the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

systematic variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects in the southern great basin united states stable carbon and oxygen isotope variations in holocene soil carbonates that formed in the unsaturated zone were examined along several elevation transects in the southern great basin united states a region with a semi arid climate our intent was to study the relationship between the stable isotopic composition of pedogenic carbonates and climate ecological variations differences in parent material and soil depth 13 c of pedogenic carbonate in three different soil profiles from different elevations decreases with soil depth indicating a decrease in the ratio of atmospheric to plantderived co 2 downprofile pedogenic carbonate at the soil air interface approaches a 13 c value in equilibrium with atmospheric co 2 in all three soils observed 13 c profiles for pedogenic carbonate can be described using a one dimensional model for 12 co 2 and 13 co 2 assuming isotopic equilibrium between soil co 2 and soil carbonate the modeled best fit to observed isotopic profiles suggests that the profile differences in part result from differing soil respiration rates at each site 13 c in deep pedogenic carbonate 50 cm varies by about 12 per mil over a 2 440 m elevation range being enriched in 13 c at the lowest elevations the slope of 13 c for these carbonates versus elevation is very similar for soils developed on carbonate and on noncarbonate parent materials depletion by 4 6 to 4 7 per mil per 1 000 m increase in altitude between 300 to 2 740 m above mean sea level for the localities studied this concordance makes it likely that there has been complete isotopic exchange between hco 3 in solution and soil co 2 prior to carbonate precipitation soil co 2 and soil respiration rates increase systematically with elevation the plantderived component of soil co 2 indicates that c 3 plants dominate the biomass at most measured sites in agreement with plant surveys calculated equilibrium fractionation factors between soil co 2 and soil carbonate are very similar to those observed again indicating complete isotopic exchange between carbon species in all the soil co 2 and soil carbonate data suggest that the 13 c variation with elevation observed in the soil carbonates results from differing soil respiration rates at each site as well as from variations in the proportion of c 3 to c 4 and cam plants in each site9s surface biomass 18 o values in pedogenic carbonates are higher at lower elevations due in part to the more positive 18 o values for meteoric waters at lower elevations the average 18 o value of deep 50 cm pedogenic carbonate at all sites however is enriched 2 4 to 3 7 per mil with respect to values we predict should be in equilibrium with the isotopic composition of local meteoric waters this suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place one or both of these processes also may explain the 18 o decrease in soil carbonate with depth observed in two of three soil profiles

factors affecting 14c ages of lacustrine carbonates timing and duration of the last highstand lake in the lahontan basin abstract two processes contribute to inaccurate 14c age estimates of carbonates precipitated within the lahontan basin nevadacalifornia low initial 14c c ratios in lake water reservoir effect and addition of modern carbon to calcium carbonate after its precipitation the mast reliable set of 14c ages on carbonates from elevations 1310 m in the pyramid and walker lake subbasins indicate that lakes in all seven lahontan subbasins coalesced 14 200 14c yr b p forming lake lahontan lake lahontan achieved its 1330 m highstand elevation by 13 800 14 c yr b p and receded to 1310 m by 13 700 14c yr b p calculations based on measured carbonate accumulation rates of the amount of time lake lahontan exceeded 1310 and 1330 m 500 and 50 yr are consistent with this chronology the timing of the lake lahontan highstand is of interest because of the linkage of highstand climates with proximity to the polar jet stream the brevity of the lahontan highstand is interpreted to indicate that the core of the southern branch of the polar jet stream remained only briefly over the lahontan basin

stromatolites in walker lake nevada great basin usa record climate and lake level changes 35 000 years ago abstract walker lake is a closed basin remnant of the large pleistocene glacial lake lahontan system that has experienced multiple high amplitude 100 200 m changes in water level over the past 40 000 years in response to changes in climate a laminated carbonate stromatolite composed of varying proportions of calcite fans and micrite was collected from a paleoshoreline located at approximately 58 m above present lake level radiocarbon dating revealed that the stromatolite spans approximately 2000 years of growth from 35 227 to 33 727 calibrated years before present ybp a time period during which paleolake level is not well constrained distinct laminae were drilled along the growth axis and the resulting powders were collected for clumped isotope analyses to generate formation temperatures lake water temperatures during stromatolite formation from which 18 o water was calculated results indicate that the stromatolite experienced an initial increase in temperature and water 18 o values followed by a decrease in both during the course of accretion the resulting temperature and isotopic data were input into a rayleigh distillation model for lakewater evaporation in order to estimate the magnitude of lake level and volume fluctuations over the course of accretion modeling results reveal a lake level decrease between 8 1 and 15 6 m followed by an increase of between 4 3 and 8 8 m during the course of stromatolite growth the results of this study indicate that walker lake experienced significant lake volume change over the course of 2000 years perhaps as a response to precipitation changes driven by fluctuations in the polar jet stream and accompanying changes in regional climate and or evaporation induced changes in lake level these results add to a growing body of research indicating that stromatolites and other lacustrine tufas represent a detailed and extensive terrestrial archive that can potentially be used to reconstruct the timing and magnitude of climate change

holocene paleoclimate history of fallen leaf lake ca from geochemistry and sedimentology of well dated sediment cores abstract millennial scale shifts in aridity patterns have been documented during the holocene in the western united states yet the precise timing severity and regional extent of these shifts prompts further study we present lake sediment core data from fallen leaf lake a subalpine system at the southern end of the lake tahoe basin for which 80 of the contemporary inflow is derived from snowpack delivered by pacific frontal storm systems a high quality age model has been constructed using 14c ages on plant macrofossils 210pb and the tsoyowata tephra datum 7 74 7 95 cal kyr bp one core captures the transition from the late tioga younger dryas glaciolacustrine package to laminated opaline clay at 11 48 cal kyr bp early holocene sedimentation rates are relatively high 1 9 mm year and cooler winter temperatures are inferred by the presence of pebbles interpreted to be transported out into the lake via shore ice there is a geochemically distinct interval from 4 71 to 3 65 cal kyr bp that is interpreted as a late holocene neopluvial characterized by depleted 13c and lower c n that point to reduced runoff of terrigenous organic matter increased winter precipitation and increased algal productivity the largest holocene signal in the cores occurs at the end of the neopluvial at 3 65 cal kyr bp and marks a shift into a climate state with variable precipitation yet is overall more arid than the neopluvial this new climate state persists for 3 ka until the little ice age low sedimentation rates 0 5 mm year the homogeneous opaline sediment and steadily increasing contributions of terrestrial vs algal organic matter in these cores suggest that the lowstand state of fallen leaf lake may have been the norm from 3 65 to 0 55 cal kyr bp punctuated by short term high precipitation years or multi year intervals capable of rapid short duration lake level rise fallen leaf lake is strongly influenced by changes in winter precipitation and temperature manifested largely by the geochemical proxies and highlights unique advantages of subalpine lakes in regional paleoclimate reconstructions

magnesium content of non marine ostracod shells a new palaeosalinometer and palaeothermometer abstract ostracods are microcrustaceans with calcitic carapaces each consisting of two valves or shells that grow by moulting and regeneration of sequentially larger valves up to nine times before reaching maturity the mg content of these valves is species dependent and is a function of their growth stage and the temperature salinity mg content and mg ca ratio of their host water newly formed partly calcified valves of the non marine nektic ostracod mytilocypris henricae have high mg contents 100 000 ppm mg in caco3 at individual shell weights of 2 g this relative mg content decreases as calcification proceeds until shell weights exceed 120 g whereupon the mg content is constant and useful as an indicator of the ostracod s environment mg ca ratios in individual ostracod valves from several species of the genera mytilocypris and australocypris from culture experiments and a series of australian lakes indicate that the valve s mg content increases as a function of increasing temperature and salinity within the range 11 25 c and for waters containing 24 2325 ppm mg the molar mg ca ratio in these ostracods fully calcified valves increases by 0 0015 or 370 ppm mg in caco3 per 1 c and per change of 125 ppm mg in solution for most mainland australian lakes a change in water composition of 125 ppm mg corresponds to a change of 3 5 in salinity for a given mg content of a lake the mg ca ratio of the water may vary within the range of common lacustrine values without significantly affecting mg uptake in the ostracod valves these relationships can provide palaeosalinities and or palaeotemperatures for ostracods recovered from continental sediments for mg partitioning an increase in temperature and salinity produce increased mg content in ostracods whereas for 18o fractionation in biogenic calcite an increase in temperature produces a decrease in 18o of the ostracod and an increase in salinity leads to an increase in 18o of the ostracod thus a combination of 18o and mg measurements on non marine ostracods should enable unique resolution of palaeotemperature and palaeosalinity variations

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

modeling of water rock interactions in an aquitard of sandy clay in the coastal area near beihai china unconsolidated sand gravel and clay deposits near beihai and in the leizhou peninsula in southern china form an unconfined aquifer aquitard and a confined aquifer water and soil samples were collected from the two aquifers in the coastal beihai area for the determination of chemical compositions minerals and soluble ions hydrogeochemical modeling of three flow paths through the aquitard are carried out using phreeqc to determine water rock interactions along the flow paths the results indicate that the dissolution of anorthite fluorite halite rhodochrosite and co2 and precipitation of potash feldspar and kaolinite may be occurring when groundwater leaks through the aquitard from the unconfined aquifer to the confined aquifer cation exchanges between na and ca can also happen along the flow paths

the use of total lake surface area as an indicator of climatic change examples from the lahontan basin abstract variation in the size of lakes in the lahontan basin is topographically constrained river diversion also has played a major role in regulating lake size in lahontan subbasins the proper gage of lake response to change in the hydrologic balance is neither lake depth level nor lake volume but instead lake surface area normalization of surface area is necessary when comparing surface areas of lakes in basins having different topographies to a first approximation normalization can be accomplished by dividing the paleosurface area of a lake by its mean historical reconstructed surface area

historical adjustments by walker river to lake level fall over a tectonically tilted half graben floor walker lake basin nevada abstract historical records of lake and river adjustments in the tectonically active north south elongated walker lake extensional basin of west central nevada provide important insight to the style and rate that rivers react to tectonic tilt in half grabens the northern part of this basin historically containing walker lake is now occupied by the south flowing walker river walker lake presently restricted to the central basin sector is a perennial water body 30 m deep sustained by and forming the terminus of walker river both the river and lake have a strongly asymmetric distribution located preferentially near the active walker lake fault bounding the western basin margin walker lake has withdrawn from the northern basin sector since 1882 due to a 45 m drop in lake level caused by human diversion of the river upstream this withdrawal has forced walker river to incrementally lengthen and to sequentially reposition its delta along the retreating northern lake margin twelve deltas have been deposited since 1882 in response to these changes the initiation of eight of the twelve post 1882 deltas was associated with channel avulsion and four with channel lengthening ten of the twelve channel and delta relocation events entailed significant westward lateral movements toward the walker lake fault illustrating the dominating influence of the basin floor tectonic tilt on river adjustments the two eastward shifts were triggered intrinsically by avulsions resulting from erosion of the outer bank of channel meanders the three phases of progressive westward shifting of the river towards the walker lake fault occurred over periods of 18 6 and 16 years respectively documenting the rapid response time of walker river to basin floor tectonic tilt despite the countering effects of the intrinsic avulsions and hindrances to lateral migration caused by the muddy substrate of the former lake bottom deposits within which the river is incised

uranium series age estimates and paleoclimatic significance of pleistocene tufas from the lahontan basin california and nevada abstract an extended chronology of lahontan basin lake levels based on uranium series age estimates correlates with the global ice volume record lake highstands occur at or shortly after times of maximum ice sheet size moderate size lakes occur when the global ice volume is about 80 of its maximum the data indicate that lake levels rise and fall relative to the proximity of the mean position of the jetstream when the continental ice sheet is above some threshold size or shape it appears that the large scale circulation and climatic conditions are right for producing lakes of moderate to large size within the lahontan basin

holocene multidecadal and multicentennial droughts affecting northern california and nevada abstract continuous high resolution 18 o records from cored sediments of pyramid lake nevada indicate that oscillations in the hydrologic balance occurred on average about every 150 years yr during the past 7630 calendar years cal yr the records are not stationary during the past 2740 yr drought durations ranged from 20 to 100 yr and intervals between droughts ranged from 80 to 230 yr comparison of tree ring based reconstructions of climate change for the past 1200 yr from the sierra nevada and the el malpais region of northwest new mexico indicates that severe droughts associated with anasazi withdrawal from chaco canyon at 820 cal yr bp calendar years before present and final abandonment of chaco canyon mesa verde and the kayenta area at 650 cal yr bp may have impacted much of the western united states during the middle holocene informally defined in this paper as extending from 8000 to 3000 cal yr bp magnetic susceptibility values of sediments deposited in pyramid lake s deep basin were much larger than late holocene 3000 0 cal yr bp values indicating the presence of a shallow lake in addition the mean 18 o value of caco 3 precipitated between 6500 and 3430 cal yr bp was 1 6 less than the mean value of caco 3 precipitated after 2740 cal yr bp numerical calculations indicate that the shift in the 18 o baseline probably resulted from a transition to a wetter 30 and cooler 3 5 c climate the existence of a relatively dry and warm middle holocene climate in the truckee river pyramid lake system is generally consistent with archeological sedimentological chemical physical and biological records from various sites within the great basin of the western united states two high resolution holocene climate records are now available from the pyramid and owens lake basins which suggest that the holocene was characterized by five climatic intervals tic and 18 o records from owens lake indicate that the first interval in the early holocene 11 600 10 000 cal yr bp was characterized by a drying trend that was interrupted by a brief 200 yr wet oscillation centered at 10 300 cal yr bp this was followed by a second early holocene interval 10 000 8000 cal yr bp during which relatively wet conditions prevailed during the early part of the middle holocene 8000 6500 cal yr bp high amplitude oscillations in tic in owens lake and 18 o in pyramid lake indicate the presence of shallow lakes in both basins during the latter part of the middle holocene 6500 3800 cal yr bp drought conditions dominated owens lake desiccated and lake tahoe ceased spilling to the truckee river causing pyramid lake to decline at the beginning of the late holocene 3000 cal yr bp lake tahoe rose to its sill level and pyramid lake increased in volume

sedimentary biomarker and isotopic indicators of the paleoclimatic history of the walker lake basin western nevada walker lake a terminal saline lake in western nevada has experienced major fluctuations in its water level due to changes in the regional climate during quaternary times as part of a paleo climatological study of western nevada we have investigated organic matter 6 3c and c n values and lipid biomarker contents of sediments deposited at various periods over the past 150 thousand years of lake history surficial sediments from two cross lake transects contain mostly lake derived organic matter diagenetic losses of organic matter are evident in deeper sediments and the proportion of aquatic and terrigenous organic materials changes in response to variations in preservational factors source identification of organic matter is complicated by the probability that walker lake has experienced desiccation at various times in its history which impacts the degree of preservation of organic substances

the late holocene dry period multiproxy evidence for an extended drought between 2800 and 1850 cal yr bp across the central great basin usa abstract evidence of a multi centennial scale dry period between 2800 and 1850 cal yr bp is documented by pollen mollusks diatoms and sediment in spring sediments from stonehouse meadow in spring valley eastern central nevada u s we refer to this period as the late holocene dry period based on sediment recovered stonehouse meadow was either absent or severely restricted in size at 8000 cal yr bp beginning 7500 cal yr bp the meadow became established and persisted to 3000 cal yr bp when it began to dry comparison of the timing of this late holocene drought record to multiple records extending from the eastern sierra nevada across the central great basin to the great salt lake support the interpretation that this dry period was regional the beginning and ending dates vary among sites but all sites record multiple centuries of dry climate between 2500 and 1900 cal yr bp this duration makes it the longest persistent dry period within the late holocene in contrast sites in the northern great basin record either no clear evidence of drought or have wetter than average climate during this period suggesting that the northern boundary between wet and dry climates may have been between about 40 and 42 n latitude this dry in the southwest and wet in the northwest precipitation pattern across the great basin is supported by large scale spatial climate pattern hypotheses involving enso pdo amo and the position of the aleutian low and north pacific high particularly during winter

lake level variation in the lahontan basin for the past 50 000 years selected radiocarbon data on surficial materials from the lahontan basin nevada and california provide a chronology of lake level variation for the past 50 000 yr a moderate sized lake connected three western lahontan subbasins the smoke creek black rock desert subbasin the pyramid lake subbasin and the winnemucca dry lake subbasin from about 45 000 to 16 500 yr b p between 50 000 and 45 000 yr b p walker lake rose to its sill level in adrian valley and spilled to the carson desert subbasin by 20 000 yr b p lake level in the western lahontan subbasins had risen to about 1265 m above sea level where it remained for 3500 yr by 16 000 yr b p lake level in the western lahontan subbasins had fallen to 1240 m this recession appears synchronous with a desiccation of walker lake however whether the walker lake desiccation resulted from climate change or from diversion of the walker river is not known from about 15 000 to 13 500 yr b p lake level rapidly rose so that lake lahontan was a single body of water by 14 000 yr b p the lake appears to have reached a maximum highstand altitude of 1330 m by 13 500 yr b p a condition that persisted until about 12 500 yr b p at which time lake level fell 100 m no data exist that indicate the level of lakes in the various subbasins between 12 000 and 10 000 yr b p during the holocene the lahontan basin was the site of shallow lakes with many subbasins being the site of one or more periods of desiccation the shape of the lake level curve for the three western subbasins indicates that past changes in the hydrologic balance and hence climate of the lahontan basin were large in magnitude and took place in a rapid step like manner the rapid changes in lake level are hypothesized to have resulted from changes in the mean position of the jet stream as it was forced north or south by the changing size and shape of the continental ice sheet

chemical and isotopic composition of modern water bodies in the lake kopais basin central greece analogues for the interpretation of the lacustrine sedimentary sequence stable isotope measurements and modem aquatic chemistry are used to aid the reconstruction of past hydrological changes recorded in a 126 ka long sediment core from lake kopais greece this is the most southeasterly european site m with a long late quaternary sequence although the lake has been artificially drained calcareous sediments from the centre of the basin 38degrees26 16n 23degrees03 01e provide a continuous record from the early part of the last interglacial to the early holocene because the physiography and hydrology are complex modem analogues for past environmental conditions are essential the modem waters are of ca mg hco3 or mg ca hco3 type reflecting the prevalence of limestones and metamorphic rocks in the catchment they show a clear evolutionary trend in delta 18 o and deltad values from the source areas to the modem lakes however the modem water bodies are less evolved than the palaeolake a larger evaporating surface higher values of delta 18 o in precipitation decreased precipitation evaporation ratios and hydrological closure increased the delta 18 o values of endogenic carbonates at different times in the past however palaeolake kopais never desiccated completely or became saline analyses of the organic fraction from the core show that i it is mainly of algal origin ii productivity and carbon cycling in the lake waters were relatively stable through time and iii the bulk delta 13 c values vary between 29parts per thousand and 25parts per thousand indicating that the lake waters were never appreciably carbon limited and that c 4 plants did not invade the catchment although significant shifts in the delta 18 o and delta 13 c values of endogenic low mg calcite are attributable mainly to past variations in water balance weak delta 18 o delta 13 c covariance during marine isotope stages mis 5e 5c suggests that the palaeolake leaked significantly through karstic sinkholes since it was effectively operating as an open system delta 18 o may have retained the isotopic imprint of increased summer precipitation between mis 5a and mis 4 strong isotopic covariance suggests minimal outflow and drier conditions than today after an increase in winter snowmelt during mis 3 the climate again became cold and dry in the full glacial mis 2 a fluctuating increase in moisture occurred during the late glacial to early holocene transition mis 2 1 c 2002 elsevier science b v all rights reserved

change in the size of walker lake during the past 5000 years benson l v meyers p a and spencer r j 1991 change in the size of walker lake during the past 5000 years palaeogeogr palaeoclimatol palaeoecol 81 189 214 in 1984 a 12 m sediment core wlc84 8 was taken from the deepest part of walker lake samples of the core were analysed for diatoms pollen carbonate mineralogy magnesium content 6180 and 613c values of the total inorganic fraction 6180 and 613c values of limnocythere ceriotuberosa 613c values of the total organic fraction grain size and magnetic susceptibility the data indicate that walker lake became shallow and probably desiccated between i 5300 4800 and 27002100 yr b p each of the organic and inorganic proxy indicators of lake size discussed in this paper was useful in determining the presence of the shallow lake intervals however none of the indicators was useful in determining the cause of the shallowlake intervals instead the types of fish living in walker lake prior to 1940 were used to demonstrate that shallow lake intervals resulted from diversion of the walker river and not from climatic aridity major changes in mineralogy and magnesium content of carbonates and major changes in diatom populations with time were found to be a function of the chemical evolution of walker lake combined with changing lake size the stable isotopes of oxygen and carbon were found to be good indicators of lake volume changes a lake level record for walker lake constructed from stable isotope data was found to be similar to a lake level record constructed using tufa and tree stump data both records indicate relatively high lake levels between 4800 2700 yr b p at 1250 yr b p and within the last 300 yr substantial declines in lake level occurred 2000 and 1000 yr b p

late holocene lake level fluctuations in walker lake nevada usa walker lake a hydrologically closed saline and alkaline lake is situated along the western margin of the great basin in nevada of the western united states analyses of the magnetic susceptibility total inorganic carbon tic and oxygen isotopic composition 18 o of carbonate sediments including ostracode shells limnocythere ceriotuberosa from walker lake allow us to extend the sediment record of lake level fluctuations back to 2700 years b p there are approximately five major stages over the course of the late holocene hydrologic evolution in walker lake an early lowstand n2400 years b p a lakefilling period 2400 to 1000 years b p a lake level lowering period during the medieval warm period mwp 1000 to 600 years b p a relatively wet period 600 to 100 years b p and the anthropogenically induced lake level lowering period b100 years b p the most pronounced lowstand of walker lake occurred at 2400 years b p as indicated by the relatively high values of 18 o this is generally in agreement with the previous lower resolution paleoclimate results from walker lake but contrasts with the sediment records from adjacent pyramid lake and siesta lake the pronounced lowstand suggests that the walker river that fills walker lake may have partially diverted into the carson sink through the adrian paleochannel between 2700 to 1400 years b p

late holocene paleohydrology of walker lake and the carson sink in the western great basin nevada usa the late holocene histories of walker lake and the carson sink were reconstructed by synthesizing existing data in both basins along with new age constraints from key sites supplemented with paleohydrologic modeling the repeated diversions of the walker river to the carson sink and then back to walker lake caused walker lake level fluctuations spanning 50 m low lake levels at about 1000 750 and 300 cal yr bp are time correlative to the ages of fluvial deposits along the walker river paleochannel when flow was directed toward the carson sink the timing and duration of large lakes in the carson sink were further refined using moisture sensitive tree ring chronologies the largest lakes required a fourfold to fivefold increase in discharge spanning decades addition of walker river flow to the carson sink by itself is inadequate to account for the required discharge instead increases in the runoff coefficient and larger areas of the drainage basin contributing surface runoff may explain the enhanced discharge required to create these large lakes

incorporation of acoustic normal mode data into tomographic inversions in the greenland sea acoustic normal mode group velocity data are extracted from tomographic receptions in the greenland sea using a combination of spatial filtering with data from a six element hydrophone array and variable time windowing the mode group velocity data together with ray travel time data are used in inversions to obtain the range average sound speed profile the modal data significantly improve near surface resolution which is where the largest oceanographic signals occur inverse results using only acoustic data are consistent with point measurements a seasoar section and sparse conductivity temperature depth data