a large landslide on the urban fringe of metropolitan phoenix arizona a granitic rock avalanche one of the largest quaternary landslides in arizona outside the grand canyon with a volume of approximately 5 25 m m 3 and a width a little under 0 5 km ran 1 km from the eastern mcdowell mountains with lateral levees and pressure ridges the rock avalanche deposit displays many features found on classic sturzstroms failure occurred along a major joint plane paralleling the slope with a dip of 448 when a major base level lowering event in the salt river system would have undermined the base of the failed slope and probably during a period of more moisture than normally available in the present day arid climate failure at the subsurface weathering front highlights the importance of the dramatic permeability change between grussified regolith and relatively fresh bedrock rock varnish microlaminations vmls dating in concert with other geomorphic evidence suggests that the rock avalanche deposit is slightly older than 500 ka the rock vanish results also have important implications for sampling strategies designed to use cosmogenic nuclide to date quaternary landslide deposits discovery of a large landslide in close proximity to the extending urban fringe of metropolitan phoenix argues for a more careful analysis of landslide hazards in the region especially where rapid development excavates bedrock at the base of steep mountain slopes and where the subsurface weathering front is near the surface d 2004 elsevier b v all rights reserved

isotopic and geochemical evidence of palaeoclimate changes in salton basin california during the past 20 kyr 1 δ18o and δ13c records in lake tufa deposits abstract investigation of 18 o and salt content of surface waters in the salton basin california shows that there is a strongly positive correlation between 18 o values and salt contents and that the 18 o of salton sea is much heavier than that of its input waters due to strong evaporation using a steady state 18 o model we have discussed the 18 o of lake cahuilla an ancient lake in the basin under through flowed closed and overflowed situations an ams 14 c dated stable isotope record of a 60 cm lake tufa slice lc 1 from the ancient shoreline of lake cahuilla indicates that the lake experienced closed and or overflowed conditions between 1 300 and 20 500 yr bp the variations in 18 o and 13 c values of lc 1 ranging from 8 52 to 2 50 pdb and from 0 8 to 3 76 respectively reflect changes in the relative humidity in salton basin and variations in the colorado river inflow and hence climatic conditions in the colorado river drainage basin the tufa record exhibits palaeoclimates of salton basin as follows 1 relatively dry climate between 20 and 18 kyr bp was followed by a wet climate between 18 and 17 kyr bp 2 decreasing effective moisture precipitation evaporation from 17 to 16 kyr bp corresponded to heinrich 1 event whereas effective moisture increased at ca 15 5 kyr bp during the trans us wet period contrasting patterns between the lc 1 record and the greenland ice core and chinese speleothem records during the bolling allerod interstadial from 15 2 to 11 7 kyr bp may be caused by age uncertainty of the lc 1 record further study of this interval is needed 3 wet warm early holocene corresponding to the maximum effective moisture period perhaps brought about by the strengthening of north american monsoon 4 toward 2 kyr bp the climate became dryer apparently resulting from weakening of the monsoons especially around 6 2 and 2 5 kyr bp 5 a wet regime occurred in the basin during the medieval warm period

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

curiosity at gale crater mars characterization and analysis of the rocknest sand shadow the rocknest aeolian deposit is similar to aeolian features analyzed by the mars exploration rovers mers spirit and opportunity the fraction of sand 150 micrometers in size contains 55 crystalline material consistent with a basaltic heritage and 45 x ray amorphous material the amorphous component of rocknest is iron rich and silicon poor and is the host of the volatiles water oxygen sulfur dioxide carbon dioxide and chlorine detected by the sample analysis at mars instrument and of the fine grained nanophase oxide component first described from basaltic soils analyzed by mers the similarity between soils and aeolian materials analyzed at gusev crater meridiani planum and gale crater implies locally sourced globally similar basaltic materials or globally and regionally sourced basaltic components deposited locally at all three locations

spatial variability of late pleistocene early holocene soil formation and its relation to early human paleoecology in northwest mexico abstract in sonora northwest mexico we have recognized the existence of paleosol units of late pleistocene early and middle holocene age 13 000 to 4 250 cal years bp at several archaeological sites with paleo indian occupations e g la playa fin del mundo el bajio el aigame and el arenoso the few paleoenviromental reconstructions from the region indicate that the end of the pleistocene was dominated by temperate climate that promoted the establishment of the first people in coexistence and interaction with the pleistocene megafauna the study of the spatial distribution of various soil units developed during late pleistocene in the region provides information about local environmental settings of the initial peopling of sonora several pedosedimentary sequences were analyzed in the different parts of sonora the age control in which was provided by archaeological and paleontological findings and or by the radiocarbon dating of carbonates and paleosol humus two trends of the late pleistocene pedogenesis have been identified the profiles located in the south center and north of the state are dominated by red soils earlier referred as big red in the archaeological literature whose characteristics are represented by the red san rafael paleosol srp the properties of srp in the lower part of the profile rubification clay accumulation hig magnetic susceptibility illuvial carbonates and redoximorphic features are indicative of a more humid environment above them is a late holocene polycyclic sequence of soils with morphological characteristics displaying a more incipient development in contrast with the sequence described above el arenoso north of caborca show a sequence of gray soils two paleosols were formed in alluvial sediments at the cantera profile ctp and el arenoso profile arp paleosols are represented by bgk horizons and evidence of weathering and clay neoformation redoximorphic processes and illuvial accumulation of carbonates we explain the differences of north western profiles by specific geomorphic conditions which imply limited soil drainage and the possibility of over wetting these processes indicate alternating a humid environment weathering rubification clay formation and redoximorphic processes and dry periods carbonates accumulation despite regional differences of the late pleistocene paleosols the comparison with the holocene soils demonstrates clear trends towards desertification in the region the first people that inhabited sonora during the late pleistocene found a more temperate and wetter climate than they encountered further to the north but subsequent generations witnessed a rapid desiccation of the region with the formation of the sonoran desert in the early holocene

a 22 000 year record of vegetation change in the north central sonoran desert abstract plant macrofossils from eleven packrat neotoma sp middens provide a history of vegetation change over the last 22 140 years at eagle eye mountain near the northern border of the sonoran desert in arizona this site is located in the arizona upland subdivision departures and arrivals of various perennial plant species during the holocene were similar to other records from more southerly sites and support earlier generalizations of van devender van devender t r 1990 late quaternary vegetation and climate of the sonoran desert united states and mexico in betancourt j l van devender t r martin p s eds packrat middens the last 40 000 years of biotic change university of arizona press tucson pp 134 165 regarding the tempo and mode of late quaternary changes in the arizona upland evergreen woodland containing pinus monophylla singleleaf pinyon juniperus osteosperma utah juniper and quercus turbinella shrub live oak occupied the site during full glacial times the latter two species but not p monophylla persisted into the early holocene and were joined by a limited number of desertscrub species including acacia greggii catclaw carnegiea gigantea saguaro and several other succulents with the arrival of many other species during the middle holocene a desertscrub community that differed considerably from the modern vegetation developed acacia greggii and cercidium floridum blue paloverde were the principal large woody species on exposed hillslopes assemblages similar in composition to the modern desertscrub did not appear until approximately 4000 years ago when the more xerophytic cercidium microphyllum foothills paloverde arrived and c floridum disappeared from hillslopes the delayed arrival of c microphyllum in comparison to other sonoran desertscrub species with similar climatic tolerances is attributed to the limited dispersal distance of its seeds by seed eating heteromyid rodents at 4540 and 6425 yr b p the cold intolerant shrub encelia farinosa was present on northeasterly aspect exposures where it is absent today suggesting slightly warmer winter conditions during the middle holocene the presence of the tree cercidium floridum and the perennial c 4 grass setaria leucopila on exposed slopes during the middle holocene indicates substantially moister conditions during that time than in the late holocene or today at sites on the xeric limits of the modern distributions of both species average annual precipitation is from 50 to 100 greater than that presently received at eagle eye mountain in particular the responses of s leucopila and cacti during the middle holocene indicate substantial increases in warm season precipitation

holocene vegetation and climate in the puerto blanco mountains southwestern arizona abstract plant macrofossils from 21 pack rat neotoma sp middens at 535 605 m from the puerto blanco mountains southwestern arizona provide and excellent history of vegetation and climate for the last 14 120 yr b p in the sonoran desert a late wisconsin juniper joshua tree woodland gave way to a transitional early holocene desertscrub with sparse juniperus californica california juniper by 10 540 yr b p important sonoran desert plants including carnegiea gigantea saguaro and encelia farinosa brittle bush were dominants riparian trees such as acacia greggii catclaw acacia prosopis velutina velvet mesquite and cerdicium floridum blue palo verde grew on dry south facing slopes in a middle holocene sonoran desertscrub in a warm wet summer climate with frequent winter freezes modern subtropical sonoran desertscrub formed about 4000 yr b p as summer rainfall and winter freezes declined cercidium microphyllum foothills palo verde sapium biloculare mexican jumping bean olneya tesota ironwood and stenocereus thurberi organ pipe cactus became dominant as riparian trees retreated to wash habitats the inferences of a latest wisconsin early holocene summer monsoonal maximum by j e kutzbach 1983 modeling of holocene climates in late quaternary environments of the united states vol 2 the holocene h e wright ed pp 271 277 univ of minnesota press minneapolis are not supported for the southwest apparently the persistence of late wisconsin circulation patterns offset any increases in insolation

reconstruction of past desert vegetation along the colorado river using packrat middens abstract the paleoecological reconstruction of pleistocene deserts along the colorado river of western north america is attempted using data from fossil packrat middens the colorado river drainage is set into a physiographic context along a gradient from the hyperarid colorado desert to the moist high elevations on the colorado plateau the pleistocene and modern distributions of individual plant species along this corridor are compared emphasizing records from the picacho peak area of the colorado desert and the eastern grand canyon in general plant species are now distributed 700 900 m higher in elevation and 400 700 km further up river than they were during the late wisconsin however some plant species have not conformed to the general pattern emphasizing the individualistic nature of species distributions in time

introducing a terrestrial carbon pool in warm desert bedrock mountains southwestern usa growth of the phoenix metropolitan area led to road cut or house platform exposures of the internal bedrock material of surrounding semiarid mountain ranges similar exposures in the surrounding sonoran and mojave deserts reveal the presence of sedimentary calcium carbonate infilling the preexisting fracture matrix of the bedrock field surveys at 31 sites with bedrock fractures filled with carbonate referred to as bffc in the following text reveal an average of 0 079 0 036 mtc m2 stored in the upper 2 m of analyzed bedrock exposures backscattered electron microscopy images indicate the presence of carbonate at the micron scale not included in this estimate of carbon storage pilot radiocarbon and sr isotope analyses suggest that one of the surveyed bffc veins was flushed into the bedrock from a nonbedrock source during the wetter last glacial period in the late pleistocene

late quaternary vegetation history of rough canyon south central new mexico usa abstract south central new mexico usa at the junction of the rocky mountains high plains and chihuahuan desert is one of the better known regions in the late quaternary of north america plant macrofossils and pollen from a packrat midden series in rough canyon new mexico allows refinement of plant distributions and paleoclimates in this transitional area since full glacial times from 17 000 to 12 000 14c yr bp pinus edulis juniperus scopulorum woodlands dominated limestone substrates between 1800 and 1490 m with pseudotsuga menziesii and other mixed conifer species restricted to shady north facing slopes juniperus deppeana the dominant juniper today above 2000 m in southern new mexico is conspicuously absent from glacial middens and must have been displaced south of the us mexico border the minimum climatic conditions for p edulis j scopulorum woodlands are ca 20 wetter and 3 5 5 c cooler july mean maximum temperatures than the modern climate at rough canyon holocene warming drying may have started as early as 12 000 14c yr bp with the extirpation of j scopulorum from rough canyon and was completed by at least 10 54014c yr bp the record for arrivals of some desert species is confounded by traces of pollen and macrofossils in some of the glacial middens which could signify either earliest occurrence or temporal mixing contamination of assemblages ams 14c dating can discriminate between early arrival and contamination in midden macrofossils but not in pollen ams dates show that choisya dumosa presently near its northern cold limits at rough canyon endured late glacial winters possibly as clonal populations some larrea tridentata leaves and pollen occur in middens dominated by conifers and oaks no longer at the site an ams date of 3205 14c yr bp on larrea leaves from one midden indicates contamination evidence for some macrofossil contamination however does not rule out the possibility that pollen of desert elements e g larrea prosopis in late glacial early holocene middens indicates their presence in the tularosa basin well ahead of their local appearance in rough canyon finally the increasing dominance of desert elements after 5000 14c yr bp in the rough canyon series and elsewhere in the northern chihuahuan desert could reflect slow postglacial migration from the south and or progressive encroachment with gradual stripping of soils formed during the last glacial period

middle holocene dry period in the northern midwestern united states lake levels and pollen stratigraphy abstract four cores from lake mendota in the yahara river valley of south central wisconsin provide pollen charcoal and sediment stratigraphic evidence of a middle holocene dry period in the northern midwest the lake level was lower between about 6500 and 3500 yr b p indicating that runoff from the upper yahara river basin may have ceased during the drier seasons of the year derived estimates of precipitation between 6500 and 3500 yr b p indicate a decrease of about 10 down to about 700 mm from the present precipitation value of 800 mm a warming between 6500 and 3500 yr b p is also interpreted based on a change of vegetation from rich mesophytic forest before 6500 yr b p to quercus savanna with increased charcoal abundances after that time after 3500 yr b p a closed quercus forest and decreased charcoal suggest a cooler and wetter climate the qualitative paleoecological interpretations quantitative precipitation reconstructions based on pollen from the region including the lake mendota data and estimates of hydrologic budget based on lake level changes all show indications of a dry and warm middle holocene evidence from a large regional array of sites also supports these interpretations

holocene climatic change in the northern midwest pollen derived estimates mapping of holocene pollen data in the midwestern united states has revealed several broadscale vegetational changes that can be interpreted in climatic terms these changes include 1 the early holocene northward movement of the spruce dominated forest and its later southward movement after 3000 yr b p and 2 the eastward movement of the prairie forest border into southwestern wisconsin by 8000 yr b p and its subsequent westward retreat after 6000 yr b p when certain basic assumptions are met multiple regression models can be derived from modern pollen and climate data and used to transform the pollen record of these vegetational changes into quantitative estimates of temperature or precipitation to maximize the reliability of the regression equations we followed a sequence of procedures that minimize violations of the assumptions that underlie regression analysis reconstructions of precipitation during the holocene indicated that from 9000 to 6000 yr b p precipitation decreased by 10 to 25 over much of the midwest while mean july temperature increased by 0 5 to 2 0 c at 6000 yr b p precipitation was less than 80 of its modern values over parts of wisconsin and minnesota after 6000 yr b p precipitation generally increased while mean july temperature decreased in the north and increased in the south the time of the maximum temperature varies within the midwest and is earlier in the north and later in the south

observations with moored acoustic doppler current profilers in the convection regime in the golfe du lion abstract in the golfe du lion south of france favorable conditions for deep winter convection exist and were documented by the medoc experiments during 1969 75 a renewed investigation of that regime with upward looking moored acoustic doppler current profilers adcps was carried out during 24 january 5 march 1987 to record the three dimensional currents associated with the deep mixing while in the earlier studies initial deep convection did not begin until fairly late in the winter season a very strong mistral around 10 january 1987 had already generated a 1arge deep mixed patch homogeneous down to around 2000 m at deployment time three adcps two working at 150 khz and one at 75 khz were moored in a triangle of 15 km sidelength at 550 780 m depth full records at 1 hour ensemble time intervals 400 pings per ensemble 8 m bin lengths were obtained by the 75 khz and one of the 150 khz adcps in mid february a second mistral hit the region with the onset of strong winds and surface cooling the

on the remote sensing of oceanic and atmospheric convection in the greenland sea by synthetic aperture radar 1 in this paper we discuss characteristic properties of radar signatures of oceanic and atmospheric convection features in the greenland sea if the water surface is clean no surface films or ice coverage oceanic and atmospheric features can become visible in radar images via a modulation of the surface roughness and their radar signatures can be very similar for an unambiguous interpretation and for the retrieval of quantitative information on current and wind variations from radar imagery with such signatures theoretical models of current and wind phenomena and their radar imaging mechanisms must be utilized we demonstrate this approach with the analysis of some synthetic aperture radar sar images acquired by the satellites ers 2 and radarsat 1 in one case an ers 2 sar image and a radarsat 1 scansar image exhibit pronounced cell like signatures with length scales on the order of 10 20 km and modulation depths of about 5 6 db and 9 10 db respectively simulations with a numerical sar imaging model and various input current and wind fields reveal that the signatures in both images can be explained consistently by wind variations on the order of 2 5 m s but not by surface current variations on realistic orders of magnitude accordingly the observed features must be atmospheric convection cells this is confirmed by visible typical cloud patterns in a noaa avhrr image of the test scenario in another case the presence of an oceanic convective chimney is obvious from in situ data but no signatures of it are visible in an ers 2 sar image we show by numerical simulations with an oceanic convection model and our sar imaging model that this is consistent with theoretical predictions since the current gradients associated with the observed chimney are not sufficiently strong to give rise to significant signatures in an ers 2 sar image under the given conditions further model results indicate that it should be generally difficult to observe oceanic convection features in the greenland sea with ers 2 or radarsat 1 sar since their signatures resulting from pure wave current interaction will be too weak to become visible in the noisy sar images in most cases this situation will improve with the availability of future high resolution sars such as radarsat 2 sar in fine resolution mode 2004 and terrasar x 2005 which will offer significantly reduced speckle noise fluctuations at comparable spatial resolutions and thus a much better visibility of small image intensity variations on spatial scales on the order of a few hundred meters index terms 3314 meteorology and atmospheric dynamics convective processes 4275 oceanography general remote sensing and electromagnetic processes 0689 4279 oceanography general upwelling and convergences 4255 oceanography general numerical modeling

boulder weathering and erosion associated with a wildfire sierra ancha mountains arizona an april may 2000 coon creek fire burned 37 5 km 2 of the sierra ancha mountains 32 3 km miles north of globe az including 25 sandstone and 19 diorite boulders surveyed in 1989 and resurveyed after the burn after the summer 2000 monsoon season and after the winter 2001 season when viewed from the perspective of cumulative eroded area both sandstone and diorite displayed bimodal patterns with 79 of sandstone boulder area and 93 of diorite boulder area undergoing either no fire induced erosion or fire induced erosion 76 mm when stretched over cumulative boulder areas erosion due to the fire averaged 26 mm for sandstone and 42 mm for diorite post fire erosion from thunderstorm summer rains averaged i mm for 5 diorite and i mm for 10 sandstone boulders while only a single diorite boulder eroded an average of 1 2 mm after the winter winter erosion removed an average of 5 5 mm from 14 sandstone boulders thus fire appears to increase a rock s susceptibility to post fire weathering and erosion processes as predicted by goudie et al earth surf process landf 17 1992 605 in contrast to experimental research indicating the importance of size in fire weathering no statistically significant relationship exists between erosion and boulder height or boulder surface area a result similar to zimmerman et al quat res 42 1994 255 these data exclude 12 original sites and 85 boulders at sites impacted by the fire that could not be relocated with a reasonable cause for the lack of relocation being boulder obliteration by the fire given evidence from 1 0 be and 2 6 al cosmogenic nuclides earth planet sci lett 186 2001 269 supporting the importance of boulders in controlling evolution of nonglaciated bouldered landscapes geol soc amer bull 76 1965 1165 fire obliteration of boulders could be an important process driving drainage evolution in nonglaciated mountains

late quaternary lacustrine history and paleoclimatic significance of pluvial lake cochise southeastern arizona abstract during the latest quaternary freshwater pluvial lakes intermittently formed in the topographically closed willcox basin arizona a lacustrine sequence of six separate high stands of lake cochise is documented by stratigraphic studies 19 radiocarbon ages and supplementary evidence two stands of pluvial lake cochise older than 14 000 yr b p reached elevations above 1290 m the prominent 1274 m shoreline of lake cochise which circumscribes the basin was largely created during a high stand between 13 750 and 13 400 yr b p during the holocene water filled the willcox basin three times to an elevation slightly below the crest of the 1274 m shoreline this occurred once during the early holocene around or before 8900 yr b p and twice during the later part of the middle holocene since the middle holocene only shallow ephemeral lakes have occupied the deflated central portion of ancient lake cochise a depression known as the willcox playa the lacustrine sequence of lake cochise provides an independent evaluation of late quaternary paleoclimatic reconstructions for southern arizona and the american southwest

localization of deep ocean convection by a mesoscale eddy abstract observations of open ocean deep convection indicate that it is a highly localized phenomenon occurring over areas of tens of kilometers in diameter the cause of this localization has been ascribed to preconditioning the local weakening of the stable density stratification associated with upwardly domed isopycnal surfaces in a surface intensified cyclonic circulation however most numerical and laboratory studies of localized convection have prescribed the localization artificially by confining the surface buoyancy loss to a circular disk in contrast in the numerical simulations described here deep convection forced by horizontally uniform buoyancy loss is localized within a region of initially weaker stratification than its surroundings the preconditioned region is associated with a cold core cyclonic eddy in geostrophic and cyclostrophic balance as in previous studies of disk shaped cooling the localized convection region undergoes baroclinic instability at late times causing the br

a 164 ka record of environmental change in the american southwest from a carlsbad cavern speleothem abstract a horizontal core 2 8 m in length drilled from the georgia giant column in carlsbad cavern provides climate information for the last 164 ka forty six alpha spectrometric u series ages determined at intervals of 7 6 cm along the core indicate five periods of deposition and five hiatuses the longest from 136 to 110 ka variations in growth rate 0 to 70 mm ka in the abundance of aragonite chalcedony and fe bearing phases and in 13c indicate that glacial intervals of the last 164 ka ois 6 4 and 2 were much wetter than today as were the colder substages 5d and 5b of ois 5 by contrast during the two warmest periods of the past 164 ka namely ois 5e and 1 there was no deposition on either side of the speleothem suggesting conditions as dry or drier than today the record from carlsbad parallels data from many other sites in the southwestern usa and northern mexico and data from marine sediments and ice cores demonstrating the extent to which ice sheet fluctuations influenced conditions in southern new mexico detailed correlation of 13c values in the georgia giant which range from 6 6 to 0 9 relative to pdb with distant speleothem records and with data from ice cores further documents the linkage of southwestern climate with global scale extent of glaciation values of 18o in the georgia giant core range from 9 7 to 4 7 relative to pdb and average 6 6 18o depleted carbonate in the georgia giant during ois 6 at a time when the world s oceans were enriched in 18o suggests that precipitation during cold intervals was brought largely by pacific air masses in fall winter and spring as a result of the southward displacement of the polar jet stream by the growth of the laurentide ice sheet termination ii marking the end of the penultimate glaciation is well defined in the core s 18o data analytical uncertainties in the radiometric ages do not preclude a start of termination ii as late as 128 ka as suggested by specmap data however data from the georgia giant core are more compatible with an earlier start like that obtained from devils hole and vostok data raising the possibility that early warming was widespread in the u s southwest region by 145 ka

holocene environmental change and vegetation contraction in the sonoran desert abstract two types of microtopographic features plant scar mounds and plant scar depressions on surfaces of barren desert pavements provide a unique record of the former presence of large perennial plants evidence of bioturbation by burrowing animals extends more than 1 m beneath each type of plant scar indicating that both features originated as large bioturbation mounds formation of bioturbation mounds in desertscrub environments is generally restricted to areas beneath widely separated large perennial plants the contrasting forms of plant scars mounds vs depressions represent time dependent changes following disappearance of the large plants and eventual cessation of bioturbation plant scar mounds represent a geologically recent episode of plant mortality whereas plant scar depressions represent the disappearance of plants at a considerably earlier time possibly at the pleistocene holocene transition contrasting spatial distributions of the two kinds of plant scars indicate that vegetation on alluvial fans has progressively contracted from a more diffuse former vegetation cover yielding the wide barren pavement surfaces present today in less arid portions of the sonoran desert spatial distribution of recent plant mortality due to persistent severe drought provides an analog of the progressive loss of plants from different parts of the landscape in the past

a holocene record from a former coastal lagoon in bahia kino gulf of california mexico a 10 m long core was recovered from the coastal flood plain on the eastern margin of the gulf of california bahia kino sonora sediments were analysed for loss on ignition magnetic susceptibility pollen diatoms ostracodes and foraminifera three levels were dated by 1 4 c the combined data suggest that the site was flooded during the middle holocene as sea level increased at about 6600 yr bp the area was a freshwater to brackish marsh dominated by typha domingensis and cyperaceae freshwater to brackish conditions suggest the presence of a local source of freshwater during this time and therefore a climate wetter than present continued rise in sea level was associated with an increase in depth and salinity by c 6350 6250 yr bp the coring site was an inner lagoon by c 6125 yr bp a central lagoon and by c 5900 yr bp the site was close to the mouth of the lagoon lower lagoon lower lagoon conditions persisted until the top of the record showing sea level stabilization which was followed by the formation of the dune ridge that presently separates the coring site from the sea

the formation of labrador sea water part ii mesoscale and smaller scale processes abstract in a previous paper clarke and gascard argued that the formation of labrador sea water was taking place in a cyclonic gyre set up each winter in the western labrador sea within the gyre and at its boundaries a number of different scales of organization are believed to be important in the formation processes the longest of these scales is the mesoscale 50 km which appears to be related to topographic rossby waves generated in the labrador current and propagating offshore the next smaller scale is an eddy scale 20 km believed to arise because the mesoscale is baroclinically unstable as shown by applying a two layer model of tang this instability is believed to promote mixing by generating frontal structures and vertical motions along them thus bringing subsurface t s maxima nearer the surface then within the mesoscale and eddy scale structures intense vertical convective cells take place at scales which are probably of the order of 1 km in three dimensions these events are short liv

some examples of detection of oceanic mesoscale eddies by the seasat synthetic aperture radar this note presents images of three dynamically different regions in the ocean to demonstrate the variety of mesoscale variabilities detected by the seasat synthetic aperture radar sar south of the grand banks of newfoundland a cold eddy is observed to form as the result of the southward intrusion of labrador sea water perhaps having led to the birth of a gulf stream extension ring off the northern coast of california features resulting from the offshore intrusions of cold upwelling water are observed two topographically generated eddies are detected near misteriosa bank on the cayman ridge in the northwestern caribbean comparisons are made with concurrent noaa 5 infrared images whenever the eddies have thermal signatures

the observation of ocean surface phenomena using imagery from the seasat synthetic aperture radar an assessment over the period july 4 to october 10 1978 the seasat synthetic aperture radar sar gathered 23 cm wavelength radar images of some 108 km2 of the earth s surface mainly of ocean areas at 25 40 m resolution our assessment is in terms of oceanographic and ocean monitoring objectives and is directed toward discovering the proper role of sar imagery in these areas of interest in general sar appears to have two major and somewhat overlapping roles first quantitative measurement of ocean phenomena like long gravity waves and wind fields as well as measurement of ships second exploratory observations of large scale ocean phenomena such as the gulf stream and its eddies internal waves and ocean fronts these roles are greatly enhanced by the ability of 23 cm sar to operate day or night and through clouds to begin we review some basics of synthetic aperture radar and its implementation on the seasat spacecraft seasat sar imagery of the ocean is fundamentally a map of the radar scattering characteristics of 30 cm wavelength ocean waves distorted in some cases by ocean surface motion we discuss how wind stress surface currents long gravity waves and surface films modulate the scattering properties of these resonant waves with particular emphasis on the mechanisms that could produce images of long gravity waves doppler effects by ocean motion are also briefly described measurements of long wavelength 100 m gravity waves using seasat sar imagery are compared with surface measurements during several experiments combining these results we find that dominant wavelength and direction are measured by seasat sar within 12 and 15 respectively however we note that ocean waves are not always visible in sar images and discuss detection criteria in terms of wave height length and direction sar estimates of omnidirectional wave height spectra made by assuming that sar image intensity is proportional to surface height fluctuations are more similar to corresponding surface measurements of wave height spectra than to wave slope spectra because seasat sar images show the radar cross section of 30 cm waves neglecting doppler effects and because these waves are raised by wind stress on the ocean surface wind measurements are possible comparison between wind speeds estimated from seasat sar imagery and from the seasat satellite scatterometer sass agreed to within 0 7 m s over a 350 km comparison track and for wind speeds from 2 to 15 m s the great potential of sar wind measurements lies in studying the spatial structure of the wind field over a range of spatial scales of from 1 km to 100 km at present the spatial and temporal structure of ocean wind fields is largely unknown because sar responds to short waves whose energy density is a function of wind stress at the surface rather than wind speed at some distance above the surface variations in image intensity may also reflect changes in air sea temperature difference thus complicating wind measurements by sar because sar images show the effects of surface current shear air sea temperature difference and surface films through their modulation of the 30 cm waves seasat images can be used to locate and study the gulf stream and related warm water rings tidal flows at inlets internal waves and slicks resulting from surface films in many of these applications sar provides a remote sensing capability that is complementary to infrared imagery because the two techniques sense largely different properties namely surface roughness and temperature both stationary ships and moving ships with their attendant wakes are often seen in sar images ship images can be used to estimate ship size heading and speed however ships known to be in areas imaged by sar are not always detectable clearly a variety of factors such as image resolution ship size sea state and winds could affect ship detection overall the role of sar imagery in oceanography is definitely evolving at this time but its ultimate role is unclear we have assessed the ability of seasat sar to measure a variety of ocean phenomena and have commented briefly on applications in the end oceanographers and others will have to judge from these capabilities the proper place for sar in oceanography and remote sensing of the ocean

late pleistocene paleohydrology near the boundary of the sonoran and chihuahuan deserts southeastern arizona usa abstract ground water discharge gwd deposits form in arid environments as water tables rise and approach or breach the ground surface during periods of enhanced effective precipitation where preserved these deposits contain information on the timing and elevation of past ground water fluctuations here we report on the investigation of a series of gwd deposits that are exposed in discontinuous outcrops along a 150 km stretch of the san pedro valley in southeastern arizona near the boundary of the sonoran and chihuahuan deserts chronologic isotopic geochemical faunal assemblage ostracodes and gastropods and sedimentological evidence collectively suggest that the elevation of the regional water table in the valley rose in response to a change in climate 50 ka ago and remained relatively high for the next 35 ka before falling during the bolling allerod warm period rebounding briefly during the younger dryas cold event and falling again at the onset of the holocene the timing of these hydrologic changes coincides closely with variations in 18o values of calcite from a nearby speleothem to the west and changes in lake levels at pluvial lake cochise to the east thus in southeastern arizona the assumption that changes in climate are reflected in all aspects of the hydrologic cycle of a region simultaneously is validated the timing of these changes also broadly coincides with variations in the gisp2 18o record which supports the hypothesis that atmospheric teleconnections existed between the north atlantic and the deserts of the american southwest during the late pleistocene

identification of modeled ocean plumes in greenland gyre ers 1 sar data oceanic convective plumes modeled with a thermobaric large eddy simulation and driven by conditions similar to those of the greenland sea are compared to observations from ers 1 synthetic aperture radar sar data from the greenland sea for the winter of 1992 in both form and size the two representations are seen to compare favorably the plume filled area of the sar image occupies a region about 20 km by 90 km at the ice edge of the open water in nordbukta the large seasonal ice retreat in the odden ice protuberance in the southern greenland gyre in the sar data the plumes appear to be ice covered while the convective return areas are open

growth of self assembling tubular structures of magnesium oxy hydroxide and silicate related with seafloor hydrothermal systems driven by serpentinization

elevational shifts of coleogyne ramossissima in the mojave desert during the little ice age abstract plant macrofossils from woodrat neotoma middens collected in the mojave desert of southern nevada were used to reconstruct the timing and magnitude of vegetation change during the past 1000 yr although vegetation at the site now is dominated by the shrub coleogyne ramossissima this species does not occur in fossil middens prior to 600 50 yr b p the appearance and persistence of c ramosissima in middens was coincident with the little ice age ca 1250 to 1850 a d and was probably related to an increase in precipitation

the last pluvial climatic episodes in the deserts of southwestern north america long term variations in the effective moisture of deserts are linked both to glacial interglacial climatic cycles and through the milankovitch theory to orbitally induced changes in solar radiation intensity1 4 for southwestern north america comparison of palaeobotanical data with model predictions of palaeoclimate reveals two distinct pluvial regimes during the late wisconsin and early holocene 23 8 kyr bp southward displacement of the aleutian low pressure centre and strengthened westerlies from 40 to 30 n were important features of the full glacial 18 kyr bp pluvial maximum increased cyclonic storms and weakened monsoons led to a winter precipitation regime a feature seen both in the fossil record5 6 and climate models7 8 dominantly zonal flow during this period contrasts with the latest wisconsin and early holocene 12 8 kyr bp when meridional circulation transported maritime tropical air into the desert interior we now show that plant macrofossil assemblages from packrat neotoma spp middens9 in the mojave desert provide evidence for increased temperatures and summer rainfall during this period10 12 the anomalously late persistence to 8 kyr bp of woodland in low latitude low elevation deserts of the south west13 is attributed to enhanced monsoonal circulation3

response of the north american monsoon to regional changes in ocean surface temperature 1 the north american monsoon nam an onshore wind shift occurring between july and september has evolved in character during the holocene largely due to changes in northern hemisphere insolation published paleoproxy and modeling studies suggest that prior to 8000 cal years bp the nam affected a broader region than today extending westward into the mojave desert of california holocene proxy sst records from the gulf of california goc and the adjacent pacific provide constraints for this changing nam climatology prior to 8000 cal years bp lower goc ssts would not have fueled northward surges of tropical moisture up the goc which presently contribute most of the monsoon precipitation to the western nam region during the early holocene the north pacific high was further north and ssts in the california current off baja california were warmer allowing monsoonal moisture flow from the subtropical pacific to take a more direct northwesterly trajectory into an expanded area of the southwestern u s west of 114 w a new upwelling record off southwest baja california reveals that enhanced upwelling in the california current beginning at 7500 cal year bp may have triggered a change in nam climatology focusing the geographic expression of nam in the southwest usa into its modern core region east of 114 w in arizona and new mexico holocene proxy precipitation records from the southwestern u s and northwestern mexico including lakes vegetation pollen and caves are reviewed and found to be largely supportive of this hypothesis of changing holocene nam climatology

convection with rotation in a neutral ocean a study of open ocean deep convection abstract the intensity and scale of the geostrophically adjusted end state of the convective overturning of a homogeneous rotating ocean of depth h at a latitude where the coriolis parameter is f induced by surface buoyancy loss of magnitude b0 are studied by numerical experiment the experiments are related to observations and laboratory studies of open ocean deep convection a numerical model based on the nonhydrostatic boussinesq equations is used the grid spacing of the model is small enough that gross aspects of convective plumes themselves can be resolved yet the domain of integration is sufficiently large to permit study of the influence of plumes on the large scale and geostrophic adjustment of the convected water numerical simulations suggest that cooling at the sea surface is offset by buoyancy drawn from depth through the agency of convective plumes these plumes efficiently mix the water column to generate a dense chimney of fluid which subsequently breaks up through the mechanism of bar

evaluating the life expectancy of a desert pavement abstract this paper integrates prior scholarship on desert pavements with a case study of pavements on stream terraces in the sonoran desert to analyze the processes and site conditions that facilitate the survival of ancient desert pavements this synthesis identifies vital factors key factors and site specific factors promoting pavement stability hyperaridity is the vital factor in pavements surviving for 106 years or more aided by minimal bioturbation and clast size reduction three key factors aid in pavements surviving for 104 to 105 years accumulation of allochthonous dust underneath pavement cobbles a flat topography and a lack of headward retreating swales or gullies a unified explanation for pavement longevity however did not emerge from a literature review because a variety of site specific factors can also promote pavement antiquity including resistant bedrock beneath the pavement disk shaped cobbles to promote dust accumulation and microclimatological and ecological reasons for minimal bioturbation both key and site specific explanations for pavement longevity apply well to a case study of pavements on stream terraces in the sonoran desert central arizona the buildup of cosmogenic 10be and in situ 14c optically stimulated luminescence and varnish microlamination ages reveal stable pavements range in age between 30 and 332 ka with conditions for longevity including flat surface topography pavements underlain by consolidated granitic bedrock a lack of headward retreating gullies and swales 87sr 86sr analyses indicating the infiltration of allochthonous dust floating disk shaped pavement cobbles and a quartzite lithology resistant to disintegration however 10be ages also indicate evidence for the instability of desert pavements on stream terraces underlain by unconsolidated playa clays and unconsolidated fanglomerate these weaker materials allowed the growth of headward retreating swales that in turn promoted exposure of newer gravels by surface erosion

the lower colorado river valley a pleistocene desert abstract a chronological sequence of plant macrofossil assemblages from twenty five pack rat middens provides a record of desert scrub vegetation for most of the last 13 380 yr b p from a hyperarid portion of the lower colorado river valley at the end of the late wisconsin and probably during much of the quaternary the picacho peak area imperial county california supported a typical mohave desert association of larrea divaricata creosote bush coleogyne ramosissima blackbrush yucca brevifolia joshua tree and y whipplei whipple yucca recent arrivals of sonoran desert plants such as olneya tesota ironwood and fouquieria splendens ocotillo suggest that the area supported relatively modern sonoran desert scrub species for relatively short periods during interglaciations

modeled radar surface signature of deep ocean convection deep ocean convection the process by which the deep waters of the world s oceans are created and renewed plays a key role in the global thermohaline circulation and hence the world s heat balance the process of deep ocean convection involves a vigorous overturning of the ocean water column down to depths of 2000 3000 m in an area probably not larger than 50 km in diameter this paper details the results of a theoretical study to identify remotely sensible surface signatures for deep ocean convection due to the all weather capability efforts have focused on the microwave part of the spectrum particularly the high resolution imaging capability of synthetic aperture radar sar the goal of this research is to use the sar surface signature or fingerprint to identify and characterize areas of convection in the open ocean this information is then used to improve model parameterizations for deep convection used in general circulation models electromagnetic simulations of remote sensing signatures of deep ocean convection have been performed based on existing hydrodynamic models simulated surface signatures of deep convection are presented for various hydrodynamic and imaging conditions along with a discussion of applicability of these simulations to real sar data key findings are the existence of a definite identifiable radar surface signature in convective regions and a set of conditions under which one would expect to observe these signatures

observations of vertical currents and convection in the central greenland sea during the winter of 1988 1989 during the winter of 1988 1989 five acoustic doppler current profilers adcps were moored in the central greenland sea to measure vertical currents that might occur in conjunction with deep mixing and convection two adcps were looking up from about 300 m and combined with thermistor strings in the depth range 60 260 m two were looking downward from 200 m and one was looking upward from 1400 m first maxima of vertical velocity variance occurred at two events of strong cold winds in october and november when cooling and turbulence in the shallow mixed layer generated internal waves in the thermocline beginning in late november the marginal ice zone expanded eastward over the central greenland sea reaching its maximum extent in late december in mid january a bay of ice free water opened over the central greenland sea leaving a wedge of ice the is odden curled around it along the axis of the jan mayen current and then northeastward and existing well into april 1989 below the ice a mixed layer at freezing temperatures developed that increased in thickness from 60 to 120 m during the period of ice cover corresponding to an average heat loss of about 40 w m 2 through brine rejection mixed layer salinity increased steadily reducing stability to underlying weakly stratified layers roach et al 1993 during the ice cover period vertical currents were at a minimum after the opening of the ice free bay successive mixed layer deepening to 350 m occurred in conjunction with cooling events around february 1 and 15 accompanied by strong small scale vertical velocity variations upward mixing of more saline waters of atlantic origin during this phase reduced the stability further generating a pool of homogeneous water of 50 km horizontal extent in the central greenland sea preconditioned for subsequent convection to greater depths individual convection events were observed during march 6 16 associated with downward velocities at the 1400 m level of about 3 cm s l one event was identified as a plume of about 300 m horizontal scale in agreement with recently advanced scaling arguments and model results and with earlier similar observations in the gulf of lions western mediterranean the deep convection occurred in the center of the ice free bay hence brine rejection did not seem necessary for its generation plume temperatures at 1400 m were generally higher than that of the homogeneous surface pool suggesting entrainment of surrounding warmer waters on the way down mean vertical velocity over a period of convection events was indistinguishable from zero suggesting that plumes served as a mixing agent rather than causing mean downward transport of water masses however different from the surface pool that was governed by mixed layer physics the water between 400 and 1400 m was not horizontally homogenized in a large patch by the sporadic plumes overall and compared to results from the gulf of lions convection activity in the central greenland sea was weak and limited to intermediate depths in winter 1988 1989

temporal variability of microparticle properties in polar ice sheets abstract four recent ice core studies reveal a consistently recurring temporal correlation between increased microparticle concentrations and lower global temperatures more negative 13 o 16 o ratios a continuous 900 year record of particle deposition from the 101 m south pole core was obtained by analyzing 6218 samples the concentration of insoluble particles with diameters 0 63 m increases substantially between a d 1450 and 1850 a period of slightly reduced global temperatures encompassing the latest neoglacial or little ice age there is evidence suggesting that some of the additional material may be volcanic although further substantiation is required the microparticle analyses of selected sections from three deep cores coupled with the respective 18 o measurements reveal that in all three cores the last glacial or late wisconsin ice contained great quantities of microparticles the ratio of the average microparticle concentration in wisconsin sections to that in holocene sections is 6 for the 905 m dome c antarctica core 3 for the 2164 m byrd station antarctica core and 12 for the 1387 m camp century greenland core microparticle increases of this magnitude can not be accounted for merely by a reduction in net accumulation these data suggest that the global atmosphere was heavily laden with suspended particulates near the end of the last major glaciation

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

global investigation of olivine on mars insights into crust and mantle compositions 1 we present the distribution of olivine on mars derived from spectral parameters based on the 1 m olivine absorption band the olivine can be defined with respect to two spectral end members type 1 corresponds to olivine with low iron content and or small grain size and or small abundance and type 2 which corresponds to olivine with higher iron content and or larger grain size and or larger abundance the spatial and statistical analysis of the global olivine distribution points out five major geological settings where olivine is detected 1 early hesperian olivine bearing smooth crater floors and flat intercrater plains throughout the southern highlands 2 olivine deposits around the three main basins argyre hellas and isidis 3 olivine in intercrater dunes crater ejecta or extended deposits in the northern plains 4 olivine associated with outcrops and sand in the floor of valles marineris and 5 olivine bearing butte outcrops in the vicinity of hellas the geological context the age and the composition of the olivine detections associated with these five major geological settings are detailed their origin and the implication of their occurrence on the composition of the martian mantle and crust as well as on the evolution of mars volcanism are discussed

thermal evolution of the greenland sea gyre in 1988 1989 slice inverses of temperature and heat content from the 1988 1989 greenland sea tomography experiment and other observations including standard conductivity temperature depth stations moored thermistors surface meteorological variables and surface ice cover are combined to better understand the thermodynamics of the greenland sea gyre thermal evolution of the gyre center seems to divide naturally into the following three periods a preconditioning phase november january during which surface salinity is increased by brine rejection from ice formation and by entrainment but in which the mixed layer deepens only slowly to a depth of some 150 200 m a deep mixing phase february march during which the surface mixed layer deepens rapidly to approximately 1500 m in the gyre center purely under the influence of local surface cooling and a restratification phase during which the products of deep mixing are replaced by arctic intermediate water flowing in from the gyre edges the onset of the deep mixing phase occurs after ice formation in the gyre center stops resulting in an area of open water where large heat fluxes can occur in surrounding regions including the odden region to the south ice is still being formed to the north and west closer to the steep topography of the continental shelf the inverse results show significant variability due to advection and large temperature and heat content fluctuations with a period of about 50 days are seen

evidence from north west canada for an early holocene milankovitch thermal maximum according to the milankovitch theory of global climatic change maximum summer solar radiation at high latitudes of the northern hemisphere occurred at 10 000 yr bp refs 1 2 in particular it predicts summer solstice radiation greater by 9 10 preliminary climate simulation experiments with these increased values of radiation confirm that high latitude land surfaces received maximal insolation at 10 000 yr refs 3 4 paradoxically however the large volume of fossil pollen and other evidence from north america indicates a maximum of holocene warmth at 7 000 6 000 yr ref 5 and a recent review of the evidence from new england suggests that the warming began at 9 000 and ended at 5 000 yr but also stresses the difficulties of interpretation in terms of climate change6 we summarize here data from sites in the north west corner of mainland canada fig 1 that directly support the milankovitch hypothesis

the impact of cold north atlantic sea surface temperatures on climate implications for the younger dryas cooling 11 10 k the sensitivity of global climate to colder north atlantic sea surface temperatures is in vestigated with the use of the giss general circulation model north atlantic ocean temperatures 18 000 b p resembling those prevalent during the younger dryas were incorporated into the model of the present climate and also into an experiment using orbital parameters and land ice characteristic of 11 000 b p the results show that with both 11 000 b p and present conditions the colder ocean temperatures produce cooling over western and central europe in good agreement with younger dryas paleoclimatic evidence cooling also occurs over extreme eastern north america although the precise magnitude and location depends upon the specification of ocean temperature change in the western atlantic despite the presence of increased land ice and colder ocean temperatures the younger dryas summer air temperatures at northern hemisphere midlatitudes in the model are warmer than those of today due to changes in the orbital parameters chiefly precession and atmospheric subsidence at the perimeter of the ice sheets

a 35 000 year vegetation and climate history from potato lake mogollon rim arizona abstract a new record from potato lake central arizona details vegetation and climate changes since the mid wisconsin for the southern colorado plateau recovery of a longer record discrimination of pine pollen to species groups and identification of macrofossil remains extend whiteside s 1965 original study during the mid wisconsin ca 35 000 21 000 yr b p a mixed forest of engelmann spruce picea engelmannii and other conifers grew at the site suggesting a minimum elevational vegetation depression of ca 460 m summer temperatures were as much as 5 c cooler than today during the late wisconsin ca 21 000 10 400 yr b p even cooler temperatures 7 c colder than today ca 800 m depression allowed engelmann spruce alone to predominate warming by ca 10 400 yr b p led to the establishment of the modern ponderosa pine pinus ponderosa forest thus the mid wisconsin was not warm enough to support ponderosa pine forests in regions where the species predominates today climatic estimates presented here are consistent with other lines of evidence suggesting a cool and or wet mid wisconsin and a cold and or wet late wisconsin climate for much of the southwest potato lake was almost completely dry during the mid holocene but lake levels increased to near modern conditions by ca 3000 yr b p

timing and distribution of alluvial fan sedimentation in response to strengthening of late holocene enso variability in the sonoran desert southwestern arizona usa abstract the integration of geomorphic mapping soil stratigraphy and radiocarbon dating of alluvial deposits offers insight to the timing magnitude and paleoclimatic context of holocene fan sedimentation near yuma arizona mapping of 3400 km2 indicates about 10 of the area aggraded in the late holocene and formed regionally extensive alluvial fan and alluvial plain cut and fill terraces fan deposits have weakly developed gravelly soils and yielded a date of 3200 2950 cal yr bp from carbonized wood alluvial plain deposits have weakly developed buried sandy soils and provided a date of 2460 2300 cal yr bp from a terrestrial snail shell precipitation records were analyzed to form historical analogues to the late holocene aggradation and to consider the role of climatic variability and extreme hydrologic events as drivers of the sedimentation the historical precipitation record indicates numerous above average events correlated to the southern oscillation index soi in the region but lacks any significant reactivation of alluvial fan surfaces the timing of aggradation from 3200 to 2300 cal yr bp correlates well with other paleoclimatic proxy records in the southwestern u s and eastern pacific region which indicate an intensification of the el nino southern oscillation enso climatic pattern and rapid climate change during this period

terrestrial conditions at the last glacial maximum and climap sea surface temperature estimates are they consistent climap 1981 seasonal reconstruction of the earth s surface at the last glacial maximum geological society of america map and chart series mc 36 boundary conditions were used as inputs to the giss general circulation model and the last glacial maximum lgm climate was simulated for six model years the simulation was compared with snow line depression and pollen inferred temperature data at low latitudes specifically for hawaii colombia east africa and new guinea the model does not produced as much cooling at low latitudes as is implied by the terrestrial evidence an alternative experiment in which the climap sea surface temperatures were uniformly lowered by 2 c produces a better fit to the land data although in hawaii model temperatures are still too warm the relatively warm climap tropical sea surface temperatures also provide for only a slight decrease in the hydrologic cycle in the model in contrast to both evidence of lgm tropical aridity and the results of the experiment with colder ocean temperatures with the climap sea surface temperatures the lgm global annual mean surface air temperature is 3 6 c colder than at present if the ocean temperatures were allowed to cool in conformity with the model s radiation balance the lgm simulation would be 5 6 c colder than today and in better agreement with the tropical land evidence

dynamics of isolated convective regions in the ocean abstract an initially resting ocean of stratification n is considered subject to buoyancy loss at its surface of magnitude b0 over a circular region of radius r at a latitude where the coriolis parameter is f initially the buoyancy loss gives rise to upright convection as an ensemble of plumes penetrates the stratified ocean creating a vertically mixed layer however as deepening proceeds horizontal density gradients at the edge of the forcing region support a geostrophic rim current which develops growing meanders through baroclinic instability eventually finite amplitude baroclinic eddies sweep stratified water into the convective region at the surface and transport convected water outward and away below setting up a steady state in which lateral buoyancy flux offsets buoyancy loss at the surface in this final state quasi horizontal baroclinic eddy transfer dominates upright plume convection by using parcel theory to consider the energy transformations taking place it is shown that the de

discovery of olivine in the nili fossae region of mars we have detected a 30 000 square kilometer area rich in olivine in the nili fossae region of mars nili fossae has been interpreted as a complex of grabens and fractures related to the formation of the isidis impact basin we propose that post impact faulting of this area has exposed subsurface layers rich in olivine linear mixture analysis of thermal emission spectrometer spectra shows surface exposures of 30 olivine where the composition of the olivine ranges from fo30 to fo70

mid to late wisconsin pollen record of san felipe basin baja california abstract a lacustrine sequence from laguna seca san felipe baja california in the southwestern sonoran desert provides the first record of mid to late wisconsin vegetation in one of the driest regions of north america pollen analysis was performed in the intermediate part of the sequence from ca 44 000 to ca 13 000 14 c yr b p according to six 14 c radiocarbon dates sedimentation of eolian sands prior to 44 000 14 c yr b p indicates dry conditions high pollen concentration of montane and chaparral species in the pollen assemblages contrast with the modern desert vegetation sixty four pollen types were identified the source of mid to late wisconsin sedimentation must have been the plant communities in the surrounding highlands of the basin mid wisconsin pollen assemblages dominated by pines junipers and artemisia reflect humid conditions in the area by late wisconsin time a significant increment in junipers indicates a lowering in the altitudinal ranges of woodlands chaparral pollen from wind pollinated species is abundant while desert plants specifically animal or insect pollinated species are poorly represented the san felipe record does not identify the last glacial maximum as the time of greatest effective moisture as suggested by pluvial lake levels and other paleoclimatic evidence in the soutwestern united states

pollen studies in the junin area central peruvian andes laguna junin is a large lake 675 km long but only 4 m deep located in the grass covered altiplano at an altitude of 4 100 m northeast of lima pollen analysis of a 30 m core indicates that from about 12 000 yr ago until some time after 3 000 yr ago about 30 of the pollen was carried in by easterly winds from the east andean forests which today are at least 600 m lower in elevation contemporaneous pollen deposition in lakes on moraines of the last glaciation west of the junin plain was dominated by local grassland types and had little contribution from this easterly source at some time after 3 000 yr ago perhaps about 1 200 yr ago the pollen influx to laguna junin from this distant forest source greatly diminished perhaps because of deforestation by increased human populations between about 12 000 and 24 000 yr ago in the junin core the sparse pollen concentration was dominated by grassland types supplemented by polylepis acaena alnus and compositae blown in from the sub puna shrublands that may have occupied much of the east andean slopes in place of the humid forest that occurs there today the silty sediment in this section of the core is interpreted as outwash from piedmont glaciers that invaded the plain especially from the cordillera to the west these glaciers left a distinctive pattern of moraines and outwash fans which served to dam tine lake basin an unconformity in the sediment covers the time from about 24 000 to 39 000 yr ago when the lake was probably dry before this time the silty sediment and the dominance of grassland and shrubland pollen types indicates an earlier interval of glaciation recorded on the landscape by an older set of moraines and outwash fans which initially dammed the lake basin

paleoclimatic estimates from water and energy budgets of east african lakes abstract the turkana nakuru elmenteita and naivasha basins in the rift valley of east africa experienced high water levels during the period of 10 000 7000 yr b p analyses of the modern hydrologic and energy budgets for these basins along with that of lake victoria were used to infer the amount of precipitation that would have been required to maintain the enlarged paleolakes of the early holocene precipitation must have been at least 150 300 mm yr 15 to 35 above the modern average the precipitation estimates were fairly consistent among the various basins but no quantitative estimate was made for the additional precipitation required to account for overflow from the rift valley lake basins discharge from the lake victoria basin around 1880 a d was considerably above the more recent average and the increased discharge into the white nile for that period might have been similar to that of the early holocene a sensitivity analysis showed that temperature changes were probably not too important for changing the hydrologic energy budget changes of albedo bowen ratio and cloudiness were likely to have been of greater importance

oxygen isotope records of holocene climate variability in the pacific northwest abstract oxygen isotope 18o measurements of authigenic carbonate from cleland lake southeastern british columbia paradise lake central british columbia and lime lake eastern washington provide a 9000 year holocene record of precipitation evaporation balance variations in the pacific northwest both cleland lake and paradise lake are small surficially closed basin systems with no active inflows or outflows lime lake is surficially open with a seasonally active overflow water isotope values from cleland and paradise plot along the local evaporation line indicating that precipitation evaporation balance is a strong influence on lake hydrology in contrast lime lake water isotope values plot on the local meteoric water line signifying minimal influence by evaporation to infer past hydrologic balance variations at a high temporal resolution we sampled the cleland paradise and lime lake sediment cores at 1 60 mm intervals 3 33 years per sample on average and measured the isotopic composition of fine grained

ice core sample measurements give atmospheric co 2 content during the past 40 000 yr recent measurements1 2 on ice samples from camp century greenland 77 10 n 61 08 w byrd station antarctica 80 01 s 110 31 w and dome c 74 40 s 125 10 e suggest that during the late part of the last glaciation the atmospheric co2 concentration was significantly lower than during the holocene further investigation of this natural increase of the atmospheric co2 concentration in the past should aid our understanding of the climatic implications of the man made co2 increase since the beginning of industrialization3 here we report new and precise measurements of the co2 concentration of the air occluded in bubbles of ice samples from camp century and byrd station using a new dry extraction technique the extracted gases were analysed with an ir laser spectrometer irls samples from 22 different depths were analysed from each core the samples are distributed over a depth interval corresponding approximately to the past 40 000 yr in addition results for ice samples from selected depth horizons from a colder region north central greenland 74 37 n 39 36 w and from a warmer region dye 3 greenland 65 11 n 43 50 w are given based on these results we estimate the trend of the atmospheric co2 concentration during the past 40 000 yr

coastal ocean fronts and eddies imaged with ers 1 synthetic aperture radar ers 1 c band synthetic aperture radar sar data were collected during the norwegian continental shelf experiment norcsex both in november 1991 during the ers 1 commissioning phase and at different seasons in 1992 and 1993 characteristic sar image expressions are observed in relation to perturbation of the surface current short wave interaction across the norwegian coastal current front for winds less than 10 12 rn s 1 in situ measurements document the existence of alternating zones of convergence and divergence coexisting with a strong near surface current shear of nearly 4f where f is the coriolis parameter across a distance of a few kilometers under calm to moderate winds i e 4 7 rn s 1 characteristic expressions of upper ocean circulation features also include the manifestation of eddies through the presence of surface film which damps the bragg waves comparison of a near coincident national oceanic and atmospheric administration advanced very high resolution radiometer image and an ers 1 sar image supports the interpretation that surface current fronts are imaged by sar in combination with an sar image simulation model the relative quantitative importance of shear convergence and divergence along the front is examined although the model formulation is simple and the absolute magnitude of the perturbations is uncertain the study shows that the sar images can sometimes be used to interpret frontal dynamics including growth and decay of meanders

coherent response of arabian sea upwelling and pollen transport to late quaternary monsoonal winds the indian summer monsoon causes large seasonal changes in the environments of both eastern africa and the arabian sea here we compare time series 140 kyr long of selected pollen types and foraminiferal upwelling faunas preserved in marine sediments to identify the frequencies of their variability and the coherence and phase of the terrestrial and marine responses to monsoonal circulation during interglacial intervals the pollen and upwelling records of the western arabian sea indicate stronger monsoons and are both coherent and in phase at periodicities near the precession of the earth s rotational axis 23 kyr we conclude that the strength of the monsoonal southwesterlies accounts for this high coherence of marine and terrestrial records during interglacial intervals low correlation during glacial phases indicates weaker monsoons and some decoupling of these two records these data indicate that two distinct modes of monsoon variability may exist an interglacial mode with strong monsoons and effective coupling of terrestrial and marine records and a glacial mode with both weaker monsoons and decreased linkage between arabian sea pollen and upwelling records

a serpentinite hosted ecosystem the lost city hydrothermal field the serpentinite hosted lost city hydrothermal field is a remarkable submarine ecosystem in which geological chemical and biological processes are intimately interlinked reactions between seawater and upper mantle peridotite produce methane and hydrogen rich fluids with temperatures ranging from 40 to 90 c at ph 9 to 11 and carbonate chimneys 30 to 60 meters tall a low diversity of microorganisms related to methane cycling archaea thrive in the warm porous interiors of the edifices macrofaunal communities show a degree of species diversity at least as high as that of black smoker vent sites along the mid atlantic ridge but they lack the high biomasses of chemosynthetic organisms that are typical of volcanically driven systems

an ocean largeheddy simulation model with application to deep convection in the greenland sea a nonhydrostatic boussinesq threehdimensional model the ocean largeheddy simulation model lolemr has been developed to study deep oceanic convection the model uses a subgridhscale parameterization of turbulence developed for largeheddy simulation models and the advection of scalars is accomplished using a monotonic scheme a set of experiments was performed using olem to provide a direct comparison with laboratory results and aircraft measurements of the atmospheric convective boundary layer the results from these experiments are in excellent agreement with laboratory and atmospheric convective boundary layer measurements of the mean profiles of zonal and vertical velocity variance potential temperature variance and heat flux the horizontal wavenumber spectra of zonal and vertical velocity are also in good agreement with laboratory measurements and kolmogorov s theoretical inertial subrange spectrum a set of experiments using a potential temperaturehsalinity profile from the central greenland sea for model initialization was conducted to study the effect of the thermobaric instability and rotation on the structure and evolution of deep oceanic convection the artificial removal of the thermobaric instability suppresses penetrative convection which is responsible for rapid changes in water properties at depths much greater than occurs for convective mixedhlayer deepening the vertical velocity and diameter 0 08 m s 1 and 300 m respectively of the penetrative plumes are in good agreement with observations from the greenland sea a period of strong penetrative convection is followed by a gradual transition to convective mixedhlayer deepening during penetrative convection the values of heat flux are about 2 times greater than convective mixedhlayer deepening in the absence of rotation the evolution of penetrative convection occurs more rapidly and vertical motions are more vigorous the presence of the horizontal component of rotation forces asymmetries in the circulation around a penetrative plume these experiments clearly demonstrate the importance of thermobaric instability and rotation on deep convection to properly model largehscale flows in regions of penetrative convection it is necessary to include these effects in the vertical mixing parameterization

on polarimetric characteristics in sar images of mesoscale cellular convection in the marine atmospheric boundary layer 1 convection is an important phenomenon in the marine atmospheric boundary layer mabl previous spaceborne radar studies of such have been limited to single polarization data and therefore their focus was on the variation in intensity of the radar return which was constrained by the existence of a single polarization image pattern representing different atmospheric and oceanic phenomena in this paper we study the polarimetric characteristics of mesoscale cellular convection mcc in the mabl using high resolution data from fully polarimetric hh vv hv and vh radarsat 2 rs 2 synthetic aperture radar sar images in conjunction with closely collocated mesoscale atmospheric model simulations to identify the mcc signatures to compare the polarimetric characteristics of mcc with those of the ocean surface our analysis also includes 641 open ocean surface quad polarization rs 2 sar images collocated with 52 national data buoy center buoys the open ocean surface sar images exhibit different polarimetric characteristics from those of mcc thus we differentiate mcc from other open ocean phenomena based on identifiable polarimetric sar characteristics