late pleistocene and holocene palaeogeography of the lower tagus valley portugal effects of relative sea level valley morphology and sediment supply abstract because of the deep glacial incision the lower tagus valley hosts a sedimentary record since 20 000 cal bp making this a unique site along the european atlantic margin with respect to palaeogeographic and sea level changes based on nine cross sections and 55 radiocarbon dates together with a newly created relative sea level curve we constructed five palaeogeographic maps of the infill of the lower tagus valley since 20 000 cal bp we illustrate that relative sea level rise and fluvial sediment supply were the prime forcing factors determining the depositional history and palaeogeographic changes around 20 000 cal bp a deeply incised braided river existed which was directly connected to the ocean across the narrow continental shelf after that 12 000 cal bp the gradually moister and warmer climate caused a change to a single channel river during the following period 12 000 7000 cal bp relative sea level rise resulted in a transgression in the lower tagus valley and the establishment of extensive tidal environments after relative sea level rise had ended 7000 cal bp the valley was progressively filled by a fluvial wedge and tidally influenced bayhead delta since 1000 cal bp the valley fill history was dominated by increased sediment input due to human induced degradation of catchment slopes generally climate was of subordinate importance during the entire studied period merely causing a single channel river resulting from the change from the cold heinrich event 1 to the temperate bolling allerod interstadial despite the tectonic activity in the region neotectonic uplift or subsidence was limited as supported by the horizontal relative sea level curve since 7000 cal bp neotectonics played a minor role due to the large distance from the fennoscandian ice sheet and the narrow continental shelf which prohibited strong glacio and hydro isostatic movements

upwelling around cabo frio brazil the importance of wind stress curl 1 data from the seawinds scatterometer on the quikscat satellite are used to estimate upwelling around cabo frio brazil due to ekman transport and ekman pumping the region close to shore up to 200 km from the coast is characterized by negative wind stress curl upwelling favorable year round with maximum values during summer and minimum values during fall integrated values from sao sebastiao island to vitoria reveal that during summer ekman pumping and ekman transport are of the same magnitude in the region estimates of ekman transport are relatively uniform along the coast during summer ekman pumping on the other hand is strongly enhanced between sao sebastiao island and vitoria the region where the coldest water on satellite images is frequently found this suggests that wind stress curl driven upwelling is a major contributor to the coldest surface water being found near cabo frio

fluvial response to late quaternary climatic and environmental change edwards plateau texas abstract radiocarbon controlled late pleistocene to modern stratigraphic frameworks for fluvial systems that drain the edwards plateau westcentral texas coupled with reconstruction of climatic and environmental changes permit development of a model for the evolution of fluvial landscapes during the past 20 000 years during this time large valleys of the edwards plateau were characterized by channel aggradation and sediment storage from 20 to 14 000 yrs b p deep excavation of bedrock valleys from ca 14 to 11 000 yr b p and deposition of extensive and complex valley fills during the last 11 000 yr valley fills contain three distinct unconformity bounded allostratigraphic units representing episodes of channel aggradation and floodplain construction during the early to middle ca 11 000 5000 yr b p and late holocene ca 5000 1000 yr b p and development of the incised channels and associated narrow floodplains of the last 1000 years early to middle holocene alluvial deposits were derived from proximal sources within the respective drainage basins whereas late holocene deposits include sediments derived from distal sources sediment supply to major valleys axes has been extremely limited during the last 1000 years alluvial sequences of the edwards plateau record fluvial responses to climatically driven changes in discharge regimes and the concentration of sediments along valley axes allostratigraphic units define time periods when the concentration of sediment exceeded stream power resulting in sediment storage whereas unconformities record widespread morphological and sedimentary adjustments unconformities between late pleistocene alluvium and holocene valley fills record bedrock valley incision in response to decreased sediment loads associated with slope stability in the uplands by contrast unconformities within the holocene valley fill record floodplain abandonment accompanied by continued channel migration and sediment storage but little additional bedrock valley cutting episodes of floodplain abandonment occurred as a result of decreased flood magnitudes following shifts to drier climatic conditions at ca 5000 and 1000 yr b p fluvial responses to climatic change were conditioned by a progressive degradation of upland soils that caused increases through time in the flashiness of flood events which in turn led to changes in processes of floodplain construction flood events on late pleistocene and early to middle holocene rivers were for the most part contained within channel perimeters and floodplains were constructed by lateral migration by contrast late holocene rivers were characterized by deep overbank flooding and floodplain construction by vertical accretion high magnitude floods were most significant from ca 2500 to 1000 yr b p when large chute channels were cut and filled on floodplain surfaces and soils developed on previously stable terrace surfaces were buried by up to 2 m of fine sands and muds

reconstruction of southwestern atlantic sea surface temperatures during the last century cabo frio continental shelf brazil modern sea surface temperatures ssts were estimated from uk 37 values of ten core top sediment samples collected under the cabo frio upwelling system and validated by comparison with satellite derived ssts uk 37 ssts were found to reflect annual sst means in the offshore area and seasonal means winter spring in the inshore and central areas the latter areas are mainly influenced by upwelling processes whereas the offshore area is under the influence of the thermal front of the brazil current bc sst variability during the last century was then reconstructed from three short sediment cores the record showed a general cooling trend in the inshore and central areas suggesting intensification of the upwelling process the trends at the offshore area reflected oscillations of the bc thermal front with piling up of warmer bc waters closer to the coast since ca 1950

deciphering holocene sea level history on the u s gulf coast a high resolution record from the mississippi delta published holocene relative sea level rsl curves for the u s gulf coast are in mutual conflict with some characterized by a smooth rsl rise akin to widely accepted eustatic sea level curves versus others including several recent ones that are characterized by a conspicuous stair step pattern with prolonged millennium scale rsl stillstands alternating with rapid meter scale rises in addition recent work in texas and alabama has revitalized the notion of a middle holocene rsl highstand estimated at 2 m above present mean sea level an extensive sampling program in the mississippi delta louisiana focused on the collection of basal peats that accumulated during the initial transgression of the pre existing consolidated pleistocene basement we used stable carbon isotope ratios to demonstrate that many of these samples accumulated in environments affected by frequent saltwater intrusion in the 30 cm zone between mean spring high water and mean sea level and we selected plant macrofossils that were subjected to ams 14c dating nearly 30 sea level index points from a 20 km2 study area on the eastern margin of the delta suggest that rsl rise followed a relatively smooth trend for the time interval 8000 3000 cal yr b p thus questioning the occurrence of major rsl stillstands alternating with abrupt rises given the narrow error envelope defined by our data set any sea level fluctuations if present would have amplitudes of 1 m although a true middle holocene highstand never occurred in the mississippi delta the high level of detail of our time series enables a rigorous test of this hypothesis correction of our data set for a hypothetical tectonic subsidence rate of 1 1 mm yr 1 assuming a constant subsidence rate compared to the tectonically relatively stable adjacent coast of texas leads to sea levels near 2 m above present during the time interval 6000 4000 cal yr b p however this model also implies a rsl position near 2 m around 8000 cal yr b p which is inconsistent both with data of this age from texas as well as with widely accepted sea level data from elsewhere we therefore conclude that a middle holocene highstand for the u s gulf coast is highly unlikely and that the entire area is still responding glacio isostatically by means of forebulge collapse to the melting of the laurentide ice sheet

changes in biological productivity and ocean climatic fluctuations during the last 1 5 kyr in the humboldt ecosystem off northern chile 27 s a multiproxy approach abstract a sedimentary box core biac072014 collected in a coastal environment in the humboldt current ecosystem hce inglesa bay 27 s northern chile was used to reconstruct the changes in biological productivity and ocean climate fluctuations during the last 1 5 kyr via geochemical mineralogical and micropaleontological analyses from 510 ce to 930 ce el nino like conditions prevailed while during the medieval climate anomaly mca 950 ce to 1450 ce la nina like conditions predominated this pattern might have resulted from weakening strengthening of the walker cell contraction expansion of the south pacific sub tropical high spsh and a predominance of warm cold phases of the pacific decadal oscillation pdo between 1820 ce and the present inglesa bay experienced a reduction in the oxygen minimum zone omz intensity and biological productivity an increase in the detritic input and a decrease in sea surface temperature sst despite the regional intensification and secular cooling 14 s and 27 s of coastal upwelling the similarity between the reduction in biological productivity and omz intensity in this region and that in the central zone of chile 36 s suggests that inglesa bay acts a transition zone in relation to the oceanographic behaviour of the hce the reduction in the omz intensity and biological productivity during the last 200 years could be explained by greater subsurface ventilation in intermediate depths due to more northward displacement of the subduction region of the eastern south pacific intermediate water espiw near 30 s in response to the strengthening of the circulation of the subtropical gyre the coastal cooling observed in the northern section of hce during the current warm period suggests that it is not possible to demonstrate that el nino like conditions promoted the reduction in biological productivity and omz intensity in inglesa bay

seaward pinching out and internal stratigraphy of the gironde incised valley on the shelf bay of biscay abstract an incised paleovalley offshore the estuary mouth of the gironde river southwest france was evidenced recently comptes rendus de l academie des sciences de paris 326 1998 701 nevertheless its seaward extension to the shelf break was still unknown new high resolution geophysical data were acquired on the continental shelf in order to follow the incision until the shelf break after processing the seismic lines the shape of the valley was identified and the valley fill in terms of sequence stratigraphy was interpreted the valley fill contains a single sequence corresponding to a fifth order cycle 20 kyr the three systems tracks described onshore by allen and posamentier journal of sedimentary petrology 63 1993 378 sepm society for sedimentary geology special publication tulsa 1994 225 are present offshore the lowstand is poorly developed and is only present in the proximal part of the incised valley the transgressive systems tract tst constitutes the bulk of the valley fill it is composed of landward prograding estuarine clinoforms in the distal part of the valley early tst phase 1 and of landward migrating tidal inlet fill deposits in the proximal part of the valley late tst phase 2 the thin early highstand systems tracts hst strata downlap seaward onto the maximum flooding surface and caps the tst as expected in this wave and tide dominated environment the tidal and wave ravinement surfaces which bound the tst are particularly well developed the valley incision tapers 50 km offshore of the estuary mouth the depth of the basal sequence boundary gradually decreases seaward and is locally truncated by the wave ravinement surface around 70 m below the mean sea level these observations indicate that during the lowstand times rivers do not always generate continuous cross shelf incised valleys they may adjust to a rapid drop in base level by modifying their channel morphology i e deep large channels located upstream change downstream to shallow anastomosed channels with a weaker erosional ability therefore the lowstand fluvial channels will be poorly developed and will eventually died out in the proximal part of the shelf because they are unable to keep pace with a phase of rapid sea level drop similar observations have already been reported for the english channel paleoriver geological society special publication london 1996 203 these de geologie marine universite de bordeaux 1 1997 265

geochemical evidence for variations in delivery and deposition of sediment in pleistocene light dark color cycles under the benguela current upwelling system abstract distinctive light dark color cycles in sediment beneath the benguela current upwelling system indicate repetitive alternations in sediment delivery and deposition geochemical proxies for paleoproductivity and for depositional conditions were employed to investigate the paleoceanographic processes involved in creating these cycles in three mid pleistocene intervals from odp sites 1082 and 1084 concentrations of total organic carbon toc vary between 3 5 and 17 1 concentrations of caco3 vary inversely to toc and al which suggests that both carbonate dissolution and terrigenous dilution contribute to the light dark cycles opal concentrations are independent of both toc and caco3 therefore eliminating diatom production and lateral transport of shelf material as causes of the light dark cycles 13corg and 15ntot values do not vary across light dark sediment intervals implying that the extent of relative nutrient utilization did not change the stable 15ntot values represent a balanced change in nitrate supply and export production and therefore indicate that productivity was elevated during deposition of the toc rich layers parallel changes in concentrations of indicator trace elements and toc imply that changes in organic matter delivery influenced geochemical processes on the seafloor by controlling consumption of pore water oxygen cu ni and zn are enriched in the darker sediment as a consequence of greater organic matter delivery redox sensitive metals vary due to loss mn and ba or enrichment mo under reducing conditions created by toc oxidation organic matter delivery impacts subsequent geochemical changes such as carbonate dissolution sulfate reduction and the concentration of metals thus export production is considered ultimately responsible for the generation of the color cycles

the effects of late quaternary climate and pco2 change on c4 plant abundance in the south central united states the late quaternary was a time of substantial environmental change with the past 70 000 years exhibiting global changes in climate atmospheric composition and terrestrial floral and faunal assemblages we use isotopic data and couple climate and vegetation models to assess the balance between c3 and c4 vegetation in texas during this period the carbon isotope composition of fossil bison mammoth and horse tooth enamel is used as a proxy for c3 versus c4 plant consumption and indicates that c4 plant biomass remained above 55 through most of texas from prior to the last glacial maximum lgm into the holocene these data also reveal that horses did not feed exclusively on herbaceous plants consequently isotopic data from horses are not reliable indicators of the c3 c4 balance in grassland biomes estimates of c4 percentages from coupled climate vegetation models illuminate the relative roles of climate and atmospheric carbon dioxide co2 concentrations in shaping the regional c4 signal c4 percentages estimated using observed modern climate vegetation relationships and late quaternary climate variables simulated by a global climate model are much lower than those indicated by carbon isotope values from fossils when the effect of atmospheric co2 concentration on the competitive balance between c3 and c4 plants is included in the numerical experiment however estimated c4 percentages show better agreement with isotopic estimates from late quaternary mammals and soils this result suggests that low atmospheric co2 levels played a role in the observed persistence of c4 plants throughout the late quaternary

coupling of millennial scale changes in sea surface temperature and precipitation off northeastern brazil with high latitude climate shifts during the last glacial period 1 high resolution records of alkenone derived sea surface temperatures and elemental ti ca ratios from a sediment core retrieved off northeastern brazil 4 s reveal short term climate variability throughout the past 63 000 a large pulses of terrigenous sediment discharge caused by increased precipitation in the brazilian hinterland coincide with heinrich events and the younger dryas period terrigenous input maxima related to heinrich events h6 h2 are characterized by rapid cooling of surface water ranging between 0 5 and 2 c this signature is consistent with a climate model experiment where a reduction of the atlantic meridional overturning circulation amoc and related north atlantic cooling causes intensification of ne trade winds and a southward movement of the intertropical convergence zone resulting in enhanced precipitation off northeastern brazil during deglaciation the surface temperature evolution at the core site predominantly followed the antarctic warming trend including a cooling prior to the younger dryas period an abrupt temperature rise preceding the onset of the bolling allerod transition agrees with model experiments suggesting a southern hemisphere origin for the abrupt resumption of the amoc during deglaciation caused by southern ocean warming and associated with northward flow anomalies of the south atlantic western boundary current

antarctic temperatures over the past two centuries from ice cores 1 we present a reconstruction of antarctic mean surface temperatures over the past two centuries based on water stable isotope records from high resolution precisely dated ice cores both instrumental and reconstructed temperatures indicate large interannual to decadal scale variability with the dominant pattern being anti phase anomalies between the main antarctic continent and the antarctic peninsula region comparative analysis of the instrumental southern hemisphere sh mean temperature record and the reconstruction suggests that at longer timescales temperatures over the antarctic continent vary in phase with the sh mean our reconstruction suggests that antarctic temperatures have increased by about 0 2 c since the late nineteenth century the variability and the long term trends are strongly modulated by the sh annular mode in the atmospheric circulation

reconstruction of se trade wind intensity based on sea surface temperature gradients in the southeast atlantic over the last 25 kyr 1 a prominent feature in the southeast atlantic is the angola benguela front abf the convergence between warm tropical and cold subtropical upwelled waters at present the sea surface temperature sst gradient across the abf and its position are influenced by the strength of southeasterly se trade winds here we present a record of changes in the abf sst gradient over the last 25 kyr variations in this sst contrast indicate that periods of strengthened se trade wind intensity occurred during the last glacial maximum the younger dryas and the mid to late holocene while heinrich event 1 the early part of the bolling allerod and the early holocene were periods of weakened se trade winds

quantitative modeling of the evolution and geometry of incised valleys abstract incised valleys are critical stratigraphic features for unraveling long term earth surface processes and depositional history and commonly exhibit stratigraphic attributes that make them desirable fluid reservoirs while there is much descriptive documentation on architecture of incised valley fills and paleoenvironmental regimes relatively little work has focused on quantitative modeling of the dynamics of incised valley evolution here we use well constrained observations of incised valleys in experiments and the field to explore controls on valley geometry and develop a simple valley model to quantify the primary dynamics of incised valley evolution we document a strong tendency for incised valleys to widen downstream independent of the details of the relative base level curve or initial surface profile due primarily to the effects of increased sediment flux this is in general agreement with measurements of experimental and natural incised valleys though the degree of widening is less in natural systems due to greater sidewall resistance and smaller water discharge relative to valley size a first order model of incised valley evolution highlights three important trends valley aggradation and widening valley incision and widening and valley incision and narrowing the model reproduces the primary geometric responses to valley formation as measured from experiments valley width and depth both increase in response to increases in 1 local relative base level fall and 2 the initial offshore water depth finally we generalize the first order controls on valley geometry via dimensional analysis to show that long term valley narrowing is not readily produced from relative base level fall alone

large scale glaciation and deglaciation of antarctica during the late eocene approximately 34 m y ago earth s climate transitioned from a relatively warm ice free world to one characterized by cooler climates and a large permanent antarctic ice sheet understanding this major climate transition is important but determining its causes has been complicated by uncertainties in the basic patterns of global temperature and ice volume change here we use an unusually well exposed coastal incised river valley complex in the western desert of egypt to show that eustatic sea level fell and then rose by 40 m 2 m y prior to establishment of a permanent antarctic ice sheet this fall in sea level is associated with a positive oxygen isotope excursion that has been interpreted to reflect global cooling but instead records buildup of an antarctic ice sheet with a volume 70 of the present day east antarctic ice sheet both the sea level fall and subsequent rise were coincident with a transient oscillation in atmospheric co2 concentration down to 750 ppm which climate models indicate may be a threshold for southern hemisphere glaciation because many of the carbon emission scenarios for the coming century predict that atmospheric co2 will rise above this same 750 ppm threshold our results suggest that global climate could transition to a state like the late eocene when a large permanent antarctic ice sheet was not sustainable

seismic imaging of the geothermal field at krafla iceland using shear wave splitting abstract shear wave splitting is emerging as a useful exploration method for geothermal reservoirs as it can detect the geometry of the fracture system the intensity of cracking and possibly changes in fluid pressure within the reservoir the method is based on the analyses of polarizations and time delays of shear waves that have been distorted by the anisotropy of the medium through which the seismic waves have propagated observations of shear wave splitting within the krafla leirhnukur geothermal field iceland using a 20 station 3 component portable seismic array have provided evidence for at least two major crack systems of microfractures oriented approximately n s and e w located microearthquakes align roughly along the e w direction of the geothermal field with shallow focal depths mostly around the injection well probably related to the ongoing injection this unexpected direction is however consistent with results from a simultaneous mt magnetotelluric survey

interannual and interdecadal variability of the south atlantic convergence zone interannual variations of the summertime january march atmospheric circulation over subtropical south america are examined during the period 1958 97 using the national centers for environmental prediction national center for atmospheric research reanalysis data it is found from an empirical orthogonal function analysis that an anomalous upper tropospheric large scale stationary eddy in the lee of the andes tends to accompany a dipole in anomalous vertical motion an anomalous cyclonic anticyclonic eddy accompanies an intensified diffuse south atlantic convergence zone sacz with anomalous descent ascent to the southwest the cold core equivalent barotropic vertical structure of the anomalous cyclonic eddy and the 200 hpa vorticity balance are both characteristic of a stationary rossby wave the tendency for the eddy to be advected downstream by the mean westerlies is compensated by meridional advection of planetary vorticity and stretching associated with vertical motion the anomalous cyclonic flow at low levels reinforces the thermally direct circulation associated with the sacz a weak funneling of submonthly rossby wave activity into this descent region is also identified the interannual time series of the eddy is significantly correlated with north south dipolar sea surface temperature sst anomalies over the southwest atlantic one standard deviation 200 hpa wind speed anomalies of up to 5 m s21 are accompanied by sst anomalies of up to 0 38c a near cyclic 15 yr component is identified which the authors corroborate from independent analyses of southwest atlantic ssts and river flows both are

shelf break upwelling driven by brazil current cyclonic meanders analysis of hydrographic data and results of numerical modeling show the occurrence of upwelling associated with the cyclonic meanders of the brazil current in the region known as the southeast brazil bight or santos bight the temperature and salinity distributions collected during summer and winter confirm the idea that meander induced shelf break upwelling plays an important role in the pumping of south atlantic central water from the slope region onto the continental shelf

does a monsoon climate exist over south america the climatology and the basic state of the summertime circulation and rainfall over south america are studied using assimilation products from the data assimilation system of goddard earth observing system 1 geos1 and satellite derived rainfall results indicate the existence of a regional summer monsoon circulation regime induced by strong diabatic heating over the subtropical south american highland centered at the altiplano plateau sensitivity of the results to the assimilation scheme is tested by comparing that with the national centers for environmental prediction ncep reanalysis and with satellite rainfall estimates results show general agreement between the model produced rainfall anomaly and the satellite estimates as well as consistency between the basic circulation features in the geos 1 and the ncep reanalyses a case study of 1989 90 south american summer monsoon sasm reveals the following characteristics 1 in late spring the onset of sasm is signaled by an abrupt merging of the upper tropospheric double westerly jets one in the subtropics and the other in the subpolar region into a single jet in the midlatitudes this is followed by the establishment of a vortex to the southeast of altiplano and occurrence of heavy precipitation over subtropical eastern brazil 2 during the mature phase of sasm the heavy rainfall zone moves over the altiplano plateau and the southernmost brazilian highland the fully established sasm features are the following a an enhancement of equatorial north atlantic trade wind which emanates from the sahara high and crosses the equator over the south american continent b a buildup of strong northwesterlies along the eastern side of the tropical andes and c development of the south atlantic convergence zone in the southernmost position with strong convective activity meanwhile the upper tropospheric return flow emerges from an anticyclone formed over the altiplano plateau crosses the equator and sinks over northwestern africa 3 the withdrawal of sasm in late summer is signaled by the resplitting of the midlatitude westerly jet at the same time the low level northwest monsoon flow diminishes reducing the moisture supply and leading to the termination of heavy precipitation over the subtropical highland results also show that the above mentioned characteristics of sasm are clearly linked to the tropospheric temperature changes over the central south american highland sensible versus latent heating over the highland are bound to play an important role in the evolution of sasm to provide further support of presence of a monsoon climate over south america sasm is compared and contrasted to the classic east asian summer monsoon easm many similar features including evolution characteristics between the two systems have been identified contrasting aspects of the sasm from the easm are also discussed it is pointed out that a number of monsoonal characteristics of the climate of south america such as the seasonal reversal of the low level wind become apparent only when the strong annual mean wind is removed based on the characteristic features and their evolution the authors conclude that a monsoon climate does exist over south america

variable response of coastal environments of the northwestern gulf of mexico to sea level rise and climate change implications for future change the results from nearly three decades of marine geological research in the northwestern gulf of mexico are compiled in an effort to understand those factors e g sea level rise sediment supply subsidence antecedent topography that influenced coastal evolution during the last eustatic cycle 120 ka to present armed with this information we evaluate coastal response to variable sea level rise of the holocene and accelerated rise during historical time to gain a better understanding of how the coast is likely to respond to future changes the early holocene evolution of northwestern gulf of mexico bays was punctuated by rapid and possibly synchronous flooding events that are interpreted as resulting from episodes of rapid sea level rise two of these events one between 8 4 and 8 0 ka and the other between 7 4 and 6 8 ka were associated with known episodes of ice sheet retreat in north america and antarctica respectively during the middle and late holocene the east texas and western louisiana coasts experienced episodes of stability and growth followed by rapid shoreline retreat while the central texas coast remained relatively stable this variability in coastal response to sea level rise resulted mainly from differences in sediment supply and the highly irregular antecedent topography on which coastal environments formed sand that nourished the evolving east and south texas as well as westernmost louisiana coasts was derived mainly from transgressive ravinement of deltas that were formed during the falling stage of sea level mis5e mis2 the loci of these deltas controlled the spatial variability of this offshore sand supply sand supply to the central texas coast has been dominated by converging longshore currents and throughout the middle to late holocene was large enough to keep pace with sea level rise moreover sand supply from rivers has varied considerably in response to climate change during the early holocene when the average rate of linear sea level rise was 4 2 mm yr the brazos colorado and rio grande rivers all formed deltas on the inner continental shelf today only the brazos contributes enough sediment to the gulf of mexico to form a delta but its sand delivery is minimal a reversal from late holocene growth of western louisiana east texas and south texas barrier islands and peninsulas to erosion occurred during the last 2 0 ka after the rate of sea level rise began to decelerate the actual timing of this reversal was diachronous across the coast and was caused by a decrease in sediment supply once offshore sand sources were bypassed by the landward advancing shoreface transgressive ravinement differences in the exact timing and rate of retreat also reflect variability in the offshore profiles of these barriers and their thickness which results from the underlying relief on the pleistocene surface the late holocene was also the time of chenier plain development in western louisiana and east texas that was marked by localized differences in growth and retreat the current rate of eustatic sea level rise in the northern gulf of mexico is in the range of 2 0 and 3 0 mm yr and is approaching rates of the early holocene this is on average about five times the long term rate of the past 4 0 ka this larger rate is associated with an increase in coastal erosion in historical time relative to long term rates current rates of gulf shoreline erosion are approaching rates of the early to mid holocene and the rate of retreat of some barriers is not sustainable core transects off central texas reflect a late holocene history of shoreface progradation but the modern shoreline is currently eroding albeit at slower rates than elsewhere along the coast overall the sand supply needed to sustain the gulf shoreline is lacking likewise baylines are experiencing erosion rates that are faster than the late holocene average and bayhead deltas are at the tipping point of catastrophic retreat spatial variability in erosion rates highlights the importance of factors such as sediment supply subsidence and anthropogenic influences on coastal evolution tropical storms and hurricanes while exerting the most noticeable coastal change merely exacerbate overall shoreline retreat and migration along the entire northwestern gulf coast the impact of human intervention to natural processes is particularly evident primarily due to alterations in river discharge and sediment supply to the coast interruptions in along shore and cross shore sand transport and increases in rates of subsidence through fluid withdrawal compared to natural changes that took place during the holocene the impacts of human activity have been virtually instantaneous the geological record indicates that the ongoing increase in the rate of sea level rise coupled with diminished sediment supply and human intervention will continue to severely impact the low gradient coastal environments of the northwestern gulf of mexico

the effect of sea level climate and shelf physiography on the development of incised valley complexes a modern example from the east china sea abstract analysis of high resolution seismic reflection and sonar data from the east china sea ecs continental shelf reveals the presence of an extremely broad 330 km and deep maximum incision of 72 m incised valley complex whose development and subsequent fill is constrained to the end of the last glacial cycle 20 000 yr bp to present results from this study indicate that sea level change climate controlled discharge and sediment supply and shelf physiography were important factors in the development and subsequent fill of the ecs incised valley complex for example wet climatic conditions during the initial marine oxygen isotope stage mis 2 fall of sea level promoted fluvial erosion of the exposed shelf however the trend toward drier conditions during the mis 2 fall of sea level slowed the overall development of the incised valley complex to the point where only minor incision occurred during the maximum lowstand furthermore the low gradient morphology of the exposed outer shelf diminished the ability of fluvial systems to incise instead fluvial systems migrated laterally creating a shallow 300 km incised valley system on the outer shelf during the late mis 2 rise of sea level accommodation was generated within the flooded reaches of the valley complex however arid climatic conditions that prevailed at this time resulted in minor sediment delivery to the transgressive shoreline via the incised valley complex thus the upper part of the drowned lowstand fluvial deposits were exposed at the sea floor and reworked into a valley wide tidal bar and tidal sheet complex wetter climatic conditions during middle to late mis 1 resulted in abundant sediment delivery to the drowned parts of the valley complex estuary and buried lowstand fluvial deposits below the depth of tidal ravinement where they remained undisturbed current sequence stratigraphic models can be applied to the late quaternary stratigraphic secession of the ecs however these models are too simplistic because they rely largely on rates and directions of sea level change to explain stratal architectures although the extent and rate of sea level change is extremely important this study shows that high frequency climate change and shelf physiography also play important roles in the development of stratigraphic architectures these factors are particularly important for the development of incised valleys where they directly influence incised valley morphology and facies distributions

controls on the geometry of incised valleys in the basal quartz unit lower cretaceous western canada sedimentary basin in southern alberta multiple episodes of fluvial erosion occurred during lower mannville basal quartz time early cretaceous creating a series of incised valley systems this study examines two of these valley networks in order to illustrate the geomorphic and genetic complexity of incised valley systems both valley networks are filled by a transgressive succession of fluvial to estuarine deposits isopach mapping of these deposits over an area of approximately 10 000 km 2 in southern alberta shows that both systems are dendritic to rectilinear in character with the trunk valley flowing from south to north along the length of the western canada sedimentary basin these systems were fed from the west south and east by a network of tributaries eustatic sea level changes may have played a role in initiating river incision but regional tectonic movements had an important influence on the history of accommodation change the periods of erosion appear to have been relatively brief because the valleys are narrow although confinement within cohesive mudstone rich paleosols of the underlying incised valley deposits may have slowed valley widening a relatively wet paleoclimate may also have contributed to the formation of narrow valleys by favoring the existence of single channel rivers the general morphology of the alberta foreland basin together with the distribution of unfilled relief associated with a preceding valley system and or of less resistant slightly older deposits determined the location of the trunk valleys uplift of the bow island arch sweetgrass arch to the east may have been responsible for a shift in the valley headwaters between the formation of the two valley systems synerosional block faulting in response to flexural loading had a significant influence on the geometry of the valley network through its control on the location and geometry of major tributary valleys the trunk valley is also significantly narrower and more deeply incised where it crosses the most pronounced uplifted block enhanced erosion at tributary junctions and valley bends produced localized areas ca 2 3 km in diameter where the valley fill is up to five times thicker and considerably coarser grained than the adjacent valley deposits such localized scour fills represent prime petroleum exploration targets

palaeohydrological characteristics and palaeogeographic reconstructions of incised valley fill systems insights from the namurian successions of the united kingdom and ireland namurian carboniferous eustatic fluctuations drove the incision and backfill of shelf crossing valley systems located in humid subequatorial regions which are now preserved in successions of the united kingdom and ireland the infills of these valleys archive the record of palaeoriver systems whose environmental hydrological and palaeogeographic characteristics remain unclear a synthesis of sedimentological data from fluvial strata of 18 namurian incised valley fills in the united kingdom and ireland is undertaken to elucidate the nature of their formative river systems and to refine regional palaeogeographic reconstructions quantitative analyses are performed of facies proportions of geometries of incised valley fills and related architectural elements and of the thickness of dune scale sets of cross strata reconstruction of the size of the drainage areas that fed these valleys is attempted based on two integrative approaches flow depth estimations from dune scale cross set thickness statistics and scaling relationships of incised valley fill dimensions derived from late quaternary examples the facies organization of these incised valley fills suggests that their formative palaeorivers were perennial and experienced generally low discharge variability consistent with their climatic context however observations of characteristically low variability in cross set thickness might reflect rapid flood recession perhaps in relation to sub catchments experiencing seasonal rainfall variations in facies characteristics including inferences of flow regime and cross set thickness distributions might reflect the control of catchment size on river hydrology the degree to which is considered in light of data from modern rivers palaeohydrological reconstructions indicate that depth estimations from cross set thickness contrast with observations of barform and channel fill thickness and projected thalweg depths exceed the depth of some valley fills limitations in data and interpretations and high bedform preservation are recognized as possible causes with consideration of uncertainties in the inference of catchment size the palaeogeography of the valley systems has been tentatively reconstructed by integrating existing provenance and sedimentological data the approaches illustrated in this work can be replicated to the study of palaeohydrological characteristics and palaeogeographic reconstructions of incised valley fills globally and through geological time

late quaternary coastal units and marine cycles correlations between northern gulf sectors abstract late pleistocene depositional and morphostratigraphic units designated in mississippi were correlated along the north gulf between texas and northwest florida subsidence resulted in thick pleistocene sequences in the north northwest due to steady inland centered uplift only a thin late pleistocene interval survived erosion on the northeast gulf neogene siliciclastics define the base of the pleistocene the open marine to paralic biloxi alluvial prairie and gulfport barrier formations were deposited during the sangamonian interglacial in sharp contrast with the atlantic south coast only a single barrier shoreline is recognized two sets of paralic deposits separated by weathering horizon and or different consolidation state indicate sangamonian shoreline fluctuations on the texas coast evidence contradicts recent suggestions of coastwise surface aggradation and of a warm interval associated with a major eustatic rise during middle late wisconsinan times

contrasting evolution of sea surface temperature in the benguela upwelling system under natural and anthropogenic climate forcings we present alkenone derived sea surface temperature sst records from three marine cores collected within the southern benguela upwelling system bus spanning the last 3 ka the sst evolution over the last 3 millennia is marked by aperiodic millennial scale oscillations that broadly correspond to climatic anomalies identified over the north atlantic region the bus sst data further suggest cooling and warming trends opposite to the temperature evolution in the moroccan upwelling region and in antarctica in contrast the last decades are marked by a cooling of unprecedented magnitude in both the benguela and moroccan upwelling systems which is not observed in the antarctic record these contrasted responses in atlantic upwelling systems triggered by natural and anthropogenic forcings shed light on how different climatic mechanisms are mediated by ocean atmosphere interactions and transmitted to the geological records of past and present climate changes citation leduc g c t herbert t blanz p martinez and r schneider 2010 contrasting evolution of sea surface temperature in the benguela upwelling system under natural and anthropogenic climate forcings geophys res lett 37 l20705 doi 10 1029 2010gl044353

reappraisal of the sequence boundary in time and space case and considerations for an su subaerial unconformity that is not a sediment bypass surface a time barrier or an unconformity abstract the sequence bounding unconformity bears the key defining traits of being a surface separating younger from older strata along which there is evidence of subaerial erosional truncation or subaerial exposure with a significant hiatus indicated van wagoner et al 1988 this subaerial component of sequence boundaries subaerial unconformity su is also broadly considered to form as a topographic surface of sediment bypass carved during relative sea level fall and buried by backfilling during relative sea level rise accordingly the su is commonly presumed to record an approximate time barrier which separates older from younger strata along its full length in this paper we show that regional composite scour rcs surfaces that are traditionally mapped as an integral component of the su were never a single subaerial topographic surface characterized by sediment bypass are not unconformities do not record an effective time barrier and form diachronously at the channel belt scale over the entire fall to rise of a base level cycle these rcs surfaces and by inference the su surfaces they comprise thus do not fully fit key defining characteristics embodied in the conceptual sequence boundary flume observations and field data show that the rcs is buried by fluvial sediment simultaneously as it is scoured accordingly the rcs is perennially covered with stored sediment during formation is only exposed as a subaerial topographic surface at the local place and time where it is undergoing active growth and forms over the duration of local marine drainage during a relative sea level cycle this cut and cover model differs greatly from more established bypass models which assume that the rcs was roughly sediment free and subaerially exposed for long durations of incision during regression and thus preserves a significant depositional hiatus upon later burial instead the rcs may commonly and locally record a hiatus more typical of a facies bounding diastem without a lacuna significantly greater than that of surfaces within the strata it binds fragments of fluvial strata may commonly and sporadically be preserved above the rcs that are older than underlying marine units overrun by this surface consequently the rcs is not an effective time barrier lateral planation by migrating and avulsing channels as the rcs expands laterally after nucleation can place younger fluvial strata over much older units which means that this surface is also composite and highly diachronous laterally at the scale of channel belts the cut and cover model has additional implications not captured by the bypass model first significant sediments may be stored within fluvial strata above the rcs during regression that are not available for contemporary falling stage and lowstand marine shorelines this can result in marine sediment starvation particularly of the sand fraction and in extreme cases can result in sand autodetachment and an absence of regressive marine reservoir sandstones second cutting of the rcs co generates a suprafluvial surface above the covering fluvial strata during regression that may be used as a mappable proxy for the conceptual maximum regressive surface mrs the mrs may be raised above this surface locally by low accommodation aggradation during lowstand normal regression but in either case preserves an approximate time line where not reworked during later transgression third valley development across the rcs does not exclusively form by landward knickpoint growth and may include complexly formed and potentially cross cutting buffer valleys su valley incision can be divided into four modes which include denudation structural buttress and buffer valley components which may work together locally and tend to have variable importance along the shore to hinterland profile although the rcs is not a good rock proxy for the conceptual sequence boundary it remains a very mappable surface which may separate facies of potentially very different origin and reservoir quality the rcs is also inseparable from the su and typically the only terrestrial erosional surface of extent in most short duration sequences its nullification as a sequence boundary would mean abandonment of depositional sequence stratigraphy as a correlation and interpretive tool within these sections an alternative to abandonment of the su as a sequence boundary is to loosen the definition of a sequence boundary to a discrete surface of erosional truncation carved landward of contemporary shorelines that is traceable beyond the scale of a single valley or comparable local system and its correlative surfaces of conformity and or non deposition and continue its use as before

the south atlantic convergence zone intensity form persistence and relationships with intraseasonal to interannual activity and extreme rainfall abstract the characteristics of intensity geographical location and persistence of the south atlantic convergence zone sacz during the austral summer are investigated intensity and spatial features of the sacz are identified by performing a factor analysis of structural properties of outgoing longwave radiation olr data the first two leading factors explain 65 of the total variance of structural properties and characterize the sacz according to intensity and location oceanic versus continental an index is constructed based on the magnitude of the factor scores to identify intense weak and oceanic continental sacz the intense sacz category is associated with negative olr anomalies over a large area of tropical south america extending from the western amazon to the atlantic ocean the weak sacz category is observed with positive olr anomalies over tropical south america and negative olr anomalies over southeastern south america oceanic and continental aspects of the sacz are related to a

sequence stratigraphy of a coastal plain incised valley estuary lake calcasieu louisiana abstract the stratigraphic profile along a 100 km section of the lake calcasieu incised valley fill was reconstructed from 87 bridge borehole records at four sites along the tidal reaches of the calcasieu river an additional 18 boreholes aligned along the chenier plain near the estuary mouth and shallow seismic data collected along 160 km of track line within the lake calcasieu central basin valley incision occurred during the d18o stage 2 sea level lowstand when the paleo calcasieu river flowed across the inner continental shelf and incised into older fluvial terraces of the prairie formation the valley floor is 57 m deep beneath the modern chenier plain and rises to 30 m along the upper reaches of the modern estuary sea level rise commenced about 20 ka and has continued episodically throughout the holocene shoreline transgression has proceeded at varying rates in response to sea level rise and the incised valley is now occupied by a wave dominated estuary fringed by the chenier plain of western louisiana lowstand deposits are poorly preserved within the calcasieu incised valley deposits constituting the transgressive systems tract tst lie directly above the lower sequence boundary at the top of the prairie formation the tst shows greatest facies diversity and clearest separation of bounding surfaces toward the present seaward end of lake calcasieu here the tst comprises three parasequences that include fluvial bayhead delta and central basin estuarine deposits multiple flooding surfaces within the tst relate to the episodic style of sea level rise highstand infilling of the valley has been characterized by nearshore marine deposition and chenier plain progradation along the lower reaches of the modern calcasieu river the valley fill comprises transgressive central basin nd landward stepping bayhead delta facies overlain by the highstand bayhead delta complex this study documents the most recent phase of deposition within the compound fill of a coastal plain incised valley and demonstrates the potential importance of fluvial controls on facies within incised valley systems

interactions between sea surface temperature over the south atlantic ocean and the south atlantic convergence zone 1 interactions between the sea surface temperature sst over the south atlantic ocean 40 s equador and the south atlantic convergence zone sacz were studied through numerical experiments with an atmospheric general circulation model agcm and an ocean general circulation model ogcm the agcm experiments showed that warm sst anomalies over the south atlantic tend to intensify the sacz and shift it northward while cool sst anomalies over the south atlantic tend to weaken the sacz the ogcm experiments on the other hand showed that the intensification of the sacz contributes to cool the underlying ocean through the reduction of incident shortwave solar radiation causing the appearance of cold sst anomalies or the weakening of pre existing warm sst anomalies the most important finding in this work was the predominance of the cloud shortwave sst negative thermodynamic feedback between the atmosphere and the ocean over the southwest tropical atlantic this is one order of magnitude larger than the dynamic feedback associated with ekman pumping the latter was verified only during strong sacz events the results suggest that negative sst anomalies often observed underlying the sacz represent an ocean response to atmospheric forcing

seaward branching coastal plain and piedmont incised valley systems through multiple sea level cycles late quaternary examples from mobile bay and mississippi sound u s a abstract most incised valleys become more organized seaward through tributaries merging with the main trunk valley late quaternary incised valleys on the mississippi and alabama inner continental shelf branch seaward although they do coalesce towards the shelf break where they feed shelf edge deltas to link fluvial systems with their associated previously mapped incised valleys on the shelf and evaluate the contribution of small coastal plain valley systems to the lowstand systems tract high resolution seismic data and cores were collected from mobile bay eastern mississippi sound and the mobile bay head delta these data show four unconformity bounded stacked units and this study focuses on the upper two regionally mappable units the upper two unconformities were sampled in core as exposure surfaces and on the basis of stratigraphic position depth of incision and 14c dates are interpreted as sequence boundaries the shallowest sequence boundary a formed in response to the oxygen isotope stage 2 sea level lowstand while the underlying sequence boundary b formed in response to an earlier lowstand stage 6 a map of sequence boundary b shows a network of seaward branching valleys 20 35 m deep and 0 6 7 7 km wide that extend across mobile bay and mississippi sound these valleys which are bounded by well developed terraces are extensions of the piedmont mobile fluvial system and the coastal plain fowl and la batre fluvial systems a map of the stage 2 sequence boundary shows that all systems generally reoccupied their previous valley positions and are separated by interfluve plateaus valley fill between sequence boundary b and the stage 2 sequence boundary is generally composed of a basal unit of alluvial sediments overlain by bay head delta deposits however stage 2 to 1 valley fill is composed entirely of central basin sediments the presence of bay head delta deposits on the inner shelf indicates this depositional environment backstepped across the estuaries to modern positions backstepping likely occurred as the low gradient paleovalleys were inundated resulting in rapid rates of transgression fluvial gradients measured on sequence boundary b and the stage 2 sequence boundary below the modern mobile bay head delta plain and the estuaries are very low 1 3 0 3 m km the mobile bay head delta and upper mobile bay are confined by steep topography which opens basinward into the low gradient shorelines surrounding lower mobile bay and mississippi sound during falling sea level channel branching likely occurred as the low gradient fluvial systems extended basinward beyond the confined topography these channels incised as sea level fell below the steeper shelf break during the lowstand stage 2 valley morphology is partially influenced by the position of the underlying stage 6 valleys both coastal plain and piedmont valley systems exhibit compound fill indicating that differentiation between these types of incised valleys cannot be based on valley fill architecture alone

the influence of valley morphology on the rate of bayhead delta progradation abstract bayhead deltas exist between the fluvial and central basin depositional environments of many incised valley fill successions prior work has shown that tributary junctions in flooded incised valleys provide pinning points or locations of stabilization for bayhead deltas during transgression the purpose of this study is to examine the influence of tributary junctions on the behavior of bayhead deltas during regression this influence is examined by using a simple numerical model that incorporates established relationships for systematic changes in valley geomorphology downstream in addition the model incorporates important observations regarding the controls on water depth in wave dominated estuarine central basins which in part controls sediment accommodation water depth in the central basin of wave dominated estuaries with high suspended sediment loads is a function of the width of the central basin parallel to the prevailing wind direction fetch a direct relationship is observed between the width of the central basin parallel to the prevailing wind direction and water depth based on data from modern estuaries in north america europe and south america our model shows that bayhead delta progradation rates increase at tributary confluences and larger deltas prograde at faster rates than smaller deltas in the case of two tributary bayhead deltas fed by systems of the same size coming together the combined bayhead delta progrades 17 6 faster this study provides one more example of the importance of autogenic processes in influencing stratigraphic architecture and the rate of shoreline changes

catchment controls and human disturbances on the geomorphology of small mediterranean estuarine systems abstract geographic signatures are physical and human induced characteristics or processes that identify comparable or unique features of estuaries along latitudinal gradients in mediterranean areas the microtidal regime and the strong seasonal and inter annual contrasts cause an alternation between relatively high runoff and arid conditions furthermore the long history of human settlement also increases the complexity in the study of these estuarine systems this study investigates these signatures of the estuaries located within the mallorcan eastern coast which are geomorphologically homogeneous because of a similar bedrock geology and holocene history a multi method approach focused on the integration of geomorphometry hydraulics historical sources and statistics was used we explore the role played by catchment morphometric parameters severe flash flood events and human disturbances in controlling the geomorphology of 10 beach barrier enclosed fluvial incised lagoons most of the lagoons discharge into calas ranging in size from 1345 to 17 537 m 2 and their related catchments are representative of the mediterranean hydrological systems multiple regression models illustrate that the size slope and drainage network development of the catchments explain the variance in length r 2 0 67 volume r 2 0 49 area r 2 0 64 circularity r 2 0 72 and average width r 2 0 81 of the lagoons depending on these catchment morphometric variables the shape of the lagoons is also determined by the occurrence of catastrophic flash floods which cause scouring and dredging whereas the ordinary flood events and sea storms promote refilling and sedimentation a historical analysis since 1850 documented 18 flood events 5 of which were catastrophic with destructive effects along the catchments and large morphological changes in coastal lagoons high intensity rainfall up to 200 mm in 2 h the geomorphometry of the catchments and the massive construction of terraces and transverse walls are involved in the generation of catastrophic flood events additionally the lagoons were altered considerably by human intervention for flood control and to allow for an increased amount of human activities within the surrounding areas although the high recurrence of catastrophic flood events causes a persistent difficulty in the human battle to dominate these ecosystems therefore the area occupied by lagoons increased between 1956 and the present time from 31 981 m 2 to 63 802 m 2 because of the high recurrence of catastrophic flood events furthermore tourism demand and a social conservation consciousness have promoted restoration and preservation since the 1990s this study has improved the geomorphological knowledge of small mediterranean estuaries affected by human disturbances in the high energy environment found in mallorca

calcification depths of planktonic foraminifera from the southwestern atlantic derived from oxygen isotope analyses of sediment trap material abstract we present a multi year record of shell fluxes and 18o of six planktonic foraminifera species globigerinoides ruber pink globigerinoides ruber white trilobatus sacculifer orbulina universa neogloboquadrina dutertrei globorotalia menardii from sediment traps located in the southwestern atlantic among the six species only the fluxes of g ruber white and n dutertrei exhibit a significant seasonal component with g ruber white showing a single flux peak in austral summer and n dutertrei exhibiting two flux peaks in spring and autumn to estimate calcification depths of the studied species we then compare their measured 18o to vertical 18o profiles predicted for each collection time from in situ temperature profiles and climatological salinity profiles for the majority of the cases the measured 18o could be accounted for by in situ calcification assuming species specific temperature 18o calibrations the resulting estimates of the calcification depth imply that each species exhibits a characteristic typical mean calcification depth the estimated calcification depths for n dutertrei mode 60 70 m and g menardii mode 70 80 m appear to track the depth of the thermocline in the region whereas the calcification depths of the remaining four species correspond to conditions in the mixed layer among the apparent mixed layer calcifiers g ruber pink and white appeared to calcify consistently shallower mode 30 40 m while t sacculifer calcified deeper mode 50 60 m because of the low flux seasonality the observed oxygen isotope offsets among the species are similar to the flux weighted mean annual 18o offsets indicating that isotopic offsets among the species in sediment samples are mainly due to different calcification depths since the habitat offsets among the species are consistent across seasons 18o in sedimentary shells can be used to track conditions in different parts of the water column and the difference in the oxygen isotope composition between surface species best represented by g ruber pink and thermocline species best represented by n dutertrei can be used as a proxy for stratification in the southwestern atlantic

drainage area and incised valley fills in texas rivers a potential explanation abstract the largest rivers draining to the gulf of mexico in texas are at more advanced stages of valley filling than rivers with smaller drainage areas with corresponding differences in alluvial morphology and architecture and avulsion style this seems to imply that the larger fluvial systems either produce more sediment relative to the accommodation space in the alluvial valleys or that they have undergone longer periods of valley aggradation however it is not clear that either of these is the case this paper presents a theoretical analysis showing that fluvial systems with larger drainage areas can produce more advanced stages of infilling than those with smaller drainage areas but with identical histories and sediment production per unit area due to the nature of the scaling relationships between drainage basin area and incised valley size and between basin area and sediment yield data for rivers in the region shows a strong linear relationship between valley width and drainage area the nonlinear relationship between drainage area and proportion of the incised valley filled is somewhat weaker but still significant and major deviations are readily explained in terms of local inherited morphology or tectonic features results show that major differences in the degree or stage of valley filling could occur due to differences in drainage basin size alone this indicates caution in interpreting incised valley fills of drainage basins of different sizes in terms of sediment supply

impact of longer term modest climate shifts on architecture of high frequency sequences cyclothems pennsylvanian of midcontinent u s a abstract pennsylvanian glacioeustatic cyclothems exposed in kansas and adjacent areas provide a unique opportunity to test models of the impact of relative sea level and climate on stratal architecture a succession of eight of these high frequency sequences traced along dip for 500 km reveal that modest climate shifts from relatively dry seasonal to relatively wet seasonal with a duration of several sequences 600 000 to 1 million years had a dominant impact on facies sediment dispersal patterns and sequence architecture the climate shifts documented herein are intermediate both in magnitude and duration between previously documented longer term climate shifts throughout much of the pennsylvanian and shorter term shifts described within individual sequences climate indicators are best preserved at sequence boundaries and in incised valley fills of the lowstand systems tracts lst relatively drier climate indicators include high chroma paleosols typically with pedogenic carbonates and plant assemblages that are dominated by gymnosperms mostly xerophytic walchian conifers the associated valleys are small 4 km wide and 20 m deep and dominated by quartz sandstones derived from distant source areas reflecting large drainage networks transgressive systems tracts tst in all eight sequences generally are characterized by thin extensive limestones and thin marine shales suggesting that the dominant control on tst facies distribution was the sequestration of siliciclastic sediment in updip positions highstand systems tracts hst were significantly impacted by the intermediate scale climate cycle in that hsts from relatively drier climates consist of thin marine shales overlain by extensive thick regressive limestones whereas hsts from relatively wetter climates are dominated by thick marine shales previously documented relative sea level changes do not track the climate cycles indicating that climate played a role distinct from that of relative sea level change these intermediate scale modest climate shifts had a dominant impact on sequence architecture this independent measure of climate and relative sea level may allow the testing of models of climate and sediment supply based on modern systems

controls on lower coastal plain valley morphology and fill architecture abstract small rivers that form at the apex of the coastal prism are common along many passive margins they typically have drainage basins 1000 km2 and their headwaters are isolated to low relief areas of the previous highstand shoreline as sea level fall exposes the apex of the coastal prism incision and drainage basin evolution of those small rivers should be strongly influenced by coastal paleotopography but previous work suggests that paleodischarge is the dominant control on incised valley dimension to examine the controls on the morphologic evolution of small incised valleys we examined 20 incised valleys in north carolina situated close to the last interglacial shoreline including coastal prism incised valleys which have well developed dendritic drainage networks on the highstand shoreline topography and tributary incised valleys which form adjacent to and merge with larger piedmont incised valleys coastal prism n 18 and tributary n 2 incised valley width measured at the common bayhead delta location is proportional to drainage basin area long term discharge however that comparison location overlaps with the knickzone only for the larger river systems the knickzone of small river systems is located down dip from the modern bay head delta which is likely due to slower rates of knickpoint migration we use geophysical and lithologic data from three incised valleys to highlight differences in regional valley morphology that can be used to distinguish between coastal prism and tributary incised valleys the newport and north coastal prism incised valleys connect to small sangamonian drainage networks of 210 km2 and 50 km2 respectively those valleys widen and deepen at the knickzone which is also where smaller tributary systems merge with the main trunk valley the scuppernong tributary incised valley has a drainage basin of 400 km2 and can be differentiated from other incised valleys based on the absence of a compound fill and continuous seaward deepening and widening from the upstream limit of the knickzone the knickzone is the junction of the scuppernong with the adjacent larger roanoke incised valley the depth of which controls base level for the scuppernong the dramatic scuppernong valley widening in a down dip direction is principally due to highly erosive bay ravinement processes associated with the adjacent much larger drowned roanoke incised valley these varying modes of valley evolution specifically controls of paleotopography on valley incision and ravinement explain the morphologies of small drowned river mouth estuaries and improve understanding of basin scale sediment transport pathways

interhemispheric comparison of deglacial sea surface temperature patterns in atlantic eastern boundary currents abstract sediment core geob 1023 5 from the eastern south atlantic was investigated at high temporal resolution for variations of sea surface temperature sst during the past 22 kyr using the alkenone u k 37 method ssts increased by 3 5 c from about 18 c during the last ice age 21 2 cal kyr bp to about 21 5 c at 14 5 cal kyr bp this warming trend associated with the deglaciation phase was followed by a cooling event with lowest ssts near 20 c persisting for about 1000 years between 13 and 12 cal kyr bp the ssts then continued to increase to about 22 5 c at the holocene climatic optimum at 7 cal kyr bp and decreased again during the late holocene to a core top value of 19 8 c that is comparable to modern annual mean sst values when compared with alkenone sst records from the eastern north atlantic our sst record indicates continuous warming throughout the deglaciation phase in the benguela current while its northern counterpart the canary current experienced prominent cooling during heinrich event 1 h1 on the other hand for the time period corresponding to the younger dryas yd cooling event the benguela sst record exhibits a cold temperature interval that corresponds to that observed in the eastern north atlantic sst records this observation suggests that interhemispheric climate response in atlantic eastern boundary current systems was different with respect to the two abrupt climate events associated with termination i for the h1 the eastern south atlantic sst record strongly supports the hypothesis that an anti phase thermal behavior in south atlantic surface waters was forced by the slowdown of the north atlantic deep water formation during cold spells in the north atlantic in contrast the abrupt cooling in the eastern south atlantic coincident with the yd period was probably induced by more vigorous global atmospheric circulation enhancing the upwelling intensity in both eastern boundary current systems this atmospheric control may have overridden any effect caused by changes in thermohaline circulation on the south atlantic ssts during the yd which leads to the assumption that the thermohaline circulation was already much closer to its interglacial mode during the yd than during the h1

seasonality of u k 37 temperature estimates as inferred from sediment trap data abstract the seasonality of sea surface temperatures sst estimated from the alkenone u k 37 index has been a debated issue since the development of the proxy using a compilation of sediment trap time series data from 34 sampling locations we show that the seasonality of maximum alkenone flux in sediment traps varies markedly across the oceans depending not only on latitude and light availability but also on local oceanographic conditions the seasonality of the alkenone flux to sediments may also be shaped by the complexity of sedimentation processes and a consistent globally applicable seasonal pattern is not apparent nevertheless u k 37 values display a world ocean scale correlation with mean annual ssts 0 m that closely resembles the standard calibration equation now established for modern surface sediment records thus with a few notable exceptions at oceanographic locations proximate to major hydrographic fronts it can be concluded that the integrated sedimentation patterns for u k 37 measured in sediment trap time series provide a measure of annual mean sst

holocene and eemian sea surface temperature trends as revealed by alkenone and mg ca paleothermometry in this study we review a global set of alkenone and foraminiferal mg ca derived sea surface temperatures sst records from the holocene and compare them with a suite of published eemian sst records based on the same approach for the holocene the alkenone sst records belong to the actualized ghost database kim j h schneider r r 2004 ghost global database for alkenone derived holocene sea surface temperature records available from http www pangaea de projects ghost while the mg ca derived sst database represents a new compilation the actualized ghost database not only confirms the sst changes previously described but also documents the holocene temperature evolution in new oceanic regions such as the northwestern atlantic the eastern equatorial pacific and the southern ocean a comparison of holocene sst records stemming front the two commonly applied paleothermometry methods reveals contrasting sometimes divergent sst evolution particularly at low latitudes where sst records are abundant enough to infer systematic discrepancies at a regional scale opposite sst trends at particular locations could be explained by out of phase trends in seasonal insolation during the holocene this hypothesis assumes that a strong contrast in the ecological responses of coccolithophores and planktonic foraminifera to winter and summer oceanographic conditions is the ultimate reason for seasonal differences in the origin of the temperature signal provided by these organisms as a simple test for this hypothesis eemian sst records are considered because the holocene and eemian time periods experienced comparable changes in orbital configurations but had a higher magnitude in insolation variance during the eemian for several regions sst changes during both interglacials were of a similar sign but with higher magnitudes during the eemian as compared to the holocene this observation suggests that the ecological mechanism shaping sst trends during the holocene was comparable during the penultimate interglacial period although this ecology hypothesis fails to explain all of the available results we argue that any other mechanism would fail to satisfactorily explain the observed sst discrepancies among proxies c 2010 elsevier ltd all rights reserved

how and where do incised valleys form if sea level remains above the shelf edge sequence stratigraphic models predict that during relative sea level fall rivers will cut incised valleys across the exposed continental shelf incision is driven by the exposure of convex up topography and consequent downstream increases in stream power modern shelf profiles from passive margin and foreland basin settings show that profile convexities occur at the shelf edge and at the current highstand coastline the coastal prism in nonglacial times which form much of earth9s history it is unlikely that the shelf edge was subaerially exposed during such periods patterns of incision would have been primarily determined by the shape of the coastal prism on the basis of modern shelf profiles from passive margin and foreland basin settings river incision of as much as 20 to 70 m would be centered upon the preceding highstand coastline and would be restricted to the inner part of the shelf deeper incised valleys would only result from exposure of the shelf edge or from the processes involved in the formation of submarine canyons

controls of subsurface temperature variability in a western boundary upwelling system 1 the mechanisms controlling subsurface temperature variability on the outer shelf in a western boundary upwelling system are quantified using observations from a mooring deployed off cabo frio brazil results from a multiple linear regression analysis reveal that in addition to low frequency variations associated with the seasonal evolution of temperature the dominant mechanisms controlling temperature variability are wind stress curl driven upwelling cross isobath transport the proximity of the brazil current to the shelf break and perhaps changes in the strength of tidal mixing associated with the spring neap cycle the influence of the proximity of the brazil current decreases strongly with depth being restricted to the top 80 m regression coefficients indicate that the relative contributions from the different forcings are roughly similar and that no single process has a dominant role explaining temperature variability near the shelf break these suggest that successful modeling efforts in the region must adequately represent each of those processes

marine sediments from southeastern brazilian continental shelf a 1200 year record of upwelling productivity abstract a sediment core from the cabo frio coastal shelf 23 19 s 41 8 w 117 m depth was analyzed for toc c n ratio organic petrography and planktonic foraminiferal content to evaluate variations in local productivity caused by changes in upwelling intensity and its relation to regional and global climatic variations during the last millennium the cabo frio core recorded the last 1200 years of sedimentation with rates varying from 0 11 to 0 32 mm yr 1 foraminiferal and organic geochemical analyses indicate the occurrence of three distinct periods of productivity from 850 ad until 1070 ad foraminifera fluxes consisting primarily of turborotalita quinqueloba indicate stronger south atlantic central water sacw transport onto the shelf which induced high biological productivity that was also recorded by high toc and marine palynomorphs content and a low c n atomic ratio this period coincided with a northward displacement of the atmospheric intertropical convergence zone itcz and south atlantic high sah systems driven by positive temperature anomalies in the north atlantic ocean during the medieval climate anomaly mca from 1070 until 1500 ad low toc flux and planktonic foraminifera fluxes and high c n atomic ratios suggest a reduction in marine productivity probably driven by reduced transport of sacw associated with the southward displacement of the sah and weakening of northeasterly winds the period between 1500 and 1830 ad which corresponds to the little ice age is marked by increased fluxes of planktonic foraminifera principally of globigerina bulloides and globigerinita glutinata these species mark an increase in productivity linked to sacw upwelling supported by the enhancement of northeasterly winds and southward displacement of the itcz and sah

rivers turned to rock late quaternary alluvial induration influencing the behaviour and morphology of an anabranching river in the australian monsoon tropics abstract late quaternary alluvial induration has greatly influenced contemporary channel morphology on the anabranching gilbert river in the monsoon tropics of the gulf of carpentaria the gilbert one of a number of rivers in this region has contributed to an extensive system of coalescing low gradient and partly indurated riverine plains extensive channel sands were deposited by enhanced flow conditions during marine oxygen isotope oi stage 5 subsequent flow declined probably associated with increased aridity however enhanced runoff recurred again in oi stages 4 3 65 50 ka aridity then capped these plains with 4 7 m of mud a widespread network of sandy distributary channels was incised into this muddy surface from sometime after the last glacial maximum lgm to the mid holocene during a fluvial episode more active than the present but less so than those of oi stages 5 and 3 this network is still partly active but with channel avulsion and abandonment now occurring largely proximal to the main gilbert flow path a tropical climate and reactive catchment lithology have enhanced chemical weathering and lithification of alluvium along the river resulting in the formation of small rapids waterfalls and inset gorges features characteristic more of bedrock than alluvial systems thermoluminescence tl and comparative optically stimulated luminescence osl ages of the sediments are presented along with u th ages of pedogenic calcrete and fe mn oxyhydroxide oxide accumulations they show that calcrete precipitated during the late quaternary at times similar to those that favoured ferricrete formation possibly because of an alternating wet dry climate intense chemical alteration of the alluvium leading to induration appears to have prevailed for much of the late quaternary but probably due to exceptional dryness not during the lgm the result has been restricted channel migration and a reduced capacity for the channel to adjust and accommodate sudden changes in bedload consequent avulsions have caused local stream powers to increase by an order of magnitude inducing knickpoint erosion local incision and the sudden influx of additional bedload that has triggered further avulsions the gilbert river while less energetic than its pleistocene ancestors is clearly an avulsive system and emphasizes the importance in some tropical rivers of alluvial induration for reinforcing the banks generating nickpoints reworking sediment and thereby developing and maintaining an indurated and anabranching river style

coalescent valley fills from the late quaternary record of tuscany italy abstract three prominent incised valley fills of post last glacial maximum age are described from the northern tuscan coast of italy stratigraphic correlation of core data along a cross section transversal to the present fluvial channel axes enables identification of a suite of genetically related valley bodies that fill the incisions made up by arno serchio and camaiore stiava rivers during the last glacial interglacial cycle the valley fills display different shapes and size but remarkably similar facies architecture valley bodies range between 5 and 10 km in width and between 30 and 45 m in thickness with width thickness ratios of about 100 300 above a lowstand and early transgressive gravel fluvial deposit the three incised valley fills display a distinctive succession of coastal plain to estuarine facies dated to about 13 8 cal ka bp radiocarbon dates document that the three valleys were active simultaneously accommodation space was rapidly created during transgression and then filled under conditions of very high sediment accumulation about 1 cm y in contrast to the more common deepening upward trend recorded by the latest pleistocene early holocene valley fill successions worldwide sedimentation in the tuscan valleys equalled or even exceeded the rate at which accommodation was created thus leading to an aggradational rather than backstepping stacking pattern of high frequency millennial scale parasequences above the valley fills and on the interfluves a thin deepening upward succession of nearshore deposits marks the rapid change from aggradational to retrogradational depositional style this is invariably overlain by a characteristic shallowing upward motif of prograding deltaic and coastal facies the maximum flooding surface which can be tracked across the whole study area on the basis of subtle palaeontologic indicators is shown to represent an almost isochronous surface dated to about 7 8 cal ka bp through examination of large scale geometry and facies attributes of the valley fills including the relationships between valley bodies and interfluves this study represents an example of how adjacent river systems with significantly different characteristics may respond simultaneously in a consistent manner to rapid changes in sea level and climate conditions

controls on late quaternary incised valley dimension along passive margins evaluated using empirical data incised valleys are canyon like features that initially form near the highstand shoreline and evolve over geological time as rivers erode into coastal plains and continental shelves to maintain equilibrium gradient profiles in response to sea level fall most of these valleys flood during sea level rise to form estuaries incised valley morphology strongly controls the rate of creation of sediment accommodation valley fill facies architecture and the preservation potential of coastal lithosomes on continental shelves and affects coastal physical processes nonetheless little is known about what dictates incised valley size and shape and whether these metrics can be used to explain principal formation processes the main control on alluvial channel morphology over human time scales is discharge this is based on numerous empirical studies and is well constrained because all variables are easily measured at this short time scale knowledge of long term river evolution over a complete glacio eustatic cycle on the contrary remains largely conceptual experimental and based on individual systems because variables that are thought to drive morphological change are not easily quantified in spite of this difficulty existing models of incised valley formation at the coast suggest that valley evolution is driven largely by downstream forcing mechanisms highlighting sea level and shelf gradient morphology as the dominant controls on valley incision although valleys are cut by rivers whose channels are a direct reflection of discharge little empirical data exist in coastal areas to address the degree to which valley evolution is governed by upstream controls the late quaternary is the best time period to examine because it provides the most complete sedimentary record and many variables including sea level tectonics substrate lithology and drainage network characteristics are accurately constrained here 38 late quaternary valleys along the coast of two different passive continental margins are compared which suggests that valley shape and size are governed primarily by upstream intrinsic controls such as discharge valley width depth and cross sectional area are found to be predictable at the highstand shoreline and are scaled with the size of their drainage basin which has important implications for estimating sediment discharge to continental shelves and deep water environments during periods of low sea level

late holocene palaeotemperatures and palaeoenvironments in the southeastern brazilian coast inferred from otolith geochemistry abstract holocene palaeoceanography and climatic reconstructions were evaluated based on proxy analyses of fish otoliths from shellmounds located along the coast of rio de janeiro state brazil modern coastal seasonal upwelling is associated with the ascension of a deep and cold water mass as a consequence of persistent ne winds that affect the climate in southeastern brazil however this seasonal influence and the effect of the holocene palaeoenvironment on shallow water are poorly known in this work coastal palaeotemperatures were estimated based on the geochemical analyses of otolith the results of the 18o and 13c analyses from holocene otoliths obtained from coastal shellmounds separated by a distance of almost 200 km show two distinctive otolith derived palaeotemperature signals in a coastal region under upwelling influence additionally this analysis suggests that the fish lived in marine waters showing similar microchemistry values composition when compared with modern marine otoliths

fluvial responses to climate and sea level change a review and look forward summary fluvial landforms and deposits provide one of the most readily studied quaternary continental records and alluvial strata represent an important component in most ancient continental interior and continental margin successions moreover studies of the long term dynamics of fluvial systems and their responses to external or allogenic controls can play important roles in research concerning both global change and sequence stratigraphy as well as in studies of the dynamic interactions between tectonic activity and surface processes these themes were energized in the final decades of the twentieth century and may become increasingly important in the first decades of this millennium this review paper provides a historical perspective on the development of ideas in the fields of geomorphology quaternary geology vs sedimentary geology and then summarizes key processes that operate to produce alluvial stratigraphic records over time scales of 103 106 years of particular interest are changes in discharge regimes sediment supply and sediment storage en route from source terrains to sedimentary basins as well as changes in sea level and the concept of accommodation late quaternary stratigraphic records from the loire france mississippi usa colorado texas usa and rhine meuse the netherlands rivers are used to illustrate the influences of climate change on continental interior rivers as well as the influence of interacting climate and sea level change on continental margin systems the paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea level change at present empirical field based research on fluvial response to climate and sea level change lags behind a the global change community s understanding of the magnitude and frequency of climate and sea level change b the sequence stratigraphic community s desire to interpret climate and especially sea level change as forcing mechanisms and c the modelling community s ability to generate numerical and physical models of surface processes and their stratigraphic results a major challenge for the future is to catch up which will require the development of more detailed and sophisticated quaternary stratigraphic sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings there is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter 102 103 years and longer 104 106 years time scales than has commonly been the case to date as well as in larger river systems from source to sink studies of quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre quaternary rock record

holocene sea surface temperatures and related coastal upwelling regime recorded by vermetid assemblages southeastern brazil arraial do cabo rj abstract in places where ocean currents cause upwelling nearshore sea surface temperatures sst are often cooler than nearby offshore waters in the arraial do cabo bay coast upper holocene aragonitic vermetids are represented by monospecific clusters of overgrowing petaloconchus varians occurring in supratidal intertidal carbonate and mixed siliciclastic carbonate deposits based on stable isotope composition 13c 18o of fossil vermetid shells radiocarbon ages and altimetric survey the upper holocene upwelling system of the cabo frio area southeastern brazil rio de janeiro is assessed in the studied region at 3700 cal years bp the maximum relative sea level rsl was 4 0 m with a sst of 20 7 c subsequently vermetid based sst decreased from 22 8 to 17 c at 3300 cal years bp with the coldest temperatures recording a strong upwelling event at around 2000 cal years bp when the rsl was at 2 m the intensification in upwelling water masses is identified by the 13c enrichment along with higher 18o in the vermetid shells the decreasing sst trend assessed from 3300 to 2000 cal years bp can be related to more frequent south atlantic coastal water intrusions on the surface layer in the mid shelf increasing the nutrient concentration in the upper layer from 1900 to 1300 cal years bp a higher sst up to 21 c occurred during the continuous sea level fall

origin and evolution of sabine lake texas louisiana abstract high resolution uniboom seismic reflection profiles and vibracores acquired from sabine lake texas during 1987 aid in the reconstruction of the bay s history seismic records show that the bay is located over an incised valley initially carved during an early lowstand tentatively assigned to 18o stage 5d thus the valley fill sequence represents more than one stage of incision and fill sediment cores collected along the flanks of the valley penetrated bay muds resting directly on pleistocene clays radio carbon dates suggest that the broad shallow bay floor was flooded approximately 4 000 years ago prior to this time the bay was confined to the narrow deep incised valley none of the cores that penetrated beyond the holocene fill contain transitional deepening upwards deposits implying either that flooding was rapid or that erosion had removed these transitional deposits cores from the upper portion of the bay were characterized by coarsening upward sequences which appear to reflect increasing fluvial input of sand with time cores from the marsh area at the southern end of the lake penetrated marsh deposits resting on flood tidal delta and bay deposits a strong dominance of the bivalve rangia cuneata a species generally found in fresh to brackish waters occurs throughout the holocene section of sediment cores carbon isotopic values of these molluscan shells are generally low and consistent with low salinities the only exception to this is seen in the very base of these cores where the microfossil assemblage and isotopic results indicate a brief period during which salinities were higher than at present otherwise the salinity structure of the bay and its fauna have changed little during the past 4 000 years

rapid 20th century increase in coastal upwelling off northwest africa near shore waters along the northwest african margin are characterized by coastal upwelling and represent one of the world9s major upwelling regions sea surface temperature sst records from moroccan sediment cores extending back 2500 years reveal anomalous and unprecedented cooling during the 20th century which is consistent with increased upwelling upwelling driven ssts also vary out of phase with millennial scale changes in northern hemisphere temperature anomalies nhtas and show relatively warm conditions during the little ice age and relatively cool conditions during the medieval warm period together these results suggest that coastal upwelling varies with nhtas and that upwelling off northwest africa may continue to intensify as global warming and atmospheric co 2 levels increase

geochronology of late pleistocene to holocene speleothemsfrom central texas implications for regional paleoclimate a detailed chronology for four stalagmites from three central texas caves separated by as much as 130 km provides a 71 000 yr record of temporal changes in hydrology and climate mass spectrometric 238 u230 th and 235 u231 pa analyses have yielded 53 ages the accuracy of the ages and the closedsystem behavior of the speleothems are indicated by interlaboratory comparisons concordance of 230 th and 231 pa ages and the result that all ages are in correct stratigraphic order over the past 71 000 yr the stalagmites have similar growth histories with alternating periods of relatively rapid and slow growth the growth rates vary over more than two orders of magnitude and there were three periods of rapid growth 71 60 ka 39 33 ka and 24 12 ka these growth rate shifts correspond in part with global glacial interglacial climatic shifts paleontological evidence indicates that around the last glacial maximum 20 ka climate in central texas was cooler and wetter than at present this wetter interval corresponds with the most recent period of increased growth rates in the speleothems which is consistent with conditions necessary for speleothem growth the temporal shift in wetness has been proposed to result

fish bone diagenesis in southeastern brazilian shell mounds and its importance for paleoenvironmental studies abstract brazilian shell mounds are relicts of prehistoric settlements characterized as distinct features on the sandy coastal plain sandy bars of coastal lagoons and rocky island they are composed of shells of edible marine mollusks fish remains and wildlife bones intermixed with sand in the coastal lagoon region of the rio de janeiro state these shell mounds range in age between 5100 and 1300 cal bp in this study we analyzed the geochemistry of the bones of the whitemouth croaker that primarily offers insight on the nature of bone diagenesis and its use for radiochronology and as isotope paleo thermometer the x ray diffractograms of bones from the tarioba shell mound exhibit elevated calcite profiles in contrast to a reduced hydroxyapatite concentration two peaks of quartz and the presence of feldspar provide evidence of exogenous materials e g sand or silt particles infilling hollow spaces within the fish bones the beirada and the ponte do girau shell mounds are characterized by the highest peaks of apatite relative to calcite which is clearly different from the result obtained for tarioba the manitiba profile is similar to the tarioba profile except for calcite peaks that are approximately three times lower than those for tarioba at a depth of 25 cm in the tarioba shell mound the redox sensitive index of diagenetic alteration reaches its maximum value suggesting a zone of accumulation in the soil horizon redox condition the 18o derived temperatures profile based on mollusks showed a consistent range from 18 1 to 24 1 c indicating seasonal events of intense upwelling of the south atlantic central water breaking the mean warm surface conditions of the brazil current diagenetic imprints of tarioba shell mound suggest humid burial conditions with the loss of hydroxyapatite and the enrichment of exogenous calcite drier depositional environmental conditions are indicated in the ponte do girau and the beirada shell mounds while intermediary depositional environmental conditions characterize the manitiba shell mound in the period represented by the shell mound samples the sea level exhibited significant oscillations and portions of the inner shelf were exposed which may have resulted in an anomalous derived temperature records these results are compatible with events of anomalous temperatures occurring in the sea level during the time span of occupation of these shell mounds

upstream controls on incised valley dimensions and fill examples from the upper mississippian mauch chunk group central appalachian basin usa abstract subsurface mapping and facies and architectural element analysis on outcrop combined with published detrital zircon geochronology and sandstone petrography are used to reconstruct a source to sink system for two incised valley fills in the upper mississippian mauch chunk group the lower stony gap incised valley is relatively broad and filled with quartzarenite fluvial facies consisting of downstream accreting elements with minimum thicknesses of 6 m cross sets within elements average 62 5 cm thick the lower princeton incised valley is relatively narrow and filled with sublitharenite fluvial facies consisting of channel elements that range in thickness from 0 25 to 3 6 m cross sets within elements average 35 cm thick quantitative estimates of drainage areas using regional hydraulic geometry curves for comparable climatic settings are consistent with order of magnitude differences for the lower stony gap sandstone 700 000 km2 and the lower princeton formation

insights into sea surface temperatures from the cayman islands from corals over the last 540 years abstract seven large corals orbicella annularis and montastrea cavernosa from grand cayman and cayman brac which grew between 1474 to 1512 ce and 1815 to 2014 ce are characterized by growth banding that reflects bi annual growth periods some of these growth bands however include micro scale bands that reflect sub annual growth phases paleotemperatures derived from the oxygen isotope composition of these corals indicate that sea surface temperature sst between 1474 to 1512 ce and 1815 to 2014 ce ranged from 18 to 34 c and included four main periods of temperature change with smaller scale warm or cool intervals superimposed on these periods cool period 1 1474 to 1512 ce coincided with decreased temperatures that existed in the northern hemisphere during the little ice age lia ca 1450 1850 ce cool period 2 1815 to 1924 ce coincided with a caribbean wide reduction in temperatures that was probably related to the final phase of the lia warm period 1 1924 to 2006 ce is characterized by an overall increase in sst consistent with the pronounced global warming since the 1970 s modern period 1 2006 2014 ce is characterized by temperatures that fluctuate around 28 5 c the current average water temperature for grand cayman the overall 3 c 0 96 c increase in sst since 1815 ce derived from the cayman corals is consistent with the caribbean and global temperature increases since the 1850 s smaller scale deviations in the cayman temperature profiles from the general caribbean global temperature trends probably reflect local factors such as increased storm and or cold air front frequencies a reduction in the size and or intensity of the atlantic warm pool shifts in the phase of the atlantic multidecadal oscillation and or weakening of the cayman basin current

control of upstream variables on incised valley dimension abstract it is well documented that sea level fell during the last glacial maximum shifting graded stream profiles out of equilibrium and causing rivers to incise into continental shelves although incised valleys have been heavily researched the interplay between upstream and downstream controls on incised valley dimension are not well constrained to address this lack of understanding we examined the cross sectional dimension of nine incised valleys located across the northern gulf of mexico margin and bounded by the sequence boundary associated with the last sea level lowstand these incised valleys are distinguished by drainage basins that vary in size by three orders of magnitude cover a margin that presently has a steep climate gradient and extend across a continental shelf that varies along strike in width and gradient incision depths vary for valleys that have similar gradient profiles but different drainage basin areas suggesting significant control of upstream variables on incised valley morphology additionally these data show a strong linear correlation between drainage basin area and incised valley cross sectional area this suggests applicability of the empirically derived relationship between modern discharge and cross sectional channel area to incised valleys when compared at the maximum highstand shoreline of the previous sequence incised valley dimension adjusts over a longer period than the lowstand and is in equilibrium with drainage basin area which is considered a proxy for long term discharge although base level fall promotes incision upstream variables control incised valley dimensions

some dynamic aspects of river geometry natural alluvial river channels in contrast to most regime or equilibrium canals are characterized by variable streamflows this paper relates channel geometry to measures of streamflow variability as distinct from mean discharge or flow magnitude a relationship between mean channel width and the mean and coefficient of variation of channel forming discharges is derived for the given mean discharge it is shown that the more variable the flow the narrower the channel is in the mean to a great extent this relationship is confirmed by data on alluvial channels in the missouri river basin variability of water discharges proves to be an important factor influencing natural river geometry this initial approach to the understanding of the dynamics of river geometry leads to the construction of a simple simulation model in which a series of channel forming discharges is generated and corresponding changing channel geometry is calculated results from the simulation indicate 1 the channel has in effect a kind of truncated memory i e the impact of an existing channel exists so long as the prevailing discharge does not exceed the present channel capacity 2 the effect of memory or the impact of the existing channel on the mean channel geometry is opposite to that of flow variability i e the memory tends to keep the channel geometry larger in the mean 3 the simulated channel width as expected increases abruptly at high discharges declining over time along a die away curve until the advent of a recorded high flow

quantitative analysis of the stratigraphic architecture of incised valley fills a global comparison of quaternary systems abstract facies models of the internal fills of incised valleys developed in shelf and coastal settings during cycles of relative sea level change are largely conceptual descriptive and qualitative in form moreover they are commonly bespoke to individual examples here a database driven quantitative statistical analysis of 87 late quaternary incised valley fills ivfs has been undertaken to assess the general validity and predictive value of classical facies models for ivfs and to investigate the relative importance of possible controls on their stratigraphic organization based on datasets from the published literature stored in a sedimentological database the geometry and proportion of systems tracts and of architectural elements of different hierarchies within ivfs are quantified these variables were analysed to assess how they vary in relation to parameters that represent potential controlling factors relative sea level stage continental margin type drainage basin area valley geometry basin physiography and shoreline hydrodynamics the stratigraphic organization of the studied coastal plain ivfs is generally consistent with that represented in facies models the primary control being the rate and magnitude of relative sea level change however results from this study demonstrate significant variability in the stratigraphic architectures of ivfs which is not accounted for by existing models variations in the facies architecture of coastal plain and cross shelf valley fills can be attributed to controls other than sea level and expressed in relationships with continental margin type basin physiography catchment area river system size and shoreline hydrodynamics the following primary findings arise from this research i compared to their counterparts on passive margins coastal plain ivfs hosted on active margins contain on average a higher proportion of fluvial deposits and a lower proportion of central basin estuarine deposits estuarine deposits tend however to be thicker this suggests a control on ivf stratigraphic architecture exerted by distinct characteristics of the tectonic setting of the host continental margins notably basin physiography rates and mode of sediment supply and nature of sediment load ii the thickness and proportion of lowstand systems tract are positively correlated with coastal plain ivf dimensions likely reflecting the role of drainage basin area in dictating the scale of the fluvial systems that carved and infilled the valleys iii positive correlations are observed between the thickness of fluvial deposits bayhead delta deposits and central basin estuarine deposits versus coastal plain ivf dimensions and valley catchment area this suggests a control exerted by the river system scale on sediment supply rates and on the accommodation determined by valley size iv positive correlations between the thickness and proportion of barrier complex deposits within cross shelf ivfs versus mean shelf gradient indicate that the geometry of the shelf might control the establishment and preservation of barrier island environments in incised valleys located on the shelf v correlations between the width of coastal plain ivfs and present day mean tidal range at the shoreline indicate that tidal dynamics may contribute to the widening of the incised valleys positive correlation is observed between the proportion of tide dominated elements in highstand ivf deposits and ivf width suggesting possible effects of interplays between hydrodynamic conditions and the geometry of incised valleys on their infills this study highlights the complexity of the internal fills of incised valleys which must be considered when attempting the application of facies models of ivfs to rock record interpretations or as predictive tools in subsurface studies

geological controls on the geometry of incised valley fills insights from a global dataset of late quaternary examples incised valleys that develop due to relative sea level change are common features of continental shelves and coastal plains assessment of the factors that control the geometry of incised valley fills has hitherto largely relied on conceptual experimental or numerical models else has been grounded on case studies of individual depositional systems here a database driven statistical analysis of 151 late quaternary incised valley fills has been performed the aim being to investigate the geological controls on their geometry results of this analysis have been interpreted with consideration of the role of different processes in determining the geometry of incised valley fills through their effect on the degree and rate of river incision and on river size and mobility the studied incised valley fills developed along active margins are thicker and wider on average than those along passive margins suggesting that tectonic setting exerts a control on the geometry of incised valley fills likely through effects on relative sea level change and river behaviour and in relation to distinct characteristics of basin physiography water discharge and modes of sediment delivery valley fill geometry is positively correlated with the associated drainage basin size confirming the dominant role of water discharge climate is also inferred to exert a potential control on valley fill dimensions possibly through modulations of temperature peak precipitation vegetation and permafrost which would in turn affect water discharge rates of sediment supply and valley margin stability shelves with slope breaks that are currently deeper than 120 m contain incised valley fills that are thicker and wider on average than those hosted on shelves with breaks shallower than 120 m no correlation exists between valley fill thickness and present day coastal prism convexity which is measured as the difference in gradient between lower coastal plains and inner shelves these findings challenge some concepts embedded in sequence stratigraphic thinking and have significant implications for analysis and improved understanding of source to sink sediment route ways and for attempting predictions of the occurrence and characteristics of hydrocarbon reservoirs

preliminary vegetation maps of the world since the last glacial maximum an aid to archaeological understanding abstract a set of preliminary broad scale vegetation map reconstructions for use by archaeologists and anthropologists is presented here for the world at the last glacial maximum 18 000 years ago the early holocene 8000 years ago and the mid holocene 5000 years ago for comparison we also give present potential maps which may be regarded as approximating the late holocene vegetation as it would or might be without agricultural modification the maps were produced through consultation with an extensive network of experts and a range of literature and map sources accompanying each regional map is a bibliography detailing the principal literature sources of evidence on late quaternary palaeovegetation and climates the maps presented here are not intended as the last word on the distribution of vegetation at each time slice they are merely a preliminary attempt at appraisal of current knowledge and opinion nevertheless together with the accompanying citation summary they should provide a valuable and readily accessible source of information on current opinion in the quaternary community it is also hoped that the maps will themselves act as a catalyst for archaeologists to use their own data to contribute to the broader climatic palaeovegetational picture

fidelity of alkenone paleotemperatures in southern cape basin sediment drifts 0 in two drift cores tn057 21 and ocean drilling program site 1089 are nearly identical during the interval of overlapping analyses mis 4 5c ssts in a nearby nondrift core tn057 6 covary with those in core tn057 21 throughout mis 1 5c while climatological ssts overlying tn057 21 and tn057 6 are similar and consistent with reconstructed holocene ssts in the nondrift core surface waters overlying tn057 21 are 6 c colder than holocene alkenone ssts in the drift core temperatures remain 6 c warmer in tn057 21 relative to tn057 6 during the 100 kyr duration of the records we hypothesize that alkenone derived ssts in tn057 21 are higher than climatological ssts in the overlying surface water and those in tn057 6 as a result of the winnowing and focusing of sedimentary alkenones produced in warmer waters to the north climatological ssts in the central and northern cape basin are 16 20 c a 1 5 offset of fine fraction d 18 o values relative to planktonic foraminifera in tn057 21 supports this hypothesis temporal changes in sediment focusing were evaluated directly using uranium series radioisotopes while higher sediment focusing factors would be expected to result in higher alkenone derived ssts if sediment advection were the primary control on down core changes in alkenone derived ssts 230 th derived focusing factors indicate no such correlation exists we conclude that alkenone paleotemperature reconstructions from southern cape basin drifts reliably record regional sst variations in the cape basin index terms 4267 oceanography general paleoceanography 1055 geochemistry organic geochemistry 1040 geochemistry isotopic composition chemistry 3022 marine geology and geophysics marine sediments processes and transport keywords alkenones cape basin thorium

warm events in the tropical atlantic abstract sea surface temperature in the eastern equatorial atlantic ocean undergoes anomalous warming events of 1 2 c every few years the warm anomalies reach their maximum strength in northern hemisphere summer when equatorial upwelling normally brings cold thermocline water to the surface by compositing surface observations from a 28 year record we are able to identify consistent features in anomalies of sst and winds the composites show that the sst anomalies in northern summer are confined to the eastern equatorial region with reduced zonal winds to the west and reduced northward trade winds to the east accompanying these changes in winds are enhanced convection near the equator caused by a southward shift and intensification of the intertropical convergence zone later in the year sst south of the equator becomes elevated as a result by spring of the year following the equatorial anomaly convection in the western side of the basin is much higher than normal to understand the ocean dynami