geodynamic evolution of the sw europe variscides 1 the early evolution of sw europe variscides started by opening of the rheic ocean at 500 ma splitting avalonia from armorica iberia subduction on the se side of rheic generated the paleotethys back arc basin 430 390 ma splitting armorica from iberia with development of porto tomar ferreira do alentejo ptfa dextral transform defining the boundary between continental armorica and finisterra microplate to the w obduction of paleotethys was followed by armorica iberia collision and emplacement of nw iberian allochthonous units at 390 370 ma whereas toward the west of ptfa there was antithetic ophiolite obduction beja acebuches and rheic ophiolites plus finisterra continental slices on top of ossa morena zone with simultaneous development of eclogites and orogenic magmatism under a flake double wedge tectonic regime continued convergence 370 ma proceeded by intracontinental deformation with progressive tightening of the ibero armorican arc through dextral transpression on the cantabrian indentor from iberia to armorica the proposed model is discussed at the light of the driving mechanism of soft plate tectonics

variscan intra orogenic extensional tectonics in the ossa morena zone evora aracena lora del rio metamorphic belt sw iberian massif shrimp zircon u th pb geochronology

response of planktonic foraminifera to glacial cycles mid pleistocene change in the southern south china sea a high resolution study 2 ka of planktonic foraminifers in 997 samples from odp site 1143 9821 72vn 113817 11ve water depth 2772 m in the southern south china sea scs reveals faunal response to glacial cycles in the last 2 1 ma most distinctive is the contrasting variations in the abundance of two tropical subtropical species that exhibit similar resistance to dissolution in modern oceans the relative and absolute abundances of globorotalia menardii are high in interglacials and low in glacials and covary with d 18 o fluctuations over the studied interval pulleniatina obliquiloculata however follow oxygen isotopes only before the mid pleistocene revolution mpr showing high abundances during glacials and low during interglacials after 850 ka three abundance maxima of p obliquiloculata are observed corresponding to three major glacial episodes marine isotope stages mis 2 12 and 16 respectively this change in abundance patterns of p obliquiloculata appears to be unique to the southern scs as in late pleistocene records from other western pacific regions including the okinawa trough and the northern scs all show co varying patterns with d 18 oa sg menardii does cross spectral analyses performed between percentages of globorotalia menardii and d 18 o records show high coherency at 41 ka obliquity and then at 100 ka eccentricity bands we suggest that the high abundances of g menardii during interglacials in the past 2 1 ma reflect warmer temperatures percentages of pulleniatina obliquiloculata vs oxygen isotope records show quite large phase difference at 41 ka obliquity band before the mpr as a contrast there are negligible phase differences in the vicinity of 100 and 41 ka after the mpr which means reverse trend between percentages of p obliquiloculata and d 18 o fluctuations the differences of p obliquiloculata from g menardii in abundance and orbital forcings are interpreted as resulting from a profound change in the regional upper ocean structure during the mpr time probably relating to a final glacial cut off of the southern scs from the indian water at 850 ka and to higher salinity during glacial times after 850 ka we speculate that this change is related to the decreased connection between the pacific and indian ocean d 2004 elsevier b v all rights reserved

deglacial and holocene evolution of the vietnam shelf stratigraphy sediments and sea level change on the vietnam shelf more than 1000 miles of shallow high resolution seismics were analyzed to unravel post glacial evolution in a tropical siliciclastic environment together with 25 sediment cores from water depths between 21 and 169 m to determine stratigraphy distribution and style of sedimentation fourty seven samples were dated with the ams c 14 technique the shelf was grouped into three regions a southern part a central part and a northern part on the broad southern shelf sedimentation is influenced by the mekong river which drains into the scs in this area here incised valley fills are abundant that were cut into the late pleistocene land surface by the paleo mekong river during times of sea level lowstand those valleys are filled with transgressive deposits the holocene sedimentation rate in this low gradient accommodation dominated depositional system is in the range of 5 10 and 25 40 cm ky at locations sheltered from currents the central shelf is narrow and the sedimentary strata are conformable here numerous small mountainous rivers reach the scs and transport large amounts of detrital sediment onto the shelf therefore the holocene sedimentation rate is high with values of 50 100 cm ky in this supply dominated depositional system the broad northern shelf in the vicinity of the red river delta shows as on the southern shelf incised valleys cut into the pleistocene land surface by paleo river channels in this accommodation dominated shelf area the sedimentation rate is low with values of 5 10 cm ky where applicable we assigned the sampled deposits to different paleo facies the latter are related to certain intervals of water depths at their time of deposition comparison with the sea level curve of hanebuth t j j stattegger k grootes p 2000 rapid flooding of the sunda shelf a lateglacial sea level record science 288 1033 1035 indicates subsidence on the central shelf which is in agreement with the high sedimentation rates in this area in contrast data from the northern shelf suggest tectonic uplift that might be related to recent tectonic movements along the ailao shan red river fault zone data from the southern shelf are generally in agreement with the sea level curve mentioned above c 2004 elsevier b v all rights reserved

sea levels during late marine isotope stage 3 or older reported from the red river delta northern vietnam and adjacent regions abstract a 60 m long sediment core from the lower red river delta in northern vietnam contains three depositional sequences consisting mostly of regressive shallow marine sediments bounded by unconformities the youngest unit represents the modern red river delta the second unit a facies succession comparable to the overlying deltaic succession formed during an earlier sea level highstand as indicated by the marine isotope stage mis 3 age obtained by radiocarbon dating the third undated unit might reflect earlier high sea levels of the middle to late pleistocene the mis 3 ages derived from shoreline related sedimentary facies are supported by records from adjacent mega deltas and shelf sites with paleoshoreline facies proximal sites from the central indochina craton show high sea levels during late mis 3 whereas distal sites from the open continental shelf indicate much lower sea levels at the same time independent globally relevant sea level reconstructions suggest that both positions have been affected by later vertical movement this discrepancy between sea level records from central cratonic sites and the continental margin can be explained by a balanced response to locally differentiated sediment loading and compaction on the shelf as is supported by published seismic data however if the complete set of radiocarbon dates is contaminated by younger material then the second recorded sea level highstand may be associated with mis 5 as no marine deposits have yet been reported in any of the three indochinese mega deltas for this time interval

carbonate dissolution fluctuations in the western equatorial pacific during the late quaternary planktonic foraminiferal test fragmentation in three cores along a depth transect from the western equatorial pacific erdc 93p 1619 m rc17 177 2600 m v28 238 3120 m thompson 1976 were examined for the last 500 kyr at sample intervals from 2 5 to 5 kyr to study the fluctuations of dissolution in the western equatorial pacific the age models were constructed by correlating the 18o records with the specmap stack imbrie et al 1984 results showed that intermediate and deep waters experienced the same patterns of dissolution through climatic cycles fragmentation varied with a greater amplitude and the carbonate ion concentration changed less in the deep than in the intermediate water dissolution has significant variance distributions and coherencies with 18o over the 100 41 and 23 kyr periods of orbital variations dissolution maxima lag ice volume minima by 6 to 20 kyr the dissolution variability was consistent with recent geochemical models which seek to explain the reduction of atmospheric co2 concentration at the last glacial maximum broecker 1982 boyle 1988

coralline red algae as high resolution climate recorders most high resolution proxy based paleoclimate research has concentrated on tropical oceans while mid and high latitude marine regions have received less attention despite their importance in the global climate system at present sclerochronological analyses of bivalve mollusks supply the bulk of annual to subannual resolution extratropical marine climate data even though interpretation is complicated by a slowdown of growth with increasing shell age hence in order to address the need for additional high resolution proxy climate data from extratropical regions we conducted the first year long in situ field calibration of the coralline red alga clathromorphum compactum in the gulf of maine united states coralline red algae are widely distributed in coastal regions worldwide and individual calcified plants can live continuously for several centuries in temperate and subarctic oceans stable oxygen isotopes extracted at subannual resolution from growth increments of monitored specimens of c compactum relate well to in situ measured sea surface temperatures during the may to december calcification period highlighting the suitability of coralline red algae as an extratropical climate archive furthermore there is a strong correlation between a 30 yr 18 o record of c compactum and an instrumental sea surface temperature record r 0 58 p 0 0008 and a proxy reconstruction derived from the bivalve arctica islandica collected in the central gulf of maine r 0 54 p 0 002

225 years of bering sea climate and ecosystem dynamics revealed by coralline algal growth increment widths bering sea climate and ecosystem dynamics have recently undergone major changes that have affected seasonal sea ice distribution and marine life including commercially important salmon fisheries unfortunately long term bering sea dynamics are poorly understood largely because of an absence of high resolution marine proxy archives here we present the first record compiled from annual growth increment widths of long lived coralline algae collected in shallow water habitats spanning the entire aleutian islands while algal growth in the aleutians exhibits a variable relationship with regional temperatures it is strongly driven by changes in solar radiation reaching the seafloor therefore it provides an exceptional archive of long term light dynamics which in the bering sea is attributed to changes in strength of the aleutian low al the dominant climate pattern of the subarctic north pacific the al is positively related to bering sea cloudiness and wind strength which in turn fosters upper ocean mixing mixing raises surface water nutrient concentrations and stimulates plankton production which is positively linked to alaskan salmon abundance enhanced clouds and plankton production increase shading on the shallow seafloor and reduce algal growth light driven algal growth rates track proxy derived salmon abundance from 1782 onward but are poorly related to temperature dominated pacific decadal oscillation pdo variability prior to the twentieth century the algal record suggests that the present day relationship of al and pdo varied historically and that salmon stocks have been more closely related to al strength via its effect on plankton abundance rather than pdo related temperatures

investigating enso and wpwp modulated typhoon variability in the south china sea during the mid late holocene using sedimentological evidence from southeastern hainan island china abstract the link between tropical cyclone tc activity in the south china sea scs and global climate change is commonly debated and there is a clear need for long term geological records of tc activity if we are to clarify this connection multi millennial high resolution paleo storm records from the scs are rare in the region and this causes difficulties for those exploring potential climate drivers of tc variability over centennial to millennial timescales and reduces our ability to fully assess the risks associated with future tc activity this paper presents an age constrained mud dominated sedimentary sequence from a coastal lagoon on hainan island china multiproxy analyses incorporating chronological lithological sedimentological and geochemical evidence were used to infer storm deposits preserved within the sequence and to reconstruct a time series of storm activity in the scs during the mid to late holocene this long sedimentary record shows that tcs were highly active over the periods 5500 to 3500 and 1700 to 0 cal yrs bp and these periods contrast with a relatively quiet period 3500 1700 cal yrs bp an apparent inverse correlation between tc reconstructions from the scs and those from the korean peninsula and japan implies an oscillating pattern across the scs and western north pacific wnp over centennial to millennial timescales a comparison between the sedimentary and paleoclimatic records implies that the el nino southern oscillation was not the only mechanism responsible for typhoon variability over the past 7500 cal yrs bp suggesting that other factors such as the thermal state of the western pacific warm pool likely also had a strong influence on both scs and wnp tc variability

relative paleointensity stack during the last 250 kyr in the northwest pacific 1 we have conducted a paleomagnetic study of 10 sediment cores recovered from the northwest pacific the purpose is to establish a regional paleointensity stack during the last 250 kyrs nopapis 250 for global coverage of paleointensity data as well as a regional reference for paleointensity assisted stratigraphy in the studied cores reductive dissolution of magnetite appears to have occurred mainly in glacial periods such horizons accompany large decreases in s ratio s 0 3t 1 irm 0 3t sirm 2 as low as 0 90 the sediments are also intercalated by frequent volcanic ash layers prerequisites for reliable relative paleointensity estimation are not satisfied at these horizons we rejected unsuitable data by quantitative criteria based on s ratio and saturation isothermal remanent magnetization sirm and constructed the nopapis 250 curve from the remaining data in the construction of the curve we chose irm as a normalizer because acquisitions of anhysteretic remanent magnetization arm are considered to be influenced by magnetic interactions among magnetic grains in the northwest pacific sediments relative intensity variation of the nopapis 250 gives a standard deviation that is 33 of the average if the normal distribution is assumed the nopapis 250 curve generally shows similar variation patterns compared with other high resolution records reported from other regions many paleointensity lows are recognized in common six out of the nine lows can be correlated with reported excursions in literature

cenozoic denudation history of southern hainan island south china sea constraints from low temperature thermochronology abstract as a large block of continental crust hainan island located in the western south china sea forms a rift shoulder to the adjacent offshore yinggehai and qiongdongnan basins and lies in the footwall of their main boundary faults we present 11 apatite fission track aft data and 16 u th sm he ages to elucidate the island s cenozoic morphotectonic evolution our data indicate that much of southern hainan island experienced a well defined cooling episode commencing in late eocene oligocene time during this time most samples cooled from 110 c to 55 15 c at a rate of 4 0 c ma following which the cooling rate decreased to 2 5 c ma assuming a constant paleogeothermal gradient of 23 c km similar to that of the present day since oligocene time when most samples cooled into the base of the aft partial annealing zone the total eroded section is estimated at a minimum of 3 5 km about two thirds of which was removed during the oligocene rapid cooling phase this implies that elevation of southern hainan island has decreased since the oligocene and this is supported by independent paleobotanical evidence although a further cooling episode since 5 ma is also suggested by aft thermal history models cooling occurred from relatively low temperatures 45 50 c where annealing kinetics are not well understood so this cannot be rigorously assessed despite evidence for increased sedimentation in offshore basins at this time our data suggest that the no 1 fault of the adjacent offshore yinggehai basin to the west which is thought to be an offshore extension of the red river fault zone was mainly active from late eocene through much of the oligocene but declined rapidly after 22 ma the marked reduction of potential sediment supply rate from hainan island into neighboring basins after that time suggests that miocene to recent sedimentation in the yinggehai basin was mainly supplied by the red river

geomagnetic paleointensity dating of south china sea sediments for the last 130 kyr relative paleointensity records from the northern south china sea northwest pacific ocean were studied in two gravity piston cores continuous mineral magnetic and paleomagnetic measurements were made using discrete sediment samples detailed rock magnetic parameters such as thermomagnetic and high field hysteresis data indicate that pseudo single domain magnetite in a narrow range of grain size and concentration is the main contributor to the remanent magnetization the uniform magnetic mineralogy meets the commonly accepted criteria for establishing relative paleointensity records the relative paleointensity rpi curves were constructed by normalizing the natural remanent magnetization nrm with isothermal remanent magnetization irm both in the 20 60 mt demagnetization state dating constraints have been provided by radiocarbon ages in the upper 400 cm of both cores furthermore we have correlated our paleointensity records with napis 75 s atlantic 1089 sint 200 and nopapis 250 to determine the chronological rpi framework for the south china sea scs pis although some temporal offsets of paleointensity features between the different records have been recognized their similar shape suggests that relative paleointensity on the 10 3 10 4 year scale is globally coherent and can provide an age framework for sediments independent of delta 18 o ages c 2009 elsevier b v all rights reserved

large scale erosional response of se asia to monsoon evolution reconstructed from sedimentary records of the song hong yinggehai and qiongdongnan basins south china sea

response of western pacific marginal seas to glacial cycles paleoceanographic and sedimentological features abstract this paper reviews the recent progress in late quaternary studies in five northwestern pacific marginal seas especially the south china sea as an example a series of marginal seas separate asia from the pacific ocean and significantly modify the material and energy flux linkage between land and sea during glacial cycles the sea level induced environmental signal was amplified in the marginal seas giving rise to drastic changes in areas and configurations of these seas and to reorganization of sea water circulation in basins since most of the western pacific marginal seas are influenced by monsoon circulation and some of these are located within the western pacific warm pool the glacial geographic changes have produced a profound impact on regional and global climate for example the decrease of sea area and sea surface temperature sst in the marginal seas was one of the factors responsible for the enhanced aridity of inland china during the glaciation glacial intensification of the winter monsoon and increased seasonality of sst in marginal seas might explain at least partly the apparent discrepancy between the tropical paleotemperature estimations based on terrestrial and open ocean records in this region as the western pacific marginal seas trap terrigenous material supplied by east asia the deep water sedimentation rates there can be one to two orders of magnitude higher than in the open ocean down slope sediment transport is more active when the sea level changes particularly during the deglaciation at least four types of carbonate cycles have been recognized in the western pacific marginal seas and each of those contains environmental signals from the surface and deep sea water as well as from the drainage basin

reconciling competing models for the tectono stratigraphic zonation of the variscan orogen in western europe abstract the late paleozoic variscan orogen in europe is the result of convergence and collision between laurussia and gondwana during closure of the rheic ocean the orogen is divided into tectonostratigraphic zones that have a distinct curvature ibero armorican arc iaa and record the late cambrian early ordovician opening of the rheic ocean the migration of terranes from the gondwanan margin towards laurussia as well as the closure of that ocean and development of the iaa three models have emerged to explain the distribution of tectonostratigraphic zones 1 indentation tectonics due to collision with laurussia by a ibero aquitanian promontory of gondwana during the devonian 2 development of the cantabrian orocline at ca 295 ma in the inner core of the iaa an interpretation supported by abundant paleomagnetic structural and geochronological data and 3 orogen scale modification due to large scale strike slip shear zones the indentor and orocline models 1 and 2 have been viewed as incompatible because the former requires curvature along the gondwanan margin prior to devonian collision with laurussia whereas the latter requires that the tectonostratigraphic zones were much more linear prior to bending at ca 295 ma recent data have rekindled the hypothesis that the cantabrian orocline is connected to a second orocline to the south central iberian orocline highlighting the possibility that inner gondwanan and outer laurussian zones of the ibero armorican arc may be structurally discordant with respect to each other implying that the geographic limits of orocline formation are presently unclear the two models can be reconciled if the geography of gondwana s leading edge was irregular but the tectono stratigraphic zones remained approximately linear within the inner zones of the putative ibero aquitanian indentor and ii deformation associated with initial collision was largely accommodated by sinistral sw iberia and dextral armorican massif motion along shear zones on either side of the promontory

reconstructing greenland ice sheet runoff using coralline algae the greenland ice sheet gris contains the largest store of fresh water in the northern hemisphere equivalent to 7 4 m of eustatic sea level rise but its impacts on current past and future sea level ocean circulation and european climate are poorly understood previous estimates of gris melt from 26 yr of satellite observations and temperature driven melt models over 48 yr show increasing melt trends there are however no runoff data of comparable duration with which to validate the relationship between the spatial extent of melting and runoff or temperature based runoff models further longer runoff records are needed to extend the melt pattern of greenland to centennial timescales enabling recent observations and trends to be put into a better historical context we have developed a new gris runoff proxy by extracting information on relative salinity changes from annual growth bands of red coralline algae we observed significant negative relationships between historic runoff relative salinity and marine summer temperature in sondre stromfjord greenland we produce the first reconstruction of runoff from a section of the gris that discharges into sondre stromfjord over several decades 1939 2002 and record a trend of increasing reconstructed runoff since the mid 1980s in situ summer marine temperatures followed an equivalent trend we suggest that since a d 1939 atmospheric temperatures have been important in forcing runoff these results show that our technique has significant potential to enhance understanding of runoff from large ice sheets as it will enable melt reconstruction over centennial to millennial timescales

a 580 kyr paleomagnetic record from the sub antarctic south atlantic ocean drilling program site 1089 1 we report geomagnetic directional paleosecular variation relative paleointensity proxies and oxygen isotope data from the upper 88 m composite depth mcd at south atlantic ocean drilling program odp site 1089 40 56 2 s 9 53 64 e 4620 m water depth the age model is provided by high resolution oxygen isotope stratigraphy augmented by radiocarbon dates from the upper 8 mcd of nearby piston core rc11 83 mean sedimentation rates at site 1089 are in the range of 15 to 20 cm kyr two intervals during the brunhes chron at 29 6 mcd 190 ka and at 48 mcd 335 ka have component magnetization directions with positive reverse polarity inclination however the excursional directions are heavily overprinted by the postexcursional field magnetite is the dominant carrier of magnetic remanence and occurs in the pseudosingle domain psd grain size an additional higher coercivity magnetic carrier characterized by low unblocking temperatures 350 c is assumed to be authigenic pyrrhotite a decrease in magnetization intensity down core is mirrored by a reduction in pore water sulfate indicating diagenetic reduction of magnetite despite down core changes in magnetic mineralogy normalized intensity records from site 1089 are comparable with high resolution paleointensity records from the north atlantic e g odp sites 983 and 984 sediment properties and sedimentation patterns within the cape site 1089 and iceland sites 983 and 984 basins are distinctly different at both millennial and orbital timescales and therefore preclude lithologic variability from being the source of this correlation variations in normalized intensity from site 1089 therefore appear to reflect changes in global scale geomagnetic field intensity

modeling paleogeographic scenarios of the last glacial cycle as a base for source to sink studies an example from the northwestern shelf of the south china sea abstract sea level sl data from the last glacial cycle lgc have been superimposed on to digital elevation models of the south china sea scs and adjacent areas to generate regional paleogeographic scenarios related to 4th to 5th order milankovitch climate cycles these scenarios at 123 65 60 5 56 20 and 0 5 kyr bp showed that the scs functioned as an oceanographic interface between the pacific and indian oceans during the lgc a late pleistocene paleo river delta hainan delta offshore west of hainan island china was an important sediment routing system on the nw shelf of the scs to understand the origin of the hainan delta better paleo reliefs of dem56kyrbp and dem65kyrbp were reconstructed using seismic stratigraphy sedimentology and back stripping methods geostatistical and geometric models of clinoforms and delta geometry as well as the courses of the reconstructed paleo distributary channels and paleo river valleys supported the interpretation that most delta sediment could be regarded as erosional products from hainan island we hypothesized that an intensification of sediment supply outpaced sl rise during the marine isotopic stages 4 3 transition resulting in a normal regression during the formation of the hainan delta morphodynamic modeling and meteorological data reanalysis further supported our interpretation that shifts in the asian monsoon system combined with local meteorological effects on hainan island and with global sl changes were the main drivers for the sediment source to sink systems at the nw scs continental margin during the lgc

clay minerals sr nd isotopes and provenance of sediments in the northwestern south china sea abstract the clay mineralogy and sr nd isotopic composition of sediments collected in the northwestern south china sea scs were investigated to understand sediment provenance and changes in the scs since the late pleistocene our results show that the clay mineral assemblages of the surface sediments are characterized by high amounts of illite and smectite and low amounts of kaolinite and chlorite the 87sr 86sr ratios of the surface sediments vary from 0 709617 to 0 734416 and end values range from 11 6 to 8 3 the clay minerals and sr nd isotope records suggest that sediments in the northwestern scs are derived from multiple sources the sediments deposited in the eastern shelf offshore of hainan originate predominantly from hainan island and south china whereas sediments in the western shelf offshore of hainan are derived mainly from indochina and hainan island however sediment source and transport mechanisms in the northwestern slope of the scs are more complicated our results suggest that input from the west may be the major sediment source but regions in the east taiwan and luzon also contribute part of the terrigenous materials downcore variations of sr nd isotopic composition in core sediments show clear glacial interglacial fluctuations higher 87sr 86sr ratios occur during glacial period indicating that the input of terrigenous materials from old continental rocks becomes one of the important sediment sources during these periods the exposure of continental shelf and southward migration of the coastline during the glacial sea level lowstand led to an increase of terrigenous supply to the northwestern slope of the scs the paleo red river and indochina are also potentially important contributors

a model study of the seasonal circulation in the gulf of maine the princeton ocean model is used to study the circulation in the gulf of maine and its seasonal transition in response to wind surface heat flux river discharge and the m2 tide the model has an orthogonal curvature linear grid in the horizontal with variable spacing from 3 km nearshore to 7 km offshore and 19 levels in the vertical it is initialized and forced at the open boundary with model results from the east coast forecast system the first experiment is forced by monthly climatological wind and heat flux from the comprehensive ocean atmosphere data set discharges from the saint john penobscot kennebec and merrimack rivers are added in the second experiment the semidiurnal lunar tide m2 is included as part of the open boundary forcing in the third experiment it is found that the surface heat flux plays an important role in regulating the annual cycle of the circulation in the gulf of maine the spinup of the cyclonic circulation between april and june is likely caused by the differential heating between the interior gulf and the exterior shelf slope region from june to december the cyclonic circulation continues to strengthen but gradually shrinks in size when winter cooling erodes the stratification the cyclonic circulation penetrates deeper into the water column the circulation quickly spins down from december to february as most of the energy is consumed by bottom friction while inclusion of river discharge changes details of the circulation pattern the annual evolution of the circulation is largely unaffected on the other hand inclusion of the tide results in not only the anticyclonic circulation on georges bank but also modifications to the seasonal circulation

forward modeling of carbonate proxy data from planktonic foraminifera using oxygen isotope tracers in a global ocean model the distribution and variation of oxygen isotopes in seawater are calculated using the goddard institute for space studies global ocean model simple ecological models are used to estimate the planktonic foraminiferal abundance as a function of depth column temperature season light intensity and density stratification these models are combined to forward model isotopic signals recorded in calcareous ocean sediment the sensitivity of the results to the changes in foraminiferal ecology secondary calcification and dissolution are also examined simulated present day isotopic values for ecology relevant for multiple species compare well with core top data hindcasts of sea surface temperature and salinity are made from time series of the modeled carbonate isotope values as the model climate changes paleoclimatic inferences from these carbonate isotope records are strongly affected by erroneous assumptions concerning the covariations of temperature salinity and 18ow habitat imposed biases are less important although errors due to temperature dependent abundances can be significant

a seismic geotraverse across the iberian variscides orogenic shortening collisional magmatism and orocline development 1 a crustal geotraverse through the iberian variscides is presented by integrating the available geological and seismic profiling data different modes of orogenic shortening are identified with varying degrees of coupling between upper and lower crust in northern and southern regions of the geotraverse a decoupling in the middle crust permits the lower crust to subduct underthrust thus compensating for strong upper crustal shortening this behavior does not result in great crustal thickening except in sectors of crustal underthrusting in southern central iberia moderate upper crustal shortening is due to a mechanically strong lower crust impeded to subduct underthrust in this region shortening is partitioned between upper and lower crust deformation being distributed in the upper crust while localized at major fault zones in the lower crust finally the central region of the geotraverse northern central iberia shows a coupled crustal deformation having given way to the largest orogenic thickening in the iberian variscides the thermal maturity of this much thickened crust originated voluminous crustal melting and concomitant normal fault detachments developed while shortening dominated in other regions theoretical models suggest that compressive stresses may prevail in the lower crust beneath the extending upper crust thus explaining the efficient syncollisional exhumation in this part of the orogen a particular feature of the iberian variscan geotraverse is the great importance of out of section mass movements mainly left lateral shear zones concentrated in two suture boundaries which displaced to the nw present coordinates central and northern iberia with respect to southern iberia

coralline algae are global palaeothermometers with bi weekly resolution abstract high resolution palaeoclimate data are required for the holocene to resolve differences recorded by current proxies the pole to pole distribution of rhodoliths coralline algae with their annual and sub annual calcite bands make these attractive candidates for such a role these bands contain climate information in the form of elemental traces in situ temperature ist was recorded at two rhodolith beds for 1 5 years the concentrations of mgco 3 and srco 3 mol deposited in lithothamion glaciale and phymatolithon calcareum over this 18 month period were determined using electron and ion microprobes highly significant linear relationships exist between mg sr and ist as well as sea surface temperature calibration between mg concentration and ist was used to obtain a 2 year temperature profile from a subfossil rhodolith thallus indicating half the seasonal peak to peak temperature amplitude earlier during the holocene than the present day both slow growing species 1 allowed sampling resolutions of 23 year 1 which is equivalent to 1 reading every 2 weeks sub monthly mg and sr records in rhodoliths make them unique globally distributed palaeothermometers which may help refine regional climate histories during the holocene

advancing mg ca analysis of coralline algae as a climate proxy by assessing la icp oes sampling and coupled mg ca δ18o analysis

the sedimentary and tectonic evolution of the yinggehai song hong basin and the southern hainan margin south china sea implications for tibetan uplift and monsoon intensification 1 the yinggehai song hong basin is one of the world s largest pull apart basins lying along the trace of the red river fault zone in the south china sea south of hainan island this basin crosscuts the rifted margin of the northern south china sea in this paper we present for the first time a regional compilation of multichannel seismic reflection data from both the strike slip and rifted margins the basins started to open after similar to 45 ma especially after similar to 34 ma the yinggehai basin was folded and inverted in the middle miocene after 21 ma in the north and 14 ma in the south before rapidly subsiding again after similar to 5 ma because of continued tectonism this subsidence has caused shale diapirism especially driven by associated sedimentation in the late pliocene 2 6 2 0 ma extension along the adjacent south hainan margin shows preferential lower crustal extension suggestive of lower crustal flow increasing toward the continent ocean transition during breakup sediment supply is reconstructed to peak in the middle miocene then falls between 14 and 10 3 ma to reach a low in the late miocene however rates rose again in the pliocene pleistocene the red river sediment budget is incompatible with climate models that propose stronger monsoon rains starting at 8 ma or with large scale river capture away from the red river after similar to 10 ma both lines of evidence point to major uplift in the red river drainage being middle miocene or older the recent preindustrial red river carried much more sediment than the average pleistocene accumulation rate indicating modest sediment buffering onshore at least in recent geologic time

the butterfly delta system of qiongzhou strait morphology seismic stratigraphy and sedimentation abstract analysis of high resolution sub bottom profiles topographical data and sediment samples reveals that the tidal delta system of qiongzhou strait is morphologically a butterfly delta system consisting of western mouth tidal delta wmtd and eastern mouth tidal delta emtd wmtd covers an area of about 11 000 km 2 and is more than two times larger than emtd 4000 km 2 wmtd is fan shaped with a tributary branch extending southwards along hainan island while emtd is typically fan shaped seismic architectures of wmtd and emtd are both characterized by a thick progradational unit overlying a thin transgression unit both wmtd and emtd start to develop at about 8 7 cal ka bp when qiongzhou strait completely opened and have the same three sedimentary facies tidal delta top tidal delta slope and tidal delta toe the formation of wmtd and emtd is attributed to qiongzhou strait s hydrodynamic regime which is dominated by the strong east west reciprocal tidal currents and influenced by the year round westward mean flow modified by the wind driven seasonal currents

a new geodynamic interpretation for the south portuguese zone sw iberia and the iberian pyrite belt genesis 1 the south portuguese zone spz constitutes the southernmost segment of the variscan iberian massif it is bounded to the north by the beja acebuches ophiolitic complex and related accretionary wedge to the south lie the iberian pyrite belt ipb and flysch deposits forming the southern extent of the zone structural analysis within the spanish side of the spz supports continuous south propagating deformation evolving from early synmetamorphic thrusting in the internal zone to thin skinned tectonics in the southern external domain the accretion of the spz to the ossa morena zone is also witnessed by the presence of various melanges observed throughout the investigated area part of the melanges observed in the ipb are related to the volcanics and mineralizations setting a key point to understand the ipb mineralizations genesis is to constrain the volcanogenic model one underestimated feature is the large amount of submarine calc alkaline ignimbritic facies implying the presence of caldera structures within the province such correlation between caldera environment and ore deposits strongly suggests that the ipb developed in a continental arc our geodynamic model proposes an early north directed subduction associated with the obduction of the oceanic crust toward the south southward this episode is immediately followed by the development of the accretionary prism while farther south a second subduction zone responsible for the arc setting of the ipb initiates subsequent visean continental collision is associated with the deposit of the south propagating flysch and the present geometry of the spz

siegenian generation of the lizard ophiolite u pb zircon age data for plagiogranite porthkerris cornwall the long controversial age of the lizard ophiolite is resolved by u pb dating of three single magmatic zircons from a plagiogranite dyke near porthkerris point this demonstrates that the axial oceanic crust was undergoing extensional ductile shearing mylonitization amphibolite facies metamorphism and probably anatexis at 397 2 2 ma in conjunction with published k ar 40 ar 39 ar and rb sr data for the complex this early devonian age predicates a protracted interval between intra oceanic magmatism and deformation on the one hand and obduction during late devonian northwestward displacement of the normannian high on the other

sea ice albedo climate feedback mechanism abstract the sea ice albedo feedback mechanism over the arctic ocean multiyear sea ice is investigated by conducting a series of experiments using several one dimensional models of the coupled sea ice atmosphere system in its simplest form ice albedo feedback is thought to be associated with a decrease in the areal cover of snow and ice and a corresponding increase in the surface temperature further decreasing the areal cover of snow and ice it is shown that the sea ice albedo feedback can operate even in multiyear pack ice without the disappearance of this ice associated with internal processes occurring within the multiyear ice pack e g duration of the snow cover ice thickness ice distribution lead fraction and melt pond characteristics the strength of the ice albedo feedback mechanism is compared for several different thermodynamic sea ice models a new model that includes ice thickness distribution the ebert and curry model the maykut and untersteiner model and the semtner level 3 an

song hong red river delta evolution related to millennium scale holocene sea level changes abstract the song hong red river delta occurs on the northwest coast of the south china sea its evolution in response to holocene sea level changes was clarified on the basis of sedimentary facies and 14 radiocarbon dates from the 40 m long duy tien core from the delta plain and using previously reported geological geomorphological and archaeological data the delta prograded into the drowned valley as a result of early holocene inundation from 9 to 6 cal kyr bp as sea level rise decelerated the sea level highstand at 2 3 m from 6 to 4 cal kyr bp allowed widespread mangrove development on the delta plain and the formation of marine notches in the ha long bay and ninh binh areas during sea level lowering after 4 cal kyr bp the former delta plain emerged as a marine terrace and the delta changed into the present tide and wave influenced delta with accompanying beach ridges delta morphology depositional pattern and sedimentary facies are closely related to holocene sea level changes in particular falling sea level at 4 cal kyr bp had a major impact on the evolution of the song hong delta and is considered to be linked to climate changes

assessing multi site δ18o climate calibrations of the coralline alga clathromorphum across the high latitude northern hemisphere abstract an increased number of climate proxy records and more refined interpretation of proxy data are crucial to improve projections of future climate at high latitudes where internal feedbacks amplify warming and established high resolution climate archives are especially sparse encrusting coralline algae are being developed as a mid to high latitude marine climate archive these long lived algae form a solid high mg calcite skeleton with annual growth bands similar to those of trees and tropical corals the oxygen isotope ratio of the algal skeleton 18oalg records local environmental and climatic factors notably sea surface temperature and seawater 18o here we assess the 18oalg climate relationship in diverse environments across the algal habitat range utilizing two species of coralline algae from the genus clathromorphum clathromorphum is widely distributed from the cold temperate north atlantic and pacific to the arctic ocean and has recently yielded numerous climate reconstructions of up to 650 years in length in this study we calibrate 18oalg of four specimens to gridded temperature and salinity data the latter a proxy for seawater 18o these specimens were collected from a variety of algal growth environments across the high latitude northern hemisphere two specimens from the aleutian archipelago one from the canadian arctic and one from the gulf of maine low winter temperatures and insolation restrict the months when algae record local climate in the 18o of their skeletons we therefore determine these response seasons by correlating monthly temperature and salinity anomalies with annual 18oalg anomalies at each site we then average gridded data over months that correlate significantly 95 confidence interval for regression with 18oalg while the timing and nature of the climate signal vary across sites we find significant relationships between 18oalg and either temperature or salinity averaged over the response season at three sites variation in local climatology among the four sites provides a physical explanation for calibration differences compounded by uncertainties stemming from the proxy chronology biological variability temporal coverage and sparse historical climate data this work takes an essential step toward reconstructing high latitude marine climate patterns with coralline algal 18o and developing algae proxy system models

are the oroclines of the variscan belt related to late variscan strike slip tectonics terra nova 23 241 247 2011 abstract early variscan structures and magnetic anomalies delineate four oroclines along the variscan belt the arcs bend the lithostratigraphic zones of the autochthon and the allochthonous terranes which include ophiolites of the rheic suture and units of gondwanan derivation subducted on both sides of the rheic ocean a transcurrent model dominated by right lateral motion explains the genesis and evolution of the oroclines and a simple plate tectonics scenario links late variscan dextral strike slip movements in the variscides to a broad intracontinental shear zone kinematically equivalent to a transform fault terra nova 00 1 7 2011

intercomparison of coral oxygen isotope data and historical sea surface temperature sst potential for coral based sst field reconstructions we examine the extent to which the large scale features of the sea surface temperature sst anomaly field are represented by a sparse observational network of coral oxygen isotope 18o time series regression of annually averaged 18o data against gridded estimates of local sst anomaly within the period 1856 1990 confirm the literature regression of 18o anomaly on sst anomaly for indo pacific corals however while interannual sst variability is generally well represented by individual coral time series observed decadal and secular variability does not always display a linear relationship to local sst anomaly instead many records appear to better recover nonlocal large scale phenomena which in turn are related to either the coral local sst or sst covariant changes in seawater 18o we employ empirical orthogonal function eof analysis to identify common patterns of variability in the coral data we find two significant patterns which are interpretable as the oceanographic signature of the el nino southern oscillation enso and as a near global warming in which the eastern equatorial pacific cools a third pattern weakly resembles the pacific decadal oscillation these modes are seen more clearly in a singular vector decomposition svd of the covariance between the coral data and the dominant patterns of large scale historical sst variability the results are consistent with those found in eof and svd analyses of sst data from the coral locations as additional coral based proxy estimates become available they will improve the resolution of the patterns recovered these results suggest that a sparse network of coral data may be used to reconstruct interannual secular and decadal sst variability for preinstrumental periods albeit with large uncertainty

tectonometamorphic evolution of the aracena metamorphic belt sw spain resulting from ridge trench interaction during variscan plate convergence 1 the aracena metamorphic belt is a high temperature low pressure ht lp band located at the southern end of the european variscan chain it marks a suture between armorica and avalonia this belt is characterized by 1 the presence of mid ocean ridge basalt derived metabasites that were affected by an inverted ht lp metamorphism related to sw verging thrusting whose thermal peak diachronously migrated eastward 2 the occurrence of a ht lp metamorphism related to an extensional event affecting continental rocks belonging to the ossa morena zone with peak temperatures that are 150 c higher than that recorded in the oceanic metabasites and 3 the presence of near trench magmatism with high mg andesite composition these and other characteristics can be interpreted in terms of a ridge trench trench triple junction that migrated along the armorican margin during variscan oblique convergence

rapid coupling between ice volume and polar temperature over the past 150 000 years a new approach to dating a continuous sea level record using speleothem u th ages shows that past variations in global ice volume occurred within centuries of polar climate change with rates of sea level rise reaching at least 1 metre per century

introduction to the river dominated shelf sediments of the east asian seas peter d clift1 jan harff2 3 jiaxue wu4 yan qiu5 department of geology and geophysics louisiana state university baton rouge la 70803 usa university of szczecin institute of marine and coastal sciences mickiewicza 18 pl 70 383 szczecin poland leibniz institute for baltic sea research seestrasse 15 d 18119 rostock warnemunde germany centre of coastal ocean science and technology sun yat sen university guangzhou 510275 china guangzhou marine geological survey china geological survey guangzhou 510760 china

sea surface temperature and salinity reconstruction from coral geochemical tracers massive scleractinian corals secrete an aragonitic skeleton which incorporates a large array of chemical tracers corals present several advantages for palaeoclimate research they grow continuously and can live up to 1000 years they are easy to date and they can be sampled at high resolution weekly to monthly resolution both live and fossil corals can be collected in the field in the past two decades significant efforts have been made to identify robust tracers of sea surface temperature sst and salinity sss in corals to date sr ca and 18o are considered to be the most reliable sst tracers although changes in seawater 18o can significantly alter sst reconstructed from coralline 18o because these variations in seawater 18o can be linked to sss changes this initial problem can in fact be turned into an advantage and provide us with an sss tracer the sst component in the coral 18o signal can either be evaluated through sr ca measurements or in some case simply filtered out however there is still much uncertainty concerning the exact mode of incorporation of trace elements and stable isotopes into the coral skeleton the effects of growth rate light intensity feeding habits ph and water chemistry are still poorly documented a review of the strength and weaknesses of sr ca and 18o is presented together with some examples of sst and sss reconstructions other potential sst tracers are also reviewed it is expected that the ability to grow corals in aquarium under controlled conditions and that the development of sophisticated analytical techniques at the micrometric level should help us understand better the robustness of each tracers and the factors controlling their incorporation in coral aragonite

diachronous post orogenic magmatism within a developing orocline in iberia european variscides 1 u pb zircon crystallization ages of 52 late variscan granitoid intrusions from nw iberia 19 from new data 33 from previous studies constrain the lithospheric evolution of this realm of the variscan belt of western europe and allow assessment of the relationship between oroclinal development and magmatism in late carboniferous early permian times the u pb ages in conjunction with a range of geological observations are consistent with the following sequence of events i oroclinal bending starts at 310 305 ma producing lithospheric thinning and asthenospheric upwelling in the outer arc of the orocline accompanied by production of mantle and lower crustal melts ii between 305 and 300 ma melting continues under the outer arc of the orocline central iberian zone of the iberian variscan belt and mid crustal melting is initiated coevally the lithospheric root beneath the inner arc of the orocline thickened due to progressive arc closure iii between 300 and 292 ma foundering of the lithospheric root followed by melting in the lithospheric mantle and the lower crust beneath the inner arc due to upwelling of asthenospheric mantle iv cooling of the lithosphere between 292 and 286 ma resulting in a drastic attenuation of lower crustal high temperature melting by 285 ma the thermal engine generated by orocline driven lithospheric thinning delamination had cooled down beyond its capability to produce significant amounts of mantle or crustal melts the model proposed explains the genesis of voluminous amounts of granitoid magmas in post orogenic conditions and suggests that oroclines and similar post orogenic granitoids common constituents of numerous orogenic belts may be similarly related elsewhere

self subduction of the pangaean global plate one of the most striking and rare occurrences in the earth s history is the amalgamation of most of the continental lithosphere into one supercontinent the most recent supercontinent pangaea lasted from 320 to 200 million years ago here we show that after the continental collisions that led to the formation of pangaea plate convergence continued in a large wedge shaped oceanic tract we suggest that plate strain at the periphery of the supercontinent eventually resulted in self subduction of the pangaean global plate when the ocean margin of the continent subducted beneath the continental edge at the other end of the same plate our scenario results in a stress regime within pangaea that explains the development of a large fold structure near the apex of the palaeotethys ocean extensive lower crustal heating and continental magmatism at the core of the continent as well as the development of radially arranged continental rifts in more peripheral regions of the plate

testing the physical oceanographic implications of the suggested sudden black sea infill 8400 years ago 1 we apply a shock capturing numerical model based on the single layer shallow water equations to an idealized geometry of the black sea and the sea of marmara in order to test the implications of a suggested sudden black sea infill 8400 years ago the model resolves the two dimensional flow upstream and downstream of the hydraulic jump provoked by the cascade of water from the sea of marmara into the black sea which would occur during a sudden black sea infill the modeled flow downstream of the hydraulic jump in the black sea would consist of a jet that is in part constrained by bathymetric contours guided by the bosporus canyon the modeled jet reaches depths of up to 2000 m and could explain the origin of the sediment waves observed at this depth at a late stage of the infill the modeled jet is attached to the coast and might account for the course of a submerged channel at the mouth of the bosporus the preservation of continuous barrier washover lagoonal fill systems occurring on the black sea shelf is however not easily reconcilable with the large flows over the southwest black sea shelf predicted by the model intensified flow in the upstream basin sea of marmara is restricted to the immediate vicinity of the bosporus suggesting that a sudden reconnection need not have disturbed sediments in the wider sea of marmara

3d analogue modeling of the south china sea a discussion on breakup pattern the opening of the south china sea is one of the most important cenozoic events in se asia in order to investigate its tectonic evolution three analogue modeling experiments were compared the modeling results suggest that rifting pattern and orientation change of the rift zone were related to initial theological stratification affected by the ductile flow of silicone lower crust and honey asthenosphere the faults became flattened especially close to the breakup area we conjecture that the slope area may bear relatively hotter and thinner lithosphere than the shelf area from the beginning of rifting due to stretching and mantle upwelling associated with this regional extension which in turn lead to the change in initial rheological stratification and therefore the rifting pattern from shelf to slope in the experiments breakup developed first at isolated points which grew and coalesced to become a single spreading area the conjugate boundaries were either all concave or all convex where a rigid massif was located at the divergent boundary stretching history was different in this case the northern and southern areas thinned rapidly and developed into two deep troughs which may finally evolve into spreading centers the shape of the massif controls the orientation and boundary shape of the spreading area it is interpreted that crustal breakup was more viscous in style and the nw sub sea basin developed along the northern trough of the zhongsha xisha massif macclesfield bank c 2008 elsevier ltd all rights reserved

late pleistocene and holocene sea level change in the australian region and mantle rheology summary spatial and temporal variations in sea level are produced by the melting of the late pleistocene ice and by the earth s response to the redistribution in surface loads by examining different parts of the sea level curves of the past 20 000 yr from geographically widely distributed regions it becomes possible to constrain models of the melting history of the ice sheets and of the earth s rheology observations from sites away from the former arctic ice sheets such as the australian and south pacific region are particularly important for constraining the total meltwater volumes added into the oceans in the past 20 000 yr and the rates at which this occurred these observations indicate that the antarctic ice sheets provided a significant contribution to the sea level rise at a rate that was approximately synchronous with the melting of the laurentide ice sheet except for the interval 9000 6000 yr ago when it may have lagged behind minor melting of the antarctic ice sheet appears to have continued throughout the late holocene differential observations of the late holocene sea level change recorded at sites in the same region are particularly useful for estimating parameters describing the earth s non elastic response to surface loading the effective parameters used here are a lithospheric thickness an upper mantle viscosity and a lower mantle viscosity describing the response below 670 km depth with the observations used here it is not possible to separate the lithospheric thickness h from the upper mantle viscosity and the viscosity results are based on the assumption that 50 h 100 km neither do these observations provide a resolution of the depth dependence of viscosity in the upper mantle and the resulting estimates are effective parameters only differential sea levels along continental margins and along the shores of large gulfs and bays constrain the effective upper mantle viscosity to be about 1 2 1020 pa s 1 while differential values from islands of different sizes are suggestive of a somewhat lower value the lower mantle taken to be below 670 km depth viscosity is about two orders of magnitude greater than this the estimated ice and rheological models explain many of the holocene sea level observations throughout the australian and southern pacific region the tilting of continental margins as exemplified by observations of variable amplitudes of the holocene high stands and the variable times at which sea levels first reached their present level along the north queensland coast and great barrier reef is well represented by these models differential holocene sea levels observed along the narrow spencers gulf of south australia are also well explained by the models and in neither case is it necessary to invoke tectonic motions predicted late holocene sea levels at small to medium sized islands are characterized by small amplitude high stands that reached their maximum values about 4000 2000 yr ago consistent with observations from the society cook and tuamotu islands

a strategy to improve the contribution of coral data to high resolution paleoclimatology abstract various geochemical tracers measured in massive coral skeletons have the potential to compliment other sources of high resolution proxy climate information e g tree rings ice cores by providing paleoclimatic data from shallow water tropical ocean regions twenty previously published coral records 19 18o and one sr ca series between 54 and 346 years in length were examined for their local and larger scale relationships el nino southern oscillation with climate series were examined in a consistent manner over the same time periods and relationships were tested for stability through time the results demonstrate a spectrum of climatic interpretation ranging from 1 no significant relationship of the coral record with either local or larger scale climate variables 2 significant relationship of the coral record with climate but the relationship is not stable through time and 3 the coral record shows a significant and temporally stable relationship with climate which explains a significant and useful proportion of climate variance it is concluded that reliance to date on analyzing only one long coral core from a site has prevented identification of coral records or parts of coral records where non climatic factors are dominating the geochemical signal various factors may cause these non climatic signals to dominate more process studies into how corals of particular species with various growth rates and from various environmental settings incorporate geochemical tracers into their skeleton are required to understand exactly what is being measured in addition it is recommended that some level of replication ideally three separate corals of geochemical tracers will ensure accurate dating of the record identification of periods when non climatic factors dominate and thus enhance the reliability of the paleoclimatic record such an approach will allow the rich archive of environmental information contained in massive coral skeletons to make a significant contribution to high resolution paleoclimatology and improve our understanding of the nature and causes of past climate variability

comparing proxies for the reconstruction of lgm sea surface conditions in the northern north atlantic abstract within the frame of the multiproxy approach for the reconstruction of the glacial ocean margo project sea surface conditions of the last glacial maximum lgm 23 19 ka were reconstructed using different proxies which were calibrated to a standardized modern hydrography in the north atlantic the revised lgm margo data set provides a comprehensive coverage including the nordic seas the data set includes reconstruction based on planktonic foraminifer assemblages dinocyst assemblages alkenone coccolithophorid biomarkers and mg ca ratios in planktonic foraminifers several hydrological features of the lgm north atlantic can be identified that are supported by all four proxies they include an extensive perennial sea ice cover along the eastern canadian and greenland margins seasonally ice free central north atlantic and norwegian sea and the winter sea ice limit being located at about 55 n all proxies also suggest significantly colder than modern sea surface conditions in the southeastern part of the north atlantic and a more zonal temperature pattern than at present with a steep sst gradient of the order of 10 c between 40 n and 45 n however in the nordic seas large discrepancies remain well above the level of uncertainty of the sst reconstructions these discrepancies might be related to stratification of the upper water mass linked to large annual amplitude of temperature with contrasting winter and summer conditions high interannual interdecadal variability or taphonomic processes affecting some of the proxies the average lgm sst in the nordic seas cannot at present be assessed with confidence however the existing evidence suggests that highly variable sea surface conditions and at least occasional advection of north atlantic waters may have characterised the glacial nordic seas

variability of marine climate on the north icelandic shelf in a 1357 year proxy archive based on growth increments in the bivalve arctica islandica a multicentennial and absolutely dated shell based chronology for the marine environment of the north icelandic shelf has been constructed using annual growth increments in the shell of the long lived bivalve clam arctica islandica the region from which the shells were collected is close to the north atlantic polar front and is highly sensitive to the varying influences of atlantic and arctic water masses a strong common environmental signal is apparent in the increment widths and although the correlations between the growth increment indices and regional sea surface temperatures are significant at the 95 confidence level they are low r 0 2 indicating that a more complex combination of environmental forcings is driving growth remarkable longevities of individual animals are apparent in the increment width series used in the chronology with several animals having lifetimes in excess of 300 years and one at 507 years being the longest lived non colonial animal so far reported whose age at death can be accurately determined the sample depth is at least three shells after ad 1175 and the time series has been extended back to ad 649 with a sample depth of one or two by the addition of two further series thus providing a 1357 year archive of dated shell material the statistical and spectral characteristics of the chronology are investigated by using two different methods of removing the age related trend in shell growth comparison with other proxy archives from the same region reveals several similarities in variability on multidecadal timescales particularly during the period surrounding the transition from the medieval climate anomaly to the little ice age

antarctic temperature and global sea level closely coupled over the past five glacial cycles sea level has varied by over one hundred metres across glacial interglacial cycles over the past 520 000 years an extended sea level reconstruction shows a strong coupling between these sea level changes and antarctic surface temperatures over the past five glacial cycles

formation and fate of sedimentary depocentres on southeast asia s sunda shelf over the past sea level cycle and biogeographic implications abstract sea level variations are the major factor controlling sedimentation as well as the biogeographic patterns at continental margins over late quaternary times fluctuations on millennial time scales produce locally complex deposits in coasts and on shelves associated with short term influence on species development this article reviews the sedimentary and biogeographic history of the tropical siliciclastic sunda shelf as an end member of continental shelves regarding extreme width an enormous sediment supply and highest biodiversity in response to rapid sea level fluctuations we describe particular depositional segments as part of a genetic succession of zones from land to the deep sea based on literature data field observations and calculation of hydro isostatic adjustment effects on changing relative sea level these segments are characterized by individual sedimentary processes and deposits and by a specific potential for material storage and re mobilization long term regressive intervals led to overall sigmoidal promoting extremely thick and wide succeeding units in contrast rapid lateral shifts of defined depocentres over long distances took place in response to short term sea level fluctuations fully isolated small scale sediment bodies formed when sea level changed at exceptionally high rates as a result of the high availability of organic rich sediments mangrove and freshwater peats formed frequently over late quaternary times the appearance of thick massive and widespread peats is mainly linked to time intervals of a sea level rise at slow rates whilst organic matter appears much more dispersely in the sediments during episodes of rapidly changing sea level the preservation potential of the regressive units is generally high due to highest initial sediment supply stabilizing soil formation during exposure and rapid subsidence preservation of depositional elements from other periods is more exceptional and either restricted to local morphological depressions or to episodes of rapid sea level change besides complex channel incision an overall lowering of the sediment surface related to erosion as deep as 20 m or more over wide areas took place mainly during sea level lowering the final export of shelf material is documented by enormous mass wasting packages on the associated continental slope from a palaeogeographic perspective the rapid formation or disappearance of special habitat zones such as mangrove fringes and extended mud flats led to species establishment or truncation in distribution in addition the opening or closure of ocean passages as narrow bridges allowing limited species crossing or as fully colonized corridors had severe impact on eco fragmentation and the expansion or contraction of species independent of such particular conditions sea level changes have been too rapid over the past climatic cycle to allow full regeneration and mature development of coast related ecosystems

stratigraphic architecture and spatio temporal variability of high frequency milankovitch depositional cycles on modern continental margins an overview abstract this study is a review of quaternary milankovitch cycles as recorded on modern continental shelves worldwide on the background of the many existing examples we focus on selected case studies from mediterranean adriatic and tyrrhenian seas and atlantic gulfs of mexico and cadiz margins that represent general and peculiar characters of middle upper pleistocene sequences forming under the control of composite 100 and 20 ka milankovitch cycles the most pervasive stratigraphic pattern displayed by shelf deposits is referred to the 100 ka sea level cycle and consists of fairly uniform depositional sequences mostly composed by regressive deposits forming during the falling limb of the sea level curve these are generally classified as falling stage systems tract fsst and display a regressive facies architecture reflecting the dominant control of sea level on many margins fsst units may show slight though significant differences with respect to highstand systems tract hst and lowstand systems tract lst regressive units more closely reflecting environmental changes and the local variability of depositional systems in contrast with the theoretical and overall scale independent model developed to predict composite stratigraphic cycles and sequences the middle upper pleistocene stratigraphic record from numerous shelf settings shows a subdued signature of the higher frequency 20 ka milankovitch cyclicity however when detectable the 20 ka architectural pattern is characterized by a relatively greater spatial and temporal variability compared to 100 ka sequences this fact likely reflects the increasing importance of factors controlling the depositional environment e g seafloor morphology oceanographic regime sediment input and dispersal etc with respect to sea level change during the shorter intervals encompassed by 20 ka cycles on this basis two end member cases have been distinguished depending on the generation or not of high frequency sequence boundaries a prerequisite to qualify the higher frequency motifs as depositional sequences these two end members are comprehensive of the highly variable patterns displayed by middle upper pleistocene shelf sequences which in turn reflect the interplay between the geological setting the dominant sea level control and the effective response of sedimentary systems the variable stratigraphic patterns of milankovitch cycles represent conceptual and practical constraints as to the classification of high frequency quaternary sequences under the general schemes of the standard sequence stratigraphy model

continental scale temperature variability during the past two millennia past global climate changes had strong regional expression to elucidate their spatio temporal pattern we reconstructed past temperatures for seven continental scale regions during the past one to two millennia the most coherent feature in nearly all of the regional temperature reconstructions is a long term cooling trend which ended late in the nineteenth century at multi decadal to centennial scales temperature variability shows distinctly different regional patterns with more similarity within each hemisphere than between them there were no globally synchronous multi decadal warm or cold intervals that define a worldwide medieval warm period or little ice age but all reconstructions show generally cold conditions between ad 1580 and 1880 punctuated in some regions by warm decades during the eighteenth century the transition to these colder conditions occurred earlier in the arctic europe and asia than in north america or the southern hemisphere regions recent warming reversed the long term cooling during the period ad 1971 2000 the area weighted average reconstructed temperature was higher than any other time in nearly 1 400 years

rheic ocean ophiolitic remnants in southern iberia questioned by shrimp u pb zircon ages on the beja acebuches amphibolites 1 the rheic ocean was a major oceanic domain between avalonia and gondwana in ordovician silurian times most of the paleozoic plate reconstructions assume that the rheic ocean suture lies within southern iberia coinciding with the contact between the south portuguese zone and the ossa morena zone this paper reports four sensitive high resolution ion micro probe shrimp u pb zircon ages from mid ocean ridge basalt morb featured rocks of the beja acebuches amphibolite unit which crops out along the boundary between the ossa morena and the south portuguese zone and is considered its most conspicuous suture unit the obtained ages range from 332 3 to 340 4 ma corresponding to the crystallization of the mafic protoliths these early carboniferous ages for the beja acebuches amphibolites imply that this unit can no longer be viewed as an ophiolite belonging to the rheic ocean suture since this oceanic domain was presumably closed in devonian times tectonic reconstructions joining in a single suture line the beja acebuches amphibolite unit in southern iberia to either the devonian lizard ophiolite in southern england or the root zone of the devonian ordovician ophiolitic units in northwest iberia must be therefore reconsidered because of the age difference we interpret the beja acebuches amphibolite unit to represent a narrow and very ephemeral realm of oceanic like crust that opened in early carboniferous times after total consumption of the rheic ocean we suggest that a mantle plume underneath southern iberia in early carboniferous times is the most plausible large scale geodynamic scenario for the formation of these morb featured rocks

holocene evolution of mud depocentres on a high energy low accumulation shelf nw iberia the high energy low accumulation nw iberian shelf features three confined holocene mud depocentres here we show that the evolution of such depocentres follows successive steps the flooding of inner shelf zones and river catchment areas by the late deglacial sea level rise provided the precondition for shelf mud deposition following this the holocene deceleration of the sea level rise caused a rapid refill of the accommodation space within river valleys subsequently the export of major amounts of fines was initiated the initial onset and loci of shelf mud deposition were related to deposition favouring conditions in mid shelf position or to the presence of morphological highs which act as sediment traps by providing protection against stronger hydrodynamic energy the detailed reconstruction of the holocene depocentre evolution shows for the first time that the expansion of such shelf mud deposits cannot only occur by linear growth off the associated sediment source rather they might develop around centres that are fully disconnected from the source of original sediment supply and expand later into specific directions based on these differences and on the connection of the individual mud depocentres to the material source we propose a conceptual subdivision of the group mid shelf mud depocentres

relative variations in geomagnetic intensity from sedimentary records the past 200 000 years abstract eighteen records of relative paleointensity from marine sediments have been compiled in order to retrace the global changes in geomagnetic intensity during the past 200 kyr before dealing with any other source of noise we focused on problems inherent to the depth versus time correlations the accuracy and resolution of dating mostly deduced from isotopic stratigraphy were identified as significant factors of distortion we found also that different time scales have been used by authors after readjustment with respect to the same time scale the records were stacked together and the statistical significance of the results tested by a bootstrap technique seventeen records shown to be coherent were combined into a synthetic curve defined as sint 200 other stacks combining various subsets of data were found to be identical to sint 200 except for changes in dispersion in fact the dispersion around sint 200 could be reduced further by improving the correlations without violating the stratigraphy a procedure which at least for some records emphasizes the need for more detailed depth time correlations another characteristic emerging from the results is that paleointensity features as short as 10 kyr are observed between 120 200 ka and can thus in principle be resolved however subsequent refinement is still necessary for this period which is documented by fewer records than the following 120 kyr finally we compared sint 200 with the records from the labrador sea and the lac du bouchet ldb both of which rely mostly on 14c chronology the two records show satisfactory agreement with sint 200 when transferred with respect to the age model established by correlating their 18o labrador and susceptibility features ldb with the 18o reference record the offset of 7 kyr at 40 ka measured in both cases between the 14c and 18o ages is higher than the value deduced from a recent model of a geomagnetic field control of 14c production 1 but is not inconsistent with recent u th dates

osl dating of late holocene coastal sediments and its implication for sea level eustacy in hainan island southern china abstract since the sea level rise is not geographically homogeneous but rather shows great regional differences optically simulated luminescence using quartz as a natural dosimeter has proved to be a powerful and reliable dating technique to determine depositional ages of young coastal sediments around the world the samples acquired from one beach ridge and two marine terraces in coastal hainan island southern china are detected osl dating for the investigation of sea level changes the results show 1 coastal sands in hainan island were well bleached before deposition and the quartz osl can date coastal sediments younger than 200 years which could be one of good indicators for paleo relative sea level highstand records 2 three coastal sediments with 4 m 3 7 m and 2 m higher than present sea level were deposited at 2 40 0 05 ka 2 92 0 17 ka and 4 26 0 10 ka respectively which indicate that the height of highstand relative sea level are higher than both mean global sea level eustacy and those records offshore southern china 3 comparisons with tropical cyclones observations around south china sea indicates that the late holocene coastal sediments of hainan island might have been reformed by tropical cyclones with a highstand sea level

formation of the maturin foreland basin eastern venezuela thrust sheet loading or subduction dynamic topography 1 the maturin basin in eastern venezuela is considered a good example of a peripheral foreland basin earthquake and tomographic data indicate that eastern venezuela is affected by the oblique subduction of the south american plate underneath the caribbean plate new forward flexural isostatic modeling of eastern venezuela has been carried out in order to determine whether the maturin basin was generated purely by thrust sheet loading from the serrania and monagas foreland thrust belts a sequence of forward models from middle miocene to present was generated for 3 profiles across the serrania del interior thrust belt the monagas foreland thrust belt and the maturin foreland basin the predictions of these models are constrained using seismic reflection and well data the flexural isostatic modeling shows that thrust sheet loading associated with the serrania del interior and monagas foreland thrust belts is insufficient to generate the observed subsidence within the maturin basin dynamic fluid flow modeling of subduction related dynamic topography of eastern venezuela has been used to investigate the influence of south american plate subduction on the generation of the accommodation space observed in the maturin basin fluid flow modeling of subduction related dynamic topography suggests that the subduction of the south american lithospheric mantle caused downward deflection of the south american crust affecting the maturin basin and the serrania thrust belt this modeling suggests that the maturin basin subsidence has two components 55 related to thrust sheet loading and 45 driven by continental subduction

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials