scalar magnetic anomaly maps of earth derived from pogo and magsat data a new pogo scalar magnetic anomaly map at 400 km altitude is presented which consists of spherical harmonics of degree 15 60 on the basis of the common features of this map with two new magsat anomaly maps dawn and dusk two scalar magnetic anomaly maps of the earth are presented using two selection criteria with different levels of stringency these selection criteria suppress the noncrustal components of the original maps by different amounts the more stringent selection criteria seek to eliminate as much contamination as possible at the expense of suppressing some anomaly signal this map is represented by spherical harmonics of degree 15 60 the less stringent selection criteria seek to retain as much crustal signal as possible at the expense of also retaining some contaminating fields this map is represented by spherical harmonics of degree 15 65 the resulting two maps are highly correlated with degree correlation coefficients greater than 0 8

reconstructing twentieth century sea surface temperature variability in the southwest pacific a replication study using multiple coral sr ca records from new caledonia 1 coral based climate reconstructions typically have not used multiple cores from a region to capture and replicate a climate signal largely because of concerns of coral conservation analytical expense and time constraints coral sr ca reproducibility through the twentieth century was investigated using three intracolony and three intercolony coral records from the reefs offshore of amedee island new caledonia different sampling resolutions were examined in coral sr ca fortnightly and monthly and 18o fortnightly monthly and seasonally as well as similar scale subsampling of the daily in situ sea surface temperature sst record the mean coral sr ca 18o and sst values do not change as a function of sampling resolution the coral sr ca signal is highly reproducible the average absolute offset between coeval monthly sr ca determinations between any two coral time series is 0 035 0 026 mmol mol 1 0 65 c which is less than twice the analytical precision of the coral sr ca measurements the stack average of the monthly coral sr ca variations and monthly anomalies are significantly correlated with monthly in situ sst 1967 1992 r 0 96 and 0 64 respectively p 0 05 and n 302 and 1 grid monthly sst data product 1900 1999 r 0 95 and 0 56 respectively p 0 05 and n 1198 the coral sr ca sst reconstruction exhibits interannual and decadal timescale fluctuations that exceed those observed in the gridded sst record which may reflect true differences between sst at a shallow reef site and those averaged over a 1 grid box or inadequacies in the methodology used to create the gridded sst product when few observations are available a warming trend of 0 6 c is observed in the twentieth century coral sr ca sst record

reconstructing seawater sr ca during the last 70 my using fossil fish tooth enamel abstract the chemical composition of past oceans records the combined effects of the evolution of life climate changes and solid earth dynamics variations in the rate of hydrothermal alteration of the oceanic crust continental weathering input and burial of marine carbonates are thought to drive the seawater sr ca ratio several methods exist for reconstructing past seawater sr ca ratio which are based on the partitioning of sr between biogenic and inorganic carbonates and seawater a compilation of reconstructed seawater sr ca ratios shows that results at variance with each other are obtained for the last 100 my leaving the question of the sr ca composition of seawater over this period unresolved here a new method for reconstructing the sr ca ratio of past seawater based on the partitioning of sr between tooth apatite of fossil fish enamel and seawater is proposed previously reported values of sr ca and 18 o po4 for a collection of fish teeth and new data allow the reconstruction of the seawater sr ca ratio evolution for the last 70 my using a new thermometer based on the sr ca ratio in fish teeth calculated sr ca ratios decrease from 14 mmol mol 1 at 70 ma to 8 mmol mol 1 at 50 ma and further increase to present day values during the pliocene the results are in agreement with values calculated from cenozoic benthic foraminifera obtained from odp and dsdp sites once the biological offsets of the partitioning of sr between apatite and water are determined fossil fish tooth bioapatite represents a material of choice for reconstructing the past seawater sr ca considering its better resistance to diagenetic alteration than for calcite and aragonite

diagenesis and geochemistry of porites corals from papua new guinea implications for paleoclimate reconstruction coral proxy records of sea surface temperature sst and hydrological balance have become important tools in the field of tropical paleoclimatology however coral aragonite is subject to post depositional diagenetic alteration in both the marine and vadose environments to understand the impact of diagenesis on coral climate proxies two mid holocene porites corals from raised reefs on muschu island papua new guinea were analysed for sr ca 18 o and 13 c along transects from 100 aragonite to 100 calcite thin section analysis showed a characteristic vadose zone diagenetic sequence beginning with leaching of primary aragonite and fine calcite overgrowths transitional to calcite void filling and neomorphic fabric selective replacement of the coral skeleton average calcite sr ca and 18 o values were lower than those for coral aragonite decreasing from 0 0088 to 0 0021 and 5 2 to 8 1 respectively the relatively low sr ca of the secondary calcite reflects the sr ca of dissolving phases and the large difference between aragonite and calcite sr ca partition coefficients the decrease in 18 o of calcite relative to coral aragonite is a function of the 18 o of precipitation carbon isotope ratios in secondary calcite are variable though generally lower relative to aragonite ranging from 2 5 to 10 4 the variability of 13 c in secondary calcite reflects the amount of soil co 2 contributing 13 c depleted carbon to the precipitating fluids diagenesis has a greater impact on sr ca than on 18 o the calcite compositions reported here convert to sst anomalies of 115 c and 14 c respectively based on calcite sr ca compositions in this study and in the literature the sensitivity of coral sr ca sst to vadose zone calcite diagenesis is 1 1 to 1 5 c per percent calcite in contrast the rate of change in coral 18 o sst is relatively small 0 2 to 0 2 c per percent calcite we show that large shifts in 18 o reported for mid holocene and last interglacial corals with warmer than present sr ca ssts cannot be caused by calcite diagenesis low level calcite diagenesis can be detected through x ray diffraction techniques thin section analysis and high spatial resolution sampling of the coral skeleton and thus should not impede the production of accurate coral paleoclimate reconstructions copyright 2003 elsevier science ltd

diagenesis of fossil coral skeletons correlation between trace elements textures and 234 u 238 u a comparative study of pleistocene fossil coral skeletons and of modern coral skeletons was carried out using petrographie and trace element analyses on a suite of pleistocene samples that had previously been studied for 234 u 230 th and u 230 th ages chen et al 1991 evidence of a range of diagenetic changes can be recognized by optical om and scanning electron microscopy sem the normal texture exhibited by modern corals under om consists of fine needles of aragonite forming a radial fibrous pattern around a central dark line center of calcification this pattern can also be seen in many fossil corals in most cases the central dark line partially disappears during diagenesis the radialfibrous pattern is obscured and there is a distinct coarsening of the radial fabric of aragonite to unoriented platy or equant aragonite crystals sem images show diagenetic textures ranging from dense structureless images of the coralline matrix with sharp boundaries at the septa walls to the development of 1 a patchy distribution of dissolution micropores partially filled with aragonite fibers in the matrix 2 aragonite needles coming from selvages in the septa walls which radiate into the septa voids using an electron microprobe and sem concentrations of na s sr and mg were measured no other trace elements were detected na s and mg contents of the matrix the fibrous micropores and radiating needles are highly variable and well correlated high concentrations of na s and mg were found in modern living corals with lower concentrations in fossil corals and fibrous micropores and the lowest value in the radiating needles the reason for the correlations of na s and mg and crystal chemistry and the response to diagenesis of these trace elements is not understood the average concentrations of na s and mg for each sample when plotted against the whole coral initial 234 u are generally correlated chen et al 1991 as all these diagenetic changes involve the recrystallization and deposition of aragonite we infer that the geologic site of diagenesis both for forming the secondary aragonitic phases and for the enhancement of the 234 u content in the fossil corals was the marine environment it is possible that the textural and na s and mg trace element contents of fossil corals be used to ascertain the reliability of fossil coral skeletons for u 230 th dating the basic problem of identifying a priori unaltered coral skeletons for 230 th dating is not yet resolved

heterogeneous diagenetic patterns in the pleistocene ironshore formation of grand cayman british west indies abstract the ironshore formation on grand cayman consists of six unconformity bounded units a to f that developed in response to repeated transgressive regressive cycles during the middle to late pleistocene corals and matrices in limestones from the rogers wreck point rwp offshore george town gt and western onshore wo areas are characterized by complex diagenetic fabrics that reflect marine bioerosion micrite envelopes internal sediments fibrous high mg calcite acicular aragonite isopachous prismatic calcite cements freshwater phreatic circumgranular cements even random blocky calcite cements and vadose meniscus calcite cements blocky calcite cements diagenesis throughout these limestones the matrices have undergone more meteoric diagenetic alteration than the corals overall however no systematic stratigraphic patterns exist to the distribution of these diagenetic fabrics and it is generally impossible to link the different phases of diagenesis with specific unconformities that cap each unit these heterogenous patterns of diagenetic features can be attributed to many intrinsic and extrinsic factors including the original compositions of the different components in the limestones the porosity and permeability of the substrate the nature of the diagenetic fluids climate and the duration of exposure during each lowstand integration of available data however indicates that maximum diagenesis took place during the lowstands denoted by the unconformities at the top of unit c marine isotope stage 7 and unit d marine isotope stage 5e when long periods of exposure were accompanied by wet climates with high annual rainfalls

empirical assessment of coral sr ca and mg ca ratios as climate proxies using colonies grown at different temperatures 1 coral strontium calcium sr ca and magnesium calcium mg ca ratios might be useful for reconstructing past sea surface temperature sst in tropical oceans where instrumental data are limited however the link between coral skeletal trace elements and sst is disputed and biological factors such as skeletal growth rate may also affect trace elements in a coral we studied the relationships between growth rate and sst and sr ca and mg ca ratios using corals porites spp cultured in thermostated tanks sr ca was controlled primarily by sst while mg ca mainly reflected the growth rate with negligible contribution from species on both the variations these relationships are consistent with modeled results of cation partitioning during aragonite crystal formation

a 200 ka pollen and oxygen isotopic record from two sediment cores from the eastern arabian sea abstract we present here a pollen record from the northern indian ocean that goes back to 200 ka the boundary between marine isotopic stages mis 7 and 6 pollen oxygen isotopic composition and organic carbon have been examined for two sediment cores from the eastern arabian sea 15 02 n and 71 41 e 13 16 n and 71 00 e to reconstruct the long term palaeoclimate and palaeovegetation of the indian subcontinent oxygen isotope data suggest that glacial periods mis 2 4 and 6 are characterised by low precipitation because of a weak southwest monsoon and a strong northeast monsoon in contrast interglacial periods mis 1 3 and 5 are marked by high fresh water input resulting from a strong southwest monsoon during the last glacial interglacial cycle sea surface temperature and surface salinity changed as a result of variations in the evaporation precipitation e p balance throughout the core the dominant pollen types are poaceae and chenopodiaceae and or amaranthaceae 50 their dominance during glacial periods mis 2 4 and 6 suggests that the climate was cold and dry this dominance is also suggestive of salinity tolerant vegetation colonizing large areas near seashore due to lower sea level or high e p conditions during interglacial periods mis 1 3 and 5 when there was high precipitation the arid taxa were sparse whereas poaceae and piperaceae were abundant hence chenopodiaceae and or amaranthaceae and artemisia are suggestive of cold and arid semi arid climate and poaceae and piperaceae of warm and wet conditions mangrove pollen is not well represented in the cores

a coral sr ca calibration and replication study of two massive corals from the gulf of mexico abstract this study examined the variations in the ratio of strontium to calcium sr ca for two atlantic corals montastraea faveolata and siderastrea siderea from the dry tortugas national park centered on 24 7 n 82 8 w in the gulf of mexico cores from coral colonies in close proximity 10s of meters and with the same environmental conditions i e depth and water chemistry were micro sampled with approximately monthly resolution and the resulting sr ca variations were calibrated with local sea surface temperature sst records replication tests for coral sr ca variations found high agreement between intra colony variations and between individual colonies of s siderea a single m faveolata colony was sampled regression analysis of monthly variations in coral sr ca and local sst revealed significant correlation on monthly and inter annual timescales verification of the calibration on different timescales found coral sr ca sst reconstructions in s siderea were more accurate than those from m faveolata especially on inter annual timescales sr ca sst calibration equations for the two species are significantly different cf sr ca 0 042 sst 10 070 s siderea sr ca 0 027 sst 9 893 m faveolata mean linear extension for m faveolata is approximately twice that of s siderea 4 63 4 31 and 8 31 mm year 1 a1 f1 and b3 respectively however seasonal sr ca variability in m faveolata is less than s siderea 0 323 0 353 and 0 254 mmol mol 1 a1 f1 and b3 respectively the reduced slope for m faveolata is attributed to physical sampling issues associated with complex time skeletal structure of m faveolata i e a sampling effect and not a growth effect since the faster growing m faveolata has the reduced sr ca variability

compatibility of high altitude aeromagnetic and satellite altitude magnetic anomalies over canada results from equivalent source distributions derived jointly from high altitude average 4 km aeromagnetic and magsat derived average 400 km magnetic anomalies over canada indicate that long wavelength components 500 2500 km in these fields are extremely compatible with one another with a correlation coefficient of 0 95 the jointly estimated anomaly field at the earth s surface can be used as a long wavelength adjustment surface for regional near surface magnetic anomaly compilations and in assessing the performance of other downward continuation techniques because near surface anomalies are not available over all regions of the world we compare the jointly estimated anomaly field to the results of two different downward continuation techniques the evaluation of anomalies at the earth s surface from spherical harmonic coefficients derived from satellite altitude data and the use of downward continuation methods based on harmonic splines numerical and visual comparisons of these downward conti

the role of skeletal porosity in aragonite neomorphism strombus and montastrea from the pleistocene key largo limestone florida abstract the neomorphism of aragonite to calcite involves complex textural and chemical alterations that are in part controlled by the degree of communication between diagenetic and ambient formation fluids two taxa montastrea annularis and strombus gigas from the vadose zone of the pleistocene key largo formation in southern florida were examined in order to evaluate the effect of initial skeletal porosity on system closure during neomorphism fabrics of replacement calcite in both taxa are similar consisting of blocky crystals largely restricted to areas of former skeletal aragonite oriented aragonite and organic inclusions result in the preservation of relic fabrics in both taxa the chemical signatures of coralline and molluscan aragonite and calcite are strongly dependent on initial skeletal porosity compared to original aragonite montastrea calcite is enriched in magnesium 1 151 64 ppm versus 2 114 619 ppm and depleted in strontium 7 397 376 ppm versus 2 510 43 ppm these data in conjunction with large calcite oxygen depletions 3 8 0 2 versus 5 7 0 3 and variable calcite carbon depletions 0 6 0 6 versus 1 3 to 7 3 demonstrate significant exchange between neomorphic front and formational fluids in contrast strombus calcite composition is largely inherited from original aragonite and is only slightly enriched in strontium and magnesium 2 299 316 ppm versus 2 519 759 ppm and 96 23 ppm versus 173 79 ppm while carbon exhibits a small depletion 5 3 0 5 versus 4 4 0 8 similarity of str mbus aragonite and calcite compositions reflects high rock water ratios in relatively closed diagenetic systems calcite oxygen depletion 0 5 0 5 versus 3 6 0 4 observed in strombus however requires some exchange between formation and neomorphic front fluids differences in the thickness of replacement calcite rims between taxa reflect variable skeletal porosities and rates of migration of neomorphic fronts neomorphism was six times faster by volume in porous montastrea than in dense strombus skeletal structures thus skeletal porosity influences degrees of system openness during aragonite neomorphism

comparison between the recent u s composite magnetic anomaly map and magsat anomaly data in order to test the validity of the magsat anomaly data the recently published u s geological survey society of exploration geophysicists composite magnetic anomaly map cmam of the conterminous united states was used as a standard and a comparison was made with these satellite data the cmam data set digitized by the phoenix corporation was resampled and continued upward to 320 km altitude this upward continued data set was compared with an independently derived magsat field at the same altitude our initial results were unsatisfactory the cmam data are dominated by a long wavelength surface increasing in amplitude by some 400 nt in a northwesterly direction across the unites states this broad trend surface was suppressed by removing a general two dimensional polynominal function having nine orders in longitude and five in latitude obtained through least squares fitting the resulting residual upward continued field was compared with the magsat data by means of correlation techniques correspondence was found between these data sets for many large amplitude anomalies for example off the east coast in kentucky oklahoma mississippi embayment georgia arizona and nebraska dissimilarities occur over the rio grande rift minnesota and wyoming the negative anomaly over the rio grande rift and the positive anomaly over the midcontinent geophysical anomaly are more pronounced in the cmam data than in the magsat results these latter discrepancies are attributed to the method used to remove external field variations from the satellite data which suppresses north south trending structures i e those lying in the orbit direction cmam base level problems localized over minnesota and wyoming are believed to cause observed discordance between satellite and aeromagnetic data in these regions this study confirms with ground truth the validity of these satellite measurements and demonstrates that satellite derived anomaly maps can be used to identify base level problems when compiling local or regional aeromagnetic surveys

assessing coral sr ca sst calibration techniques using the species diploria strigosa the coral species diploria strigosa is a promising archive for paleoclimate reconstruction in the tropical atlantic but limited work has been accomplished thus far to quantify the relationship between strontium to calcium ratios and sea surface temperatures in this species in this study we collected three modern d strigosa coral colonies from anegada british virgin islands to refine the use of this species as a paleoclimate archive three regression techniques including ordinary least squares reduced major axis and weighted least squares were used to assess how assumptions implicit in these regression methods influence the calibration our analysis demonstrated that regression slopes were strongly impacted by the assumptions about data uncertainty we recommend using the unbiased weighted least squares regression technique for calibrating the sr ca paleothermometer especially when precise local sea surface temperature data are unavailable combining our sr ca data with previously published data from this species results in a multi site multi colony temperature sensitivity of 0 046 0 001 mmol mol c for mean centered monthly data 0 059 0 001 mmol mol c for monthly anomalies and 0 063 0 004 for annual anomalies we suggest these relationships are the best available characterization of the temperature dependence of sr ca in d strigosa and can be utilized in future paleoclimate reconstructions

effect of diagenesis on the sr o and c isotope composition of late cretaceous mollusks from the western interior seaway of north america evaluating the effects of diagenesis on the isotopic compositions of sr o and c in marine carbonates is critical to their use as proxies in reconstructing information on the salinity temperature and dissolved inorganic carbon of ancient oceans we have analyzed a series of samples of mollusk shells from the baculites compressus zone late campanian of the pierre shale of south dakota samples included outer shell material and septa of cephalopods collected inside and outside concretions preservation was evaluated using light microscopy scanning electron microscopy sem trace element analysis and x ray diffraction all of the material consists of aragonite based on x ray diffraction an sem preservation index pi was established based on comparison of the microstructure of the fossil material with that of modern nautilus excellent preservation pi 5 was characterized by well defined nacreous plates with discrete angular boundaries in contrast samples showing fused nacreous plates with indistinct boundaries were rated poor pi 1 87sr 86sr ratios vary with preservation and average 0 707648 000021 n 10 for excellent preservation pi 5 0 707615 000028 n 5 for good preservation pi 3 0 707404 000074 n 7 for fair preservation pi 2 and 0 707261 000053 n 8 for poor preservation pi 1 these data suggest that as the quality of the preservation declines the mean 87sr 86sr ratio decreases and the standard error of the mean increases oxygen and carbon isotope analyses of the same specimens also show decreases with preservation and 18o 13c and 87sr 86sr are well correlated suggesting that these tracers are all altered as the pi decreases the sr ca ratio increases as preservation decreases indicating that sr is added to the shell material during diagenesis in contrast mg ca shows no trend with preservation if the increasing sr concentration and decreasing 87sr 86sr of the shell material with decreasing preservation represents the addition of sr to the shell during diagenesis we calculate that the added sr had 87sr 86sr ranging from 0 707582 to 0 707032 potential sources of the added sr include older marine carbonates and weathering of volcanic ash layers present in the shale the mechanisms of alteration likely include epitaxial growth of strontianite on the original shell aragonite and isotopic exchange of c and o between alteration fluids and shell carbonate we conclude that sem preservation criteria are effective in screening shell material that records original isotopic values and that variations in sr o and c isotope composition in well preserved material can be used to assess paleoenvironmental parameters such as salinity and temperature our results also indicate that assessing preservation is a critical prerequisite to the determination of numerical ages of shell material using strontium isotope stratigraphy

milankovitch forcing of the last interglacial sea level during the last interglacial sea level was as high as present 4000 to 6000 years before peak northern hemisphere insolation receipt 126 000 years ago the sea level results are shown to be consistent with climate models which simulate a 3 to 4 c july temperature increase from 140 000 to 130 000 years ago in high latitudes with all northern hemisphere land areas being warmer than present by 130 000 years ago the early warming occurs because obliquity peaked earlier than precession and because precession values were greater than present before peak precessional forcing occurred these results indicate that a fuller understanding of the milankovitch climate connection requires consideration of fields other than just insolation forcing at 65 n

sst artifacts in coral proxy records produced by early marine diagenesis in a modern coral from rabaul papua new guinea 1 we investigated the effects of early marine diagenesis on the skeletal geochemistry of a porites coral collected live offshore of rabaul papua new guinea the lowermost 14 cm of the 1 9 m coral core contains physical evidence of alteration which is clearly visible in x radiograph sem and petrography images abrupt and significant increases in coral 18o and sr ca and decreases in coral mg ca occur at the transition from unaltered to altered skeleton all of which imply significant sst cooling if the altered nature of the coral skeleton went unrecognized screening for the effects of early marine diagenesis should become a standard procedure in coral climate studies

impact of skeletal dissolution and secondary aragonite on trace element and isotopic climate proxies in porites corals restricted zones of recent dissolution and secondary aragonite infilling were identified in a coral core collected in 1986 from a living massive porites colony from the central great barrier reef australia secondary aragonite needles 20 m long cover skeletal surfaces deposited from 1972 to late 1974 and increase bulk density by 10 dissolution is observed above this zone whereas older skeleton is pristine we investigate the impact of both types of early marine diagenesis on skeletal geochemistry and coral paleoclimate reconstructions by comparison with similar records from eight contemporary porites colonies collected at nearby reefs secondary aragonite overgrowth causes anomalies in skeletal density mg ca sr ca u ca o and c the secondary aragonite is consistently associated with a cool temperature anomaly for each of the sea surface temperature sst proxies o sst 1 6 c sr ca sst 1 7 c mg ca sst 1 9 c u ca sst 2 8 c dissolution through incongruent leaching also causes cool sst artifacts but only for trace element ratios mg ca sst 1 2 c sr ca sst 1 2 c u ca sst 2 1 c the sequence of preference with respect to dissolution of coral skeleton in seawater is mg ca sr u rigorous screening of coral material for paleoclimate reconstructions is therefore necessary to detect both dissolution and the presence of secondary minerals the excellent agreement between apparent sst anomalies generated by different modes of diagenesis means that replication of tracers within a single coral cannot be used to validate climate proxy interpretations poor replication of records between different coral colonies however provides a strong indication of nonclimatic artifacts such as dissolution and secondary aragonite copyright 2007 by the american geophysical union

temporal and spatial variations in the diagenetic fabrics and stable isotopes of pleistocene corals from the ironshore formation of grand cayman british west indies abstract on grand cayman the unconformity bounded units a to f in the ironshore formation represent repeated cycles of deposition and subaerial exposure that were associated with the dramatic oscillations in sea levels that characterized the middle to late pleistocene montastrea annularis and acropora palmata the dominant corals found in units a to f in the rogers wreck point area and offshore george town area reflect these changes with their complex mosaics of marine aragonite cements bioerosion internal sediments and meteoric calcitization of coral skeleton dissolution diagenetic features the distribution of the diagenetic fabrics throughout this sequence however is not predictable the randomness in the degree of skeletal calcitization is shown by the lack of systematic variation in calcitization from units a to f and the fact that the degree of skeletal calcification in m annularis is higher than that in a palmata in the rogers wreck point area but less than in a palmata in the george town cores the stable isotope compositions 13c 18o of the corals from units a to f plot along the same trend line with their positions on that trend reflecting the amount of meteoric diagenesis they have undergone the variable styles and degrees of diagenesis evident in the corals from the ironshore formation reflect 1 the variable impact of intrinsic e g skeletal architecture porosity of coral and extrinsic e g sea level climate factors during each phase of diagenesis and 2 temporal effects associated with the diagenetic overprinting that took place during each successive phase of diagenesis this means that the diagenetic fabrics are not stratigraphically ordered and that it is impossible to correlate specific diagenetic phases with specific sea level lowstands or highstands

an assessment of long wavelength magnetic anomalies over canada the reliability of the long wavelength portion 300 km of the magnetic field over canada as represented by the national aeromagnetic anomaly database compiled by the geological survey of canada gsc is assessed by comparison with two independent data sets a high altitude country wide survey carried out by the former earth physics branch epb and data from the magsat and pogo satellite missions the different altitudes at which each data set was measured 300 m 4 km and 400 km and their different resolution and time span of observations allow a determination of the integrity of selected wavelength bands in each data set the upward continued epb and magsat pogo fields compare well for wavelengths of 300 2500 km the gsc data show significant differences to the former indicating that the levelling and merging of several hundred individual surveys has degraded the longer wavelength components of the magnetic field replacing the gsc wavelength components 300 km with those from the epb field

long wavelength aeromagnetic anomaly map of the conterminous united states total intensity magnetic anomaly unflltered and low pass filtered profile and contour maps of the conterminous united states have been prepared from data provided by the u s naval oceanographic office9s project magnet survey the maps are useful for regional geological investigations because the anomalies particularly on the filtered maps that emphasize long wavelength anomalies can be correlated with known major geologic features the most intense positive long wavelength anomaly occurs over precambrian mafic basement rocks in eastern tennessee and kentucky other examples of prominent positive anomalies occur over the great valley of california and the colorado plateau and along the appalachian fold belt in contrast prominent negative long wavelength magnetic anomalies occur over the cascade mountains mississippi embayment and southern rocky mountains and marginally to the positive anomaly related to the mid continent rift

geometric consequences of ductile fabric development from brittle shear faults in mafic melt sheets evidence from the sudbury igneous complex canada abstract compared to felsic igneous rocks the genetic relationship between brittle and ductile fabric development and its influence on the geometry of deformed mafic melt sheets has received little attention in structural analyses we explore these relationships using the sudbury igneous complex sic as an example the sic is the relic of a layered impact melt sheet that was transformed into a fold basin the sudbury basin during paleoproterozoic deformation at the southern margin of the archean superior province we studied brittle and ductile strain fabrics on the outcrop and map scales in the southern sudbury basin notably in the norite and quartz gabbro layers of the sic here deformation is heterogeneous and occurred under variable rheological conditions evident by the development of brittle shear fractures brittle ductile shear zones and pervasive ductile strain the mineral fabrics formed under low to middle greenschist facies metamorphism whereby brittle deformation caused hydrolytic weakening and ductile fabric development principal strain axes inferred from all structural elements are collinear and point to a single deformation regime that led to thinning of sic layers during progressive deformation ductile fabric development profoundly influenced the orientation of sic material planes such as lithological contacts and magmatic mineral fabrics more specifically these planar structural elements are steep where the sic underwent large magnitudes of thinning i e in the south limb of the sudbury basin here the actual tilt component of material planes is likely smaller than its maximum total rotation 60 inferred from inclined igneous layering in the norite our field based study shows that ductile fabric development from brittle faults can have a profound influence on the rotational components of primary material planes in deformed igneous melt sheets

how long and how stable was the last interglacial abstract surface ocean indicators in the north atlantic during marine isotope stage mis 5 correlate closely with the vegetational succession in northeastern france the melisey i silty layer which marks the end of the last interglacial biozone in la grande pile pollen record appears coeval with the polar front advance c24 registered in the core v29 191 by a sharply increased presence of ice rafted detritus and the cold water foraminifer neogloboquadrina pachyderma sinistral since this event is younger than the peak of mis 5d the last interglacial as recognized in northern france correlates not only with the mis 5e but also with a substantial part of mis 5d the last interglacial in la grande pile was twice as long as the holocene and the climate in its first half was apparently not less stable than during the current interglacial if the future natural climates were to develop as analogs of the past then the onset of the next glacial environments on land would be still many millennia ahead

early marine diagenesis in corals and geochemical consequences for paleoceanographic reconstructions detecting the potential geochemical consequences of early marine diagenesis is essential for establishing the validity of past climate reconstructions from coral we present coral skeletal 18o and sr ca data for two long coral cores spanning 1839 1994 ad at ningaloo reef western australia one of which includes significant secondary precipitation of marine inorganic aragonite long term trends in reconstructed sea surface temperatures ssts for the well preserved coral correlate strongly with instrumental sst records spanning the 20th century in contrast the 18o and sr ca for the diagenetically altered coral give identical cool sst anomalies of 4 5 c as a consequence of the addition of secondary aragonite enriched in 18o and sr our results indicate that cross checking of paleoclimate reconstructions with two supposedly independent paleothermometers may not be valid and that coral records showing cooler ssts in the past need to be interpreted with caution furthermore modern coral records with long term trends in 18o indicating recent warming and freshening of the ocean can be potentially explained by early marine diagenesis

magnetic anomaly map of north america data presented on the magnetic anomaly map in the continental areas have largely been derived from published map sources however these maps for the most part have been digitized and subjected to various processing steps in preparation for compositing the marine areas of the map consist mostly of digital data track except in the gulf of mexico caribbean sea and the continental shelf areas of alaska where the data were obtained from digitized maps

coral record of equatorial sea surface temperatures during the penultimate deglaciation at huon peninsula uplifted coral terraces at huon peninsula papua new guinea preserve a record of sea level sea surface temperature and salinity from the penultimate deglaciation remnants have been found of a shallow water reef that formed during a pause similar to the younger dryas in the penultimate deglaciation at 130 000 2000 years ago when sea level was 60 to 80 meters lower than it is today porites coral which grew during this period has oxygen isotopic values and strontium calcium ratios that indicate that sea surface temperatures were much cooler 22 2 c than either last interglacial or present day tropical temperatures 29 1 c these observations provide further evidence for a major cooling of the equatorial western pacific followed by an extremely rapid rise in sea level during the latter stages of termination ii

palaeoenvironmental records from fossil corals the effects of submarine diagenesis on temperature and climate estimates the geochemistry of coral skeletons may reflect seawater conditions at the time of deposition and the analysis of fossil skeletons offers a method to reconstruct past climate however the precipitation of cements in the primary coral skeleton during diagenesis may significantly affect bulk skeletal geochemistry we used secondary ion mass spectrometry sims to measure sr mg b u and ba concentrations in primary coral aragonite and aragonite and calcite cements in fossil porites corals from submerged reefs around the hawaiian islands cement and primary coral geochemistry were significantly different in all corals we estimate the effects of cement inclusion on climate estimates from drilled coral samples which combine cements and primary coral aragonite secondary 1 calcite or not vert similar2 aragonite cement contamination significantly affects sr ca sst estimates by 1 c and 0 4 to 0 9 c respectively cement inclusion also significantly affects mg ca b ca and u ca sst estimates in some corals x ray diffraction xrd will not detect secondary aragonite cements and significant calcite contamination may be below the limit of detection not vert similar1 of the technique thorough petrographic examination of fossils is therefore essential to confirm that they are pristine before bulk drilled samples are analysed to confirm that the geochemistry of the original coral structures is not affected by the precipitation of cements in adjacent pore spaces we analysed the primary coral aragonite in cemented and uncemented areas of the skeleton sr ca b ca and u ca of primary coral aragonite is not affected by the presence of cements in adjacent interskeletal pore spaces i e the coral structures maintain their original composition and selective sims analysis of these structures offers a route to the reconstruction of accurate ssts from altered coral skeletons however mg ca and ba ca of primary coral aragonite are significantly higher in parts of skeletons infilled with high mg calcite cement we hypothesise this reflects cement infilling of intraskeletal pore spaces in the primary coral structure

strontium in coral aragonite 2 sr coordination and the long term stability of coral environmental records we have used x ray diffraction xrd and sr k edge extended x ray absorption fine structure exafs to determine the structural state of sr in a suite of coral aragonite samples our samples encompassed a selection of coral species porites lobata porites lutea pocillopora eydouxi montastrea annularis pavona gigantea and pavona clavus including some commonly used for palaeoenvironmental reconstruction aragonite was the only carbonate observed by xrd we refined the isolated exafs against structural models for sr in aragonite and two phase strontianite aragonite mixes our data are indistinguishable from sr ideally substituted in aragonite and strontianite was present below detection levels estimated at 5 of sr present comparisons of recent and ancient coral aragonite show no sign of exsolution either by spinodal decomposition or by the direct nucleation of strontianite domains published diffusion rates of sr in ionic solids support the view that exsolution would occur prohibitively slowly coral aragonites are metastable materials with slow diffusion kinetics that have the potential to encode environments over timescales of millions of years

reproducibility of geochemical and climatic signals in the atlantic coral montastraea faveolata 1 monthly resolved 41 year long stable isotopic and elemental ratio time series were generated from two separate heads of montastraea faveolata from looe key florida to assess the fidelity of using geochemical variations in montastraea the dominant reef building coral of the atlantic to reconstruct sea surface environmental conditions at this site the stable isotope time series of the two corals replicate well mean values of 18o and 13c are indistinguishable between cores compare 0 70 versus 0 68 for 13c and 3 90 versus 3 94 for 18o mean values from the sr ca time series differ by 0 037 mmol mol which is outside of analytical error and indicates that nonenvironmental factors are influencing the coral sr ca records at looe key we have generated significant 18o sea surface temperature sst r 0 84 and sr ca sst r 0 86 calibration equations at looe key however these equations are different from previously published equations for montastraea variations in growth parameters or kinetic effects are not sufficient to explain either the observed differences in the mean offset between sr ca time series or the disagreement between previous calibrations and our calculated 18o sst and sr ca sst relationships calibration differences are most likely due to variations in seawater chemistry in the continentally influenced waters at looe key additional geochemical replication studies of montastraea are needed and should include multiple coral heads from open ocean localities complemented whenever possible by seawater chemistry determinations

coral windows onto seasonal climate variability in the northern caribbean since 1479 mean surface ocean conditions in the caribbean were up to 2 c cooler than today at times during the little ice age the seasonal context for such mean state changes is important for determining the mechanisms involved we reconstructed surface ocean conditions in southwest puerto rico at approximately monthly resolution over eight 4 12 year periods during the last 520 years to test if the seasonal cycles of temperature or salinity varied with mean state we carried out paired analyses of sr ca and 18o for two coral cores the 18o data contained clear annual cycles and were significantly correlated to temperature during the 20th century calibration periods 1993 2004 and 1902 1912 r 0 73 the sr ca data contained high frequency noise that obscured the seasonal cycles although the centennial variability matched that of the coral 18o indicating a common forcing that is likely temperature the seasonal coral 18o amplitude averaged 0 60 0 17 with none of the periods significantly different from the most recent the simplest explanation is that the amplitudes of seasonal seawater 18o and temperature variations were not different from today previous work in the southern caribbean indicates that the intertropical convergence zone was shifted southward or weaker during the little ice age and we speculate about how this could occur with no apparent affect on seasonality in the northern caribbean

high temporal resolution mg ca and ba ca records in modern porites lobata corals 1 secondary ion mass spectrometry sims was used to determine mg ca and ba ca variations across two skeletal structures the fasciculi and the centers of calcification cocs in two porites lobata corals of different linear extension rates from oahu hawaii both corals exhibit large mg and ba heterogeneity which is not related to sea surface temperature sst or composition higher concentrations of ba occur in the fasciculi and higher mg in the cocs of the slowly extending coral compared to the fast growing coral mg and ba concentrations are significantly higher in the cocs of both corals compared to the fasciculi trace element variations may reflect changes in the calcifying fluid composition or changes in skeletal trace element incorporation regressions between mg ba and sr reported in a prior publication indicate that the skeletal incorporation of each element is affected by a different factor or combination of factors smoothed sims records of ba ca variations across the fasciculi of the fast growing coral follow the seasonal trend predicted from sst and expected seawater chemistry variations smoothed sims mg ca records do not correlate with sst indicating that sims mg ca records cannot be used to estimate past ssts

geopotential field anomaly continuation with multi altitude observations abstract conventional gravity and magnetic anomaly continuation invokes the standard poisson boundary condition of a zero anomaly at an infinite vertical distance from the observation surface this simple continuation is limited however where multiple altitude slices of the anomaly field have been observed increasingly areas are becoming available which are constrained by multiple boundary conditions from surface airborne and satellite surveys this paper describes the implementation of continuation with multi altitude boundary conditions in cartesian and spherical coordinates and investigates the advantages and limitations of these applications continuations by eps equivalent point source inversion and the ft fourier transform as well as by scha spherical cap harmonic analysis are considered these methods were selected because they are especially well suited for analyzing multi altitude data over finite patches of the earth such as those covered by the admap database in general continuations constrained by multi altitude data surfaces are invariably superior to those constrained by a single altitude data surface due to anomaly measurement errors and the non uniqueness of continuation

orbital control of low latitude seasonality during the eemian 1 we used sr ca and stable isotope data from well dated and preserved corals from the northeastern caribbean to determine the seasonal environmental conditions for four continuous years during the eemian the last time the earth was in a prolonged warm phase we determined that the seasonal range in sst during the eemian was 25 30 c this is 1 2 larger than at present and caused primarily by winter cooling and only to a small degree by summer warming as climate modeling studies indicate the bias towards colder winters can be explained by changes in low latitude insolation induced by altered orbital parameters modulated by atmospheric co2 levels that were lower than today milankovitch forcing at higher latitudes was probably less important

a high resolution calibration of sr ca thermometry using the caribbean coral montastraea annularis 1 a relationship has been established between the sr ca ratio in the skeleton of the scleractinian coral montastraea annularis and sea surface water temperature in south florida in order to obtain this correlation specimens of montastraea annularis were transplanted to a site at a local reef where every two to three months throughout a 2 year period the corals were stained with alizarin red s and where water temperature which annually ranges between 20 and 30 c was continually monitored at the end of the experimental period the coral skeleton was sampled at a rate of 50 samples per year each sample corresponding to only around 20 g of calcium carbonate for the 2 5 year period the sr ca ratio exhibited excellent correlation in the first year r2 0 83 sr ca mmol mol 10 11 0 0452 sst c but a rather poorer correlation in the second year r2 0 68 sr ca mmol mol 10 09 0 0406 sst c averaging the data into monthly values for year 1 we determined a relationship of sr ca mmol mol 10 165 0 0471 sst c on the basis of the excellent correlation between temperature and sr ca we feel that this relationship is the most accurate discrepancies in the second year are suggested to arise from slight sampling errors relative to the stain lines

the intermediate wavelength magnetic anomaly maps of the north atlantic ocean derived from satellite and shipborne data summary two intermediate wavelength magnetic anomaly maps of the north atlantic ocean are derived based on satellite and marine magnetic observations the satellite map is produced from the covariant features of pogo and magsat dawn and magsat dusk magnetic anomalies the marine map is compiled using shipborne data collected since 1965 the two maps are in excellent agreement over well defined anomalies both in location and amplitude suggesting that these anomalies are real and reflect magnetization contrasts in the oceanic lithosphere both maps show the intermediate wavelength seafloor spreading anomalies of the cretaceous quiet zone of the central north atlantic ocean as well as the negative seafloor spreading anomaly of the labrador sea caused by dominantly reversed polarity periods the iceland hotspot alpha ridge azores high king s trough and the rockall microcontinent have positive anomalies there is no consistent magnetic signature associated with the ocean continent boundary although the deep sedimentary basin of nova scotia is delineated by a well defined negative anomaly

diagenesis in live corals from the gulf of aqaba i the effect on paleo oceanography tracers abstract the effect of early diagenesis on trace element abundance in coral skeleton was studied in live coral heads porites from the nature reserve reef nrr elat gulf of aqaba northern red sea petrography of the corals shows diagenetic features of dissolution recrystallization and secondary aragonite precipitation pore filling which are most extensive in the oldest part of the coral coral porewaters were extracted with a special setup and were analyzed for chemical composition the total alkalinity and sr deficit in pore water as compared to reef water is consistent with both precipitation of secondary aragonite and recrystallization of primary skeleton the present rate constant of pore filling by secondary aragonite was estimated by a water replacement experiment to be 0 0015 y 1 which equals to pore filling rate of 1 5 0 3 kg aragonite per year the corals show clear seasonal fluctuations in sr ca ratios that are interpreted as reflecting changes in sea surface temperature sst yet the secondary aragonite is characterized by a significantly higher sr ca ratio than the average ratio in primary aragonite thus measuring a mixed sample of pristine and secondary aragonite may produce erroneous about 2 c lower sst estimates by the sr ca thermometers it appears that the sr ca ratio a major proxy for paleo environmental marine studies is sensitive to subtle pore filling and replacement of the original coral matrix by secondary aragonite in the marine environment

seasonal changes in sea surface temperature and salinity during the little ice age in the caribbean sea deduced from mg ca and 18o 16o ratios in corals abstract the oxygen isotopic composition 18 o of coral skeletons reflects a combination of sea surface temperature sst and the 18 o of seawater which is related to sea surface salinity sss in contrast the magnesium calcium mg ca ratio of a coral skeleton reflects sst independent of salinity by using the relationships among coral mg ca ratios coral 18 o seawater 18 o and sst it is possible to determine past sst and sss uniquely such determinations were made and calibrated using the mg ca ratio and the 18 o of the modern part of a 3 m long coral core montastrea faveolata collected from the southwest coast of puerto rico in the caribbean sea where both sst and sss changes seasonally and the seawater 18 o measured at the coral site our results yielded three relationships coral mg ca sst 18 o coral 18 o water sst and 18 o water sss with these calibration equations seasonal changes in sst and sss during the little ice age lia in the caribbean sea were reconstructed the 18 o and mg ca ratio of the coral skeleton between 1699 and 1703 suggests that the sst during the lia was approximately 2 c cooler than present with the sss showing greater seasonal changes as well these results are in good agreement with climate based reconstruction from corals based on oxygen isotopes although the possibility of some uncertainty remain in our estimation including long term decadal scale trends in climate

interpreting sea surface temperature from strontium calcium ratios in montastrea corals link with growth rate and implications for proxy reconstructions 1 we analyzed strontium calcium ratios sr ca in four colonies of the atlantic coral genus montastrea with growth rates ranging from 2 3 to 12 6 mm a 1 derived sr ca sea surface temperature sst calibrations exhibit significant differences among the four colonies that cannot be explained by variations in sst or seawater sr ca for a single coral sr ca ratio of 8 8 mmol mol 1 the four calibrations predict ssts ranging from 24 0 to 30 9 c we find that differences in the sr ca sst relationships are correlated systematically with the average annual extension rate ext of each colony such that sr ca mmol mol 1 11 82 0 13 0 058 0 004 ext mm a 1 0 092 0 005 sst c this observation is consistent with previous reports of a link between coral sr ca and growth rate verification of our growth dependent sr ca sst calibration using a coral excluded from the calibration reconstructs the mean and seasonal amplitude of the actual recorded sst to within 0 3 c applying a traditional nongrowth dependent sr ca sst calibration derived from a modern montastrea to the sr ca ratios of a conspecific coral that grew during the early little ice age lia 400 years b p suggests that caribbean ssts were 5 c cooler than today conversely application of our growth dependent sr ca sst calibration to sr ca ratios derived from the lia coral indicates that ssts during the 5 year period analyzed were within error 1 4 c of modern values

diagenesis in pleistocene 80 to 500 ka corals from the ironshore formation implications for paleoclimate reconstruction abstract fossil corals provide a unique opportunity for paleoclimate research because they can be dated and they incorporate climate controlled seawater proxies into their aragonitic skeletons during growth coral skeletons however can only produce reliable environmental information if they have not been diagenetically altered an issue that becomes increasingly probable as the age of the corals increase although commonly used analytical techniques such as thin section scanning electron microscopy and x ray diffraction can highlight obvious mineralogical changes subtle changes in the trace element and isotopic composition of the skeletons may not be evident this premise is assessed by examining orbicella annularis and montastrea cavernosa corals from the pleistocene ironshore formation units a f on grand cayman 80 500 ka to determine the diagenetic effects on both physical and chemical properties of corals in the ironshore formation the corals in units a and c were altered in a semi open diagenetic system by seawater diluted by meteoric water which resulted in chemical diagenesis that changed the elemental and isotopic composition of the corals even though their aragonitic skeletons show no obvious signs of change in contrast the limestones in unit b have been pervasively recrystallized in an open diagenetic system by meteoric waters that caused both chemical and physical changes the corals in units d to f however underwent minimal diagenesis and show no evidence of alteration for altered corals from the ironshore formation elevated mg ca and low sr ca ratios provide evidence of subtle chemical diagenetic changes even in corals that have retained their primary aragonitic skeleton thus corals that are formed of 95 wt aragonite show no evidence of cementation and have mg ca ratios 8 0 mmol mol 1 18o values 5 7 and 13c values 3 0 are ideal candidates for paleoclimate reconstruction adoption of these criteria shows that the corals from units d to f can be used to calculate sea surface temperatures sst whereas those from units a to c cannot be used for this purpose the calculated sst and the corresponding temperature profiles derived from the corals in units d to f are consistent with global sst reconstructions during the pleistocene unit d corals record an overall increase in sst which is consistent with elevated temperatures associated with marine isotope stage mis 5e whereas units e and f record overall cooling which is consistent with the end of the peak interglacials of mis 5c and 5a respectively

limitations on digital filtering of the dnag magnetic data set for the conterminous u s the magnetic data set compiled for the decade of north american geology dnag project presents an important digital data base that can be used to examine the north american crust the data represent a patchwork from many individual airborne and marine magnetic surveys however the portion of data for the conterminous u s has problems that limit the resolution and use of the data now that the data are available in digital form it is important to describe the data limitations more specifically than before the primary problem is caused by datum shifts between individual survey boundaries in the western u s the dnag data are generally shifted less than 100 nt in the eastern u s the dnag data may be shifted by as much as 300 nt and contain regionally shifted areas with wavelengths on the order of 800 to 1400 km the worst case is the artificial low centered over kentucky and tennessee produced by a series of datum shifts a second significant problem is lack of anomaly resolution that arises primar

merging airborne magnetic surveys into continental scale compilations regional compilations of airborne magnetic data are becoming more common as national databases grow grids of the magnetic survey data are joined together to form geological province scale or even continental scale compilations the advantage of these compilations is that large tectonic features and geological provinces can be better mapped and interpreted we take a holistic approach to the joining of survey grids the leveling of the grids into a regional compilation is treated as a single inverse problem we use the weighted least squares method to find the best adjustment for each survey grid such that the data value differences in the grid overlap areas are minimized the method spreads any inconsistencies between grids among all of the grid overlap areas and minimizes the introduction of long wavelength errors into the composite grid this is an improvement on the conventional approach of joining grids sequentially a comparison of leveled data over western australia with diurnally corrected long aero

highstands during marine isotope stage 5 evidence from the ironshore formation of grand cayman british west indies abstract the ironshore formation on grand cayman is formed of six unconformity bounded packages units a f units a b c and d known from the subsurface in the northeastern part of grand cayman formed during marine isotope stages mis 11 9 7 and 5e respectively unconformities at the tops of units a b and c are highlighted by terra rossa and or calcrete layers strata in core obtained from wells drilled in george town harbour and exposed on the west part of grand cayman belong to unit d and the newly defined units e and f corals from unit e yielded th u ages of 104 ka whereas conch shells from unit f gave ages of 84 ka unit e equates to mis 5c whereas unit f developed during mis 5a th u dating of corals and conchs from the ironshore formation on the western part of grand cayman shows that unit d formed during the mis 5e highstand whereas units e and f developed in association with highstands at 95 110 ka mis 5c and 73 87 ka mis 5a unit e 5 m thick in the offshore cores is poorly represented in onshore exposures unit f which unconformably overlies unit d at most localities is formed largely of fossil poor cross bedded ooid grainstones the unconformity at the top of unit d a marine erosional surface with up to 2 5 m relief is not characterized by terra rossa or calcrete in the offshore cores or onshore exposures unit d formed with a highstand of 6 m asl whereas units e and f developed when sea level was 2 to 5 asl and 3 to 6 m asl respectively thus the highstands associated with mis 5e 5c and 5a were at similar elevations

glacial interglacial sea surface temperature changes in the southwest pacific ocean over the past 360 ka abstract the phase relationship between climate parameters during terminations gives insight into deglaciation mechanisms by combining foraminiferal mg ca and alkenone thermometers with planktonic and benthic foraminiferal 18o we determined the phase relationship between local sea surface temperature sst and global seawater 18o changes in the coral sea in the southwestern pacific over the last 360 ka the onset of the sst warming preceded the seawater 18o change by several ka for termination i ii and iii during termination i the sst warming started at 20 ka bp earlier than atmospheric co2 rise suggesting that the greenhouse effect was not the main trigger of this early warming compilation of 14c dated sst records from the whole pacific during termination i reveals that the onset of the warming is generally earlier in the southern and the tropical pacific than in the north pacific this spatio temporal warming pattern suggests linkage between the southern ocean and tropical pacific the early tropical warming could provide heat and moisture to the northern high latitudes modifying radiative balance and precipitation over ice sheets at the onset of deglaciation

antarctic temperature and global sea level closely coupled over the past five glacial cycles sea level has varied by over one hundred metres across glacial interglacial cycles over the past 520 000 years an extended sea level reconstruction shows a strong coupling between these sea level changes and antarctic surface temperatures over the past five glacial cycles

limitations of the long wavelength components of the north american magnetic anomaly map the magnetic anomaly map of north america and its related data set provide the opportunity not only to view the obvious short wavelength anomalies 2600 km are strongly affected by core field components that have not been completely removed from the north american data set furthermore the piecewise matching of the magnetic anomalies of adjacent survey areas in the map compilation has contaminated the intermediate wavelength anomalies 300 2600 km

200 k y paleoclimate record from death valley salt core a 186 m long core dv93 1 from death valley california composed of interbedded salts and muds contains a 200 k y record of closed basin environments and paleoclimates interpreted on the basis of sedimentology ostracodes homogenization temperatures of fluid inclusions in halite and correlation with shoreline tufa the 200 k y paleoclimate record is dominated by two dry and or warm and wet and cold cycles that occurred on a 100 k y time scale these cycles begin with mud flat deposits 192 ka to bottom of core and 60 ka to 120 ka wetter and or colder conditions produced greater effective moisture saline pan and shallow saline lake evaporites overlie mud flat sediments 186 ka to 192 ka and 35 ka to 60 ka eventually enough water entered death valley to sustain perennial lakes that had fluctuating water levels and salinities 120 ka to 186 ka and 10 ka to 35 ka when more arid conditions returned mud flat deposits accumulated on top of the perennial lake sediments completing the cycle 120 ka and 10 ka of particular significance are the major lacustrine phases 10 ka to 35 ka and 120 ka to 186 ka oxygen isotope stages 2 and 5e 6 which represent markedly colder and wetter conditions than those of modern death valley of the two major lake periods the penultimate glacial lakes were deeper and far longer lasting than those of the last glacial

u sr and mg in holocene and pleistocene corals a palmata and m annularis abstract mg sr and u concentrations are reported for living holocene dead and pleistocene montastrea annularis and acropora palmata in an effort to characterize starting materials and identify diagenetic effects in unrecrystallized skeletal aragonite the data indicate that skeletogenesis of minor elements is a taxa specific process yielding different mg sr and u values for each species during diagenesis sr concentrations increase and mg concentrations decrease in both species u diagenesis appears to be affected by skeletal structure establishment of u concentration ranges for modern corals provides a criterion for selecting samples for dating concentration changes in mg and sr during diagenesis limit their usefulness as paleo environmental indicators

a cenozoic seawater sr ca record from benthic foraminiferal calcite and its application in determining global weathering fluxes a cenozoic multi species record of benthic foraminiferal calcite sr ca has been produced and is corrected for inter specific offsets typically less than 0 3 mmol mol and for the linear relationship between decreasing benthic foraminiferal sr ca and increasing water depth the water depth correction determined from holocene late glacial maximum and eocene paleowater depth transects is not vert similar0 1 mmol mol km the corrected cenozoic benthic foraminiferal sr ca record ranges from 1 2 to 2 0 mmol mol and has been interpreted in terms of long term changes in seawater sr ca enabling issues related to higher resolution variability in sr ca to be ignored we estimate that seawater sr ca was not vert similar1 5 times modern values in the late cretaceous but declined rapidly into the paleogene following a minimum in the eocene seawater sr ca increased gradually through to the present day with a minimum superimposed on this trend centered in the late miocene by assuming scenarios for changing seawater calcium concentration and using published carbonate accumulation rate data combined with suitable values for sr partition coefficients into carbonates the seawater sr ca record is used to estimate global average river sr fluxes these fluxes are used in conjunction with the seawater strontium isotope curve and estimates of hydrothermal activity tectonic outgassing to calculate changes in global average river 87sr 86sr through the cenozoic the absolute magnitude of sr fluxes and isotopic compositions calculated in this way are subject to relatively large uncertainties nevertheless our results suggest that river sr flux increased from 35 ma to the present day roughly two fold accompanied by an overall increase in 87sr 86sr by not vert similar0 to 0 001 between 75 and 35 ma river 87sr 86sr also increased by not vert similar0 001 to 0 002 but was accompanied by a decrease two to three fold in river sr flux

effects of diagenesis on paleoclimate reconstructions from modern and young fossil corals abstract the integrity of coral based reconstructions of past climate variability depends on a comprehensive knowledge of the effects of post depositional alteration on coral skeletal geochemistry here we combine millimeter scale and micro scale coral sr ca data scanning electron microscopy sem images and x ray diffraction with previously published 18o records to investigate the effects of submarine and subaerial diagenesis on paleoclimate reconstructions in modern and young sub fossil corals from the central tropical pacific in a 40 year old modern coral we find secondary aragonite is associated with relatively high coral 18o and sr ca equivalent to sea surface temperature sst artifacts as large as 3 and 5 c respectively secondary aragonite observed in a 350 year old fossil coral is associated with relatively high 18o and sr ca resulting in apparent paleo sst offsets of up to 2 and 4 c respectively secondary ion mass spectrometry sims analyses of secondary aragonite yield sr ca ratios ranging from 10 78 to 12 39 mmol mol significantly higher compared to 9 15 0 37 mmol mol measured in more pristine sections of the same fossil coral widespread dissolution and secondary calcite observed in a 750 year old fossil coral is associated with relatively low 18o and sr ca sims sr ca measurements of the secondary calcite 1 96 9 74 mmol mol are significantly lower and more variable than sr ca values from more pristine portions of the same fossil coral 8 22 0 13 mmol mol our results indicate that while diagenesis has a much larger impact on sr ca based paleoclimate reconstructions than 18o based reconstructions at our site sims analyses of relatively pristine skeletal elements in an altered coral may provide robust estimates of sr ca which can be used to derive paleo ssts

joint inversion of gravity and magnetic anomalies of eastern canada the power spectra and degree correlation of the surface topography and free air gravity anomalies of eastern canada show that the gravity anomalies are subdivided into three parts the short wavelength components 30 170 km shorter than 30 km are not well resolved largely arise from density perturbations in the crust and to a lesser extent from the surface topography and moho undulation whereas the contribution of intracrustal sources to the intermediate wavelength components 170 385 km is comparable with that of the topography the long wavelength components 385 1536 km are overcompensated at the moho we present a crustal model for the intermediate and long wavelength components which takes into account the surface topography density perturbations in the crust and moho undulation with a certain degree of isostatic compensation the general characteristics of this model resemble the crustal structure revealed from seismic measurements the reduced to pole magnetic anomalies of eastern canada sh

climate variability and land ocean interactions in the indo pacific warm pool a 460 ka palynological and organic geochemical record from the timor sea climatic conditions in the western timor sea and the adjacent northwestern part of australia are reconstructed for the last 460 ka based oil geochemical and palynological proxy records of paleoproductivity and land vegetation precipitation from images core md01 2378 reduced precipitation and elevated productivity characterize glacial stages whereas enhanced precipitation and reduced productivity are typical of interglacial stages a long term reduction in precipitation over the last 320 ka occurred in two steps at approximately 300 ka and 180 ka bp that are clearly recognizable in the pollen record variations in paleoproductivity and paleoclimate in the timor sea and adjacent landmasses appear to be driven by similar mechanisms that are related to the precession control led australian monsoon system c 2005 elsevier b v all rights reserved

seawater strontium and sr ca variability in the atlantic and pacific oceans abstract seawater sr and sr ca exhibit spatial gradients of 2 3 globally with the deep ocean more enriched relative to the surface in latitudinal transects the highest surface values are found at high latitudes and associated with areas of upwelling a pronounced upper ocean vertical sr gradient is attributable to the production of celestite skeletons by surface dwelling acantharia coupled to a shallow dissolution cycle the upper ocean residence time of sr with respect to celestite cycling is much shorter than its global oceanic residence time although the magnitude of seawater sr ca variability is relatively small it is significant with respect to high precision paleoceanographic applications sr ca gradients in the contemporary ocean also complicates evaluating quaternary changes in seawater sr ca that may have resulted from other processes such as aragonite recrystallization during sea level low stands

sea level highstands over the last 500 000 years evidence from the ironshore formation on grand cayman british west indies abstract the ironshore formation up to 19 m thick in the rogers wreck point area of grand cayman is divided into the unconformity bounded units a b c and d the unconformities are highlighted by caliches and or terra rossa th u dates from aragonitic corals indicate that unit a formed at 400 ka unit b 346 ka unit c 229 ka and unit d 131 ka these ages correlate with the highstands of the last four interglacial periods and probably represent marine isotope stages 5 unit d 7 unit c 9 unit b and 11 unit a the limestones in units a d which have similar biotic and lithologic characteristics represent deposition in shallow water on a narrow coastal shelf unit a has a high faunal diversity and was deposited in open marine conditions whereas units b c and d were deposited in quieter water lagoons that probably had fringing reefs along their sea ward edges although grand cayman is located on the cayman ridge close to an active spreading center and transform fault the island has undergone little or no vertical movement over the last 500 ky available evidence indicates that sea level at the time of deposition of each unit relative to present sea level was unit a 9 0 to 5 5 m unit b 3 0 to 0 5 m unit c 2 5 to 1 1 m and unit d 2 5 to 6 0 m these data are good estimates of eustatic sea level highstands over the last 500 ky