surface water temperature salinity and density changes in the northeast atlantic during the last 45 000 years heinrich events deep water formation and climatic rebounds we developed a new method to calculate sea surface salinities sss and densities ssd from planktonic foraminiferal 18o and sea surface temperatures sst as determined from planktonic foraminiferal species abundances sst sss and ssd records were calculated for the last 45 000 years for biogeochemical oceanic flux study bofs cores 5k and 8k recovered from the northeast atlantic the strongest feature is the dramatic drop in all three parameters during the heinrich ice rafting events we modelled the possibility of deepwater formation in die northeast atlantic from the ssd records by assuming that the surface waters at our sites cooled as they flowed further north comparison with modelled north atlantic deepwater densities indicates that there could have been periods of deepwater formation between 45 000 and 30 000 14c years b p interrupted by iceberg meltwater input of heinrich event 3 and 4 at 27 000 and 38 000 14c years b p and during the holocene no amount of cooling in the northeast atlantic between 30 000 and 13 000 years could cause deep water to form because of the low salinities resulting from the high meltwater inputs from icebergs our records indicate that after each heinrich event there were periods of climatic rebound with milder conditions persisting for up to 2000 years as indicated by the presence of warmer and more saline water masses after these warm periods conditions returned to average glacial levels these short term cold and warm episodes in the northeast atlantic are superimposed on the general trend towards colder conditions of the last glacial maximum lgm heinrich event 1 appears to be unique as it occurs as insolation rose and was coeval with the initial melting of the fennoscandian ice sheet we propose that meltwater input of heinrich event 1 significantly reduced north atlantic deep water formation reducing the heat exchange between the low and high latitudes thus delaying deglaciation by about 1500 radiocarbon years 2000 calendar years

acceleration of near surface strong winds in a dry idealised extratropical cyclone to understand near surface strong winds in extratropical cyclones a simulation of a dry idealised baroclinic wave is presented the forces that accelerate the winds are analysed using the terms in the horizontal momentum equation two regions of strong near surface winds developed within the simulation one to the east of the low centre and the other to the southwest the flow to the east resembling the cold conveyor belt accelerated as it passed through the strong pressure gradient associated with the warm frontal zone this acceleration was reduced by friction near the surface the winds to the southwest were characterised by three airstreams one airstream consisted of air parcels that started north of the warm front near the surface accelerated north of the warm front encircled the low and continued to accelerate to the southwest of the low the increases in wind speed in this airstream also part of the cold conveyor belt resulted from the along flow pressure gradient force being greater than friction the second airstream consisted of air parcels that descended west of the cold front and maintained their speed during descent until they were slowed either by friction in the boundary layer or as they moved southward against the local pressure gradient between these two airstreams a third airstream was characterised by air parcels that accelerated during descent from the mid to lower troposphere whilst moving around the bent back front this airstream bears some resemblance to the sting jet and was accelerated by the pressure gradient force on descent until it encountered increased friction or moved against the local pressure gradient

a composite study of comma clouds and their association with severe weather over the great plains abstract sixty eight comma cloud systems over the great plains during two spring seasons were examined using satellite imagery and rawinsonde data composite soundings were produced for each of ten distinct parts of the comma cloud in order to describe quantitatively the atmospheric structure associated with wave cyclones that produced 585 severe weather events composite sectionals and soundings document the different kinematic and thermodynamic environment of each part of the comma cloud system relative wind isentropic analyses show air flow relative to the storm and provide additional evidence that the clear region intruding northward east of the cyclone center is an area of strong ascent of dry air with a previous history of subsidence stability computations from the mean soundings suggest that the most likely location for severe weather is near the central part of the comma tail in agreement with the tabulated severe weather reports a case study from 21 22 march 1981 is conducted to investigate

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

the relationship between water masses and benthic ostracod assemblages in the western coral sea southwest pacific abstract the bathymetric distribution of 67 ostracod genera identified in 42 sediment samples water depth range 370 3776 m from the western coral sea is documented statistical analyses of this dataset support preliminary observations that the vertical distribution of the ostracod fauna is largely controlled by the three water masses present in the studied area four ostracod assemblages are recognised assemblage i consisting mainly of ostracods present in the deep water assemblage ii consisting of ubiquitous ostracods and ostracods mostly confined to the antarctic intermediate water and assemblages iii and iv with ostracods characteristic of the western south pacific central water temperature food supply and dissolved oxygen level are believed to be the most important factors influencing the ostracods bathymetric zonation the present work establishes the potential of ostracods for use in palaeoceanographic reconstruction in the western pacific ocean

the sting at the end of the tail damaging winds associated with extratropical cyclones strong surface winds often accompany the low level jets that occur along the cold fronts of extratropical cyclones but there is evidence that the strongest surface winds occur in a distinctly different part of a certain class of cyclone the most damaging extratropical cyclones go through an evolution that involves the formation of a bent back front and cloud head separated from the main polar front cloud band by a dry slot when the cyclone attains its minimum central pressure the trailing tip of the cloud head bounding the bent back front forms a hook which goes on to encircle a seclusion of warm air the most damaging winds occur near the tip of this hook the sting at the end of the tail observations of the great storm of october 1987 in south east england are re examined in some detail to study this phenomenon the cloud head is shown to have a banded structure consistent with the existence of multiple mesoscale slantwise circulations air within these circulations leaves the hooked tip of the cloud head and enters the dry slot much faster than the rate of travel of the cloud head tip implying rapid evaporation and diabatic cooling immediately upwind of the area of damaging surface winds the circumstantial evidence from the observational study leads one to hypothesize that the mesoscale circulations and the associated evaporative heat sinks may play an active role in strengthening the damaging winds regardless of how important this role may be the evolution of the cloud pattern seen in satellite imagery is a useful tool for nowcasting the occurrence and location of the worst winds copyright 2004 royal meteorological society

near surface strong winds in a marine extratropical cyclone acceleration of the winds and the importance of surface fluxes a rapidly developing extratropical cyclone named tini brought strong winds to ireland and the united kingdom on 12 february 2014 a mesoscale model simulation is used to analyze the development of the strong winds through the terms in the horizontal momentum equation the maximum of near surface wind speed equatorward of the cyclone was composed of two different airstreams that underwent different paths to acceleration first horizontally moving air in the cold conveyor belt was accelerated by the along flow pressure gradient force but was decelerated by friction second descending air accelerated into the eastern end of the maximum of near surface wind speed and was associated in part with a sting jet caused by the increasing along flow horizontal pressure gradient force at lower levels when this descending air entered the boundary layer it too was decelerated by surface friction surface fluxes of heat and moisture were necessary to destabilize and deepen the boundary layer allowing mixing of the strongest winds from the free troposphere down to the surface a simulation with the surface fluxes turned off during cyclogenesis showed a more stable boundary layer around the bent back front which inhibited the strongest winds from reaching the surface the descent of the sting jet air was associated with a maximum in quasigeostrophic omega which consisted of both synoptic scale and mesoscale descent the latter associated with frontolysis occurring at the end of the bent back front thus the near surface wind maximum was created by the synoptic scale and mesoscale dynamics whereas localized moist processes were negligible

the role of moist processes in the formation and evolution of mesoscale snowbands within the comma head of northeast u s cyclones abstract the role of moist processes in regulating mesoscale snowband life cycle within the comma head portion of three northeast u s cyclones is investigated using piecewise potential vorticity pv inversion modeling experiments and potential temperature tendency budgets snowband formation in each case occurred along a mesoscale trough that extended poleward of a 700 hpa low this 700 hpa trough was associated with intense frontogenetical forcing for ascent a variety of pv evolutions among the cases contributed to midlevel trough formation and associated frontogenesis however in each case the induced flow from diabatic pv anomalies accounted for a majority of the midlevel frontogenesis during the band s life cycle highlighting the important role that latent heat release plays in band evolution simulations with varying degrees of latent heating show that diabatic processes associated with the band itself were critical to the development and maintenance of the band however changes in the meso

interpretation of satellite imagery of a rapidly deepening cyclone model output and observational data are used to interpret in detail satellite images of a distinctive cloud system several hundred kilometres long which was observed before and during rapid cyclonic development that occurred over england conceptual models are forwarded which account for the structure of the major cloud areas and upper level moisture fields as observed by water vapour imagery immediately prior to and following the onset of vigorous cyclogenesis the cloud system corresponded to what r b weldon refers to as a baroclinic leaf cloud and was characterized by ana cold frontal ascent the baroclinic leaf lay within an area of enhanced ascent ahead of a major upper level trough a jet streak which originated upstream propagated rapidly around the base of the upper trough a tongue of dry air centred on the left flank of this jet streak lay immediately upstream of the leaf cloud and had a major influence on its subsequent development this intrusion of dry air was well represented by the meteorological office fine mesh model which showed it as a pronounced tongue of recently descended air with high potential vorticity which originated in the upper troposphere and lower stratosphere rapid cyclogenesis occurred as the dry intrusion overran low level air of high w within a warm conveyor belt at the southern tip of the leaf cloud interaction of the dry intrusion and baroclinic leaf cloud is shown to be particularly important in accounting for the detailed distribution of weather it also suggests a way of pinpointing the location and timing of vigorous cyclogenesis

the sting at the end of the tail model diagnostics of fine scale three dimensional structure of the cloud head this is the second in a series of papers on the sting at the end of the tail a mesoscale region of potentially damaging surface winds that can occur close to the evaporating tip of a cloud head wrapped around the bent back front of an extratropical cyclone in the first paper the sting phenomenon was identified from a purely observational study of the great storm of october 1987 in the present paper an observationally validated forecast run from a high resolution numerical weather prediction model is used to examine the evolving three dimensional structure of the sting phenomenon it is shown that the damaging surface winds in the october 1987 storm were due to a well defined mesoscale sting jet sj identifiable as a coherent ensemble of trajectories originating in cloudy air at about 650 hpa there is evidence of multiple mesoscale slantwise circulations and the sj appears to form within the descending part of these circulations air within the sj descends to the 900 hpa level over a period of about 4 h during which time it accelerates from less than 20 to above 45 m s 1 with extremes greater than 50 m s 1 although the wet bulb potential temperature of air in the sj remains constant during its descent to 900 hpa evaporation leads to a reduction of up to 5 k or more in dry bulb potential temperature in some parts of the jet the sj is situated behind the primary cold front and is distinct from the associated warm conveyor belt low level jet it is also distinct from the cold conveyor belt low level jet which remains below and behind it as the sj skirts the bent back front crown copyright 2005

a simple model for the synoptic analysis of cold fronts a split cold front model with an over running upper front or humidity front ahead of a surface front or humidity front is shown to provide a useful representation of the principal characteristics of many katafronts the use of such a model leads to more consistent analyses especially of cloud and rain than are achieved using unmodified classical concepts

patterns of ice rafted detritus in the glacial north atlantic 40 55 n the observation by heinrich 1988 that during the last glacial period much of the input of ice rafted detritus to the north atlantic sediments may have occurred as a succession of catastrophic events rekindled interest on the history of the northern ice sheets over the last glacial period in this paper we present a rapid method to study the distribution of these events both in space and time using whole core low field magnetic susceptibility we report on approximately 20 cores covering the last 150 to 250 kyr well defined patterns of ice rafted detritus appear during periods of large continental ice sheet extent although these are not always associated within their maxima most of the events may be traced across the north atlantic ocean for the six most recent heinrich layers hl two distinct patterns exist hl1 hl2 hl4 hl5 are distributed along the northern boundary of the glacial polar front over most of the north atlantic between 40 and 50 n hl3 is more restricted to the central and eastern part of the northern atlantic the nd sr isotopic composition of the material constituting different heinrich events indicates the different provenance of the two patterns hl3 has a typical scandinavia arctic icelandic young crust signature and the others have a large component of northern quebec and northern west greenland old crust material these isotopic results obtained on core su 9008 from the north american basin are in agreement with the study by jantschik and huon 1992 who used k ar dating of silt and clay size fractions of an eastern basin core me 68 89 these data confirm the large spatial scale of these events and the enormous amount of ice rafted detritus they represent

mesoscale analysis of arc rainbands in a dry slot a series of almost concentric are shaped narrow rainbands was observed travelling at 140 km h 1 and producing severe wind gusts over parts of england their structure and environment have been analysed using radar and satellite imagery mesoscale model diagnostics surface observations and additional rawinsonde ascents obtained during the fronts and atlantic storm track experiment fastex the multiple rainband event is shown to have been associated with part of a dry intrusion characterized by a mesoscale vortex cold pool the event occurred within the dry slot region of a small frontal cyclone where the mesoscale pool of cold dry air was overrunning warm sector air continuous wind profiles from a uhf radar together with a well located rawinsonde at the epicentre of the arc rainbands showed that the major anomaly in the cold pool was an area of locally stronger winds 40 m s 1 at 800 hpa colocated with the temperature minimum at that level the observed orientation of the rainbands is explained in terms of the cold frontal structure at this level triggering ascent of the underlying warm moist air the multiple nature of the arc rainbands remains unexplained the possibilities of mesoscale gravity waves and conditional symmetric instability are both considered

ostracod faunas and water masses across the continental margin off southwestern africa changes in composition of modern benthic ostracod faunas across the continental margin of southwestern africa occur at boundaries between and within major water masses a mixed layer antarctic intermediate water aaiw boundary at 200 m an aaiw salinity minimum zone at 650 m an aaiw bathyal thermocline at 1000 m and the aaiw north atlantic deep water nadw boundary at 1500 m in addition two population changes occur within the nadw at 1 8 2 0 km and 2 0 3 0 km the antarctic bottom water assemblage is sparse and poorly preserved

reconstructing late quaternary deep water masses in the eastern arctic ocean using benthonic ostracoda abstract the distribution of ostracoda in three long cores from the deep eastern arctic ocean was studied to determine the palaeoceanographical history of the eurasian basin during the late quaternary the samples for this study were obtained from the lomonosov ridge morris jesup rise and yermak plateau during the arctic 91 expedition ostracoda previously studied in coretops at the same sites as the present study have shown that individual species have a strong association with different water masses and bathymetry throughout the late quaternary cores exhibit ostracod rich layers separated by barren intervals on the basis of biostratigraphical isotopic and palaeomagnetic data the fossiliferous levels are interpreted as representing interglacial stages the twenty most significant species were selected for subsequent quantitative investigation using cluster and factor analyses in order to determine similarity and variance between the assemblages an additional statistical method employing modern analogues and the squared chord distance dissimilarity coefficient was utilised to compare the present late quaternary fossil samples with a modern arctic database the results reveal a major faunal division within the arctic ocean deep water aodw highly abundant and diverse assemblages within the cores were found to group and have good analogues with the recent bathyal depth 1000 2500 m upper aodw assemblages conversely assemblages with low abundance and diversity correlate well with abyssal depth 3000 m lower aodw assemblages the palaeoceanographical history is complicated by the influence of adjacent water masses such as canada basin deep water cbdw greenland sea deep water gsdw and most importantly arctic intermediate water aiw which all had an influence on the ostracod assemblages during the late quaternary an enhanced flow of warm saline aiw into the eurasian basin results in species rich upper aodw assemblages having good analogues down to 2750 m in the water column in contrast lower aodw assemblages influenced by cold well oxygenated gsdw give analogues at depths as shallow as 1000 m the faunal changes are the consequence of rapid climatic fluctuations in the eastern arctic ocean during the late quaternary that are intrinsically linked to palaeoceanographical alternations in warm and cold current inflow from adjacent basins

convective destabilization by a tropopause fold diagnosed using potential vorticity inversion there is observational evidence to suggest that at the time tropopause folds in extra tropical cyclones are descending into the mid troposphere there is frequently a destablization of the lower troposphere to moist convection here we consider the dynamical reasons for such a linkage using so called potential vorticity pv attribution concepts in particular pv inversion is used to find the wind shear attributable to the tropopause fold itself then this shear is used to quantify the tendency to generate regions of potential instability for an observed case of a modest tropopause fold it is found that the pv anomaly contained in the tropopause fold contributed substantially to the instantaneous convective destabilization in the sense of increasing the potential instability indeed at some locations it overcame a tendency to stabilize by the atmosphere without the fold on the other hand only a fraction of the region with increased potential instability experienced sufficient large scale ascent to lead to convection and it remains to be seen whether folds in general make a significant contribution to the generation of potential instability that can actually be realized the importance of tropopause folds or indeed of tropopause depressions in general in the context of convection is that their small horizontal scale has the potential to focus and amplify any convective destabilization locally this may account for the localization of outbreaks of severe convective weather which it is important to forecast accurately currently numerical weather prediction models often do not handle these small scales very accurately

origin of strong winds in an explosive mediterranean extratropical cyclone abstractduring 2 3 december 2012 the black sea and east coast of romania were affected by a rapidly deepening mediterranean cyclone the cyclone developed a bent back front along which short lived

high resolution analysis of frontal fracture abstract a mesoscale array of dropwindsondes released in a small rapidly deepening frontal wave cyclone in the eastern north atlantic during the fronts 92 experiment has been assimilated into a 17 km grid mesoscale model nested within the meteorological office s operational limited area model the mesoscale model reproduced the evolving cloud pattern with cloud head and dry slot seen in satellite imagery it also revealed a well defined evolution in the three dimensional thermodynamic structure associated with the process known as frontal fracture the frontal fracture was revealed most clearly in the pattern of wet bulb potential temperature w which was distorted by an effective differential rotation the rotation increasing with height this led to backward tilted w surfaces and ana cold frontal characteristics in the cloud head to the north of the center of rotation and to forward tilted w surfaces and kata cold frontal characteristics in the dry slot to the south of the center of rota

conditional symmetric instability in sting jet storms sting jets are transient mesoscale jets of air that descend from the tip of the cloud head towards the top of the boundary layer in severe extratropical cyclones and can lead to damaging surface wind gusts this recently identified jet is distinct from the well documented jets associated with the cold and warm conveyor belts one mechanism proposed for their development is the release of conditional symmetric instability csi here the spatial distribution and temporal evolution of several csi diagnostics in four severe storms are analysed a sting jet has been identified in three of these storms for comparison we also analysed one storm that did not have a sting jet even though it had many of the apparent features of sting jet storms the sting jet storms are distinct from the non sting jet storms by having much greater and more extensive conditional instability ci and csi csi is released by ascending air parcels in the cloud head in two of the sting jet storms and by descending air parcels in the other sting jet storm by contrast only weak ci to ascending air parcels is present at the cloud head tip in the non sting jet storm csi released by descending air parcels as diagnosed by decaying downdraught slantwise convective available potential energy dscape is collocated with the sting jets in all three sting jet storms and has a localised maximum in two of them consistent evolutions of saturated moist potential vorticity are found we conclude that csi release has a role in the generation of the sting jet that the sting jet may be driven by the release of instability to both ascending and descending parcels and that dscape could be used as a discriminating diagnostic for the sting jet based on these four case studies copyright 2011 royal meteorological society and british crown copyright the met office

late quaternary paleoceanography of the eurasian basin arctic ocean we reconstructed late quaternary deep 3000 4100 m and intermediate depth 1000 2500 m paleoceanographic history of the eurasian basin arctic ocean from ostracode assemblages in cores from the lomonosov ridge gakkel ridge yermak plateau morris jesup rise and amundsen and makarov basins obtained during the 1991 polarstern cruise modern assemblages on ridges and plateaus between 1000 and 1500 m are characterized by abundant relatively species rich benthic ostracode assemblages in part reflecting the influence of high organic productivity and inflowing atlantic water in contrast deep arctic eurasian basin assemblages have low abundance and low diversity and are dominated by krithe and cytheropteron reflecting faunal exchange with the greenland sea via the fram strait major faunal changes occurred in the arctic during the last glacial interglacial transition and the holocene low abundance low diversity assemblages from the lomonosov and gakkel ridges in the eurasian basin from the last glacial period have modern analogs in cold low salinity low nutrient greenland sea deep water glacial assemblages from the deep nansen and amundsen basins have modern analogs in the deep canada basin during termination 1 at intermediate depths diversity and abundance increased coincident with increased biogenic sediment reflecting increased organic productivity reduced sea ice and enhanced inflowing north atlantic water during deglaciation deep nansen basin assemblages were similar to those living today in the deep greenland sea perhaps reflecting deepwater exchange via the fram strait in the central arctic early holocene faunas indicate weaker north atlantic water inflow at middepths immediately following termination 1 about 8500 7000 year b p followed by a period of strong canada basin water overflow across the lomonosov ridge into the morris jesup rise area and central arctic ocean modern perennial sea ice cover evolved over the last 4000 5000 years late quaternary faunal changes reflect benthic habitat changes most likely caused by changes in the import of cold deepwater of greenland sea origin and warmer and middepth atlantic water to the eurasian basin through the fram strait and export of arctic ocean deepwater

the role of evaporating showers in the transfer of sting jet momentum to the surface the most damaging winds in a severe extratropical cyclone often occur just ahead of the evaporating ends of cloud filaments emanating from the so called cloud head these winds are associated with low level jets lljs sometimes occurring just above the boundary layer the question then arises as to how the high momentum is transferred to the surface an opportunity to address this question arose when the severe st jude s day windstorm travelled across southern england on 28 october 2013 we have carried out a mesoanalysis of a network of 1 min resolution automatic weather stations and high resolution doppler radar scans from the sensitive s band chilbolton advanced meteorological radar camra along with satellite and radar network imagery and numerical weather prediction products we show that although the damaging winds occurred in a relatively dry region of the cyclone there was evidence within the llj of abundant precipitation residues from shallow convective clouds that were evaporating in a localized region of descent we find that pockets of high momentum were transported towards the surface by the few remaining actively precipitating convective clouds within the llj and also by precipitation free convection in the boundary layer that was able to entrain evaporatively cooled air from the llj the boundary layer convection was organized in along wind rolls separated by 500 to about 3000 m the spacing varying according to the vertical extent of the convection the spacing was greatest where the strongest winds penetrated to the surface a run with a medium resolution version of the weather research and forecasting wrf model was able to reproduce the properties of the observed llj it confirmed the llj to be a sting jet which descended over the leading edge of a weaker cold conveyor belt jet

attribution of strong winds to a cold conveyor belt and sting jet a high resolution version of the wrf weather research and forecasting model has been used to study the fine structure of a cloud head and its associated cold conveyor belt jet cj and sting jet sj in an intense extratropical cyclone that produced damaging surface winds in northern ireland and central scotland on 3 january 2012 the model was run with many different initialisation times and physical parametrisations and a run was selected that verified well against a variety of observations new methods have been devised to visualise the 3d structure of the cj and sj and to attribute strong surface winds to one or other of them and the validity of regarding the sj as a semi lagrangian feature has been assessed the model suggests that whereas the cj remained mainly below the 850hpa level as it circulated around the bent back front the sj consisted of a stream or streams of air within the bent back frontal zone that first ascended from close to the surface into the middle and upper level parts of the cloud head before descending from evaporating cloud filaments at the tip of the cloud head and reaching the top of the boundary layer slightly ahead of the cj the simulations did not support the idea that either the evaporation or conditional symmetric instability csi played a major role in the development of these jets the strong gusts up to 47ms 1 w hich were recorded on the north coast of ireland appear to have been due mainly to the cj which by then was undercutting the sj the sj was responsible for stronger surface winds than the cj several hours earlier during the initial stage of frontal fracture but only for a limited period

species composition and glacial interglacial variations in the ostracode fauna of the northeast atlantic during the past 200 000 years sediment core m23414 from the rockall plateau north atlantic covering the last two climatic cycles marine isotope stages mis 7 to 1 was investigated for glacial interglacial variations in the deep sea benthic ostracode fauna a highly diversified ostracode fauna including 98 species was found two climate related assemblages were identified associated with interglacial and peak glacial periods respectively the interglacial group occurs during the end of mis 7 5 and 1 and is composed of the genera henryhowella pelecocythere echinocythereis cytherella bradleya aversovalva and eucytherura the glacial group consists of the genera acetabulastoma which is known as sea ice indicator in the modern arctic ocean polycope bythoceratina rhombobythere and some species possibly belonging to the genus pseudocythere and is found during mis 6 4 and 2 these longer term variations within the ostracode fauna seem related to the particular glacial and interglacial climate conditions that affected both deep water production as well as primary production in the surface waters however a detailed comparison of ostracode abundances with the occurrence of events marked by increased ice rafted debris reveals also much shorter term climate related changes in the ostracode fauna thus the temporal fluctuations within ostracode assemblages reflect long and short term alterations of the deep sea environment that are clearly linked to climate changes

benthonic ostracods and deep watermasses a qualitative comparison of southwest pacific southern and atlantic oceans abstract the upper depth limits of the dominant cosmopolitan deep water benthonic ostracod taxa present in five localities in the southern ocean kerguelen plateau southeast australian continental slope and southwest pacific chatham rise tasman sea coral sea are compared to investigate the degree to which the position of intermediate and deep watermasses antarctic intermediate water aaiw deep water dw and antarctic bottom water aabw control the vertical faunal succession although none of the taxa studied is restricted to one watermass their upper depth limits appear to be closely related to the position of antarctic intermediate water aaiw taxa showing the most consistent pattern include krithe upper depth limit above aaiw poseidonamicus upper depth limit in lower aaiw but in underlying deep water on the kerguelen plateau and pterygocythere mucronalatum dw but in aabw on the kerguelen plateau bathyal above approximately 1000 m upper depth levels of taxa species diversity species turnover and changes in the proportion of the dominant deep sea taxa krithe and poseidonamicus match closely that of the atlantic ocean dingle and lord 1990 however the upper depth limits of the abyssal taxa poseidonamicus and dutoitella appear to be very different in the cape basin se atlantic and the sw pacific with respect to watermass characteristics for example in the atlantic poseidonamicus has its upper limit within lower north atlantic deep water nadw whereas in the sw pacific it occurs consistently within the aaiw these discrepancies in the upper depth level of abyssal taxa between the pacific and atlantic oceans suggest that different watermasses or other environmental variables control their upper range in different oceanic basins it follows that these differences must be taken into account if deep sea ostracods are to be used as a reliable means to trace modern or reconstruct ancient watermass pathways between ocean basins

surface and deep water changes in the subpolar north atlantic during termination ii and the last interglaciation to reconstruct the history of water mass exchange between the ne atlantic and the nordic seas sediment cores from 2 km water depth were studied across termination ii tii and through the last interglaciation mis5e during early tii the sudden appearance of the low latitude planktonic foraminifera beella megastoma is noted in both regions along with a steep decrease in benthic foraminiferal 18o since other proxies indicate that surface waters were cold and stratified because of meltwater conditions which prevented near surface thermohaline circulation and vertical convection in the nordic seas water mass exchange between the two areas occurred at the subsurface during later tii surface conditions changed and this subsurface circulation style was eventually replaced by vertical convection in the nordic seas b megastoma vanished from the record together with ice rafted debris ird at the end of tii while subpolar foraminiferal abundance rose peak interglacial conditions with intensive vertical convection now fully developed generating a bottom water temperature gradient of 4 c between the two areas however surface water temperatures deteriorated in the nordic seas already notably before ird recurred and 18o increased at the end of mis5e

mesoscale dynamics of cold fronts structures described by dropsoundings in fronts 87 the fronts 87 project was a european experiment to make mesoscale observations to deduce the dynamics of active cold fronts approaching north west europe with a minimum of orographic influences in this paper data from dropsoundings made by the meteorological office s c 130 research aircraft are analysed the aircraft flew a pattern with 4 or 5 runs oriented approximately at right angles to the front but with each run displaced in the along front direction by about 100 km the dropsondes gave soundings to a height of approximately 7 km with a cross frontal spacing of 20 km at best and 60 km on average between 30 and 50 soundings were made in each event over an area of 500 500 km2 these data are unique in their mesoscale resolution over a synoptic scale region this was made possible by the ability to track up to 5 sondes in the air at any time several new aspects of cold front dynamics have been identified from these data the approach here is to treat each run as an instantaneous cross frontal section the discussion is centred on the hypotheses postulated before the experiment these were intended to allow verification or refutation of aspects of models of frontal dynamics such as those embodied in semi geostrophic theory a minimal and purely objective analysis has been performed on the data presented here but the high resolution of the dropsonde observations permits evaluation of differentiated quantities such as potential vorticity pv with some confidence issues raised here include the degree of thermal wind balance the structure of conserved variables such as equivalent potential temperature and absolute momentum the cross frontal circulation and the role of diabatic processes such as the evaporation of snow and the potential vorticity structure on the mesoscale and its interpretation the intention is to present an integrated view of the dynamical structure of fronts in the light of theoretical rather than conceptual or airflow models

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

deep sea benthic foraminiferal assemblage response to a surface ocean productivity gradient a test a transect of samples from the eastern equatorial pacific where surface ocean productivity is the only changing environmental variable was used to test the response of benthic foraminiferal assemblages to an open ocean productivity gradient the transect runs along the east pacific rise from the highly productive waters near the equator to the oligotrophic south pacific subtropical gyre surface sediment benthic assemblages show progressive change along the transect with strong compositional shifts corresponding to the rapid productivity gradient near the equator and to the position of the southern convergence near 18 19 s the relationship of the assemblages to surface ocean productivity was tested by statistical regression of quantitative estimates of productivity on the assemblage principal component scores calculated for each sampling location the regression yielded an r squared of 0 87 demonstrating a clear relationship between surface ocean productivity and deep sea benthic foraminiferal assemblage composition the species most important to this relationship display a consistent response to oceanic productivity for long stretches of geologic time this conservative behavior and the results of the regression analysis indicate that benthic foraminiferal assemblages can be used to estimate surface ocean productivity for the geologic past

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

late quaternary deep ocean circulation a review of paleoceanographic studies dealing with late quaternary deep water circulation in the oceans is presented these studies which are based on the analysis of deep sea benthic foraminiferal faunal and geochemical data and sedimentological data are discussed in light of physical oceanographic conditions in the modern ocean we include in this review a re evaluation of benthic foraminiferal data from north atlantic and southern ocean piston cores and suggest that the dominance of uvigerina during glacial intervals reflects increased amounts of organic carbon at the sea floor compared to modern values a number of geochemical studies have suggested that the production or characteristics of north atlantic deep water nadw changed during glacial times although these changes have been thought to result from a cessation of overflow water from the norwegian greenland seas it is suggested here that seasonal sea ice cover was possible over southern portions of the norwegian sea during glacial intervals the presence of seasonally open water would have allowed norwegian sea overflow water to have been produced although perhaps at lower volumes and with different hydrographic properties than at present the record of antarctic bottom water aabw circulation does not show a simple relationship with paleoclimatic oscillations indicating that changes in oceanographic conditions in the southern ocean had little effect on aabw formation the aabw record contrasts with the glacial interglacial cycles of nadw suggesting no direct link between aabw and nadw circulation a variety of data suggests that changes in pacific deep water circulation occurred as a result of glacial production of north pacific deep water or from an increased flux of southern ocean water

benthic ostracods and deep water masses in the atlantic ocean ostracod faunas at six locations are compared and related to distributions in an atlantic ocean wide data base five widely developed vertical faunal sequences are recognised at particular levels within deep water masses henryhowella fauna lower part of antarctic intermediate water krithe fauna upper north atlantic deep water poseidonamicus bosquetina fauna upper part of lower nadw dutoitella fauna lower part of lower nadw legitimocythere fauna antarctic bottom water these faunas are correlated with previously established deep water benthic foraminiferal assemblages and their possible palaeo oceanographic use is discussed

distribution of coccoliths in surface sediments in the norwegian greenland sea abstract the distribution of coccoliths has been examined in 20 surface sediment samples along an east west transect in the norwegian sea based on the abundance and species richness of coccoliths three biogeographic zones have been established along this transect the distribution of coccolith assemblages in the surface sediments appears to match closely with the locations of the different surface water masses in the norwegian greenland sea