oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

late cenozoic arctic ocean sea ice and terrestrial paleoclimate sea otter remains found in deposits of two marine transgressions bigbendian and fishcreekian of the alaskan arctic coastal plain which occurred between 2 4 and 3 ma suggest that during these two events the southern limit of seasonal sea ice was at least 1600 km farther north than at present in alaskan waters perennial sea ice must have been severely restricted or absent and winters were warmer than at present during these two sea level highstands paleomagnetic faunal and palynological data indicate that the later transgression fishcreekian occurred during the early part of the matuyama reversed polarity chron amino acid diagenesis in fossil mollusks suggests that since the later transgression the effective diagenetic temperature edt in the deposits has been about 16 c which is about 7 c colder than modern values and slightly colder than the edt calculated for the past 125 ka such a low edt suggests that permafrost and perennial sea ice have been present nearly continuously since this transgression permafrost probably was absent however during the earlier bigbendian transgression permafrost and extensive perennial sea ice may have been initiated during the late stages of climatic cooling that spanned the gauss normal matuyama reversed polarity chron boundary and led into the first major late cenozoic glaciation of the northern hemisphere

origin nature and world climate effect of arctic ocean ice cover during the cenozoic an open water arctic ocean changed to the modern permanently ice covered condition significant world climate modification accompanied this change but the precise role of the arctic ocean in major pleistocene climate events is controversial the present ice cover averages 3 m thickness but there are theories that during the pleistocene it was antarctic like several thousand metres thick the time of origin of the ice cover is placed as young as 0 7 myr ago and as old as the middle miocene any theory concerned with origin nature and climatic response of the arctic ice cover must consider the ocean s sediment record

biostratigraphy and late cenozoic paleoceanography of the arctic ocean foraminiferal lithostratigraphic and isotopic evidence detailed studies of benthonic foraminifera stable isotopes and lithofacies in cores from the southeastern alpha ridge central arctic ocean reveal some new aspects of arctic ocean paleoceanography high ratios of benthonic to planktonic foraminifera are found in most of the quaternary sediment units and ratios of 1 1 appear to characterize the arctic deep water sediments benthonic foraminifera in the carbonate mud unit m show a succession of calcareous species reflecting increased influx of norwegian sea bottom water to the arctic ocean during the past 0 4 m y foraminiferal and lithological data indicate less uniform sedimentation during a warmer interval from 0 4 to 0 6 ma when most of the silty lutite unit l was deposited at the cesar site lower pleistocene units j to i contain less limestone and more dolomite and they contain a uniform faunal assemblage with low numbers of calcareous foraminifera upper pliocene units h to ab contain rare limestone and relatively large amounts of do lomite and quartz sand middle to upper pliocene units ab to a3 are marked by abundant sand sized ferromanganese coated particles which in many cases have a silt nucleus hence much of the coarse sand in these units does not indicate increased ice rafting the pliocene sediments mostly contain a low diversity assemblage of agglutinated foraminifera but a mixed calcareous arenaceous fauna occurs in a short interval above the matuyama gauss boundary 2 4 ma stable isotopic curves occur within sequences which broadly correspond to stages 1 9 of the global record below stage 9 the record is discontinuous strong vertical mixing apparently prevailed during most of the pliocene and early pleistocene then decreased during the past 0 4 m y owing to damping by a perennial ice cover isotopic and foraminiferal data however suggest that an interval of perennial sea ice also occurred during the late pliocene at the time of the earliest glacial event recorded in the north atlantic

the contribution of the greenland and barents seas to the deep water of the arctic ocean the deep waters of the arctic ocean are traditionally held to be fed by an influx of norwegian sea deep water nsdw via the northward flowing west spitsbergen current discrete sample and ctd observations obtained from the greenland spitsbergen passage in august 1981 during the transient tracers in the ocean tto north atlantic expedition showed a 100 m thick layer of modified greenland sea deep water gsdw colder and fresher than nsdw at 2500 m spreading northward along the bottom of a deep unimpeded channel underneath the nsdw since the available data indicate that arctic ocean deep water aodw has a higher salinity than nsdw mixing of nsdw and gsdw can not produce aodw therefore other sources such as the peripheral arctic shelf seas must contribute dense saline water to the arctic ocean concentrations of 137cs and 90sr observed in aodw are greater than those observed in gsdw and nsdw the concentrations of these radionuclides on the barents sea shelf are sufficiently high and in the correct relative proportions to support this proposition

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

saline outflow from the arctic ocean its contribution to the deep waters of the greenland norwegian and iceland seas abstractsince 1985 various investigators have proposed that norwegian sea deep water nsdw is formed by mixing of warm and saline deep water from the arctic ocean with the much colder and fresher deep water formed by convection in the greenland sea gsdw we here report on new observations which suggest significant modification and expansion of this conceptual model we find that saline outflows from the arctic ocean result in several distinct intermediate and deep salinity maxima within the greenland sea the southward transport of the two most saline modes is probably near 2 sv mixing of gsdw and the main outflow core found over the greenland slope derived from about 1700 m in the arctic ocean cannot by itself account for the properties of nsdw instead the formation of nsdw must at least in part involve a source which in the arctic ocean is found below 2000 m the mixing of various saline outflows is diapycnal while significant nsdw production appears to occur in northern fram strait large amounts of saline arctic ocean outflow also traverse the western greenland sea without mixing and enter the iceland sea during the past decade deep convection in the greenland sea has been greatly reduced while deep outflow from the arctic ocean appears to have continued resulting in a markedly warmer slightly more saline and less dense deep regime in the greenland sea american geophysical union 1991

stratigraphy and paleoceanography of pliocene deposits of karaginsky island eastern kamchatka u s s r abstract the lithology and paleontology of pliocene deposits from karaginsky island off eastern kamchatka peninsula u s s r are described in order to provide a paleoceanographic reconstruction of this region of the eastern north pacific ocean the stratigraphic sequence is divided into three suites the limimtevayamian the ust limimtevayamian and the tusatuvayamian which correspond to three standard pacific diatom zones the thalassiosira oestrupii neodenticula koizumi n kamtschatica and n koizumi the entire sequence is further subdivided into six members and 18 distinct beds on the basis of molluscan assemblages and three members and seven beds on the basis of benthic foraminiferal assemblages marine ostracodes are described from the limimtevayamian suite the marine invertebrate assemblages from karaginsky island provide evidence that 1 ocean water temperatures were warmer than today about 4 ma and again about 3 5 3 0 ma 2 several arctic atlantic species of molluscs and ostracodes migrated to the eastern north pacific between 4 2 3 0 ma presumably through the proto bering strait 3 many species found in the karaginsky island pliocene represent pacific taxa which migrated through the arctic into the north atlantic during the late pliocene

microfaunal evidence for elevated pliocene temperatures in the arctic ocean the migration of thermophilic marine ostracoda into the arctic ocean during the pliocene indicates that winter and summer ocean temperatures around arctic margins were 0 c and 3 c respectively and that ice free conditions existed for most or all of the arctic by at least 3 5 3 0 ma probably earlier the opening of the bering strait allowed marine organisms to migrate through the arctic ocean mostly from the pacific ocean migrant taxa such as cythere hemicythere and neomonoceratina are known from pliocene deposits of alaska and canada as well as neogene deposits of the north pacific and atlantic oceans on the basis of ecological and zoogeographic information on ostracode species from more than 800 modern core top samples for the north atlantic north pacific and arctic oceans we determined winter and summer temperature tolerances for migrant taxa to be at or above about 0 c and 3 c this suggests ice free summers and probably a perennially ice free arctic ocean in some regions elevated water temperatures in the arctic ocean between 3 5 and 2 0 ma is supported by evidence for late pliocene increased meridional heat transport in the north atlantic ocean

thermohaline circulation in the arctic mediterranean seas the renewal of the deep north atlantic by the various overflows of the greenland scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north the arctic ocean and the greenland iceland and norwegian seas collectively called the arctic mediterranean the traditional site of deep ventilation for these basins is the greenland sea but a growing body of evidence also points to the arctic ocean as a major source of deep water this deep water is relatively warm and saline and it appears to be a mixture of dense brine enriched shelf water with intermediate strata in the arctic ocean the deep water exits the arctic ocean along the greenland slope to mix with the greenland sea deep water conversely very cold low salinity deep water from the greenland sea enters the arctic ocean west of spitsbergen within the arctic ocean the lomonosov ridge excludes the greenland sea deep water from the canadian basin leaving the latter warm saline and rich in silica in general the entire deep water sphere of the arctic mediterranean is constrained by the greenland scotland ridges to circulate internally therefore it is certain of the intermediate waters formed in the greenland and iceland seas which ventilate the north atlantic these waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface induced signals into the deep north atlantic

forested arctic evidence from north greenland shallow water marine sediments of the kap kabenhavn formation at lat 82 30 n perry land north greenland contain an abundance of well preserved remains of terrestrial vegetation and invertebrate fauna indicative of a mosaic of forest tundra environments having similarities to present conditions in labrador the presence of foraminifera faunas marine molluscs and one mammal species supported by studies of paleomagnetism and amino acid diagenesis suggests an age of 2 ma at the pliocene pleistocene transition at this time the arctic tree line was located 2500 km to the north of its present position in the northwest atlantic region and forest tundra vegetation existed in lowland areas bordering on an arctic ocean without perennial sea ice cover

a quantitative micropaleontologic method for shallow marine peleoclimatology application to pliocene deposits of the western north atlantic ocean abstract a transfer function was developed to estimate summer and winter paleotemperatures for arctic to tropical regions of the western north atlantic ocean using fossil ostracode assemblages q mode factor analysis was run on ostracode assemblages from 100 modern bottom sediment samples from continental shelves of north america greenland and the caribbean using 59 ostracode taxa seven factors accounting for 80 of the variance define assemblages that correspond to frigid subfrigid cold temperate mild temperate warm temperate subtropical and tropical climatic zones multiple regression of the factor matrix against observed february and august bottom temperatures yielded an astracode transfer function with an accuracy of about 2 c the transfer function was used to reconstruct middle pliocene 3 5 3 0 ma shallow marine climates of the western north atlantic during the marine transgression that deposited the yorktown formation virginia and north carolina the duplin formation south and north carolina and the pinecrest beds florida middle pliocene paleowater temperatures in virginia averaged 19 c in august and 13 5 c in february about 5 c to 8 c warmer than at comparable depths off virginia today august and february water temperatures in north carolina were 23 c and 13 4 c in south carolina about 23 c and 13 5 c and in southern florida about 24 6 c and 15 4 c marine climates north of 35 n were warmer than today south of 35 n they were about the same or slightly cooler thermal gradients along the coast were generally not as steep as they are today the north atlantic transfer function can be applied to other shallow marine pliocene and pleistocene deposits of eastern north america

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

micropaleontological evidence for increased meridional heat transport in the north atlantic ocean during the pliocene the middle pliocene approximately 3 million years ago has been identified as the last time the earth was significantly warmer than it was during the last interglacial and holocene a quantitative micropaleontological paleotemperature transect from equator to high latitudes in the north atlantic indicates that middle pliocene warmth involved increased meridional oceanic heat transport

high eustatic sea level during the middle pliocene evidence from the southeastern u s atlantic coastal plain the middle pliocene approximately 3 5 2 5 ma was a period of global warmth preceding the growth of major northern hemisphere ice sheets the authors report on eustatic sea level for the middle pliocene based on microspaleontologic study of marine deposits of the duplin formation of south carolina and north carolina the duplin was deposited during a middle pliocene marine transgression that formed the orangeburg scarp a prominent wave cut geomorphic paleoshoreline of the southeastern u s atlantic coastal plain they concluded that 1 the scarp in south carolina was formed mostly during the middle pliocene 3 5 3 0 ma 2 eustatic sea level was about 35 plus minus 18 m higher than modern sea level the scarp has been uplifted about 50 65 m since the middle pliocene and 3 ocean water temperatures along eastern north america were warmer when the scarp was formed that they are at present

modeling pliocene warmth modeling studies relevant to the question of pliocene warmth are reviewed although significant regional climate variations may be due to pliocene changes in orography and ocean circulation these changes do not appear sufficient to explain inferred globally increased warmth climate modeling studies for a doubling of co2 suggest high latitude temperature increases approximately comparable to inferred warming during the pliocene i suggest that such a co2 increase may be primarily responsible for the pliocene temperature increase downdraw of co2 since the pliocene is consistent with some geochemical indications of enhanced weathering in the pleistocene however additional proxy testing of this hypothesis is required the co2 models also predict tropical sea surface warming of 2 3 c and winter temperature warming in central eurasia 50 70 n of 4 10 c predictions that distinguish co2 from some other mechanisms enhanced scrutiny of pliocene records from the above regions may prove a valuable test of the co2 hypothesis finally although a co2 increase may be responsible for pliocene warmth this time interval should not be cited as a direct analog for a future greenhouse warming as the future climate will have a significant nonequilibrium response because of the rapid rate of change of forcing despite these limitations enhanced study of pliocene climates may be very valuable as an independent source of validation of co2 doubling simulations

climatic effects of reduced arctic sea ice limits in the giss ii general circulation model in this paper we present results of an atmospheric general circulation model gcm experiment in which arctic sea ice limits were substantially reduced in all months march sea ice limits were set equivalent to modern september limits and all sea ice was removed in september sea ice coverage for other months varied between these two extremes this climate sensitivity experiment makes predictions about mean northern hemisphere atmospheric conditions including temperature pressure wind patterns and precipitation consistent with these boundary constraints the major effects of reduced sea ice limits are observed in winter they include large regional warming of the circum arctic region northward migration of the icelandic low pressure system and strengthening of the azores high changes in net heating over the north atlantic ocean suggest that increases in sea surface temperatures and salinities in this region would also accompany reductions in arctic sea ice limits in the wind field a weakening of the polar easterlies and an intensification of cyclonic circulation over the norwegian greenland sea suggest that surface water exchange between the atlantic and arctic would increase when sea ice limits are reduced however zonally averaged changes in strength of the westerlies or upper level jet stream are minimal the late pliocene cooling of the north atlantic ocean and north american arctic margin may have been linked in part to the development of perennial sea ice cover

late neogene climate evolution of the central arctic ocean abstract because no sediment of post eocene to late miocene or pliocene age has been recovered from the central arctic ocean oceanographic conditions during the middle cenozoic are unknown the oldest late cenozoic sediment is glacial marine and contains agglutinated foraminifera a few calcareous organisms are present in the oldest late cenozoic sediment with an age of 2 4 ma but at approximately the time as deposition of lithostratigraphic unit f sometime between 2 0 and 1 5 ma there was an abrupt and dramatic increase in calcareous species diversity and abundance in the central arctic ocean many of the newly introduced species are atlantic in origin preliminary evidence suggests that the introduction of a moderately large and diverse calcareous fauna at this time corresponds to the lowering of the arctic ocean ccd level and this may be explained by increased circulation with the northern greenland sea details of the change in threshold values in the fram strait required for the introduction of relatively warmer and carbonate rich water into the central arctic ocean are unknown there is evidence that spreading rates along the north atlantic nansen ridge system increased during the pleistocene and this may have permitted increased circulation between the north atlantic and the central arctic ocean this important change in arctic ocean circulation corresponds to increased pleistocene seasonality in the northern hemisphere

arctic ocean chronology confirmed by accelerator 14c dating the role of the arctic ocean in earth s climatic and oceanographic development is significant but has become controversial because of disagreements concerning a reliable arctic chronology the first arctic ocean chronology based on u th and 14c data was in agreement with magnetostratigraphy developed later but these data have been challenged by recent amino acid diagenesis dates new accelerator 14c data support the earlier u th magnetostratigraphic dates and confirm the reliability of the established arctic ocean chronology