climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

comparison of ice water classification in fram strait from c and l band sar imagery in this paper an algorithm for ice water classification of c a nd l band dual polarization synthetic aperture radar data is presented a comparison of the two different frequencies is made in order to investigate the potential to improve classification results with multi frequency data the algorithm is based on backscatter intensities in co a nd cross polarization and autocorrelation as a texture feature the mapping between image features and ice water classification is made with a neural network accurate ice water maps for both frequencies are produced by the algorithm and the results of two frequencies generally agree very well differences are found in the marginal ice zone where the time difference between acquisitions causes motion of the ice pack c band reliably reproduces the outline of the ice edge while l band has its strengths for thin ice calm water areas within the icepack the classification shows good agreement with ice water maps derived from met no ice charts and radiometer data from amsr 2 variations are found in the marginal ice zone where the generalization of the ice charts and lower accuracy of ice concentration from radiometer data introduce deviations usage of high resolution dual frequency data could be beneficial for improving ice cover information for navigation and modelling

discrimination of open water from sea ice in the labrador sea using quad polarized synthetic aperture radar abstract a method to differentiate open water from sea ice using quad polarization c band synthetic aperture radar sar imagery is presented based on the roughness properties of the sea surface scattering facets and the polarization ratio pr between vv and hh polarization backscatter from the sar images in quad polarization sar images the normalized radar cross section nrcs which is linked to sea surface roughness can be used to derive the orientation angle shift and its standard deviation as well as to compute the measured polarization ratio pr an x bragg backscatter model is explored to calculate a theoretical look up table for the polarization ratio as a function of incidence angle dielectric constant orientation angle shift and its standard deviation thus ocean surface backscatter can be identified as open water or sea ice by comparing the measured pr with a theoretical model for pr the proposed method is validated by comparison to collocated optical video images and manual visual interpretations estimates of the size shape and locations of open water from our method are shown to be in good agreement with observed data the overall accuracy of our algorithm is about 96 the classification accuracy for sea ice and open water is about 96 and 94 respectively

a middle pleistocene shallow marine interglacial sequence inner silver pit southern north sea pollen and dinoflagellate cyst stratigraphy and sea level history abstract the sand hole formation is a pleistocene seismic stratigraphic unit of restricted distribution in the inner silver pit southern north sea pollen and dinoflagellate cyst analyses of this formation penetrated by british geological survey borehole 81 52a and three juxtaposed vibrocores enables division of the formation into two sequences of contrasting palaeoclimatic affinity the lower sequence contains poorly preserved pollen assemblages of low concentration dominated by residual reworked elements and is coincident with cold shallow marine dinoflagellate cyst and foraminiferal assemblages this sequence overlies till and glacimarine sediments of the anglian elsterian swarte bank formation and is also interpreted as late anglian elsterian in age the upper sequence contains well preserved high concentration pollen spectra recording the latter half of an interglacial stage with hoxnian affinities the strong terrigenous signal preserved in this sequence suggests a subtidal depositional setting within a region of freshwater influence correlation of the vibrocores with the longer record preserved in borehole 81 52a indicates that interglacial sedimentation rates increase southwards towards a suggested terrigenous source in the wash area the first half of the interglacial cycle is missing indicating that a hiatus is present between the two sequences preserved within the sand hole formation but the termination of the interglacial is clearly preserved the spatial and temporal distribution of the sediments and bounding unconformities in the region are consistent in recording the transgressive ravinement surface highstand systems tract and subsequent regression within an interglacial eustatic cycle the character age and elevation of the preserved facies is typical of a glacio isostatically controlled emergence cycle and lends support to the notion that this temperate stage oxygen isotope stage 9 immediately followed extensive glaciation during the late anglian elsterian

microphysical characteristics of overshooting convection from polarimetric radar observations the authors present observations of the microphysical characteristics of deep convection that overshoots the altitude of the extratropical tropopause from analysis of the polarimetric radar variables of radar reflectivity factor at horizontal polarization zh differential reflectivity zdr and specific differential phase kdp identified overshooting convective storms are separated by their organization and intensity into three classifications organized convection discrete ordinary convection and discrete supercell convection composite analysisof identifiedstorms foreach classification reveals microphysical featuressimilar tothose found inpreviousstudiesofdeepconvection withdeepcolumnsofhighlypositivezdrandkdprepresentinglofting of liquid hydrometeors within the convective updraft and above the melting level in addition organized and discrete supercell classifications show distinct near zero zdr minima aligned horizontally with and at altitudes higher than the updraft column features likely indicative of the frequent presence of large hail in each case composites for organized convective systems show a similar zdr minimum throughout the portion of the convective core that is overshooting the tropopause corresponding to zh in the range of 15 30dbz and negative kdp observations in agreement with the scattering properties of small hail and or lump or conical graupel additional analyses of the evolution of overshooting storms reveals that the zdr minima indicative of hail in the middle and upper troposphere and graupel in the overshooting top are associated with the mature and decaying stages of overshooting respectively supporting their inferred contributions to the observed polarimetric fields

exploring links between arctic amplification and mid latitude weather 1 this study examines observed changes 1979 2011 in atmospheric planetary wave amplitude over northern mid latitudes which have been proposed as a possible mechanism linking arctic amplification and mid latitude weather extremes we use two distinct but equally valid definitions of planetary wave amplitude termed meridional amplitude a measure of north south meandering and zonal amplitude a measure of the intensity of atmospheric ridges and troughs at 45 n statistically significant changes in either metric are limited to few seasons wavelengths and longitudinal sectors however in summer we identify significant increases in meridional amplitude over europe but significant decreases in zonal amplitude hemispherically and also individually over europe and asia therefore we argue that possible connections between arctic amplification and planetary waves and implications of these are sensitive to how waves are conceptualized the contrasting meridional and zonal amplitude trends have different and complex possible implications for midlatitude weather and we encourage further work to better understand these

mapping of different sea ice regimes using images from sentinel 1 and alos synthetic aperture radar airborne c and l band synthetic aperture radar sar images were acquired for three test sites over different sea ice regimes around svalbard in march 2007 complemented by optical imagery environmental data and ice observations one objective was to use the high resolution low noise radar data for investigations on the technical performance of european space agency s sentinel 1 mission for sea ice mapping the other to assess the potential gain of additional use of l band sar data currently available from advanced land observing satellite alos the airborne sar images were employed to simulate data products resembling the interferometric wide swath mode iwsm of sentinel 1 and alos palsar fine resolution mode frm in order to quantify the information loss due to the higher noise level and coarser spatial resolution at the iwsm noise level zones of deformation level ice and new ice can be well separated at like polarization at cross polarization the noise level is too high for a robust automated classification including thin ice but deformed and level ice can be discriminated palsar frm is on average better suited to distinguish deformed and level ice over all ice regimes it was worse for separating new from thicker level ice at two test sites for the third test site with very few patches of new ice the palsar frm showed larger intensity contrasts between new and level ice than sentinel 1 iwsm the spatial resolution provided by the iwsm and frm is sufficient to identify most ice features and types without ambiguities typical characteristics of the imaged ice regimes are described

late quaternary marine mollusca as palaeoenvironmental proxies a compilation and assessment of basic numerical data for ne atlantic species found in shallow water abstract temperature salinity and depth limits are given for selected molluscs from boreal and arctic regions of the ne atlantic and adjacent shelf seas the significance of the data for palaeoenviromental analysis is briefly discussed

multifrequency polarimetric synthetic aperture radar observations of sea ice the first known fully polarimetric airborne synthetic aperture radar sar data set of sea ice is introduced images were acquired in the beaufort bering and chukchi seas in march 1988 during a campaign for validation of defense meteorological satellite program special sensor microwave imager radiometer ice products statistics of the magnitude phase and polarization of complex backscattered signals recorded by the jet propulsion laboratory three frequency sar are examined in detail for various scenes with different ice characteristics the full stokes matrix information generated from c l and p band data characterize the scattering behavior of different ice types polarization ratios and phase differences between linear copolarized returns are used for discrimination between particular image features and mechanisms are suggested for the observed polarimetric characteristics results indicate that combinations of frequency and polarization enhance current capability to distinguish ice of different properties using single frequency fixed polarization micro wave radar a specific example is the polarimetric identification of new ice formation which may not be easily distinguished in ers 1 5 3ghz vv polarization sar data such findings are consistent with theoretical model simulations of scattering characteristics of sea ice overall these preliminary results demonstrate that radar polarimetry will likely add a new dimension to our current capability for extracting geophysically important ice variables using radar remote sensing methods

kinematic microphysical and electrical aspects of an asymmetric bow echo mesoscale convective system observed during steps 2000 1 five hours of detailed observations of the asymmetric bow echo mesoscale convective system on 11 12 june 2000 during the steps project are presented data sources included polarimetric and doppler radars a vhf lightning mapper and the national lightning detection network nearly every 99 vhf lightning source occurred within 10 km of the convective line charge identification within the much of the convective line revealed evolution during the first 3 h from a normal polarity dipole upper positive charge near 9 km msl 30 c over mid level negative charge near 7 km 16 c to a normal polarity tripole with the addition of lower positive charge near 4 km 1 c during the final 2 h the charge structure resembled an inverted dipole with negative charge overlaying positive when the bow echo occurred during hour 2 part of the cells associated with severe winds developed an inverted tripolar charge structure and produced predominantly positive cloud to ground lightning stratiform lightning was infrequent normally initiating in the convective line and propagating rearward along two pathways a downward sloping upper pathway near 9 km and a more common constant altitude lower pathway near 6 km 10 c some flashes initiated within the stratiform region during this time but only after stratiform reflectivities increased significantly in the mixed phase region these flashes initiated near the bright band 4 km and tapped negative charge above and positive charge below possible mechanisms to explain the observations are discussed

last interglacial and early glacial circulation in the northern north atlantic ocean abstract studies of marine records from the northwestern european shelf and the northern north atlantic suggest that last interglacial environments were less stable in this area than in the mid latitude atlantic the influx of atlantic water masses to the northern north atlantic was generally higher and the meridional temperature gradient was steeper during the last interglaciation than during the holocene strong north south sea surface temperature gradients during the early weichselian indicate a generally low influx of atlantic water to the northern north atlantic even during interstades

last interglacial and holocene climatic development in the norwegian sea region ocean front movements and ice core data planktonic foraminiferal evidence suggests that the ocean front systems between polar and atlantic surface waters in the norwegian sea generally were located closer to greenland during oxygen isotope substage 5e than in the holocene during both these periods oscillations have occurred in the position of the fronts in the western norwegian sea region the substage 5e influence of warm atlantic waters was interrupted by a return to polar conditions these findings support both ice core data and evidence from europe that the last interglacial was a period of rapid climatic shifts

method for detection of leads from sentinel 1 sar images the university of bremen the german excellence initiative deutsche forschungsgemeinschaft dfg

eemian interglacial record in the northwestern european part of the soviet union abstract in the territory under discussion the eemian period correlates with stage 5e of the deep sea record continental and marine beds of the interglacial have been identified at more than a hundred sites pollen stratigraphy at the sites includes seven assemblage zones of wide geographical extent the eemian climate was milder and more humid than today during the climate optimum the mean january temperature above the baltic was 4 8 c higher the author supports the theory on the connection between the eemian and white sea basins through the system of shallow sounds and the lakes of onega and ladoga the eemian deposits serve as an excellent key horizon for the study area furnishing a good basis for palaeoclimatic conclusions and speculations for the future

determining electric fields in thunderclouds with the radiotelescope lofar an analysis is presented of electric fields in thunderclouds using a recently proposed method based on measuring radio emission from extensive air shower events during thunderstorm conditions this method can be regarded as a tomography of thunderclouds using cosmic rays as probes the data cover the period from december 2011 till august 2014 we have developed an improved fitting procedure to be able to analyze the data our measurements show evidence for the main negative charge layer near the 10 isotherm this we have seen for a winter as well as for a summer cloud where multiple events pass through the same cloud and also the vertical component of the electric field could be reconstructed on the day of measurement of some cosmic ray events showing evidence for strong fields no lightning activity was detected within 100 km distance for the winter events the top heights were between 5 and 6 km while in the summer typical top heights of 9 km were seen large horizontal components in excess of 70 kv m of the electric fields are observed in the middle and top layers

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

electrical evolution during the decay stage of new mexico thunderstorms 1 the electric field e at the ground beneath a thunderstorm often exhibits an end of storm oscillation eoso during the storm s decay phase in which e typically undergoes three polarity changes over a period of 30 75 min to determine why the surface e oscillates the timing of the eoso polarity changes of a multicellular storm in new mexico has been compared to a series of balloon radar and lightning data three in situ balloon soundings provide vertical profiles of e and inferred charge regions just before and during the eoso these data have been compared to the evolving precipitation structure determined from orthogonal range height scans of two radars and to several other parameters including lightning mapping array data before the eoso began the storm had the typical electrical structure of the late mature stage estimates of the total charge magnitudes in each of the principal regions before and during the eoso ranged from 7 to 33 c the comparisons indicate that surface e polarity changes during the eoso were 1 primarily owing to the successive fallout of three of the four principal charge regions in the storm s mature stage charge structure modified by 2 the growth or decay of the charge regions as they descended and 3 changes in the screening charges at the upper and lower cloud boundaries more limited data from two other decaying storms indicate that similar in cloud evolution was probably occurring during their eosos

the relationship between lightning type and convective state of thunderclouds thunderstorm case studies and earlier observations are described which illuminate the relationship between cloud vertical development and the prevalence of intracloud ic and cloud to ground cg lightning a consistent temporal evolution starting with peak ic activity changing to predominant cg activity and concluding with strong outflow microburst suggests that ice is responsible for both the electrical i e lightning and dynamical i e microburst phenomena the ic activity is attributed to the updraft driven accumulation of graupel particles in the central dipole region and the subsequent cg activity to the descent of ice particles beneath the height of the main negative charge the subsequent descent and melting of ice particles beneath the height of the 0 c isotherm are associated with the acceleration of the downdraft and outflow the ic lightning precursor can provide a valuable short term 5 10 min warning for microburst hazard at ground level

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

relationships between lightning location and polarimetric radar signatures in a small mesoscale convective system abstract on 19 june 2004 the thunderstorm electrification and lightning experiment observed electrical microphysical and kinematic properties of a small mesoscale convective system mcs the primary observing systems were the oklahoma lightning mapping array the koun s band polarimetric radar two mobile c band doppler radars and balloonborne electric field meters during its mature phase this mcs had a normal tripolar charge structure lightning involved a midlevel negative charge between an upper and a lower positive charge and flash rates fluctuated between 80 and 100 flashes per minute most lightning was initiated within one of two altitude ranges 3 6 or 7 10 km msl and within the 35 dbz contours of convective cells embedded within the convective line the properties of two such cells were investigated in detail with the first lasting approximately 40 min and producing only 12 flashes and the second lasting over an hour and producing 105 flashes in both lightning was initiated in or nea

the flickering switch of late pleistocene climate change polar ice contains a unique record of past climate variations previous greenland ice cores have documented relatively warm interstadial periods during the last glaciation and short centuryscale returns to colder conditions during the glacial to interglacial warming see for example ref 1 these climate features have also been observed to varying degrees in ocean sediment cores2 4 and terrestrial pollen and insect records5 7 here we report electrical conductivity measurements from a new greenland ice core which confirm these previous observations and also reveal a hitherto unrecognized mode of rapid climate variation fluctuations in ice conductivity on the scales of 5 20 years reflect rapid oscillations in the dust content of the atmosphere this flickering between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation

radar and lightning observations of normal and inverted polarity multicellular storms from steps abstract this study discusses radar and lightning observations of two multicellular storms observed during the severe thunderstorm electrification and precipitation study the lightning mapping array data indicated that the charge structure of the 19 june 2000 storm was consistent with a normal polarity tripole while the 22 june 2000 storm exhibited an overall inverted tripolar charge structure the 19 june storm consisted of weaker convection and produced little to no hail and moderate total flash rates peaking between 80 and 120 min 1 the cells in the 22 june 2000 storm were much more vigorous exhibited strong broad updrafts and produced large quantities of hail as well as extraordinary total flash rates as high as 500 min 1 the national lightning detection network nldn indicated that the 19 june storm produced mostly negative cloud to ground cg lightning while the 22 june storm produced predominantly positive cg lightning peaking at 10 min 1 just after two cells merged however the los al

climate variations in europe over the past 140 kyr deduced from rock magnetism rapid shifts in climate during the last glacial are now well documented particularly from the oxygen isotope records of the two greenland ice cores grip1 2 and gisp23 in the grip record1 2 these climate events are also seen during the preceding eemian interglacial which may be an analogue for the future climate warmed by the greenhouse effect but these shifts are not found in the eemian section of the gisp2 core3 casting doubt on whether the rapid shifts in the grip oxygen isotope record really do represent a climate signal here we present magnetic susceptibility pollen and organic carbon records from maar lake deposits in the massif central france these data provide an independent record of past climate and we find that they correlate well with the ice core records during the last glacial during the eemian two rapid cooling events seen in our record also correlate with those seen in the grip ice core supporting the idea that rapid climate change did occur in the eemian interglacial and demonstrating that it extended to continental europe

pollen stratigraphy of late pleistocene marine sediments at norre lyngby and skagen north denmark abstract two cores from north denmark norre lyngby 2 and skagen 3 have been investigated palynologically the sediment examined is correlated with the eemian interglacial stage oxygen isotope substage 5e and part of the early weichselian the skagen 3 core includes only the latter part of the interglacial the pollen assemblages in both cores significantly differ from nearby terrestrial records reflecting the nature of the depositional environment taphonomic processes and current regime during a time of higher eustatic sea level the upper part of the norre lyngby 2 core contains an assemblage which is correlated with the early weichselian brorup interstadial the norre lyngby 2 sequence also includes a characteristic sub biozone not seen in the danish terrestrial sequence which represents a climatic deterioration similar to that observed in the foraminiferal assemblages from the same samples the pollen sequence appears to have been influenced by changes in source area and surface water circulation which supports the interpretation of the cooling events given by the foraminiferal record

an analysis of eemian climate in western and central europe on the basis of 31 pollen diagrams and additional data for botanical macrofossils an analysis is made of the last interglacial eemian climatic history in western and central europe the main tool for this analysis is the climatic indicator species method only selected woody species are used for the quantification of data partial climatic range diagrams are presented for abies alba acer monspessulanum acer tataricum buxus sempervirens tilia tomentosa the problem of time correlation and pollen zonation of the eemian is discussed the climatic analysis itself is based on an improved version of the indicator species method in this version not every site is analysed for its climatic values instead maps and tables on the migrational history of hedera ilex buxus abies and species of acer tilia and abies are the basis for climatic maps showing respectively january and july isotherms for the periods of the corylus zone e4a and the carpinus zone e5 it is concluded that mean january temperatures were as much as 3 c higher at amsterdam the netherlands than at present and mean temperatures in july were 2 c higher however the thermal maximum in winter was later zone e5 than the summer thermal maximum zone e4a winter temperatures changed parallel to rise and fall of global sea level precipitation changes are more difficult to estimate in the first part of the eemian precipitation must have been relatively low but from zone e4b onward it increased to higher values reaching 800 mm and probably substantially more in zones e5 and e6 hence the eemian climate was in its beginning relatively more contintental and later from e4b onward more oceanic however as compared with the holocene the eemian climate was generally speaking more oceanic

incidence angle correction of sar sea ice data based on locally linear mapping radar backscatter variations that occur because of incidence angle effects constrain the application of scanning synthetic aperture radar scansar data for sea ice monitoring and observations in this paper a class based correction is proposed for normalizing each class in scansar data to a nominal incidence angle two tested sea ice synthetic aperture radar sar data sets were acquired a data set for the gulf of saint lawrence which was obtained by the radarsat 2 satellite and a data set for the bohai sea which was obtained by the envisat advanced synthetic aperture radar an unsupervised classification is performed on each image block prior to normalization and the incidence angle range of each image block is approximately 5 because the distribution of the backscatter coefficients in the azimuth band is discrete and nonlinear the class based locally linear mapping llm technique is implemented based on the assumption that a small quantity of sorted backscatter coefficients is locally linear this algorithm is a transplantable and easily applied method that requires limited ground data and it is also a semiautomated technique because nearly all of its parameters can be adaptively determined during the image analysis the results demonstrate that llm corrected scansar images appear to have more detailed textures and the natural signal variability in the radar data is preserved which indicates that the llm produces better results compared with the histogram based alike hist alike technique when correcting the incidence angle in the sea ice sar data the results of the data analysis in this paper show that the width of the azimuth band should be selected based on the extent of variation in the incidence angle and the reference band can be calculated based on the maximum interclass distance principle the intercomparisons also reveal that the proposed algorithm can improve the accuracy of supervised classifications

rapid interglacial climate fluctuations driven by north atlantic ocean circulation recent data from the grip ice core1 3 in greenland suggest that the climate of the last eemian interglacial period was much less stable than that of the present interglacial rapid transitions between warm and cold periods were found to occur on timescales of just a few decades the north atlantic climate during the eemian period was also shown to be characterized by three states respectively warmer than similar to and colder than today1 2 recent data from the nearby gisp2 ice core have revealed some discrepancies with these findings which remain to be resolved4 5 here we present simulations using an idealized global ocean model which suggest that the north atlantic ocean has three distinct circulation modes each of which corresponds to a distinct climate state we find that adding a simple random component to the mean freshwater flux which forces circulation can induce rapid transitions between these three modes we suggest that increased variability in the hydrological cycle associated with the warmer eemian climate could have caused transition between these distinct modes in the north atlantic circulation which may in turn account for the apparent rapid variability of the eemian climate

marine evidence for climatic instability during the last interglacial in shelf records from northwest europe data from the greenland ice sheet and continental records from europe have indicated climatic fluctuations during the last interglacial eemian oxygen isotope substage 5e similar fluctuations have not however been documented previously from marine environments here we show the existence of two cold events during substage 5e in two marine benthic foraminiferal shelf records from northwest europe and suggest that these cooling events are a result of fluctuations in the strength of the north atlantic surface water circulation

high resolution climate records from the north atlantic during the last interglacial the two deep ice cores recovered by the grip1 and gisp22 projects at summit greenland agree in detail over the past 100 000 years3 and demonstrate dramatic climate variability in the north atlantic region during the last glacial before the current period of holocene stability this glacial climate instability has subsequently been documented in the marine sedimentary record of surface ocean conditions in the north atlantic4 before 100 kyr ago the two ice core records are discrepant however casting doubt on whether the oxygen isotope fluctuations during the last interglacial eemian seen in the grip core1 5 represent a true climate signal here we present high resolution records of foraminiferal assemblages and ice rafted detritus from two north atlantic cores for the interval 65 kyr to 135 kyr ago extending the surface ocean record back to the eemian the correlation between our records and the greenland ice core records is good throughout the period in which the two ice cores agree suggesting a regionally coherent climate response during the eemian our marine records show a more stable climate than that implied by the grip ice core suggesting that localized phenomena may be responsible for the variability in the latter record during the eemian

sea ice type maps from alaska synthetic aperture radar facility imagery an assessment synthetic aperture radar sar imagery received at the alaska sar facility is routinely and automatically classified on the geophysical processor system gps to create ice type maps we evaluated the wintertime performance of the gps classification algorithm by comparing ice type percentages from supervised classification with percentages from the algorithm the rms difference for multiyear ice is about 6 while the inconsistency in supervised classification is about 3 the algorithm separates first year from multiyear ice well although it sometimes fails to correctly classify new ice and open water owing to the wide distribution of backscatter for these classes our results imply a high degree of accuracy and consistency in the growing archive of multiyear and first year ice distribution maps these results have implications for heat and mass balance studies which are furthered by the ability to accurately characterize ice type distributions over a large part of the arctic

x c and l band sar signatures of newly formed sea ice in arctic leads during winter and spring abstract we examine an extensive synthetic aperture radar sar data set from the arctic ocean spanning a time period from january to june 2015 with the aim of identifying multi polarization parameters that can be used to accurately separate newly formed sea ice from the surroundings newly formed sea ice areas both provide favourable routing for ship traffic and are key to arctic climate science because they enable heat exchange between the ocean and the atmosphere our data set encompasses three different frequencies x c and l band at a range of incidence angles and were acquired under different environmental conditions our results suggest that by combining the scattering entropy and the co polarization ratio we can successfully separate the newly formed sea ice from open water and thicker sea ice within all three frequencies throughout the winter and spring season we observe a high correlation between scattering entropy values calculated using quad polarization c and l band data and scattering entropy values calculated using the same scenes reduced to the co polarization channels hh and vv we therefore conclude that dual polarization hh and vv x band scenes can be directly used to complement quad polarimetric c and l band scenes for studies of newly formed sea ice to confine the quad polarimetric data sets to their co polarization channels one can ensure a higher signal to noise ratio incidence angles below 35 are needed to keep the signal to noise ratios sufficiently high for the scattering entropy and co polarization ratio due to its lack of incidence angle dependency the polarization difference can provide additional support in newly formed sea ice studies the regular coverage of the arctic ocean with c band sar means that such scenes should to be included in any automatic monitoring however x and l band sar can based on their difference in penetration depth provide additional information about newly formed sea ice types and surface structure

luminescence dating of archaeological materials using a new technique based on single aliquot measurements abstract a dating method based on single aliquot luminescence dose determination was applied to quartz and feldspars from heated archaeological materials the problem of changes of sensitivity to radiation resulting from signal erasure in regeneration measurements was studied in some detail and a new method based on single aliquot regeneration measurements within an added dose framework which appears to eliminate the problem of sensitivity change is proposed preliminary dating results mainly using quartz obtained with the new method are presented

an objective method for computing advective surface velocities from sequential infrared satellite images using cross correlations between sequential infrared satellite images an objective technique is developed to compute advective sea surface velocities cross correlations are computed in 32 x 32 pixel search second image and 22 x 22 template first image windows from gradients of sea surface temperature computed from the satellite images velocity vectors computed from sequential images of the british columbia coastal ocean generally appear coherent and consistent with the seasonal surface current in the region during periods of strong wind forcing as indicated by maps of sea level pressure the image advective velocities are stronger and more coherent spatially and appear to cross surface temperature gradients when winds are weaker the advective velocities correspond better with the infrared temperature patterns suggesting the increased contribution of the geostrophic current to the surface flow velocities determined from coincident near surface drogued 5 10 m buoys positioned every half hour by internal loran c units in mid june show excellent agreement with the image advective velocities in addition conductivity temperature and depth ctd measurements taken during the buoy tracking confirm the homogeneity of the upper 10 m and ctd derived geostrophic currents are consistent with

arctic sea ice circulation and drift speed decadal trends and ocean currents 1 we examine the basinwide trends in sea ice circulation and drift speed and highlight the changes between 1982 and 2009 in connection to regional winds multiyear sea ice coverage ice export and the thinning of the ice cover the polarity of the arctic oscillation ao is used as a backdrop for summarizing the variance and shifts in decadal drift patterns the 28 year circulation fields show a net strengthening of the beaufort gyre and the transpolar drift especially during the last decade the imprint of the arctic dipole anomaly on the mean summer circulation is evident 2001 2009 and enhances summer ice area export at the fram strait between 2001 and 2009 the large spatially averaged trends in drift speeds winter 23 6 decade summer 17 7 decade are not explained by the much smaller trends in wind speeds winter 1 46 decade summer 3 42 decade notably positive trends in drift speed are found in regions with reduced multiyear sea ice coverage over 90 of the arctic ocean has positive trends in drift speed and negative trends in multiyear sea ice coverage the increased responsiveness of ice drift to geostrophic wind is consistent with a thinner and weaker seasonal ice cover and suggests large scale changes in the air ice ocean momentum balance the retrieved mean ocean current field from decadal scale average ice motion captures a steady drift from siberia to the fram strait an inflow north of the bering strait and a westward drift along coastal alaska this mean current is comparable to geostrophic currents from satellite derived dynamic topography

meteorological and electrical conditions associated with positive cloud to ground lightning abstract meteorological and electrical conditions associated with the occurrence of positive cloud to ground cg lightning i e lightning that lowers positive charge to ground are examined results from case studies in winter and summer storms reveal common features and lend support to the tilted dipole hypothesis lightning bipoles whose lengths range from the convective scale to the mesoscale are aligned with the vertical wind shear with a predominance of negative locations in proximity to the deepest convection and a mixture of positive and negative locations displaced downshear from the deepest convection comparisons with radar data show that all lightning events am located within a distance of 10 20 km of precipitation extending from the surface to several kilometers above the o c isotherm electrostatic field measurements beneath precipitation removed from the deepest convection indicate a positive dipole structure and a tilting deformation by vertical wind shear these observations suggest

combined observations of arctic sea ice with near coincident colocated x band c band and l band sar satellite remote sensing and helicopter borne measurements in this study we compare colocated near coincident x c and l band fully polarimetry sar satellite images with helicopter borne ice thickness measurements acquired during the norwegian young sea ice 2015 n ice2015 expedition in the region of the arctic ocean north of svalbard in april 2015 the air borne surveys provide near coincident snow plus ice thickness surface roughness data and photographs this unique data set allows us to investigate how the different frequencies can complement one another for sea ice studies but also to raise awareness of limitations x band and l band satellite scenes were shown to be a useful complement to the standard sar frequency for sea ice monitoring c band for lead ice and newly formed sea ice identification this may be in part be due to the frequency but also the high spatial resolution of these sensors we found a relatively low correlation between snow plus ice thickness and surface roughness therefore in our dataset ice thickness cannot directly be observed by sar which has important implications for operational ice charting based on automatic segmentation

holocene paleoceanography and paleoenvironments of the skagerrak kattegat scandinavia paleoceanographic and paleoenvironmental interpretations based on foraminifera sedimentary data radiocarbon dates and stable isotope measurements were derived from two sections in the skagerrak a 115 m thick holocene marine section drilled onshore at skagen near the northernmost tip of jutland denmark and a 9 m piston core from the skagerrak north of skagen the foraminiferal data show that arctic subarctic environments in the deep skagerrak kattegat area were succeeded by boreal conditions at 9 6 ka this was a result of northward migration of the atlantic polar front and inflow of warm atlantic water into the area through the norwegian channel a gradual warming of the water masses after 9 6 ka is indicated by the data rare foraminifera and high sedimentation rates are found between approximately 8 6 ka and 7 6 ka at both core locations the modern foraminiferal assemblages of the area were fully established at 7 6 ka indicating that the modern circulation pattern in the skagerrak kattegat after the opening of the english channel and the danish straits was not established before this date at 5 5 ka a sudden change to coarser sediments higher energy environments and the appearance of the foraminifer eoeponidella laesoeensis is recorded in the skagen core this indicates a rapid change in the hydrography reflecting altered meteorological and hydrographic conditions in the skagerrak kattegat including a strengthening of the jutland current and increased inflow of north sea water into the kattegat the event is interpreted as a response to cooling at the end of the holocene climatic optimum in late atlantic time and possibly reflects a rapid cooling event of north atlantic surface water masses

polarimetric sar data compensation for terrain azimuth slope variation this paper addresses the problem of polarimetric sar polsar data correction for changes in radar cross sections which are caused by azimuth slopes most radiometric slope corrections remove slope effects to account for the effective scattering pixel area however few studies address the slope effect on the radar cross section as a function of polarization states the authors propose two approaches to compensate for this azimuth slope effect for polsar data in the first approach the digital elevation model dem obtained from interferometric sar or from other means is used to estimate orientation angles and in the second approach orientation angles are derived directly from the polsar data they have developed three new methods to implement this second approach one is based on the right right and left left circular polarizations and the other two are based on cloude s and huynelt s decompositions the results are compared with the original polarization signature method using the dem generated orientation angles as the reference polsar data is then compensated using the derived orientation angles significant changes were observed in many elements of the coherency matrix the compensated polsar data should improve the accuracy of geophysical parameter estimation techniques nasa jpl airsar data for an area in central california is used for illustration

palaeoecology and geochemistry of shallow marine ostracoda from the sand hole formation inner silver pit southern north sea abstract ostracods were obtained from the sand hole and swarte bank formations of tappin 1991 in bgs borehole 81 52a cored from the inner silver pit southern north sea the faunal assemblages were dominated by sarsicytheridea punctillata elofsonella concinna and acanthocythereis dunelmensis the assemblages recovered reflect a transition from glaciomarine conditions in the swarte bank formation up into a cold temperate marine environment in the sand hole formation with deteriorating temperatures indicated at the top of the interval studied the palaeoecology of the ostracod assemblages recovered is compared to foraminiferal data from the same section and to ostracod data from other hoxnian holsteinian sites in north western europe these data are also discussed in the light of evidence indicating that there was a barrier across the southern north sea when the sediments examined were deposited sarsicytheridea were used for trace element mg ca sr ca and stable isotope 18 o 13 c analyses a calibration equation for the calculation of temperature from mg ca ratio was successfully established from analysis of modern sarsicytheridea modern sr ca data could not be used to establish a calibration for salinity since there was too much scatter in the data ostracods were also analysed to examine the changing ratios of mg and sr as a proxy for temperature and salinity changes in the hoxnian of the southern north sea mg ca data indicated a deterioration in temperature from 36 20 m to the top of the section studied of 9 c oxygen stable isotopic analyses from the same species measured through the same core intervals did not exhibit a trend but their values were indicative of normal marine salinities carbon stable isotope analyses performed at the same time as the oxygen analyses indicate that there may have been high productivity in the region of deposition of the sand hole formation implying deposition in a region of freshwater influence

electrical and multiparameter radar observations of a severe hailstorm using data from the 11 cm csu chill multiparameter radar the simultaneous evolution of the radar inferred precipitation structure and electrical characteristics of a severe hailstorm is investigated we compare the substorm point discharge current intracloud ic lightning flash rate cloud to ground cg lightning flash rate ground strike location and flash polarity to the progression of precipitation types and amounts this study is unique in that it presents multiparameter radar observations of a thunderstorm complex which exhibited an extremely high ic to cg ratio ic cg 20 70 and predominantly positive cg lightning over 74 after it became severe producing large hail and weak tornadoes in particular we investigate the reported relationship between large hail and positive cg lightning although a direct correlation is found between a rapid increase in ic cg the first positive cg lightning flashes and the initial production of hail aloft the temporal and spatial behavior of large hail and positive cg lightning appear to be anticorrelated as broad peaks in the positive cg flash rate lag relative maxima in the fallout of large hail by up to 30 min the majority of positive ground strikes were adjacent to the main precipitation core in a region of light rain and little or no hail at the surface aloft radar data indicated that ice crystals were aligned vertically in a strong electric field corona point observations at the surface indicate that these regions adjacent to the convective core were characterized by net positive charge aloft possible mechanisms to explain these observations are discussed

automated extraction of pack ice motion from advanced very high resolution radiometer imagery multiple subarea cross correlations have been computed from visible advanced very high resolution radiometer images of the beaufort sea in an automated technique to detect pack ice motion the computational method is an application of the well known matched filter and consists of subdividing the first image into a set of subareas and correlating each reference subarea against the appropriate region of the second image the correlation functions are processed to determine a set of local maxima which define end point vectors of ice displacements from the subarea centers resulting velocities agree well with estimates of ice movement obtained by manually measuring invariant ice feature displacements the velocity fields show the spatial structures of ice motion over scales of 100 500 km with a high degree of pattern consistency and agreement with simple surface wind driving

northern north sea benthic ostracoda modern distribution and palaeoenvironmental significance the ostracod faunas of the northern north sea exhibit a depth related distribution that is controlled by substrate and hydrographic conditions four biofacies are defined on the basis of total live dead counts sandy substrates shallower than 110 m are characterized by robertsonites tuberculatus and cytheropteron latissimum these species are replaced by acanthocythereis dunelmensis and palmenella limicola on sandy muds in the fladen ground 110 150 m muellerina abyssicola dominates from 175 250 m in the norwegian channel giving way to krithe praetexta at greater depths on soft bottom substrates the results are compared with data from the skagerrak and the western european shelf area temperature ranges for the commonest taxa show that north sea faunas contain endemic western european species temperature range on average 2 20 c some southern species 5 26 c and taxa that range to high latitudes 2 to 14 c southern species are confined to the southern and western margins of the north sea

interglacial and glacial climate oscillations in a marine shelf sequence from northern denmark a multidisciplinary study abstract a 22 5 m long marine shelf sequence in northern denmark covers the climatic shifts from glacial environments through interglacial and into early glacial conditions the interglacial was interrupted by two cool intervals also the early glacial succession experienced oscillations of the climate and a period with ameliorated temperature conditions has been separated as an interstadial these results are based on a multidisciplinary high resolution study of lithology foraminifera ostracods macrofauna diatoms and stable isotopes in a silty clay sequence from a borehole at norre lyngby 70 5 48 0 m depth the lithostratigraphy and the variations in depositional environment in the area is supported by a reflection seismic profile across the core site the chronostratigraphy is discussed on the basis of biostratigraphical correlation and seismostratigraphy as well as optically stimulated luminescence osl dating and amino acid measurements the biostratigraphy and the osl dates suggest an eemian age for the interglacial while amino acid results point to an older age if the interglacial is confirmed as eemian we believe that the succeeding interstadial period is likely to be correlated with the brorup interstadial the climatic changes in this eastern part of the north sea region are closely linked with changes in the north atlantic circulation pattern and the environmental fluctuations at norre lyngby are therefore believed to reflect fluctuations in the past regional climatic and oceanic system

the relationship between precipitation and lightning in tropical island convection a c band polarimetric radar study one of the primary scientific objectives of the maritime continent thunderstorm experiment was to study cloud electrification processes in tropical island convection in particular the coupling between ice phase precipitation and lightning production to accomplish this goal a c band polarimetric radar was deployed in the tropics 11 68s 130 88e for the first time accompanied by a suite of lightning measurements using observations of the propagation corrected horizontal reflectivity and differential reflectivity along with specific differential phase rain and ice masses were estimated during the entire life cycle of an electrically active tropical convective complex known locally as hector over the tiwi islands on 28 november 1995 hector s precipitation structure as inferred from these raw and derived radar fields was then compared in time and space to the measured surface electric field cloud to ground cg and total lightning flash rates and ground strike locations during hector s developing stage precipitating convective cells along island sea breezes were dominated by warm rain processes no significant electric fields or lightning were associated with this stage of hector despite substantial rainfall rates aided by gust front forcing a cumulus merger process resulted in larger taller and more intense convective complexes that were dominated by mixed phase precipitation processes during the mature phase of hector lightning and the surface electric field were strongly correlated to the mixed phase ice mass and rainfall merged convective complexes produced 97 of the rainfall and mixed phase ice mass and 100 of the cg lightning as hector dissipated lightning activity rapidly ceased as evidenced from the multiparameter radar observations the multicell nature of hector resulted in the continuous lofting of supercooled drops to temperatures between 2108 and 2208c in discrete updraft cores during both the early and mature phases the freezing of these drops provided instantaneous precipitation sized ice particles that may have subsequently rimed and participated in thunderstorm electrification via the noninductive charging mechanism

milankovitch theory viewed from devils hole variations in the oxygen isotope content 18o of late quaternary deep sea sediments mainly reflect changes in continental ice mass1 and hence provide important information about the timing of past ice ages because these sediments cannot yet be dated directly beyond the range of radiocarbon dating 40 50 kyr ages for the 18o record have been generated2 3 by matching the phase of the changes in 18o to that of variations in the earth s precession and obliquity adopting this timescale yields a close correspondence between the time varying amplitudes of these orbital variations and those of a wide range of climate proxies4 lending support to the milankovitch theory that the earth s glacial interglacial cycles are driven by orbital variations recently winograd et al 5 reported a record of 18o variations in a fresh water carbonate sequence from devils hole nevada dated by u th disequilibrium6 they concluded that the timing of several of the features in the record which reflects changes in the temperature of precipitation over nevada as well as changes in the isotopic composition of the moisture source5 7 showed significant deviations from that predicted by milanko vitch theory here we demonstrate that applying the devils hole chronology to ocean cores requires physically implausible changes in sedimentation rate moreover spectral analysis of the devils hole record shows clear evidence of orbital influence we therefore conclude that transfer of the devils hole chronology to the marine record is inappropriate and that the evidence in favour of milankovitch theory remains strong

doppler radar signatures of developing thunderstorms and their potential to indicate the onset of cloud to ground lightning abstract the capability of doppler weather radars to short term forecast the initiation of thunderstorms and the onset of cloud to ground cg lightning is examined doppler weather radar data from 28 thunderstorms were analyzed from august 1990 in the central florida environment these radar echoes were associated with cg lightning strike locations from the national lightning detection network and two lightning detection systems operated by the u s air force in the vicinity of kennedy space center from a time history of these radar echoes it was found that a 10 dbz echo first detected near the freezing level may be the first definitive echo of a future thunderstorm this thunderstorm initiation signature is often accompanied by low altitude convergence and divergence at the top of the radar echo the observed lead times between this thunderstorm initiation signature and the first detected cg lightning strike ranged from 5 to 45 min with a median lead time of 15 min all lightning producing radar echo

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

thunderstorm electrification a case study the paper presents interpretation of triple doppler radar observations of a thunderstorm that occurred at the kennedy space center florida precipitation particle motions inside the storm as evaluated from the three radial velocity radar data sets are presented in a selected vertical plane throughout the storm development these data are interpreted and compared with observations of vhf radio emission sources and lightning charge centers derived from an earlier analysis krehbiel 1981 the main feature of the particle motion field is the persistence at nearly the same altitude throughout the entire period of analysis of a balance level characterized by a zero value of the precipitation particle mean vertical velocity further analysis based on considerations of radar reflectivity and air velocity suggests the presence at this altitude of relatively large precipitation particles suspended in an updraft the lightning negative charge centers appear to be less than 1 km above the particle balance level

electrical and polarimetric radar observations of a multicell storm in telex abstract on 28 29 june 2004 a multicellular thunderstorm west of oklahoma city oklahoma was probed as part of the thunderstorm electrification and lightning experiment field program this study makes use of radar observations from the norman oklahoma polarimetric weather surveillance radar 1988 doppler three dimensional lightning mapping data from the oklahoma lightning mapping array lma and balloon borne vector electric field meter efm measurements the storm had a low flash rate 30 flashes in 40 min four charge regions were inferred from a combination of lma and efm data lower positive charge near 4 km and midlevel negative charge from 4 5 to 6 km msl from 0 to 6 5 c were generated in and adjacent to a vigorous updraft pulse further midlevel negative charge from 4 5 to 6 km msl and upper positive charge from 6 to 8 km from 6 5 to 19 c were generated later in quantity sufficient to initiate lightning as the updraft decayed a negative screening layer was present near the storm top

hydrography and mollusc faunas of the baltic and the white sea north sea seaway in the eemian abstract palynologically dated mollusc and cirriped faunas from a region extending from the north sea through the baltic and karelia to the arkhangelsk region show that the hydrography of the baltic was very different from the holocene for 2 2 5 ka in the early eemian a seaway existed from the barents to the north sea through karelia until it was severed at the present continental watershed to the north of lake onega after this the ladoga onega trough remained an arm of the baltic for several millennia the benthic faunas are comparable to the holocene but their boundaries were displaced much further into the baltic notable differences from the holocene are the absence or rarity of the macoma balthica biocoenosis and the presence of cold portlandia dominated biocoenoses in karelia in the belt sea and western baltic winter sea surface temperatures and salinity were higher than now by ca 6 c and 15 and the distinctly brackish top layer was missing at the same time cold bottom water 2 5 c with a tendency to anoxia characterised the karelian arm of the baltic water exchange through this area was inhibited by the constriction to the north of lake onega and the basin and threshold bathymetry water transport through the white sea baltic seaway was too sparse to play an active role in the north atlantic surface circulation or climatic change in the region the high salinity and temperature in the belt sea and western baltic persisted throughout the eemian and are explained by wider and deeper passage from the north sea to kattegat wider straits through denmark higher salinity in the north sea higher evaporation as well as more dispersed fresh water supply the advection of oceanic water into the baltic culminated in the early eemian before the carpinus zone and probably resulted in an oceanic climate in the baltic region while at the same time cold winters produced cold bottom water in the karelian arm

polarimetric characteristics of sea ice in the sea of okhotsk observed by airborne l band sar the phased array l band sar palsar aboard the advanced land observing satellite alos is capable of globally acquiring fully polarimetric data in order to confirm the ability of l band polarimetric synthetic aperture radar sar to investigate sea ice before the alos launch we conducted a field experiment using an airborne polarimetric and interferometric sar pi sar in the sea of okhotsk in 1999 this paper presents the analyzed results of data acquired in that experiment the extracted polarimetric parameters of several ice types suggested that polarimetric coherences and phase differences between right right rr and left left ll are good candidates for discriminating ice types the polarimetric anisotropy as well as the beta angle of the first eigenvector calculated in the polarimetric decomposition procedure are alternative parameters that are sensitive to ice type differences due to the low depolarization characteristics of open water it could be discriminated from sea ice by scattering entropy in all incidence angle ranges from the relation between ice thickness and the polarimetric parameters we found that backscattering coefficients and vertical vv to horizontal hh backscattering ratio are highly correlated with ice thickness since the ratio is sensitive to ice surface dielectric constants a simple simulation using the integral equation method surface model was conducted by using the physical parameters of typical sea ice a two dimensional ice thickness map was derived from an empirical relation between the vv to hh backscattering ratio and ice thickness

microfossils foraminifera ostracoda from an eemian last interglacial tidal flat sequence in south west denmark abstract the north west european coastal plain was indented by several shallow bays and expanses of tidal flat sedimentation during the eemian interglacial one of these bays at hojer south west denmark has been the subject of intensive research and several lines of evidence indicate an eemian age this paper discusses the foraminifera and ostracoda present in these deposits three phases of accumulation are recognized an initial brackish tidal flat grading into a more open tidal flat environment a phase of shallow subtidal deposition turritella ton when water depths may have attained 15 20 m and a final phase of shallowing conditions reflecting a fall in sea level the warm climate which prevailed during the eemian enabled the migration of certain species of more southerly affinity into the north sea these include the foraminifera elphidium lidoense elphidium translucens quinqueloculina aspera and quinqueloculina seminulum var jugosa and the ostracoda callistocythere cf praecincta carinocythereis whitei semicytherura arcachonensis and aurila aff a prasini none of these taxa are present in the holocene faunas of the north sea and only two are known from holsteinian interglacial deposits these taxa are therefore considered as index fossils for the eemian in this region

molecular record of secular sea surface temperature changes on 100 year timescales for glacial terminations i ii and iv high resolution palaeoclimate records based on oxygen isotope data have provided important insights into climate variability and rates of natural climate change on about a thousand year timescale1 3 little is known4 however about the variation of climate and of palaeoceanographic conditions throughout the quaternary on timescales of less than 1 000 years at frequencies far greater than those of the milankovitch orbital cycles here we show that such high time resolution is possible from molecular stratigraphic studies based on biomarker organic molecules alkenones we have sampled alkenone stratigraphic records at 70 to 200 yr intervals across glacial terminations i ii and iv in sediment cores from oop site 658 off northwest africa5 sea surface temperatures ssts derived from the alkenone uk37 index6 8vary rapidly beyond the range of analytical noise by up to 2 5 c in 300 yr showing hitherto unknown cycles with about 600 yr periodicities some of the changes parallel similar events in the oxygen isotope stratigraphy sst oscillations may be linked in part to abrupt breakdowns in atlantic deep water ventilation resulting from meltwater events of quaternary glacial terminations3 9 10

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

vostok ice core a continuous isotope temperature record over the last climatic cycle 160 000 years a continuous deuterium profile along the 160 000 year vostok ice core antarctica is interpreted in terms of atmospheric temperature changes this climatic record is the awaited terrestrial complement of the deep sea records supporting the existence of a relation between the pleistocene climate and orbital forcing

palynology aminostratigraphy and u series dating of marine gortian interglacial sediments in cork harbour southern ireland abstract palynological analysis amino acid epimerization analysis and uranium thorium disequilibrium age determination of three irish interglacial cores support the suggestion that there may have been more than one holsteinian style temperate interval in europe the cores were taken from estuarine deposits beneath glacial diamicton in cork harbour southwest ireland the pollen records an incomplete temperate stage the biotic signature is similar to those from several interglacial sites in ireland and is considered part of the gortian group the pollen signature is holsteinian hoxnian in character amino acid epimerization analysis suggests the deposits to be oxygen isotope stage 7 in age whereas uranium thorium disequilibrium suggests a minimum stage 5 age possible correlatives of the gortian group in europe are suggested

eemian and early weichselian 140 60 ka paleoceanography and paleoclimate in the nordic seas with comparisons to holocene conditions paleoceanographic and paleoclimatic time series were extracted from norwegian iceland and greenland sea the nordic seas sediment sequences covering the time intervals 60 140 ka and 0 15 ka on the basis of stable isotope stratigraphy planktonic foraminiferal faunas and sedimentological methods the proxy temperature records from the norwegian iceland sea display a number of high frequency and high amplitude variations within the last interglacial the eemian indicating marked changes in heat flux at high northern latitudes eemian holocene comparisons document that the climate of the norwegian iceland sea in the last interglacial was less stable than that of the present interglacial and that the distribution of surface water masses in the eemian differed from that of the holocene within the greenland sea uniform cold conditions prevailed throughout both interglacials cooling of the nordic seas as well as the initial growth of the surrounding ice sheets began within the eemian interval before the main increase in global ice volume heat flux to the nordic seas was significantly higher during the interglacials than at any time during the early weichselian 60 113 ka and no marked stadial interstadial changes in sea surface temperature and deep water ventilation are documented in the early weichselian records contrary to the pattern found in north atlantic sediment records however fluctuations in planktonic foraminiferal content planktonic 13c and ice rafting on suborbital timescales mostly comparable in number and age to the stadial interstadial fluctuations in the greenland ice cores are demonstrated in our records the ice rafted detritus records provide a more detailed account of ice sheet variability than previously known for the early weichselian period and demonstrate that glaciers advanced to sea level somewhere around the nordic seas several times during this interval

a stochastic dynamical model of arctic sea ice abstractthe noise forcing underlying the variability in the arctic ice cover has a wide range of principally unknown origins for this reason the analytical and numerical solutions of a stochastic arctic sea ice model are analyzed with both additive and multiplicative noise over a wide range of external heat fluxes f0 corresponding to greenhouse gas forcing the stochastic variability fundamentally influences the nature of the deterministic steady state solutions corresponding to perennial and seasonal ice and ice free states thus the results are particularly relevant for the interpretation of the state of the system as the ice cover thins with f0 allowing a thorough examination of the differing effects of additive versus multiplicative noise in the perennial ice regime the principal stochastic moments are calculated and compared to those determined from a stochastic perturbation theory described previously as f0 increases the competing contributions to the variability of the destabilizing sea

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

eemian climate fluctuations observed in a european pollen record recent ice core data from greenland1 2 suggest that the climate during the last interglacial period the eemian was more unstable than that of the holocene about 10 000 years ago to the present being characterized in particular by a series of cold episodes each lasting about 70 to 750 years subsequent analysis of a second greenland ice core3 4 however failed to corroborate the details of these eemian climate fluctuations a result that may be attributable to the effects of ice flow4 to resolve this discrepancy it is imperative to seek alternative sources of information about the eemian climate here we present climate reconstructions from pollen data from the annually laminated eemian lake sediment record at bispingen5 and from the eemian and holocene peat records at la grande pile6 the former record indicates that an initially warm period of 2 900 yr was followed by cooling and a series of colder episodes one of which had winter temperatures comparable to those at the end of the preceding cold stage the latter records show greater climate instability during the eemian than the holocene these results are in broad agreement with those from the grip ice core but contrast both with the gisp2 core3 4 and with recent high resolution marine records from the north atlantic7 8

a middle pleistocene glacial interglacial succession in the inner silver pit southern north sea abstract benthic foraminiferal data from the depth interval between 42 0 and 30 5 m in the inner silver pit core 81 52a in the southern north sea has revealed a glacial interglacial succession comprising a 5 m thick interglacial deposit the foraminiferal assemblages initially indicate ice proximal conditions zone 52 1 from a deglaciation period a transitional zone zone 52 2 with faunal indication of relatively deeper water and slightly higher but still subarctic temperature conditions is followed by a true interglacial succession called the inner silver pit interglacial with increased faunal diversity and with a high content of warm water species zone 52 3 a decrease in water depth is registered towards the top of the interglacial succession the assemblage in the topmost sample zone 52 4 indicates a return to high arctic glacial marine conditions foraminiferal faunas in three vibrocores obtained from the slopes of the neighbouring inner silver pit valley are correlated with the interglacial assemblages in zone 52 3 and with the succeeding glacial marine zone 52 4 of the inner silver pit core 81 52a based on the degree of isoleucine epimerisation in benthic foraminifera the interglacial deposit is referred to the middle pleistocene and a correlation with oxygen isotope stage 9 is suggested

a comprehensive habit diagram for atmospheric ice crystals confirmation from the laboratory airs ii and other field studies abstract recent laboratory experiments and in situ observations have produced results in broad agreement with respect to ice crystal habits in the atmosphere these studies reveal that the ice crystal habit at 20 c is platelike extending to 40 c and not columnar as indicated in many habit diagrams found in atmospheric science journals and texts these diagrams were typically derived decades ago from laboratory studies some with inherent habit bias or from combinations of laboratory and in situ observations at the ground observations that often did not account for habit modification by precipitation from overlying clouds of varying temperatures habit predictions from these diagrams often disagreed with in situ observations at temperatures below 20 c more recent laboratory and in situ studies have achieved a consensus on atmospheric ice crystal habits that differs from the traditional habit diagrams these newer results can now be combined to give a comprehensive description of ice crystal habits

eemian climatic and hydrographical instability on a marine shelf in northern denmark abstract benthic foraminifera and stable isotope data from the last interglaciation eemian substage 5e from a borehole at skagen denmark provide evidence for major environmental and hydrographic changes during this period during the first millennium of the eemian water masses covering northern denmark became gradually warmer temperate conditions prevailed during most of the interglaciation but these were interrupted by two periods with decreased water temperatures the first cooling event s 1 was not very distinct at skagen but the second event s 2 seen in both the foraminiferal and oxygen isotope record represents a large shift to subarctic conditions carbon isotopes indicate a change in ocean circulation during both events no comparable climate variations are seen within the holocene record at the site the final cooling of the water masses associated with the substage 5e 5d boundary occurred within a few hundred years these last interglacial climatic changes were probably caused by variations in strength and or position of the north atlantic drift possibly as a result of varying vigor of the atlantic conveyor in addition minor variations in the fossil assemblages also indicate fluctuations in the inflow of atlantic water to the skagerrak kattegat area during the warm intervals of substage 5e

benthic foraminiferal and stable isotope evidence for a younger dryas style cold spell at the saalian eemian transition denmark abstract benthic foraminiferal and stable isotope studies of two borings from the island of anholt denmark reveal a continuous late saalian eemian sequence with an overall gradual warming interrupted by a short term temperature deterioration comparable with the younger dryas cold spell the sequence is correlated to the global deep sea stable isotope record based on environmental evidence given by foraminiferal faunas and stable isotopes the following environmental changes in the anholt cores can be attributed to the global variations 1 1 an interstadial phase the flakket interstadial which had a duration of about 1000 years is correlated to stable isotope event 6 01 2 2 the following cold spell the kattegat stadial spanning about 1000 years represents most of the interval between isotope events 6 01 and 6 0 3 3 a phase of rapid warming within about 1000 years bsotope events 6 0 and 5 53 4 4 a sea level change within the eemian between isotope events 5 53 and 5 51

paleoenvironmental changes in the norwegian sea and the northeast atlantic during the last 2 8 m y deep sea drilling project ocean drilling program sites 610 642 643 and 644 sedimentological isotopic and magnetostratigraphic investigations of ocean drilling program and deep sea drilling project sites 642 643 644 and 610 document the oceanographic and climatic evolution of the norwegian sea and the northeastern atlantic over the last 2 8 m y the results show that a major expansion of the scandinavian ice sheet to the coastal areas took place at about 2 56 ma relatively severe glacials appeared until about 2 ma the period 2 6 1 2 ma experienced in general cold surface water conditions with only a weak influx of temperate atlantic water as compared with late quaternary interglacials the norwegian sea was a sink of deep water through this period but deepwater ventilation was reduced and calcite dissolution was high compared with the holocene deep water formed by other mechanisms than it does today between 2 and 1 2 ma the glaciations in scandinavia were small a transition toward larger glacials took place during the period 1 2 to 0 6 ma corresponding to warmer interglacials and reduced calcite dissolution only during the last 0 6 m y has the oceanographic and climatic system of the norwegian sea varied in the manner described in previous studies of the late quaternary a strong thermal gradient was present between the norwegian sea and the northeastern atlantic during the matuyama 2 5 0 7 ma this is interpreted as a sign of a more zonal and less meridional climatic system over the region compared with the present situation

electrification life cycle of incipient thunderstorms this work evaluates how clouds evolve to thunderstorms in terms of microphysical characteristics and produces the first intracloud ic and cloud to ground cg lightning flashes observations of 46 compact isolated thunderstorms during the 2011 2012 spring summer in southeast brazil with the x band polarimetric radar and two and three dimensional lightning location systems demonstrated key parameters in a cloud s vertical structure that produce the initial electrification and lightning activity the majority 98 of the first cg flashes were preceded by approximately 6 min by intracloud ic lightning the most important aspect of the observations going into this paper which came originally from the visual examination of a large number of thunderstorms is that an initial positive differential reflectivity zdr associated with supercooled raindrops evolved to reduced zdr and even negative values in the cloud layer between 0 and to 15 c before and during the time of the initial lightning suggesting evolution from supercooled raindrops to frozen particles promoting the formation of the conical graupel an enhanced negative specific differential phase kdp down to 0 5 km 1 in the glaciated layer above 40 c was predominantly observed at the time of the first cg flash indicating that ice crystals such as plates and columns were being vertically aligned by a strong electric field these results demonstrate that the observations of zdr evolution in the mixed layer and negative kdp in the upper levels of convective cores may provide useful information on thunderstorm vigor and lightning nowcasting

rapid changes in ocean circulation and heat flux in the nordic seas during the last interglacial period the apparent similarity of climate variability in the north atlantic region in the last interglacial period1 5 and the present interglacial holocene has recently been challenged by the rapid oscillations in climate conditions indicated by some marine6 7 and terrestrial climate records8 10 for the last interglacial ocean circulation in the northern north atlantic seems to be intimately coupled to the processes of climate change on various time scales11 12 so that climate variability and the associated mechanisms of change should be well recorded by sediments from these high latitudes previous studies in this region5 13 have indeed indicated an apparently less stable last interglacial climate than at middle latitudes of the north atlantic ocean4 here we present detailed records from marine sediments in the nordic seas of oceanographic conditions during the last interglacial the records show three large sea surface temperature fluctuations a weakening of the east west sea surface temperature gradient with time and changes in deep water properties in contrast similar analyses of a core from the same region indicate that sea surface temperature during the holocene has been relatively stable our data along with those from the labrador sea7 indicate rapid changes in ocean circulation and oceanic heat fluxes at high northern latitudes during the last interglacial which may have been associated with marked temperature changes on adjacent continents

iceberg detection in open and ice infested waters using c band polarimetric synthetic aperture radar icebergs can cause a significant threat to shipping offshore oil and gas production facilities and subsea pipelines synthetic aperture radar sar is a well established tool for detecting and monitoring sea ice objects in the often dark and cloud covered polar regions however detection of small icebergs floating in nonhomegeous sea clutter environments is still a challenging task we propose a new methodology for automatic identification of potential icebergs in high resolution polarimetric sar images the algorithm adopts to various sea ice conditions and it tackles high iceberg density situations and heterogeneous background conditions in the marginal ice zone results from a time series of radarsat 2 data containing numerous icebergs broken off from glaciers in kongsfjorden on svalbard demonstrate that the approach is viable

topography of the top chalk surface on and offshore denmark abstract a time structure map of the top of the upper cretaceous danian chalk group the top chalk surface in the entire danish sector is presented the present topography of the top chalk surface is a result of various erosional and tectonic events taking place during the cenozoic the analysis shows that the cenozoic is characterised by significant reactivation of the mesozoic structural elements of which the central graben the ringkobing fyn high and the sorgenfrei tornquist zone are the most important a tectonically controlled relief caused the generation of widespread sheet like erosion on the ringkobing fyn high and incisions along the margins of ringkobing fyn high during the mid paleocene incisions in the northern part of the danish sector formed valleys which probably transported sediment towards the west the present topography of top chalk in the eastern part of the danish sector is highly influenced by the late cenozoic erosion of the uplifted eastern margin of the north sea basin the topography of top chalk also reflects the distribution of mobile zechstein salt as collapse structures follow the pitch out line of mobile salt onto the ringkobing fyn high and numerous salt structures deformed the top chalk surface

sea ice concentration estimation during melt from dual pol sar scenes using deep convolutional neural networks a case study high resolution ice concentration maps are of great interest for ship navigation and ice hazard forecasting in this case study a convolutional neural network cnn has been used to estimate ice concentration using synthetic aperture radar sar scenes captured during the melt season these dual pol radarsat 2 satellite images are used as input and the ice concentration is the direct output from the cnn with no feature extraction or segmentation postprocessing the absolute mean errors of the generated ice concentration maps are less than 10 on average when compared with manual interpretation of the ice state by ice experts the cnn is demonstrated to produce ice concentration maps with more detail than produced operationally reasonable ice concentration estimations are made in melt regions and in regions of low ice concentration