model experiments on large tabular iceberg evolution ablation and strain thinning antarctic tabular icebergs are important active components of the ice ocean system to investigate the relevance of inherent ice dynamics to iceberg evolution we developed a numerical model based on the fundamental equations of ice shelf flow and heat transfer forced by environmental parameters of the ice ocean atmosphere system model experiments with idealized icebergs of constant density show that the strain thinning rate for a typical iceberg with a thickness of 250 m and a temperature of 158c is about 1 m a 1 sensitivity studies for different scenarios of environmental conditions confirmed the reliability of our model a 5 year simulation of the evolution of iceberg a 38b yielded a mean decrease in thickness from 220 m to 106 3 m 95 of which was caused by basal melting 1 by surface melting and 4 by strain thinning we found iceberg spreading decelerating by about 75 and ice temperatures being strongly affected by progressive erosion of the relatively warm basal layers and warming in the uppermost part according to the model results basal melting is the primary cause of change of iceberg geometry during drift whereas strain thinning is only relevant in cold areas where basal melting is low

climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

rapid oscillations in vostok and grip ice cores we investigate the spectral properties of climatic times series derived from two recent ice cores in greenland and east antarctica we find that the signals behave in a similar way in the high frequency part of their spectra the rapid oscillations found in the grip ice core were closely correlated to heinrich events a comparable spectral feature is detected in the vostok ice core we discuss the possibilities of connections between the two hemispheres and proper ice sheet oscillations in the light of simple oscillating climate models

temperature investigation and modeling on the filchner ronne ice shelf antarctica during the german antarctic field season 1989 90 hot water drilling was performed on filchner ronne ice shelf fris at 77s 52w to investigate the temperature depth profile and the bottom melting rate which are significant parameters for mass and energy balance studies of the ice shelf re measurements of installed chains in 1991 92 yielded reliable results taking glaciological geodetical and geophysical data on a flow line through the central part of fris we developed a two dimensional thermal model to re construct the measurements from a steady state temperature depth profile about 550 km upstream on mollereisstrom under consideration of mass and energy conservation a basal layer of 350 m of marine ice was calculated with thermal properties depending on salinity and temperature in areas with strong basal freezing nearly iso thermal depth profiles in the marine ice layer are derived further downstream in areas of basal melting a nearly cubic temperature depth profile is observed

searching for eustasy in deglacial sea level histories abstract perturbations to the earth s gravity field and solid surface associated with glacial isostatic adjustment gia cause the total observable sea level change to depart from the eustatic curve which is defined as a spatially uniform height shift of the ocean surface to accommodate any mass gained lost from grounded ice in this study we apply a state of the art model of gia induced sea level change to quantify the magnitude and spatial form of this departure at the global scale for a range of model parameters with an aim to identify regions that are well suited to obtain accurate and precise estimates of eustatic sea level and therefore past grounded ice volume in general our results indicate that eustatic sea level is not a directly measurable quantity and so must be estimated by subtracting a model derived estimate of non eustatic contributions from observations in this regard we use our results to isolate regions where this procedure can be applied with optimal accuracy and precision that is where 1 the gia predictions are relatively insensitive to plausible ranges in input parameters and 2 where the non eustatic contribution is small i e the predicted sea level closely approximates the eustatic value we present maps that can be employed by the field community to identify areas where sea level reconstructions would be well suited to arrive at robust estimates of eustatic sea level note that sea level changes associated with tectonic motion and changes in ocean water temperature salinity which also lead to departures from eustasy are not considered in this analysis

extending the vostok ice core record of palaeoclimate to the penultimate glacial period the ice core record of local temperature dust accumulation and air composition at vostok station antarctica now extends back to the penultimate glacial period 140 200 kyr ago and the end of the preceding interglacial this yields a new glaciological timescale for the whole record which is consistent with ocean records temperatures at vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one concentrations of co2 and ch4 correlate well with temperature throughout the record

origin of the northern atlantic s heinrich events as first noted by heinrich 1988 glacial age sediments in the eastern part of the northern atlantic contain layers with unusually high ratios of ice rafted lithic fragments to foraminifera shells he estimated that these layers are spaced at intervals of roughly 10 000 years in this paper we present detailed information documenting the existence of the upper five of these layers in odp core 609 from 50 n and 24 w their ages are respectively 15 000 radiocarbon years 20 000 radiocarbon years 27 000 radiocarbon years about 40 000 years and about 50 000 years we also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers although we are not of one mind regarding the origin of these layers we lean toward an explanation that the heinrich layers are debris released during the melting of massive influxes of icebergs into the northern atlantic these sudden inputs may be the result of surges along the eastern margin of the laurentide ice sheet

mid pacific microatolls record sea level stability over the past 5000 yr there has been geographical variation in sea level since rapid postglacial melting of polar ice ceased similar to 6 k y ago reflecting isostatic adjustments of earth and ocean surfaces to past and ongoing redistribution of ice and water loads a new data set of over 100 fossil microatolls from christmas kiritimati island provides a holocene sea level record of unparalleled continuity living reef flat corals grow up to a low tide level adjacent fossil microatolls long lived porites corals up to several meters in diameter occur at similar elevations 0 1 m and extensive fossil microatolls in the island interior are at consistent elevations within each population collectively they comprise an almost continuous sequence spanning the past 5 k y indicating that locally sea level has been within 0 25 m of its present position and precluding global sea level oscillations of one or more meters inferred from less stable locations or using other sea level indicators this mid pacific atoll is tectonically stable and far from former ice sheets the precisely surveyed and radiometrically dated microatolls indicate that sea level has not experienced significant oscillations in accordance with geophysical modeling which implies that the eustatic contribution from past ice melt and the isostatic adjustment of the ocean floor to loading largely cancel each other at this site

ocean circulation beneath filchner ronne ice shelf from three dimensional model results a high resolution three dimensional ocean circulation model is applied to the cavity beneath filchner ronne ice shelf fris the model predicts predominantly barotropic currents which form a series of cyclonic gyres in the deep basins and anticyclonic circulations around the islands the surface circulation can be such that the water moves in the direction of decreasing or increasing ice thicknesses in the former case leading to freezing while melting at the ice shelf base results in the latter case the pattern of melting and freezing is consistent with known distributions of marine ice and melting areas beneath fris an anticyclonic circulation around the korff and henry ice rises with melting west of korff ice rise and freezing on the eastern side and north of henry ice rise is the main source for an ice pumping mechanism that produces the observed large marine ice body in the central filchner ronne ice shelf the estimates for net melting for realistic conditions at the open ocean boundary are 40 50 km 3 yr 1 indicating that ice shelf ocean interaction is an important contribution to the mass balance of the ice shelf

terrigenous sedimentation and coral reef growth a conceptual framework abstract the role of terrigenous and non framework carbonate sedimentation has not been prominent in models of coral reef growth and evolution we derive and discuss a semi quantitative model which relates coral reef growth to sedimentation the model is independent of coral biology and is based upon the relative net rates of framework and non framework sediment accumulation and or removal the model might enable some forecasting of long term responses to changes in sedimentation regime and other environmental factors the occurrence of turbid zone reefs is successfully explained in regions of very high turbidity but with little or no net sediment accumulation potential future use of the model may include aiding prediction of the effects of other geological and oceanographic factors on the growth or demise of coralline communities

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

growth and structure of fringing reefs in a muddy environment south thailand abstract most fringing reefs of the se coast of phuket thailand have wide up to 300 m intertidal reef flats and narrow 2 5 m reef fronts that abut the muddy forereef only a few meters deep these reefs prograde by splitting toppling and regeneration of reef front massive corals notably porites lutea splitting of massive corals is greatly aided by the boring action of upogebia sp shrimps and by planes of weakness developed within the colony skeleton by nestling bivalves the large size of toppled blocks ensures that some of the uppermost polyps are viable above the soupy forereef sediment surface cores indicate that the reefs are essentially tabular features consisting of mainly massive reef front corals grown on muddy foundations that have shallowing upwards sediment haracteristics 14c ages and leveling data of fossil former reef front corals exposed on the reef flat suggest that reef growth started in the mid holocene when sea level was at least 0 8 m higher than now since then the rate of lateral reef progradation has averaged 40 mm yr the preservation potential of these reefs is low because of the combination of a lack of organic or inorganic binding of the corals into a rigid frame and the unconsolidated nature of the underlying sediments

a portable electrical based percussion coring system for use in deep water this article describes a sediment coring system that can be used in deep water 30 to 60 m with no aid from divers the system is light and compact enough to be operated by three persons and transported in a small boat and or in a small airplane a core tube penetrates into sediments with the force caused by percussion of a water proof electric hammer driven by a generator on the boat with this device four sand cores were retrieved from a lagoon floor at depths ranging from 40 m to 58 m a flexible vinyl tube is used as a core liner and it provides an exact measure of core recovery

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

holocene coral reef development under windward and leeward locations at ishigaki island ryukyu islands japan abstract coral reef growth is largely controlled by the wave energy associated with ocean swells and local winds this growth has responded to changes in wave conditions that evolved in concert with holocene sea level changes we analyzed holocene facies of the ibaruma and fukido reefs of ishigaki island southern ryukyu islands in the context of temporal and spatial changes in wave conditions by comparing present day coral assemblages and internal fossil reef facies four major coral assemblages that developed under different wave energy conditions were recognized six cores recorded a holocene reef sequence consisting of four sedimentary facies that differed in the relative volumes of four coral taxa acropora digitifera and acropora hyacinthus and lesser amounts of favia stelligera and montastrea curta holocene windward reef growth began at 7820 cal years bp after flooding of the pleistocene reef limestone surface the ensuing reef growth kept up with the rapid sea level rise a vertical growth rate of 7 5 m 1000 years during reef nucleation and early growth stages decreased to 3 5 m 1000 years during the main stage of reef framework development the uppermost part of the windward reef consisted of a very robust framework unlike the open framework of the leeward reef ages indicated that the uppermost leeward reef was ca 3000 years younger than the uppermost windward reef these variations in facies development and timing were caused by differences in local wind driven wave conditions

spectral analysis and modeling of microcyclostratigraphy in late paleozoic glaciogenic rhythmites parana basin brazil we investigate the depositional time scale of lithological couplets fine sandstone siltstone siltstone mudstone from two distinctive outcrops of permo carboniferous glacial rhythmites in the itarare group parana basin brazil resolving the fundamental issue of time scale for these rhythmites is important in light of recent evidence for paleosecular variation measured in these sequences spectral analysis and tuning of high resolution gray scale scans of sediment core microstratigraphy which comprises pervasive laminations reveal a comparable spectral content at both localities with a frequency suite interpreted as that of short term climate variability of recent and modern times this evidence for decadal to centennial scale deposition of these lithological couplets is discussed in light of the varvic character i e annual time scale that was previously assumed for the rhythmites

milankovitch band forcing of sub milankovitch climate variability during the pleistocene climate variability at periods from 10 kyr to 12 kyr that originates from milankovitch band forcing is quantified at three locations for the late pleistocene eastern equatorial pacific ocean drilling program site 846 eastern equatorial atlantic odp site 663 and northeastern atlantic deep sea drilling project site 609 variability at these periods is not present in the primary milankovitch forcing so no linear linkage to milankovitch band variations is possible however these periods are equal to harmonics of precession band oscillations the magnitude of interactions between processes that occur at different timescales can only be resolved in time series data through application of higher order statistics through such an application we demonstrate that up to 75 of the variance in the 10 to 12 kyr band in the sediment records is nonlinearly transferred from precession band 19 23 kyr variations within the millennial to sub milankovitch band defined as the band of variance ranging from 15 to 2 kyr approximately 1 3 of the variability in the records studied is consistent with a low frequency milankovitch band origin this variability may derive from high sensitivity of the tropics to summertime insolation in both hemispheres relative to wintertime insolation a mechanism having equatorial origin and related to low latitude precession variations appears consistent with the observations because the phase coupling between 10 to 12 kyr oscillations and precession is resolved this result has implications for development of models which seek to explain global climate variations on this timescale

influence of wave energy on holocene coral reef development an example from ishigaki island ryukyu islands japan abstract wave energy induced by ocean swell and local winds is an important factor controlling the coral reef development here we compare and contrast facies ages and accretion rates of reefs that developed independently along windward and leeward margins of the same island as both reefs face the open ocean swells provide a background of low to medium energy condition with additional energy along windward margins due to prevailing winds this similarity of the wave energy regimes medium to high energy produced a similar framework facies that was constructed by robust branching acropora however much greater lateral accretion rates were observed in the high energy reef than in the medium energy reef also coral cobble facies were only found in the medium energy reef indicating that the reef framework was more susceptible to storm breakage than that in the high energy reef these differences are attributable to the differing biological and ecological responses of corals to wave energy and water motion

a diagnostic analysis of heinrich glacial surge events the episodes of ice rafted detritus ird accumulation identified in north atlantic sediment cores indicate periods of abnormal iceberg production mainly of the laurentide ice sheet in this paper we develop further a scaling theory of these so called heinrich events leading to a general criterion for basal melting of an ice sheet which we take as a necessary condition for surging and streaming this criterion depends not only on the physical properties of ice sheets and the magnitude of the geothermal and viscous heating but also on the history of changes in ice elevation atmospheric carbon dioxide and sea surface temperature the thermal effects of which at the top of an ice sheet are transmitted with a time delay to the basal boundary by thermal advection we apply this criterion to various past and present ice sheets showing their general vulnerability to surging in greater detail we use estimates of the time variations of ice volume specmap carbon dioxide vostok and north atlantic sea surface temperature site k708 1 to estimate when basal melting conditions prevailed for the laurentide ice sheet over the past 140 000 years thereby making it vulnerable to heinrich type surges a reasonable level of agreement is obtained with the observed record of north atlantic ird activity including the six numbered heinrich events as well as earlier activity of this kind that occurred when the ice volume was lower

holocene sea level change and evolution of a mixed coral reef and mangrove system at iriomote island southwest japan abstract exposed fossil microatolls and core samples from a coral reef and a mangrove forest at the yutsun river mouth iriomote island southwest japan reveal the internal structure and temporal changes in the sedimentary processes of a mixed reef mangrove system evidence from the core samples and fossil microatolls suggests sea level reached its present position before 5100 cal yr b p and a relative sea level highstand of 1 1 1 2 m above the present sea level occurred from 5100 to 3600 cal yr b p this was followed by a gradual fall in relative sea level the tectonically corrected sea level curve indicates a stable sea level after 5100 cal yr bp with a sea level highstand of up to 0 4 m between 5100 and 3600 cal yr b p a nearshore reef dominated by massive porites and arborescent acropora initially developed at 6500 3900 cal yr b p reef development was potentially terminated by relative sea level fall and sediment discharge from the yutsun river that affected the backreef environment an offshore coral reef reached present day sea level by 1000 cal yr b p forming a wave break that enabled the foundation of mangrove forest on the fringing reef after 1000 cal yr b p the reef development was significantly delayed compared with other coral reefs in the region with similar medium to high energy conditions but it provided a calm environment in the backreef area that allowed the development of mangroves these features demonstrate the chronology and causal relationship between coral reef and mangrove development under the influence of holocene sea level change and river discharge

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

coral reefs at 34 n japan exploring the end of environmental gradients we describe the architecture and development of the highest latitude coral reefs currently known on earth located in japan at 34 n the reefs are distributed within turbid inner bays and undergo winter sea surface temperatures ssts that fall to 13 c well below the generally accepted lower limit 18 c in winter of tropical coral reef formation despite low ssts and high turbidity coring indicates reefs ranging to 555 cm in thickness since ca 4 3 k y ago the reefs exhibit high adaptability to this extremely marginal environment variability of the tsushima warm current and the asian monsoon could have affected the evolution of these reefs the corals are dominantly faviids in contrast to acropora and porites that tend to dominate low latitude tropical subtropical reefs defining the end of the distributional range the reefs serve as baselines for understanding coral reef distribution along sst and turbidity gradients

the response of glaciers to climatic persistence 1 attribution of past glacier fluctuations to changes in the climate requires character2 izing glacier mass balance variability the available observational records which are 3 relatively short are consistent with random fluctuations uncorrelated in time plus 4 an anthropogenic trend however longer records of other climate variables suggest 5 that in fact there is a degree of temporal persistence associated with internal that 6 is unforced climate variability and that it varies with location and climate variable 7 therefore it is likely that climatic persistence does exist for mass balance but that 8 records are too short to confirm its presence or establish its magnitude with conven9 tional statistical tests extending previous work we explore the impact of potential 10 climatic persistence on glacier length fluctuations we use a numerical model and a 11 newly developed analytical model to establish that even a degree of persistence so 12

meltwater input to the southern ocean during the last glacial maximum three records of oxygen isotopes in biogenic silica from deep sea sediment cores from the atlantic and indian sectors of the southern ocean reveal the presence of isotopically depleted diatomaceous opal in sediment from the last glacial maximum this depletion is attributed to the presence of lids of meltwater that mixed with surface water along certain trajectories in the southern ocean an increase in the drainage from antarctica or extensive northward transport of icebergs are among the main mechanisms that could have produced the increase in meltwater input to the glacial southern ocean similar isotopic trends were observed in older climatic cycles at the same cores

evidence for the episodic turn on and turn off of turbid zone coral reefs during the late holocene sea level highstand terrigenous sediment accumulation within nearshore marine environments is regarded as a major factor inhibiting carbonate production and coral reef accretion while recent ecological and geological research into reef development under long term terrigenous sediment influence questions the overly simplistic nature of such views understanding of the time scales of reef initiation and growth and the morphodynamics of reef accretion in these settings remains limited here we present evidence to support recent suggestions that once established rapid reef accretion and progradation is possible but that the restricted accommodation windows in which such reefs develop often result in short lived ephemeral phases of reef building specifically we describe two discrete periods of reef growth within one small 600 m wide coastal embayment around a high island on the terrigenous sediment dominated inner shelf of the central great barrier reef australia these reef building phases occurred at either end of the holocene sea level highstand the first during the late postglacial marine transgression and early highstand 6900 4500 calibrated cal yr b p the second following the late holocene regression and stillstand 1600 cal yr b p to present an 3000 yr hiatus occurred between these events probably as a function of subtle changes in sea level and associated shoreline morphodynamics

optimizing significance testing of astronomical forcing in cyclostratigraphy the recognition of astronomically forced milankovitch climate cycles in geological archives marked a major advance in earth science revealing a heartbeat within the climate system of general importance and key utility power spectral analysis is the primary tool used to facilitate identification of astronomical cycles in stratigraphic data but commonly employed methods for testing the statistical significance of relatively high narrow band variance of potential astronomical origin in spectra have been criticized for inadequately balancing the respective probabilities of type i false positive and type ii false negative errors this has led to suggestions that the importance of astronomical forcing in earth history is overstated it can be readily demonstrated however that the imperfect nature of the stratigraphic record and the quasiperiodicity of astronomical cycles sets an upper limit on the attainable significance of astronomical signals optimized significance testing is that which minimizes the combined probability of type i and type ii errors numerical simulations of stratigraphically preserved astronomical signals suggest that optimum significance levels at which to reject a null hypothesis of no astronomical forcing are between 0 01 and 0 001 i e 99 99 9 confidence level this is lower than commonly employed in the literature 90 99 confidence levels nevertheless in consonance with the emergent view from other scientific disciplines fixed value null hypothesis significance testing of power spectra is implicitly ill suited to demonstrating astronomical forcing and the use of spectral analysis remains a difficult and subjective endeavor in the absence of additional supporting evidence

historic 1771 meiwa tsunami confirmed by high resolution u th dating of massive porites coral boulders at ishigaki island in the ryukyus japan 1 the chronicles of the ryukyu kingdom describe at least four coastal inundation events at ishigaki island during the seventeenth through nineteenth centuries the 1771 meiwa earthquake tsunami which killed 12 000 people another earthquake tsunami 1687 and two events with unrecorded causes 1625 and 1714 we used a high resolution u th method to date well preserved surface parts of massive porites spp coral head boulders that had been cast ashore and found that the ages of two boulders correspond to the 1771 event one large porites boulder diameter 4 m was dated to 1625 suggesting that that event was also a large inundation event calibrated 14c ages based on a newly estimated local value for the radiocarbon marine reservoir effect clustered around 1625 and 1771 suggesting that these events were larger than the others our study demonstrated that porites boulders have enormous potential value for studies of paleoinundation events such as tsunamis and extreme storms

fringing reef growth and morphology a review abstract fringing reefs are generally not simple veneers of coral growth along tropical shorelines extensive research over the past few decades based on radiocarbon dating of holocene reef deposits has indicated that they can develop in a complex variety of ways even though the surface morphology may appear relatively simple the principal factor that appears to determine the growth and morphology of fringing reefs is the available accommodation space sea level fluctuations are important primarily because the sea surface determines the absolute accommodation space for a given reef this means that a reef established during a period of sea level rise will be able to accrete vertically as space is created above it if however the reef establishes at or grows to the sea surface thereby occupying all the available accommodation space it can no longer accrete vertically and begins to build laterally the morphology and chronostratigraphy of a range of holocene fringing reefs are described on the basis of which six fringing reef growth models are identified in model a the fringing reef is established at depth and primarily accretes vertically towards the sea surface reef growth in model b initiates at sea level and due to the lack of vertical accommodation space grows laterally model c has a similar morphology to model b however the reef progrades over a non reefal sediment wedge episodic lateral and vertical growth occurs in model d with a stepwise progradation of the reef front the remaining models are characterised by seaward reef framework behind which unconsolidated sediments accumulate in model e reef crest growth forms a barrier leading to the development of a backreef lagoon model f has a similar morphology to model e except that the reef crest is formed by hurricane rubble accumulation rather than framework accretion and is periodically reworked

a comparison of the vostok ice deuterium record and series from southern ocean core md 88 770 over the last two glacial interglacial cycles taking advantage of the fact that the vostok deuterium d record now covers almost two entire climatic cycles we have applied the orbital tuning approach to derive an age depth relation for the vostok ice core which is consistent with the specmap marine time scale a second age depth relation for vostok was obtained by correlating the ice isotope content with estimates of sea surface temperature from southern ocean core md 88 770 both methods lead to a close correspondence between vostok and md 88 770 time series however the coherence between the correlated d and insolation is much lower than between the orbitally tuned 8d and insolation this reflects the lower accuracy of the correlation method with respect to direct orbital tuning we compared the ice and marine records set in a common temporal framework in the time and frequency domains our results indicate that changes in the antarctic air temperature quite clearly lead variations in global ice volume in the obliquity and precession frequency bands moreover the average phase we estimated between the filtered d and insolation signals at precessional frequencies indicates that variations in the southern high latitude surface temperature could be induced by changes in insolation taking place during a large period of the summer in northern low latitudes or winter in southern low latitudes the relatively large lag found between vostok d variations and obliquity driven changes in insolation suggests that variations in the local radiative balance are not the only mechanism responsible for the variability in surface temperature at those frequencies finally in contrast to the cross spectral analysis method used in previous studies the method we use here to estimate the phases can reveal errors in cross correlations with orbitally tuned chronologies

ice shelf basal melting at the grounding line measured from seismic observations analysis of seismic data provides a new technique to measure basal melting of an ice shelf close to the grounding line internal reflections have been observed within the ice on a seismic reflection profile at the grounding line of ronne ice shelf the changes in ice thickness above and below these reflections have been used in a steady state model to calculate the basal mass flux of the ice shelf soon after the ice begins to float strain rates within the ice calculated during the modeling agree with values from nearby survey data the calculated melt rates range between 0 and 7 m yr 1 with an estimated standard error of 2 4 m yr 1 in reasonable agreement with earlier estimates based on surface glaciological observations limitations in the method include the difficulties in determining reflector geometry from a single seismic section and also the limitations imposed by the assumption of steady state additional seismic data would greatly reduce these limitations

the power spectral density of atmospheric temperature from time scales of 10 2 to 106 yr after removing annual variability power spectral analyses of local atmospheric temperature from hundreds of stations and ice core records have been carried out from time scales of 10 2 to 106 yr a clear sequence of power law behaviors is found as follows 1 from 40 ka to 1 ma a flat spectrum is observed 2 from 2 ka to 40 ka the spectrum is proportional to f 2 where f is the frequency and 3 below time scales of 2 ka the power spectrum is proportional to f 1 2 at time scales less than 1 month we observe that the power spectra of continental stations become proportional to f 3 2 while maritime stations continue to have power spectra proportional to f 1 2 down to time scales of 1 day to explain these observations we model the vertical transport of heat in the atmosphere as a stochastic diffusion process the power spectrum of temperature fluctuations at the earth s surface expected from this model equation in a two layer geometry with thermal and eddy diffusion properties appropriate to the atmosphere and the ocean and a radiation condition at the top of the atmosphere agrees with the observed spectrum the difference in power spectra between continental and marine stations can be understood with this approach as a consequence of the air mass above a maritime station exchanging heat with both the atmosphere above and the ocean below while a continental station exchanges heat mostly with the atmosphere above

holocene sea level record from corals reliability of paleodepth indicators at ishigaki island ryukyu islands japan abstract holocene sea level change provides direct evidence of the melting of ice sheets however our understanding of the timing and course of such change is limited by a lack of information regarding environmental condition of corals for example holocene sea level curves are compiled based on water depths estimated from the occurrence of a small number of coral species as species identification is difficult work the error associated with this method of estimating sea level exceeds 2 5 m in addition there generally occurs a difference in the living water depth of corals between high energy reefs and low to moderate energy reefs this difference in living water depth also results in an error in reconstructed sea level curves in the present study we analyzed drill core and recorded the vertical distribution of corals at the high energy ibaruma reef and low to moderate energy fukido reef ishigaki island ryukyu islands japan analyses of corymbose acropora a digitifera massive goniastrea g retiformis massive pocillopora p verrucosa massive platygyra p ryukyuensis and other corals enables the accurate reconstruction of a sea level curve because these species are distributed in a narrow range with a weighted mean m w error of between 0 5 and 2 5 m these observation data from ibaruma and fukido reefs can be used to reconstruct holocene sea level curves based on drill core data from ibaruma reef however the two reefs yield contrasting sea level curves the curve reconstructed based on data from fukido reef is several meters deeper than that reconstructed based on data from ibaruma reef this discrepancy reflects the different energy levels of the two reefs high energy at ibaruma reef and low to moderate energy at fukido reef therefore the accurate reconstruction of a holocene sea level curve requires the identification of species from drill core and observations of the vertical distribution of species at the present day reef at a location close to the drilling site the holocene sea level curve reconstructed based on drill core data from ibaruma reef reveals a rapid sea level rise of approximately 7 5 m kyr 1 between 8000 and 6000 cal years bp the rate of sea level rise decreased from 7 5 to 3 5 m kyr 1 between 6000 and 5000 cal years bp a mid holocene highstand occurred at around 5000 cal years bp at a level of approximately 3 2 5 m above the present mean sea level the increase in ocean volume corresponding to this sea level rise indicates that melting of the antarctic ice sheet continued beyond 6000 cal years bp as most of the northern hemisphere ice sheets had melted by 6000 cal years bp resulting in sea levels similar to those of the present day

role of the thermohaline circulation in the abrupt warming after heinrich events evidence of rapid climate oscillations during the last glacial period has been identified in climate records from greenland ice cores1 2 and ocean sediments in the north atlantic3 4 these records show that periods of gradual cooling are terminated by abrupt warming events5 with the coldest periods coinciding with the deposition of ice rafted debris so called heinrich events throughout the north atlantic heinrich events are thought to be a signature of massive iceberg discharges owing to collapse of the laurentide ice sheet bond et al 5 have proposed that the decrease in meltwater flux following collapse and retreat of the ice sheet enhanced the ocean s thermohaline circulation6 thereby increasing advection of heat from the tropics and giving rise to abrupt climate warming here we test this idea using a simple ocean model coupled to a model of a periodically surging ice sheet we find that massive discharges of icebergs first stop the thermohaline circulation because of the consequent freshwater influx cooling the north atlantic region this is followed by a rapid restart of the circulation leading to abrupt warming thus our model can reproduce the qualitative features of the climate oscillations seen in the ice core and ocean records

sensitivity of subglacial lake vostok s flow regime on environmental parameters abstract subglacial lakes provide unique habitats but the exact nature of physical and geochemical conditions are still a matter of debate and await direct sampling of water due to its isolation from external atmospheric forcing other environmental parameters influence the flow characteristics within the lake in this study we use an improved treatment of the physical processes at the ice water boundary interface to identify and quantify the impact of 1 the geothermal heat flux 2 the heat flux from the lake into the ice 3 the influence of the salinity of the lake water and 4 the ice thickness on the size of the freezing area and the freeze melt rates we show that the modelled basal mass imbalance that is the produced melt water minus the re frozen water depends on the geothermal heating as well as the heat flux into the ice the circulation and the temperature distribution within subglacial lake vostok are rather stable against variations of geothermal heat flux heat flux into the ice sheet salinity of the lake and small changes of the ice thickness above the lake however the flow regime for any subglacial lake with less than 2000 m ice thickness above will be substantially different from those that experience higher pressures this is because the buoyancy temperature relationship reverses at this depth

oceanographic conditions south of berkner island beneath filchner ronne ice shelf antarctica we have made oceanographic measurements at two sites beneath the southern filchner ronne ice shelf hot water drilled access holes were made during january 1999 allowing conductivity temperature depth ctd profiling and the deployment of instrument moorings the ctd profiles show that the entire water column is below the surface freezing point we estimate the summer flux of water between the two sites to be 2 106 m3 s 1 the summer potential temperature salinity properties of the water column suggest that this flow is part of a recirculation in the deepest part of the subice shelf cavity and the filchner depression the recirculation is driven by a combination of the melting of deep basal ice and the freezing that results from the depressurization of the cold buoyant water as it ascends the ice shelf base the source of the water was high salinity shelf water hssw produced in the ronne depression this is the water that provides the external heat necessary for the strong melting at the deep grounding lines in the vicinity of foundation ice stream instruments moored at the drill sites show that during the winter hssw formed on the berkner shelf flows beneath the ice shelf and largely displaces the recirculating water from the two sites this provides an externally driven through flow that is warmer nearer the surface freezing point and slower than the internal recirculation and which is low enough in density to escape the filchner depression

nonlinear variability of the climatic system from singular and power spectra of late quaternary records stable isotope records from seven marine cores and one ice core provide invaluable information on the intricate behavior of the climatic system over time scales of 104 to 105 years these records in conjunction with a simple coupled climate model help us understand major mechanisms of paleoclimatic variability the time intervals covered by the records include the last glacial interglacial cycle in spite of the difference in the nature of the records common features are revealed by advanced spectral analysis tools the dominant features are the presence of orbital frequencies on the one hand and a low number of internal degrees of freedom on the other the climatic system appears therefore to act on the quaternary time scales considered as a forced nonlinear oscillator the internal mechanisms giving rise to the aperiodic oscillations include ice albedo feedback precipitation temperature feedback and interactions between the ice sheets and the bedrock

a climate model with cryodynamics and geodynamics we present a highly simplified zero dimensional model of the climatic system the model attempts to incorporate mechanisms important on the time scale of glaciation cycles namely 104 105 years in particular the radiation balance of the ocean atmosphere the plastic flow of continental ice sheets and the viscous flow of the upper mantle are taken into account the stress is on the interaction between the cryosphere ice sheets and the asthenosphere upper mantle which had not been taken into account in previous energy balance or ice sheet models of climate weertman 1976 kallen et al 1979 the model exhibits free self sustained oscillations of an amplitude and period comparable to those found in the paleoclimatic record of glaciations viz o 10 deg k and o 104 years respectively such oscillations had already been found in the simpler model of kallen et al 1978 1979 the fact that nonlinear self sustained oscillations also obtain for the present slightly more complex model is interesting it offers mild support to the idea that unforced oscillations can actually exist in the real climatic system itself these oscillations are characterized by a quarter phase lag between ice extent and global temperature given that the climatic system is a nonlinear oscillator with a period of o 104 years it is expected that astronomical forcing at 19 000 23 000 and 41 000 years will lead to subharmonic oscillations with a period close to 100 000 years the dominant period of glaciation cycles such effects have already been noticed in the work of birchfield and weertman 1978 with an even simpler model including only glacial dynamics the careful study of the interplay between internal mechanisms and external forcing with comparable time scales represents an interesting challenge to the theory of ice ages the results of such theoretical studies can also provide guidance for observational work in particular periodicities of o 104 years in the climate record and phase lags between ice volume and temperature appear to be supported by the most recent paleogeochemical investigations ruddiman and mclntyre 1981

reconciling discrepancies between uk37 and mg ca reconstructions of holocene marine temperature variability significant discrepancies exist between the detrended variability of late holocene marine temperatures inferred from mg ca and uk37 proxies with the former showing substantially more centennial scale variation than the latter discrepancies exceed that attributable to differences in location and persist across various calibrations indicating that they are intrinsic to the proxy measurement we demonstrate that these discrepancies can be reconciled using a statistical model that accounts for the effects of bioturbation sampling and measurement noise and aliasing of seasonal variability the smaller number of individual samples incorporated into mg ca measurements relative to uk37 measurements leads to greater aliasing and generally accounts for the differences in the magnitude and distribution of variability an inverse application of the statistical model is also developed and applied in order to estimate the spectrum of marine temperature variability after correcting for proxy distortions the correction method is tested on surrogate data and shown to reliably estimate the spectrum of temperature variance when using high resolution records applying this inverse method to the actual mg ca and uk37 data results in estimates of the spectrum of temperature variance that are consistent this approach provides a basis by which to accurately estimate the distribution of intrinsic marine temperature variability from marine proxy records

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

high frequency paleovariability in climate and co2 levels from vostok ice core records the high resolution of the vostok records provides a unique look at the causes of paleoclimatic variability during the last complete glacial cycle the records present strong evidence for the interaction between orbital forcing and internal physico chemical mechanisms of variability this interaction appears to account for the great wealth of spectral features found in the records

holocene antarctic melting and lithospheric uplift history of the southern okinawa trough inferred from mid to late holocene sea level in iriomote island ryukyu japan abstract relative sea level deduced from fossil oysters and mangroves are reported for iriomote island ryukyus southwestern japan radiocarbon dated fossil oysters as well as previously analyzed mangrove muds are compared to geophysical and glacio hydro isostatic adjustment gia models that describe earth deformation due to changing surface loading the holocene high stand hhs inferred from oyster fossils saccostrea echinata and saccostrea malaboensis is 2 7 m at ca 3500 years ago after which sea level gradually fell to present level the hhs magnitude attributed to gia for the last ca 4000 is between 1 and 1 5 m above present day sea level and the residual indicates the long term lithospheric uplift rate of the island the timing of peak hhs also indicates that late holocene melting mainly from antarctica ceased by approximately 4000 years ago

1200 year paleoecological record of coral community development from the terrigenous inner shelf of the great barrier reef increased terrestrial sediment and nutrient yields are regarded as significant threats to coral reef health within the central great barrier reef lagoon where water quality has reportedly declined since european settlement since ca a d 1850 inner shelf reef conditions have purportedly deteriorated however the link between reef decline and water quality change remains controversial primarily because of a lack of pre european period ecological baseline data against which to assess contemporary ecological states here we present a high resolution record of reef accretion and coral community composition from a turbid zone nearshore reef on the inner shelf of the great barrier reef the record is based on six radiocarbon date constrained cores and extends back to ca 1200 calibrated yr b p results demonstrate not only the potential for coral communities to initiate and persist in settings dominated by fine grained terrigenous sediment accumulation but also that a temporally persistent but low diversity suite of corals has dominated the reef building community at this site for at least the past millennium furthermore the coral assemblages exhibit no evidence of community shifts attributable to post european water quality changes while extrapolation of these findings to other turbid zone reefs must remain tentative the study raises important questions about the resilience of inner shelf reefs that are under terrestrial sediment influence and subject to elevated turbidity conditions and demonstrates the potential to develop detailed millennial time scale coral community records from holocene reef systems

anatomy of a modern coral reef flat a recorder of storms and uplift in the late holocene abstract cores from kabira reef ishigaki island southwest japan reveal the internal structure and temporal changes in sedimentary process of a complete coral reef flat the reef crest caught up with sea level at about 4000 yr bp since then it expanded oceanward and the reef pavement has grown landward the backreef structure is composed of bioclasts derived from the reef framework of all the bioclasts corals and coralline algae are most abundant coral fragments coarser than 3 0 o have dominated the backreef sediments since about 2000 yr bp benthic foraminiferal tests first occurred at about 4000 yr bp and their abundance increased significantly starting around 2000 yr bp shallowing of the reef crest is also indicated by the presence of the shallow water benthic foraminifera baculogypsina sphaerulata tests after 2000 yr bp the date 2000 yr bp is coincident with tectonic uplift at kabira reef kawana 1989 we consider this uplift to have caused a relative sea level fall that aided the deposition of coral fragments transported from the reef pavement by storms the relative sea level fall also caused subaerial exposure of the reef crest during low tides and the transition of reef building organisms from corals to shallow water species of benthic foraminifera resulting in a change noticeable in the constituents of backreef sediments the results of this study suggest that the coral reef flat and especially the backreef can be a faithful recorder of relative sea level changes

vostok ice core a continuous isotope temperature record over the last climatic cycle 160 000 years a continuous deuterium profile along the 160 000 year vostok ice core antarctica is interpreted in terms of atmospheric temperature changes this climatic record is the awaited terrestrial complement of the deep sea records supporting the existence of a relation between the pleistocene climate and orbital forcing

northern hemisphere glaciation and the evolution of plio pleistocene climate noise 1 deterministic orbital controls on climate variability are commonly inferred to dominate across timescales of 104 106 years although some studies have suggested that stochastic processes may be of equal or greater importance here we explicitly quantify changes in deterministic orbital processes forcing and or pacing versus stochastic climate processes during the plio pleistocene via time frequency analysis of two prominent foraminifera oxygen isotopic stacks our results indicate that development of the northern hemisphere ice sheet is paralleled by an overall amplification of both deterministic and stochastic climate energy but their relative dominance is variable the progression from a more stochastic early pliocene to a strongly deterministic late pleistocene is primarily accommodated during two transitory phases of northern hemisphere ice sheet growth this long term trend is punctuated by stochastic events which we interpret as evidence for abrupt reorganization of the climate system at the initiation and termination of the mid pleistocene transition and at the onset of northern hemisphere glaciation in addition to highlighting a complex interplay between deterministic and stochastic climate change during the plio pleistocene our results support an early onset for northern hemisphere glaciation between 3 5 and 3 7 ma and reveal some new characteristics of the orbital signal response such as the puzzling emergence of 100 ka and 400 ka cyclic climate variability during theoretical eccentricity nodes

the use of barnacles to measure and date relative sea level changes in the ryukyu islands japan abstract fossil intertidal barnacles are excellent indicators of recnet sea level stands even those of short duration especially on elevated rocky coasts this paper deals with problems related to finding sampling cleaning dating and interpreting the altimetric significance of fossil barnacle samples collected in a living position the distribution and ecology of octomeris sulcata tetraclitella and chthamalus are described examples are provided for the reconstruction of relative sea level variations due to sudden uplift movements okinawa and toku islands to gradual uplift movements kume island and to a slight relative emergence since ca 600 yr b p that has been reported for the first time in several ryukyu islands

a 150 000 year climatic record from antarctic ice during much of the quaternary the earth s climate has undergone drastic changes most notably successive glacial and interglacial episodes the past 150 kyr includes such a climatic cycle the last interglacial the last glacial and the present holocene interglacial a new climatic time series for this period has been obtained using 18 o data from an antarctic ice core

holocene sea level change and antarctic melting history derived from geological observations and geophysical modeling along the shimokita peninsula northern japan 1 a mid to late holocene sea level record based on combined geomorphological geological and micropaleontological observations was obtained from well developed wave cut benches subaerially exposed along the shimokita peninsula northern japan results indicate that the benches were formed during mid to late holocene sea level transgressions reaching a maximum highstand level of 2 m above present at about 4 000 years ago this timing corresponds to an abrupt order of magnitude decrease in sedimentation rate as recorded in a core recovered from proximal mutsu bay in addition glacio hydro isostatic adjustment due to crustal deformation in response to postglacial sea level rise was modeled and results are consistent with the reconstructed local 2 m highstand given that meltwater contributions from the major north american and european ice sheets had largely ceased by 7 000 years ago these independent lines of evidence taken together indicate that melting of the antarctic ice sheet ended by 4 000 years ago