges the 35 interpreted platforms have rugged dipping surfaces left behind by erosion with an average gradient of 5 range 2 10 eroded distance of 436 m 78 1119 m and depth of platform edge of 25 m 5 56 m to evaluate the latter depths we computed seabed orbital speeds due to surface waves at the platform edges depths of platform edges correlate only modestly with those speeds suggesting that platform surfaces have adjusted to wave conditions with a wide range of particle sizes and hence thresholds of motion the largest retreat distances 800 m are associated with platforms of the central azores islands which are exposed to higher waves however retreat rates are highly varied 0 08 12 5 m yr and weakly correlated with measures of wave power suggesting that waves are only a secondary influence given that lack of correlation we suspect that the main factor contributing to variability arises from varied cliff resistance to erosion blocks between joints in lava flows and hence resistance to erosion vary greatly in size from the thicker and less densely jointed a flows to the thinner and shell like layered lavas in p hoehoe flows

foredeep tectonics and carbonate platform dynamics in the huon gulf papua new guinea hawaii mr1 side scan sonar and six channel seismic reflection data reveal a history of carbonate platform growth drowning and back stepping in the huon gulf papua new guinea this is one of the few modern sites where active carbonate platform development and foredeep subsidence are linked 230 th methods date aragonitic shallow water corals recovered from a modern depth of 2000 m at 348 10 ka this documents rapid subsidence of the huon gulf in response to the encroaching finisterre mountains at an average rate of 5 7 mm yr for the past 348 k y the highest subsidence rate reported from any foredeep setting carbonate deposition has moved toward the foreland at an average rate of 110 mm yr over the same period comparisons of the measured age with sea level history derived from the oxygen isotope record suggest that the reefs may have formed during sea level lowstands and drowned during rapid rates of sea level rise

new evidence of hawaiian coral reef drowning in response to meltwater pulse 1a abstract fossil coral reefs are valuable recorders of glacio eustatic sea level changes as they provide key temporal information on deglacial meltwater pulses mwps the timing rate magnitude and meltwater source of these sea level episodes remain controversial despite their importance for understanding ocean ice sheet dynamics during periods of abrupt climatic change this study revisits the west coast of the big island of hawaii to investigate the timing of the 150 m h1d terrace drowning off kawaihae in response to mwp 1a we present eight new calibrated 14c ams ages which constrain the timing of terrace drowning to at or after 14 75 0 33 0 42 kyr bp coeval with the age of reef drowning at kealakekua bay u th age 14 72 0 10 kyr bp 70 kms south along the west coast integrating the chronology with high resolution bathymetry and backscatter data detailed sedimentological analysis and paleoenvironmental interpretation we conclude the h1d terrace drowned at the same time along the west coast of hawaii in response to mwp 1a the timing of h1d reef drowning is within the reported uncertainty of the timing of mwp 1a interpreted from the iodp expedition 310 tahitian reef record

variations in 129i 127i ratios in recent marine sediments evidence for a fossil organic component abstract the value of the pre bomb 129 i 127 i ratio in the hydrosphere is important for the use of this isotope system for dating and tracing purposes in order to determine this value and to examine spatial variability 129 i 127 i ratios were measured in 25 sediment samples from five cores taken at geographically distinct coastal areas the results indicate a pre anthropogenic 129 i 127 i ratio of 1500 10 15 in good agreement with values derived from previous sediment and groundwater studies results from shallow sediments show that the layer of bioturbation is dominated by the addition of anthropogenic 129 i the good agreement between results for this layer from different cores supports the understanding that marine iodine is isotopically homogeneous and associated with organic material which is actively remineralized at the sediment water interface lower ratios down to 354 10 15 corresponding to an age of 32 5 ma and larger variations than expected were found in sections of the cores below the layer of bioturbation these observations can be explained by the presence of refractory fossil organic material transported by rivers to the sediments from uplifted continental shales the results suggest that marine iodine is present in two forms a labile component which is isotopically homogeneous and a refractory component which is associated with kerogen or other fossil organic compounds whose 129 i 127 i ratio reflects the age of these compounds 129 i 127 i ratios can be used to identify and date fossil organic material in recent sediments the presence of which can alter the assumptions underlying models of the global carbon cycle

continuous record of reef growth over the past 14 k y on the mid pacific island of tahiti two boreholes were drilled through coralgal sequences in the barrier reef edge of the mid pacific island of tahiti and their bases were radiometrically dated at 10 23 0 05 and 13 77 0 05 ka thousand calendar years the sequences are composed mainly of the reef edge acropora gr danai robusta and hydrolithon onkodes assemblage occasionally replaced by reef slope tabular acropora neogoniolithon or domal porites lithophyllum assemblages the response of reef growth to sea level rise has varied according to the framework type and vertical accretion rates have ranged from 9 3 to 20 6 mm yr 1 from a general trend of long term continuous sea level rise tracked by growth the reef edge coralgal assemblages have experienced two distinct changes controlled by the antecedent paleotopography and internal reef processes during the past 13 8 k y at tahiti there is no evidence of any reef drowning event primarily caused by global glacio eustatic perturbations as has been recorded in the caribbean

coastal lava flows from mauna loa and hualalai volcanoes kona hawaii a major carbonate reef which drowned 13 ka is now submerged 150 m below sea level on the west coast of the island of hawaii a 25 km span of this reef was investigated using the submersiblemakali i the reef occurs on the flanks of two active volcanoes mauna loa and hualalai and the lavas from both volcanoes both underlie and overlie the submerged reef most of the basaltic lava flows that crossed the reef did so when the water was much shallower and when they had to flow a shorter distance from shoreline to reef face lava flows on top of the reef have protected it from erosion and solution and now occur at seaward projecting salients on the reef face these relations suggest that the reef has retreated shoreward as much as 50 m since it formed a 7 km wide shadow zone occurs where no hualalai lava flows cross the reef south of kailua these lava flows were probably diverted around a large summit cone complex a similar shadow zone on the flank of mauna loa volcano in the kealakekua bay region is downslope from the present mauna loa caldera which ponds mauna loa lava and prevents it from reaching the coastline south of the mauna loa shadow zone the 150 m reef has been totally covered and obscured by mauna loa lava the boundary between hualalai and mauna loa lava on land occurs over a 6 km wide zone whereas flows crossing the 150 m reef show a sharper boundary offshore from the north side of the subaerial transition zone this indicates that since the formation of the reef hualalai lava has migrated south mantling mauna loa lava more recently mauna loa lava is again encroaching north on hualalai lava

discovery of a submerged relic reef and shoreline off grand cayman further support for an early holocene jump in sea level abstract drilling close to the base of a submerged sea cliff on the terraced eastern shelf of grand cayman has revealed a relic acropora palmata reef at a depth of 21 m below msl ten cores from its crest are principally composed of cobble sized clasts of a palmata set in a matrix of cemented skeletal grainstone the clasts have a distinctive succession of encrusters that indicate rapid burial a photophilic association of crustose coralline algae foraminifera and vermetid gastropods superimposed by a cryptic association of sclerosponges foraminifera and serpulids in addition to rapid burial u th thermal ionization mass spectrometer tims dating of coral clasts within 1 m of the relic reef surface indicates minor temporal mixing with ages between 8 9 and 8 1 ka such mixing and rapid burial is consistent with a hurricane deposit and is identical to deposits found on the crests of modern reefs in relation to its age the preservation of a 18 5 m intertidal notch cut into the submerged sea cliff on the western shelf of grand cayman implies that the crest of the relic reef has been lowered 1 5 2 m by marine abrasion bioerosion at a rate of 0 25 mm yr 1 reconstructing this eroded section using average holocene accretion rates indicates that the reef likely ceased accreting at 7 6 ka at a depth of 19 m comparing these data with other relic reefs in the caribbean indicates that the relic reef on grand cayman died within 160 years of relic reefs on barbados st croix st thomas and north florida this narrow interval of reef demise also coincides with the time when modern reefs were establishing themselves some 4 9 m higher upslope a fact that can only be resolved by invoking a rapid 6 m jump in sea level 7 5 ka ago such a jump would also account for two unexplained events around this time the restricted interval of global delta initiation and the catastrophic flooding of the glacially lowered black sea

reef growth and volcanism on the submarine southwest rift zone of mauna loa hawaii a marine sampling program utilizing the pisces 5 submersible operated by the hawaii undersea research laboratory noaa has confirmed the presence of a major submerged coral reef offshore from ka lae south point hawaii the top of the reef is now 150 160 m below sea level radiocarbon and useries dating indicates that it drowned about 13 9 ka by the combined effects of island subsidence 2 5 mm year and the rapid rise of sea level at the end of the last glaciation so that the relative submergence rate of more than 10 mm year exceeded the upward growth rate of the reef the submerged reef caps the offshore part of the southwest rift zone ridge of mauna loa which has apparently undergone little volcanic activity offshore since 170 ka and possibly since 270 ka this fact suggests that rift zone activity is becoming increasingly restricted toward the upper part of the volcano a condition possibly heralding the end of the shield building stage

radiocarbon calibration curve spanning 0 to 50 000 years bp based on paired 230 th 234 u 238 u and 14 c dates on pristine corals abstract radiocarbon dating is the most widely used dating technique in the world recent advances in accelerator mass spectrometry ams and sample preparation techniques have reduced the sample size requirements by a factor of 1000 and decreased the measurement time from weeks to minutes today it is estimated that more than 90 percent of all measurements made on accelerator mass spectrometers are for radiocarbon age dates the production of 14 c in the atmosphere varies through time due to changes in the earth s geomagnetic field intensity and in its concentration which is regulated by the carbon cycle as a result of these two variables a radiocarbon age is not equivalent to a calendar age four decades of joint research by the dendrochronology and radiocarbon communities have produced a radiocarbon calibration data set of remarkable precision and accuracy extending from the present to approximately 12 000 calendar years before present this paper presents high precision paired 230 th 234 u 238 u and 14 c age determinations on pristine coral samples that enable us to extend the radiocarbon calibration curve from 12 000 to 50 000 years before present we developed a statistical model to properly estimate sample age conversion from radiocarbon years to calendar years taking full account of combined errors in input ages and calibration uncertainties our radiocarbon calibration program is publicly accessible at http www radiocarbon ldeo columbia edu along with full documentation of the samples data and our statistical calibration model

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

prodigious submarine landslides on the hawaiian ridge the extensive area covered by major submarine mass wasting deposits on or near the hawaiian ridge has been delimited by systematic mapping of the hawaiian exclusive economic zone using the side looking sonar system gloria these surveys show that slumps and debris avalanche deposits are exposed over about 100 000 km2 of the ridge and adjacent seafloor from kauai to hawaii covering an area more than 5 times the land area of the islands some of the individual debris avalanches are more than 200 km long and about 5000 km3 in volume ranking them among the largest on earth the slope failures that produce these deposits begin early in the history of individual volcanoes when they are small submarine seamounts culminate near the end of subaerial shield building and apparently continue long after dormancy consequently landslide debris is an important element in the internal structure of the volcanoes the dynamic behavior of the volcanoes can be modulated by slope failure and the structural features of the landslides are related to elements of the volcanoes including rift zones and fault systems the landslides are of two general types slumps and debris avalanches the slumps are slow moving wide up to 110 km and thick about 10 km with transverse blocky ridges and steep toes the debris avalanches are fast moving long up to 230 km compared to width and thinner 0 05 2 km they commonly have a well defined amphitheater at their head and hummocky terrain in the lower part oceanic disturbance caused by rapid emplacement of debris avalanches may have produced high level wave deposits such as the 365 m elevation hulopoe gravel on lanai that are found on several islands most present day submarine canyons were originally carved subaerially in the upper parts of debris avalanches subaerial canyon cutting was apparently promoted by the recently steepened and stripped slopes of the landslide amphitheaters

rapid sea level fall and deep ocean temperature change since the last interglacial period we have dated huon peninsula papua new guinea and barbados corals that formed at times since the last interglacial period applying both 230 th and 231 pa dating techniques as a test of age accuracy we show that marine isotope stage mis 5e ended prior to 113 1 8 0 7 kyr when sea level was 319 m during mis 5b sea level was 357 m at 92 6 8 0 5 kyr having dropped about 40 m in approximately 10 kyr during the mis 5c 5b transition sea level then rose more than 40 m during the mis 5b 5a transition also in about 10 kyr mis 5a lasted until at least 76 2 8 0 4 kyr at a level of 324 m at that time combined with earlier data that places mis 4 sea level at 381 m at 70 8 kyr our late mis 5a data indicate that sea level fell almost 60 m in less than 6 kyr 10 6 m kyr during the mis 5 4 transition the magnitude of the drop is half that of the glacial interglacial amplitude and approximatelyequivalent to the volume of the present dayantarctic ice sheet during this interval the minimum average rate of net continental ice accumulation was 18 cm yr likely facilitated by efficient moisture transport from lower latitudes at three specific times 60 6 8 0 3 50 8 8 0 3 and 36 8 0 2 kyr during mis 3 sea level was between 385 and 374 m sea level then dropped to 3107 m at 23 7 8 0 1 kyr early in mis 2 before dropping further to last glacial maximum lgm values and then rising to present values during the last deglaciation times of rapid sea level drop correspond to times of high winter insolation at low northern latitudes and high winter latitudinal gradients in northern hemisphere insolation supporting the idea that these factors mayhave resulted in high water vapor pressure in moisture sources and efficient moisture transport to high latitude glaciers therebycontributing to glacial buildup we combined our sea level results with deep sea n 18 o records as a means of estimating the temperature and ice volume components in the marine n 18 o record this analysis confirms large deep ocean temperature shifts following mis 5e and during termination i deep ocean temperatures changed bymuch smaller amounts between mis 5c and 2 maximum temperature shift in the deep pacific is about 2 whereas the shift at a site in the atlantic is 4 under glacial conditions temperatures at both sites are near the freezing point the shift in the atlantic is likelycaused bya combination of changing proportions of northern and southern source waters as well as changing temperature at the sites where these deep waters form

holocene reef accretion southwest molokai hawaii u s a abstract two reef systems off south molokai hale o lono and hikauhi separated by only 10 km show strong and fundamental differences in modern ecosystem structure and holocene accretion history that reflect the influence of wave induced near bed shear stresses on reef development in hawaii both sites are exposed to similar impacts from south kona and trade wind swell however the hale o lono site is exposed to north swell and the hikuahi site is not as a result the reef at hale o lono records no late holocene net accretion while the reef at hikauhi records consistent and robust accretion over late holocene time analysis and dating of 24 cores from hale o lono and hikauhi reveal the presence of five major lithofacies that reflect paleo environmental conditions in order of decreasing depositional energy they are 1 coral algal bindstone 2 mixed skeletal rudstone 3 massive coral framestone 4 unconsolidated floatstone and 5 branching coral framestone bafflestone at hale o lono 10 cores document a backstepping reef ranging from 8 100 cal yr bp offshore to 4 800 cal yr bp nearshore a depauperate community of modern coral diminishes shoreward and seaward of 15 m depth due to wave energy disrupted recruitment activities and physical abrasion evidence suggests a change from conditions conducive to accretion during the early holocene to conditions detrimental to accretion in the late holocene reef structure at hikauhi reconstructed from 14 cores reveals a thick rapidly accreting and young reef maximum age 900 cal yr bp living coral cover on this reef increases seaward with distance from the reef crest but terminates at a depth of 20 m where the reef ends in a large sand field the primary limitation on vertical reef growth is accommodation space under wave base not recruitment activities or energy conditions interpretations of cored lithofacies suggest that modern reef growth on the southwest corner of molokai and by extension across hawaii in general is controlled by wave induced near bed shear stress related to refracted north pacific swell holocene accretion patterns here also reflect the long term influence of wave induced near bed shear stress from north swell during late holocene time this finding is consistent with other studies e g grigg 1998 cabioch et al 1999 that reflect the dominance of swell energy and sea level in controlling modern and late holocene accretion elsewhere in hawaii and across the pacific and indian oceans notably however this result is refined and clarified for hawaii in the hypothesis of rooney et al 2003 stating that enhancement of the el nino southern oscillation beginning approximately 5000 years ago led to increased north swell energy and signaled the end to net accretion along exposed coastlines in hawaii the exposure of hale o lono to north swell and the age of sea floor there ca 4 800 cal yr bp coupled with the lack of north swell incidence at hikauhi and the continuous accretion that has occurred there over the last millennium strongly supports the enso reef hypothesis as outlined by rooney et al 2003 other factors controlling holocene reef accretion at the study site are relative sea level position and rate of rise and wave sheltering by laau point habitat suitable for reef accretion on the southwest shore of molokai has shrunk throughout the holocene

coral indicators of past sea level change a global repository of u series dated benchmarks fossil corals provide valuable data for reconstructing past sea levels as they are often well preserved in the fossil record and can be dated with u series methods here we present a global and internally consistent database of usingle bondth dated fossil coral sea level indicators including full consideration of all known associated uncertainties both vertical and chronological we include carefully determined taxon specific depth distributions rather than blanket depth uncertainty terms as used in most previous work this is based on a synthesis of extensive modern ecological information on depth ranges these ranges are found to be spatially variable between ocean basins between regions and on sub regional scales because depth itself is not limiting instead depth distributions arise from complex physical chemical and biological interactions with coral reef growth distribution and composition one of the main causes for recognition of the greater depth variability of coral taxa has been the routine inclusion of deep diving and rov surveys in coral ecological studies over the past few decades which has broken through the shallow water bias of early surveys by adding frequent observations on deeper occurrences although more are needed it is also clear from our assessment that coral habitat depth distributions must be determined on the species level to reduce uncertainties in reconstructions of past sea levels and that application to sea level studies then requires these studies also to identify fossil corals to the species level samples identified only to the genus level give rise to wide uncertainties in habitat depth and hence sea level our database contains extensive metadata to assist evaluations of dating quality as well as geomorphic and stratigraphic metadata we demonstrate with examples how such metadata can help to evaluate sea level reconstructions for example by identifying outlier points one example discusses the last interglacial lig where we use the available data with their uncertainties to assess probabilistically the time at which local sea levels exceed that of the present which yields a mean age of 124 6 ka with 95 probability bounds at 118 5 and 129 5 ka we conclude with identification of key outstanding issues relating to i current incomplete understanding of tectonic setting including the current lack of independent verification of uplift subsidence rates and reliance of somewhat unsatisfactory and circular use of the elevation of last interglacial deposits ii the depth distributions of coral taxa and iii the complete documentation of stratigraphic geomorphological and other contextual information with suggestions for strategies to address these issues

natural iodine 129 as an environmental tracer abstract iodine 129 t 1 2 16 my is a naturally occurring tracer which can be used to study hydrologic and geologic processes on time scales up to 100 my the pre bomb atmospheric ratio 129 i i should have been constant in time and space and is the starting value in ground water recharge subsequent ratio changes in ground water should be determined by isotope contributions from three sources recharge water iodine leached from the formation and in situ uranium fission the mathematical expression of these time dependent processes forms the basis for dating and tracing applications the expected behavior of natural 129i in ground water is compared to results from field studies ground water samples from the great artesian basin australia provide an estimate of the atmospheric equilibrium ratio 6 10 13 down gradient changes in water up to 1 my old suggest that subsurface production can be significant the usefulness of 129i as an indicator of brine source and age is verified in brines collected in and around louisiana salt domes the method leads to ages of 7 and 9 my for two brine pockets trapped within jurassic salt and 32 to 40 my for oil field brines in miocene sands adjacent to the domes the results demonstrate the capability of tandem accelerator mass spectrometry to measure as few as 107 atoms of 129i in 10 mg i with 10 precision although such atom sensitivity can be achieved otherwise the accelerator technique is necessary to measure naturally low pre 1945 cosmogenic isotope ratios

diagenesis of magnetic minerals in recent haemipelagic sediments rapidly deposited sediments from marine and lake environments are being used increasingly to study decadal to millennial fluctuations in the earth s magnetic field the objectives are to gain more fundamental understanding of the geodynamo and to establish a new dating technique for sediments while lacustrine sections are generally restricted to temperate latitude glacial lakes 20 000 yr old rapidly deposited marine sediments along continental margins potentially offer continuous high resolution yet long term records of geomagnetic secular variation however to interpret the sedimentary magnetic record accurately geochemical processes that affect the reliability of the magnetic signal must be understood we now report downcore magnetic profiles from undisturbed kasten cores taken in rapidly deposited laminated sediments from the gulf of california and in bioturbated haemipelagic muds on the oregon continental slope which give apparently reliable directions but show dramatic decreases in the intensities of natural nrm and artificial arm irm remanences with depth downcore porewater and solid sulphur analyses show concave down decreases in porewater sulphate and systematic increases in pyrite and metastable monosulphides the maximum curvature of the sulphide profile occurs directly below the high magnetization zone combined with other compositional and mineralogical analyses these data suggest that due to oxidative decomposition of organic matter magnetites and other iron oxides become progressively reduced and subsequently sulphidized and pyritized with depth iron reduction seems to occur before sulphide formation changes in magnetic stability parameters are consistent with selective dissolution of the finer sized grains causing downcore coarsening of the magnetic fraction

drowning of the 150 m reef off hawaii a casualty of global meltwater pulse 1a we present evidence that the drowning of the 2150 m coral reef around hawaii was caused by rapid sea level rise associated with meltwater pulse 1a mwp 1a during the last deglaciation new u th and 14 c accelerator mass spectrometry dates combined with reinterpretation of existing radiometric dates constrain the age of the coral reef to 15 2 14 7 ka u th age indicating that reef growth persisted for 4 3 k y following the end of the last glacial maximum at 19 ka the drowning age of the reef is roughly synchronous with the onset of mwp 1a between 14 7 and 14 2 ka dates from coralline algal material range from 14 to 10 cal ka calibrated radiocarbon age 1 4 k y younger than the coral ages a paleoenvironmental reconstruction incorporating all available radiometric dates high resolution bathymetry dive observations and coralgal paleobathymetry data indicates a dramatic rise in sea level around hawaii ca 14 7 ka paleowater depths over the reef crest increased rapidly above a critical depth 30 40 m drowning the shallow reef building porites corals and causing a shift to deep water coralline algal growth preserved as a crust on the drowned reef crest

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

129i and 36cl concentrations in waters of the eastern clear lake area california residence times and source ages of hydrothermal fluids abstract the clear lake area of northern california is the location of hot spring activity some of which is associated with the formation of au and hg deposits we measured 129 i i and 36 cl cl ratios in nine warm springs formation springs six cold springs with elevated levels of cl and i mineral springs and five springs of recent meteoric origin dating of the i in the formation waters indicated that sources of i in these waters are formations with minimum ages between 60 and 80 ma this age range is in good agreement with the ages of the franciscan complex and the great valley sequence the dominant formations in this area because the mineral waters are essentially formation waters diluted with meteoric water i in these waters is of the same origin residence times of the waters were calculated based on the build up of129i and 36cl as a consequence of the presence of u and th in the crust the residence time of the formation waters in the great valley sequence the location for most of these springs was probably not longer than 84 000 yr the concentrations found for 36cl and 129i in the mineral waters indicate that these waters have residence times of similar magnitude in formations such as the franciscan complex or the clear lake volcanics which have slightly higher levels of u and th than the great valley sequence