oxygen and carbon isotope record of east pacific core v19 30 implications for the formation of deep water in the late pleistocene north atlantic abstract a detailed oxygen and carbon isotope record has been obtained from benthic foraminifera in core v19 30 from the carnegie ridge on the south side of the panama basin expressing these records and the oxygen and carbon isotope records previously published for atlantic core m 12392 on a common timescale it is apparent that the oxygen isotope records are very similar but that the carbon isotope records are quite different by obtaining the carbon isotope gradient between the two sites as a function of time we show that the production of north atlantic deep water has varied over a wide range during the late pleistocene and that the pattern of variation is not simply related to the well known oxygen isotope record although the two oxygen isotope records are very similar changes in the interoceanic gradient are detectable and support the hypothesis that in the glacial mode the north atlantic was colder and less oxygenated than it is today shackleton s 1 1977 interpretation whereby the carbon isotope record from the atlantic core reflects changes in the terrestrial biomass is an over simplification however the record from the pacific core v19 30 probably can be explained in these terms since it probably approximates the carbon isotope record of global mean oceanic dissolved co 2

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

techniques for determining opal in deep sea sediments a comparison of radiolarian counts and x ray diffraction data abstract detailed records of two estimators of the biogenic silica content of deep sea sediments x ray diffraction analysis opal concentrations and quantitative radiolarians per gram counts from microscope slides were compared in downcore sediments from northwest pacific core rc14 105 to evaluate and to intercalibrate the two techniques both the degree to which the data were similar and the degree to which inferences from the data were similar were considered although both data sets are internally consistent and reflect surface water processes they are not equivalent and there is no way to convert one linearly into the other the numbers of radiolarians per gram of sediment appear to respond to the same factors which control the fluctuations in the radiolarian assemblage distrbutions in the area the opal contents respond to the factors which control the total siliceous productivity of the area

a hemispheric circulation asymmetry during late tertiar recent data obtained within the deep sea drilling project legs 28 29 35 36 in the southern oceans revealed that the formation of antarctic sea ice started 38 m y b p ago at the begin of the oligocene the antarctic ice cap reached nearly its present volume during the middle miocene 14 12 m y b p and a volume greater than the present during the messinian 6 5 m y b p apart from local mountain glaciations the first large scale glaciation of the northern continents was developed about 3 m y b p followed by the formation of the arctic sea ice which has probably survived more than 20 fully developed interglacials certainly during the last 0 7 m y this evolution indicates a period of about 10 m y during which east antarctica was highly glaciated while the arctic ocean was essentially ice free this asymmetric pattern is compared with the present asymmetry unipolar versus bipolar glaciation the annually averaged position of the meteorological equator had then displaced from about lat 6 n to day to about 10 n some estimates of the heat budget terms in polar latitudes at a glaciated continent and at an ice covered ocean are given a preliminary review of paleoclimatic data reveals significant shifts of the position of the climatic belts at both hemispheres these shifts coincide rather well with an extrapolation of the actual seasonal variations which confirm a simple equation for the latitude of the subtropical anticyclonic belts as the boundary between ferrel and hadley regimes finally the role of equatorial upwelling as correlated with an asymmetric circulation pattern for the water balance is outlined these asymmetries may become of major importance if an expected rise of co2 level above an estimated threshold should restore an ice free arctic ocean

biogenic budgets of particle rain benthic remineralization and sediment accumulation in the equatorial pacific abstract budgets of organic c corg cac03 and opal have been constructed for the palisades ny pacific equatorial region at 140 w between 5 n and 5 s measurements of the rain and benthic remineralization rate of biogenic materials have been adjusted and normalized to account for sampling biases sea surface temperature serves as a master variable in normalizing sediment trap and benthic remineralization data to average conditions the rain and remineralization rates for corg are nearly equal 0 40 0 05 and 0 46 0 06 mmol m 2 d 1 respectively thus only a minor fraction of this constituent is buried rain and dissolution rates for biogenic opal are similarly balanced 0 3 0 06 and 0 36 0 01 mmol m 2 d 1 and consistent with the value for opal burial 0 0 0 004 the cac03 budget appears to have changed during the holocene the best estimates of modern cac03 dissolution 0 58 0 03 mmol m 2 d 1 and rain rate 0 61 0 06 are consistent with230th normalized carbonate accumulation rates for the late holocene 0 1 mmol m 2 d 1 however the balance between dissolution and rain is not consistent with early holocene carbonate accumulation 0 3 mmol m 2 d 1 and this imbalance suggests 1 a recent increase in the rate of cac03 dissolution on the sea floor or 2 a decrease in the rain rate of carbonate particles modeling230th profiles in sediments from this region define the last 3000 years as the duration of increased dissolution or decreased particle rain 231pa 230th ratios in sediments indicate that particle rain rates have remained constant or possibly increased slightly through the holocene two potential causes for increased dissolution were investigated a change in deep water carbonate saturation or a change in co g cac03 rain ratios a model describing carbonate dissolution as a function of the degree of undersaturation and the amount of organic carbon oxidation within sediments indicates that the recent increase in dissolution is more likely due to changes in bottom water chemical composition we propose that pacific ocean bottom water carbonate ion concentration has decreased by 10 15 m over the last 3000 years

quaternary fluctuations in the northern hemisphere trade winds and westerlies the mass accumulation rate and grain size of the total colian component isolated from pelagic sediment in two north pacific cores piston core kk75 02 under the prevailing westerlies and deep sea drilling project site 503 beneath the trade winds have been used to evaluate changes in the intensity of atmospheric circulation and source area aridity over the past 700 000 yr the eolian grain size a direct indicator of wind intensity fluctuates at periodicities similar to those calculated for the earth s orbital parameters of precession obliquity and eccentricity both sites display greater variability in wind intensity prior to 250 000 yr ago eolian accumulation rates an indicator of source area aridity fluctuate at periodicities similar to those of the glacial interglacial cycles lower eolian accumulation rates during colder glacial times most likely reflect increased glacial age humidity at central asian and central american source areas

climatically forced organic carbon burial in equatorial atlantic and pacific oceans over the past ten years sedimentary geochemists have noted that climate changes associated with pleistocene glaciations have had a pronounced effect on the rate of organic carbon burial found in the tropical oceans1 4 in particular two to five times higher organic carbon accumulation rates have been observed for the 18 kyr bp glacial maximum than for the holocene in several short sediment cores from both oceans see fig 1 here i present 300 kyr time series for organic carbon mass accumulation rate from four sediment cores two each from the equatorial pacific and atlantic and show that orbital forcing of global climate has strongly affected the rate of organic carbon burial in the equatorial oceans

quaternary history of calcium carbonate fluctuations in the western equatorial indian ocean somali basin abstract a study of the quaternary history of calcium carbonate fluctuations in the equatorial indian ocean based on the swedish deep sea expedition core 154 demonstrates that the calcite compensation depth ccd was shallower during interglacial periods than during glacials higher percentages of calcium carbonate lower percentages of dissolution resistant planktonic foraminifera and lower values of the berger dissolution index suggesting better calcium carbonate preservation are recorded during glacial periods and or at glacial interglacial transitions in contrast interglacial periods are marked by stronger calcium carbonate dissolution the data indicate that dissolution is the main controlling factor of calcium carbonate in the western equatorial indian ocean higher dissolution during interglacial periods and enriched 13 c are due to higher noncarbonate productivity and enhanced antarctic bottom water aabw ventilation in the equatorial indian ocean

palaeooceanographic significance of bottom current fluctuations in the southern ocean hiatuses in the sedimentary record of the southern ocean are usually attributed to erosion by high velocity bottom currents1 3 to test for palaeoclimatic mechanisms which intensified bottom circulation however the timing of increases in bottom current velocity must be known as the sedimentary record of the period of initial erosion is lost within the hiatus the timing of increased velocity must be determined in cores which are adjacent to the axis of highest velocity4 5 in those cores the accumulation rates are reduced due to the current but a record of the period of initiation of scour is preserved as a zone of particle size winnowing of the fine fraction3 4 the timing of major episodes of bottom current intensification in the south australian basin for the past 4 5 myr are reported here for the first time and may be used to examine the role of palaeoclimatic fluctuations on bottom current intensity

origin of detrital fluxes in the southeast indian ocean during the last climatic cycles because of a close relationship between detrital flux variations and magnetic susceptibility ms flux ms cm 3 of bulk sediment multiplied by the linear sedimentation rate variations in the southeast indian basin of the southern ocean ms flux profiles have been used to examine the spatial and temporal detrital flux changes in this basin during the last climatic cycle results indicate a general increase in detrital material input during the coldest periods suggesting a widespread phenomenon at least on the basin scale mineralogical data geochemical data and 87sr 86sr isotopic ratios have been used to determine the origin and transport mechanisms responsible for increased detrital flux during glacial periods mineralogical and geochemical data show that these glacial highs are due to increases in both kerguelen crozet volcanic and antarctic detrital inputs the 87sr 86sr isotopic composition of the 45 m fraction indicates that the kerguelen crozet province contributes to at least 50 of the coarse particule input to the west this contribution decreases eastward to reach less than 10 these tracers clearly indicate that the crozet kerguelen province was a major source region of detrital in the western part of the basin during glacial times in contrast material of antarctic origin is well represented in the whole basin fine and coarse fractions because of the minor amount of coarse particles in the sediments volcanic particles from kerguelen and crustal particles from antarctica have most probably been transported by the antarctic bottom water current and or the circumpolar deepwater current during glacial periods as is the case today nevertheless the presence of coarse particles even in low amount suggests also a transport by ice rafting sea ice and icebergs originated from both kerguelen and antarctic sources however the relative importance of both hydrographic and ice rafting modes of transport cannot be identified accurately with our data during low sea level stands glacial maximum periods increasing instability and erosion of the continental platform and shallow plateaus could have resulted in a more efficient transfer of crustal and volcano detrital material to the southeast indian basin at the same time extension of the grounded ice shelves over the continental margins and increase in the erosion rate of the antarctic ice sheet could have induced a greater input of ice rafted detritus ird to southern ocean basins enhancement of the circumpolar deepwater current strength might have also carried a more important flux of detrital material from kerguelen however an increase in the bottom water flow is not necessarily required

vertical geodesy without slope dependent errors a proposed hydrostatic pressure level using water at 4 c abstract bilham r 1983 vertical geodesy without slope dependent errors a proposed hydrostatic pressure level using water at 4 c in p vyskocil m a wassef and r green editors recent crustal movements 1982 tectonophysics 97 337 349 conventional vertical geodesy using spirit levelling has two fundamental shortcomings it is expensive to perform and it is associated with systematic errors that are temperature and slope dependent a hydrostatic level is described that in theory can more than double the speed of 1st order levelling and provide a measurement precision of better than 1 cm per vertical kilometer of traverse in the favoured design digital quartz pressure transducers are used to measure the pressure at each end of a 100 200 m long flexible tube containing water at its maximum density the entire instrument is maintained at 4 1 c by truck mounted machinery at the leading end of the hydrostatic level the digitally recorded measurements are expected to provide a single set up resolution better than 0 1 mm over a vertical range of 4 10 m a random error of 0 3 mm km of horizontal traverse and a vertical precision of the order of one part in 105 independent of weather conditions

production and accumulation of calcium carbonate in the ocean budget of a nonsteady state present day production of caco3 in tne world ocean is calculated to be about 5 billion tons bt per year of which about 3 bt accumulate in sediments the other 40 is dissolved nearly half of the carbonate sediment accumulates on reefs banks and tropical shelves and consists largely of metastable aragonite and magnesian calcite deep sea carbonates predominantly calcitic coccoliths and planktonic foraminifera have orders of magnitude lower productivity and accumulation rates than shallow water carbonates but they cover orders of magnitude larger basin area twice as much calcium is removed from the oceans by present day carbonate accumulation as is estimated to be brought in by rivers and hydrothermal activity 1 6 bt suggesting that outputs have been overestimated or inputs underestimated that one or more other inputs have not been identified and or that the oceans are not presently in steady state one missing calcium source might be groundwater although its present day input is probably much smaller than that of rivers if as seems likely caco3 accumulation presently exceeds terrestial and hydrothermal input this imbalance presumably is offset by decreased accumulation and increased input during lowered sea level shallow water accumulation decreases by an order of magnitude with a 100 m drop in sea level while groundwater influx increases because of heightened piezometric head and the diagenesis of metastable aragonite and magnesian calcite from subaerially exposed shallow water carbonates

radiolarian assemblage distributions and paleoceanography of the eastern equatorial pacific ocean during the last 127 000 years abstract mathematical treatment q mode factor analysis of radiolarian species abundance data in equatorial pacific core tops yields four oceanographically meaningful assemblages the distribution of these assemblages in surface sediments can be related to the major surface and subsurface characteristics of the equatorial circulation system western tropical mixed layer flow coastal upwelling and the oxygen minimum layer eastern equatorial divergence upwelling and the equatorial undercurrent and the subtropical water masses of both hemispheres changes in the distribution of radiolarian assemblages during the glacial interglacial cycle spanning the last 127 000 yr are observed in two equatorial pacific piston cores these changes reflect fluctuations in the boundaries of equatorial water masses in response to variations in the position and strength of the tradewind system and tend to precede major glacial interglacial transitions by several thousand years a history of atmospheric circulation in the equatorial pacific has been developed for the last 127 000 yr fluctuations in tradewind intensity north south shifts in the latitudinal position of the tradewind maxima and perhaps a change in the zonality of the tradewinds during the last 127 000 yr have been inferred from downcore quartz abundance and radiolarian assemblage distribution patterns oxygen isotopic fluctuations during the last 127 000 yr indicate that continental ice volume was much greater during glacial stage 2 29 000 b p to 11 000 b p than during glacial stage 4 73 000 b p to 61 000 b p large changes in atmospheric and oceanic circulation patterns also are indicated by the distribution of radiolarian assemblages during the two glacial periods during stage 2 oceanic circulation was more intense the southeast tradewind maximum was closer to the equator and wind stress was more meridional than during stage 4

late quaternary history of atmospheric and oceanic circulation in the eastern equatorial pacific abstract four radiolarian assemblages have been defined in recent seafloor sediments of the equatorial pacific ocean the distribution of these assemblages corresponds to the modern pattern of oceanic circulation and water mass structure in this region the eastern pacific shallow permanent thermocline and the equatorial undercurrent peru current upwelling and the oxygen minimum the subtropical water mass warm western tropical water and the north equatorial countercurrent in twelve cores chosen to transect the region both longitudinally and latitudinally the distribution of these four assemblages has been reconstructed for six time intervals during the last 127 000 years 18 000 b p glacial stage 2 36 000 b p and 52 000 b p interstadial stage 3 65 000 b p glacial stage 4 82 000 b p and 120 000 b p interglacial stage 5 atmospheric and oceanic circulation changes through time have been inferred from the reconstructed microfossil assemblage distributions changes in assemblage distributions indicate that variations in intensity direction and mean position of the tradewinds caused marked changes in the oceanic circulation patterns through the last glacial cycle near the end of interglacial stage 5 the disappearance of the north equatorial countercurrent from the eastern pacific suggests that the mean position of the tradewinds was shifted to the south approximately 5 of latitude relative to the modern position so that the northeast trades prevented the flow of the north equatorial countercurrent into the eastern pacific near the end of interstadial stage 3 a change in wind direction occurred from predominantly zonal winds which enhance equatorial divergence and surfacing of the equatorial undercurrent to more meridional winds which enhance coastal upwelling associated with the peru current in the tropical pacific ocean late quaternary changes in atmospheric and oceanic circulation are linked with times of continental ice sheet growth in the northern hemisphere i e the interglacial to glacial transitions across oxygen isotope stage boundaries 5 4 and 3 2 the major changes in circulation seem to occur a few thousand years in advance of the glacial episodes at or near periods of ice sheet growth this relationship indicates that changes in atmospheric circulation in the tropics led and influenced the development of conditions suitable for polar and continental ice sheet growth in the northern hemisphere

bottom current pathways in the argentine basin revealed by mean silt particle size regional circulation patterns in the deep sea are very difficult to determine because of time constraints on the acquisition of large physical oceanographic data sets from abyssal depths in addition the large number of long term 1 yr current meter arrays needed to delineate bottom current pathways are extremely costly an alternative method for inferring benthic flow patterns described here is to map the mean size of the silt fraction of sediment on the sea floor because of the availability of a large number of core samples in the argentine basin the particle size approach provides a useful method for determining bottom current pathways in that deep basin

the plio pleistocene climatic record of the tropical andes sequences of lake sediments on the high plains of the colombian cordillera oriental at an altitude of c 2500 m represent some 5 or 6 ma the last glacial interglacial cycle is well documented in the sediments of lake fuquene very long sequences up to 350 m long cores were collected in the high plain of bogota representing more than 3 5 ma pollen diagrams are now available covering that time and representing the longest known continuous terrestrial record available they were dated using potassium argon and fission track methods on material from intercalated volcanic ash layers the pollen diagrams can be interpreted in terms of shifting vegetation zones and these in turn enable us to draw approximate temperature and humidity curves the temperature curve for the last 3 5 ma can be correlated with deep sea curves oxygen isotopes temperature an important change in rhythm and intensity seems to take place at approximately 3 1 ma and a cold period that should correspond in time with the pre tiglian of western europe is conspicuous

a new approach to paleoclimatic research using linear programming abstract one of the most frequently attempted correlations in quaternary research is between insolation and paleoclimatic data yet there are a large number of insolation time series that could potentially explain a quaternary dataset individually or in combination we computed 342 insolation time series varying by latitude time of year and time of day for fitting to four different paleoclimatic records foraminiferal 18 o from specmap temperatures inferred from vostok antarctica ice cores marine accumulation rates of a freshwater diatom melosira originating from tropical africa lakebeds and 18 o variations in calcite at devil s hole nevada we developed two inductive linear programming models that solve for the weighted combination of insolation curves that minimize either the average or maximum residual from the proxy curve each of the four proxy records lagged and unlagged was solved by both model types on average our composite insolation curves fit the proxy records 48 76 better than does june daily insolation at 60 n the key insolation curve of the milankovitch paradigm globally high latitude insolation 60 70 n and s and insolation at specific times of day noon or non noon as opposed to daily dominated the results regionally the model tended to select insolation curves from absolute latitudes similar to those of the proxy records the fact that these results are plausible given known biophysical processes combined with the fact that a small number of curves repeatedly accounted for a disproportionate share of the explanation suggest strongly that the correlations found are not happenstance despite the inductive method used

near synchroneity of new zealand alpine glaciations and northern hemisphere continental glaciations during the past 750 kyr the brunhes magnetochron 0 730 kyr at deep sea drilling project site 594 off eastern south island new zealand comprises up to 100 m of alternating units of pelagic and hemipelagic ooze formed during interglacial and glacial periods respectively the youngest hemipelagic interval corresponds to glacial isotope stage 2 and can be correlated with extensive glacial and glacio fluvial deposits of the late last glaciation 27 13 kyr bp on south island inferring the same genetic link for the other hemipelagic sediment units down core we show here that as many as 12 major episodes of expanded alpine glaciation have occurred on south island in the past 730 kyr each of these glacial episodes coincided with a period of significant 18o enrichment 2 in the core resulting from changes in ocean isotope composition associated with major growth phases of the northern hemisphere ice sheets the inferred history of alpine glaciations on this remote south pacific island appears to be closely phase locked 3 kyr to world wide climate changes

proxy evidence from the gartnerkofel 1 core carnic alps austria for hypoxic conditions in the western tethys during the end permian mass extinction event abstract the most severe mass extinction in the phanerozoic in the latest permian period 251 9 ma has been attributed to environmental effects related to the massive coeval siberian flood basalt eruptions a potential causal link between the eruptions and the marine extinctions arises from lethal global warming from greenhouse gas emissions and the resulting development of widespread hypoxic conditions in the warm oceans the 331 m gartnerkofel 1 core carnic alps austria penetrated the permian triassic boundary interval in a western tethys shallow carbonate ramp setting we calculated u th ratios and element enrichment factors for u cr v co and ni using the previously published raw elemental data from the core these redox sensitive proxy calculations provide evidence for an 60 ky long episode of anoxic to euxinic ocean conditions in the shallow western tethys at the time of the abrupt end permian mass extinction epme subsequent fluctuating dysoxic conditions were coincident with a negative excursion of 13ccarb that is estimated to have lasted 450 ky in the earliest triassic at the gk 1 site these findings in a high deposition rate section support previous reports of widespread anoxia in the western tethys and in the oceans in general coincident with the epme and its aftermath

a 420 000 year record of cyclicity in oceanic and atmospheric processes from the eastern equatorial pacific samples from the upper portion of a cyclic pelagic carbonate sediment sequence in deep sea drilling project dsdp hole 503b 4 0 n 95 6 w are the first group to be analyzed for paleoceanographic and paleoclimatic proxy indicators of ice volume deep ocean and surface water circulation and atmospheric circulation in order to resolve the complex origin of the cyclicity temporal resolution is taken from the 18o time scale most other parameters are calculated in terms of their mass flux to the seafloor caco3 percent in the sediments fluctuates in the well known pacific pattern and is higher during glacial times the fluxes of opal and organic carbon have patterns similar to each other and show a variability of a factor of 2 5 to 4 the longer organic carbon record shows flux maxima during both glacial and interglacial times the accumulation patterns of both opal and organic carbon suggest that the variability in surface water productivity and or seafloor preservation of those materials is not simply correlated to glacial or interglacial periods eolian dust fluxes are greater during interglacial periods by factors of 2 to 5 indicating that eolian source regions in central and northern south america were more arid during interglacial periods the record of eolian grain size provides a semiquantitative estimation of the intensity of the transporting winds the eolian data suggest more intense atmospheric circulation during interglacial periods opposite to the anticipated results we interpret this observation as recording the southerly shift of the intertropical convergence zone to the latitude of hole 503b during glaciations