vegetation and environmental changes in northern anatolia between 134 and 119 ka recorded in black sea sediments this multiproxy study on se black sea sediments provides the first detailed reconstruction of vegetation and environmental history of northern anatolia between 134 and 119 ka here the glacial interglacial transition is characterized by several short lived alternating cold and warm events preceding a meltwater pulse 130 4 131 7 ka the latter is reconstructed as a cold arid period correlated to heinrich event 11 the initial warming is evidenced at 130 4 ka by increased primary productivity in the black sea disappearance of ice rafted detritus and spreading of oaks in anatolia a younger dryas type event is not identifiable the eemian vegetation succession corresponds to the main climatic phases in europe i the quercus juniperus phase 128 7 126 4 ka indicates a dry continental climate ii the ostrya corylus quercus carpinus phase 126 4 122 9 ka suggests warm summers mild winters and high year round precipitation iii the fagus carpinus phase 122 9 119 5 ka indicates cooling and high precipitation and iv increasing pinus at 121 ka marks the onset of cooler drier conditions generally pollen reconstructions suggest altitudinal latitudinal migrations of vegetation belts in northern anatolia during the eemian caused by increased transport of moisture the evidence for the wide distribution of fagus around the black sea contrasts with the european records and is likely related to climatic and genetic factors

migrating and nonmigrating semidiurnal tides in the upper atmosphere excited by tropospheric latent heat release migrating and nonmigrating semidiurnal tides

spatial arrangement of soil mantle in glacis de buenavista mexico as a product and record of landscape evolution abstract factors controlling spatial soil organization have recently attracted the attention of soil scientists because they can contribute to regional management of soil resources we present here a case study in the glacis de buenavista mexico an extended volcanic piedmont in order to develop an integral understanding of its soil cover as a product and at the same time as a record of the main stages of landscape evolution three phenomena were considered luvisol and vertisol type soils and pedosediments all of them analyzed in terms of their development degree clay content macro and micromorphology selective extractions of fe fe d fe o silicon si o and aluminum al o weathering index and clay mineralogy luvisols represented in the ahuatenco mexicapa and buenavista sections are located in the northern and central part of the area they are red clayey polygenetic soils that show strong weathering with high kaolinitic clay content and high weathering index values clay illuviation and reductomorphic processes combined with vertic features in some parts of the profiles vertisols dominate the central and southern portion of the glacis they exhibit cracking angular blocks with wedge like shapes slickensides and stress cutans the pedogenesis of the vertisol type is clearly associated with the presence of smectitic minerals in the clay fraction as a product of neoformation factors controlling this pedodiversity are relief which affects bioclimatic differentiation within the studied landsurface and defines the lateral redistribution of moisture and dissolved substances and time luvisols represent a longer pedogenetic phase that started in the late pleistocene according to the age of buried paleosols while vertisols mainly originated in the late holocene according to the age of buried organic horizons pedosediments are located in the central area of the glacis here past and present geomorphic processes interact to produce the greatest soil diversity the recent human induced erosion partly destroyed polycyclic luvisols and exposed ancient subsurface pedosedimentary strata at the same time it produced patches of unconsolidated pedosediments consisting mostly of redeposited luvisol materials

longitudinal variability of low latitude total electron content tidal influences 1 recently nighttime ultraviolet uv observations obtained by image fuv and timed guvi instruments have revealed a longitudinal wave number four pattern in the nighttime airglow intensity and in the position of the equatorial anomalies during equinox and high solar flux conditions in the present study we have extended this work and determined the longitudinal variability of the low latitude total electron content tec climatology during different geophysical conditions with a special emphasis on the longitudinal wave number four structure in the low latitude ionosphere we have used more than 5 million low latitude topex tec observations covering the entire 13 years of topex tec data from august 1992 until october 2005 this data set was used to determine the local time seasonal solar cycle and geomagnetic activity dependence of the longitudinal variability of tec at equatorial and low latitudes and in particular to address the existence and evolution of the wave number four longitudinal pattern under these conditions our study shows that the wave number four pattern is created during the daytime hours at equinox and june solstice but is absent or washed out by other processes during december solstice during equinox the wave number four pattern is created around noon with well defined longitudinal enhancements in the low latitude tec these enhancements which are symmetric about the geomagnetic equator during this season last for many hours and can be clearly seen past midnight the longitudinal patterns are found to be nearly identical between the vernal march april and autumnal september october equinoxes and largely independent of the solar cycle conditions the wave number four pattern is also observed during geomagnetically active conditions indicating that the processes that create this pattern are also present during active times the variations between the well defined longitudinal maxima and minima are of the order of 20 during june solstice the wave number four pattern is also observed in the afternoon hours but in contrast to the equinox cases it exhibits a strong hemispheric asymmetry and is not observed during the night the low latitude tec exhibits clear longitudinal variations during december solstice with large daytime enhancements over the east asian and pacific regions and a third enhancement emerging in the afternoon over the atlantic ocean but a clear wave number four pattern is not observed during this season although the equatorial and low latitude tec values exhibit clear longitudinal patterns during all seasons a significant amount of scatter remains in the tec data that is not accounted for by changes in the solar cycle the season or the local time or by the longitudinal variability this remaining scatter is largest near the poleward edges of the anomalies and is of the order of 40

alluvial archives of the nochixtlan valley oaxaca mexico age and significance for reconstructions of environmental change abstract a reconnaissance of the nochixtlan valley confirms that thick alluvial deposits of the late quaternary are both well preserved and well exposed along the heavily incised modern streams their geometry and age were ascertained by logging representative cutbank exposures and radiocarbon dating buried palaeosols the last four cut and fill cycles recorded cover the period since 14 000 bp but older alluvial insets are also present contrary to previous reconstructions the streams have had an arroyo type morphology throughout the late quaternary the climatic oscillations at the transition from the pleistocene to the holocene seem to be expressed in the alternating formation of clayey organic rich cumulic a horizons and the precipitation of secondary carbonates rapid though intermittent aggradation set in after 10 300 bp in response to the establishment of a rather dry warm and strongly seasonal climate and of open canopy forest or scrub on slopes the unstable arroyo floodplains offered a favorable niche for the establishment of secondary vegetation and foragers exploiting annual and heliophilous plants after 4000 bp sedentary farmers cleared the valley of its natural vegetation increasing sediment transfers and the frequency of local cut and fill cycles they modified streams intentionally by building long flights of cross channel agricultural terraces known as lama bordos the remains of which are preserved in many cutbanks the oldest specimen dated goes back to ca 3000 bp a remarkably synchronous incision swept through the fluvial system close to 800 bp possibly as a result of a marked climatic shift or valley wide changes in land use the widespread gullying of the latest pre conquest settlements and fields suggests the introduction of grazing or the collapse of hillside terraces as cause but coeval alluvial fills have not yet been positively identified

sources of glacial moisture in mesoamerica paleoclimatic records from mesoamerica document the interplay between atlantic and pacific sources of precipitation during the last glacial stage and holocene today and throughout much of the holocene the entire region receives its principal moisture in the summer from an interaction of easterly trade winds with the equatorial calms glacial records from sites east of 95 w in guatemala florida northern venezuela and colombia record dry conditions before 12 ka however west of 95 w glacial conditions were moister than in the holocene for example pollen and diatom data show that lake patzcuaro in the central mexican highlands was cool deep and fresh during this time and fossil pinyon needles in packrat middens in chihuahua sonora arizona and texas indicate cooler glacial climates with increased winter precipitation cold gulf of mexico sea surface temperatures and reduced strength of the equatorial calms can explain arid full and late glacial environments east of 95 w whereas an intensified pattern of winter westerly air flow dominated hydrologic balances as far south as 20 n overall cooler temperatures may have increased effective moisture levels during dry summer months in both areas

the fate of iron in waters from a coastal environment impacted by metallurgical industry in northern italy hydrochemistry and fe isotopes abstract the source and cycling of fe in groundwaters from the phreatic aquifer which characterizes a site impacted by metallurgical activity in a coastal area of northern italy adriatic sea have been investigated by fe isotope analyses h o sr stable isotope systematics and major and trace element chemistry waters are characterized by circum neutral to alkaline ph and dissolved o 2 zoning and range from a low salinity ca mg hco 3 type to a brackish na cl type resulting from seawater intrusion the o h isotopic data indicate that the ca mg hco 3 waters originate from meteoric precipitation that infiltrated at elevated altitudes and that a variable seawater fraction in some cases exceeding 90 characterizes the na cl type waters the fe content ranges from 0 48 to 9 99 mg l and from 2 50 to 43 8 mg l in low salinity and brackish waters respectively the 56 fe value varies over the wide range from 0 87 to 5 29 in low salinity waters and between 2 15 and 2 34 in brackish waters the isotopically lighter compositions are interpreted as reflecting isotopic fractionation during repeated cycling of fe precipitation positive 56 fe values might indicate either a higher solubility of oxyhydroxides which during diagenesis preferentially incorporated the isotopically heavier fraction of fe or the leaching of the foundry landfill disposal which characterizes the site

fluvial response to holocene climate change in low order streams of central mexico alluvial sequences constitute a recognised source of information on past environmental change but one that has scarcely been tapped in central mexico this paper reviews what is currently known about the holocene alluvial stratigraphy of the region focusing on the interplay between climate and the pace and style of sedimentation in the incised headwater reaches of stream networks the records obtained in five different drainage basins four in the state of tlaxcala and one in guanajuato are presented and compared to published reconstructions of climate change a near synchronous incision of all stream networks occurred close to 10 200 14c a bp in response to an increase in precipitation and stream discharge a spell of very humid but markedly seasonal conditions ensued resulting in the formation of wet meadows along streams and the accumulation of thick fine textured valley fills dominated by cumulic soil a horizons after 9100 14c a bp a transition to a warmer and more arid climate provoked the thinning of vegetation cover on slopes accelerated runoff and increased sediment delivery to streams the aggradation of coarser textured valley fills poor in organic matter set in it ceased or slowed down significantly after a few millennia as the studied stream reaches achieved a near graded condition adjusted to the relatively stable climate arid mid holocene conditions are also reflected in the abundant precipitation of secondary carbonates in guanajuato at 3100 14c a bp higher precipitation caused more frequent flooding and a resumption of aggradation shortly after that date sedentary farmers colonised tlaxcala agriculture altered runoff and sediment delivery to streams and accelerated cut and fill cycles on a scale that masked the impact of any climatic fluctuations guanajuato was colonised later and its alluvial record suggests the persistence of a humid climate at least until 1000 14c a bp copyright 2009 john wiley sons ltd

early mid pleistocene environments in the valsequillo basin central mexico a reassessment the valsequillo basin in central mexico has been of interest due to the presence of megafauna and evidence for early human occupation but research has been controversial it has been suggested that extensive and deep lakes characterised the early pleistocene environment but sediment exposure is highly fragmentary and reliable dating has been difficult here we report for the first time early pleistocene palaeoenvironmental reconstructions using stable isotopes diatoms tephra and pollen we studied several stratigraphic sections of mainly non volcanic rocks containing the 1 3 ma xalnene ash as a stratigraphic marker the isotope and other proxy data show that topographically low points in the basin were occupied by spring fed shallow water lakes during the early mid pleistocene with a trend to drier conditions the basin was a dynamic volcaniclastic environment during this period with the production of the toluquilla volcano sequence and other rhyolitic dacitic volcanic ashes interbedded with the lake sediments at the sections studied there is no evidence from the sections for extensive and deep lakes before or after the xalnene ash deposition the presence of lakes in the basin during the early pleistocene would have made it attractive for megafauna

climatic and human controls on the late holocene fire history of northern israel article i nfo article history received 5 april 2013 available online 27 august 2013 long term fire histories provide insight into the effects of climate ecology and humans on fire activity they can be generated using accumulation rates of charcoal and soot black carbon inlacustrine sediments this study uses both charcoal and black carbon and other paleoclimate indicators from lake kinneret sea of galilee israel to reconstruct late holocene variations in biomass burning and aridity we compare the fire history data with a re gional biomass burning reconstruction from 18 different charcoal records and with pollen climate and popula tion data to decipher therelativeimpacts of regional climate vegetation changes and human activity on fire we showalong termdecline in fireactivityoverthepast3070 years fromhighbiomassburning 3070 1750 cal yr bp to significantly lower levels after 1750 cal yr bp human modification of the landscape e g forest clearing agriculture settlement expansion and early industry in periods of low to moderate precipitation appears to have been the greatest cause of high biomass burning during the late holocene in southern levant while wetter climate apparently reduced fire activity during periods of both low and high human activity

ecosystem responses to climate and disturbances in western central mexico during the late pleistocene and holocene abstract central mexico is a complex area with late quaternary volcanic activity climatic diversity and a long history of human occupation pollen microcharcoal and magnetic susceptibility analyses of two sedimentary sequences from lake zirahuen in western central mexico spanning the last 17 000 years provide evidence of a highly dynamic environment during the late glacial pinus forest developed around the lake indicating cold and dry conditions during the last deglaciation climatic amelioration was recorded at 13 5 ka driving a strong and rapid change in vegetation composition and increase in lake levels from the latest pleistocene to early holocene a hiatus probably related to an erosive event is recognized in the northern sequence the central sequence spans the entire holocene and reveals three periods of important ecological changes during the early holocene a first episode between 9 5 and 9 0 ka with a decrease in pine forest seems to have been associated with summer insolation increases a second peak of forest change at 8 2 ka and was probably associated with the cold oscillation documented in the north atlantic a third abrupt change was evident from 7 5 to 7 1 ka with an anomalous plant community related to wetter holocene climates and possible to a volcanic event an episode of dry conditions was recorded from 4 5 to 4 2 ka which was related to an increase in enso activity human influence over the landscape was evident from 3 5 ka to the present the zirahuen records offer a complex history of a landscape characterized by short and long term vegetation changes associated with factors ranging from global climate to local disturbances

vegetation in western central mexico during the last 50 000 years modern analogs and climate in the zacapu basin the late glacial and the transition towards the holocene marked a period of significant environmental change at a global scale in western central mexico few records span beyond the holocene and little is known about pleistocene climatic and environmental variability here we report on the pollen record of a composite sequence made of three cores that cover the last 50 ka thousands of calibrated radiocarbon years before present in the zacapu basin western central mexico 1970 m asl the conjunction of modern pollen rain from the area with the composite fossil pollen sequence from cores cantabria cantabria 1 and cemca point 1 provided a detailed history of the vegetation of the area recognition of modern environmental patterns through individual modern pollen taxa proved difficult but multivariate analysis separated different vegetation types no modern analog communities relative to the modern vegetation cover of the area were evident especially during periods of drought apparently summer precipitation was significant before 40 ka and after the deglaciation however this moisture source declined from 40 to 10 ka because tradewinds from the gulf of mexico were blocked by the eastern mountains of central mexico as a result of lower temperatures by contrast westerly and northerly winds were enhanced by maximum ice cover from 19 to 17 ka providing abundant winter precipitation and therefore preventing extreme drought in the area copyright 2012 john wiley sons ltd

iron concentrations in selected groundwater samples from the lower friulian plain northeast italy importance of salinity high amounts of iron up to 14 mg l were found in groundwater samples from marano lagoon in the friuli venezia giulia plain northeast italy in order to characterize groundwater hydrochemistry in the area an investigation has been conducted on 35 wells that were monitored since 2006 leaching tests were performed under anaerobic conditions with deionized and saline waters on two core samples in the area to study the iron release from soils to groundwater collected data indicated the main role of salinity in metal leaching and highlighted spatial correspondence between high levels of chloride and iron to understand the mechanism of groundwater salinization sulphate chloride ratio has been investigated and a statistical relation between salinity ph and iron was found these data do not show any relation between past activities and high iron groundwater contents high iron concentrations are diffuse in the whole area and therefore comparable to background values consequently the study states that no remediation plan should have been made for iron concentrations in this area

sta cruz atizapan a 22 ka lake level record and climatic implications for the late holocene human occupation in the upper lerma basin central mexico abstract the upper lerma is a high altitude basin with three water bodies linked by the lerma river this basin has a long archaeological history characterised by the establishment of settlements within the lacustrine ecosystem itself man made islands during the late classic to epiclassic ad 550 900 which were abandoned by the end of the epiclassic the upper lerma is an ideal site to study climatic and environmental conditions during the period of human occupation as well as during the last full glacial interglacial cycle two sediment cores stcrz 9 54 m and almoloya del rio 5 12 m were recovered from the highest lake in the system chignahuapan ten radiocarbon dates provide chronologies for these sequences in which the tres cruces tephra c 8500 yr bp and the upper toluca pumice c 11 600 yr bp serve as stratigraphic markers magnetic properties loss on ignition and diatom analyses were used to infer lake level fluctuations during the last c 22 000 yr bp the late pleistocene environment was characterised by a freshwater lake high sediment input and variable lake levels are recorded during the last glacial maximum c 19 000 16 000 yr bp while slightly higher water levels and reduced sediment input are recorded during the late glacial c 16 000 11 000 yr bp a short episode of shallow conditions is inferred by c 12 400 yr bp holocene lake levels were generally shallower and three episodes of very shallow slightly alkaline waters are identified the first dates to the early holocene c 11 000 7000 yr bp the second is centred at c 4600 4500 yr bp the third occurred between c 2000 and 800 yr bp c 200 bc ad 1100 calibrated ages with very shallow water after c 1400 yr bp ad 550 calibrated age lake level increased after c 800 yr bp these three shallow water events are also recorded at other sites in central mexico indicating regional climatic trends rather than local events a deeper water phase occurred between 7000 and 6400 6200 yr bp the last shallow water phase correlates with the classic and epiclassic periods ad 200 900 and shallowest conditions occurred in the late classic to epiclassic c ad 550 900 when the construction of man made islands reached a peak an increase in lake level after c 800 yr bp ad 1100 calibrated age may have led to the abandonment of this life strategy

rates of pedogenic processes in volcanic landscapes of late pleistocene to holocene age in central mexico abstract the transmexican volcanic belt and its many volcanic fields of different ages offer good opportunities to study soil development on volcanic tephra of intermediate to basaltic composition we studied a soil chronosequence within the sierra chichinautzin volcanic field scvf south of the basin of mexico and aimed to establish the rates of pedogenic processes this field has been active for around 50 000 years and produced 221 cinder cones with their respective lava flows we selected 11 sites located on 14 c dated lava flows of ages between 1800 and 30 500 bp at 3100 3200 m above sea level covered with pine fir forest with an ustic soil moisture regime and an isomesic soil temperature regime we also included a younger site 1000 bp and three older sites 100 000 years two at 3100 masl and one at 2600 masl from nearby volcanic fields to widen the time frame of the chronosequence soil profile samples were analysed for total organic carbon as well as for mineral neoformations related to clay contents selective chemical extractions and x ray diffraction analyses within the scvf the total soil thickness carbon accumulation and al si and fe extracted with acid ammonium oxalate increased linearly with age on surfaces up to 10 000 years old at rates of 19 cm ky 1 4 1 kg c m 2 ky 1 4 6 kg al 2 7 kg si and 2 kg fe m 2 ky 1 respectively crystalline clay and iron oxide formation reach a maximum at the oldest site located at 2600 masl of 1650 kg clay m 2 and 70 kg fe d m 2 their increase is linear up to ages of 10 000 years at rates of 22 kg clay m 2 ky 1 and 2 8 kg fe d m 2 ky 1 thereafter the rates are much slower allophane and allophane like minerals dominate in the clay fraction at all sites of the chronosequence and small amounts of halloysite can be identified in soils older than 6200 years while kaolinite was only identified at the three oldest sites 100 000 years the linear increases of all indicators of pedogenesis in the first 10 000 years are presumably driven by recurrent tephra deposition during this time frame thereafter erosion and colluviation processes seem to disturb pedogenesis changing its rates and redistributing its products in the landscape

late pleistocene and holocene paleoenvironments of chalco lake central mexico abstract in order to establish paleoenvironmental conditions during the late quaternary four cores from the basin of mexico central mexico were drilled in chalco lake located in the southeastern part of the basin the upper 8 m of two parallel cores were studied using paleomagnetic loss on ignition pollen and diatom analyses based on 11 14c ages the analyzed record spans the last 19 000 14c yr b p volcanic activity has affected microfossil abundances both directly and indirectly resulting in absence or reduction of pollen and diatom assemblages important volcanic activity took place between 19 000 and 15 000 yr b p when the lake was a shallow alkaline marsh and an increase of grassland pollen suggests a dry cold climate during this interval abrupt environmental changes with increasing moisture occurred from 15 000 until 12 500 yr b p the lake level increased and the pollen indicates wetter conditions the highest lake level is registered from 12 500 to ca 9000 yr b p the end of the pleistocene is characterized by an increase in humidity from 9000 until ca 3000 yr b p chalco lake was a saline marsh and the pollen record indicates warmer conditions after 3000 yr b p the lake level increased and human disturbance dominates the lacustrine record

the last glacial maximum in the basin of mexico the diatom record between 34 000 and 15 000 years bp from lake chalco lacustrine sediments from a section of a core extracted from the central part of the former lake chalco were analysed for diatom content radiocarbon dates and tephra correlations bracket the period under study between 34 and 15 ka bp according to the diatom stratigraphy chalco was an alkaline saline lake during the interval 34 31 5 ka bp after 31 5 ka bp it went through a shallower and more concentrated phase until ca 23 5 ka bp at ca 23 5 ka bp a major environmental change took place during which lake chalco was transformed from an saline alkaline pond into a freshwater lake previous archaeological work at tlapaocya indicates that humans entered the basin slightly after this environmental change by ca 22 ka bp at 19 ka bp another reduction in water level occurred with the onset of a period of quick fluctuations between slightly acidic and neutral water these variations were probably associated with intensified volcanic activity that affected the area between 19 and 15 ka bp

volcanomagnetic signals during the recent popocatepetl mexico eruptions and their relation to eruptive activity abstract an interdisciplinary approach correlating magnetic anomalies with composition of the ejecta in each eruption as well as with seismicity was used to study the effect of magmatic activity on the local magnetic record at popocatepetl volcano located 65 km southeast of mexico city eruptions began on december 1994 and have continued with dome growth and ash emissions since then the tlamacas tla geomagnetic total field monitoring station located 5 km away from popocatepetl s crater was installed in december 1997 in order to detect magnetic anomalies induced by this activity spatial correlation and weighted difference methods were applied to detect temporal geomagnetic anomalies using tla s record and the teoloyucan magnetic observatory as a reference station weighted differences were applied to cancel the effects of non vulcanogenic external field variations magnetic anomalies over a 2 year time span were classified into four types correlating them with geochemical seismic and visual monitoring of the volcanic activity magnetic anomalies are believed to be caused by magma injection and gas pressure build up which is sensitive to vent morphology and clearing during eruption although some anomalies appear to be thermally related changes in the stress field are very important most magnetic anomalies are short time signals that reverse to baseline level decreasing anomalies 0 5 to 6 8 nt precede eruptions by 1 8 days the presence of a mafic magmatic component was determined by mineral examination and silica and magnesium analyses on the ejecta from the 1997 1999 eruptions whole rock analyses ranged from dacitic 65 sio 2 to andesitic 57 sio 2 with 2 6 6 mgo the higher mgo lower silica samples contain forsteritic olivine fo90 sio 2 does not increase and mgo does not increase with time suggesting ascent of small magma pulses which are consistent with the magnetic data

terdiurnal migrating tide signature in ionospheric total electron content we report the latitudinal seasonal and solar cycle variations of terdiurnal migrating tide i e terdiurnal westward wave number 3 tw3 signature in ionospheric total electron content tec our investigations are based on the jpl global ionospheric maps gims during 1999 2011 the absolute amplitude of tw3 exhibits maximum values in the magnetic equatorial region which reaches about 8 tecu under high solar activity and 1 5 tecu under low solar activity the relative amplitude of zonal mean tec in equatorial region however shows persistent patterns from 1999 to 2011 with little solar activity dependence the relative amplitude of tw3 has a peak of similar to 10 in the magnetic equatorial region and a second one of similar to 7 at magnetic middle latitudes 30 degrees 50 degrees at high latitudes in local winter seasons the maximum relative amplitude occurs which varies between 8 and 15 with slightly larger amplitudes in the northern hemisphere the global structure of tw3 signature in tec should shed some light on the coupling between the ionosphere thermosphere and the lower atmosphere

limnologic history of lago de patzcuaro michoacan mexico for the past 48 000 years impacts of climate and man abstract lago de patzcuaro lies at an elevation of 2035 m 19 36 n 101 39 w on the west part of the volcanic meseta central of mexico about 50 km east southeast of morelia pollen diatom and geochemical records from a 15 m core taken in 6 m of water continuously track vegetation and limnological changes in the patzcuaro basin for the past 48 ky calendar years pine oak and alder pollen dominate both the wisconsin and holocene vegetation record and indicate that this region did not witness strongly arid climates during that time before the holocene juniperus type and artemisia pollen document cooler climates of more effective moisture at least seasonally isoetes characterizes the full and late glacial interval 25 13 ka and implies along with the diatoms aulacoseira and stephanodiscus cool deep freshwater conditions at lago de patzcuaro the freshest and deepest lacustrine phase in the lake occurred 38 to 25 ka during this time lago de patzcuaro may have drained into the lerma river system between 30 and 10 ka diatom species that bloom in the winter and early spring imply moisture during those seasons evaluation of contemporaneous marine and terrestrial records west and east of lago de patzcuaro suggests that this moisture probably originated from westerly storm tracks shifted south by the laurentide ice sheet after 10 ka lago de patzcuaro became shallower and more eutrophic rooted aquatic plants prospered under a climate regime of negative hydrologic budgets increased seasonality and moisture arriving during the summer as it does today the lake became alkaline enough by the mid holocene to deposit ostracode rich marls at the core site for the first time in the past 48 ky indigenous agriculture in the patzcuaro drainage and around the lake appears about 4 ka with the appearance of zea and chenopodiineae pollen iron and potassium track increased soil erosion and planktic diatoms cyclostephanos record nutrients flushed into the lake from the drainage basin

tidal variability in the ionospheric dynamo region 1 the seasonal and interannual variability of migrating sun synchronous and nonmigrating solar atmospheric tides at altitudes between 100 and 116 km are investigated using temperature measurements made with the saber instrument on the timed spacecraft during 2002 2006 quasi biennial variations of order 10 15 in migrating diurnal and semidiurnal tidal amplitudes are found presumably due to modulation by the quasi biennial oscillation qbo as the tides propagate from their troposphere and stratospheric sources to the lower thermosphere a number of nonmigrating tidal components are found that have the potential to produce significant longitudinal variability of the total tidal fields the most prominent of these i e those that appear at amplitudes of order 5 10 k in a 5 year mean climatology include the zonally symmetric s 0 diurnal tide d0 the eastward propagating diurnal and semidiurnal tides with zonal wave numbers s 2 de2 and se2 and s 3 de3 and se3 and the following westward propagating waves diurnal s 2 dw2 semidiurnal s 1 sw1 s 3 sw3 and s 4 sw4 and terdiurnal s 5 tw5 these waves can be plausibly accounted for by nonlinear interaction between migrating tidal components and stationary planetary waves with s 1 or s 2 or by longitudinal variations of tropospheric thermal forcing additional waves that occur during some years or undergo phase cancellation within construction of a 5 year climatology include dw5 se1 se4 sw6 te1 tw1 and tw7 it is anticipated that the winds that accompany all of these waves in the 100 170 km region will impose longitudinal variability in the electric fields produced through the ionospheric dynamo mechanism thereby modulating vertical motion of the equatorial ionosphere and the concomitant plasma densities in addition to the wave 4 modulation of the equatorial ionosphere that has recently been discovered and replicated in modeling studies the waves revealed here will generate wave 1 sw1 sw3 d0 dw2 wave 2 sw4 tw1 wave 3 de2 se1 wave 4 de3 se2 dw5 sw6 te1 tw7 wave 5 se3 and wave 6 se4 components of this ionospheric variability depending on year and time of year however the absolute and relative efficiencies with which these waves produce electric fields remains to be determined

lake levels since about 40 000 years ago at lake chalco near mexico city abstract diatoms magnetic susceptibility organic content and14c ages of sediments from a 26 m core suggest that lake chalco in the southern part of the basin of mexico went through a series of major fluctuations during the late pleistocene and the holocene before ca 39 00014c yr b p the lake was very deep about 8 10 m alkaline and saline it then became shallow

fluvial processes and paleopedogenesis in the teotihuacan valley mexico responses to late quaternary environmental changes a paleosol sequence in the teotihuacan valley was studied in order to reconstruct landscape evolution during the late pleistocene holocene in a cut belonging to a river gully san pablo the sequence is constituted by 4 pedostratigraphic units labeled as sp1 sp4 separated by volcanogenic alluvial colluvial sediments sp4 at the base of the sequence has a prismatic structure clay cutans and vertic features sp3 shows abundant signs of zooturbation krotovinas and clay cutans both paleosols are interpreted to have formed in stable humid forest landscapes during marine isotope stage 3 mis3 however towards the end of mis3 these conditions alternated with the periods of contrasting seasonal climate the overlying sp2 unit is a pedocomplex demonstrating 2 petrocalcic horizons combined with redoximorphic features the pedocomplex merges laterally with gradually stratified gleyic channel deposits gravels in the base to fine sand and silt in the top the age of the lower caliche is 24 000 bp and thus sp2 formed during mis2 including the last glacial maximum lgm the environmental conditions during lgm are mostly dry with stages of high humidity evidenced by gleyic processes and fluvial activity at the end of the pleistocene the landscape becomes highly unstable and pedogenesis is replaced by sedimentation new paleochannels cut through the previously formed paleosols these channels are infilled by poorly sorted sediments with no gradation the configuration of all paleochannels is nne ssw nearly at 90 to the modern san pablo river flow geomorphic stability during the early and middle holocene allowed the development of sp1 in a dry environment the a horizon of this paleosol has been dated at 2900 bp it is well developed with strong vertic features this paleosol is thought to have formed the soil cover when the classic period teotihuacan culture flourished in the valley between the first and third centuries ad soils above sp1 are poorly developed and erosion deposition processes predominate over pedogenesis recent landscape instability is due to human activities that intensified erosion processes during the classic and especially the postclassic and colonial periods

accuracy of cosmogenic ages for moraines analyses of all published cosmogenic exposure ages for moraine boulders show an average age range of 38 between the oldest and youngest boulders from each moraine this range conflicts with the common assumption that ages of surface boulders are the same as the age of the landform the wide spread in boulder ages is caused by erosion of the moraine surface and consequent exhumation of fresh boulders a diffusion model of surface degradation explains the age range and shows that a randomly sampled small set of boulders n 3 7 will always yield a lower age limit for the moraine the model indicates that for identical dating accuracy six to seven boulders are needed from old and tall moraines 40 000 100 000 yr 50 100 m initial height but only one to four boulders from small moraines 20 000 100 000 yr 10 20 m by following these guidelines the oldest obtained boulder age will be 90 of the moraine age 95 probability this result is only weakly sensitive to a broad range of soil erosion rates our analysis of published boulder ages indicates that 3 of all moraine boulders have prior exposure and 85 of these boulders predate the dated moraine

assessment of gps global ionosphere maps gim by comparison between code gim and topex jason tec data ionospheric perspective 1 we performed a comprehensive comparison between gps global ionosphere map gim and topex jason t j total electron content tec data for the periods of 1998 2009 in order to assess the performance of gim over the global ocean where the gps ground stations are very sparse using the gim model constructed by the center for orbit determination in europe at the university of bern the gim tec values were obtained along the t j satellite orbit at specific locations and times of measurements and then binned into various geophysical conditions for direct comparison with the t j tec on the whole the gim model was able to reproduce the spatial and temporal variations of the global ionosphere as well as the seasonal variations however the gim model was not accurate enough to represent the well known ionospheric structures such as the equatorial anomaly the weddell sea anomaly and the longitudinal wave structure furthermore a fundamental limitation of the model seems to be evident in the unexpected negative differences i e gps t j at night represent the plasmaspheric contribution to gps tec which is maximized reaching up to 100 of the corresponding t j tec values in the early morning sector in particular the relative differences decreased with increasing solar activity and this may indicate that the plasmaspheric contribution to the maintenance of the nighttime ionosphere does not increase with solar activity which is different from what we normally anticipate

the late glacial moraine sequences in mexico is the evidence for the younger dryas event abstract geomorphologic paleopedologic tephrostratigraphic and palynologic investigations together with radiocarbon dates provide ages for several late quaternary glacier on the volcanoes of central mexico on the volcanoes la malinche nevado de toluca and iztaccihuatl glacier advances have been dated older than 12 000 yr b p and between about 10 000 and 8500 yr b p the glacial chronostratigraphies from different volcanoes do not indicate a younger dryas glacial advance during the late quaternary phases with glacier advances can be correlated to changes in laurentide ice sheet meltwater discharge into the gulf of mexico on the one hand and into the north atlantic ocean on the other hand the central mexican glacial history shows a regional pattern that is different from that of the rocky mountains of the south american andes

observational evidence of ionospheric migrating tide modification during the 2009 stratospheric sudden warming 1 in this paper modifications of the ionospheric tidal signatures during the 2009 stratospheric sudden warming ssw event are studied by applying atmospheric tidal analysis to ionospheric electron densities observed using radio occultation soundings of formosat 3 cosmic the tidal analysis indicates that the zonal mean and major migrating tidal components dw1 sw2 and tw3 decrease around the time of the ssw with 1 5 4 hour time shifts in the daily time of maximum around eia and middle latitudes the typical ionospheric ssw signature a semi diurnal variation of the ionospheric electron density featuring an earlier commencement and subsidence of eia can be reproduced by differencing the migrating tides before and during the ssw period our results also indicate that the migrating tides represent 80 of the ionospheric tidal components at specific longitudes suggesting that modifications of the migrating tides may be the major driver for producing ionospheric changes observed during ssw events accounting for greater variability than the nonmigrating tides that have been the focus of previous studies

tepexpan revisited a multiple proxy of local environmental changes in relation to human occupation from a paleolake shore section in central mexico abstract building up a scenario of late pleistocene holocene environmental change and human landscape interactions in central mexico one of the key areas for the natural and cultural history of america requires development of local paleoenvironmental reconstructions we studied the tepexpan section at the edge of texcoco a paleolake near the mouth of teotihuacan valley as a multiproxy record of the environmental dynamics at the shore in the basin of mexico throughout the period of human occupation the section is located in an ecotone affected by intensive and variable geomorphic processes and includes lacustrine fluvial and volcanic sediments as well as paleosols our chronological scale is based on 6 ams 14c dates from pollen concentrates and paleosol organic matter the lower segment of the section dominated by the lacustrine sediments yielded pollen spectra in the upper segment the record is based on the pedogenetic characteristics of paleosols different proxies agree in demonstrating the general trend although some reversals are apparent of decreasing effective moisture since mis3 it is reflected first in the increase of herbaceous pollen after 27 ka bp the decrease of lake level the cessation of lacustrine sedimentation and beginning of marsh soil development at 10 ka bp and finally the shift from hydromorphic to dryland semiarid pedogenesis in the late holocene we assume that this trend was climatically controlled whereas the deposition of sedimentary layers enriched with tephra are related to the pulses of volcanic activity the pedosedimentary features associated with the upper soil are human induced comparing the proposed scheme of environmental change with the archaeological record we propose that the initial settlers late paleolithic hunters could have utilized the wet swampy meadows which expanded on the basin bottom as the lake level lowered and provided the niche for large herbivores during the pleistocene holocene transition development of agriculture and the network of permanent settlements are believed to be linked to the formation of well drained soils in the methodological perspective the study shows the potential of ecotones as highly dynamic and sensitive systems that may archive valuable paleoecological records

integrated geoelectrical resistivity and hydrogeochemical methods for delineating and mapping heavy metal zone in aquifer system a novel study on using geoelectrical resistivity soil property and hydrogeochemical analysis methods for delineating and mapping of heavy metal in aquifer system is presented in this paper a total of 47 surveys of geoelectrical resistivity with wenner configuration were conducted to determine the subsurface and the groundwater characteristics the groundwater sample from 53 existing wells and 2 new wells has been analyzed to derive their water chemical content the chemical analysis was done on the soil sample obtained from new two wells and from selected locations the water and soil chemical analysis results from the new two wells were used as calibration in resistivity interpretation the occurrence of heavy metal in aquifer system was expected to detect using the geoelectrical resistivity survey for the whole study area the result of groundwater analysis shows that the groundwater sample contains a relatively low concentration of fe 0 3 mg l elongating from the south up to the middle region while in the middle and the northwestern fe concentration is relatively high around 12 mg l chemical analysis of soil sample shows that in the lower resistivity zone 18 m al and fe concentrations are comparatively high with an average of 68 000 and 40 000 mg kg respectively starting from the middle to the northwestern zone the resistivity value appears to be low it is definitely caused by higher al and fe concentration within the soil and it is supported also by lower total anion content in the groundwater while the resistivity value of more than 40 m in aquifers is obtained in the zone which fe concentration is relatively lower in the soil but not present in the groundwater correlation fe concentration in the soil and fe concentration in the groundwater sample shows the trend of positively linear however the al concentration in soil has no correlation with al content in groundwater finally the probability of high heavy metal zone in the aquifer system is easily delineated by the distribution of geoelectrical resistivity presented in depth slice shapes which extend from the boundary range composite batholith in the north to the northwest

evidence for stratosphere sudden warming ionosphere coupling due to vertically propagating tides 1 observations of the global positioning system gps total electron content tec are used to study the coupling between the 2009 sudden stratospheric warming ssw and ionospheric perturbations the observations reveal both migrating and nonmigrating perturbations to the semidiurnal tide in the equatorial ionization anomaly crest region that are associated with changes in electric fields induced by the tidal dynamo in particular a significant enhancement is observed in the nonmigrating semidiurnal westward propagating tide with zonal wavenumber 1 sw1 in gps tec during the ssw the sw1 perturbations in the low latitude ionosphere are found to oscillate with a similar period as planetary wave 1 activity in the northern hemisphere stratosphere this connection is attributed to the nonlinear interaction between tides and planetary waves and strongly supports the theory that planetary wave tide interaction is the primary mechanism coupling ssws to ionospheric variability enhancements are also observed in the nonmigrating semidiurnal tide with zonal wavenumber 0 s0 during this time period and may be related to the nonlinear interaction between the migrating semidiurnal tide and planetary wave 2 the connection between planetary wave 2 and s0 is however less clear which may be attributed to differences in the zonal mean zonal winds in the mesosphere and lower thermosphere during the times of peak planetary wave 1 and planetary wave 2 activity we conclude that the changing zonal winds during ssws play an important role in the coupling between ionospheric variability and the forcing from planetary waves of lower atmospheric origin during ssws

cosmogenic 36cl accumulation in unstable landforms 2 simulations and measurements on eroding moraines cosmogenic 36cl surface exposure ages obtained for multiple boulders from single landforms are usually characterized by a variance larger than that of the analytical methods employed this excessive boulder to boulder variability progressively more profound with increasing age of landforms is due to removal of soil and gradual exposure of boulders at the surface in our gradual exposure model boulders are initially buried in moraine matrix with time erosion lowers the moraine surface and the boulders are gradually exposed to cosmic rays because the cosmic ray intensity changes with depth the boulders are subjected to variable production rates of the cosmogenic 36cl initial depth of boulders and their chemical composition are variable which results in different amounts of the accumulated cosmogenic 36cl and thus different apparent ages of boulders the shape of the resulting distribution of the apparent ages and the coefficient of variation depend on the erosion depth while the first moment is a function of the true surface age and the erosion depth these properties of the apparent age distributions permit calculation of the surface age the erosion depth and also the average erosion rate we tested the model calculations using 26 boulders from a late pleistocene moraine at bishop creek sierra nevada california the set exhibited a bimodal distribution of the 36cl surface exposure ages we interpreted the older mode as the result of gradual exposure and the younger one as the result of surficial processes other than soil removal the 10 samples that constitute the older mode produced a distribution which closely matches the modeled distribution calculated using an age of 85 kyr and erosion depth of 570 g cm 2 this age is the same as an independent estimate obtained from cation ratio studies and the calculated erosion depth is very close to the erosion depth of 600 g cm 2 based on a simple analytical model of soil erosion these results indicate that our statistical model adequately describes effects of soil erosion on accumulation of cosmogenic 36cl the approach can be used to simultaneously obtain the true landform age and the erosion rate from apparent 36cl ages and thereifore may help in evaluation of surface exposure ages of eroding landforms

paleosol organic matter and pedogenic carbonates and paleontological δ13c records applied to the paleoecology of late pleistocene holocene in mexico abstract stable isotopes of carbon 13 c in terrestrial geological materials paleosol humus and carbonates as well as fossil bones collagen and tooth enamel are established as highly specific records on paleoenvironmental characteristics it was assumed that comparing the results of different types of materials on regional or local scales provides more accurate and reliable reconstructions and even opens new aspects of interpretation this was tested by the comparison of the data obtained from the late pleistocene paleosols and or remains of pleistocene megafauna in various locations in northwestern mexico sonora paleosols formed in mis3 mis2 and mis1 central northern mexico san luis potosi teeth corresponding to mis2 and mis1 and central southern mexico puebla paleosols corresponding to mis3 and mis2 and teeth associated with these paleosols and state of mexico teeth corresponding to mis2 the results of isotopic studies are complemented with other paleoenvironmental proxies the 13 c values of paleosols of sonora is 19 8 to 16 95 in organic matter and shows little difference between paleosols and holocene soils 13 c values of pedogenic carbonates are 6 4 to 4 52 in san luis potosi the 13 c values of paleosol are 12 16 in organic matter in puebla they vary from 24 6 in paleosols to 15 16 in the modern surface soil pointing to contrasting vegetation change the 13 c values in fossils range from 10 7 to 1 2 in slp of 2 73 and 2 93 in puebla and 6 5 to 1 3 in state of mexico the 13 c values of paleosols and analysis of megafauna in northwest and central northern mexico matched each other indicating mixed c3 c4 vegetation while for central southern mexico paleosols indicated predominance of c3 plants and megafauna indicated mixed c3 c4 composition in general the results indicate that in northern mexico environmental conditions were slightly wetter than at present while for the central area there was a large change in the environmental conditions of high humidity in mis3 and mis2 with a trend to drier climates in mis1

wind induced salt wedge intrusion in the tiber river mouth rome central italy the wind effect on river water quality was illustrated by means of thermohaline measurements carried out in the tiber river in may 2012 the survey was carried out using a boat in stations located in the two tiber branches fiumara grande and traiano canal thermohaline variables salinity and temperature were used to describe the water type patterns and to define the salt wedge position although the river flow rate was rather high saltwater intrusion happened wind data suggested that the more probable cause of salt wedge intrusion was the wind action especially wind speeds higher than 4 m s are able to dominate the sea current at surface layers determining an increase in the sea level therefore westerly winds determined a seawater inflow in the river mouths

diurnal nonmigrating tidal oscillations forced by deep convective clouds the global distribution of latent heat released by the diurnal oscillations in deep convective precipitating clouds is investigated as a forcing mechanism of diurnal nonmigrating atmospheric tidal modes the seasonal distribution of this forcing is deduced from 3 hour temporal resolution infrared 11 m radiance measured by four geostationary and two polar orbiting satellites which was transformed into the zonal wavenumber domain yielding migrating and non migrating oscillations the dominant wavenumbers in the forcing include the westward propagating 5 2 and 1 oscillations the eastward propagating 3 oscillation and the standing oscillation these dominant wavenumber oscillations were decomposed into hough functions to describe their meridional structure a vertical profile of latent heating rate was estimated and the dominant 22 tidal modes were used in an f plane model to determine the middle atmospheric response to this tropospheric forcing the f plane model was also excited using heating rates associated with the solar insolation absorption by water vapor the magnitude of the model atmosphere diurnal winds from both water vapor and latent heat is similar at certain locations this response suggests that the superposition of many nonmigrating tidal modes forced by the latent heat release of precipitating clouds is important in understanding the middle atmospheric circulation

magnetic properties of lake sediments from lake chalco central mexico and their palaeoenvironmental implications lake chalco 99 0 w 19 5 n in the basin of mexico was formed during the pleistocene after the emplacement of the chichinautzin volcanic field that closed the former drainage system the lake sediment record has been influenced by a number of factors including glacial interglacial cycles local volcanism erosion of soils and anthropogenic disturbances the magnetic properties of the lake sediments and the associated tephra layers of the last 16500 yr have been studied it is found that the magnetic properties of the lake chalco sediments are very distinctive magnetic concentration varies by a factor of 1000 and magnetic stability also varies over an extremely wide range the predominant magnetic mineral is titanomagnetite in addition to an imperfect antiferromagnetic phase possibly goethite an unusually large range of coercivities is found in certain of the tephras down core variations in magnetic properties closely follow climatic environmental changes previously established by other proxy methods the late pleistocene and late holocene lake sediments display a higher concentration of magnetic minerals than the early middle holocene sediments in the non volcanic sediments fluctuations in the magnetic concentration reflect changes in both the intensity of erosion as represented by ferrimagnetic and paramagnetic minerals and by the maturing of soils as represented by geothite copyright 2000 john wiley sons ltd

reconstruction of late pleistocene climate in the valsequillo basin central mexico through isotopic analysis of terrestrial and freshwater snails we aim to reconstruct the climatic and environmental conditions in the valsequillo basin during the deposition of the valsequillo gravels between c 40 000 and 8000 years ago when large mega fauna and potentially humans occupied the basin fossil freshwater fossaria sp and sphaeriidae family and terrestrial polygyra couloni holospira sp and cerionidae family snail shells from sections within the barranca caulapan were collected for oxygen and carbon stable isotope analysis oxygen and carbon isotopes in terrestrial and freshwater snail shells relate to local climatic parameters and environmental conditions prevailing during the lifetime of the snail whole shell isotope analysis showed that c 35 000 years ago climate in the valsequillo basin was similar to the present day between c 35 000 and 20 000 bp conditions became increasingly dry after which conditions became wetter again although this record is truncated intra shell isotopic analyses show that the amount of precipitation varied seasonally during the late pleistocene if people did reach this part of the americas in the late pleistocene they would have experienced changing long term and seasonal climatic conditions and would have had to adapt their life strategies accordingly

monthly tidal temperatures 20 120 km from timed saber 1 the saber instrument on the timed satellite provides unprecedented geographical coverage for the determination and study of atmospheric tides however the slow local time precession rate of timed can cause longer term temperature variations to alias into the tidal signals a new method of analyzing satellite data for tides has been developed to circumvent this difficulty but at the expense of temporal resolution of the tidal fields i e 120 day mean tidal structures are obtained in this work we apply this method to saber temperature data to derive a series of 120 day mean tidal structures extending between 20 and 120 km altitude 50 s 50 n latitude and centered on each month from september 2003 to september 2004 in addition to the migrating sun synchronous diurnal and semidiurnal tides a number of nonmigrating tides are revealed in the saber measurements some of these waves are thought to originate via nonlinear coupling between the migrating tides and the stationary planetary wave with zonal wave number s 1 other nonmigrating tidal components appear to be forced by latent heating due to deep tropical convection of the latter the eastward propagating diurnal tide with s 3 is dominant and is as large as the migrating diurnal tide during some months of particular interest is the wave 4 structure with respect to longitude that characterizes both the diurnal and semidiurnal total tidal fields this feature is a result of the predominant wave 4 topography land sea longitude dependence at the surface which is reflected in the diurnal and semidiurnal components of the latent heating rates due to deep tropical convection the ability of the global scale wave model gswm to approximate the observed tidal fields including the wave 4 total tidal structures is also assessed

late quaternary lacustrine paleoenvironments in the cuenca de mexico abstract a late quaternary paleolimnological history from the mexican highlands has been obtained by diatom analysis of short cores and stratigraphic sections of lake and marsh sediments from the cuenca de mexico the large endorheic graben basin that holds mexico city the records dated by radiocarbon and tephrochronologic methods extend back to about 30 ka bp and document the presence of extensive saline lakes in the basin until 25 ka bp thereafter lake levels fell and marginal sites became shallow and fresh under the influence of surficial drainage and especially spring discharge a shallow saline lake existed 18 ka bp in texcoco the central and lowest basin in the system reflecting moderately increased effective moisture at that time by 16 ka bp lake texcoco had become so shallow that diatoms were no longer preserved however marginal sites nourished by spring flow recorded changes in the local hydrologic balance resulting from increased infiltration at higher elevations these changes appear to coincide with glacial advances between about 14 and 10 ka bp on the volcanic mountains surrounding the basin dry climates with reduced infiltration characterized the early holocene but by 5 ka bp a modest increase in precipitation established the modern climatic regime these lacustrine records offer important insights for evaluating the paleoenvironmental history of the cuenca de mexico based on other evidence they confirm glaciological stratigraphic and palynologic data that suggest dry climates and the absence of large pluvial lakes in the cuenca de mexico during and after the full glacial but document climates of significantly increased precipitation at least 10 ka prior to 18 ka bp

the diurnal cycle of tropical convection the diurnal cycle of tropical convection is investigated with global cloud imagery constructed from 11 m radiance measurements taken aboard six satellites four harmonics of the diurnal cycle are resolved in the cloud imagery with about 50 km horizontal resolution to isolate deep convective activity from other processes which cause diurnal fluctuations in longwave radiance an index of deep convective activity is constructed by thresholding to brightness temperatures less than 230 k significant diurnal amplitude of deep convection is found only over tropical landmasses over the tropical oceans the diurnal cycle is weak and is barely discernible from the background red spectrum of convective variance nonetheless oceanic convection exhibits a systematic diurnal fluctuation with maximum intensity in the early morning nocturnal subsidence along the cloud free equator is postulated to play a role in forcing diurnal variation in the intertropical convergence zones other mechanisms are also implied to contribute as a similar early morning maximum in deep convection is seen even where no adjoining cloud free regions occur the diurnal cycle of deep convection is found to be organized on planetary scales predominantly in nonmigrating modes i e modes with phase speeds not equal to that of the sun the nonmigrating modes are postulated to be produced by the nonuniform distribution of convective centers the nonmigrating zonally symmetric component is found to be especially large while the role of this mode in forcing diurnal variations of the tropospheric circulation e g the hadley cell is questionable its role in modulating the ionospheric electric potential is well established discrepancies with the traditional notion that cloud to ground lightning is the dominant mechanism by which the earth is negatively charged are discussed in particular the probable role of nonlightning producing clouds e g the stratiform portion of convective complexes in diurnally modulating the negative charge on earth is discussed

tephrochronology of the toluca basin central mexico abstract the major element glass geochemistry of 10 late pleistocene and holocene tephras found in the toluca basin in the trans mexican volcanic belt is reported for the first time as a key step towards establishing a tephrochronology for the region the context for this tephrochronology is provided by a review of late quaternary volcanism of the basin new tephra samples were collected from reference profiles around the basin in order to establish major element glass geochemical data for tephras described in previous publications but not previously analysed in addition cores were taken from the basin floor to extend the known spatial distribution of the tephra layers and establish correlations with the lacustrine record improved chronological control has been provided by seven new ams and conventional radiocarbon dates on the major tephras geochemical data are presented for 10 tephras ranging in age from ca 25 000 bp lower toluca pumice to about 8500 bp tres cruces tephra based on geochemical data it is possible to correlate between sites within the toluca basin and between the toluca basin and the basin of mexico the basis for a tephrochronological framework has been established

a high elevation holocene pollen record from iztaccihuatl volcano central mexico pollen data from 3860 m in the agua el marrano valley on the northwest side of iztaccihuatl volcano southeastern part of the basin of mexico 198n combined with data on the glacial chronology and tephrochronology document holocene climatic and vegetation changes near the present timberline glacial advances occurred between 12 000 and 10 500 cal yr bp milpulco 1 and between 8300 and 7300 cal yr bp milpulco 2 a 450 cm core was drilled in sediments accumulated in a milpulco 1 moraine depression the sequence covers the last 11 000 cal yr bp according to three 14 c dates and the presence of a distinctive pumice deposit dated elsewhere at 5700 cal yr bp the pollen record of agua el marrano shows barren conditions after glacier retreat followed by a gradual colonization by elements of the alpine grasslands around 10 900 cal yr bp this plant community remained until c 7200 cal yr bp between c 7200 cal yr bp and 6500 cal yr bp coniferous forest grew close to or at the site but alpine grasslands were re established between 6500 cal yr bp and c 5000 cal yr bp apparently in connection with mid holocene dry conditions recorded in central mexico the upper timberline attained its modern altitude 4000 m in the last 3000 years during this period no significant changes are observed in the pollen spectra comparison with other palaeoecological records from central mexico suggests that the timberline fluctuated in response to both temperature and precipitation changes during the holocene

tepexpan palaeoindian site basin of mexico multi proxy evidence for environmental change during the late pleistocene late holocene the tepexpan palaeoindian skeleton was discovered in 1947 close to the former lake texcoco margin in the basin of mexico the find has been the object of considerable interest and discussion over the last 60 years regarding its real age and archaeological interpretation here we report new ams radiocarbon dates associated with the sedimentary succession at tepexpan with ages between 19 110 90 and 612 22 14c years bp and a new uranium series date for the skeleton with an age of 4700 200 years bp that indicates a mid holocene age the sedimentary succession was studied in detail using stable isotopes diatoms organic geochemistry and tephrochronology the multi proxy evidence suggests large changes around the margins of lake texcoco in terms of the balance between aquatic and terrestrial plants c3 and c4 plants saline alkaline and freshwater conditions volcanic activity marginal reworking of lake sediments and input from the drainage basin through the late pleistocene late holocene these changes had large impacts on the prehistoric human populations living by the lake shores since the late pleistocene in the basin of mexico

paleosols bones phytoliths and δ13c signatures of humus and teeth in the alluvial sequence of axamilpa puebla inferences for landscape evolution and megafauna paleoecology during mis 3 2 in southern mexico abstract alluvial paleosol sedimentary sequences containing animal fossils and paleobotanical and paleopedological archives have a potential for reconstructing quaternary paleoenvironments in southern mexico and for understanding the paleoecology of pleistocene megafauna in the section of axamilpa river four pedostratigraphic units were recognized the lower gleyic and vertic pedological units are at the end of marine isotopic stage mis 3 while the upper humic and most probably calcic units correspond to mis 2 according to the radiocarbon dates of humus the micromorphological analysis indicates an incipient development and syn sedimentary character of paleopedogenesis in the periodically water saturated environment indicated by redoximorphic features hydrogenic carbonates and low values of magnetic susceptibility in most strata the 13 c values of the paleosol humus range from 22 6 to 24 7 indicating a c3 vegetation whereas in the modern soil it is higher 15 2 pointing to an abundance of the c4 and cam plants the 13 c signature of the vegetation inferred from the teeth enamel of the fossil fauna appeared to be less negative than that of humus from corresponding paleosols the alimentary preferences of the paleofauna which fed on grasses with high proportion of c4 plants explain this difference the phytolith analysis shows dominance in conifer forms followed by c4 and c3 grasses the content of conifer phytoliths is progressively reduced towards the top of the sequence we interpret the late pleistocene landscape of this area as a heterogeneous forest grassland landscape with the forest shrinking through time and the grass areas increasing swampy floodplain meadows inferred from paleopedological results could provide a habitat for grassy vegetation both isotope and phytolith records demonstrate a contrasting difference between pleistocene and recent vegetation dominated by xerophytic shrubs and succulents this vegetation change could play important role in the extinction of pleistocene megafauna

palynological and magnetic susceptibility records of lake chalco central mexico abstract pollen and magnetic susceptibility data from a 11 27 m long core drilled in the central part of lake chalco 99 00 w 19 15 n located at the southeastern part of the basin of mexico are interpreted in terms of paleoenvironmental changes the record of this subtropical highland lake dated by radiocarbon methods spans approximately 24 000 yr b p and documents changes in climate vegetation lake level and volcanic activity seven palynozones were established by using the method of cluster analysis for correlation purposes zones 7 6 and 5 between 20 600 and 18 300 yr b p indicate reduced forests with extensive grasslands relatively high input of sediments by water discharge of surface streams and high lake level the evidences obtained in zone 4 between 18 300 and 17 500 yr b p suggest a dry and warm climate with xerophytic vegetation lower lake level and erosion rates zone 3 between 17 500 and 10 000 yr b p shows a trend to increasing moisture and cooler temperatures volcanic activity during this period is intense and strongly influences the natural environments at around 12 000 yr b p a clear expansion of forests and fulfillment of the lake recorded at the beginning of the holocene an oak forest expansion and a lowering of lake levels are initiated and by the mid holocene zone 2 subhumid temperate conditions are detected although lake level continues to be low the human impact is recorded in the last 4000 yr

the comparative importance of de3 se2 and spw4 on the generation of wavenumber 4 longitude structures in the low latitude ionosphere during september equinox 1 numerical simulations are performed to investigate the generation of the wave 4 longitude variation in the low latitude ionosphere due to the diurnal eastward propagating nonmigrating tide with zonal wavenumber 3 de3 semidiurnal eastward propagating nonmigrating tide with zonal wavenumber 2 se2 and stationary planetary wave 4 spw4 from a fixed local time perspective the de3 se2 and spw4 all appear as wave 4 structures in longitude and thus each of these waves must be considered as a potential source of the wave 4 variation in the ionosphere both thede3 and spw4 are found to produce significant wave 4 variations in the equatorial verticale bdrift velocity and in the ionospheric peak density nmf2 at 15 n magnetic latitude the daytime wave 4 variation in nmf2 is driven by the combination of verticale bdrift variability and in situ effects due largely to meridional neutral winds the simulation results indicate that these2 is not a contributor to the wave 4 longitude variation our results further demonstrate that the actual wave 4 longitude variation is due to a combination of thede3 and spw4 we therefore conclude that in addition to the de3 the spw4 also needs to be considered as an important driver of the wave 4 longitude variation in the low latitude ionosphere we additionally present evidence for the generation of thespw4 due to the nonlinear interaction between the migrating diurnal tide and the de3 and demonstrate the impact of de3 variability on the amplitude of the spw4

climatic variability over the last 30 000 years recorded in la piscina de yuriria a central mexican crater lake the trans mexican volcanic belt provides an excellent setting for reconstruction of late quaternary climate from different natural archives moreover human impact on the landscape since the mid holocene provides a good opportunity to investigate the complex interplay of natural and anthropogenic forcing of landscape change however despite the wealth of records understanding of the environmental history of the region and its wider significance for climate change across the northern neotropics remains incomplete we present a radiocarbon dated multiple proxy sedimentology sedimentary geochemistry ostracods diatoms stable isotopes record of climatic and environmental change based on the lacustrine sediments from la piscina de yuriria a hydrologically closed volcanic crater in the northern tmvb much of the last glacial interval was characterised by low effective moisture associated with a weakened north american monsoon nam although the interval from 30 000 to 27 500 abp experienced abrupt changes in rainfall the period corresponding to the late glacial stadial was also dry and the lake may have dried out at this time there was a change to wetter but variable conditions during the early holocene as the nam strengthened progressive drying during the later holocene was accompanied by phases of catchment disturbance which were partly the result of human impact

paleoecological studies at lake patzcuaro on the west central mexican plateau and at chalco in the basin of mexico abstract a 1520 cm sediment core from lake patzcuaro michoacan mexico is 44 000 yr old at the base all parts of the core have abundant pollen of pinus pine alnus alder and quercus oak with frequent abies fir the interval dated from 44 000 to 11 000 yr ago has a homogeneous flora characterized by abundant juniperus juniper pollen and frequent artemisia sagebrush it is believed to represent an appreciably drier and colder climate than at present the holocene at lake patzcuaro is characterized by a moderate increase in pinus pollen and the loss of juniperus pollen as the modern type of climate succeeded alnus was abundant until about 5000 yr ago its abrupt decrease with the first appearance of herbaceous weed pollen may reflect the cutting of lake shore and stream course alder communities for agricultural purposes or it may simply reflect a drying tendency in the climate pollen of zea corn appears at lake patzcuaro along with low peaks of chenopod and grass pollen at 3500 yr b p apparently recording a human population large enough to modify the natural environment as well as the beginning of agriculture a rich aquatic flora in this phase suggests eutrophication of the lake by slope erosion in the most recent period corn is absent from the sediments perhaps reflecting a change in agricultural practices the environment changes at lake patzcuaro are similar to and correlate with those in the cuenca de mexico where diatom stratigraphy from the chalco basin indicates fluctuations in lake levels and lake chemistry in response to variations in available moisture before 10 000 yr ago climates there were cool and dry and the chalco basin was occupied by a shallow freshwater marsh that drained north to lake texcoco where saline water accumulated by evaporation increases in effective moisture and possible melting of glaciers during the holocene caused lake levels to rise throughout the cuenca de mexico and lake texcoco flooded the chalco basin with brackish water after 5000 yr ago such flooding decreased and shallow freshwater ponds and marshes were restored in the chalco basin this environmental change coincides with the appearance of zea pollen and suggests cultural control of lake levels and salinity

spatial variability of environment change in the teotihuacan valley during the late quaternary paleopedological inferences the teotihuacan valley mexico has been the object of considerable interest because of its importance in the context of human history in america although archeological research has been extensively conducted to understand causes of the decline of teotihuacan culture no sufficient scientific evidence has been provided this paper is focused on paleopedological evidence especially properties that constitute soil memory in order to reconstruct the spatial distribution of environment variability during the late pleistocene and holocene three profiles that include modern soils and buried paleosols were studied in different geomorphic positions uplands cerro gordo site cg lower talus slope transition to valley bottom maseca ma and the mouth of the valley at the ancient border of the former texcoco lake this last site is near tepexpan te where some of the oldest human remains in mexico were recovered the oldest paleosol is at cg at 3000 m a s l it is dated at 22 000 yr bp and exhibits a truncated profile with a very well developed bt horizon dominated by kaolinite with phytoliths of c3 plants all of its features are related to a humid probably warm environment it was classified as a luvisol this paleosol is buried by another luvisol dated at 13 000 yr bp with morphological characteristics similar to the previous soil although clay mineralogy consists mostly of halloysite and a higher percentage of c4 plant phytoliths is apparent in ma the oldest paleosol was not recognized it is probable that the two paleosols found in cg merge into one at ma which shows strong redoximorphic features but high percentages of c4 plant phytoliths and halloysitic clays at the te site paleosols are less developed fluvisols modern soil cover also varies in relation to its geomorphic position in cg it is a phaeozem while in ma and te present day soils have carbonate accumulation we interpret prevailing conditions during the last glacial maximum in the teotihuacan valley to be humid with a tendency towards drying at the end of pleistocene dry conditions prevail in the valley today

longitudinal structure of the equatorial anomaly in the nighttime ionosphere observed by image fuv 1 the far ultraviolet imager fuv on board the image satellite provides an instantaneous global view of the oi 135 6 nm nightglow with 2 min time resolution because the oi 135 6 nm emission from the nighttime ionosphere is determined by the line of sight integrated plasma density the nightglow images are useful for studying the nighttime low latitude ionosphere globally with the image fuv 135 6 nm observations from march to june 2002 we have examined the global characteristics of the nighttime equatorial anomaly ea by constructing a constant local time map lt map in which pixels within an assigned local time range are extracted from the image fuv nightglow images obtained over an observation period of 3 days or more and are put together to compose a global distribution map of emission intensities at that local time these lt maps show that the development of the ea has a significant longitudinal structure in which peaks and dips of the crest emission intensity and the crest latitude have about 90 longitudinal separation in the longitude range from 0 to 250 although there is not enough data over the american sector this result suggests that the ea longitudinal structure has a prominent zonal component of the wave number 4 the observed longitudinal structure of the nighttime ea could not be fully explained by factors such as the empirical electric field and neutral wind models the geomagnetic declination angle or the displacement of the geomagnetic equator from the geographic equator to explain the observed longitudinal structure of the ea in particular the wave number 4 feature we may need to consider other forcing for example nonmigrating tide originated from the lower atmosphere

quantitative estimates of orbital and millennial scale climatic variability in central mexico during the last 40 000 years abstract diatom based transfer functions for salinity precipitation and temperature were developed using a training set that included data from 40 sites along central mexico these transfer functions showed good performance parameters and were subsequently applied to the previously published diatom record from lake chalco southern basin of mexico heinrich stadials hs 3 to hs 0 were reconstructed as cold and dry events with hs 2 representing the coldest and driest conditions while hs 1 shows a complex bimodal cooling pattern orbital scale variability is also recorded high and variable lake salinities from 34 to 29 ka bp marine isotope stage 3 mis 3 corresponded with times of maximum summer insolation and evidences of frequent fires mis 2 was identified as a cold period with low lake salinity associated with low evaporation with two cold intervals during the minima in spring 25 5 ka bp and summer 20 ka bp insolation the 20 ka bp cold event together with hs 2 24 23 ka bp defined a bimodal maximum cooling during the last glacial maximum lgm 24 5 19 5 ka bp within the range of pollen based estimates further supporting a maximum tropical cooling of 4 5 c for the lgm the deglacial 19 5 11 5 ka bp showed the highest precipitation anomalies with three peaks that closely correlated with glacier advances in the nearby mountains iztaccihuatl the early holocene marked a change towards high lake salinities and the highest positive temperature anomalies 3 5 c during a peak in summer insolation even though at orbital scale chalco showed a nearly opposite trend to the record from the more southerly lake peten itza guatemala at millennial scale it showed a common pattern of cold and dry conditions during hss comparable to other tropical latitude sites in the northern hemisphere and further supporting the idea that there is a strong coupling between tropical and higher latitudes climates in particular with the north atlantic

a 6 000 year record of environmental change from the eastern pacific margin of central mexico abstract the transition from the mid to late holocene in mesoamerica saw increasing complexity in spatial patterns of change records from the western part of the region are sparse with lacustrine sequences affected by long term anthropogenic disturbance or lacking chronological resolution here we present a continuous palaeoecological and geochemical record from laguna de juanacatlan a remote lake in the mountains of the western tmvb diatom assemblages xrf scanning data and bulk organic geochemistry from a well dated 7 25 m laminated sequence were combined with summary pollen data from a 9 m partially laminated core to provide a continuous record of catchment and lake ecosystem changes over the last c 6000 years relatively humid conditions prevailed prior to c 5 1 cal ka which supported dense oak pine forest cover around a deep stratified lake a trend towards drier conditions began c 5 1 cal ka intensifying after 4 0 cal ka consistent with weakening of the north american monsoon between 3 0 and 1 2 cal ka lower lake levels and variable catchment run off are consistent with increasing enso influence observed in the late holocene in the neotropics from 1 2 to 0 9 cal ka a marked change to catchment stability and more intense stratification reflected drier conditions and or reduced rainfall variability and possibly warmer temperatures after 0 9 cal ka conditions were wetter with an increase in catchment disturbance associated with the combined effects of climate and human activity in recent decades the lake ecosystem has changed markedly possibly in response to recent climate change as well as local catchment dynamics

mineral and organic components of the buried paleosols of the nevado de toluca central mexico as indicators of paleoenvironments and soil evolution abstract results of earlier studies of quaternary tephra paleosol sequences in central mexico revealed contradictions between paleopedological and lacustrine records to settle the contradictions selected quantitative characteristics of mineral and organic components of the paleosols pt1 pt7 from the nevado de toluca sequence were studied as independent paleoclimate proxies mineralogical composition of sand and clay fractions allows assessment of weathering and secondary mineral formation both being climate dependent processes stable carbon isotope ratios of humus and phytolith morphology indicate paleovegetation in all paleosols the sand fractions consist mainly of unstable volcanogenic minerals although the grains have weathering features short durations of pedogenesis are responsible for limited weathering status the clay fraction is dominated by halloysite and dehydrated halloysite in units pt1 pt4 which suggests drier periods during paleosol formation whereas major amounts of kaolinite in the units pt5 pt7 indicate extended humid pedogenesis 13c values of pt2 pt4 humus are intermediate between those characteristic of c3 and c4 plants phytolith assemblages which include both forms of c3 dominant and c4 minor quantities grasses agree with carbon isotope data these data indicate plant cover changes driven by wet dry paleoclimate oscillations the new results showing drier stages during the formation of late pleistocene paleosols pt2 and pt3 correct the primary interpretation of these units as indicating only humid pedogenesis and settles the contradiction between paleopedological and lacustrine records

longitudinal structure of the equatorial ionosphere time evolution of the four peaked eia structure 1 longitudinal structure of the equatorial ionosphere during the 24 h local time period is observed by the formosat 3 cosmic f3 c satellite constellation by binning the f3 c radio occultation observations during september and october 2006 global ionospheric total electron content tec maps at a constant local time map local time tec map referred as lt map can be obtained to monitor the development and subsidence of the four peaked longitudinal structure of the equatorial ionosphere from lt maps the four peaked structure starts to develop at 0800 1000 lt and becomes most prominent at 1200 1600 lt the longitudinal structure starts to subside after 2200 2400 lt and becomes indiscernible after 0400 0600 lt in addition to tec ionospheric peak altitude also shows a four peaked longitudinal structure with variation very similar to tec during daytime the four peaked structure of the ionospheric peak altitude is indiscernible at night with global local time maps of ionospheric tec and peak altitude we compare temporal variations of the longitudinal structure with variations of e b drift from the empirical model our results indicate that the observations are consistent with the hypothesis that the four peaked longitudinal structure is caused by the equatorial plasma fountain modulated by the e3 nonmigrating tide additionally the four maximum regions show a tendency of moving eastward with propagation velocity of several 10 s m s

geochemical and microbiological zonation of the middendorf aquifer south carolina we consider the nature and origin of the chemical and microbiological zonation of the cretaceous middendorf aquifer in the coastal plain of south carolina in light of the chemical evolution of groundwater along a flow path there some types of microbial activity most notably aerobic respiration and iron reduction lead to a net generation of acid as co2 but reaction of groundwater with minerals in the aquifer consumes the acid driving up ph and controlling the evolution of the groundwater s major ion chemistry the thermodynamic energy available to the various functional groups of microbes except the autotrophic hydrogen oxidizing methanogens is everywhere along the flow path sufficient to drive microbial growth the concentrations of acetate formate and lactate do not vary systematically from zone to zone along the flow path as might be expected if each zone were dominated by a single functional group of microbes the overall rate of microbial respiration in the aquifer appears to be limited by the rate of the initial fermentation of organic matter we found no compelling evidence indicating that one functional group of microbes excludes others from any of the aquifer s zones sulfate reduction for example may be non existent in the high iron zone associated with iron reduction or may account for up to 90 of the respiration occurring there zonation of the groundwater into high iron and low iron facies may result from a minor change along the aquifer in the balance between the activities of iron and sulfate reducers

some problems in the late quaternary pollen records of central mexico basins of mexico and zacapu most pollen analyses of late quaternary sediments have been carried out in closed basins of the trans mexican neovolcanic belt in central mexico climatic changes have been inferred from these pollen data however some problems arise from reinvestigations the dominance of a few pollen types in general pinus quercus and alnus is almost constant among these records in spite of the importance of vulcanism and tectonism in the evolution of this region no effects of these factors are evident from the pollen records some of the problems are illustrated in the pollen records from lake texcoco and lake chalco in the basin of mexico and lake zacapu in michoacan

a reevaluation of cosmogenic 36cl production rates in terrestrial rocks we have measured 36cl in a suite of 33 rock samples having well constrained exposure histories and ages the 36cl production parameters were estimated by minimizing the squared deviations between the 36cl and independent ages yielding the following production parameters spallation and muon production from ca 2940 200 atoms 36cl mole ca 1 yr 1 spallation from k 6020 400 atoms 36cl mole k 1 yr 1 and neutron production in air 586 40 fast neutrons g air 1 yr 1 the new production constants for spallation on ca and thermal neutron activation are in good agreement with previous results but that for spallation on k is about 50 larger the past decade has seen a rapid growth in the application of terrestrial cosmogenic nuclides produced by cosmic ray particles within rocks at the earth surface nuclear cross sections particularly for reactions initiated by neutrons and muons are not known with sufficient accuracy so production rates for these nuclides must be empirically calibrated using independently dated geological samples direct production estimates for 36cl were first obtained by zreda et al 1991 who measured 36c1 in mineral separates from granitic boulders on moraine crests at chiatovitch creek in the eastern white mountains of california and nevada this data set was the best available at the time but since then several factors have prompted a reevaluation of the 36cl production rates one is that zreda et al 1994 have shown that there can be significant scatter of the cosmogenic ages of individual glacial boulders toward ages younger than that of the moraine due to soil erosion a second factor is that a much wider range of samples is now available for this purpose finally recent theoretical advances in calculating production by thermal neutron absorption liu et al 1994 now permit more realistic calibration of this reaction

geochemical characterization of late pleistocene and holocene tephra layers from the basin of mexico central mexico in order to aid palaeoenvironmental research of late pleistocene and holocene deposits of central mexico tephra layers collected from the sediments of the texcoco and chalco sub basins in the southern part of the basin of mexico are geochemically characterized and used as stratigraphic markers the tephra layers range in composition from basaltic andesites to rhyolites and are calc alkaline the tephras range in age from 34 000 to ca 260014c yr b p new names are used informally to designate correlated tephras the tlahuac tephra is present in chalco at a depth of 18 m in the southeastern part of texcoco at a depth of around 10 m and at the tlapacoya archaeological site where it had been mistakenly described as basaltic this basalt andesite tephra is dated to at least 34 00014c yr b p the tlapacoya 1 tephra is dated to between 15 020 450 and 14 430 190 yr b p and is present in all chalco sections the tlapacoya 2 tephra corresponds to the previously described pomez gruesa con fragmentos de andesita ca 14 400 yr b p and is present in all chalco and texcoco sections the likely source of these three tephras is the volcano popocatepetl tephra ii at chalco dates to 12 520 135 yr b p and correlates with the upper toluca pumice from nevado de toluca volcano these represent the first geochemical glass shard analysis of tephras from the basin of mexico and so further research is necessary before a reliable tephrochronology can be established

23 000 yr of vegetation history of the upper lerma a tropical high altitude basin in central mexico abstract pollen analysis on a 9 54 m sediment core from lake chignahuapan in the upper lerma basin the highest intermontane basin in central mexico 2570 m asl documents vegetation and limnological changes over the past 23 000 14c yr the core was drilled near the archaeological site of santa cruz atizapan a site with a long history of human occupation abandoned at the end of the epiclassic period ca 900 ad six radiocarbon ams dates and two well dated volcanic events the upper toluca pumice with an age of 11 600 14c yr b p and the tres cruces tephra of 8500 14c yr b p provide the chronological framework for the lacustrine sequence from ca 23 000 14c yr b p to ca 11 600 14c yr b p the plant communities were woodlands and grasslands based on the pollen data the glacial advances mii 1 and mii 2 correlate with abundant non arboreal pollen mainly grasses from ca 21 000 to 16 000 14c yr b p and at ca 12 600 14c yr b p during the late pleistocene lake chignahuapan was a shallow freshwater lake with a phase of lower level between 19 000 and 16 000 14c yr b p after 10 000 14c yr b p tree cover in the area increased and a more variable lake level is documented late holocene ca 3100 14c yr b p deforestation was concurrent with human population expansion at the beginning of the formative period 1500 b c agriculture and manipulation of the lacustrine environment by human lakeshore populations appear at 1200 14c yr b p 550 a d with the appearance of zea mays pollen and abundant charcoal particles

hydrogeochemical investigations and groundwater provinces of the friuli venezia giulia plain aquifers northeastern italy water resources are a key factor particularly for the planning of the sustainable regional development of agriculture as well as for socio economic development in general a hydrochemical investigation was conducted in the friuli venezia giulia aquifer systems to identify groundwater evolution recharge and extent of pollution temperature ph electric conductivity total dissolved solids alkalinity total hardness sar ca2 na k mg2 cl so42 no3 hco3 water quality and type saturation indexes and the environmental stable isotope 18o were determined in 149 sampling stations the pattern of geochemical and oxygen stable isotope variations suggests that the sub surface groundwater from phreatic and shallow confined aquifers is being recharged by modern precipitations and local river infiltrations four hydrogeological provinces have been recognised and mapped in the friuli venezia giulia plain having similar geochemical signatures these provinces have different degrees of vulnerability to contamination the deep confined groundwater samples are significantly less impacted by surface activities and it appears that these important water resources have very low recharge rates and would therefore be severely impacted by overabstraction