hurricanes and climate in the caribbean during the past 3700 years bp a multiproxy analysis of lacustrine sediments cored in grand case pond at saint martin north of the lesser antilles archipelago reveals three distinct climatic periods for the last 3700 years from 3700 to 2500 yr cal bp and from 1150 yr cal bp to the present carbonate mud deposition occurred in connection with pond lowstands these periods were also punctuated by severe drought events marked by gypsum laminae and hurricane landfalls leading to marine sand inputs into the pond the intermediate time interval from 2500 to 1150 yr cal bp is typified by black organic mud deposition suggesting that hypoxic to anoxic conditions prevailed at the pond bottom these were probably linked with a perennial pond highstand and reflect more uniform and wetter climatic conditions than today the carbon isotopic composition of the ostracod perissocytheridea bisulcata shows that the lowest 13c values are recorded during the hypoxic periods as a consequence of bacterial recycling of isotopically depleted org

kaneohe acoustic thermometer further validated with rays over 3700 km and the demise of the idea of axially trapped energy the kaneohe acoustic source transmitted 133 hz 60 ms resolution signals over 3709 km from oahu at 183 m depth to a naval receiver at 1433 m depth near northern california ray theory successfully models the acoustic multipaths whose travel times are unambiguously tracked between 1983 89 despite the fact that the sound bounces one or more times from the oahu slope before becoming trapped in the sound channel the eigenrays are inclined at about 15 at the axis of the sound channel the upper turning depths of the eigenrays are insensitive to realistic perturbations along the section this supports the finding that the changes in delay of 0 2 s between 1983 89 are due to temperature and not due to changes in the multipaths compared with transmission through a smoothed representation of the ocean s acoustic waveguide the mesoscale and submesoscale features vertically scatter axially trapped energy about 200 and 800 m respectively the submesoscale structure may be associated with internal waves scatt

north pacific thermocline variations on enso timescales abstract the north pacific thermocline 250 to 400 m is studied using xbt observations acquired during the 1970s and 1980s interannual variations 3 5 yr timescales in thermocline temperature with o 0 1 c amplitude at 400 m are found to exhibit westward propagation throughout the extratropical north pacific up to 45 n southward of 30 n the features propagate intact across the basin from the eastern boundary to the western boundary northward of 30 n the features can be observed to propagate only as far as the date line the observed midlatitude thermocline anomalies are often related to tropical enso events in that they occur most strongly after the development of tropical el nino or la nina conditions and propagate westward from near the eastern boundary in the midlatitudes but it is found that the observed midlatitude thermocline anomalies have larger phase speeds than theoretically predicted free baroclinic rossby waves also the observed anomalies have larger wavelength and faster propagati

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

age and significance of fossil white spruce picea glauca tunica hills louisiana mississippi abstract radiocarbon dates indicate a farmdalian through woodfordian age for fossil white spruce picea glauca in the tunica hills a greater time span than previously documented these dates furthermore require revision of the ages of fluvial terrace deposits in the region spruce bearing terrace 1 sediments previously regarded as late woodfordian to holocene age are of farmdalian to late holocene age terrace 2 sediments previously assigned a sangamonian or farmdalian age are of probable altonian age plant fossils in terrace 1 sediments represent two climatically and temporally distinct assemblages a cool temperate farmdalian woodfordian assemblage dominated by white spruce but including deciduous hardwoods suggestive of an oak hickory association and a warm temperate holocene assemblage composed of southern hardwoods and nonarboreal species representative of the modern flora of the tunica hills locally fossils of white spruce have been reworked into younger terrace 1 sediments containing the warm temperate plant assemblage the transition from the cool temperate flora to the modern warm temperate flora in the tunica hills probably occurred around 12 000 yr b p

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

lake sediment record of late holocene hurricane activities from coastal alabama coastal lake sediments contain a stratigraphically and chronologically distinct record of major hurricane strikes during late holocene time frederic a category 3 hurricane that struck the alabama coast on the gulf of mexico in 1979 left a distinct sand layer in the nearshore sediments of lake shelby as a result of storm tide overwash of beaches and dunes sediment cores taken from the center of lake shelby contain multiple sand layers suggesting that major hurricanes of category 4 or 5 intensity directly struck the alabama coast at ca 3 2 3 0 2 6 2 2 1 4 and 0 8 ka 14 c yr with an average recurrence interval of 600 yr the alabama coast is likely to be struck by a category 4 or 5 hurricane within the next century

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

a comparison of multiple proxy data sets for paleoenvironmental conditions as derived from freshwater bivalve unionid shell freshwater mussel shells from middle and late holocene strata at an archaeological site in mississippi u s a are examined for morphological and chemical differences that could be related to changing paleoenvironmental conditions although significant differences are noted the different data sets provide contradictory or unclear results suggesting that reliance upon single data sets is an unwarranted practice

winter to winter recurrence of sea surface temperature salinity and mixed layer depth anomalies abstract the mean seasonal cycle of mixed layer depth mld in the extratropical oceans has the potential to influence temperature salinity and mixed layer depth anomalies from one winter to the next temperature and salinity anomalies that form at the surface and spread throughout the deep winter mixed layer are sequestered beneath the mixed layer when it shoals in spring and are then re entrained into the surface layer in the subsequent fall and winter here we document this re emergence mechanism in the north pacific ocean using observed ssts subsurface temperature fields from a data assimilation system and coupled atmosphere ocean model simulations observations indicate that the dominant large scale sst anomaly pattern that forms in the north pacific during winter recurs in the following winter the model simulation with mixed layer ocean physics reproduced the winter to winter recurrence while model simulations with observed ssts specified in the tropical pacific and a 50 m slab in the north pacific did not this difference between the model results indicates that the winter to winter sst correlations are the result of the re emergence mechanism and not of similar atmospheric forcing of the ocean in consecutive winters the model experiments also indicate that sst anomalies in the tropical pacific associated with el nino are not essential for re emergence to occur the recurrence of observed sst and simulated sst and sss anomalies are found in several regions in the central north pacific and are quite strong in the northern 50 n part of the basin the winter to winter autocorrelation of sss anomalies exceed those of sst since only the latter are strongly damped by surface fluxes the re emergence mechanism also has a modest influence on mld through changes in the vertical stratification in the seasonal thermocline

sea ice anomalies observed in the greenland and labrador seas during 1901 1984 and their relation to an interdecadal arctic climate cycle two independent ice data sets from the greenland and labrador seas have been analyzed for the purpose of characterizing interannual and decadal time scale sea ice extent anomalies during this century sea ice concentration data for the 1953 1984 period revealed the presence of a large positive anomaly in the greenland sea during the 1960s which coincided with the great salinity anomaly an upper ocean low salinity water mass that was observed to travel cyclonically around the northern north atlantic during 1968 1982 this ice anomaly as well as several smaller ones propagated into the labrador sea and then across to the labrador and east newfoundland coast over a period of 3 to 5 years a complex empirical orthogonal function analysis of the same data also confirmed this propagation phenomenon an inverse relation between sea ice and salinity anomalies in the greenland labrador sea region was also generally found an analysis of spring and summer ice limit data obtained from danish meteorological institute charts for the period 1901 1956 indicated the presence of heavy ice conditions i e positive ice anomalies in the greenland sea during 1902 1920 and in the late 1940s and generally negative ice anomalies during the 1920s and 1930s only limited evidence of the propagation of greenland sea ice anomalies into the labrador sea was observed however probably because the data were from the ice melt seasons on the other hand several large ice anomalies in the greenland sea occurred 2 3 years after large runoffs in the early 1930s and the late 1940s from northern canada into the western arctic ocean similarly a large runoff into the arctic during 1964 1966 preceded the large greenland sea ice anomaly of the 1960s these facts together with recent evidence of climatic jumps in the northern hemisphere tropospheric circulation suggest the existence of an interdecadal self sustained climate cycle in the arctic in the greenland sea this cycle is characterized by a state of large sea ice extent overlying an upper layer of cool relatively fresh water that does not convectively overturn which alternates every 10 15 years with a state of small sea ice extent and relatively warm saline surface water that frequently overturns

tidal wetland record of holocene sea level movements and climate history abstract paleontological geochemical and lithological indicators of former marine and nonmarine influence are correlated between 13 cores from a tidal wetland wolfe glade on the southeast coast of delaware bay twenty new radiocarbon dates are used to establish the chronostratigraphy of marsh facies sediment iron content weight loss on ignition and remains of plants diatoms and foraminifera known to tolerate specific tidal inundation cycles are used to describe cored facies originating from supratidal intertidal and subtidal salt marsh subenvironments pollen assemblages are used to infer local holocene climate fluctuations and to reconstruct paleoenvironments during marsh evolution the record of paleoclimatology suggests the atlantic chron was warm with variable humidity in the region whereas the subboreal was dominated by cool and humid conditions the subatlantic was warmer and initially dryer with a cool humid phase prior to about 1 ka returning to warmer humid conditions in the last several centuries local relative sea level movements are characterized by five rapid short term episodes when the rate of sea level rise accelerated relative to the rate of marsh aggradation these episodes are recorded by transgressive facies contacts at 5 3 0 2 ka 4 4 0 2 ka 3 25 0 2 ka and 1 8 0 2 ka sidereal years an earlier transgressive facies contact dated 6 9 0 2 ka is probably not the product of a true sea level movement sea level movements are recorded throughout the marsh as palustrine or high marsh peats or peaty overlain by lower intertidal or subtidal marine deposits several features suggest that these episodes are local relative transgressions produced by short term accelerations in the rate of sea level rise relative to marsh aggradation the contemporaneity and apparent suddenness of marine inundations the sequence of facies indicating marine drowning the presence of similar events in marshes elsewhere in delaware bay and the marsh wide extent of indicative facies transitions we propose that the rapid and frequent sea level movements observed in wolfe glade are the result of surges and relaxations in the gulf stream and associated spin up and partial collapse of the north atlantic gyre in response to winds generated by changes in the north atlantic atmospheric thermal gradient associated with holocene climate fluctuations

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

eddies in the eastern gulf of alaska from topex poseidon altimetry eddy activity in the gulf of alaska goa is evidenced to fluctuate with the el nino southern oscillation enso cycle altimetry from topex poseidon is used to study eddy formation along a single descending track in the far eastern goa from late 1992 through late 1998 the track is sampled between 45 n and 60 n where it is roughly parallel to the eastern boundary the geoid and mean currents are removed from the data through extraction of the temporal mean at each point the resulting anomalies are passed through a matched filter designed to detect gaussian signals embedded in noise the filter is optimized to detect eddies with amplitude 10 cm and diameters roughly 50 350 km both anticyclonic and cyclonic structures are examined the distribution of eddies in space is similar for both anticyclonic and cyclonic eddies with most occurring between 50 n and the northern limits of the goa few eddies of either sign were found south of 50 n anticyclonic eddies are stronger and have a broader distribution of amplitudes typically 5 30 cm compared to cyclonic features which are more symmetrically distributed over 5 15 cm the detection of weak 15 cm eddies is sensitive to the filter threshold but detection of larger amplitude eddies is robust the average amplitude of anticyclonic eddies increases following the 1993 1994 1995 and 1998 el nino events eddy amplitude appears to vary with enso strength the strongest eddies detected form in early 1998 these results support previous numerical studies of eddy development in the eastern goa

the reemergence of sst anomalies in the north pacific ocean abstract sea surface temperature sst data and two different upper ocean temperature analyses are used to study the winter to winter recurrence of sst anomalies in the north pacific ocean the ssts recur when temperature anomalies that form in the deep ocean mixed layer in late winter early spring are isolated from the atmosphere in the summer seasonal thermocline and then reemerge at the surface when the mixed layer deepens during the following fall winter this reemergence mechanism is evaluated over the basin by correlating the time series of the leading pattern of ocean temperature anomalies in the summer seasonal thermocline 60 85 m in august september with sst anomalies over the course of the year the results indicate that the dominant large scale sst anomaly pattern that forms in the north pacific during late winter with anomalies of one sign in the central pacific and the opposite sign along the coast of north america is sequestered in the seasonal thermocline in summer and returns to the

interdecadal variability in a numerical model of the northeast pacific ocean 1970 89 abstract variations in the thermocline depth of the northeast pacific ocean during 1970 1989 are investigated using a reduced gravity numerical model forced by the local surface wind stress and at the southern land ocean boundary by a coastal kelvin wave signal three experiments are presented with forcings by wind only kelvin wave only and a combination of both the wind forcing generates an anticyclonic gyre circulation with mostly annual variations the kelvin waves along the coast excite rossby waves that propagate into the basin interior producing changes in upper layer thickness related to changes in thermocline depth that last for years after the kelvin signal has passed two sequential upwelling kelvin waves in 1973 and 1975 produce upwelling rossby waves that reduce the mean upper layer thickness by approximately 10 20 m during 1976 this shift is reinforced by later upwelling events lasting until the early 1980s the authors present a new hypothesis that the previously known climate shift o

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

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

late quaternary records of vegetation and fire in southeastern north carolina from jones lake and singletary lake abstract we conducted fossil pollen charcoal and geochemical analyses of sediment cores from jones lake and singletary lake spanning the last 50 000 cal yr b p to examine the linkages between climate vegetation and fire activity on the atlantic coastal plain and particularly emphasize changes since the last glacial maximum application of the modern analog technique mat to fossil pollen data allowed for quantitative estimates of holocene climate but pleistocene assemblages had no modern analogues preempting their use for quantitative reconstructions the mat data indicate markedly lower mean annual precipitation and temperatures during the late pleistocene relative to the holocene increased charcoal accumulation during interstadials indicates increased fire activity during these warm intervals geochemical data 13c 15n c n and pollen concentrations indicate a sparsely vegetated pleistocene landscape that produced few fires followed by an increase in biomass and fire activity around the lakes during the holocene transition a quercus spp maximum in the early holocene is associated with low charcoal abundances while increased dominance of pinus spp during the middle holocene is associated with dramatic increases in charcoal it is unclear if the quercus pinus transition was the result of changing fire regimes or if the fire regime changed in response to vegetation the regional asynchronicity of the quercus pinus transition may indicate another forcing mechanism besides climate change such as prehistoric human activity is responsible for the ecological change macroscopic charcoal and c n ratios reach unprecedented values during the late holocene possibly as a result of deforestation by both prehistoric native americans and later immigrant populations

palaeoclimatic implications of a storm erosion record from late holocene lake sediments north island new zealand abstract a ca 2250 year storm history has been identified from a high resolution lake sediment record from the east coast of the north island new zealand this event based chronology identifies 340 storms in the pre european record the record is largely one of natural variability without human impacts layers of minerogenic sediment representing the products of individual storm events are clearly visible in lake cores these storm sediment pulses derived mainly from landslides record the frequency and magnitude of storms clusters of pulses identify six periods of high sedimentation and associated erosion before european settlement a d 1878 at least five of these are interpreted as periods of higher rainfall and probably warmer temperatures since historic records show that most large storms are derived from the subtropics tropics most of the storm periods correspond to warm climate intervals previously identified from new zealand and from southern hemisphere palaeoclimatic evidence the mapara 2 period ca 2090 1855 cal yr b p was the stormiest other periods were of shorter duration the mapara 2 period occurred at times of sustained warmth in the tasmanian and chilean tree ring records which might suggest hemispheric warming at this time one storm period burrell which occurred during the historical enso record was at a time of moderately high enso activity three earlier periods also appear to show responses to enso two storm periods correspond to previously proposed new zealand wide periods of increased erosion and sedimentation estimates of palaeo storm rainfalls from relationships between storm rainfall and sediment thickness of historical events suggest that storm pulses ca 12 mm thick represent palaeo storms of ca 450 mm rainfall

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

interannual variability in the gulf of alaska during the 1991 94 el nino abstract mass and heat budgets in the gulf of alaska during the 1991 94 el nino are examined using hydrographic data from several cruises undertaken as part of the international north pacific ocean climate program and the repeated canadian hydrographic sections out to ocean weather station papa the geostrophic ocean circulation resulted in convergence of heat into the region in spring 1992 and spring 1993 the advective heat convergence in spring 1992 corresponded to an average surface heat flux from the ocean to the atmosphere of about 74 w m 2 in comparison with only 30 w m 2 during spring 1993 the larger ocean heat loss to the atmosphere in 1992 followed a winter of large tropical sst anomalies and anomalously low pressure in the aleutian low

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

patterns of holocene climatic change in the midwestern united states the holocene pollen sequence in the minnesota area is asymmetric around the so called prairie period the early holocene is dominated by elm with pine in the north and the late holocene by oak the elm zone is interpreted as a manifestation of summer monsoonal rains enhanced by the milankovitch insolation maximum and the pine in the north is interpreted as a result of summer cooling near the retreating ice sheet as the summer insolation waned during the holocene its associated monsoonal rains from the caribbean moisture source lasted longer in the south northeastern iowa and southern wisconsin where the inferred mesic elm forest changed to prairie as late as 5000 yr b p compared to 8000 yr b p in minnesota and 9000 yr b p in the dakotas

sources of interannual baroclinic waves in the eastern subtropical north pacific abstract subsurface temperature and surface salinity observations along the great circle transect between san francisco and honolulu are used to investigate the source of annual baroclinic long waves in the eastern subtropical north pacific ocean long term mean 15 day values 1966 74 of depth of the 9 c isotherm indicative of thermocline depth and of surface salinity are each fit by least squares method with a time varying cosine yielding phase and amplitude of the mean annual cycle at standard locations every 92 6 km 50 mi along the transect local wind stress curl is expected to influence the observed depth of the 9 c isotherm through the mechanism of ekman pumping therefore its annual cycle is computed in a manner like that of the depth of the 9 c isotherm and its effect removed from the latter the residual annual cycle has phase and amplitude profiles along the transect that closely resemble that of model annual baroclinic long waves emanating from a line source of large amplitude wind st

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

detection of the fast kelvin wave teleconnection due to el nino southern oscillation previous analyses of the ocean state along the western american coast have often indicated unexpectedly slow and limited propagation of coastally trapped kelvin waves associated with the e1 nifio southern oscillation in contrast theoretical and numerical ocean models demonstrate that these kelvin waves are a rapid and long range teleconnection between the low and high latitude pacific ocean strongly impacting both the surface coastal currents and nutrient upwelling sea level variations along the western coast of north america are reexamined under the assumption that tropically forced kelvin waves are produced in bursts of several months duration a cross correlation analysis restricted to mid 1982 to mid 1983 is performed between galapagos island and stations along western central and north america a coastally trapped kelvin wave is revealed to propagate at a speed of 2 3 m s from the tropical pacific to the aleutian island chain the observed phase speed agrees with the estimated speed of a kelvin wave based on the average density profile of the ocean near the coast weakere1 nifio events in 1986 1987 and 1991 1992 appear to contain a combination of this remotsignal and local wind forcing the wave propagation speed calculated from the spectrhl phase is shown to be sensitive to the presence of other noise processes in the observations this is demonstrated through an analysis of a synthetic sea level data set that contains many of the essential features of the real sea level data a relatively small level of red noise can give a 100 expected error in the estimated propagation speed this suggests a new explanation for this important inconsistency within dynamical oceanography

wind driven interdecadal variability in the eastern tropical and south pacific 1 simulated interface elevation anomalies with a reduced gravity model forced by observed wind stress are used to investigate the origin of thermocline depth fluctuations in the eastern tropical and south pacific at interdecadal timescales it is found that interdecadal thermocline depth fluctuations in the eastern equatorial pacific and along the western coast of the americas are fundamentally driven by zonal wind fluctuations in the western equatorial pacific thus positive negative interface elevation anomalies which correspond to shallower deeper thermocline depths in the eastern tropical pacific and along the west coast of central and south america are related to easterly westerly anomalies in the western sector of the equatorial pacific however off equatorial wind fluctuations maintain and reinforce the interdecadal variability observed along the eastern equatorial pacific and along the west coast of south america in the latter region equatorial off equatorial wind forcing is relatively more important equatorward poleward of 30 s in the eastern equatorial pacific interface elevation anomalies are negatively correlated with sea surface temperature sst at interdecadal timescales according to our results the sst interdecadal anomalies are in part 50 60 driven by wind fluctuations likely through the modulation of vertical advection of cold waters which depends primarily on the thermocline depth forced remotely or locally by winds this relationship was especially strong during the 1970s and 1980s a period characterized by the larger zonal wind stress interdecadal fluctuations observed in the western equatorial pacific

north pacific gyre oscillation synchronizes climate fluctuations in the eastern and western boundary systems abstract recent studies have identified the north pacific gyre oscillation npgo as a mode of climate variability that is linked to previously unexplained fluctuations of salinity nutrient and chlorophyll in the northeast pacific the npgo reflects changes in strength of the central and eastern branches of the subtropical gyre and is driven by the atmosphere through the north pacific oscillation npo the second dominant mode of sea level pressure variability in the north pacific it is shown that rossby wave dynamics excited by the npo propagate the npgo signature in the sea surface height ssh field from the central north pacific into the kuroshio oyashio extension koe and trigger changes in the strength of the koe with a lag of 2 3 yr this suggests that the npgo index can be used to track changes in the entire northern branch of the north pacific subtropical gyre these results also provide a physical mechanism to explain coherent decadal climate variations and ecosystem changes between the no

estimating the intensity of rock discontinuities this paper presents an approach for estimating the intensity of discontinuities and formulating intensity and orientation as a fracture tensor specifically the size distribution and the number of discontinuities are estimated first from which the fracture tensor is then derived discontinuity size distribution is inferred from the trace data sampled in circular windows by using a general stereological relationship between the true trace length distribution and the discontinuity diameter distribution assuming circular shaped discontinuities because the measured trace lengths are biased a method is proposed to estimate the true trace length distribution for circular window sampling circular window sampling has the advantage of automatically eliminating the orientation bias when estimating the true trace lengths a method is then presented with which the total number of discontinuities in an objective volume can be estimated from the number of discontinuities observed in normal size boreholes and using the inferred discontinuity diameter from the circular window sampling on the rock surface with the derived size distribution and number of discontinuities the intensity of discontinuities which is the total surface area of discontinuities per unit volume can then be calculated and included in a new definition of a fracture tensor an application of the approach to analyze simulated discontinuities produces satisfactory results