evidence for preservation of crustal root beneath the proterozoic lapland kola orogen northern fennoscandian shield derived from p and s wave velocity models of polar and hukka wide angle reflection and refraction profiles and fire4 reflection transect 1 we present an analysis of the crust and upper mantle in the northern fennoscandian shield based on new p and s wave 2 d velocity models of the polar and hukka wide angle reflection and refraction profiles and results of a new seismic reflection experiment in finland finnish reflection experiment the profiles are almost collocated and crossed the proterozoic lapland kola orogen a substantial difference of the depth of the wide angle moho 40 42 km and the reflection moho 47 50 km was found in order to explain this difference we compared the velocity models to published values of vp and vp vs for the main types of lower crustal and mantle rocks we found that the main reason for disagreement is that the wide angle moho and the reflection moho correspond to different petrological boundaries in the southwest and northeast portions of the profiles the wide angle moho marks contact of either anorthositic or granulitic lower crust with a reflective layer in the upper mantle composed of peridotites and pyroxenites the reflection moho represents the bottom of this lower layer in the center of the profile the wide angle moho marks the top of a large eclogitic body in the upper mantle representing a well preserved crustal root beneath the lapland kola orogen formed because of the collision of three former archaean crustal blocks terranes or microcontinents lack of postorogenic tectonic collapse suggests another mechanism for stabilization of the lithosphere in the area upper mantle reflectors at depth of 65 75 km may mark the upper boundary of the cold and mechanically strong archaean upper mantle wedge alternatively these reflectors may represent a top of uplifted asthenosphere that can explain preservation of crustal root

reorganization of deep ocean circulation accompanying a late cretaceous extinction event deep ocean circulation may be a significant factor in determining global climate1 5 increases in the flux of warm saline waters from low to high latitudes would enhance the poleward transport of heat and thus help maintain the warm conditions at high latitudes typical of globally warm greenhouse periods but controversy exists1 2 as to whether the ocean s thermohaline circulation can transport enough heat to bring about the temperature distributions of these times such as the mid cretaceous and early eocene here we present stable isotope records of ocean temperature and salinity that indicate that bottom waters in late cretaceous oceans of the southern hemisphere became cooler and less saline at the same time about 70 myr ago as widespread biotic changes3 6 8 these findings support the idea that changes in deep ocean circulation can act as a climate switch

paleoceanographic modeling of temperature salinity profiles from stable isotopic data temperature salinity t s profiles in ancient seawater can be estimated from oxygen isotopic compositions of well preserved calcitic fossils sampled from known paleodepth gradients the proposed model uses isotopic compositions of fossils to determine possible combinations of temperature and salinity during deposition given estimates of average salinity isotopic composition and net global hydrologic fractionation for ancient oceans increasing density with depth constrains those combinations to narrow ranges this graphic method superposes curves for density and isotopic composition in t s space to reveal possible ancient t s profiles application of this method to oxygen isotope data from ordovician brachiopods deposited on the eastern continental slope of north america demonstrates its usefulness and yields a stable seawater column in which brackish intermediate waters overlie warmer more saline deep waters

early maastrichtian stable isotopes changing deep water sources in the north atlantic we propose that the observed short term stable isotope fluctuations reflect changes in high and low latitude intermediate to deep water sources based on a high resolution stable isotope record of planktic and benthic foraminifera from the early maastrichtian 71 3 to 69 6 ma of blake nose dsdp site 390a north atlantic sources of these waters may have been the low latitude eastern tethys and high latitude north atlantic changes in intermediate to deep water sources were probably steered by eccentricity controlled insolation fluctuations lower insolation favored the formation of high latitude deep waters due to positive feedback mechanisms resulting in high latitude cooling this led to a displacement of low latitude deep waters at blake nose higher insolation reduced intermediate to deep water formation in high latitudes yielding a more northern flow of low latitude deep waters

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

deep circulation in the late cretaceous oxygen isotope paleotemperatures from inoceramus remains in d s d p cores abstract inoceramus is an epibenthic bivalve which lived in a wide variety of paleoenvironments encompassing a broad range of paleodepths a survey of all cretaceous sediments from deep sea drilling project legs 1 69 and 75 revealed over 500 inoceramus specimens at twenty sites of these 47 well preserved late cretaceous specimens from the south atlantic pacific and indian oceans were analyzed for oxygen and carbon isotopes the specimens exhibit small internal isotopic variability and oxygen isotopic paleotemperatures that are consistent with a deep sea habitat paleotemperatures ranging from 5 to 16 c show that late cretaceous oceans were significantly warmer than the present oceans the data suggest that deep water was formed both by cooling at high latitudes and by evaporation in the subtropics

does ice drive early maastrichtian eustasy a large 30 40 m rapid 1 m y earliest maastrichtian sea level drop inferred from new jersey sequence stratigraphic records correlates with synchronous 18o increases in deep water benthic and low latitude surface dwelling planktonic foraminifera the coincidence of these events argues for the development of a moderate sized ice sheet during the early maastrichtian

a benthic foraminiferal record of middle to late pliocene 3 15 2 85 ma deep water change in the north atlantic abstract records of benthic foraminifera from north atlantic dsdp site 607 and hole 610a indicate changes in deep water conditions through the middle to late pliocene 3 15 to 2 85 ma quantitative analyses of modern associations in the north atlantic indicate that seven species fontbotia wuellerstorfi cibicidoides kullenbergi uvigerina peregrina nuttallides umboniferus melonis pompilioides globocassidulina subglobosa and epistominella exigua are useful for paleoenvironmental interpretation the western north atlantic basin site 607 was occupied by north atlantic deep water nadw until 2 88 ma at that time n umboniferus increased indicating an influx of southern ocean water sow the eastern north atlantic basin hole 610a was occupied by a relatively warm water mass possibly northeastern atlantic deep water neadw through 2 94 ma when sow more strongly influenced the site these interpretations are consistent with benthic 18o and 13c records from 607 and 610a raymo et al 1992 the results presented in this paper suggest that the north atlantic was strongly influenced by northern component deep water circulation until 2 90 2 95 ma after that there was a transition toward a glacially driven north atlantic circulation more strongly influenced by sow associated with the onset of northern hemisphere glaciation the circulation change follows the last significant sst and atmospheric warming prior to 2 6 ma

continental runoff and early cenozoic bottom water sources the dominance of warm saline bottom water during the mid cretaceous and the early cenozoic has been inferred from sea floor sediment records an interpretation supported by early ocean general circulation model experiments thermohaline circulation depends in part on upper ocean salinities however early ocean models neglected continental runoff a potentially critical factor in the salinity budget of the surface ocean our early eocene ocean model sensitivity tests show that model deep water sources can be enhanced diminished or turned off by varying the treatment of continental runoff in the atmosphere ocean moisture flux calculation failure to treat surface runoff adequately thus has important implications for the simulation of thermohaline flow and formation of warm saline bottom water variations in runoff could have led to rapid changes in the relative importance of high latitude versus subtropical deep water such as may have occurred during the late paleocene early eocene boundary interval 53 6 56 2 ma

mid cretaceous ocean circulation results from model sensitivity studies a series of ocean general circulation model gcm experiments for mid cretaceous continental paleogeography with atmospheric forcing prescribed from atmospheric gcm experiments are utilized to investigate the nature of the mid cretaceous ocean circulation the experiments illustrate a tethys system of clockwise currents and predominant eastward flow in marked contrast with earlier reconstructions this result is apparently robust for changes in bathymetry and in the degree of planetary warmth changes in sea level have the largest potential to produce alternative circulation characteristics two major current systems outside of tethys dominate the model simulation the site of bottom water formation is the north pacific however in a sensitivity experiment for a warmer climate the eastern tethys became a site of deep water formation

global environmental changes preceding the cretaceous tertiary boundary early late maastrichtian transition stable carbon oxygen and strontium isotope data from maastrichtian planktic and benthic foraminifera from southern high latitude ocean drilling program sites 690 750 and 761 reveal major changes in climate and ocean chemistry during the early to late maastrichtian transition some 4 to 6 m y prior to the cretaceous tertiary k t boundary the 18o results suggest accelerated cooling resulting in the lowest marine temperatures of the late cretaceous the late maastrichtian rise in the seawater 87sr 86sr ratio begins at the time of this change and suggests increased rates of continental weathering and or runoff the 13c values show a negative shift of 0 5 followed by a positive shift of 1 these 13c fluctuations may reflect change in deep water chemistry with cooling variation in reduced carbon storage in coastal areas caused by eustatic sea level fluctuation and increased surface water productivity these findings contradict the common representation of stable and climatically equable environmental conditions in the latest cretaceous before the k t boundary event

thermohaline instability in the north atlantic during meltwater events stable isotope and ice rafted detritus records from core so75 26kl portuguese margin a benthic isotope record has been measured for core so75 26kl from the upper portuguese margin 1099 m water depth to monitor the response of thermohaline overturn in the north atlantic during heinrich events evaluating benthic 18o in ts diagrams in conjunction with equilibrium c fractionation implies that advection of mediterranean outflow water mow to the upper portuguese margin was significantly reduced during the last glacial 15 compared to 30 today the benthic isotope record along core so75 26kl therefore primarily monitors variability of glacial north atlantic conveyor circulation the 14c accelerator mass spectrometry ages of 13 54 07 and 20 46 12 ka for two ice rafted detritus ird layers in the upper core section and an interpolated age of 36 1 ka for a third ird layer deeper in the core are in the range of published 14c ages for heinrich events h1 h2 and h4 marked depletion of benthic 13c by 0 7 1 1 during the heinrich events suggests reduced thermohaline overturn in the north atlantic during these events close similarity between meltwater patterns inferred from planktonic 18o at site 609 and ventilation patterns inferred from benthic 13c in core so75 26kl implies coupling between thermohaline overturn and surface forcing as is also suggested by ocean circulation models benthic 13c starts to decrease 1 5 2 5 kyr before heinrich events hl and h4 fully increased values are reached 1 5 3 kyr after the events indicating a successive slowdown of thermohaline circulation well before the events and resumption of the conveyor s full strength well after the events benthic 13c changes in the course of the heinrich events show subtle maxima and minima suggesting oscillatory behavior of thermohaline circulation a distinct feature of thermohaline instability in numerical models inferrred gradual spin up of thermohaline circulation after hl and h4 is in contrast to abrupt wanning in the north atlantic region that is indicated by sudden increases in greenland ice core 18o and in marine faunal records from the northern north atlantic from this we infer that thermohaline circulation can explain only in part the rapid climatic oscillations seen in glacial sections of the greenland ice core record

deep water in the late maastrichtian ocean 1 stable isotopic data from benthic foraminifera indicate the occurrence of at least three deepwater masses in the late maastrichtian ocean given mean oceanic 18ow of 1 0 the temperature of the coolest intermediate depth waters was 5 7 c that of the deepest waters was 10 c and that of the warmest intermediate waters was 13 15 c the cool intermediate depth water mass probably originated in the high latitude southern ocean the deepest waters originated at least partly in the northern atlantic the source region for the warmest intermediate depth water mass is unknown although much of the late maastrichtian deep water was probably preconditioned for winter sinking by low or middle latitude evaporation no more than 11 of late maastrichtian deep water could have been directly actuated by low latitude sea surface evaporation at least in the southern atlantic and indian oceans heat transport by upwelling of deep water was not the primary cause of mild sea surface and coastal temperatures

variability in late cretaceous climate and deep waters evidence from stable isotopes abstract strong climatic and temperature fluctuations mark the late campanian and maastrichtian as indicated by stable isotope records from the equatorial pacific site 463 and middle and high latitude south atlantic sites 525 689 and 690 the first major global cooling decreased intermediate water temperatures iwt by 5 6 c between 73 70 ma at the same time sea surface temperature sst decreased by 4 5 c in middle and high latitudes intermediate waters iw temporarily warmed by 2 c in low and middle latitudes between 70 68 5 ma global cooling resumed between 68 5 65 5 ma when iwt decreased by 3 4 c and sst by 5 c in middle latitudes about 450 ka before the cretaceous tertiary boundary rapid global warming increased iwt and sst by 3 4 c though sst in the tropics changed little during the last 200 ka of the maastrichtian climate cooled rapidly with iwt and sst decreasing by 2 3 c during the global cooling at 71 70 ma and possibly at 67 65 5 ma the sources of cold intermediate waters in the equatorial pacific indo pacific and south atlantic were derived from the high latitude north pacific in contrast during the global climate warming between 65 2 65 4 ma the middle latitude south atlantic was closest to the source of iw production and implies that the low latitude tethys played a major role in global climate change climate changes sea level fluctuations and associated restricted seaways appear to be the most likely mechanisms for the alternating sources of iw production

constraints from paleotracer data on the north atlantic circulation during the last glacial maximum we investigate the extent to which the paleotracers 13c and 18o constrain the north atlantic ocean general circulation during the last glacial maximum lgm the distinction is made in this work between the depiction of water mass distributions and the inference of the oceanic circulation the 13c data indicate that water masses formed in the north atlantic and in the southern ocean were distributed differently during the lgm but the extent of the differences cannot be quantified because of uncertainties in the end member composition reasonable choices of values for the end members produce volumes of lower north atlantic deep water nadw significantly smaller than in the modern atlantic in agreement with previous studies to explore the range of circulations consistent with this water mass distribution a coarse resolution inverse model of the north atlantic is constrained with 13c and 18o paleodata the model shows that the glacial period tracer distribution is fully consistent with the circulation rates estimated for the modern ocean however the paleodata are also consistent with a circulation rate of one half the modern flux of nadw and indeed there are an infinite number of rates of deep water movement that are possible to remove this ambiguity the central need is for a data type capable of setting the overall rates of water movement i e a clock such as that provided by geostrophy or a well sampled radioactive tracer

deep sea paleotemperature record of extreme warmth during the cretaceous oxygen isotope analyses of well preserved foraminifera from blake nose 30 n paleolatitude north atlantic and globally distributed deep sea sites provide a long term paleotemperature record for the late albian maastrichtian interval that is difficult to reconcile with the existence of significant cretaceous ice sheets given reasonable assumptions about the isotopic composition of cretaceous seawater our results suggest that middle bathyal water temperatures at blake nose increased from 12 c in the late albian through middle cenomanian to a maximum of 20 c during the latest cenomanian and earliest turonian bottom waters were again 12 c during the middle campanian and cooled to a minimum of 9 c during the maastrichtian correlative middle bathyal foraminifera from other ocean basins yield paleotemperature estimates that are very similar to those from blake nose comparison of global bottom water temperatures and latitudinal thermal gradients suggests that global climate changed from a warm greenhouse state during the late albian through late cenomanian to a hot greenhouse phase during the latest cenomanian through early campanian then to cool greenhouse conditions during the mid campanian through maastrichtian

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

interspecies variation in stable isotopic signals of maastrichtian planktonic foraminifera we measured stable isotopic signals of the largest specimens of all abundant species of planktonic foraminifera in late maastrichtian samples from three atlantic mid latitude and high latitude sites each sample is marked by a relatively small interspecies range of 18o values 1 2 to 0 8 each also exhibits an interspecies range of 13c values that resembles those of modern assemblages at similar latitudes 2 8 to 0 9 with greater ranges at lower latitudes these results indicate that late cretaceous planktonic foraminifera inhabited water masses characterized by a relatively narrow range of temperatures but may have occupied an array of niches as ecologically diverse as that of modern taxa maastrichtian taxa exhibit more complex relationships between skeletal morphology and vertical and seasonal paleohabitat affinities than previous paleoecologic models have assumed for example keeled taxa were not limited to cold or deep habitats and serial taxa appear to have occupied both warm near surface niches and the coolest or most saline habitats the isotopic differences between species indicate that apparent variation in maastrichtian stable isotopic signals strongly depends on the taxa analyzed narrowly constrained size fractions of rugoglobigerina species may provide a good estimate of relative variation in isotopic equilibria of near surface summer paleoconditions at low and middle latitudes gublerina species laeviheterohelix species and planoglobulina multicamerata appear the likeliest candidates for consistently tracking relative variation in isotopic equilibria of the coldest or most saline paleohabitats of maastrichtian planktonic foraminifera these isotopic results suggest that upper water column thermal gradients may have been only 3 to 5 c in mid latitude and high latitude regions they also suggest that the western and central atlantic mid latitude summer seasurface may have been much cooler or saltier in the maastrichtian than it is today finally they corroborate previous estimates of 10 c surface water at southern high latitudes

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

variability in the deep and intermediate water circulation of the atlantic ocean during the past 25 000 years northern hemisphere modulation of the southern ocean the relative flux of north atlantic deep water nadw out of the atlantic can be monitored in the southern ocean where high 13c nadw mixes rapidly with low 13c recirculated pacific water before forming antarctic bottom water aabw by using 13c measured in benthic foraminifera as a water mass tracer it is shown that the southern ocean was dominated by pacific water with little nadw contribution during the last glaciation these tracer results document the direct physical connection between insolation controlled northern hemisphere oscillations and changes in the chemical and physical properties of southern ocean water the 13c records from the deep tropical atlantic document the transition from an atlantic dominated by southern ocean water during the last glaciation to an atlantic dominated by nadw during the holocene with more southern ocean water in the deep atlantic during the last glaciation the boundary between nadw and southern ocean water was north of its modern position allowing more southern ocean water to enter the eastern atlantic through the romanche fracture zone carbon isotope records from the caribbean and mediterranean seas suggest that the influence of mediterranean overflow water mow extended to the caribbean during the last glaciation and therefore was a volumetrically much more important water mass in the intermediate depth atlantic than it is today

pollutant advective spreading in beach sand exposed to high energy tides abstract this paper presents field measurements in which dye solute was injected into coastal sand to investigate contaminant advection in intertidal beach sand the measurements show the pathways of a contaminated plume in the unsaturated zone during both the flood and ebb tides a prescribed amount of dye tracer solution was directly injected through the topsoil with average porosity 0 3521 0 01 at predetermined locations of the river mersey s outer estuarial beach during ebb tide the injected dye was monitored sampled and photographed over several tidal cycles the distinctive features of the plume full two dimensional cross sections sediments and water table depth were sampled in situ close to the injection point differing from previous contaminant monitoring tests in aquifers the advective movement is attributed to tidal impact which is different from contaminant transport in aquifers the experimental results show that plumes have significantly large spatial variability diverging upwards and converging downwards with a conical geometric shape which is different from the usual spherical elliptical shape reported in literature the mean vertical motion of the plume reaches three times the top width within ten tidal cycles exceeding the narrow bottom width by a factor of order 2 the observed transport features of the plume within the beach sand have significant relevance to saltwater intrusion surface water and groundwater quality the field observations are unique and can serve as a valuable benchmark database for relevant numerical studies

maastrichtian foraminiferal and paleoceanographic changes on milankovitch timescales milankovitch scale alternations in maastrichtian hemipelagic strata from ocean drilling program hole 1050c blake nose provide a natural experiment of paleoceanography and foraminiferal paleoecology in a tropical subtropical greenhouse ocean cycles are 30 50 cm thick and thought to reflect the 21 kyr precessional cycle high planktic 18o values are correlated with high planktic but low benthic 13c values indicating that cooler and or more saline surface waters were associated with higher productivity high productivity intervals are also characterized by high ca concentrations enrichment in feldspar and kaolinite and high relative abundance of heterohelix spp globigerinelloides spp and laeviheterohelix glabrans conversely low productivity intervals have low planktic 18o values high fe and ti concentrations enrichment in quartz illite and chlorite and relative increases in globotruncana spp and pseudoguembelina spp potential forcing mechanisms for observed covariation include cyclic variation in water column stratification variation in continental nutrient fluxes and changes in the intensity of upwelling

late cretaceous chronology of large rapid sea level changes glacioeustasy during the greenhouse world we provide a record of global sea level eustatic variations of the late cretaceous 99 65 ma greenhouse world ocean drilling program leg 174ax provided a record of 11 14 upper cretaceous sequences in the new jersey coastal plain that were dated by in tegrating sr isotopic stratigraphy and biostratigraphy backstripping yielded a late cre taceous eustatic estimate for these sequences taking into account sediment loading com paction paleowater depth and basin subsidence we show that late cretaceous sea level changes were large 25 m and rapid k1 m y suggesting a glacioeustatic control three large d 18 o increases are linked to sequence boundaries others lack sufficient d 18 o data consistent with a glacioeustatic cause and with the development of small 10 6 km 3 ephemeral ice sheets in antarctica our sequence boundaries correlate with sea level falls recorded by exxon production research and sections from northwest europe and russia indicating a global cause although the exxon record differs from backstripped estimates in amplitude and shape

on the structure and origin of major glaciation cycles 2 the 100 000 year cycle climate over the past million years has been dominated by glaciation cycles with periods near 23 000 41 000 and 100 000 years in a linear version of the milankovitch theory the two shorter cycles can be explained as responses to insolation cycles driven by precession and obliquity but the 100 000 year radiation cycle arising from eccentricity variation is much too small in amplitude and too late in phase to produce the corresponding climate cycle by direct forcing we present phase observations showing that the geographic progression of local responses over the 100 000 year cycle is similar to the progression in the other two cycles implying that a similar set of internal climatic mechanisms operates in all three but the phase sequence in the 100 000 year cycle requires a source of climatic inertia having a time constant similar to 15 000 years much larger than the other cycles similar to 5 000 years our conceptual model identifies massive northern hemisphere ice sheets as this larger inertial source when these ice sheets forced by precession and obliquity exceed a critical size they cease responding as linear milankovitch slaves and drive atmospheric and oceanic responses that mimic the externally forced responses in our model the coupled system acts as a nonlinear amplifier that is particularly sensitive to eccentricity driven modulations in the 23 000 year sea level cycle during an interval when sea level is forced upward from a major low stand by a milankovitch response acting either alone or in combination with an internally driven higher frequency process ice sheets grounded on continental shelves become unstable mass wasting accelerates and the resulting deglaciation sets the phase of one wave in the train of 100 000 year oscillations whether a glacier or ice sheet influences the climate depends very much on the scale the interesting aspect is that an effect on the local climate can still make an ice mass grow larger and larger thereby gradually increasing its radius of influence