japan sea oxygen isotope stratigraphy and global sea level changes for the last 50 000 years recorded in sediment cores from the oki ridge abstract we obtained twenty ams accelerator mass spectrometry radiocarbon dates 2 tephra layer chronologies and a planktonic foraminiferal 18 o stratigraphy for the last 50 000 years from japan sea cores from the oki ridge in this paper we report ams 14 c results that allow us to reconstruct a high resolution chronology of the cores and discuss millennial scale climate changes recorded in japan sea sediments the sedimentation rate for the site increased dramatically from the glacial stage to the holocene as a result of significant hydrological changes associated with deglaciation and global sea level rise a lighter 18 o anomaly for the planktonic foraminifers was found during the lgm last glacial maximum this shift corresponds to a freshening of the japan sea surface waters and is mainly due to a global sea level drop rather than anomalously warm ssts sea surface temperatures as previously reported our record combined with the global sea level data suggests that the lgm started about 30 kyr ago and that the salinity of the japan sea became fresher than at present the ssts during mis marine oxygen isotope stage 3 were relatively stable and global sea level was not lower than ca 80 m the surface water of the japan sea attained normal saline levels following the younger dryas cold event and reached the present day 18 o values 7 kyr ago

origin dimensions and distribution of remobilized carbonate deposits in a tectonically active zone eocene thebes formation sinai egypt abstract determination of the distribution and mechanism for carbonate dominated mass transport sediments is often compromised by the scale and access to exposures consequently many studies lack the resolution to capture the heterogeneity and dimensions of mass transport deposits this study documents the size shape and stratal assemblage of remobilized carbonates in the eocene thebes formation in the hammam faraun fault block hffb of western sinai revealing the complexities of carbonate mass transport deposits at sub seismic scale present day pseudo three dimensional exposure of the thebes formation in a large fault block formed during the opening of the gulf of suez allowed for lateral and down dip measurement of slope and basinal facies in the field and from photos remobilized facies were digitized in the photos and evaluated using image analysis software a technique with a wide range of applications to outcrop studies of sedimentary architecture debris flow deposits in the lower section of the thebes formation comprises clasts with differing fossil assemblages a relative sea level rise at the start of upper thebes formation deposition resulted in basinal sediments comprising periodic incursions of high density turbidite grainstones encased within a background of planktonic foraminiferal wackestones foraminiferal assemblages of remobilized facies imply multiple sources on the carbonate platform demonstrating the effect of short lived tectonism on slope instability and deposition of mass transport deposits the results of the study confirm that tectonism associated with the syrian arc fold belt which altered the style of basin sedimentation between egypt and syria persisted into the eocene at least as far south as wadi araba in the western desert and hammam faraun in sinai in addition the shape size and extent of the two dominant remobilized facies debris flows and grainstone turbidites are influenced by their mud rich versus grainy compositions

patterns of deglacial warming in the pacific ocean a review with emphasis on the time interval of heinrich event 1 abstract based on a compilation of currently available records of past sea surface temperature sst variability estimated from a variety of different proxies the regional scale deglacial sst development in the pacific ocean is tentatively classified into four endmember types the subtropical and tropical pacific is characterized by a continuous deglacial warming without marked interruption during the time interval of heinrich event 1 h1 whereas the subarctic north pacific exhibits centennial scale warm cold oscillations during this time interval sst records from marginal seas of the pacific show a deglacial warming interrupted by a cooling event coeval with h1 followed by a marked bolling sst increase a single sst record from the southwestern subantarctic pacific displays a continuous deglacial warming across h1 followed by an antarctic cold reversal type cooling during the allerod thus in contrast to the deglacial sst development in the atlantic which has been inferred to be overwhelmingly driven by the redistribution of heat through changes in the meridional overturning circulation moc none of the open oceanic pacific sst records reviewed here displays any obvious and or dominant response to the reduction of the moc and or the reorganization of atmospheric circulation during h1 within the limits of absolute chronologies all tropical and subtropical pacific sst records show an onset of deglacial warming at 19 1 ka coeval with the onset of the deglacial rise in sea level

deglacial sea surface temperatures of the western tropical pacific a new look at old coral 1 using secondary ion mass spectrometry sims ion microprobe techniques we generated annual sr ca cycles with subweekly resolution from chunks of porites coral retrieved from a tahiti barrier reef drill core 149 w 17 s representing the period 13 650 to 13 100 years b p the centers of pristine skeletal septa were selectively targeted with a 10 m diameter ion beam spot avoiding adjacent pore spaces occupied by secondary aragonite needles applying a sr ca sea surface temperature sst calibration equation derived from modern tahiti porites having the same low growth rate as the fossil specimens we obtained ssts 0 5 1 5 c cooler during the bolling allerod relative to the present day with no significant change in seasonality on the contrary we estimate that analysis of bulk samples would yield excessively cool sr ca based sst estimates due to the occupation by secondary aragonite crystals of up to 50 of the skeletal pore space in the ancient samples we find that growth rate effects on coral sr ca further depress the apparent mean annual derived ssts by 3 c and amplify the apparent seasonality by selectively enhancing wintertime cooling our microscale analysis of pristine skeleton and application of an appropriate growth dependent calibration yield sr ca derived ssts that are in good agreement with those derived from mg ca ratios of calcitic foraminifera which indicate a continuous postglacial warming of the western tropical pacific in phase with the warming of the tropical atlantic

bundled turbidite deposition in the central pandora trough gulf of papua since last glacial maximum linking sediment nature and accumulation to sea level fluctuations at millennial timescale since last glacial maximum 23 19 ka earth climate warming and deglaciation occurred in two major steps bolling allerod and preboreal interrupted by a short cooling interval referred to as the younger dryas 12 5 11 5 ka b p in this study three cores mv 33 mv 66 and md 40 collected in the central part of pandora trough gulf of papua have been analyzed and they reveal a detailed sedimentary pattern at millennial timescale siliciclastic turbidites disappeared during the bolling allerod and preboreal intervals to systematically reoccur during the younger dryas interval subsequent to the final disappearance of the siliciclastic turbidites a calciturbidite occurred during meltwater pulse 1b the holocene interval was characterized by a lack of siliciclastic turbidites relatively high carbonate content and fine bank derived aragonitic sediment the observed millennial timescale sedimentary variability can be explained by sea level fluctuations during the last glacial maximum siliciclastic turbidites were numerous when the lowstand coastal system was located along the modern shelf edge although they did not occur during the intervals of maximum flooding of the shelf during meltwater pulses 1a and 1b siliciclastic turbidites reappear briefly during the younger dryas an interval when sea level rise slowed stopped or perhaps even fell the timing of the calciturbidite coincides with the first reflooding of eastern fields reef an atoll that remained exposed for most of the glacial stages

trace element variations in fossil corals from tahiti collected by iodp expedition 310 reconstruction of marine environments during the last deglaciation 15 to 9 ka abstract climate responses and changes in marine environments during the last deglaciation have been controversial and few paleoceanographic data are available from the tropical south pacific though this region is crucial in the investigations of ocean atmosphere interactions integrated ocean drilling program expedition 310 was conducted to establish the time course of the postglacial sea level rise at tahiti in the south pacific a principal objective of this expedition was to examine the variation of marine environments during the last deglaciation as fossil porites coral is ideal for assessing past marine environments we selected only porites specimens from the many coral specimens retrieved examined them by xrd and dated them by the 14c method in all we obtained 17 pristine porites specimens composed of only aragonite with ages from 15 to 9 ka then we measured mg ca ba ca and u ca ratios and cd contents as proxies for upwelling and sea surface temperature higher ba ca ratios and cd content together with lower reconstructed ssts using u ca ratios in the coral specimens between 12 6 and 9 8 cal ka compared to around 15 cal ka suggest that upwelling and or entrainment of subsurface water into mixed layer was enhanced around tahiti during this period this finding is consistent with previous reports and supports the idea that the south pacific was characterized by la nina like conditions at least from 12 6 to 9 8 cal ka

sediment flux across the great barrier reef shelf to the queensland trough over the last 300 ky the continental margin off northeast australia comprising the great barrier reef gbr platform and queensland trough is the largest tropical mixed siliciclastic carbonate depositional system in existence we describe a suite of 35 piston cores and two ocean drilling program odp sites from a 130 240 km rectangular area of the queensland trough the slope and basin setting east of the central gbr platform oxygen isotope records physical property magnetic susceptibility and greyscale logs analyses of bulk carbonate content and radiocarbon ages at these locations are used to construct a high resolution stratigraphy this information is used to quantify mass accumulation rates mars for siliciclastic and carbonate sediments accumulating in the queensland trough over the last 31 000 years for the slope highest mars of siliciclastic sediment occur during transgression 1 0 million tonnes per year mt yr 21 and lowest mars of siliciclastic 0 1 mt yr 21 and carbonate 0 2 mt yr 21 sediment occur during sea level lowstand carbonate mars are similar to siliciclastic mars for transgression and highstand 1 1 1 4 mt yr 21 in contrast for the basin mars of siliciclastic 0 0 1 mt yr 21 and carbonate sediment 0 2 0 4 mt yr 21 are continuously low and within a factor of two for lowstand transgression and highstand generic models for carbonate margins predict that maximum and minimum carbonate mars on the slope will occur during highstand and lowstand respectively conversely most models for siliciclastic margins suggest maximum and minimum siliciclastic mars will occur during lowstand and transgression respectively although carbonate mars in the queensland trough are similar to those predicted for carbonate depositional systems siliciclastic mars are the opposite given uniform siliciclastic mars in the basin through time we conclude that terrigenous material is stored on the shelf during sea level lowstand and released to the slope during transgression as wave driven currents transport shelf sediment offshore q 2000 elsevier science b v all rights reserved

deepwater carbonate deposition in response to re flooding of carbonate bank and atoll tops at glacial terminations the late quaternary has experienced large glacial interglacial climatic variations and related 10 s to 100 meters high amplitude sea level fluctuations at milankovich frequencies from 10 s to 100 kyr during which carbonate platform tops have been exposed and re flooded in many occasions this study focuses on the accumulation of calci turbidites the aragonite onset sharp increase in fine sediments and their timing in deep basins adjacent to carbonate platforms a particular emphasis is developed on the occurrence of the first gravity flow event and aragonite onset sharp increase and their linkage to the initial re flooding of the platform tops during deglaciations three basins adjacent to isolated platforms in the bahamas the northern nicaragua rise and the gulf of papua were selected to represent pure carbonate versus mixed systems in quiescent versus tectonically active settings and various carbonate bank top morphologies ranging from atoll to relatively deeply and narrowly flooded flat top banks in spite of these differences each record illustrates a clear relationship between the timing of platform top re flooding and initiation of significant carbonate export by gravity flows and low density plumes into the surrounding basins the concept of re flooding window is introduced to characterize the prolific period of time during which bank and atoll tops are flooded enough to produce large export of bank derived aragonite and of calci turbidites in adjacent basins according to our datasets the main re flooding windows have occurred mainly on the last part of the sea level rise at each glacial termination t those periods being marked by some of the highest rates of sea level rise the analysis of a long piston core from the earthquakes prone walton basin northern nicaragua rise demonstrates that sea level not seismic activities played a major role as trigger mechanism for the initiation of gravity flows since the last four glacial interglacial transitions and supports the existence of an extra glacial termination during the early portion of the transition from mis 7 4 to mis 7 3 tiiia

reply to comment by cahyarini et al on a snapshot of climate variability at tahiti at 9 5 ka using a fossil coral from iodp expedition 310

ground surface temperature and the detection of permafrost in the rugged topography on ne qinghai tibet plateau abstract the thermal regime of permafrost in the rugged topography on parts of the qinghai tibet plateau qtp remains ambiguous due to general inaccessibility and inconvenient investigations with geophysical prospecting while the relatively easy implementations of monitoring ground surface temperature gst may facilitate the investigations of permafrost thermal state here surface freezing and thawing and the relationship between gst and permafrost temperature are investigated in the bayan har mountains ne qtp on the basis of 22 monitoring sites results demonstrate that unlike the air temperature ta mainly controlled by elevation the gst is complicately influenced by elevation and the surface characteristics such as vegetation local soil textures as well as the exposure to solar radiation mean annual gst magst ranges from 1 1 c to 3 1 c and is averaged at 0 8 c magst generally decreases at a lapse rate of 1 1 c 100 m in relation to elevation surface freezing and thawing processes depend on topography and local surface characteristics the onset of unstable thawing stable thawing unstable freezing and stable freezing are averaged at 6 april 2015 15 may 2015 14 october 2015 and 21 october 2015 based on the relationship between magst and the ground temperature at the depth of zero annual amplitude gst likely serves as a reliable indicator of the thermal state of permafrost for the 22 sites it is estimated that the lowest tzaa of permafrost is 3 4 c and the thickest permafrost is 106 2 m however detailed investigations of subsurface characteristics are indispensable for the accurate inference of permafrost

siliciclastic sediment across the north queensland margin australia a holocene perspective on reciprocal versus coeval deposition in tropical mixed siliciclastic carbonate systems abstract according to conventional models of reciprocal sedimentation for tropical mixed siliciclastic carbonate systems shedding of carbonate material dominates slope and basin sedimentation during transgression and highstand while siliciclastic deposition dominates during lowstand this understanding permeates the stratigraphic literature and is the accepted depositional model on the great barrier reef gbr margin the results of this study however document coeval carbonate and siliciclastic highstand deposition on the gbr slope and basin seafloor sediment from queensland trough slopes and basin floor east of the gbr contains 20 to 50 terrigenous siliciclastic material one hundred and twenty six sediment samples were obtained from core tops and sediments grabs previously retrieved from shelf slope and basin environments of the north queensland margin these samples were analyzed for their carbonate content mineralogy and major element composition the amount of terrigenous siliciclastic material in sediment from the north queensland margin can be approximated by three independent methods 1 the noncarbonate residual 2 the sum of quartz clays and feldspars and 3 the sum of sio2 al2o3 fe2o3 and tio2 all three tracers show a distinct distribution of siliciclastic sediment across the margin shelf siliciclastic content is highest on the inner shelf decreasing eastward toward the gbr with the exception of relatively high siliciclastic content in several interreef passages queensland trough siliciclastic content is highest on the slope and basin between 15 and 17 s latitude decreasing to the south and east although the relative abundances of quartz and clay minerals vary across the margin the chemistry suggests a similar origin for the siliciclastic material moreover the zone of high siliciclastic abundance in queensland trough reflects enhanced siliciclastic accumulation siliciclastic material escapes the outer shelf to queensland trough through interreef passages between 15 and 17 s latitude it is then focused to the south by ocean currents siliciclastic sediment is likely sourced from a combination of rivers transporting holocene sediment to the gbr shelf and late pleistocene sediment eroded from the outer shelf and reworked to queensland trough siliciclastic material crosses the shelf although the mechanisms e g river plumes nepheloid layers tidal currents cyclones mushroom jets remain poorly constrained however shelf width is clearly an important factor in allowing cross shelf transport to occur mass balance calculations indicate that up to 13 of the late holocene annual riverine sediment output may be delivered to queensland trough modern and ancient mixed system depositional models must be reevaluated to allow for the possibility of coeval siliciclastic and carbonate deposition

glacial versus interglacial sedimentation rates and turbidite frequency in the bahamas the southern tongue of the ocean is a 1300 m deep flat floored basin in the bahamas that receives large amounts of sediment from the carbonate platforms surrounding it on three sides we have examined five 8 13 m long piston cores and determined bulk sedimentation rates turbidite frequency and turbidite accumulation rates for the past two glacial and interglacial periods the mean of bulk sedimentation rates is four to six times higher in interglacial periods average accumulation rates of recognizable turbidites are higher by a factor of 21 to 45 and interglacial turbidite frequency is higher by a factor of 6 to 14 sediment composition indicates that increased interglacial rates are due to higher accumulation of platform derived material additional data from other bahamian basins as well as published material from the caribbean strongly suggest that highstand shedding is a general trend in pure carbonate depositional systems carbonate platforms without a siliciclastic component export more material during highstands of sea level when the platform tops are flooded and produce sediment the response of carbonate platforms to quaternary sea level cycles is opposed to that of siliciclastic ocean margins where sediment is stored on the inner shelf during highstands and passed on to continental rises and abyssal plains during lowstands of sea level

empirical assessment of coral sr ca and mg ca ratios as climate proxies using colonies grown at different temperatures 1 coral strontium calcium sr ca and magnesium calcium mg ca ratios might be useful for reconstructing past sea surface temperature sst in tropical oceans where instrumental data are limited however the link between coral skeletal trace elements and sst is disputed and biological factors such as skeletal growth rate may also affect trace elements in a coral we studied the relationships between growth rate and sst and sr ca and mg ca ratios using corals porites spp cultured in thermostated tanks sr ca was controlled primarily by sst while mg ca mainly reflected the growth rate with negligible contribution from species on both the variations these relationships are consistent with modeled results of cation partitioning during aragonite crystal formation

high resolution planktic foraminiferal record of the last 13 300 years from the upwelling area off chile abstract a high resolution sedimentary record spanning the last deglacial and holocene periods was obtained by studying the deep sea sediment core gik 17748 2 retrieved from 2545 m water depth in the valparaiso basin chilean continental slope southeast pacific 32 45 00 s 72 02 00 w ams 14 c measurements and oxygen isotope analyses of the planktic foraminifera species globigerina bulloides and neogloboquadrina pachyderma dex indicate an age of 13 3 ams 14 c kyr b p at the base of the core 383 cm and sedimentation rates ranging between 9 and 92 cm kyr foraminiferal assemblages and accumulation rates were analysed in order to investigate variations in paleoceanography and paleoproductivity in the southern peru chile current during the last 13 kyr changes in foraminiferal assemblages indicate a sequence of three major hydrographic regimes at the site of the core 1 deglacial sediments are characterised by variable faunal compositions generally reflecting strong upwelling and high productivity 2 during the early and middle holocene upwelling and thus productivity decreased as indicated by an elevated relative abundance of n pachyderma dex and the importance of the subtropical surface water of the peru chile countercurrent increased as indicated by higher relative amounts of n dutertrei 3 for the last 3 kyr variable faunal assemblages indicate variable competing environmental conditions characterised on one hand by increased upwelling reflected by an elevated relative abundance of n pachyderma sin and on the other hand by warmer conditions deduced from a higher relative abundance of n dutertrei probably due to more frequent and more intense el nino events in addition hints for slightly cooler conditions between 11 4 and 10 7 kyr b p might be related to a younger dryas event in this region

spatial and temporal variability of ground surface temperature and active layer thickness at the margin of maritime antarctica signy island a calm grid with a data logger system to monitor the active layer thermal regime was established on signy island 60 43 s 45 38 wat 80 m a s l in december 2005 the active layer at each of the 36 nodes of the grid was monitored measuring the ground temperature at least at 4 different depths between 0 02 and 0 4 m at the end of the summer season in addition within the grid we selected four sites closely spaced in a ray of 25 m three of which with the same topographical characteristics north facing aspect but different vegetation coverage one bare ground bg1 and two sites with different vegetation andreaea sp and sanionia uncinata and the fourth bg2 it is as bg1 a bare ground but with south facing aspect in particular 4 thermistors were located at depths of 0 02 0 3 0 6 and 0 9 m at bg2 and at the andreaea sp site 9 thermistors at 0 02 0 3 0 6 1 1 2 1 4 1 6 2 and 2 5 mat bg1 and at 0 02 and 0 6 mof depth at sanionia site generally with the same aspect a thick vegetation cover as in sanionia site provides a greater insulative effect than a thinner vegetation cover as in andreaea site or bare ground bg1 because vegetation both shades and insulates the ground resulting in a reduction in summer heat flux ground surface temperature gst was colder and more buffered in spring and summer under the vegetated ground than in bg1 although the coldest gst and lowest thawing degree days tdd were recorded at bg2 and related to its southern aspect our data confirm that air temperature is the main driver of gst as already reported both in the arctic and antarctic we also found that the effect of air temperature changes seasonally being drastically reduced in winter and to a lesser extent in fall and spring when there is generally thin snow cover b30 cm during the summer when snow cover is usually absent the air temperature is the dominant driver although incoming radiation also had an effect on the northern exposed bare ground and to a lesser extent on the vegetated and southerly exposed bare ground the active layer ranges between 81 and 185 cm on the 4 continuously monitored sites and considering the sites with the same aspect it is thicker under bare ground between 10 up to more than 100 than under vegetated ground confirming previous observations in the arctic and antarctic however at our sites climate forcing has no effect on the active layer thickness enhancing the role of soil properties including the periods of high moisture content and lateral flow of water the lack of a statistically significant regressions between gst and active layer thickness could be due to the limited study period four years and or to the variationwith timeof changes in soil characteristics such as soilmoisture and the possible occurrence of non conductive heat transfer processes including the lateral flow of water further data are required to understand the role of moisture and possible ground water circulation within the active layer to explain the unexpected strong dichotomy between the gst regime and active layer thickness

hydraulic conductivity of active layer soils in the mcmurdo dry valleys antarctica geological legacy controls modern hillslope connectivity abstract spatial variability in the hydraulic and physical properties of active layer soils influences shallow groundwater flow through cold desert hydrological systems this study measures the saturated hydraulic conductivity and grain size distribution of 90 soil samples from the mcmurdo dry valleys mdv antarctica primarily from taylor valley to determine what processes affect the spatial distribution of saturated hydraulic conductivity in a simple mineral soil dominated natural hillslope laboratory we find that the saturated hydraulic conductivity and the grain size distribution of soils are organized longitudinally within taylor valley soils sampled down valley near the coast have a higher percentage of fine sized sediments fine sand silt clay and lower saturated hydraulic conductivities than soils collected up valley near taylor glacier 1 3 10 2 vs 1 2 10 1 cm s soils collected mid valley have intermediate amounts of fines and saturated hydraulic conductivity values consistent with a hydrogeologic gradient spanning the valley from high inland to low near the coast these results suggest the organization of modern soil properties within taylor valley is a relict signature from past glaciations that have deposited soils of decreasing age toward the mouth of the valley modified by fluvial activity acting along temporal and microclimate gradients

are seawater sr ca variations preserved in quaternary foraminifera abstract high precision measurements of sr ca in planktonic foraminifera for the last 150 ka reveal sr ca variations of up to 12 on glacial interglacial time scales although records showing the largest variations appear to be strongly influenced by selective dissolution other records show sr ca variations of 3 5 that do not covary with indicators of dissolution intensity and that are reproduced in sites of contrasting quaternary dissolution histories these systematic variations are characterized by high sr ca ratios during glacial maxima followed by steep decreases during deglaciation and gradual increases through interstadial periods closely following 18 o curves foraminiferal sr ca variations may reflect changes in the sr ca ratio of seawater or they may be due to kinetically or biologically induced changes in sr partitioning coupled numerical models of the sr and ca budgets of the ocean reveal that sea level changes together with large changes in river fluxes and carbonate accumulation rates can produce seawater sr ca variations that approximate both the shape and amplitude of foraminiferal sr ca variations however such extreme changes in river and carbonate fluxes conflict with existing data on carbonate accumulation rates and sr isotopic constraints on the magnitude of variations in the river flux smaller variations 1 3 in the sr ca ratio of seawater likely characterize quaternary glacial cycles changes in sr partitioning due to glacial interglacial changes in the carbonate ion concentration and other environmental factors likely produce additional variation in the sr ca record of planktonic foraminifera

climate swings come into focus the last glacial period was far from quiet during so called heinrich events large armadas of icebergs were shed from the ice sheet that covered much of north america the tracks of debris left by the melting icebergs can still be seen in sediment cores from the north atlantic in their perspective broecker and hemming 1 report from a recent miniconference that attempted to chart the climatic impacts of these events 1 http www sciencemag org cgi content short 294 5550 2308

abrupt changes in early holocene tropical sea surface temperature derived from coral records for many high latitude regions of the globe it is now clear that the transition to modern climate following the last glacial maximum was punctuated by a number of rapid and substantial climate oscillations1 2 in contrast relatively little is known about how the tropics responded to the deglaciation because few high resolution records are available from lower latitudes corals have recently been shown to provide an important source of tropical climate records because they can be easily and accurately dated using either 14c or 230th and because past sea surface temperatures can be recovered from the sr ca ratios in coral skeletons here we use this technique to derive several early holocene sea surface temperature records from a coral drill core recovered from espiritu santo vanuatu in the tropical southwest pacific ocean these records indicate that sea surface temperatures in this region were depressed by as much as 6 5 c below modern values at 10 350 calendar years bp but rose very abruptly during the following 1 500 years this temperature increase lags the post younger dryas increase observed in a coral record from the tropical atlantic ocean3by about 3 000 years an unexpected phase shift that may ultimately shed light on the mechanisms of deglacial climate change

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

coral barium calcium record of mid holocene upwelling activity in new caledonia south west pacific abstract a variety of inimical factors i e sea surface temperature nutrient input nature of substrates were invoked previously to explain the retardation in reef settlement in new caledonia during the holocene in order to clarify the respective role played by temperature and nutrient level in the growth of fringing reefs along the southwest coast of the island trace element ratios i e sr ca and ba ca were used respectively as a paleothermometer and as a tracer of nutrient load from modern and mid holocene about 6000 calendar years old massive porites coral colonies the results obtained from the modern coral record indicate that near the outer barrier reef upwelling activity is controlled by southeast winds blowing in summer by contrast along the southwest coastline the fringing reefs are subjected to barium input mainly derived from weathering of barite rich rocks cropping out in the adjacent mainland comparison between the fossil and modern coral sr ca and ba ca records shed light on three different aspects of the mid holocene climate and coral reef evolution in new caledonia 1 the variability of paleo sea surface temperature sst seems to have been similar to the modern one although the island probably experienced sst about 1 c higher than at present 2 upwelling activity appears to have been greater than at present barium being supplied from the open sea to coastal zones by strong wind generated upwelling currents in relation to cooling events 3 the onset of reef development in the southwest areas of new caledonia was delayed due to the stronger upwelling of nutrient enriched waters during the early middle holocene the flowing of upwelled waters over the southwest coastal areas began at 8200 calendar years bp and ceased at the time when the outer barrier reef crest reached present day sea level about 5500 to 5000 calendar years ago

annual cycles of u ca in coral skeletons and u ca thermometry abstract we have discovered annual variations in the 238 u 40 ca ratio of porites coral skeletons measurements were made using thermal ionization mass spectrometric techniques yielding precisions of 2 2 for 238 u 40 ca and l 2 for 88 sr 40 ca coralline aragonite subsamples weighed 2 mg enabling submillimeter sampling resolution corresponding to monthly temporal resolution the annual nature of the cycles was confirmed by comparison with annual banding observable in x radiographs for two modern and one fossil sample the amplitude of the u ca variation ranges from 6 to 23 well outside of analytical error as annual u ca cycles appear to be a general feature of primary coralline aragonite the preservation of such features will be important in identifying unaltered coral for u series dating studies u ca variations mimic and are in phase with annual variations in 88 sr 40 ca for a given fractional shift in sr ca the fractional shift in u ca is about 6 times larger for the two modern corals 238 u 40 ca is strongly anticorrelated with measured temperature suggesting that 238 u 40 ca has potential as a paleothermometer if temperature is the only significant control on coralline 238 u 40 ca we reach the following conclusions from analyses of fossil samples a vanuatu sample which grew halfway through the last deglaciation gives u ca temperatures 4 to 5 c below modern values u ca thermometry applied to published data for barbados corals indicates that 1 temperature generally correlates with sea level 2 glacial temperatures stages 2 and 4 were 4 to 6 c lower than interglacial temperatures stages 7a 5e and 1 and 3 temperatures rose from glacial to interglacial values early in the last deglaciation thermometry applied to papua new guinea corals indicates that 1 temperatures were 5 to 6 c lower than interglacial temperatures from 13 to 10 ky bp then rose to present values 9 ky bp 2 the temperature depression between 13 and 10 ky bp is consistent with low temperatures observed in vanuatu during the same time interval and 3 the papua new guinea deglacial temperature history differs from that of barbados the results generally support estimates of tropical temperatures obtained from sr ca thermometry and snow line elevation data but disagree with those based on foram transfer functions a thermodynamic model suggests that coralline 238 u 40 ca may also be sensitive to marine carbonate ion concentration raising the possibility that some of the observed glacial interglacial 238 u 40 ca variation may result from glacial interglacial carbonate ion changes however the key experiments that might establish a coralline 238 u 40 ca carbonate ion relationship have yet to be performed

enso tropical extratropical climate teleconnections and mechanisms for holocene debris flows along the hyperarid coast of western south america 17 24 s abstract el nino the warm phase of the enso cycle involves ocean climate anomalies in the tropical pacific ocean and in the extratropics which frequently result in heavy rainfall episodes along the equatorial and subtropical regions of western south america here we investigate meteorological mechanisms producing heavy rains floods and debris flows along the less known hyperarid coasts of southern peru and northern chile to evaluate the paleoclimate significance of holocene debris flow deposits our results reveal that heavy rainfall over the coast of southernmost peru occurs either during austral summer at the mature stage of el nino in connection with warmer sea surface temperatures and anomalous jet streams off northern chile or during the previous austral winter spring associated with equatorward shifted pacific south america psa atmospheric teleconnection patterns at antofagasta in northern chile such events occur almost exclusively in the latter season when deeper psa related anomaly poles extend their influence equatorwards beyond central chile during non el nino conditions short lived heavy rainfall episodes in southernmost peru can be associated with similar albeit weaker or less persistent circulation anomalies in addition to that a seasonally enhanced low level southerly flow provides orographic uplift rainfall favourable conditions by the andes at the 18 s coastal bend ultimately the trigger for rainfall events in all seasons and phases of the enso cycle was invariably connected with mid troposphere wave disturbances from mid latitudes the chronostratigraphy of debris flow deposits from both areas and its comparison with other paleoclimate records at the western side of the andes suggests that the enso related teleconnection patterns operated only during the second half of the holocene supporting an onset of modern el nino manifestations at 5300 5500 cal bp and increased frequency of major events during recent times we suggest that several debris flows dated between 12 900 and 8400 cal bp in southernmost peru previously interpreted as an indication of strong el nino events were associated with short and intense heavy rainfall episodes similar to those described here during the late winter spring season in non el nino conditions concomitant with stronger low level southerlies strengthened south eastern pacific subtropical anticyclone and intensified coastal upwelling

environmental significance of microbialites in reef environments during the last deglaciation in situ microbialites occurring in reef rocks dredged between 80 and 130 m water depth on the modern fore reef slopes of tahiti and the marquesas islands yield ages ranging from 17 100 2900 to 4410 2250 years bp suggesting that they played a prominent role during the last deglacial sea level rise microbialites developed in both shallow and deep water depositional environments where they characterize various zones of the reef tracts reef crests upper reef slopes deep fore reef slopes reflecting contrasting scenarios of microbialite development involving reefal microbialites in shallow water settings and slope microbialites that formed in environments deeper than 10 20 m and extending down to more than 100 m reefal microbialites correspond to a late stage of encrustation of the dead parts of coral colonies or more commonly of related encrusting organisms red algae and foraminifers thus forming surface crusts slope microbialites generally form the ultimate stage of a biological succession indicating a deepening sequence whereby shallow water corals and associated encrusting organisms are replaced by deeper water assemblages of red algae and foraminifers before microbialite growth the precipitation of phosphatic iron manganese crusts and the deposition of planktonic micritic limestones on the microbialites characterize a deepening upward sequence the widespread development of microbialites in reef sequences from the last deglaciation characterizes a period of environmental degradation consequential on the rapid sea level rise and abrupt climatic changes of that time the reported biological succession reflects changes in water quality and especially an increase in nutrients in shallow water settings increased alkalinity and nutrient availability in interstitial waters were related to surface fluxes and terrestrial groundwater seepage while slope environments were exposed to continuous upwelling of nutrient rich deeper waters during the last deglacial sea level rise the age differences between corals and overlying slope microbialites range from 1600 to 8400 years based on high precision u series age measurements of both corals and microbialites and indicates that a significant time several thousand years elapsed between the development of the coralgal frameworks and the growth of slope microbialite crusts microbialites cannot be considered as part of the drowning event some 14 000 years ago that resulted in the demise of reef frameworks in the 90 110 m present depth range but are substantially younger

active layer dynamics in three topographically distinct lake catchments in byers peninsula livingston island antarctica abstract topography exerts a key role in controlling permafrost distribution in areas where mean annual temperatures are slightly negative one such case is the low altitude environments of maritime antarctica where permafrost is sporadic to discontinuous below 20 40 m asl and continuous at higher areas and active layer dynamics are thus strongly conditioned by geomorphological setting in january 2014 we installed three sites for monitoring active layer temperatures across byers peninsula livingston island south shetland islands at elevations between 45 and 100 m the sites are situated in lake catchments lakes escondido cerro negro and domo that have different geomorphological and topographical conditions our objective was to examine the role of topography and microclimatic conditions in determining the active layer thermal regime in order to identify the factors that control geomorphic processes in these lake catchments at each site a set of loggers was installed to monitor air temperature at snow thickness swt and soil temperature st down to 80 cm depth mean annual air temperatures maat showed similar values in the three sites 2 7 to 2 6 c whereas soil temperatures showed varying active layer thicknesses at the three catchments the ground thermal regime was strongly controlled by soil properties and snow cover thickness and duration which is influenced by local topography geomorphological processes operating at the lake catchment scale control lacustrine sedimentation processes and both are dependent on the combination of topographical and climatic conditions therefore the interpretation of lake sediment records from these three lakes requires that soil thermal regime and snow conditions at each site be taken into account in order to properly isolate the geomorphological environmental and climatic signals preserved in these lake records

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

rapid collapse of northern larsen ice shelf antarctica in january 1995 4200 square kilometers of the northern larsen ice shelf antarctic peninsula broke away radar images from the ers 1 satellite complemented by field observations showed that the two northernmost sections of the ice shelf fractured and disintegrated almost completely within a few days this breakup followed a period of steady retreat that coincided with a regional trend of atmospheric warming the observations imply that after an ice shelf retreats beyond a critical limit it may collapse rapidly as a result of perturbated mass balance

biotic and abiotic factors influencing soil properties across a latitudinal gradient in victoria land antarctica abstract through the cooperative efforts of the scientific committee on antarctic research scar evolution and biodiversity in antarctica eba project and the latitudinal gradient project lgp a monitoring network was established in victoria land in 2002 to assess the impacts of climate change on vegetation soils active layer dynamics and permafrost across a latitudinal gradient in this study we report on the key factors influencing soil development across the gradient including vegetation parent material characteristics and climate physical and chemical soil properties at depths of 2 8 and 10 20 cm were investigated at 7 sites and on 14 permanent plots from apostrophe island in northern victoria land 73 30 s 167 50 e to granite harbour in southern victoria land 77 00 s 162 26 e along the ross sea coast the relationships among vegetation parent material and regional climate and soil properties were tested with principal component analyses there were no significant correlations or relationships in soil properties across the climate gradient in fact local microclimatic appears to be more effective than the regional gradient in influencing the properties microclimate was also important relative to active layer depth and vegetation distribution lithology was strongly related to several chemical parameters notably extractable al fe ca k but was unrelated to grain size distribution vegetation was related to the chemistry of the surface soil layer including nitrate organic carbon c n ratio and water content and also the active layer depth penguins had the greatest influence on soil properties in initiating the development of ornithogenic soils further analyses on soil properties including a greater number of sites will be required to represent more extensively the lithological variability and to extend the latitudinal extremes of the gradient the results presented here are an important reference for future monitoring activities in victoria land

late pleistocene history of turbidite sedimentation in a submarine canyon off the northern great barrier reef australia cores from slopes east of the great barrier reef gbr challenge traditional models for sedimentation on tropical mixed siliciclastic carbonate margins however satisfactory explanations of sediment accumulation on this archetypal margin that include both hemipelagic and turbidite sedimentation remain elusive as submarine canyons and their role in delivering coarse grained turbidite deposits are poorly understood towards addressing this problem we investigated the shelf and canyon system bordering the northern ribbon reefs and reconstructed the history of turbidite deposition since the late pleistocene high resolution bathymetric and seismic data show a large paleo channel system that crosses the shelf before connecting with the canyons via the inter reef passages between the ribbon reefs high resolution bathymetry of the canyon axis reveals a complex and active system of channels sand waves and local submarine landslides multi proxy examination of three cores from down the axis of the canyon system reveals 18 turbidites and debrites interlayered with hemipelagic muds that are derived from a mix of shallow and deep sources twenty radiocarbon ages indicate that siliciclastic dominated and mixed turbidites only occur prior to 31 ka during marine isotope stage mis 3 while carbonate dominated turbidites are well established by 11 ka in mis1 until as recently as 1 2 ka the apparent lack of siliciclastic dominated turbidites and presence of only a few carbonate dominated turbidites during the mis2 lowstand are not consistent with generic models of margin sedimentation but might also reflect a gap in the turbidite record these data suggest that turbidite sedimentation in the ribbon reef canyons probably reflects the complex relationship between the prolonged period 25 ka of mis3 millennial sea level changes and local factors such as the shelf inter reef passage depth canyon morphology and different sediment sources on this basis we predict that the spatial and temporal patterns of turbidite sedimentation could vary considerably along the length of the gbr margin

filling the gap a 60 ky record of mixed carbonate siliciclastic turbidite deposition from the great barrier reef abstract late pleistocene to holocene margin sedimentation on the great barrier reef a mixed carbonate siliciclastic margin has been explained by a transgressive shedding model this model has challenged widely accepted sequence stratigraphic models in terms of the timing and type of sediment i e carbonate vs siliciclastic deposited during sea level oscillations however this model documents only hemipelagic sedimentation and the contribution of coarse grained turbidite deposition and the role of submarine canyons in this process remain elusive on this archetypal margin here we present a new model of turbidite deposition for the last 60 ky in the north eastern australia margin using high resolution bathymetry 58 new and existing radiometric ages and the composition of 81 turbidites from 15 piston cores we found that the spatial and temporal variation of turbidites is controlled by the relationship between sea level change and the variable physiography along the margin siliciclastic and mixed carbonate siliciclastic turbidites were linked to canyons indenting the shelf break and the well developed shelf edge reef barriers that stored sediment behind them turbidite deposition was sustained while the sea level position allowed the connection and sediment bypassing through the inter reef passages and canyons carbonate turbidites dominated in regions with more open conditions at the outer shelf and where slope confined canyons dominated or where canyons are generally less abundant the turn on and maintenance of carbonate production during sea level fluctuations also influenced the timing of carbonate turbidite deposition we show that a fundamental understanding of the variable physiography inherent to mixed carbonate siliciclastic margins is essential to accurately interpret deep water coarse grained deposition within a sequence stratigraphic context

decelerated mass loss of hurd and johnsons glaciers livingston island antarctic peninsula a new 10 year surface mass balance smb record of hurd and johnsons glaciers livingston island antarctica is presented and compared with earlier estimates on the basis of local and regional meteorological conditions and trends since johnsons is a tidewater glacier we also include a calving flux calculation to estimate its total mass balance the average annual smb over the 10 year observation period 2002 11 is 0 15 0 10 m w e for hurd glacier and 0 05 0 10 m w e for johnsons glacier adding the calving losses to the latter results in a total mass balance of 0 09 0 10 m w e there has been a deceleration of the mass losses of these glaciers from 1957 2000 to 2002 11 which have nearly halved for both glaciers we attribute this decrease in the mass losses to a combination of increased accumulation in the region and decreased melt the increased accumulation is attributed to larger precipitation associated with the recent deepening of the circumpolar pressure trough while the melt decrease is associated with lower summer surface temperatures during the past decade

impact of environmental parameters on coral reef development and drowning forward modelling of the last deglacial reefs from tahiti french polynesia iodp expedition 310 the sedimentological and chronological analysis of the last deglacial reef sequences of tahiti french polynesia drilled during the integrated ocean drilling program expedition 310 provide a high resolution data set allowing a well constrained forward modelling study this study represents the first attempt to model in three dimensions the coral reef development of tahiti during the last deglacial sea level rise 23 000 to 6000 cal yr bp using the software dionisos developed by ifp energies nouvelles it allows the testing of the reconstructed last deglacial sea level curve and the different environmental parameters for example wave energy and sediment fluxes that could have influenced the reef development these last deglacial reef sequences form two prominent ridges occurring seaward of the living barrier reef that consist of successive submerged reefs these reefs have been prone to drowning because the window of maximum carbonate production rate is inhibited by high water turbidity sediment supply from a nearby river shallow depth of wave action and substrate availability these factors combined with rapid sea level rise have driven the growth of retrograding reef pinnacles local factors substratum nature sediment supply and wave energy were the main processes that induced the drowning of the inner ridge whereas interplay of local and global factors acceleration of the sea level rise was responsible for the drowning of the outer ridge this particular acceleration of sea level rise of 16 m between 14 6 ka and 14 ka bp corresponds to meltwater pulse 1a

an analysis of the stability of thawing slopes ellesmere island nunavut canada active layer detachment slides are locally common on fosheim peninsula ellesmere island where permafrost is continuous the active layer is 0 5 0 75 m thick and summer temperatures are unusually

from platform top to adjacent deep sea new source to sink insights into carbonate sediment production and transfer in the sw indian ocean glorieuses archipelago abstract over the past ten years a huge amount of source to sink studies have aimed to unravel the tectonic climatic and other processes that shape the landscape from mountains to the deep ocean interestingly these studies have been mainly dedicated to siliciclastic or mixed systems for which the connection between drainage basins continental shelves slope and basin environments are often well constrained here we present a study focusing on a source to sink study dedicated to a pure carbonate system located in the sw indian ocean glorieuses archipelago extensive field sampling and geophysical acquisition across the carbonate platform have allowed us to estimate the composition the lateral variability and volumes of neritic sands deposited on the platform top additional seismic and bathymetric surveys across the platform interior illustrate the presence of plurimetric sandy bodies deposited along the leeward platform edge corresponding to the export of carbonate sediments from the platform top toward the platform edge under the influence of dominant currents and wind driven processes high resolution seismic bathymetric data and sediment cores acquired along the leeward slope and basin adjacent to the carbonate platform highlight the presence of channel levee complexes and turbiditic lobes which have accumulated on the seafloor on top of a 250 m thick sedimentary basin at 2000 3400 m water depth our study points out that carbonate sands and aragonitic mud produced on the platform top during the holocene have been shed to the adjacent basin we also demonstrate that this routing system was active at least throughout the last three glacial interglacial cycles this study has important consequences for our understanding of carbonate sedimentation processes occurring in the vicinity of isolated carbonate platforms 1 it highlights the role of oceanographic conditions in the distribution of sediment on a platform top and its export along the platform edge and the adjacent basin 2 it contributes to quantify the productivity of a carbonate platform as well as its sediment storage capacity 3 a first estimate of a carbonate source to sink system is proposed demonstrating that 0 57 km3 of sediments have been produced during the holocene 0 3 km3 being presently stored on the platform and the remaining having been exported to the deep basin

vegetation colonization of permafrost related landslides ellesmere island canadian high arctic 1 relationships between vegetation colonization and landslide disturbance are analyzed for 12 active layer detachments of differing ages located in three areas of the fosheim peninsula ellesmere island 80 n we discuss vegetation as an age index for landslides and a way to assess the time needed for complete recolonization of the surfaces since landslide detachment vegetation on undisturbed terrain is similar in the three areas but is more highly developed and complex inland due to a warmer summer climate on a regional scale the location of the area is as important as the effect of landslide age on vegetation colonization because of the influence of mesoclimatic conditions on vegetation development on a landscape scale there is a positive relationship between landslide age and vegetation development as represented by total vegetation cover floristic composition and successional stage consequently vegetation can be used at this scale as an indicator of landslide age fifty years are required to restore vegetation patches to a floristic composition similar to communities occurring in undisturbed conditions but with lower floristic richness and a discontinuous cover and without well developed layering the shorter time needed for landslide recovery in the area with the warmest summer climate confirms the sensitivity of arctic vegetation to small differences in air temperature this could trigger a set of interlinked feedbacks that would amplify future rates of climate warming

reef core insights into mid holocene water temperatures of the southern great barrier reef the tropical and subtropical oceans of the southern hemisphere are poorly represented in present day climate models necessitating an increased number of paleoclimate records from this key region to both understand the earth s climate system and help constrain model simulations here we present a site specific calibration of live collected massive porites sr ca records against concomitant in situ instrumental water temperature data from the fore reef slope of heron reef southern great barrier reef gbr the resultant calibration and a previously published acropora calibration from the same site was applied to subfossil coral material to investigate holocene water temperatures at heron reef u th dated samples of massive porites suggest cooler water temperatures with reduced seasonal amplitude at 5 2 ka 2 76 1 31i c cooler than present and 7 ka 1 26i c cooler than present at heron reef these results contrast the previous suggestion of a mid holocene thermal maximum in the central gbr around 5 35 ka and 4 48 ka yet may be explained by differences in temperature of the shallow ponded reef flat central gbr and the deeper reef slope waters this study and potential large reservoir correction errors associated with early radiocarbon dates combining coral based water temperature anomaly reconstructions from the tropical and subtropical western pacific indicates a coherent temperature response across the meridional gradient from indonesia and papua new guinea down to the southern gbr this similarity in reconstructed temperature anomalies suggests a high probability of an earlier expression of a mid holocene thermal maximum on the gbr between 6 8 and 6 0 ka

variability of surface ocean radiocarbon and stable isotopes in the southwestern pacific we present high precision radiocarbon 14c results and stable isotope 18o and 13c records for a coral from heron island 23 s 152 e and new stable isotope 18o and 13c records for annual coral bands from abraham reef 22 s 153 e in the southern great barrier reef studied earlier druffel and griffin 1993 these tracers provide unique information on the regional water mass history and together these data allow us to constrain the variability of circulation in the upper pacific over the past four centuries first we observe decreases in 18o of coral from abraham reef and heron island indicating an increase in sea surface temperature and or a decrease in surface salinity since 1850 second the small suess effect value 14c decrease from 1880 to 1955 due mostly to fossil fuel co2 observed previously at abraham reef druffel and griffin 1993 is confirmed in the measurements reported here from the heron island coral this value is low compared to those observed in other areas of the ocean druffel 1997 druffel and linick 1978 nozaki et al 1978 between 1880 and 1955 third we report alterations in the correlation between el nino events and the occurrence of low 14c which is indicative of long term change s in circulation in the sw pacific the 14c shifts reported here are not large but even small temporal changes in prebomb 14c suggest that important changes in the large scale state of the ocean have occurred such as a temporal change in circulation

large variations of surface ocean radiocarbon evidence of circulation changes in the southwestern pacific radiocarbon 14c and stable isotope 18o and 13c records are presented for biannual samples from a 323 year banded coral series collected from the southern great barrier reef australia the high precision 14c record contains variations on an interannual timescale that are particularly large between a d 1680 and 1730 by comparison with tree ring 14c records stuiver and quay 1980 m stuiver personal communication 1992 it is clear that these shifts were not caused by changes in the 14c of atmospheric co2 changes in vertical mixing and large scale advective changes involving source waters to the western coral sea region are likely processes that could account for these large 14c variations most low 14c values for the period a d 1635 1875 coincide with el nino southern oscillation enso events as reported by quinn et al 1987 for the eastern tropical pacific however enso does not explain all of the variations especially during 1875 1920 when 14c values remained high cross spectral analysis of the early half of the 14c and 18o records a d 1635 1795 reveals that the 6 year period is coherent this coherency is not present in the latter half a d 1797 1957 of the isotope records these data support the concept of century timescale changes in the nature of enso as it is manifest in the southwestern pacific our coral record shows no evidence of a suess effect the lowering of 14c from late 1800s through 1955 due mainly to co2 input from fossil fuel burning this is coincident with the change we observe in the nature of enso and is further evidence that a long term change in mixing of upper waters occurred in this region

mixed carbonate siliciclastic sedimentation along the great barrier reef upper slope a challenge to the reciprocal sedimentation model abstract results of studies involving numerous cores and odp holes along the great barrier reef gbr margin and adjacent queensland trough and queensland plateau have challenged the use of a reciprocal sedimentation model to describe the sedimentary response of slope and basin settings to glacioeustatic sea level fluctuations upper slope sedimentation results from the relationships between sea level fluctuations antecedent topography and regional climate that play an important role in the type and amount of sediment deposited on the upper slope during glacial deglacial and interglacial times during the last glacial maximum lgm 20 ka ago upper slope sediments generally lacked siliciclastic material and are characterized by very low accumulation rates whereas early deglacial time termination i ti deposits are dominated by a siliciclastic and neritic carbonate pulse siliciclastic sedimentation was significantly reduced in the holocene while carbonate sedimentation remains elevated a new borehole iodp expedition 325 hole m0058a hole 58a recovered 82 of a 40 4 m hole on the upper slope east of noggin passage on the central gbr margin near cairns australia hole 58a provides a detailed sedimentary record during termination ii tii marine isotope stage 6 5e mis 6 5e deglacial transition and through most of interglacial mis 5 this hole along with two others odp leg 133 holes 820a and 819a from the upper slope east of grafton passage show carbonate siliciclastic cyclicity as the result of glacioeustatic change with the gbr shelf sedimentation at hole 58a is consistent with that of previous studies along the gbr margin focusing on the lgm to present and extends the upper slope sedimentary record back to tii and interglacial mis 5 a siliciclastic pulse similar to the one during ti occurred during the penultimate deglaciation tii however the maximum neritic aragonite export to the upper slope occurred not during peak mis 5e highstand when sea level was a few meters above modern position but subsequently during a time mis 5d to 5a when lowered sea level fluctuated between 30 and 50 m below present sea level siliciclastic sediments were reworked and exported to the upper slope when the lowstand fluvial plain was re flooded whereas neritic carbonate export to the slope reached a maximum when sea level fell and much of the mid to outer shelf re entered the photic zone subsequent to a drowning interval thus this analysis refines the mixed sedimentation models of upper slope sedimentation along the central gbr margin during the penultimate deglacial transgression and subsequent interglacial early and late highstand this study provides further evidence that mixed carbonate siliciclastic margins do not always behave in a predictable manner and that mixed margins both modern and ancient would benefit from detailed study of sediment transport in the context of sea level rise and fall

tropical view of quaternary sequence stratigraphy siliciclastic accumulation on slopes east of the great barrier reef since the last glacial maximum generic models of continental margin evolution predict that siliciclastic fluxes to slopes should be maximal and minimal during major sea level lowstands and transgressions respectively here we document the opposite for the northeast australian margin the largest extant mixed siliciclastic carbonate depositional system cores from slopes of this margin consistently contain siliciclastic rich intervals 0 3 1 m thick in the upper few meters radiocarbon dates of planktonic foraminifera show that this interval was deposited between 12 and 7 ka and represents greatly increased siliciclastic fluxes during late transgression this massive terrigenous discharge to slopes occurred along at least 450 km of the margin irrespective of modern variations in bathymetry or climate although we cannot dismiss a significantly different early holocene climate with greatly enhanced sediment discharge available data instead suggest that rivers aggraded on the shelf during lowstand because of an extensive subaerially exposed reef system this phenomenon may occur on other margins rimmed by reefs requiring a major revision of concepts used to interpret mixed siliciclastic carbonate systems

recent atmospheric warming and retreat of ice shelves on the antarctic peninsula in 1978 mercer1 discussed the probable effects of climate warming on the antarctic ice sheet predicting that one sign of a warming trend in this region would be the retreat of ice shelves on the antarctic peninsula analyses of 50 year meteorological records have since revealed atmospheric warming on the antarctic peninsula2 3 and a number of ice shelves have retreated4 8 here we present time series of observations of the areal extent of nine ice shelves on the antarctic peninsula showing that five northerly ones have retreated dramatically in the past fifty years while those further south show no clear trend comparison with airtemperature data shows that the pattern and magnitude of ice shelf retreat is consistent with the existence of an abrupt thermal limit on iceshelf viability the isotherm associated with this limit having been driven south by the atmospheric warming ice shelves therefore appear to be sensitive indicators of climate change

massive siliciclastic discharge to slopes of the great barrier reef platform during sea level transgression constraints from sediment cores between 15 s and 16 s latitude and possible explanations abstract the northeast australian continental margin including the great barrier reef gbr platform provides an outstanding modern analogue for understanding sedimentation in tropical mixed siliciclastic carbonate depositional systems previous studies of cores from this margin have suggested that in contrast to widely accepted models maximum siliciclastic fluxes to slopes over the last 30 ky occurred when sea level transgressed the shelf ca 11 7 ka rather than when sea level was at a lowstand before 18 ka however climate and bathymetry can affect regional sediment deposition significantly and the cores examined to date have come from the southern queensland trough where the margin has a wet tropical climate and a broad shelf 50 km with gradual slopes in this study we examine the abundance and accumulation of siliciclastic material in four cores from lower slopes of the northern queensland trough where rivers drain a drier region and debouche onto a narrow shelf with steep incised slopes similar to previously examined cores all cores contain a dark greyish brown horizon within the upper few meters this horizon represents a low in carbonate content and corresponding high in siliciclastic material primarily clay and oxygen isotope stratigraphy shows that it was deposited during late transgression nominally between 11 and 7 ka moreover mass accumulation rate calculations demonstrate that this horizon reflects a significant rise in siliciclastic fluxes when combined with the previous work to the south it appears that slopes all along a large portion of the northeast australian continental margin received greatly enhanced inputs of siliciclastic material during late transgression independent of proximal climate and bathymetry two general explanations are offered for this observation 1 climate change induced highly variable riverine discharge over the past 30 ky with a prominent maximum coincident with late transgression or 2 the shelf stores large quantities of siliciclastic sediment during lowstand and releases this material to the slope during late transgression in either case siliciclastic accumulation on the northeast australia continental margin behaves completely opposite to predictions from conventional models

mid holocene climate in new caledonia southwest pacific coral and pmip models monthly resolved results abstract the mid holocene climate is characterized by an insolation seasonality decrease in the southern hemisphere but measurements of its actual impact on monthly resolved sea surface temperature sst in the southwest pacific region are still insufficient a new caledonian 5 5 ka cal bp coral provides a 20 year long seasonally resolved record of ocean surface conditions as inferred from coral sr ca and ba ca results were compared to monthly series of paleoclimate modeling intercomparison project phase 2 pmip2 model simulations anomalous stable isotope and u ca values are observed in a restricted area of the skeleton related to dissolution features the mid holocene sst seasonal amplitude mean and variability are higher than presently in new caledonia the increased seasonal amplitude in the mid holocene being most probably due to the occurrence of colder winters other southwest pacific mid holocene coral data showed also such an increased seasonal amplitude this could mean that the south pacific convergence zone spcz was weaker or reached locations more northerly than at present which could fit with northward shifts of the inter tropical convergence zone itcz during south hemisphere winter inversely strong rainfalls during the summer deduced from the ba ca signal and reconstructed sea surface salinity sss were interpreted as reflecting pronounced southwestward shifts of the spcz in summer as those occurring today during la nina events none of the six pmip2 models used reproduce the proxy based mid holocene increase of sst seasonal amplitude model maps show a less intense spcz in winter that would be consistent with higher sst seasonal amplitude finally we stress the need for more seasonally resolved data to validate this enhanced mid holocene sst seasonal amplitude in the southwest pacific region and to better understand the underlying mechanisms

shelf edge delta and reef development on a mixed siliciclastic carbonate margin central great barrier reef the great barrier reef gbr is the world s largest extant mixed silicilastic carbonate margin previous research on the great barrier reef has suggested that the extensive barrier reef system may act as an impermeable barrier and limit the development of delta systems during lowstands but sufficient geophysical data to support this hypothesis are lacking we use dense sparker seismic and sub bottom profiler data to better understand the structure of a large lobe shaped feature 10 km 10 km on the shelf edge of the central gbr and the interactions between siliciclastic and carbonate sedimentary systems interpreted sparker seismic contains prograding clinoforms and suggest that the lobe shaped feature was a river dominated shelf edge delta a delta on the shelf edge implies that the presence of an exposed barrier reef was not a major impediment to deposition and that other adjacent lobe shaped features are also deltaic deposits the shelf edge deltas were deposited onto a broad upper slope terrace that allowed continued progradation and limited incision when sea level fell below the shelf edge delta foresets are commonly colonized by coral reefs but the spatial and temporal relationship between reefs and some deltaic units remains unclear the presence of multiple shelf edge deltas that link to previously mapped burdekin river paleo channels indicates a complex history of sedimentation with the burdekin river delta migrating up to 100 km along the gbr margin during the late quaternary regional bathymetric data suggest that large modern or recent shelf edge deltas are rare on the gbr and that there was a broad range of sedimentary processes operating along the margin of the gbr during periods of low sea level

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

syn sedimentary deformation as a mechanism for the initiation of submarine gullies on a carbonate platform to slope transition browse basin australian north west shelf abstract syn sedimentary deformation and submarine channel initiation are both important processes influencing the stratigraphic development and reservoir properties of carbonate platforms based on a high resolution 3d seismic dataset our study shows that platform margin parallel syn sedimentary faulting in the vicinity of the clinoform breakpoint can lead to the indention of channel heads that subsequently grow and expand in headward and downslope direction the carbonate dominated miocene succession of the browse basin on the australian north west shelf reveals a distinct submarine channel system during a time of overall platform progradation the progradation occurs over a drowned eocene to lower miocene carbonate ramp which formed a large scale inflection previous studies investigated the architecture of the carbonate platform containing a large neogene barrier reef system we present a high resolution 3d seismic study of the contemporaneous platform to slope transition landward of first significant gullies a distinct network of margin parallel small scale arcuate faults is observed active faulting during appearance of the first gullies is exhibited by growth strata which are located directly basinward of the faults these steep 65 85 small scale faults are characterized by throws of 5 25 ms twt and show a tendency to merge laterally and vertically with adjacent faults syn sedimentary deformation associated with these faults likely triggered slope failure and the generation of turbidity currents finally leading to the growth of the gullies by headward and downslope erosion

recent shallowing of the thaw depth at crater lake deception island antarctica 2006 2014 abstract the western antarctic peninsula region is one of the hot spots of climate change and one of the most ecologically sensitive regions of antarctica where permafrost is near its climatic limits the research was conducted in deception island an active stratovolcano in the south shetlands archipelago off the northern tip of the antarctic peninsula the climate is polar oceanic with high precipitation and mean annual air temperatures maat close to 3 c the soils are composed by ashes and pyroclasts with high porosity and high water content with ice rich permafrost at 0 8 c at the depth of zero annual amplitude with an active layer of about 30 cm results from thaw depth ground temperature and snow cover monitoring at the crater lake calm s site over the period 2006 to 2014 are analyzed thaw depth td was measured by mechanical probing once per year in the end of january or early february in a 100 100 m with a 10 m spacing grid the results show a trend for decreasing thaw depth from ci 36 cm in 2006 to 23 cm in 2014 while maat as well as ground temperatures at the base of the active layer remained stable however the duration of the snow cover at the calm s site measured through the snow pack factor sf showed an increase from 2006 to 2014 especially with longer lasting snow cover in the spring and early summer the negative correlation between sf and the thaw depth supports the significance of the influence of the increasing snow cover in thaw depth even with no trend in the maat the lack of observed ground cooling in the base of the active layer is probably linked to the high ice water content at the transient layer the pyroclastic soils of deception island with high porosity are key to the shallow active layer depths when compared to other sites in the western antarctic peninsula wap these findings support the lack of linearity between atmospheric warming and permafrost warming and induce an extra complexity to the understanding of the effects of climate change in the ice free areas of the wap especially in scenarios with increased precipitation as snow fall

the effect of skeletal mass accumulation in porites on coral sr ca and δ18o paleothermometry 1 paleotemperature estimates based on coral sr ca have not been widely accepted because the reconstructed glacial holocene shift in tropical sea surface temperature 4 6 c is larger than that indicated by foraminiferal mg ca 2 4 c we show that corals over estimate changes in sea surface temperature sst because their records are attenuated during skeletogenesis within the living tissue layer to quantify this process we microprofiled skeletal mass accumulation within the tissue layer of porites from australasian coral reefs and laboratory culturing experiments the results show that the sensitivity of the sr ca and 18o thermometers in porites will be suppressed variable and dependent on the relationship between skeletal growth rate and mass accumulation within the tissue layer our findings help explain why 18o sst sensitivities for porites range from 0 08 c to 0 22 c and are always less than the value of 0 23 c established for biogenic aragonite based on this observation we recalibrated the coral sr ca thermometer to determine a revised sensitivity of 0 084 mmol mol c after rescaling most of the published sr ca sst estimates for the indo pacific region for the last 14 000 years 7 c to 2 c relative to modern fall within the 95 confidence envelope of the foraminiferal mg ca sst records we conclude that two types of calibration scales are required for coral paleothermometry an attenuated porites specific thermometer sensitivity for studies of seasonal to interannual change in sst and importantly the rescaled 0 084 mmol mol c sr ca sensitivity for studies of 20th century trends and millennial scale changes in mean sst the calibration scaling concept will apply to the development of transfer functions for all geochemical tracers in corals

rupture lengths and temporal history of significant earthquakes on the offshore and north coast segments of the northern san andreas fault based on turbidite stratigraphy piston gravity and jumbo kasten cores were collected from channel and canyon systems draining the northern california continentalmargintoinvestigatetherecordofperiodicholoceneturbiditesforpossibleconnectiontolargemagnitudeearthquakeson the adjacent northern san andreas fault poorly known channel systems were mapped with multibeam sonar to define pathways and channel confluences cores sampled all major and many minor channel systems extending from cape mendocino to just north of monterey bay sampling both along and across channels was done and particular attention was paid to channel confluences as these areas afford opportunities to test for synchronous triggering of turbidity currents while at sea all cores were scanned using a geotek multisensor core logger mscl which collects high resolution photography p wave velocity gamma ray density and magnetic susceptibility data from the unsplit cores lithology was logged visually and cores were later imaged with x radiography we use 14 c ages relative dating tests at channel confluences and stratigraphic correlation using physical properties to determine

interdecadal variation in the extent of south pacific tropical waters during the younger dryas event during the younger dryas event about 12 000 years ago the northern hemisphere cooled by between 2 and 10 degrees c refs 1 2 whereas east antarctica experienced warming but the spatial signature of the event in the southern mid latitudes and tropics is less well known as records are sparse and inconclusive here we present high resolution analyses of skeletal sr ca and 18o 16o ratios for a giant fossil diploastrea heliopora coral that was preserved in growth position on the raised reef terraces of espiritu santo island vanuatu in the southwestern tropical pacific ocean our data indicate that sea surface temperatures in vanuatu were on average 4 5 1 3 degrees c cooler during the younger dryas event than today with a significant interdecadal modulation the amplified annual cycle of sea surface temperatures relative to today indicates that cooling was caused by the compression of tropical waters towards the equator the positive correlation in our record between the oxygen isotope ratios of sea water and sea surface temperatures suggests that the south pacific convergence zone which brings 18o depleted precipitation to the area today was not active during the younger dryas period

classification of submarine canyons of the australian continental margin abstract submarine canyons influence oceanographic processes sediment transport productivity and benthic biodiversity from the continental shelf to the slope and beyond however not all canyons perform the same function the relative influence of an individual canyon on these processes will in part be determined by its form shape and position on the continental margin here we present an analysis of canyon geomorphic metrics using an updated national dataset of 713 submarine canyons surrounding mainland australia these metrics attributes for each canyon are used to classify them into canyon types across a hierarchy of physical characteristics separately for shelf incising n 95 and slope confined blind n 618 canyons we find that the canyon metrics describe a wide variety of canyon form and complexity that is consistent with a population of canyons that has evolved at different rates around the australian margin since the break up of gondwana the large number of slope confined canyons is interpreted to reflect dominance of slope mass wasting processes over erosive turbidity flows from fluvial and shelf sources on an arid continent the distribution of submarine canyons around the australian margin is not regular with clusters occurring in the east southeast west and southwest where the margin is steepest the classification result provides a quantitative framework for describing canyon heterogeneity for application in studies of geological controls on individual canyons canyon oceanography and canyon biodiversity