variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

late pleistocene braided rivers of the atlantic coastal plain usa abstract infrared landsat imagery band 4 clearly reveals braided river patterns on late pleistocene terraces of unglaciated rivers in the atlantic coastal plain of the southeastern united states a region that presently exhibits meandering patterns that have existed throughout the holocene these pleistocene braided patterns provide a unique global example of river responses to late quaternary climate changes in an unglaciated humid subtropical region at 30 35 north latitude detailed morphological and chronological results are given for the oconee altamaha river valley in georgia and for the pee dee river valley in south carolina including 15 optically stimulated luminescence osl dates and four radiocarbon dates correlative examples are drawn from additional small to large rivers in south and north carolina osl and radiocarbon 14 c dates indicate distinct braiding at 17 30 ka within oxygen isotope stage 2 ois 2 and braiding probably existed at least during parts of ois 3 and possibly ois 4 back to ca 70 ka the chronology suggests that braiding is the more common pattern for the late quaternary in the southeastern united states braided terraces appear to have been graded to lower sea levels and are onlapped by holocene floodplain deposits up to 10 60 km from the coast the braiding probably reflects the response of discharge and sediment yield to generally cooler and drier paleoclimates which may have had a pronounced runoff season sedimentation of eolian dunes on the braid plains is coeval with braiding and supports the conclusion of dry soils and thin vegetation cover during the late pleistocene our chronological data contribute to a body of literature indicating that reliable osl age estimates can be obtained from quartz rich bed load sand from braided rivers based on good correlations with both radiocarbon dates from braided fluvial sediment and osl dates from stratigraphically correlative eolian sand

gisp2 oxygen isotope ratios the gisp2 oxygen isotope record with its high resolution detail yields crucial information on past climate change the glacial 18o oscillations of the gisp2 core with their very fast onsets are templates of a prototype oscillation of variable duration with an amplitude of 3 9 the halfway mark of the cold warm transition is reached in 2 years the top is reached in 50 years the 18o time gradient of the leading front is about 7 8 per 100 yr after reaching the top 18o slowly declines by 0 14 per 100 yr the duration of 18o decline varies from a couple of centuries for fast oscillations to about 4000 yr for slower ones the subsequent 18o downturn during the warm cold transition has a 18o time gradient of 3 2 per 100 yr and lasts about 80 yr

the carolina sandhills quaternary eolian sand sheets and dunes along the updip margin of the atlantic coastal plain province southeastern united states the carolina sandhills is a physiographic region of the atlantic coastal plain province in the southeastern united states in chesterfield county south carolina the surficial sand of this region is the pinehurst formation which is interpreted as eolian sand derived from the underlying cretaceous middendorf formation this sand has yielded three clusters of optically stimulated luminescence ages 1 75 to 37 thousand years ago ka coincident with growth of the laurentide ice sheet 2 28 to 18 ka coincident with the last glacial maximum lgm and 3 12 to 6 ka mostly coincident with the younger dryas through final collapse of the laurentide ice sheet relict dune morphologies are consistent with winds from the west or northwest coincident with modern and inferred lgm january wind directions sand sheets are more common than dunes because of effects of coarse grain size mean range 0 35 0 59 mm and vegetation the coarse grain size would have required lgm wind velocities of at least 4 6 m sec accounting for effects of colder air temperatures on eolian sand transport the eolian interpretation of the carolina sandhills is consistent with other evidence for eolian activity in the southeastern united states during the last glaciation

the younger dryas cold interval as viewed from central greenland abstract greenland ice core records provide an exceptionally clear picture of many aspects of abrupt climate changes and particularly of those associated with the younger dryas event as reviewed here well preserved annual layers can be counted confidently with only 1 errors for the age of the end of the younger dryas 11 500 years before present ice flow corrections allow reconstruction of snow accumulation rates over tens of thousands of years with little additional uncertainty glaciochemical and particulate data record atmospheric loading changes with little uncertainty introduced by changes in snow accumulation confident paleothermometry is provided by site specific calibrations using ice isotopic ratios borehole temperatures and gas isotopic ratios near simultaneous changes in ice core paleoclimatic indicators of local regional and more widespread climate conditions demonstrate that much of the earth experienced abrupt climate changes synchronous with greenland within thirty years or less post younger dryas changes have not duplicated the size extent and rapidity of these paleoclimatic changes

comment on holocene aridity and storm phases gulf and atlantic coasts usa by ervin g otvos 2005 quaternary research 63 368 373

fluvial activity in major river basins of the eastern united states during the holocene in the eastern united states existing paleo reconstructions in fluvial environments consist primarily of site specific investigations of climate and human impacts on riverine processes this paper

abrupt cooling of antarctic surface waters and sea ice expansion in the south atlantic sector of the southern ocean at 5000 cal yr b p antarctic surface waters were warm and ice free between 10 000 and 5000 cal yr b p as judged from ice rafted debris and microfossils in a piston core at 53 s in the south atlantic this evidence shows that about 5000 cal yr b p sea surface temperatures cooled sea ice advanced and the delivery of ice rafted detritus ird to the subantarctic south atlantic increased abruptly these changes mark the end of the hypsithermal and onset of neoglacial conditions they coincide with an early neoglacial advance of mountain glaciers in south america and new zealand between 5400 and 4900 cal yr b p rapid middle holocene climate changes inferred from the taylor dome ice core antarctica cooling and increased ird in the north atlantic and the end of the african humid period the near synchrony and abruptness of all these climate changes suggest links among the tropics and both poles that involved nonlinear response to gradual changes in northern hemisphere insolation sea ice expansion in the southern ocean may have provided positive feedback that hastened the end of the hypsithermal and african humid periods in the middle holocene

late quaternary climate in the ridge and valley of virginia u s a changes in vegetation and depositional environment a contribution to the north atlantic seaboard programme of igcp 253 termination of the pleistocene abstract browns pond virginia in the ridge and valley physiographic province contains a record of changing vegetational and depositional environments that dates to 17 130 bp six cores were retrieved in a transect of the pond pollen and macrofossils were identified from the longest central core and a series of ams radiocarbon dates obtained from identified macrofossils and sediment the pollen and macrofossil record combined with laterally consistent changes in lithostratigraphy reveal a changing climate from 17 300 to 14 100 bp a closed boreal forest of pinus picea abies grew at the site pinus dominates the pollen assemblage while picea and abies dominate the macrofossil assemblage subtle increases in more thermophilous and mesophytic taxa indicate gradual climate amelioration after the full glacial a marked increase in alnus at 14 100 bp signals an increase in moisture possibly related to the global evidence for rapid climate change at 14 000 bp at this central appalachian site abies and alnus are found in relatively greater amounts in the late glacial forest than previous studies indicated low organic contents and evidence of gleyed conditions seen in the core transect from 10 000 to 8000 bp point towards low water levels in the early holocene approximately coincident with the expansion of quercus

holocene paleohydrology of little salt spring florida based on ostracod assemblages and stable isotopes abstract ostracod assemblages and the 18o and 13c records of cytheridella ilosvayi provide a 12 000 yr paleohydrological reconstruction of little salt spring a sinkhole lake and underwater archaeological preserve in west central florida the ostracod record documents relative changes in water temperature and hydrologic characteristics of the lacustrine system that are the result of warming air temperatures changes in the relative contributions of input waters shallow vs deep groundwater rainfall patterns and relative sea level rise during the holocene the data indicate that lss was initially supplied by relatively low amounts of direct rainfall and surface runoff as the spring s location was closer to the recharge area and far from the freshwater saltwater interface at about 11 000 yr bp lss became groundwater supported initially by a shallow freshwater aquifer with low 18o composition until 5700 yr bp and after that time by 18o enriched and increasingly mineralized groundwater originating from a deeper carbonate aquifer as the regional water table rose bringing the saltwater interface closer to the location of lss which at this time was becoming a groundwater discharge area the data also shows that the most abrupt and pronounced hydrologic changes occurred during the late holocene with an interval of low 18o values 2 86 between 2700 and 2000 yr bp followed by a stepped increase in 18o composition with maximum values 1 46 between 1100 and 900 yr bp over these periods to the present time the ostracod assemblage is characterized by brackish species cyprideis spp and limnocythere floridensis it is inferred that the interval of decreased isotopic values indicates mixing with saline water during dry climatic conditions while the interval of more enriched isotopic values suggest saltwater intrusion during a period of presumably a sea level highstand although some discrepancies exist between other records from the northern caribbean region and the one from lss with regards to the exact timing for the late holocene drying and subsequent increase in rainfall conditions the differences between the records may be explained by greater continental influences on ocean atmosphere interactions on the florida peninsula a highly complex groundwater mixing balance in lss and by a better constrained age model in the other records

paleochannels indicating wet climate and lack of response to lower sea level southeast georgia large meandering paleochannels on the flood plain of the middle ogeechee river in southeast georgia represent wet paleoclimate during late pleistocene and early holocene time and show no indication of downcutting in response to eustatically lower sea level radiocarbon dates indicate that the paleomeanders were active at 31 28 ka and 8 5 4 5 ka bivariate regression models that correlate modern channel dimensions to the discharge of low magnitude floods 1 5 yr recurrence interval indicate that paleodischarge of floods during those times was at least double that of modern floods thus suggesting a wetter paleoclimate these data corroborate independent studies of pollen and paleoclimate simulations that indicate wet early to middle holocene 9 3 ka conditions that were characterized by intensified monsoonal circulation paleoclimate conditions at 31 28 ka are less well known our analysis of the middle ogeechee river flood plain indicates the absence of base level response downcutting to eustatic sea level lowering because the beds of the paleochannels are at approximately the same elevation as the bed of the modern channel this supports recent arguments that the geomorphic response of coastal plain streams to sea level lowering is most apparent in deltaic and shelf environments and may not be recognized very far upstream from the coast

late pleistocene and holocene environments of the southeastern united states from the stratigraphy and pollen content of a peat deposit on the georgia coastal plain abstract a 5 4 m peat core from the sandy run creek src valley in the upper coastal plain of georgia shows that before 30 ka the valley had an aggradational sandy floor with shallow swales and low ridges of 1 2 m amplitude suggesting a braided stream pattern and a low water table the climate from 30 25 ka was cool and dry and the vegetation open grassland with stands of pine and spruce that produced few fires at ca 16 ka a warmer wetter climate caused src to meander and incise the valley fill removing some previously deposited sediment at the site of our peat core so that sediments of 13 ka rest directly on sediments deposited at 25 ka after ca 13 ka higher groundwater levels initiated vertical accretion of floodplains allowing peat accumulation in shallow depressions across the valley pollen from the younger dryas period ca 13 11 ka indicates a cool moist environment of open oak woodland mesic trees riparian populations of alder and reduced levels of pine by the early to mid holocene tupelo and oak dominated over pine indicating wetter conditions while sand stringers in peat record periodic heavy rains an elevated water table and intervals of substantial runoff cooling after ca 4 5 ka brought drier and more variable conditions fires increased and southern pine replaced tupelo and oak the absence of sand stringers in peat younger than 4 5 ka indicates fewer intense rainfall events

computation of t phase coda t phases result from the conversion of seismic to acoustic energy at the seafloor in the vicinity of an earthquake epicenter the time frequency characteristics of t phase coda are observed to be strongly dependent upon the bathymetry of the ocean floor in the source region thus earthquakes from the same geographic area generate similar t phase coda in this study detailed bathymetry and sound speeds computed from the levitus atlas are used to simulate the t phase amplitudes which would be recorded at distances of several thousand kilometers from these natural sound sources it is hypothesized that seismic acoustic coupling occurs over a distributed region of the ocean floor with seismic energy being scattered into low order modes in shallow water comparison with observed coda indicates that t phase onset times and durations are modeled quite accurately with this simple method the feasibility of using this method to determine accurate source times and locations for small suboceanic earthquakes given

variability of particle size characteristics of sheetwash sediments and fluvial suspended sediment in a small semiarid catchment kenya abstract the variability of particle size characteristics for sheetwash sediments and fluvial suspended sediments are presented data for three representative storm events are described for a small 0 30 km2 erodible semiarid catchment suspended sediment output per event ranged from 340 to 810 t km 2 ninety eight percent of the suspended sediment was less than 63 m and was supplied from remobilization of stored colluvium discharge and particle size class relationships were complex for individual storm events but were best described by third order polynomial functions results of a one way analysis of variance showed that concentrations of total suspended sediment silt and sand varied significantly between storm events temporal variation of clay concentration in runoff were not significant suggesting that a single hillslope source area contributed to the channel subsystem the mean grain size and sorting of sheetwash sediments were significantly different from fluvial suspended sediment for individual storm events sheetwash sediments were coarser and more poorly sorted than fluvial suspended sediments enrichment ratios indicated selective erosion and transport of silt and clay and preferential deposition of sands

quaternary paleoecology of the lower mississippi valley copyright c 1996 elsevier science b v all rights reserved in 1938 clair a brown published his classic paleobotanical discoveries from the tunica hills of southeastern louisiana indicating ice age plant migrations of more than 1100km brown collected fossils of both boreal trees such as white spruce picea glaucar and southern coastal plain plants from deposits mapped as the port hickey prairier river terrace by harold n fisk subsequent revisions of terrace mapping radiocarbon dating and paleoecological analysis reconciled browns conceptual and stratigraphic mixingr of these two ecologically incompatible fossil plant groups an older terrace 2 of sangamonian to altonian ager contains the warm temperate assemblage a younger terrace 1 of farmdalian woodfordian and holocene ager includes full glacial and late glacial remains of both boreal and cool temperate plants and a warm temperate suite of plants dates from the holocene interglacial new plant fossil localities with radiocarbon chronologies are now available from within the lower mississippi valley of missouri and arkansas as well as from the adjacent ozark plateaus the interior low plateaus of kentucky and tennessee and the bordering blufflands of tennessee mississippi and louisiana these studies demonstrate that glacial and interglacial patterns of vegetation have been influenced by regional changes in climate glacial runoff and regime of the mississippi river

chronology of inland eolian dunes on the coastal plain of georgia usa most inland eolian dunes associated with rivers on the georgia coastal plain probably date to glacial periods direct dating of the dune sand by optically stimulated luminescence dating combined with limiting ages from radiocarbon dating shows that dunes formed during isotope stage 2 stage 3 the transition between stages 4 and 5 and isotope stage 6 or earlier most of the dates indicate dune activity between 30 000 and 15 000 years ago holocene activity included limited and local reworking of the crests of some thick dunes along streams that flow from the piedmont

mid holocene climates of the americas a dynamical response to changed seasonality simulations of the climatic response to mid holocene 6 ka bp orbital forcing with two coupled ocean atmosphere models foam and csm show enhancement of monsoonal precipitation in parts of the american southwest central america and northernmost south america during northern hemisphere summer the enhanced onshore flow that brings precipitation into central america is caused by a northward displacement of the inter tropical convergence zone driven by cooling of the equatorial and warming of the northern subtropical and mid latitude ocean ocean feedbacks also enhance precipitation over the american southwest although the increase in monsoon precipitation there is largely driven by increases in land surface temperature the northward shift in the equatorial precipitation band that causes enhanced precipitation in central america and the american southwest has a negative feedback effect on monsoonal precipitation in northern south america the simulations demonstrate that mid holocene aridity in the mid continent of north america is dynamically linked to the orbitally induced enhancement of the summer monsoon in the american southwest with a spatial structure wet in the southwest and dry in the mid continent similar to that found in strong monsoon years today changes in winter precipitation along the west coast of north america in central america and along the gulf coast caused by southward displacement of the westerly storm tracks indicate that changes in the northern hemisphere winter monsoon also play a role in regional climate changes during the mid holocene although the simulations with foam and csm differ in detail the general mechanisms and patterns are common to both the model results thus provide a coherent dynamical explanation for regional patterns of increased or decreased aridity shown by vegetation lake status and aeolian data from the americas

late quaternary climates and river channels of the atlantic coastal plain southeastern usa abstract late quaternary river patterns and sedimentation styles reflect past climate changes in atlantic drainages of eastern georgia and the carolinas past climate episodes for the region are summarized from pollen and eolian sedimentary records that exhibit correlation to major changes in river channel patterns records of past river responses are derived from luminescence and radiocarbon dated landforms and strata slow tectonic uplift does not explain temporal changes in channel patterns drainage networks have not received meltwater from continental or mountain glaciers eustatic influence would have been most pronounced on the now submerged continental shelf prior to 6 ka and currently manifests only within 60 80 km of the present highstand shoreline human impact overshadows climatic changes during historic time but was negligible during prehistoric time the late quaternary fluvial system primarily responded to climatic fluctuations that drove changes in vegetation precipitation and runoff patterns prehistoric meandering paleochannels of the holocene stand as important references to guide natural channel rehabilitation efforts during the coldest climate phases of the late wisconsin stage ca 30 16 ka when forest vegetation was sparse and interspersed with grasses and herbs many rivers and streams were braided with eolian dunes on the floodplains the terminal wisconsin stage ca 16 11 ka exhibited rapid warming and forest expansion characterized by pronounced change from braided to meandering patterns with intermediate forms of sandy scroll bar patterns the younger dryas cold excursion is not readily apparent in the regional fluvial record unusually large meandering channels of the terminal wisconsin stage continue into the first half of the holocene and indicate significantly larger bankfull flood discharges during those times than during the last half of the holocene bankfull channels during the last half of the holocene retained meandering patterns but decreased to modern like dimensions suggesting more modern like flood regimes no clear fluvial response occurs to the presumed middle holocene climatic optimum hypsithermal the medieval warm period and little ice age or to recent instrumentally observed fluctuations in climate but little research has been done in these realms

pre holocene and holocene pollen records of vegetation history from the florida peninsula and their climatic implications abstract pre holocene sediments may be found in sinkhole lakers or filled sinkholes in the florida peninsula lake tulane in south central florida yielded a core of 18 5 m under 22 7 m of water the core extends from the present to ca 50 000 yr b p it is age controlled by twenty radiocarbon dates the pre holocene shows alternating peaks of pinus pine dominated and quercus ambrosia oak ragweed dominated vegetation the pine peaks correlate in detail with heinrich events h1 to h5 this demonstrates linkage between continental and oceanic climate events the pine peaks are thought to link with periods of relatively high precipitation and warm gulf water during ice advances oak ragweed peaks are thought to indicate aridity when the gulf and north atlantic surface waters were cooled by melwater from retreating ice sheets lake grizelle is afilled sinkhole with several climatic episodes recorded in pollen counts which are separated from the holocene by a hiatus marked by thick sand it is representative of a category of fossil lakes in florida which promise to contain long and perhaps interglacial pollen records sheelar lake records the end of the wisconsin and the assembling of a species rich forest of mesic trees such as fagus beech close to or south of their present southern geographic limits this forest is believed to be ancestral to the mesic deciduous forest which invaded eastern north america in the next 3000 yr

the anatomy of a climatic oscillation vegetation change in eastern north america during the younger dryas chronozone century scale climate changes reshaped circulation patterns over the north atlantic and adjacent regions during the last glacialto interglacial transition here we show that vegetation across eastern north america shifted dramatically at the beginning and end of the younger dryas chronozone ydc 12 900 11 600 cal yr b p when changes in ocean circulation rapidly cooled and then warmed the north atlantic sea surface on both the site specific scale and the continental scale vegetation changed only gradually during the millennia before 15 000 13 000 cal yr b p and after 11 000 9000 cal yr b p the ydc but climate changes ca 12 900 and 11 600 cal yr b p altered the vegetation on both spatial scales within centuries plant associations changed and some taxa rapidly migrated hundreds of kilometers 300 km within b100 yr in limited regions near the north atlantic coast abrupt cooling ca 12 900 cal yr b p resulted in a return to earlier vegetation types elsewhere however the vegetation patterns during the ydc were distinct from those of both earlier and later intervals they indicate abrupt non reversing seasonal temperature changes that were probably related to atmospheric circulation changes during the ydc rather than to the direct influence of north atlantic sea surface temperatures atmospheric circulation patterns during the ydc were unique within the last 21 000 yr because of a unique combination of climate controls insolation ice sheet extent and atmospheric composition were significantly different from their full glacial states even when the north atlantic returned to near full glacial conditions the ydc vegetation patterns demonstrate 1 rapid ecological responsiveness to abrupt climate change and 2 spatially varied patterns of ydc climate change r 2002 elsevier science ltd all rights reserved

an atlas of the distribution of calcium carbonate in sediments of the deep sea historical observations of the concentration of calcium carbonate in global deep sea sediments are compiled and compared with a new gridded field of seawater co3 concentration to reveal regional variations in the calcite lysocline the most obvious mode of variability of the calcite lysocline is the thickness of the lysocline defined here as the difference in overlying water carbonate saturation co3 between high and low calcite sediments with a thicker lysocline in the atlantic than in the pacific i attribute this variation to differences in the delivery rate of terriginous material a recent model for the lower glacial atmospheric pco2 proposed to change the relationship between the depth of the lysocline and the co3 of the water column by changing the rain rate ratio of organic carbon to calcite production the rain ratio model archer and maier reimer 1994 i search the data set for analogs to the proposed glacial world by looking for a link between the regional climate at the sea surface and the depth of the lysocline below the co3 at the carbonate compensation depth ccd in the tropics appears to be 10 20 mol kg 1 co3 more undersaturated than in high latitudes but this is smaller than the 40 mol kg 1 shift required by the model in addition the general resemblance of the glacial lysocline to the present day requires that the proposed shift in co3 at the ccd be globally uniform rather than locally variable as climate forcing would probably generate i conclude that the rain ratio model would probably require some globally uniform perturbation during glacial time such as a change in ocean si content if it is to explain the entire pco2 decrease observed in the glacial atmosphere finally i grid the sedimentary data to estimate that the inventory caco3 which is available to neutralize fossil fuel co2 is approximately 1600 gt carbon a quantity which may be exceeded by fossil fuel release in the next several centuries

terminal pleistocene braided to meandering transition in rivers of the southeastern usa abstract thirteen paleomeanders on the oldest parts of meander belts on floodplains in the coastal plain of georgia and the carolinas southeastern usa were selected for radiocarbon dating to determine the onset of meandering following braiding during the late pleistocene during oxygen isotope stage 2 the radiocarbon ages were compared to previously reported late pleistocene ages for braid bars and eolian dunes results indicate that meandering commenced at circa 15 000 to 16 000 cal years bp and continued throughout the terminal pleistocene and holocene correlation with other paleoenvironmental records indicates that this shift to meandering was associated with global warming and moister conditions in the southeastern united states that led to a denser vegetation cover and a reduction in sediment yield the shift to meandering was also associated with some incision and terracing of the late pleistocene braided fluvial surfaces paleodischarge of the bankfull condition of early holocene meandering channels was apparently greater than under modern conditions suggesting wetter conditions at that time than at present this braided to meandering transition in the southeastern united states provides an example of river response to global climate change in a relatively low latitude region of the world that was not influenced by glacial or periglacial landscape conditions

reconstruction of prehistoric landfall frequencies of catastrophic hurricanes in northwestern florida from lake sediment records abstract sediment cores from western lake provide a 7000 yr record of coastal environmental changes and catastrophic hurricane landfalls along the gulf coast of the florida panhandle using hurricane opal as a modern analog we infer that overwash sand layers occurring near the center of the lake were caused by catastrophic hurricanes of category 4 or 5 intensity few catastrophic hurricanes struck the western lake area during two quiescent periods 3400 5000 and 0 1000 14 c yr b p the landfall probabilities increased dramatically to ca 0 5 per yr during an hyperactive period from 1000 3400 14 c yr b p especially in the first millennium a d the millennial scale variability in catastrophic hurricane landfalls along the gulf coast is probably controlled by shifts in the position of the jet stream and the bermuda high

late quaternary inland dunes of southern louisiana and arid climate phases in the gulf coast region abstract thirty five sand hills that form six scattered groups rise abruptly from the flat late pleistocene coastal plain in southeastern louisiana new studies confirm their eolian origin for the first time several late wisconsin to early holocene episodes of arid climate conditions have been recognized and dated in this currently humid warm temperate subtropical region periods of dune formation and reactivation 28 800 to 7900 yr b p were determined by the thermoluminescence method the onset of the current climate in this gulf coastal region postdates early holocene time the textural and structural homogeneity of the ridge lithosomes good sorting of their sand fraction and the dominantly orange hues of the dune sediments contrast with the underlying yellowish brown to light brown sandy silts and the well stratified occasionally gravelly sands of the underlying alluvial prairie formation sharply defined unconformable ridge bases symmetrical oval occasionally parabolic mound shapes and steep slopes confirm the dune origins the dominant orientations of ridges and ridge chains clearly reflect paleowind directions age comparison with dunes of the lower mississippi valley the northeastern eastern gulf of mexico coast and south atlantic coastal areas confirms the existence of at least seasonally dry climate conditions from early wisconsin to middle holocene times the onset of the modern humid subtropical climate phase in this region thus dates back only to the middle holocene

holocene aridity and storm phases gulf and atlantic coasts usa abstract a bottomland flora that prevailed between 9900 and 6000 cal yr b p in a north carolina stream valley may not reflect a regionally much wetter atlantic climate coeval with record drought in the great plains region and assumed dry gulf coastal conditions such conditions were inferred for 6000 1000 yr ago when the bermuda high may have consistently occupied summer positions far to the ne arid episodes coeval with the little river local wet interval are known from eolian sediments and pollen spectra in the atlantic and the gulf coastal plain for multiple reasons the regional extent intensity and duration of coastal aridity and alternating wet phases and the bermuda high positions are not yet adequately constrained the climate and edaphic causes for the steadily growing predominance of southern pines over hardwoods achieved between 8900 and 4200 cal yr b p at different sites at different times are similarly still unresolved new data from shelby lake al reconfirms that no credible field or other proxy evidence exists for a previously postulated catastrophic gulf hurricane phase in the late holocene

wet early to middle holocene conditions on the upper coastal plain of north carolina usa abstract a peat core from a cutoff paleochannel of little river on the upper coastal plain of north carolina provides a continuous pollen record of environmental change for the past 10 500 years and includes a sedimentary record of overbank floods palynological and sedimentary data indicate that the early to middle holocene was wetter than previously suggested from lake sites in the southeastern united states the period from 9000 to 6100 cal yr b p is characterized by high pollen percentages of nyssa and quercus but low percentages of pinus fifteen large overbank flood events are present within this period 5 floods 1000 yr in contrast only 6 large overbank flood events occurred since 6100 cal yr b p 1 flood 1000 yr the increases in moisture and flood events probably were controlled by changes in atmospheric circulation related to shifts in the position of the bermuda high sea surface temperatures and el nino activity that together may have affected the frequency of large floods generated from tropical storms in the region

prospects for interregional correlations using wisconsin and holocene aridity episodes northern gulf of mexico coastal plain abstract luminescence dating of extensive dune fields and associated eolian sandsheets provided a chronology of recently recognized pleistocene and early holocene dry climate episodes in the currently humid warm temperate northern northeastern gulf of mexico region scattered parabolic dunes and clusters of intersecting parabolic dunes along with elongated shore transverse and shore parallel dunes developed these landforms occur in a 390 km long and 2 to 3 km wide semicontinuous belt in southeast alabama and northwestern florida dune elevations reach 22 m sangamon coastal barrier sectors were the primary source of the eolian sand deflation was coeval with early wisconsin to mid holocene marine low sea levels and associated distant shorelines early holocene dune dates were synchronous with indications of a hypsithermal dry interval in southeast louisiana the yucatan and the south atlantic seaboard overlapping with dry episodes in yucatan and the high plains texas dunes and louisiana and texas prairie mounds especially in the southwest texas coast still dominated by dry climate suggests intervals of early to late holocene drought the dates provide the basis for identifying and correlating wisconsin early and late holocene climate phases between currently semiarid and humid coastal and interior areas they contribute to future studies including interregional paleoclimate modeling although pleistocene coastal eolian deposition coincided with glaciation in the northern interior and with cooler temperatures of a reduced gulf of mexico holocene aridity phases may have been related to major variations in the position of high pressure cells storm tracks and branches of the jet stream and even to prolonged la nina conditions

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

evidence for warm wet heinrich events in florida analyses of pollen and plant macrofossils from a new core spanning the past 60 000 years from lake tulane florida show a strong antiphase relationship in temperature between florida and the north atlantic region during the pleistocene oak scrub and prairie phases were coeval with long intense dansgaard oeschger interstadials warm periods that initiated bond cycles pine phases were coeval with the north atlantic long stadials cold periods that ended bond cycles and were terminated by heinrich events lake levels were higher during pine phases and climate was wetter however climate in florida was also warmer during these phases which were cold periods in the north atlantic perhaps diminution of thermohaline circulation before and during heinrich events reduced northward heat transport and retained warmth in the subtropical atlantic and gulf of mexico

late pleistocene paleowind directions atlantic coastal plain u s a abstract parabolic dunes transverse dunes and fields of irregular dunes are common along the left banks the north or east sides of streams of the atlantic coastal plain from georgia to delaware and probably beyond similar dunes occur in the appalachian piedmont but are less common the features have been eroded to some extent and are normally recognizable on topographic maps only as areas of irregular topography with wet and dry depressions the larger parabolic dunes can be recognized on aerial photographs and satellite images because the associated soils are poor and the vegetative cover relatively sparse the dunes are of eolian origin and late pleistocene in age it is thought that most of the dunes are late wisconsin in age and contemporary with the carolina bays a small sample of paleowind directions based on average directions of parabolic dune axes indicates that late wisconsin winds in georgia were westerly and grain sizes suggest that the winds were stronger than present day coastal winds of the area paleowind directions shift progressively toward the south across the carolinas and are southwesterly in north carolina they change abruptly to the northwest in the delmarva peninsula following the theory that carolina bays are former lakes that are elongated perpendicular to the effective wind direction the fact that paleowind directions derived from carolina bay orientations are virtually identical to those from parabolic dune orientations strongly supports the wind orientation theory of carolina bay origin and confirms the validity of the small sample of directions obtained from parabolic dunes by analogy with dunes of the eastern shore of lake michigan and the atlantic and pacific coasts the atlantic coast plain dunes do not necessarily indicate arid conditions the sediment load of some streams may have been sandier than at present and streams with sandy braided channels may have been common

pollen and macrofossils from wisconsinan interstadial sediments in northeastern georgia pollen and plant macrofossil analyses and dating both tams and conventional 14 c of wetland sediments from the nodoroc site in the piedmont region of northeastern georgia identified two depositional episodes of interstadial ca 26 000 22 000 yr b p and mid to late holocene 3600 yr b p age interstadial pollen assemblages were dominated by pinus and quercus with carya picea and abies also present in significant amounts the interstadial assemblages had lower pinus and higher quercus pollen percentages than apparently contemporaneous assemblages from sites in the southern appalachians and coastal plain interstadial macrofossils included two needle morphotypes of pinus subgenus pinus possibly indicating local occurrence of two pinus species one of the needle morphotypes is consistent with pinus banksiana but other species cannot be ruled out comparison of conventional and tams 14c dates illustrates problems in obtaining accurate age models from wetlands and ponds characterized by shallow or fluctuating water levels low sedimentation rates and vegetation growing on the depositional surface

a 50 000 year record of climate oscillations from florida and its temporal correlation with the heinrich events oscillations of pinus pine pollen in a 50 000 year sequence from lake tulane florida indicate that there were major vegetation shifts during the last glacial cycle episodes of abundant pinus populations indicate a climate that was more wet than intervening phases dominated by quercus oak and ambrosia type ragweed and marsh elder the pinus episodes seem to be temporally correlated with the north atlantic heinrich events which were massive periodic advances of ice streams from the eastern margin of the laurentide ice sheet possible links between the tulane pinus and heinrich events include hemispheric cooling the influences of mississippi meltwater on sea surface temperatures in the gulf of mexico and the effects of north atlantic thermohaline circulation on currents in the gulf