variations in mode of formation and temperature of oceanic deep waters over the past 125 000 years marked changes in the deep water temperature of the different oceanic basins during the past 125 kyr are revealed by a detailed comparison of the oxygen isotopic composition ofbenthicforaminiferafrom sediment cores taken from the norwegian sea and the pacific atlantic and southern oceans the last interglacial deep water temperatures were similar to the modern ones at the 5e 5d transition around 115 kyr bp the deep water temperatures dropped below approximately 0 c in the pacific and southern indian oceans in the atlantic ocean the deep water temperature dropped in 2 successive steps at 115 and 75ky bp the global ocean deep water temperatures were in the 0 to 1 c range for the whole of the last ice age isotope stages 4 2

mantle reflections beneath the montana great plains on consortium for continental reflection profiling seismic reflection data a systematic search for reflections from the upper mantle has been carried out on 2000 km of consortium for continental reflection profiling seismic reflection data from 14 different sites across the united states the general observation from these data is the striking contrast between the generally pervasive reflectivity of the crust and the relative lack of coherent reflectivity in the upper mantle a contrast that cannot always be attributed to lack of signal penetration in order to image more of the upper mantle section on the seismic data seismic field files were increased from 16 to 28 s two way travel time by extended correlation processing while the results reveal an upper mantle generally devoid of laterally continuous coherent energy pronounced local reflections called here the lonesome lake complex are observed at upper mantle travel times beneath the montana plains reflections at mantle travel times do not ensure mantle reflectors as other mechanisms operating at shallower levels in the crust may be responsible for the observed reflections however multiple reflections and converted waves from the crust are unlikely explanations for the lonesome lake complex although energy from outside the plane of profile cannot be ruled out circumstantial evidence suggests that these reflections are likely due to intramantle heterogeneity the lonesome lake complex joins examples of upper mantle reflectivity observed on other deep seismic data worldwide in establishing the mantle as an productive target for future deep seismic surveys

increased productivity in the eastern equatorial pacific during the last glacial maximum 19 000 to 14 000 yr b p a widespread pronounced enrichment in the organic carbon content occurs at shallow depths in eastern equatorial pacific sediments the c org peak is shown by radiocarbon dating to be temporally coincident with the last stage 2 or wisconsin glacial maximum in contrast caco 3 profiles show less overall variation which appears to be partly a function of the location of the sediments relative to the lysocline consideration of the iodine c org ratio in the sediments rules out enhanced preservation as a cause of the stage 2 organic carbon enrichment the peak instead must have resulted from a significant increase in productivity during the glacial maximum

was deep water formed in the north pacific during the late quaternary cadmium evidence from the northwest pacific abstract a benthic foraminifera cd ca record dating from the last glacial period to the holocene for a high sedimentation rate core recovered from the northwest pacific is reported it shows that the deep water water depth of 2700 m cadmium concentration was about 50 lower in the last glacial period than in the holocene at 15 kyr b p the beginning of deglaciation a minimum cd ca is recorded which is almost the same as that of the modern north atlantic considering previously obtained cadmium records from the northwesternmost and western equatorial pacific a steep gradient in the deep water cadmium concentration between the western equatorial pacific and the northwest pacific from the last glacial to deglacial periods has been estimated in contrast to cadmium records benthic foraminifera 13 c records in these regions showed similar increasing trends during this time span and no large difference in 13 c can be observed between these two regions this discordance between these two nutrient tracers may come from the change in the 13 c phosphate relationship in the ocean during the late quaternary although we cannot absolutely rule out other possibilities we suggest that there was a convection cell in the northwest pacific during the last glacial period and at the beginning of deglaciation period the turnover rate of this cell increased and cadmium concentration in the northwest pacific significantly decreased

nature of the eastern boundary of the rio grande rift from cocorp surveys in the albuquerque basin new mexico reprocessing and synthetic seismic modeling of cocorp profiles across the eastern margin of the rio grande rift at abo pass new mexico suggest that synthetic and antithetic cenozoic normal faults sole into or are truncated by a northwest dipping listric master fault which bounds the eastern side of the basin and reaches a depth of at least 10 km beneath the southern albuquerque basin this fault appears to project toward the surface position of the los pinos cenozoic normal fault which lies basinward of and trends parallel to a mapped laramide duplex thrust zone the los pinos fault may sole into the older thrust reactivating this preexisting compressional structure at depth a lateral change in reflection amplitude and frequency is conspicuous across the eastern rift margin analysis demonstrates that source coupling is the main cause of a much deteriorated signal below the rift basin although complex ray paths and attenuation by the graben fill may contribute

carbon isotopic changes in benthic foraminifera from the western south atlantic reconstruction of glacial abyssal circulation patterns oxygen and carbon isotopic analyses have been performed on the benthic foraminifer planulina wuellerstorfi in seven late quaternary cores from the vema channel rio grande rise region the cores are distributed over the water depth interval of 2340 to 3939 m which includes the present transition from north atlantic deep water nadw to antarctic bottom water aabw the carbon isotopic records in the cores vary as a function of water depth the shallowest and deepest cores show no significant glacial interglacial difference in 13c four of the five cores presently located in the nadw have benthic foraminiferal 13c that is lower during glacial isotopic stages based on bathymetric gradients in 13c we conclude that like today there were two water masses present in the vema channel during glacial intervals a water mass enriched in 13c overlying another water mass depleted in 13c the largest gradient of change of 13c with depth however occurred at 2 7 km 1 km shallower than the present position of this gradient on the basis of paleontologic and sedimentologic evidence we consider it unlikely that the nadw aabw transition shallowed to this level reduced carbon isotopic gradients between the deep basins of the north atlantic and pacific oceans during the last glaciation suggest that production of nadw was reduced lower production of nadw may have modified the local abyssal circulation pattern in the vema channel region

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

the identification of mantle reflections below hungary from deep seismic profiling abstract in the 1970 s the eotvos lorand geophysical institute performed seismic reflection deep sounding experiments with multiple coverage in several parts of the pannonian basin posgay 1975 one of the most interesting results was that arrivals were received in the time range corresponding to the depth of the asthenosphere they were interpreted as reflections posgay et al 1981 conspicuous arrivals from the time range of the asthenosphere 15 20 s were also received along the pannonian geotraverse in 1987 in the majority of sections published in other countries the upper mantle seems to be transparent the present paper discusses investigations and preliminary results which lead to the conclusion that this apparent transparency is due to the frequency range below 10 hz being neglected in both signal generation and recording in most deep continental reflection surveys the seismogeological conditions of the pannonian basin are certainly favourable for reflection studies of the upper mantle the correctness of the assumption that arrivals from the time range of the asthenosphere are primary reflections is subjected to further investigation and conclusions are made concerning the structure of the asthenosphere

crustal extension and magmatic processes cocorp profiles from death valley and the rio grande rift new crustal scale information on the interaction between normal faulting and magmatic activity is provided by recent cocorp deep seismic reflection profiles in death valley california and by reprocessing of the cocorp data from the socorro area of the rio grande rift new mexico the most striking feature on the seismic sections from these areas is a prominent subhorizontal series of reflectors at mid crustal depth previous studies have suggested that thin tabular magma bodies lie within the mid crustal reflective zones in addition because they are traced without apparent offset beneath faults both mapped at the surface and interpreted from the cocorp data these mid crustal horizons are here inferred to be detachments or zones of tectonic decoupling upper crustal cenozoic faults do not appear to penetrate deeper than 15 km in death valley and 13 km in the rio grande rift in death valley these faults are relatively planar with moderate dips 20 to 35 and appear to bound large basement rocks one such zone of normal faults can be traced from the magma body inferred at 15 km depth beneath central death valley to the surface location of a 690 000 yr old basaltic cinder cone listric and low to moderate angle normal faults are evident on the reprocessed new mexico data and constitute the structural component of upper crustal extension in particular a listric master fault traceable to depths as great as 13 km is inferred to underlie the albuquerque basin unlike the death valley data no faults are observed to merge with the socorro magma body per se rather subhorizontal to moderately west dipping packages of reflections are imaged between the base of the faulted upper crust 13 km depth and the mid crustal magma body about 20 km depth the middle crust marks a major rheological boundary between the faulted upper crust and a ductile lower crust extending by penetrative flow and intrusion events seen in the middle and lower crust are generally subhorizontal and prominent layering is observed a band of reflections attributed to the crust mantle boundary is evident on most seismic sections the upper mantle appears seismically transparent on some of the profiles the events attributed to the base of the crust are the deepest in a series of strong and continuous reflections at least one of which is a layer of magma this association supports the suggestion that magmatic intrusions are a probable cause for the high reflectivity observed in the deep crust of many extensional terranes

intracrustal complexity in the united states midcontinent preliminary results from cocorp surveys in northeastern kansas unusually clear indications of complex structure in the mid to lower crust is revealed by seismic reflection surveys in northeastern kansas this complexity contrasts markedly with the layer cake simplicity of both the overlying sedimentary cover and most previous crustal models for the central united states seismic sections collected by cocorp consortium for continental reflection profiling as part of a major east west traverse across the neniaha ridge and midcontinent geophysical anomaly indicate that below a thin relatively flat layered paleozoic sedimentary section the deep crust is characterized by numerous dipping and arcuate reflections and diffractions in many places layered and crosscutting these reflections suggest convoluted three dimensional folded faulted and intruded structures specific identification of these deep features may be possible if future surveys can trace them to accessible depths the basement above these reflection complexes contains significantly fewer reflections consistent with but not necessarily diagnostic of the granitic terrane that dominates basement drill hole samples in the region among the events at these shallower basement depths are several east dipping reflections some of which may be major faults travel times corresponding to expected moho depths about 36 km are characterized less by specific reflections than by an apparent decrease in the density and number of reflections while evidence of crustal heterogeneity is common among deep reflection studies the kansas seismic results outlined in this brief report stand out as being unusually clear representations of such

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

cadmium chemical tracer of deepwater paleoceanography the oceanic distribution of cadmium resembles that of phosphorus because the cadmium content of foraminiferal shells is governed by the cadmium content of seawater planktonic and benthic fossil shells can be used to infer nutrient distributions within ancient oceans empirical studies demonstrate that cadmium in benthic foraminiferal shells is related to the bottom water composition through a proportionality constant d 2 9 this constant is the same for each of the species studied cibicidoides wuellerstorfi cibicidoides kullenbergi nuttallides umbonifera and uvigerina spp downcore cadmium data from high quality pacific and atlantic sediment cores suggest that the cadmium inventory of the ocean did not change significantly between the most recent glacial maximum and the present hence changes in the cadmium content of fossils at a site directly reflect changes in nutrient distributions due to altered oceanic circulation patterns studies of cadmium in pleistocene sediments show that deep ocean circulation patterns were significantly different during the most recent glacial maximum in the western north atlantic ocean the nutrient content of waters from 2500 to 3500 m was twice as high during glacials as during interglacial periods signifying an increase in the proportion of waters of antarctic origin in this depth interval and a decrease but not a cessation in the flux of north atlantic deep waters through this depth range below 3500 m the nutrient increase was greater indicating a higher proportion of antarctic bottom water above 2500 m the nutrient content was lower during glacial periods than it has been during interglacial times the cd content of high latitude north atlantic and southern ocean surface waters does not show a significant glacial interglacial change which argues against theories for changes atmospheric carbon dioxide that require changes in high latitude nutrient concentrations

the late pleistocene history of surface water δ13c in the sulu sea possible relationship to pacific deepwater δ13c changes a reconstruction of late pleistocene surface water carbon isotopic 13c variability is presented from ocean drilling program odp site 769 in the sulu sea in the western tropical pacific the sulu sea is a shallowly silled back arc basin with a maximum sill depth of 420 m site 769 was drilled on a bathymetric high in 3643 m of water and has average late pleistocene sedimentation rates of 8 5 cm kyr the oxygen isotope record 18o of globigerinoides ruber at site 769 shows a strong correlation with the specmap stacked 18o record attesting to the continuity of sediment archive at the site surface 13c displays consistent glacial interglacial variability which averages 0 9 and has varied from 0 75 to 1 1 over the last 800 kyr comparison to surface water 13c records in the south china sea and western tropical pacific suggests that the glacial interglacial surface 13c variability is regional in scale planktonic 13c data from odp site 677 in the eastern pacific is also coherent with the site 769 additionally we have found that the site 769 surface 13c record is coherent at periods of 100 and 41 kyr with deepwater 13c records from the pacific the highest correlation occurs with the deep eastern pacific where benthic 13c data from cores rc13 110 and odp site 677 closely match the sulu sea surface water record we evaluate several possible controls of surface water 13c in the sulu sea that may explain the coherent timing with pacific deepwater 13c records these include variations in terrestrial organic matter flux to the basin the upwelling of subsurface water and productivity changes and the influx of western pacific intermediate water to the sulu sea our preferred explanation involves a region of upper intermediate water upwelling in the far western pacific which has been shown to outgas co2 from subsurface waters into surface waters upwelling also occurs in the area of panama basin site 677 these equatorial upwelling zones could potentially provide a route by which pacific intermediate water can modulate the 13c composition of certain pacific surface water locations future reconstructions of late pleistocene surface water 13c variability in the western pacific and indonesian seas will be required to further evaluate the source of the glacial interglacial surface water 13c change

oxygen isotope constraints on surface ocean temperatures published oxygen isotope results from benthic and planktonic foraminifera are used to constrain the extent to which surface ocean temperatures in the tropics changed between glacial and interglacial time the possible impacts of bioturbation and of the redistribution of 18o16o ratios within the sea putting aside the oxygen isotope results are consistent with the climap project conclusion that tropical ocean temperatures remained within 2 c of their present value

evolution of atlantic pacific δ13c gradients over the last 2 5 m y the evolution of interocean carbon isotopic gradients over the last 2 5 m y is examined using high resolution 13c records from deep sea cores in the atlantic and pacific oceans over much of the northern hemisphere ice ages relative reductions in north atlantic deep water production occur during ice maxima from 2 5 to 1 5 ma glacial reductions in nadw are less than those observed in the late pleistocene glacial suppression of nadw intensified after 1 5 ma earlier than the transition to larger ice sheets around 0 7 ma at a number of times during the pleistocene 13c values at dsdp site 607 in the north atlantic were indistinguishable from eastern equatorial pacific 13c values from approximately the same depth odp site 677 indicating significant incursions of low 13c water into the deep north atlantic atlantic pacific 13c values converge during glaciations between 1 13 1 05 m y 0 83 0 70 m y and 0 46 0 43 m y this represents a pseudo periodicity of approximately 300 kyr which cannot easily be ascribed to global ice volume or orbital forcing this partial decoupling at low frequencies of the 18o and 13c signals at site 607 indicates that variations in north atlantic deep water circulation cannot be viewed simply as a linear response to ice sheet forcing

comparison of atlantic and pacific paleochemical records for the last 215 000 years changes in deep ocean circulation and chemical inventories abstract detailed cd ca and 13 c data have been obtained for benthic foraminifera from western north atlantic and equatorial pacific sediment cores in the modern ocean both tracers are closely linked to nutrient distributions the sedimentary records for both tracers indicate that bottom waters overlying the atlantic site have been nutrient depleted relative to those at the pacific site over the last 215 000 years from this evidence it is reasonable to infer that there has been a continuous net flux of nutrient depleted water from the western north atlantic into the pacific this exchange has undergone significant fluctuations with the export of nutrient depleted atlantic water diminishing by about a factor of two relative to the inflow from southern ocean sources over the last 215 000 years carbon isotope fluctuations in both regions are dominated by variable storage of isotopically light carbon on continents with a lesser contribution from these deep ocean circulation changes the cadmium signal in the north atlantic is dominated by changes in deep ocean circulation patterns cadmium shows less variability in the pacific which may reflect changes in the global average cadmium content or minor changes in deep pacific circulation patterns using these records to estimate global averages it appears that glacial ocean water had 22 more cd and 0 46 less 13 c than the modern ocean these numbers are estimates which may be revised as more data become available although they are not likely to be as much as 20 in error for cd or 0 2 for 13 c relative north atlantic deep water nadw formation rates are modulated with a significant 41 kyr periodicity linked to obliquity induced variations in high latitude insolation nadw lags 8 2 kyr behind insolation however

13c record of benthic foraminifera in the last interglacial ocean implications for the carbon cycle and the global deep water circulation the 13c 12c ratios of upper holocene benthic foraminiferal tests genera cibicides and uvigerina of deep sea cores from the various world ocean basins have been compared with those of the modern total carbon dioxide tco2 measured during the geosecs program the 13c difference between benthic foraminifera and tco2 is 0 07 0 04 for cibicides and 0 83 0 07 for uvigerina at the 95 confidence level 13c analyses of the benthic foraminifera that lived during the last interglaciation isotopic substage 5e about 120 000 yr ago show that the bulk of the tco2 in the world ocean had a 13c value 0 15 0 12 lower than the modern one at the 95 confidence level reflecting a depletion compared to the present value of the global organic carbon reservoir regional differences in 13c between the various oceanic basins are explained by a pattern of deep water circulation different from the modern one the antarctic bottom water production was higher than today during the last interglaciation but the eastward transport in the circumpolar deep water was lower

two dimensional time dependent hurricane overwash and erosion modeling at santa rosa island abstract a 2dh numerical model which is capable of computing nearshore circulation and morphodynamics including dune erosion breaching and overwash is used to simulate overwash caused by hurricane ivan 2004 on a barrier island the model is forced using parametric wave and surge time series based on field data and large scale numerical model results the model predicted beach face and dune erosion reasonably well as well as the development of washover fans furthermore the model demonstrated considerable quantitative skill upwards of 66 of variance explained maximum bias 0 21 m in hindcasting the post storm shape and elevation of the subaerial barrier island when a sheet flow sediment transport limiter was applied the prediction skill ranged between 0 66 and 0 77 in a series of sensitivity tests in which several hydraulic forcing parameters were varied the sensitivity studies showed that the variations in the incident wave height and wave period affected the entire simulated island morphology while variations in the surge level gradient between the ocean and back barrier bay affected the amount of deposition on the back barrier and in the back barrier bay the model sensitivity to the sheet flow sediment transport limiter which served as a proxy for unknown factors controlling the resistance to erosion was significantly greater than the sensitivity to the hydraulic forcing parameters if no limiter was applied the simulated morphological response of the barrier island was an order of magnitude greater than the measured morphological response

paired carbon isotope and cadmium data from benthic foraminifera implications for changes in oceanic phosphorus oceanic circulation and atmospheric carbon dioxide abstract the carbon isotope and cadmium content of foraminiferal shells from oceanic sediments provides information on past chemical distributions in the ocean starting from reasonable assumptions it can be shown that paired data on both tracers provides more information than does either separately the slope of paired isochronous 13c and cd ca data from fossil benthic foraminifera depends on oceanic p cd and gd 13c p ratios the zero cd ca intercept of this line depends on mean oceanic 13c p and the 13c p ratio given data sufficient to define oceanic mean 13c and cd contents it is possible to place quantitative constraints on the product of the c p redfield ratio and mean oceanic phosphorus and to estimate a circulation parameter which is independent of changes in ocean chemical inventories with the limited available data no significant changes in oceanic p cd can be detected between the holocene and most recent glacial maximum if this data is taken to be representative of the whole ocean then the p and cd contents of the ocean were about 17 higher during the last glacial maximum than at present ocean box models indicate that this change in oceanic p and a 2 c deep ocean cooling during glacials would cause a 47 ppmv reduction in atmospheric pco2 during glacial intervals

oxygen and carbon isotopic composition of ordovician brachiopods implications for coeval seawater one hundred and two articulate brachiopods and twenty one marine cements from ordovician strata were analyzed for oxygen and carbon isotopes these together with 200 previously published analyses of ordovician brachiopods mostly of upper ordovician age define a general trend of increasing 18o values with decreasing age from a minimum of 10 5 in the earliest ordovician to a maximum of 1 5 at the ordovician silurian boundary the 13c values show a general positive correlation with 18o and increase from 2 5 in the earliest ordovician to as high as 7 at the ordovician silurian boundary the magnitudes of ordovician excursions for both 18o and 13c are similar to those reported previously for the entire phanerozoic different genera of brachiopods from the same stratigraphie level did not yield any large differences in their isotopic compositions suggesting that vital effects did not influence decisively the isotope values of the studied skeletal parts petrographic examination and trace element analyses indicate that brachiopod shells from llandeilo to ashgill strata are well preserved and thus may have retained their primary isotopic signatures the same criteria for the tremadoc arenig and some llanvirn brachiopods suggest partial diagenetic alteration of 18o values in these samples but this does not preclude their utility as a recorder of a primary 13c signal the observed 18o trend for the well preserved portion of the record may reflect progressive cooling during ordovician perhaps complemented by a changing 18o values of seawater the latter could have been a consequence of a net increase in the rate of high temperature water rock interaction relative to its low temperature counterpart as indicated also by the large coeval decrease of marine 87sr86sr superimposed on the above long term 18o trend is a positive excursion of about 2 at the end of the ordovician probably reflecting a large expansion of polar ice caps the magnitude of this excursion indicates a degree of glaciation comparable to that at the height of the quaternary glacial episodes the secular 13c trend may reflect a progressive increase in marine organic productivity and or enhanced organic deposition in the ordovician oceans particularly noticeable at the time of the terminal ordovician glaciation

growth of a manganese nodule from peru basin a radiochemical anatomy abstract attempts have been made to study the entire growth history of a manganese nodule from the northern part of peru basin in the pacific using radiochemical profiles of 230 th 232 th 227 th 230 th and 10 be 9 be combined with the observations on fe mn contents and textural variation the radiochemical data indicate that the nodule grew more or less concentrically throughout most of its existence since it formed 1 5 my ago receiving mn from both bottom water and pore water this condition appeared to have changed about 180 ky ago when the growth became asymmetric in that the top and bottom sides became fixed in their relative positions on the sea floor since then the bottom side accreted with a fast rate of close to 200 mm my apparently fueled by the supply of diagenetically remobilized mn in pore water from the sediment substrate in the meantime the top side accumulated at about 6 mm my a value which is in the normal range for deep sea nodules having their mn supplied from the hydrogenous source

geochemical and sedimentological studies of a box core from the western sector of the peru basin abstract the distribution of sediments micronodules and manganese nodules which has been studied in a number of cores from the peru basin is clearly related to the proximity of the basin to the c c d and to the equatorial high productivity zone one core from the peru basin has been looked at in considerable detail in this core an extensively bioturbated calcareous siliceous rich upper sedimentary unit is underlain by an overconsolidated dark brown clay characteristic differences in mineralogy and chemistry are observed in the composition of these sediment types with the dark brown clays having higher contents of mn fe co ni cu zn and p than the sediments of the upper horizon in addition these dark brown clays contain montmorillonite as the principal clay mineral whereas the sediments of the upper sediment horizon consist of montmorillonite kaolinite and illite micronodules are much more abundant in the coarse fraction 40 m of the dark brown clay horizon than in the upper sedimentary unit and are characterized by higher mn fe ratios and higher ni and cu contents than those from the upper sediment horizon this reflects the fact that these overconsolidated sediments are well oxidized and that element remobilization from the micronodules has not taken place within this sediment type in the upper sedimentary unit there is a sharp drop in the mn fe ratio and ni and cu contents of the micronodules immediately beneath the sediment surface reflecting the selective migration of mn and other transition elements such as ni and cu from the micronodules buried managanese nodules are found at two horizons within the sediment column these nodules show characteristic differences in their surface texture compared to surface nodules but no marked difference in composition the buried nodules are not associated with any well defined feature such as a sedimentary hiatus it is suggested that nodules are maintained at the sediment surface by bioturbation buried nodules are simply those nodules that have failed to be maintained at the sediment water interface

constraints on deep water formation from the oceanic distributions of 10be 1 an analysis of the oceanic distribution of cosmogenic 10be shows that deep waters are formed by descending of cold dense surface waters at a rate of 18 sv 106 m3 s 1 in the northern north atlantic and 21 sv of which 17 sv enters the pacific in the antarctic over the last mixing cycle of 800 years lending support to the estimates based on radiocarbon and nutrient distributions it also indicates that deep water production in the northern north atlantic is 50 higher averaging over the recent 100 years than over the last mixing cycle suggesting a possible increase in the thermohaline ventilation of the north atlantic during the past century

the cause of the glacial to interglacial atmospheric co2 change a polar alkalinity hypothesis in an attempt to create a scenario for the cause of the glacial to interglacial co2 change recorded in air trapped in polar ice we call on an increase in the alkalinity of polar surface waters in this way we circumvent a major deficiency of the polar nutrient scenarios of sarmiento and toggweiler 1984 siegenthaler and wenk 1984 and knox and mcelroy 1984 namely our scenario does not require a drop in the nutrient content of polar surface waters in conformity with the demonstration by boyle 1988a b that the cadmium content of planktonic foraminifera from polar regions did not decrease from late glacial to holocene time the rise in alkalinity required by our model is a natural consequence of the demise during glacial time of north atlantic deep water as a major force in ocean circulation and of the nutrient maximum deepening of boyle 1988b rather than being original our hypothesis builds on the concept basic to the polar nutrient hypotheses namely that the co2 partial pressure in polar waters controls that for both the atmosphere and warm surface ocean it also requires the alkalinity increase in surface waters produced by boyle s nutrient deepening

carbon and oxygen isotopic disequilibria of recent deep sea benthic foraminifera abstract the carbon and oxygen isotopic compositions of 149 samples of benthic foraminifera from deep sea core tops indicate that none of the nine species studied secrete calcium carbonate in isotopic equilibrium with ambient bottom water uvigerina pyrgo murrhina and oridorsalis tener are the closest to 18o equilibrium with average deviations about 0 4 while planulina wuellerstorfi and p murrhina are the closest to 13c equilibrium with average deviations about 1 p wuellerstorfi shows the most systematic relationship between 13c and bottom water apparent oxygen utilization the intraspecific variabilities in 18o and 13c suggest that estimates of bottom water paleotemperatures can be made to a precision of 0 7 c while estimates of past apparent oxygen utilization aou can be made to 35 mol kg based on intraspecific comparisons of the recent samples with fossils no temporal changes in the degree of either 18o or 13c disequilibrium have been detected for planulina wuellerstorfi uvigerina oridorsalis tener and globocassidulina subglobosa

deep crustal structure of the precambrian basement beneath northern lake michigan midcontinent north america a deep seismic reflection profile in northern lake michigan midcontinent north america provides a cross section of the crust across the 1850 ma penokean orogen in which an early proterozoic island arc complex was deformed between two converging archean continental masses the island arc crust is about 40 km thick and has a few kilometres of intensely reflective rocks near its base above which it is variably reflective to transparent the archean terranes have thicker crust as much as 50 km the lower 20 25 km of which is strongly reflective abrupt offsets of moho near terrane boundaries may have been preserved since accretion during the penokean orogeny

moho reflectivity and seismic signal penetration abstract analysis of amplitude decay and frequency change is applied to determine limits of seismic signal penetration on deep seismic reflection data collected by lithoprobe and the consortium for continental reflection profiling cocorp changes in spectral frequency content are efficiently monitored with averaged instantaneous frequency and bandwidth results from montana show pronounced increases in average frequency and slight drops in amplitude associated with a die out of reflections at the moho results from quebec show amplitude and frequency change occurring through the moho on lines with and without moho reflections these contrasting observations confirm both adequate signal penetration and that the differences in moho reflectivity are representative of geologic differences

a three dimensional perspective on the evolution of archaean crust lithoprobe seismic reflection images in the southwestern superior province in 1990 1991 the lithoprobe project completed 450 km of seismic reflection profiles across the late archaean crust of the southwestern superior province the results define a broad three fold division of crust upper crust in the abitibi greenstone belt is non reflective and is a 6 8 km veneer of volcanic and plutonic supracrustal rocks whereas in the sediment gneiss dominated pontiac subprovince upper crust comprises shallow northwest dipping turbidite sequences mid crust in both the abitibi and the pontiac subprovinces is interpreted as imbricate sequences of metasedimentary and metaplutonic rocks lower crust in both subprovinces has a horizontal layer parallel strycture which may represent interleaved mafic intermediate gneisses the seismic signature of the northern abitibi greenstone belt may be represented in an exposed 25 km crustal section in the kapuskasing stuctural zone preliminary tectonic models based on the seismic data are consistent with a plate tectonic scenario involving oblique subduction and imbrication of sedimentary plutonic and volcanic sequences the northern abitibi supracrustal sequences either represent an allochthon or overlie an allochthonous underthrust metasedimentary and plutonic sequence which may be equivalent to a metasedimentary subprovince such as the pontiac or quetico seismic velocities have yet to be defined however crustal thicknesses are relatively constant at 35 40 km the thinnest crust is adjacent to the grenville front where moho is very well defined

carbon isotopic variations on glacial to interglacial time scales in the ocean modeling and implications downcore variations in the deep sea 13c signal as recorded in benthic foraminifera are a function of past changes in global organic carbon inventory and ocean circulation thus the carbon isotopic composition of fossil benthic foraminifera constitutes a valuable geochemical proxy for reconstructing paleooceanographic conditions this study examines the mean ocean 13c 12c variations due to the climatically induced changes in the size of the two organic carbon pools terrestrial biomass forest soil and continental shelf sediment through modeling the paired foraminiferal 13c 18o data in the literature it is estimated that during the past several hundred thousand years in late quaternary transfer of organic carbon between these two pools and the ocean in response to glacial interglacial climate and sea level changes has resulted in global oceanic 13c fluctuations with a mean amplitude of about 0 32 the transfer has accounted for about two thirds of the observed carbon isotopic shift in the deep eastern pacific ocean circulation accounting for the remaining one third of 13c amplitude variations in the deep north atlantic ocean it has accounted for about one third of the shift of the two organic carbon reservoirs forest soil is roughly 2 5 times more responsible than shelf sediment in altering the mean carbon isotopic composition of the quaternary oceans destruction of organic matter from the shelf sediment reservoir is responsible for raising the oceanic nutrient inventory during glacial times by about 4 relative to the present interglacial level a level which is difficult to be assessed by the cadmium proxy marine deposition of organic carbon in glacial oceans increased by 3 10 in spite of a reduction in terrestrial biomass during ice ages isolating out the global climatic signals in 13c records shows that since about 300 kyr ago there has been a trend of increasing organic carbon accumulation toward the present at least in the equatorial e pacific it also shows that the contrast between the 13c values hence nutrient content of deep water in the atlantic and pacific observed in today s ocean was smaller during glacial periods in the northwestern indian ocean the global climate corrected 13c results reveal interglacial intensification of the monsoon driven upwelling and productivity back to at least oxygen isotopic stage 11 circa 400 kyr b p

the sources and deposition of organic matter in the late quaternary pigmy basin gulf of mexico abstract the concentration and carbon isotopic composition 13c of sedimentary organic carbon corg n c ratios and terrigenous and marine 13corg endmembers form a basis from which to address problems of late quaternary glacial interglacial climatic variability in a 208 7 m hydraulic piston core dsdp 619 from the pigmy basin in the northern gulf of mexico while interpretations of sedimentary 13corg time series records are often not unique paired analyses of 13corg and n c are consistent with the hypothesis that the corg in the pigmy basin is a climatically determined mixture of c3 photosynthetic terrigenous and marine organic matter confirming the earlier 13corg model of sackett 1964 a high resolution 1 4 2 9 ka sample 13corg record shows that sedimentary organic carbon in interglacial oxygen isotope sub stages 1 and 5a b are enriched in 13c average 1 values are 24 2 1 2 o and 22 9 0 7 o relative to pdb respectively while glacial isotope stage values 2 are relatively depleted 25 6 0 5 concentrations of terrigenous and marine sedimentary organic carbon are calculated for the first time using 13corg and corg measurements and empirically determined terrigenous and marine 13corg endmembers the net accumulation rate of terrigenous organic carbon is 4 3 2 6 times higher in isotope stages 2 4 than in sub stages 1 and 5a b recording higher erosion rates of terrigenous organic material in glacial times the concentration and net accumulation rates of marine and terrigenous corg suggest that the nutrient bearing plume of the mississippi river may have advanced and retreated across the pigmy basin as sea level fell and rose in response to glacial interglacial sea level change

high resolution benthic foraminifer δ13c records in the south china sea during the last 150 ka abstract high resolution 13c ratios of benthic foraminifer cibicidoides wuellerstorfi in core md97 2151 from the southern south china sea scs and core so50 31kl from the northern scs indicate deep water variations in the scs during the last 150 ka the 13c records of both show a general variation pattern with higher 13c during interglacial periods than glacial periods and rapid increases during terminations this variation pattern resembles those of the west pacific intermediate deep water the sources of the scs deep water and the general variation of global deep water indicating that the variation of the scs deep water is largely controlled by global factors such as carbon cycles and global deep water circulation spectra analysis exhibits robust milankovitch cycles in the scs deep water 13c again supporting global controls significant semi precession cycles can also be seen in the spectra implying that changes of local surface productivity also influence the scs deep water 13c

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

three dimensional mapping of seismic reflections from the crust and upper mantle northwest of scotland abstract a survey area 190 km by 110 km to the northwest of scotland on the uk continental shelf has been the site of intense exploration using the deep seismic reflection technique a closely spaced grid of deep reflection data totalling 1600 line km has been acquired by the birps group between 1981 and 1987 the majority of the data were recorded to 15 s two way travel time 50 km depth profiles with recording times up to 60 s 230 km depth were also acquired the survey includes a two ship synthetic aperture profile the slave line which synthesises a 0 16 km offset cdp profile the main features revealed and consistently imaged across the survey area by this combined dataset are an upper crust containing half graben style basins bounded to the west by planar faults a reflective lower crust and dipping and sub horizontal high amplitude reflections within the mantle three dimensional mapping of the dipping reflectors shows a complex package of reflections which updomes into the lower crust in the central area of the survey disrupting the moho and continuing into the uppermost mantle where it thins to a couplet of reflections in the north and south of the survey area this structure is observed only in the mantle to a depth of 80 km this dataset is unique in deep seismic reflection profiling in terms of the quality of the image returned the great depth to which reflections are imaged and the intensity of surveying of the lower crust and upper mantle the continuity and strength of the reflectors seen on these records show that even at the great depths at which these structures exist the seismic reflection technique is able to image them as high amplitude coherent and highly continuous reflections the reflections are interpreted as shear zones or faults within the lower crust and upper mantle this indicates that in this part of the world at least both the lower crust and upper mantle are able to sustain discrete zones of deformation

deep circulation of the north atlantic over the last 200 000 years geochemical evidence variations in the cadmium calcium ratio of north atlantic deep water are recorded in the fossil shells of benthic foraminifera the oceanic distribution of cadmium is similar to that of the nutrients hence the cadmium calcium ratio in shells records temporal variations in nutrient distributions data from a north atlantic sediment core show that over the past 200 000 years there has been a continuous supply of nutrient depleted waters into the deep north atlantic the intensity of this source relative to nutrient enriched southern waters diminished by about a factor of 2 during severe glaciations this evidence combined with carbon isotope data indicates that the continental carbon inventory may have been less variable than previously suggested

changes in the distribution of δ13c of deep water σco2 between the last glaciation and the holocene carbon isotopic measurements on the benthic foraminiferal genus cibicidoides document that mean deep ocean 13c values were 0 46 lower during the last glacial maximum than during the late holocene the geographic distribution of 13c was altered by changes in the production rate of nutrient depleted deep water in the north atlantic during the late holocene north atlantic deep water with high 13c values and low nutrient values can be found throughout the atlantic ocean and its effects can be traced into the southern ocean where it mixes with recirculated pacific deep water during the glaciation decreased production of north atlantic deep water allowed southern ocean deep water to penetrate farther into the north atlantic and across low latitude fracture zones into the eastern atlantic mean southern ocean 13c values during the glaciation are lower than both north atlantic and pacific 13c values suggesting that production of nutrient depleted water occurred in both oceans during the glaciation enriched 13c values in shallow cores within the atlantic ocean indicate the existence of a nutrient depleted water mass above 2000 m in this ocean

cadmium and delta13c paleochemical ocean distributions during the stage 2 glacial maximum changes in heat and salt transport by ocean currents have been implicated in ice age climate cycles weyl 1 968 newell 1 974 broecker et al 1 990b in addition to the direct physical effects of the ocean on climate the ocean carbon system controls atmospheric co2 and the co2 fluctuations documented in ice core bubbles barnola et a1 1 987 neftel et a1 1 988 are thought to be a significant factor in climate oscillations hansen et al 1 984 dramatic changes in oceanic circulation patterns and carbon system chemistry have occurred during the late quaternary glacial interglacial global climate cycles boyle keigwin 1 982 curry lohmann 1 983 shackleton pisias 1 984 boyle keigwin 1 987 duplessy et al 1 988 curry et al 1 988 broecker et al i 990a these changes in the ocean system may be significant driving forces in the progression of ice age co2 cycles toggweiler sarmiento 1 985 ennever mcelroy 1 985 wenk siegenthaler 1 985 boyle 1 988a b broecker peng 1 990 the oceanic distributions of c513c cd and other carbon system linked properties are controlled by the interaction between biological uptake and decomposition with the general circulation of the ocean because records of past oceanic cd and c5 1 3c are preserved in shells of planktonic and benthic foraminifera

deep seismic reflection characteristics of the continental crust four types of seismic reflection fabrics appear to characterize the continental crust 1 a cratonic fabric dominated by diffractions and dipping reflections but lacking a pronounced reflection moho 2 regions of thin skinned foreland deformation with abundant shallow but sparse deep reflections 3 a unidirectional fabric that dips toward the hinterland and may represent a crustal scale ramp zone and 4 zones of highly layered lower crust and high amplitude reflection moho the first three types are commonly observed in transects across single mountain belts but the fourth appears to correspond to regions of elevated lower crustal temperatures such as those encountered in rift provinces and perhaps elsewhere

changes in east atlantic deepwater circulation over the last 30 000 years eight time slice reconstructions using 95 epibenthic 13c records eight time slices were reconstructed to trace the distribution of east atlantic deepwater and intermediate water masses over the last 30 000 years our results show that there have been three distinct modes of deepwater circulation near the stage 3 2 boundary the origin of north atlantic deep water nadw was similar to today mode 1 however after late stage 3 the source region of the nadw end member shifted from the norwegian greenland sea to areas south of iceland mode 2 a reduced nadw flow persisted during the last glacial maximum with constant preformed 13c values the nutrient content of nadw increased markedly near the azores fracture zone from north to south probably because of the mixing of upwelled antarctic bottom water aabw from below which then advected with much higher flux rates into the northeast atlantic later the spread of glacial meltwater over the north atlantic led to a marked short term ventilation minimum below 1800 m about 13 500 14c years ago mode 3 the formation of nadw recommenced abruptly north of iceland 12 800 12 500 years ago and reached a volume approaching that of the holocene in the younger dryas 10 800 10 350 years b p another short term shutdown of deepwater formation followed between 10 200 and 9 600 years b p linked to a further major meltwater pulse into the atlantic each renewal of deepwater formation led to a marked release of fossil co2 from the ocean the likely cause of the contemporaneous 14c plateaus over the last 9000 years deepwater circulation varied little from today apart from a slight increase in aabw about 7000 14c years ago it is also shown that the oxygenated mediterranean outflow varied largely independent of the variations in deepwater circulation over the last 30 000 years

modeling the dynamics of terrestrial carbon storage since the last glacial maximum a dynamic global vegetation model dgvm was used to simulate global terrestrial carbon storage and stable carbon isotope composition changes for the last 21000 years a paleoclimate scenario was provided by interpolation of coupled agcm mixed layer ocean model experiments co2 atm data were obtained from the byrd and taylor dome ice core records according to the model results terrestrial carbon storage at the last glacial maximum lgm 21 ka was 821 pg c less than today the modeled isotopic composition delta 13 c of total terrestrial carbon at lgm was enriched by 1 5parts per thousand compared to present during the deglaciation 17 9 ka vegetation expanded rapidly into formerly glaciated areas and carbon storage correspondingly increased increasing npp sustained a continuing increase in terrestrial carbon storage through the holocene these results do not support the published hypothesis that terrestrial co2 outgassing drove the ca 20 ppm increase in co2 atm after 8 ka they are consistent with an alternative explanation based on the oceanic caco3 compensation response to the extraction of carbon from the atmosphere ocean system during the deglaciation

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

benthic foraminiferal δ13c and accumulation rates of organic carbon uvigerina peregrina group and cibicidoides wuellerstorfi the glacial to interglacial 13c records of the benthic foraminifera cibicidoides wuellerstorfi and the uvigerina peregrina group from deep sea cores cannot be adjusted by a generally valid constant the 13c values of the u peregrina group largely correlate with the accumulation rates of organic carbon suggesting a local habitat effect those of c wuellerstorfi vary independently with respect to the carbon flux and record fluctuations in the 13c of the ambient bottom water isotopic composition