diatom response to the holocene climatic optimum on the north icelandic shelf abstract a diatom record from core md992275 on the north icelandic shelf reveals palaeoclimatic and palaeoceanographic changes during the time interval 9000 to 5600 cal year bp the study period includes the holocene climate optimum hco as widely known in the north atlantic region a comparison with data for the last 2000 years and with the present day surface sediment diatom assemblages shows that there was considerably stronger influence of atlantic water masses in the area during the hco than in the late holocene and today the results of cluster analysis and principal component analysis divide the studied period into three intervals each characterised by a specific diatom assemblage the assemblages indicate changes in the interaction of the relatively warm irminger current ic and the cold east greenland current egc and east icelandic current eic the north icelandic shelf was strongly affected by the ic during the interval 8000 6800 cal year bp which may be the warmest period of the holocene during the intervals 9000 8000 and 6800 5600 cal year bp the influence of the ic was relatively weak and that of the egc and eic increased correspondingly the well known 8200 cal year bp cooling event shown in many records from the north atlantic is reflected by a relatively strong influence of the egc and eic between about 8300 and 8100 cal year bp in our record however the diatom assemblages show that the inferred circulation change did not bring the strength of the ic down to the levels seen at present and during the last two millennia

reinterpretation of two diatom species from the west greenland margin thalassiosira kushirensis and thalassiosira antarctica var borealis hydrological consequences abstract two representatives of the planktonic diatom genus thalassiosira commonly associated together in the moderate to high latitude north atlantic ocean are demonstrated to be significantly different in both morphology and autecology thalassiosira antarctica comber var borealis fryxell doucette et hubbard mostly resting spores is a dominant species of the early spring phytoplankton bloom around greenland and in the arctic in most paleoclimatic paleoenvironmental studies of the last decades thalassiosira kushirensis takano resting spores r s have probably been included in t antarctica var borealis the present study of phytoplankton from ctd probes and a single surface sediment sample from a multi core and comparative analyses of piston cores from the west greenland margin show these taxa to be good indicators of environmental and hydrological changes related to the distribution of water masses in the studied area t antarctica var borealis is interpreted as an indicator of northern cold water influx especially increased meltwater input during spring bloom whereas t kushirensis r s appears to be related to temperate waters of atlantic origin and probably reflects reduced meltwater influx and increased ocean forcing an abundance of t kushirensis r s during the little ice age lia is interpreted to reflect an enhanced influence of the west greenland current wgc in this region

application of rock mass classification techniques to weak rock masses a case study from the ruahine range north island new zealand rock mass classification systems were first generated for use in engineering applications but their potential for utilization in geomorphic studies has since been recognized these techniques were mostly developed for hard rock environments and questions remain about their applicability to weak rocks here the applicability of three rock mass classification techniques rock mass strength rms rock mass rating rmr and slope mass rating smr to weak rock masses was analyzed techniques incorporated parameters such as uniaxial compressive rock strength discontinuity condition and orientation and groundwater ratings rock mass classification values were determined from 14 profiles sited on recently excavated road cuttings on the saddle road in the ruahine range north island new zealand this is an important transport route across the north island s axial ranges with the road excavated into weak late pliocene early pleistocene mudstone mean slope and minimum slope angle were measured at each

diatoms from the surface sediments of the south china sea and their relationships to modern hydrography abstract a principal components analysis of diatoms in surface sediment samples from the south china sea scs shows a clear relationship between the spatial distributions of diatoms and the current pattern of the region six diatom assemblages are distinguished representing environments with different hydrological characteristics the neritic planktonic species thalassionema nitzschioides is the dominant component in the surface sediment diatoms with relatively small changes throughout the scs suggesting that the water mass exchanges between the scs and the pacific and indian oceans are relatively small the strongest impact of the warm oceanic water occurs in the northeasternmost part of the scs where assemblage v is located with nitzschia marina azpeitia nodulifera azpeitia neocrenulata rhizosolenia bergonii and thalassionema frauenfeldii as main taxa warm oceanic planktonic species n marina r bergonii and a neocrenulata can be used as indicators of warm oceanic waters flowing into the scs in paleoceanographic reconstructions of the area in particular in tracking the water from the western pacific including the kuroshio current it may however be problematic to use another tropical oceanic planktonic species a nodulifera as an environmental indicator because of its strong resistance to dissolution thus possibly further transport

long term rates of denudation in t he dry valleys transantarctic mountains southern victoria land antarctica bases on in situ produced cosmogenic 21ne abstract concentrations of cosmogenic 21 ne 21 ne c measured in quartz have been used to estimate long term rates of denudation for contrasting landscape components in the dry valleys area of the transantarctic mountains southern victoria land antarctica samples of beacon supergroup sandstones and granitic basement were collected from two contrasting landscape elements low relief high elevation surfaces and rectilinear slopes to assess variations in rates of denudation with topographic position the sample sites for rectilinear slopes were selected because of proximity to 40 ar 39 ar dated lavas and ash avalanche deposits all 21 ne 20 ne ratios are significantly greater than the atmospheric value and concentrations of 21 ne c were calculated from the measured 21 ne values assuming an atmospheric composition for the trapped component apparent exposure ages calculated from the concentrations of 21 ne c assuming no denudation since exposure range from 3 78 4 66 ma for samples from the high elevation plateau surface and 0 61 2 48 ma for samples from the rectilinear slopes exposure ages for 3 he c were 2 to 42 times lower than those derived from the abundances of 21 ne c because of preferential diffusive loss of 3 he c from the quartz lattice concentrations of 3 he c were therefore not used in the calculation of rates of denudation we interpret the abundances of 21 ne c as reflecting variations in the rates of denudation rather than exposure age in view of independent evidence for prolonged exposure 15 ma of bedrock surfaces at the sample sites calculated maximum rates of denudation range from 0 26 1 02 m ma 1 for the rectilinear slopes down to only 0 133 0 164 m ma 1 for the high elevation surface sites these rates are comparable to other estimates of denudation rates for the dry valleys derived from analyses of cosmogenic isotopes but are around two orders of magnitude lower than the long term mean rate over the past 50 ma estimated from fission track thermochronology combined with the preservation of volcanic deposits dating back to the mid miocene these 21 ne c data demonstrate that only minimal modification of the landscape has occurred in the dry valleys over at least the past 15 ma this significant conclusion supports the view that the east antarctic ice sheet has been essentially stable over this period rather than experiencing major fluctuations as late as the pliocene as has previously been suggested

biogeographical patterns and environmental controls of phytoplankton communities from contrasting hydrographical zones of the labrador sea the labrador sea is an important oceanic sink for atmospheric co2 because of intensive convective mixing during winter and extensive phytoplankton blooms that occur during spring and summer therefore a broad scale investigation of the responses of phytoplankton community composition to environmental forcing is essential for understanding planktonic food web organisation and biogeochemical functioning in the labrador sea here we investigated the phytoplankton community structure 4 m from near surface blooms 1 2 mg chla m 3 occurred on and near the shelves in may and in offshore waters of the central labrador sea in june due to haline and thermal stratification respectively sea ice related fragilariopsis cylindrus and f oceanica and arctic diatoms fossula arctica bacterosira bathyomphala and thalassiosira hyalina dominated the relatively cold 0 c and fresh salinity 33 waters over the labrador shelf e g on the southwestern side of the labrador sea where sea ice melt and arctic outflow predominates on the northeastern side of the labrador sea intense blooms of the colonial prymnesiophyte phaeocystis pouchetii and diatoms such as thalassiosira nordenskioeldii pseudo nitzschia granii and chaetoceros socialis occurred in the lower nutrient waters nitrate 3 6 m of the west greenland current the central labrador sea bloom occurred later in the season june and was dominated by atlantic diatoms such as ephemera planamembranacea and fragilariopsis atlantica the data presented here demonstrate that the labrador sea spring and early summer blooms are composed of contrasting phytoplankton communities for which taxonomic segregation appears to be controlled by the physical and biogeochemical characteristics of the dominant water masses

the deglaciation over laurentian fan history of diatoms ird ice and fresh water abstract a high resolution diatom census coupled with other proxy data from laurentian fan lf provides a detailed description of the last deglaciation bringing new insight to that period by revealing directly the timing of sea ice formation and melting cold events heinrich event 1 h1 and the younger dryas yd were multiphase events h1 16 8 15 7 cal kyr bp was defined by a two pulse release of icebergs promoting sea ice formation melting of sea ice after h1 corresponds to a cold and fresh anomaly that may have kept the bolling colder than the allerod at 13 6 cal kyr bp a cooling trend culminated with sea ice formation marking the yd onset 12 8 cal kyr bp the decrease in sea ice 12 2 cal kyr bp led to a yd second phase characterized by very cold winters however the contribution of warm water diatoms tends to increase at the same time and the yd gradual end 11 6 cal kyr bp contrasts with its abrupt end in greenland ice cores the yd cannot be regarded as an event triggered by a fresh water input through the laurentian channel since only one weak brief input nearly 1000 yrs after its onset is recorded very cold and cool conditions without ice mark the following preboreal a northward heat flux between 10 8 and 10 2 cal kyr bp was interrupted by the increased influence of coastal waters likely fed by inland melting there was no further development of sea ice or ice drift then

diatom surface sediment assemblages around iceland and their relationships to oceanic environmental variables canonical correspondence analysis of diatoms from surface sediment samples and oceanographic environmental variables shows that summer and winter sea surface temperatures water depth and winter sea surface salinity are the main environmental factors affecting diatom distribution around iceland of these summer sea surface temperature is the most important five diatom assemblages are distinguished and the distribution of these assemblages is clearly correlated with oceanic current patterns in the region the sea ice diatom assemblage is limited to the area where the east greenland current polar water has its strongest influence and the cold diatom assemblage is basically controlled by the less cold east icelandic current modified polar water the mixing diatom assemblage results from the interaction between the cold east greenland and east icelandic currents and the warm irminger current the warm diatom assemblage is located in the area dominated by the irminger current and may be used as an indicator of warm water masses atlantic water the coastal diatom assemblage is the only one strongly influenced by both water depth and summer water temperatures

late holocene summer sea surface temperatures based on a diatom record from the north icelandic shelf diatom assemblages from a high resolution core on the north icelandic shelf reveal a general late holocene cooling trend which is interrupted by three relatively warm periods diatom data from sur

surface water temperature changes in the high latitudes of the southern hemisphere over the last glacial interglacial cycle a set of numerical equations is developed to estimate past sea surface temperatures sst from fossil antarctic diatoms these equations take into account both the biogeographic distribution and experimentally derived silica dissolution the data represent a revision and expansion of a floral data base used previously and includes samples resulting from progressive opal dissolution experiments factor analysis of 166 samples 124 holocene core top and 42 artificial samples resolved four factors three of these factors depend on the water mass distribution one subantarctic and two antarctic assemblages factor 4 corresponds to a dissolution assemblage inclusion of this factor in the data analysis minimizes the effect of opal dissolution on the assemblages and gives accurate estimates of sst over a wide range of biosiliceous dissolution a transfer function dtf 166 34 4 is derived from the distribution of these factors versus summer sst its standard error is 1 c in the 1 to 10 c summer temperature range this transfer function is used to estimate sst changes in two southern ocean cores 43 s and 55 s which cover the last climatic cycle the time scale is derived from the changes in foraminiferal oxygen and carbon isotopic ratios the reconstructed sst records present strong analogies with the air temperature record over antarctica at the vostok site derived from changes in the isotopic ratio of the ice this similarity may be used to compare the oceanic isotope stratigraphy and the vostok time scale derived from ice flow model the oceanic time scale if taken at face value would indicate that large changes in ice accumulation rates occurred between warm and cold periods

late quaternary paleoceanography of the western baffin bay region evidence from fossil diatoms seven marine cores from the east coast of baffin island were examined for variations in diatom content the cores have good age control and were used for holocene paleoceanographic reconstruction

the value of rock mass classification systems for weak rock masses a case example from huntly new zealand three published rock mass classification systems rmr smr rms were applied to weak waikato coal measure mudrocks in order to assess their value as indicators of rock mass conditions and stable slope angles the smr classification gives the most sensitive measure of rock mass conditions for the slopes studied but none of the systems adequately predicts observed slope angles regression analysis indicates that where conditions for failure by sliding along discontinuities exist the slopes are most sensitive to the discontinuity parameters of parallelism dip angle and spacing further when the discontinuities are oriented favourably with respect to the slope slope angles are most sensitive to intact rock strength and groundwater this is supported by geomorphic evidence low angle natural slopes developed on unfavourable discontinuity sets are well predicted by published equations associated with both the rmr and rms classification systems steeper slopes developed on favourable discontinuities are at a much lower angle than the equations predict and show evidence of extensive creep application of the present rock mass classification systems to these weak rocks is thus only appropriate when conditions exist under which the rocks fail by sliding on unfavourably oriented discontinuities where this does not occur the contribution of intact strength to the rock mass strength is greatly overestimated by all of the rock mass classification systems studied development of a separate rock mass classification for these conditions is not seen as appropriate hence recognition of the favourability or otherwise of the discontinuity sets is crucial to dealing with these rocks a stereonet overlay that facilitates this division is presented

surface sediment diatom distribution and holocene paleotemperature variations in the greenland iceland and norwegian sea one hundred and four surface sediment samples and two piston cores from the greenland iceland and the norwegian gin sea hopkins 1988 were analyzed diatoms were common to abundant in most surface sediment samples and throughout the holocene q mode factor analysis allowed the definition of six significantly different floral assemblages which explained 91 7 of the total variance mapping of the six factors showed their close affinity to hydrographic regimes these are the norwegian atlantic current assemblage thalassionema nitzschioides paralia sulcata proboscia alata arctic water assemblage thalassiosira gravidaspores sea ice assemblage nitzschia grunowii nitzschia cylindra thalassiosira hyalina arctic norwegian waters mixing assemblage rhizosolenia hebetata f semispina rhizosolenia borealis atlantic assemblage thalassiosira oestrupii and norwegian arctic waters mixing assemblage thalassiosira gravida vegetative cells transfer functions gint2 relating factor distributions to winter february and summer august surface water temperatures were generated the transfer functions have a standard error of estimate of 1 5 c august and 1 0 c february downcore studies of core 52 43 from the norwegian basin and core 57 5 from the iceland plateau revealed diatom abundance and sea surface paleotemperature trends in the area during the holocene the first appearance of diatoms in cores 52 43 and 57 5 occurs within the vedde ash layer 10 600 years b p and the saksunarvatn ash layer 9100 years b p respectively diatom abundances increase steadily throughout the pre boreal atlantic time to 25 and 35 million valves per gram dry sediment in the norwegian basin and iceland plateau cores respectively application of the temperature transfer functions gint2 to the two holocene records revealed higher than present sea surface temperatures during the boreal atlantic chronozones for the iceland plateau and during the middle younger dryas sub boreal chronozones for the norwegian basin core temperatures decreased steadily since then with a slight increase to the present values both the iceland and the norwegian seas experienced a strong influx of temperate atlantic surface waters in the beginning of the holocene sea surface temperatures dropped steadily in the latter part of the holocene as the influx of the atlantic surface waters diminished

environmental changes off north iceland during the deglaciation and the holocene foraminifera diatoms and stable isotopes abstract a combined study of foraminifera diatoms and stable isotopes in marine sediments off north iceland records major changes in sea surface conditions since about 15 800 cal years yr bp results are presented from two gravity cores obtained at about 400 m water depth from two separate sedimentary basins on each side of the submarine kolbeinsey ridge the chronology of the sedimentary record is based partly on ams 14c dates partly on the vedde and the saksunarvatn tephra markers as well as the historical hekla ad 1104 tephra during the regional deglaciation the planktonic foraminiferal assemblages are characterised by consistently high percentages of sinistrally coiled neogloboquadrina pachyderma however major environmental variability is reflected by changes in stable isotope values and diatom assemblages low 18o values indicate a strong freshwater peak as well as possible brine formation by sea ice freezing during a pre bolling interval greenland stadial 2 corresponding to the heinrich 1 event the foraminifera suggest a strong concurrent influence of relatively warm and saline atlantic water and both the foraminifera and the diatoms suggest mixing of cold and warm water masses similar but weaker environmental signals are observed during the younger dryas greenland stadial 1 around the level of the vedde ash each freshwater peak is succeeded by an interval of severe cooling both at the beginning of the bolling allerod interstadial complex greenland interstadial 1 and during the preboreal presumably associated with the onset of intense deep water formatiom in the nordic seas the holocene thermal optimum between 10 200 and about 7000 cal years yr bp is interrupted by a marked cooling of the surface waters around 8200 cal yr bp this cold event is clearly expressed by a pronounced increase in the percentages of sinistrally coiled n pachyderma corresponding to a temperature decrease of about 3 c a general cooling in the area is indicated after 7000 6000 cal yr bp both by the diatom data and by the planktonic foraminiferal data after a severe cooling around 6000 cal yr bp the planktonic foraminiferal assemblages suggest a warmer interval between 5500 and 4500 cal yr bp minor temperature fluctuations are reflected both in the foraminiferal and in the diatom data in the upper part of the record but the time resolution of the present data is not high enough to pick up details in environmental changes through the late holocene

the formation of labrador sea water part i large scale processes abstract data obtained in the western labrador sea during march 1976 by hudson are analysed to show that new labrador sea water was being formed at this time on the basis of hydrographic and moored current meter data it is hypothesized that a 200 km scale cyclonic gyre forms in winter in the western labrador sea and that this gyre retains the developing deep mixed layers in this general area long enough for the transformation to labrador sea water to take place using a model it is demonstrated that water columns found along the western boundary of the labrador sea can be modified by cooling evaporation and mixing to form deep mixed layers with the properties of labrador sea water approximately 105 km3 of new labrador sea water was formed in 1976 an estimate that is consistent with earlier estimates of mean annual production rates this water 2 9 c 34 84 is some 0 6 c cooler and 0 06 fresher than that defined by lazier 1973 from his data collected in 1966 the variation of labrador sea water

modeling water isotopologues during the last glacial implications for quantitative paleosalinity reconstruction quantitative paleosalinity reconstructions with reasonable uncertainties remain a challenge in paleoceanography in this study we focus on stable isotope based methods 18o and 2h to derive paleosalinity we use the water isotopes enabled fully coupled atmosphere ocean vegetation land surface three dimensional model of intermediate complexity iloveclim to simulate the climate and water isotopes during the last glacial maximum lgm and heinrich event 1 we investigate how the isotopes in water can be used as reliable proxies to quantitatively reconstruct past changes in seawater salinity our results demonstrate that a quantitative salinity reconstruction during glacial conditions based on present day regional 18o salinity relationships can lead to considerable errors up to 25 g kg in certain regions however we show that these eventual uncertainties on paleosalinity reconstruction can be reduced by allowing for model derived regional 18o salinity relationships to vary through time our results indicate a rather stable dependence between 2h and 18o in surface seawater during the lgm this suggest that quantitative reconstruction of salinity based on the 2h measurement of alkenones 2ha might be possible if the slope and the intercept of the regression between the fractionation factor 2ha 2hsw and salinity can be sufficiently tightly constrained in open ocean conditions we confirm that pairing water isotopologues has a strong potential to reduce uncertainties on quantitative paleosalinity reconstructions also under glacial boundary conditions

accelerator mass spectrometry radiocarbon stratigraphies in deep labrador sea cores paleoceanographic implications foraminiferal accelerator mass spectrometry ams 14c ages and benthic planktonic age differences in surface layer sediments of labrador sea are influenced by bioturbation and by changes in the relative abundance of foraminiferal species carrying the 14c signal using benthic mixing models we demonstrate that inverse benthic planktonic age differences can be generated when the effect of benthic mixing and abundance change exceeds apparent age differences between surface water and deep water ams 14c ages obtained put constraints on the timing of major paleoceanographic changes in the basin notably on the history of the western boundary undercurrent which was clearly reinitiated during the mid deglaciation and intensified during the last 2 3 ka

holocene climate variability reflected in diatom derived sea surface temperature records from the subpolar north atlantic a detailed investigation of two deep sea sediment cores from the gardar drift in the subpolar north atlantic cores md99 2251 and md99 2252 has been undertaken to determine the extent of holocene

holocene north atlantic surface circulation and climatic variability evidence from diatom records diatom analyses have been performed on a 425cm long holocene marine sediment sequence from the north atlantic south of iceland and a 920cm sediment core spanning the last c 7500 years from skalafjord faeroe islands additional core data include stable isotopes and results from magnetic susceptibility measurements while chronostratigraphic control has been provided by ams 14c measurements the diatom records reveal distinct changes in north atlantic surface circulation and climate that have been correlated with published terrestrial and marine records initial holocene warming is dated at 9900 14c years bp and after a preboreal cold spell enhanced north atlantic current activity and warming prevailed from 9600 to 8800 14c years bp from 8800 to 8000 4c years bp the advection of warm atlantic water masses weakened presumably under atmospheric circulation conditions characterized by a dominating negative nao prior to the holocene climatic optimum 6000 5000 14c years bp distinct hydrographic gradient

drainage evolution and exhumation history of the eastern himalaya insights from the nicobar fan northeastern indian ocean abstract the eastern himalayan syntaxis where the yarlung tsangpo sharply bends is one of the areas experiencing most rapid exhumation on earth the rapid exhumation is often regarded as the result of capture of the yarlung tsangpo by the brahmaputra river however both the timing of integration of the yarlung tsangpo brahmaputra river and initiation of the rapid syntaxial exhumation are debated as the ultimate sedimentary trap of the yarlung tsangpo brahmaputra river the nicobar fan is a window to look into the drainage evolution and exhumation history of the eastern himalaya international ocean discovery program expedition 362 drilled the nicobar fan for the first time recovering fan sediments dating back to the early miocene 19 ma we apply trace elements and sr nd isotopes to investigate the provenance of the sediments in the nicobar fan with the aim of constraining the timing of integration of the yarlung tsangpo brahmaputra river and initiation of the rapid syntaxial exhumation the geochemical and sr nd isotope compositions indicate an eastern himalayan source dominated by the greater himalaya with significant gangdese arc contribution and primarily carried by the brahmaputra river flux of gangdese arc material appears to have been continuous from the base of the nicobar fan suggesting that the yarlung tsangpo brahmaputra river has been established at least since 19 ma synchronously with the sharp rise in sedimentation rate the abrupt change of geochemical and isotope compositions at 9 2 ma indicates an increase in erosion of the greater himalaya as the result of initiation of rapid exhumation in the broad syntaxial region the proportion of greater himalayan material increased again at 3 5 1 7 ma consistent with a younger pulse of rapid exhumation focused in the core of the syntaxis since 3 5 ma our results show that initiation of the rapid syntaxial exhumation postdated integration of the yarlung tsangpo brahmaputra river by at least 10 m y therefore tectonic uplift rather than river capture could be responsible for the initiation of the rapid syntaxial exhumation

the biogeography and ecology of common diatom species in the northern north atlantic and their implications for paleoceanographic reconstructions abstract sound knowledge of present day diatom species and their environments is crucial when attempting to reconstruct past climate and environmental changes based on fossil assemblages for the north atlantic region the biogeography and ecology of many diatom taxa that are used as indicator species in paleoceanographic studies are still not well known using information contained in large diatom environment calibration datasets can greatly increase our knowledge on diatom taxa and improve the accuracy of paleoenvironmental reconstructions a diatom calibration dataset including 183 surface sediment samples from the northern north atlantic was used to explore the distribution and ecology of 21 common northern hemisphere diatom taxa we define the ecological responses of these species to april sea ice concentrations and august sea surface temperatures assts using huisman olff fresco hof response curves provide distribution maps temperature optima and ranges and high quality light microscope images based on the results we find species clearly associated with cold warm and temperate waters all species have a statistically significant relationship with asst and 15 species with sea ice of these actinocyclus curvatulus fragilariopsis oceanica and porosira glacialis are most abundant at high sea ice concentrations whereas coscinodiscus radiatus shionodiscus oestrupii thalassionema nitzschioides thalassiosira angulata thalassiosira nordenskioeldii and thalassiosira pacifica are associated with low sea ice concentrations ice free conditions interestingly some species frequently used as sea ice indicators such as fragilariopsis cylindrus show similar abundances at high and low sea ice concentrations with no statistically significant relationship to sea ice

rock mass strength and the form of some inselbergs in the central namib desert a rock mass strength classification involving eight parameters has been applied to selected inselbergs in the namib desert the inselbergs are formed of schists gneiss granite and marble their slope inclinations are in a strength equilibrium with their rocks the study suggests that the strength classification is consistent and has a general validity and that rock slopes undergoing uniform weathering retreat to form slopes which are adjusted to their rock mass strength this is a more general statement than the common hypothesis of parallel retreat the favoured hypothesis of slope evolution in the namib is one of retreat rather than downwearing

identification of strength equilibrium rock slopes further statistical considerations strength equilibrium slopes are rock slopes whose gradient and rock mass strength rms are in adjustment the identification of such slopes depends on the accurate specification of the strength equilibrium envelope previous attempts to delimit the envelope are reviewed and modifications are proposed that permit its more rigorous statistical definition because can be measured much more reliably than rms the structural relation between these variables is estimated by regressing rms on and the strength equilibrium envelope is defined by the 95 per cent confidence limits the analysis is performed on a data set of 268 rock slopes representing all the data on rms and hitherto employed in published studies of strength equilibrium slopes

transfer functions between diatom assemblages and surface hydrology in the southern ocean interpretation of the distribution of 31 marine diatom species and two silicoflagellate genera in 28 core tops from the atlantic and west indian sectors of the southern ocean by q mode factor analysis allows definition of three significantly different floral assemblages one associated with subantarctic and two with antarctic waters these three areas are clearly delineated by prominent oceanographic limits the antarctic convergence and the maximum retreat of sea ice during the summer season a set of palaeoecological transfer functions is derived by comparison between the distribution of these associations and surface water hydrological parameters using these equations estimated summer temperatures from core top floral assemblages range from 12 c in the north of the study area to 2 0 c near the southernmost cores the standard errors of estimate are 1 1 c for summer temperatures 1 5 months year for sea ice cover 0 2 mg atp l for sea surface phosphate concentrations numerical tests of these paleoecological equations demonstrate their usefulness to reconstruct the evolution of the surface oceanography of the austral ocean at different periods of the last climatic cycle

surface oceanographic changes in the eastern labrador sea nannofossil record of the last 31 000 years abstract calcareous nannofossils in two ams 14c dated piston cores from the eastern labrador sea yield oceanographic information of the last 31 kyr moderate nannofossil productivity and abundance of north atlantic warm water taxa in the southern labrador sea core 91 045 094p suggest cool surface ocean condition between 31 and 26 thousand years ago ka the irminger current was absent in this interval thus we attribute this cool condition to weak advection of north atlantic water from the southeast we found evidence of cold and or seasonally ice covered surface conditions between 26 and 13 ka in the southern labrador sea and between 31 and 12 6 ka in the northeastern labrador sea core 90 013 013p increase of nannofossil productivity and abundance of north atlantic taxa at about 10 7 ka in core 91 045 094p suggests that the southern labrador sea was influenced by warm north atlantic surface water the polar water of the labrador current had little or no influence on the surface ocean in this area before 9 ka the labrador current started to flow or intensify after 9 ka and became strong by 8 4 ka the northeastern labrador sea remained cold until 8 4 ka perhaps because of discharge of cold meltwater from the greenland ice sheet at this time productivity increased sharply and the assemblage of nannofossils changed these suggest a significant improvement in surface ocean conditions and the establishment of the warm irminger current which marked the onset of the modern circulation pattern characterized by warm west greenland current and strong labrador current

recent arctic marine diatom assemblages from bottom sediments in baffin bay and davis strait abstract this study investigates the present geographical boundaries and environmental limits of the diatom flora in the baffin bay and davis strait area seventy four sea floor surface samples were examined the raw data were analyzed with the cabfac factor analysis program five factor assemblages explaining 87 of the observed variance emerged from this test the statistically most important assemblage is the baffin current assemblage composed ofthalassiosira gravida spores the second assemblage is the summer pack ice assemblage consisting ofactinocyclus curvatulus with a lesser contribution ofthalassiosira trifulta a third assemblage dominated bythalassiosira hyalina is located along the southwest coast of greenland indicating low ice concentration the fourth assemblage consists ofporosira sp spores and indicates fast ice conditions the fifth assemblage is dominated bythalassionema nitzschioides andporosira glacialis vegetative cells and indicates the coastal environment diatoms found in the sediment belong to discrete assemblages which reflect differences in water masses such as salinity and ice conditions these findings should assist in the interpretation of paleoceanographic conditions in the region when diatom assemblages are studied in piston core sediments

a diatom based sea ice reconstruction for the vaigat strait disko bugt west greenland over the last 5000 yr abstract a diatom based sea ice concentration sic transfer function was developed by using 72 surface samples from west of greenland and around iceland and validated against associated modern sic canonical correspondence analysis on surface sediment diatoms and monthly average of sic indicated that april sic is the most important environmental factor controlling the distribution of diatoms in the area justifying the development of a diatom based sic transfer function the agreement between reconstructed sic based on diatoms from west greenland and the satellite and modelled sea ice data during the last 75 yr suggests that the diatom based sic reconstruction is reliable for studying the palaeoceanography off west greenland relatively warm conditions with a strong influence of the irminger current ic were indicated for the early part of the record 5000 3860 cal yr bp corresponding in time to the latest part of the holocene thermal maximum between 3860 and 1510 cal yr bp april sic oscillated around the mean value 55 and during the time interval 1510 1120 cal yr bp and after 650 cal yr bp was above the mean indicating more extensive sea ice cover in disko bugt agreement between reconstructed april sic and changes in the diatom species suggests that the sea ice condition in disko bugt was strongly influenced by variations in the relative strength of two components of the west greenland current i e the cold east greenland current and the relatively warm ic further analysis of the reconstructed sic record suggests that solar radiation may be an important forcing mechanism behind the historic sea ice changes

transfer function between surface sediment diatom assemblages and sea surface temperature and salinity of the labrador sea abstract q mode factor analysis cabfac of 38 diatom species in 66 surface sediment samples from the labrador sea allowed the definition of six assemblages explaining 95 69 of the total variance the first assemblage 40 12 of the total variance is represented by thalassiothrix longissima a species characteristic of the irminger current and associated with the west greenland current the second assemblage 34 52 of the total variance is represented by thalassiosira gravida resting spores a cold water species associated with the labrador current a third assemblage 11 43 of the variance represented by chaetoceros spp is concentrated in the northeastern section of the labrador sea and associated with upwelling and high productivity the fourth the fifth and the sixth assemblages represented respectively by coscinodiscus marginatus coscinodiscus oculus iridis and coscinodiscus divisus and nitzschia frigida are less significant and account respectively for 4 95 2 62 and 2 04 of the total variance transfer functions derived by relating factor assemblages to surface water temperature and salinity august and february give standard errors of estimate of 0 93 c august and 0 64 c february for temperature and of 0 58 august and 0 45 february for salinity high correlations between the measured and estimated parameters confirm the validity of the paleoecological equations for the reconstruction of the labrador sea paleoclimate

refinement of a technique for determining rock mass strength for geomorphological purposes use of a field technique recently devised by selby for the measurement of rock mass strength has resulted in the understanding of the relationship between rock mass strength and slope form it is suggested that the accuracy of rock mass strength assessments may be enhanced by further subdividing the rating scales for intact rock strength and the spacing of partings the relationship between rock mass strength and gradient is reformulated using southern african data and statistically based confidence limits for identifying strength equilibrium slopes are proposed

diatom evidence of climatic change in holsteinsborg dyb west of greenland during the last 1200 years diatom assemblages from holsteinsborg dyb on the west greenland shelf were analysed with high temporal resolution for the last 1200 years a high degree of consistency between changes in frequency

a diatom based reconstruction of early holocene hydrographic and climatic change in a southwest greenland fjord abstract a diatom based reconstruction of surface water paleoclimatic and paleoceanographic changes in ameralik fjord southwest greenland is presented for the holocene interval 8800 to 3600 cal yrs b p a minor episode of cold surface water conditions is found at ca 8000 7800 cal yrs b p this may be due to the local conditions in the fjord and linked to the culmination of a strong melt water outflow rather than reflecting the widespread north atlantic 8 2 ka cooling event warming of surface water condition from 7800 to 7100 cal yrs b p probably corresponding to the early and warmest part of the holocene thermal maximum htm in this region is reflected in the diatom assemblages and supported by other proxies the west greenland current wgc influences the fjord strongly during this interval indicating enhanced advection of atlantic water masses derived from the irminger current ic a major sedimentary change with a hiatus between 6800 and 4400 cal yrs b p prevents a reconstruction of mid holocene paleoceanograpy the final and less prominent part of the htm is found after 4400 cal yrs b p previous studies from the same site have shown this final stage of the htm to end at 3200 cal yrs b p with the onset of the neoglaciation our study provides further evidence that the marine sedimentary record from west greenland fjords yields paleoenvironmental information reflecting a significant link between local and large scale north atlantic oceanographic and climatic changes

geological controls on rock mass classification of coal from huntly east mine new zealand abstract rock mass rating rmr measurements from 65 sites within huntly east underground coal mine are presented all measurements are in coal for which the dominant discontinuities are vertical cleat basic rmr values using two discontinuity spacings are presented overall rmr based on the average spacing of all individual discontinuities and cleat zone rmr based on the average spacing between zones of cleat cleat orientations are highly variable but on average approximately parallel horizontal stress axes face cleat follows maximum horizontal stress axis butt cleat follows minimum horizontal stress axis contours of rmr variations throughout the mine are used to compare rock mass conditions with geological structure it is apparent that 1 rmr is least within downthrown fault blocks and particularly immediately on the downthrown sides of faults and greatest in upthrown fault blocks and 2 rmr contours parallel horizontal stress axes within fault bounded blocks and bend to parallel faults at block boundaries from similar contours for parameters contributing to rmr the rock quality designation rqd groundwater rating and discontinuity condition rating create most of the observed variations in rmr rqd is determined from the measured discontinuity frequency and hence is a measure of the degree of fracturing of the rock mass this is interpreted as influencing the groundwater and condition parameters directly by allowing greater water ingress discontinuity frequency is greatest least spacing in the immediate vicinity of faults and in downthrown fault blocks generating low rmr values within fault blocks rqd varies little so rmr contours align with cleat orientations as rmr contours faults stress field and cleat orientation are clearly interrelated there is unequivocally a connection between rmr and structural geology this allows some predictive capacity in terms of ground conditions if geological features can be accurately defined through either drilling programs or seismic surveys then ground conditions may be predicted before panels are driven

a multi proxy reconstruction of oceanographic conditions around the younger dryas holocene transition in placentia bay newfoundland abstract a marine sediment core from placentia bay off the south coast of newfoundland was studied to reconstruct past oceanographic conditions based on a multiproxy approach including diatoms benthic foraminifera grain size analysis ip25 x ray fluorescence calcium carbonate and total organic carbon content based on 6 radiocarbon dates the 513 5 cm long core spans the age interval from ca 13 to 10 cal kyrs bp and thus captures the transition from the younger dryas stadial into the holocene at sub decadal resolution the younger dryas was characterized by cold arctic water taxa of diatoms and benthic foraminifera and a stratified water column with high sea ice cover and low productivity due to strong influence of the labrador current during the second half of the younger dryas after ca 12 2 cal kyrs bp the influence of the labrador current gradually decreased and sea ice conditions became more variable the transition towards the holocene is characterized by a sequence of events starting with turnovers in the biogenic proxies followed by an abrupt retreat of sea ice and a rise in productivity these events are believed to be related to a northward migration of the gulf stream labrador current oceanic front the younger dryas termination is directly followed by a detrital carbonate layer associated with the final phase of the heinrich 0 event linked to laurentide ice sheet dynamics during the early holocene productivity remained high with minimal sea ice cover reduced stratification and stronger influence of warmer gulf stream derived waters

sea surface temperatures in disko bay during the little ice age caution needs to be exercised before assigning thalassiosira kushirensis resting spore as a warm water indicator in palaeoceanographic studies