last interglacial eemian hydrographic conditions in the southeastern baltic sea ne europe based on dinoflagellate cysts abstract a rich organic walled dinoflagellate cyst and pollen record from the licze borehole in northern poland has been used to reconstruct the hydrographic history of the southeastern baltic sea during the last interglacial eemian stage late pleistocene warm saline waters ca 10 15 psu entered the site from the north sea within the first few hundred years of the eemian corresponding to the pinus betula e1 or pinus betula ulmus e2 regional pollen assemblage zones rpaz by about 300 years beginning of rpaz e3 dinoflagellate cyst assemblages were already indicating summer sea surface salinities in excess of about 15 psu and temperatures that perhaps exceeded 27 c warm and saline conditions of 15 20 psu or more at least twice present levels persisted throughout the early eemian a rise in sea level at licze appears to correlate with a similar event in eastern denmark as both coincide with the increase in corylus ca 750 years into the interglacial this sea level rise might therefore have a basinwide extent and appears to correspond to an opening of the danish belts there is little if any evidence of arctic waters throughout the sequence whereas dinoflagellate cysts reflect sustained high salinites within the upper water column a concomitant increase in abundance of the chlorococcalean alga pediastrum within the carpinus corylus alnus e5 rpaz indicates an escalating freshwater input presumably from the proto vistula whose mouth was nearby this suggests the development of a thin seasonal low salinity surface layer below which dinoflagellates lived in more saline waters increasing fluvial influence suggests shallowing through rpaz e5 this study is the first to document dinoflagellate cysts from the eemian of the southeastern baltic sea and reveals a flora with distinctive lusitanian mediterranean affinities

rheological transitions in progressive melting of rock and their geological constraints from the fuhu metatexite diatexite profile in guangdong province se china abstract integration of the published experimental data of partially melted amphibolite orthogneiss granite and aplite reveals the existence of three rapid strength drops of the rock assemblage at melt fraction around 7 21 and 41 respectively the first and the last drops are equivalent to the well known melt connectivity transition mct and solid to liquid transition slt the drop at melt fraction around 21 is newly identified and termed as the framework melting transition fmt the fmt is defined as the transition from eutectic quartz feldspars melting to refractory biotite melting the three rheological transitions are well constrained by the geological data from the fuhu profile in guangdong province se china this profile is a 15 m high cliff rocks exposed on the profile are zoned as mottled stripped narrow banded and wide banded migmatites and diatexitic granite from the top of the profile downwards the leucosome proportions of the zones measured on the outcrops combined with the experimental data of the partially melted rocks have significant implications for understanding the role of rheological transitions during crustal melting the mct which corresponds to the boundary between the mottled and the narrow banded migmatites suggests the segregation of melt within the partially melted system along with the compaction of matrix thus the mct is deemed to be the transition of the partially melted system from matrix supported melt stored in pore space to framework supported melt stored in foliation bedding space of protolith the fmt corresponding to the boundary between the narrow and the wide banded migmatites denotes the inception of melting of the solid framework mechanically the fmt can be regarded as the transition of the framework from compaction to fusion and geochemically the transition from eutectic melting of quartz feldspars to that of refractory biotite the increasing melt due to framework melting after the fmt is basically limited within the solid framework until the melt fraction exceeding the slt the slt is geologically constrained by the in situ metatexite diatexite transition that is also termed as magma interface mi the slt mi represents the upper limit of a crustal magma layer because of the downward increasing temperature and melt fraction there should be no consecutive layer of felsic rock existed in the space between the slt mi and the mafic lower crust except the isolated rock blocks within the magma layer

slope water current over the laurentian fan on interannual to millennial time scales the strength and position of surface and deep currents in the slope water south of newfoundland are thought to vary as a coupled system in relation to the dipole in atmospheric sea level pressure known as the north atlantic oscillation nao paleoceanographic data from the laurentian fan used as a proxy for sea surface temperature reveal that surface slope waters north of the gulf stream experienced warming during the little ice age of the 16th to 19th centuries and support the notion of an nao driven coupled system the nao may be a useful model for millennial scale ocean variability during interglacial climate states

organic walled microfossils and geochemical tracers sedimentary indicators of productivity changes in the north water and northern baffin bay during the last centuries analyses performed on 26 surface sediment samples collected with a box corer at 17 stations throughout the north water and northern baffin bay 75 791n 68 801w revealed abundantorganic walled microfossils most ly dinoflagellate cysts 10 3 10 4 cysts g 1 and organic linings of benthic foraminifers 10 2 10 3 ol g 1 as well as high organic carbon concentrations 0 87 2 81 dry weight these data indicate high productivity in both the pelagic and benthic environments of the north water and slightly lower productivity in northern baffin bay the data also showed calcium carbonate and biogenic silica dissolution throughout the study area the dinocyst assemblages were relatively uniform in the north water and dominated by heterotrophic taxa algidasphaeridium minutum and brigantedinium spp whereas northern baffin bay assemblages were dominated by autotrophic taxa notably operculodinium centrocarpum and spiniferites elongatus the difference between these two assemblages may be related to higher diatomaceous primary production in the north water than in northern baffin bay since diatoms constitute the principal food source of heterotrophic dinoflagellates the biogeographical boundary between the north water and northern baffin bay has been maintained for at least the last few centuries as shown by analyses of microfossils and geochemical tracers in two sediment cores one taken in the southeastern part of the north water 76117 0 n 72102 0 w and the other in northeastern baffin bay 75135 0 n 70148 0 w the analyses of the north water core revealed relatively uniform microfossil assemblages and organic carbon fluxes ranging from 1 1 to 1 5 mg corg cm 2 yr 1 for the last few centuries which corresponded to 4 6 of the present annual primary production in the euphotic zone these data suggest high productivity and relatively stable conditions in the polynya on a decadal time scale in the northeastern baffin bay core the analyses indicated generally lower organic carbon fluxes ranging from 0 3 to 0 6 mg corg cm 2 yr 1 and from the microfossil data significant variations in sea surface conditions at this lower latitude over the last centuries r 2002 elsevier science ltd all rights reserved

sea surface conditions in northernmost baffin bay during the holocene palynological evidence the analysis of cores collected in northernmost baffin bay from within the area of the north water polynya permits definition of a composite sedimentary sequence ca 12 m thick spanning the last 10 000 14 c yr with only a few discontinuities palynological analyses were performed in order to reconstruct changes in surface water conditions and biogenic production transfer functions using dinocyst assemblages were applied to estimate sea surface temperature sst and salinity as well as the seasonal duration of sea ice cover at the base of the record prior to 9300 14 c yr bp dinocysts and organic linings of benthic foraminifers are sparse indicating harsh conditions and low productivity after ca 9300 14 c yr bp the increased concentration of benthic foraminifers up to 10 3 linings cm 3 and dinocyst fluxes 10 2 10 3 cysts cm 2 yr 1 reveals high biological productivity related to open water conditions the early to middle holocene from ca 9000 to ca 3600 14 c yr bp is marked by relatively high species diversity in dinocyst assemblages and the significant occurrence of autotrophic taxa such as spiniferites elongatus pentapharsodinium dalei and impagidinium pallidum this assemblage suggests conditions at least as warm as at present from ca 6400 to ca 3600 14 c yr bp transfer functions indicate warmer conditions than at present with sst in august fluctuating up to 5 5 c after 3600 14 c yr bp the dinocyst record suggests a trend of decreasing temperature toward modern values marked by recurrent cooling events copyright 2001 john wiley sons ltd

haskell 1935 revisited the haskell 1935 value of 1021 pa s for mantle viscosity is a classic and enduring constraint on the rheology of the earth s interior we revisit this inference using spherically symmetric self gravitating maxwell viscoelastic earth models our inference is based on both forward and inverse analyses of decay times associated with uplift at two sites considered by haskell angerman river sweden and oslo norway rather than the raw relative sea level rsl data at these sites we demonstrate that predictions of the decay time associated with the angerman river data are insensitive to variations in both the late pleistocene ice load history and the lithospheric thickness of the earth model the predictions at oslo are sensitive to both these inputs and hence decay times at this site provide a remarkably robust constraint on mantle viscosity we derive a constraint on the average viscosity of the mantle of 0 65 1 10 1021 pa s where the average resolved by the data encompasses a region which extends from the base of the lithosphere to a depth of near 1400 km this indicates that many previous analyses which have invoked the haskell value of 1021 pa s as a constraint on the average upper mantle i e above 670 km depth viscosity alone have misinterpreted the resolving power of the inference furthermore our analysis indicates that a number of apparently contradictory inferences of viscosity based on fennoscandian data satisfy the new rigorous interpretation of the haskell constraint finally we demonstrate how the ambiguity in the upper mantle lower mantle viscosity contrast associated with the haskell average may be reduced by invoking decay time constraints estimated from rsl curves in hudson bay a preliminary inversion of decay times at angerman river and richmond gulf in hudson bay suggests a contrast of approximately an order of magnitude between the average viscosities of the upper mantle and the top 1000 km of the lower mantle however a conclusive analysis in this regard must await the determination of consistent decay time estimates for the hudson bay region

mid to late holocene hydrological and climatic variability in disko bugt central west greenland diatom and lithological analyses were carried out on two sediment cores from disko bugt and the adjacent kangersuneq fjord west greenland in order to investigate mid to late holocene 6 9 0 7 kyr bp hydrographic and climatic variability while the disko bugt record is found to reflect mainly west greenland current wgc fluctuations that can be linked to north atlantic circulation variability the fjord record appears to be more representative of local climate conditions the records demonstrate that the period of investigation was marked by a late holocene thermal maximum beginning at c 4 8 kyr and ending between 3 5 and 3 1 kyr bp encompassing a colder period between c 4 0 and 3 8 kyr bp an episode of higher surface water temperature is also indicated in disko bugt between 2 2 and 1 5 kyr bp in contrast the record from kangersuneq fjord suggests persisting cooler summer surface waters for this interval interpreted to be attributable to increased meltwater outflow the warming episode recogni

late holocene north atlantic climate seesaws storminess changes and greenland ice sheet gisp2 palaeoclimates the oxygen isotope record of palaeotemperature from greenland ice cores has for many years been the kingpin of climate reconstructions for the north atlantic region and northern europe an air temperature seesaw between greenland and northern europe first described in ad 1765 is also well known and is related to the north atlantic oscillation nao whereas the nao index series is based on instrumental records of air pressure the north atlantic climate seesaw has conventionally been based on air temperature records here we describe relationships between this seesaw mechanism and the greenland gisp2 oxygen isotope chronology of air temperature variations as well as relationships between gisp2 na sea salt variations and instrumental records of north atlantic storminess the gisp2 proxy air temperature record is calibrated for the last 130 years with instrumental weather records for west greenland while the na series is compared with instrumental records of north atlantic storminess change reconstruction of an annual series of these climate parameters for the last 1000 years shows that during the mediaeval warm period there were no years characterized by high na extremes high north atlantic storminess but there were many years when there were extremes of temperature remarkably there were no years of exceptionally low air temperature and high na precipitation at gisp2 between ad 1650 and 1710 a period of time that in northern europe incorporates the period of maximum little ice age cooling it would appear also that for the last thousand years the most extreme seesaw winters when gisp2 temperatures were very low and na concentrations were high occurred in discrete clusters and pairs of years

holocene environmental variability in southern greenland inferred from lake sediments abstract sediments from qipisarqo lake provide a continuous holocene paleoenvironmental record from southern greenland following deglaciation and glacio isostatic emergence of the basin from the sea 9100 cal yr b p proxies of lake paleoproductivity including biogenic silica and organic matter increased markedly until 6000 cal yr b p and thereafter remained stable over the ensuing warm three millennia subsequent decreases in these proxies most dramatically between 3000 and 2000 cal yr b p show the lake s responses to initial neoglacial cooling intervals of ameliorated limnological conditions occurred between 1300 and 900 and between 500 and 280 cal yr b p briefly interrupting the decreasing trend in productivity that culminated in the little ice age increased lake productivity during the latter half of the 20th century which reflects the limnological response to circum arctic warming still has not reached peak holocene values the neoglacial climate of the last 2000 yr includes the most rapid high amplitude environmental changes of the past nine millennia the norse thus migrated around the north atlantic ocean region in the most environmentally unstable period since deglaciation lacustrine sediment records provide a context with which to consider future environmental changes in the labrador sea region in particular any future warming will be superposed on a regional climate system that is currently exhibiting highly unstable behavior at submillennial timescales

the recession of the inland ice margin during the holocene climatic optimum in the jakobshavn isfjord area of west greenland recent subsurface mapping of parts of the greenland inland ice margin in the region of jakobshavn isbrae indicates that the fjord system in the period of at least 2700 4700 calendar yr b p was more ice free than at present and that the front of the glacier was at least 15 km behind the present position the 14c datings of subfossils brought to the present ice margin fit with the climatic records from ice cores and confirm the favourable conditions for greenland s first settlers the sarqaq people who arrived in the region about 4000 yr ago to find hunting grounds 10 20 larger than the present

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

foraminiferal reconstruction of mid to late holocene ocean circulation and climate variability in disko bugt west greenland benthic foraminifera from two cores collected from disko bugt a large marine embayment in west greenland are used to investigate hydrographic changes during the mid to late holocene the records document fluctuations in the west greenland current wgc linked to large scale changes in north atlantic circulation and for one core impacts of local climate changes in particular changes in the cold east greenland current egc and the warm more saline irminger current ic influence the wgc and propagate into disko bugt the cores record subsurface warming associated with the holocene thermal maximum htm from c 6 to 5 ka cal bp gradual cooling of wgc from 5 ka cal bp was interrupted by an abrupt warm interval from 3 9 to 3 5 ka cal bp before cooling became more prominent from 3 5 to 2 ka cal bp this cold period corresponds to the well documented northern hemisphere cooling of the neoglacial and we interpret it as reflecting enhanced flux from the egc and reduced ic flux to the wgc in disko b

pleistocene deglaciation and the earth s rotation implications for mantle viscosity summary recent results from the analysis of postglacial rebound data suggest that the viscosity of the earth s mantle increases through the transition region models which fit both relative sea level and free air gravity data have viscosities which increase from a value near 1022 poise in the upper mantle beneath the lithosphere to a value of about 1023 poise in the lower mantle in this paper we analyse the effect of deglaciation upon the earth s rotation and thereby show that the observed secular trend polar wander evident in the ils ipms pole path and measurements of the non tidal acceleration of the length of day are both consistent with the viscosity profile deduced from postglacial rebound the two analyses are therefore mutually reinforcing

holocene climate changes in southern greenland evidence from lake sediments a holocene lake sediment record is presented from lake n14 situated on angissoq island 15 km off the main coast of southern greenland the palaeoclimatic development has been interpreted on the basis of flux and percentage content of biogenic silica clastic material organic material and sulphur as well as sedimentation rate moss content and magnetic susceptibility a total of 43 radiocarbon dates has ensured a reliable chronology it is argued that varying sediment composition mainly reflects changing precipitation by analogy with the present meteorological conditions in southern greenland holocene climate development is inferred between 11550 and 9300 cal yr bp temperature and precipitation increase markedly but this period is climatically unstable from 9300 yr bp conditions become more stable and a holocene climatic optimum characterised by warm and humid conditions is observed from 8000 to 5000 cal yr bp from 4700 cal yr bp the first signs of a climatic deterioration are observed and from 3700 cal yr bp the climate has become more dry and cold superimposed on the climatic long term trend is climate variability on a centennial time scale that increases in amplitude after 3700 cal yr bp a climatic scenario related to the strength and position of the greenland high pressure cell and the iceland low pressure cell is proposed to explain the holocene centennial climate variability a comparison of the lake n14 record with a terrestrial as well as a marine record from the eastern north atlantic ocean suggests that the centennial climate variability was uniform over large areas at certain times less

late holocene atlantic bottom water variability in igaliku fjord south greenland reconstructed from foraminifera faunas a high resolution record of late holocene subsurface water mass characteristics in outer igaliku fjord south greenland is presented based on benthic foraminifera faunas from core po 243 451 collected from a water depth of 304 m strati cation with atlantic water masses present in the lower part of the water column is suggested to have prevailed during the last 3200 cal years except for a period referred to as the mediaeval warm period mwp during the mwp c ad 885 1235 the outer part of igaliku fjord experienced enhanced vertical mixing and a high hydrodynamic energy level which we ascribe to increasing wind stress through this period corresponding to the period of the norse settlement the transition from the mwp to the little ice age lia shows a two step pattern with a short climatic amelioration around ad 1520 before maximum cooling occurred the intensified wind stress and the overall environmental change are suggested to have contributed to the loss of the norse settlement in greenland periods with strong stratification and marked in uence of atlantic subsurface water masses around 2 6 1 3 ka bp and during the lia are correlated to north atlantic holocene ice rafting events reported by bond et al 1997

late glacial and holocene palaeoceanography of the north icelandic shelf high resolution gravity cores and box cores from the north icelandic shelf have been studied for palaeoceanographic history based on lithological and biostratigraphical foramin iferal data results from two outer shelf cores covering the last 13 6 k 14 c yr bp are presented in this paper the sediments accumulated in north south trending basins on each side of the kolbeinsey ridge at water depths of ca 400 m sedimentation rates up to 1 5 m kyr 1 are observed during the late glacial and holocene the vedde and saksunarvatn tephras are present in the cores as well as the hekla 1104 a new tephra kol gs 2 has been identified and dated to 13 4 k 14 c yr bp and another tephra geochemically identical to the borrobol tephra has been found at the same level at present the oceanographic polar front is located on the north icelandic shelf which experiences sharp oceanographic surface boundaries between the cold east icelandic current and the warmer irminger current past changes in sedimentological and biological processes in the study area are assumed to be related to fluctuations of the polar front the area was deglaciated before ca 14 kyr bp but there is evidence of ice rafting up to the end of the gs 1 greenland stadial 1 younger dryas period increasing again towards the end of the holocene foraminiferal studies show a relatively strong gs 2 pre 13 kyr bp palaeo irminger current followed by severe cooling and then by unstable conditions during the remainder of the gi 1 greenland interstadial 1 bolling allerod and gs 1 younger dryas another cooling event occurred during the preboreal before the holocene current system was established at about 9 kyr bp after a climatic optimum between 9 and 6 kyr bp the climate began to deteriorate and fluctuate copyright 2000 john wiley sons ltd

a dinoflagellate cyst record for the last 0 7 ma from the rockall plateau northeast atlantic ocean organic walled dinoflagellate cyst analysis of samples previously used to establish a high resolution oxygen and carbon isotope stratigraphy for the last 0 7 ma in the northeastern atlantic is detailed data from hole 552a leg 81 of the deep sea drilling project drilled on the western flank of the rockall plateau reveal peaks of dinoflagellate cyst recovery relatable with isotope stages 1 11 13 and 17 cysts most prersistently present include the oceanic impagidinium species nematosphaeropsb labyrinthea ostenfeld reid and the ubiquitous operculodinium centrocarpum deflandre cookson wall the results offer a correlation between the oceanic oxygen isotope stratigraphy and the dinoflagellate cyst record the potential for further correlation with the extensive quaternary marine sequences of the continental shelf around the british isles is explored the dinoflagellate cyst signal is an important factor in understanding oceanographic changes both at the surface and at depth

the skaergaard layered series part iii non dynamic layering layering in the skaergaard intrusion has been divided into two introduction general types one produced by magmatic flow and another by recent studies of the structural and textural features of processes resulting from variations of rates of nucleation and crysthe skaergaard intrusion mcbirney nicolas 1997 tallization and in the case of the layered series by compactionhave distinguished two broad types of layering one related processes modal variations caused by shifts of cotectic produced by the dynamic effects of magmatic flow and proportions produce thick layers which in the layered and upper another by processes that operate in situ such as varied border series are diffuse and normally lack strong foliation and nucleation and growth of crystals recrystallization or by lineation in the marginal border series the layers are thinner and compaction related mechanisms we refer to layering sharper possibly because the rate of accumulation was slower formed by these latter processes as non dynamic to oscillatory nucleation may have played a role in producing fineemphasize that it is not the result of fluid dynamic scale cyclic layers but it was less important than solution and processes although most layering combines elements of reprecipitation during slow cooling and ostwald ripening evidence more than one process the contribution of each mechfor compaction is found in deformed plagioclase laths and a relative anism can usually be recognized from its distinctive form deficiency of incompatible elements in rocks formed on the floor and setting layering related to compaction becomes sharper with increasing the distinguishing features of dynamic magmatic layheight in the layered series until it suddenly disappears above the ering have been described in part ii of this series mcbirtrough horizon near the base of upper zone b mechanical sorting ney nicolas 1997 they are best seen near the steep during compaction may have produced crude layering but if it did margins of the layered series in what wager brown the evidence has long since been destroyed by the superimposed effects 1968 referred to as the cross bedded zone where the of solution and reprecipitation when interstitial liquid rose through layering is disrupted by slumping and channeling and the overlying crystals and re equilibrated with them numerical the rocks have a marked foliation and lineation simulations illustrate how small differences of surface energy caused layering not associated with magmatic flow takes a by variations of grain size textural dependence of solubility and variety of forms but we can distinguish two general pressure solution can cause segregation of minerals into layers during end members each of which has a distinct origin and solution and reprecipitation characteristics the first results from varied rates of

seasonality of the north atlantic oscillation abstract monthly sea level pressure slp data from the national centers for environmental prediction reanalysis for 1948 99 are used to develop a seasonally and geographically varying mobile index of the north atlantic oscillation naom naom is defined as the difference between normalized slp anomalies at the locations of maximum negative correlation between the subtropical and subpolar north atlantic slp the subtropical nodal point migrates westward and slightly northward into the central north atlantic from winter to summer the naom index is robust across datasets and correlates more highly than eof coefficients with historical measures of westerly wind intensity across north atlantic midlatitudes as measured by this mobile index the nao s nodes maintain their correlation from winter to summer to a greater degree than traditional nao indices based on fixed stations in the eastern north atlantic azores lisbon iceland when the naom index is extended back to 1873 its annual values during

magma ascent by porous flow porous flow of buoyant liquid through partially molten rock is regarded as the initial transport process leading to magma segregation in the mantle recent work has identified the importance of matrix deformation and compaction in this process we present finite difference calculations based on a generalized form of darcy s law that includes matrix deformation in two dimensional cartesian and cylindrical coordinates we emphasize the existence of solitary wave solutions called magmons these waves are regions of locally high porosity that ascend through regions of low uniform porosity they differ from diapirs where the liquid and matrix ascend together the one dimensional waves that were previously reported are found to be unstable in two dimensions breaking down to form two dimensional waves of circular cross section both the development of the instability and the form of the two dimensional waves are supported by theoretical analysis numerical experiments in which two dimensional waves collide show that the extent to which they are conserved after collision depends on the lateral offset of the waves the conservation can be very good in other cases larger waves appear to grow at the expense of smaller waves although the quantification of the relevant permeability and rheological parameters remains uncertain geophysically plausible estimates suggest wavelengths of kilometers and velocities of centimeters per year in our preliminary assessment of the relevance of these results to igneous processes we find that magmons are unlikely to be important in regions of broad upwelling such as beneath spreading centers here the transport of liquid adjusts to match the supply by melting and compaction processes are not important if liquid is supplied from below to a stable partially molten region of the asthenosphere it is expected to ascend in magmons this may occur beneath oceanic volcanic centers or in subcontinental mantle it is possible that magma ascent in magmons leads to spatial and temporal episodicity of volcanic activity if higher level processes do not obscure this influence the waveform of a magmon ascends faster than the liquid within the magmon so new liquid is taken in from above while original liquid is lost from below consequently magmons can mobilize small degrees of partial melt and deliver it rapidly to the surface

hydrography and climate of the last 4400 years in a sw greenland fjord implications for labrador sea palaeoceanography a multiproxy record including benthic foraminifera diatoms and xrf data of a marine sedi ment core from a sw greenland fjord provides a detailed reconstruction of the oceanographic and cli matic variations of the region during the last 4400 cal years the lower part of our record represents the final termination of the holocene thermal maximum after the onset of the neoglaciation at approxi mately 3 2 ka cal bp the fjord system was subject to a number of marked hydrographical changes that were closely linked to the general climatic and oceanographic development of the labrador sea and the north atlantic region our data show that increased advection of atlantic water irminger sea water from the west greenland current into the labrador sea was a typical feature of northeast atlantic cool ing episodes such as the little ice age and the european dark ages while the advection of irminger sea water decreased significantly during warm episodes such as the mediaeval warm period and the roman warm period whereas the mediaeval warm period was characterized by relatively cool climate as suggested by low meltwater production the preceding dark ages display higher meltwater runoff and consequently warmer climate when compared with european climate these regional climate anomalies indicate persisting patterns of advection of colder respectively warmer air masses in the study region dur ing these periods and thus a long term seesaw climate pattern between west greenland and europe

a 1600 year history of the labrador current off nova scotia a multicore from emerald basin on the conti nental margin off nova scotia has a modern 14 c age at the top and other 14 c dates indicate a linear sedimenta tion rate of 30 cm ka to 1600 calendar years bp this rate is great enough to record century to millennial scale changes in the surface and deep 250 m waters in the basin that are influenced by the labrador current we applied five proxies for seawater temperature changes to the sediments of emerald basin including the percent abundance and the oxygen isotope ratio d 18 o of the polar planktonic foraminifer n pachyderma s the unsaturation ratio of alkenones u k 37 produced by prymnesiophyte phytoplankton and the d 18 o and mg ca of benthic foraminifera all five proxies indicate the ocean warmed suddenly sometime in the past 150 years or so the exact timing of this event is uncertain because 14 c dating is inaccurate in recent centuries but this abrupt warming probably correlates with widespread evidence for warming in the arctic in the nineteenth century because the canadian archipelago is one of the two main sources for the labrador current warming and melting of ice caps in that region may have affected labrador current properties before this recent warming sea surface temperature was continually lower by 1 2 c and bottom water was colder by about 6 c in emerald basin these results suggest that there was no medieval warm period in the coastal waters off nova scotia because there is also no evidence of medieval warming in the canadian archipelago it seems likely that coastal waters from baffin bay to at least as far south as nova scotia were continually cold for 1500 of the past 1600 years

palynofacies analysis and organic walled dinoflagellate cysts in late holocene sediments from igaliku fjord south greenland this study characterizes late holocene past 3300 years variations in organic matter deposition in the outer part of igaliku fjord south greenland and uses this information to assess palaeohydrographic conditions except for two all residues were characterized by abundant organic matter with amorphous material dominating the late holocene sediments in the deeper parts of the outer igaliku fjord have generally been deposited under anoxic to suboxic conditions with relatively low terrestrial freshwater influx the organic walled dinoflagellate cyst assemblages suggest the continuous presence of water masses derived from the east greenland current while changes in sea surface temperature during the last 3300 years have also been interpreted terrestrial influx was reflected by the continuous occurrence of leaf tissue which increased in abundance in sediments younger than ad 960 pseudo amorphous phytoclasts occurred in sediments older than ad 770 and sporomorphs were rare throughout acritarchs and o

distribution of organic walled dinoflagellate cysts in surface sediments from transects across the polar front offshore southeast greenland the polar front along the southeast greenland margin denotes the contrasting hydrographic properties of the polar and atlantic water masses on either side the remains of planktonic organisms in underlying sediments are expected to reflect these contrasts to test this we quantitatively analysed the organic walled dinoflagellate cyst dinocyst assemblages in surface sediments from transects across the present day polar front on the southeast greenland margin proportional differences are found between the composition of the dinocyst assemblages on either side of the polar front the influence of polar water can be traced in the dinocyst record as high abundances of algidasphaeridium minutum and the presence of pentapharsodinium dalei the influence of atlantic water is reflected in the presence of operculodinium centrocarpum and selenopemphix quanta all samples include taxa from both environments but the quantitative composition of the cyst assemblages clearly reflects the hydrographic features of the overlying surface water masses copyright 2001 john wiley sons ltd

environmental change in eastern greenland during the last 1300 years evidence from foraminifera and lithofacies in nansen fjord 68 n lithofacies and benthic foraminiferal analyses of two sediment cores bs1191 k13b and k14 from nansen fjord eastern greenland show evidence of changing oceanographic and sea ice conditions from

early holocene palaeoceanography and deglacial chronology of disko bugt west greenland two new cores from disko bugt a large marine embayment in west greenland are used to assess the deglacial chronology and palaeoceanography of the area during the early holocene deglaciation of the main part of disko bugt is directly dated for the first time to a minimum of ca 10 2 ka cal bp by this time the jakobshavn isbrae ice stream had retreated to the eastern margins of disko bugt initial deglaciation took place before the relatively warm west greenland current wgc was initiated a strengthening in the wgc is identified from ca 9 2 ka cal bp accompanied by retreat of the ice stream to a shallow bank immediately west of the present day jakobshavn isfjord while in this position the calving and melting ice stream produced large volumes of sediment and meltwater the large volumes of meltwater prevented the relatively warm waters of the wgc reaching the eastern margins of disko bugt the ice stream remained grounded on this bank for over a thousand years until ca 7 9 ka cal bp when reduced sedimentation rates and an increase in boreal fauna point to its retreat inside the present day fjord system

upper mantle beneath southeast asia from s velocity tomography 1 we present a three dimensional s velocity model of the se asian western pacific upper mantle with 400 km lateral resolution using the novel automated multimode inversion technique we processed 4038 vertical component seismograms and extracted 22 708 linear equations with uncorrelated uncertainties that constrain upper mantle structure we used time frequency windows to select signal with negligible proportion of scattered energy the windows included the fundamental rayleigh mode and s and multiple s waves the observed range of s velocity variations is the widest 17 18 in the upper 150 km of the mantle high velocity continental roots can reach beyond the present extent of the overlying archean proterozoic crust by 500 km beneath some precambrian units the roots are absent which can be attributed to deformation and gradual destruction of the ancient lithosphere at 120 150 km s velocity beneath some cratons reaches 4 8 km s this can be accounted for by thermal and compositional effects beneath the hainan island area a low velocity anomaly is observed from near the surface to the bottom of our model the hot spot type volcanism here may be caused by the deep mantle hainan plume a low velocity mantle domain underlies the south central sea of japan surrounded on the surface by intraplate volcanoes a deep seismicity gap is present near 40 n in the pacific slab subducting below and may result from a plume slab interaction a high velocity anomaly is present in the transition zone beneath the northern boundary of the yangtze craton we propose that the anomaly corresponds to subducted continental lithosphere stagnant atop the 660 km discontinuity

holocene palaeoclimatic reconstruction in northern iceland approaches and results abstract the period since the mid 19th century when instrumental meteorological recording first started in iceland has shown climate conditions close to or even at both holocene minimum and optimum levels the 19th century part of the little ice age represents a thermal minimum whilst the warmest decades of the 20th century are close to the estimated holocene thermal maximum a model describing sea ice climate ela relationships in northern iceland for this period has been developed providing a calibrated proxy climate record as a basis for palaeoclimatic reconstruction for the holocene as a whole glacier advances in the periods around 4700 bp around 4200 bp ca 3200 3000 bp around 2000 bp around 1500 bp and around 1000 bp based on radiocarbon dating and tephrochronology mark climatic minima of the post preboreal holocene when conditions were comparable to the extremes in the second half of the 19th century compared to optimal holocene thermal conditions with temperatures at least as high as in the 1930s the range of holocene temperature variation was ca 3 k this was accompanied by a doubling in precipitation from the thermal minima to the maxima

solitary waves in magma dynamics we investigate the stability of the one dimensional solitary waves solutions of the equations proposed by mckenzie to model the ascent of melts in the earth interior we show that for small porosity and two dimensional horizontal disturbances with long wavelength these solitary waves are unstable we also exhibit two and three dimensional solitary wave solutions of the mckenzie equations

late holocene environment and climatic changes in ameralik fjord southwest greenland evidence from the sedimentary record sedimentological and geochemical xrf data together with information from diatom and benthic foraminiferal records of a 3 5 m long gravity core from ameralik fjord southern west greenland is used for reconstructing late holocene environmental changes in this area the changes are linked to large scale north atlantic ocean and climate variability ams 14c dating of benthic foraminifera indicates that the sediment core records the last 4400 years and covers the termination of the holocene thermal maximum htm the late htm 4 4 3 2 ka bp is characterized by high accumulation rates of fine silty sediments related to strong meltwater discharge from the inland ice the htm benthic foraminiferal fauna demonstrates the presence of well ventilated saline bottom water originating from inflow of subsurface west greenland current water of atlantic irminger sea origin the hydrographic conditions were further characterized by limited sea ice probably related to a mild and relatively windy winter climate af

holocene thermal maximum in the western arctic 0 180 w the spatio temporal pattern of peak holocene warmth holocene thermal maximum htm is traced over 140 sites across the western hemisphere of the arctic 0 180 w north of 60 n paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer than present conditions at 120 of these sites at the 16 terrestrial sites where quantitative estimates have been obtained local htm temperatures primarily summer estimates were on average 1 6 0 8 c higher than present approximate average of the 20th century but the warming was time transgressive across the western arctic as the precession driven summer insolation anomaly peaked 12 10 ka thousands of calendar years ago warming was concentrated in northwest north america while cool conditions lingered in the northeast alaska and northwest canada experienced the htm between ca 11 and 9 ka about 4000 yr prior to the htm in northeast canada the delayed warming in quebec and labrador was linked to the residual laurentide ice sheet which chilled the region through its impact on surface energy balance and ocean circulation the lingering ice also attests to the inherent asymmetry of atmospheric and oceanic circulation that predisposes the region to glaciation and modulates the pattern of climatic change the spatial asymmetry of warming during the htm resembles the pattern of warming observed in the arctic over the last several decades although the two warmings are described at different temporal scales and the htm was additionally affected by the residual laurentide ice the similarities suggest there might be a preferred mode of variability in the atmospheric circulation that generates a recurrent pattern of warming under positive radiative forcing unlike the htm however future warming will not be counterbalanced by the cooling effect of a residual north american ice sheet

contribution palynostratigraphique dinokystes pollen et spores a la connaissance de la mer de champlain coupe de saint cesaire quebec high resolution continental pollen and spores and marine dinoflagellate cysts microfloral records were obtained from a section consisting of about 0 5 m of glaciolacustrine and 2 5 m of champlain sea deposits at the saint cesaire site the pollen and spore assemblages indicate the existence of a regional open vegetation of shrub tundra to forest tundra fluctuations in the percentages of picea and shrub and herb taxa are related to regional afforestation and paleogeographical evolution of the basin the champlain sea sediments contain an abundant dinocyst flora dominated by operculodinium centrocarpum brigantedinium spp and algidasphaeridium minutum which indicate cold arctic conditions in surface waters fluctuations in concentration 102 104 cm 3 and relative abundance of dinocyst species are attributed to changes in dinoflagellate productivity and paleoceanographic conditions notably paleosalinity morphological variations of operculodinium centrocarpum and algidasphaeridium minutum led to

melt segregation and matrix compaction the mush continuity equation compaction segregation time implications summary two phase aggregates a special case of which is partially molten systems are commonly modelled as an interpenetrating flow of two viscous liquids and are therefore described in terms of the fluid mechanics the governing equation set of fluid mechanics describing a two phase aggregate is incomplete as it consists of nine equations momentum and mass conservation equations for each phase and an energy conservation equation in ten unknowns six velocity components two pressures temperature and melt fraction in this paper the general equation closing the governing equation set is derived it explicitly expresses the condition of the coupling between the liquid percolation and porosity volume change due to which the medium continuity is maintained therefore the equation may be referred to as the mush continuity equation the character of the closed set solutions is demonstrated using 1 d isothermal models by examples of melt segregation inside a bounded low melting degree zone and sediment compaction at the bottom of a reservoir the compaction segregation style and time are controlled by the compaction segregation parameter c l c 2 and compaction segregation length depending on the mushy layer thickness l matrix permeability k characteristic porosity 0 and matrix and fluid viscosities at low c which approximately corresponds to low viscosity liquids kimberlites carbonatites the compaction segregation time scales as l 1 which effectively constrains the molten region thickness at the moment of the segregation and appears to explain the small volume and clustering of low viscosity magma eruptions characteristic of kimberlites at high c the porosity evolves through a formation of a series of isolated waves which could provide an explanation for the rhythmicity observed in large layered plutons

variable north atlantic climate seesaw patterns documented by a late holocene marine record from disko bugt west greenland abstract the reconstruction of past sea surface conditions in the labrador sea is essential for understanding climate fluctuations in the north atlantic region we here study late holocene sea surface conditions off west greenland in order to elucidate the possible relationship between a north atlantic seesaw and centennial to millennial scale climate fluctuations in the labrador sea region for that purpose we have studied the particulate organic matter especially dinoflagellate cysts and acritarchs from two marine sediment cores from disko bugt central west greenland our data show significant variations in sea surface temperature and sea ice cover during the last ca 3200 years after a cooling at ca 2 9 ka cal bp presumably related to the neoglacial cooling seen in large parts of the northern hemisphere the area was subjected to significant variability both in the entrainment of atlantic water west greenland current water and in atmospheric temperatures from 2 0 1 5 ka cal bp corresponding to the later part of the roman warm period the area experienced a return to a stronger influx of atlantic water and an increased fresh water influx from land probably related to increased precipitation or to melt water outflow from the nearby inland ice the dark ages 1 5 1 3 ka cal bp were characterised by an only minor cooling of the surface waters however as seen in other records from the labrador sea region the beginning of the medieval warm period 1 3 0 9 ka cal bp signified a severe cooling presumably due to a significant reduction in atlantic water entrainment the cold conditions continued through the little ice age after 0 9 ka cal bp although the area seems to have experienced a minor decrease in sea ice cover until 0 5 ka cal b p after which sea ice cover may again have increased the period of modern warming is not represented in our data our study shows that a north atlantic oscillation type pattern played a significant role in the late holocene centennial to millennial scale climate fluctuations in the labrador sea region however this cannot explain the full complexity of the climate signal the fact that a simple pattern of cold versus warm climate scenario does not exist demonstrates that it will hardly be feasible to select the correct baseline data set when modelling future climate development

late holocene dinoflagellate cysts as indicators for short term climate variability in the eastern laptev sea arctic ocean a sediment sequence from the eastern laptev sea shelf siberian arctic russia has been studied for dinoflagellate cysts in order to reconstruct sea surface conditions during the late holocene variability of assemblage composition and derived sea surface temperature estimates indicate that the neoglacial cooling was not a gradual climate change from 2510 to 900 cal yr bp relatively stable conditions with temperatures that were warmer than today were punctuated by a few cooling events in summer on centennial time scales during these events temperatures reached modern values this suggests that modern conditions may have been established abruptly within a short period in the past 1000 yr which is not documented in our record copyright 2001 john wiley sons ltd

diatom evidence of hydrographic changes and ice conditions in igaliku fjord south greenland during the past 1500 years biostratigraphic diatom analyses were carried out on two sediment cores from igaliku fjord south greenland in order to reconstruct hydrographic and climatic fluctuations during the late holocene ad 550 to present pronounced differences in hydrographic setting of the coring sites provide palaeoenvironmental information of both local and more regional character five diatom zones were identified from the subfossil diatom records each describing a hydrographic setting two major climate periods the mediaeval warm period ad 800 1250 and the little ice age ad 1580 1850 that were separated by a variable transitional period were recognized prior to these periods a cold and presumably moist climate regime prevailed between ad 500 and 700 cooling events were identified during the mediaeval warm period in the period ad 960 to 1140 the diatom data demonstrate that marked hydrographic changes occurred in the course of a relatively short timespan beginning at about ad 1300 and culminating around

palynofacies analysis and organic walled dinoflagellate cysts as indicators of palaeo hydrographic changes an example from holocene sediments in skalafjord faroe islands abstract this study documents holocene variations in organic matter deposition from ca 6350 cal yr bc to ad 1430 in skalafjord faroe islands and uses this information to assess palaeo hydrographic conditions the chronology of the interval studied is based on five ams 14 c ages based on the total sedimentary organic content the sediments dating to ca 6350 cal yr bc to ad 160 have been deposited under dysoxic bottom water conditions suggesting good ventilation in the water column the sediments dating to ca ad 160 1090 have been deposited under decreasing oxygen availability from ad 1090 to 1430 suboxic bottom water conditions characterised the fjord high terrestrial influx characterised most sediments in the study interval however moderate terrestrial influx was recorded in sediments dating to ca 6350 5670 cal yr bc based on the dinoflagellate cyst assemblages changes in the nutrient availability were inferred in the waters of the fjord over the study period the nutrients were minimal at ca 6350 5670 cal yr bc they increased in the interval ca 5670 685 cal yr bc and became very abundant at ca 685 cal yr bc to ad 1260 a decreasing trend in nutrient availability was inferred in sediments of age ca ad 1260 1430 a qualitative approach was used for the reconstruction of holocene sea surface temperature conditions based on dinoflagellate cyst and acritarch assemblages the estimated sea surface parameters highlighted the mid holocene final stage of the climatic optimum ca 6350 5300 cal yr bc the neo glaciation period ca 5300 cal yr bc to ad 260 a general climatic amelioration during the period ca ad 260 1090 and a cooling at ca ad 1090 1260

warming and freshening of baffin bay 1916 2003 1 regression analysis of historical hydrographic data is used to determine changes in temperature and salinity in baffin bay for the time period from 1916 to 2003 we find two distinct sets of changes in the baffin first areas affected by the atlantic inflow to baffin bay show substantial and statistically significant warming trends in the more than 2000 m deep basin the warming peaks at 0 11 0 06 c decade at 700 m depth below the 640 m sill depth of davis strait connecting baffin bay to the north atlantic ocean a vertical heat flux divergence of 0 25 w m2 is required to warm baffin bay below 900 m by the amount observed the required heat appears to be advected from the shelf and slope regions of the eastern labrador sea via davis strait along the west greenland shelf break and diffuses vertically and horizontally into the deep central basin the north atlantic oscillation index accounts for about 30 of the interannual variance of temperature fluctuations below the davis strait sill depth second areas affected by arctic inflow to baffin bay show a marginally significant freshening of up to about 0 086 0 039 psu decade this freshening trend extends along the western margin of baffin island to davis strait and into the labrador sea the freshening in the northern reaches of baffin bay is similar in size to that at its southern reaches temporal variability of annual composites between these locations appears to be in phase suggesting a swift transition of arctic waters at 76 n to labrador sea waters at 62 n

holocene climatic records from agassiz ice cap ellesmere island nwt canada four ice cores from the top of the agassiz ice cap and down a flow line have been variously analysed for 8 18o ecm solid conductivity and ice melt layer stratigraphy stratigraphic correlation

paleoceanographic reconstructions of surface ocean conditions in the greenland iceland and norwegian seas through the last 14 ka based on diatoms prior reconstructions of the last glacial maximum and the holocene did not include detailed paleoclimate data from the greenland iceland and norwegian gin seas which cover sensitive areas for oceanographic boundaries sea ice distribution and deep water formation in order to fill this gap we studied nine well dated sediment cores from this area and reconstructed the paleoceanographic conditions of the surface gin seas at 2000 year intervals since 13 400 bp based on the diatom record results show that a n s extending sea ice free corridor had opened along norway already at 13 400 bp indicating a northward flow of a branch of the north atlantic drift possibly caused by a change in the jet stream flow due to the decreased height of the north american ice sheet a major change of climatic conditions occurred over the gin seas as the insolation anomaly reached its maximum around 9000 bp when the sea ice cover and the oceanic fronts retreated to a northwesterly position along greenland and the ocean temperatures rose the first half of the holocene is recorded as the warmest period during the last 13 400 bp in the gin seas the duration of this climatic optimum decreased both toward the north and toward the margins of the area the second half of the holocene is characterized by a cooling trend in step with the decreasing insolation these results support the proposal of imbrie et al 1992 that the gin seas region acts as an initial responder to insolation changes

distribution patterns of dinoflagellate cysts and other organic walled microfossils in recent norwegian greenland sea sediments dinoflagellate cysts and other organic walled microfossils have been studied in recent surface sediments from the entire norwegian greenland sea more than 30 taxa have been recognized of which only few show a distinct distribution pattern and allow description of four assemblages the occurrence of most taxa is related to the relatively warmer waters of the norwegian sea algidaspaeridium minutum s 1 brigantedinium simplex and impagidinium pallidum are the only species showing a preference for colder water masses two species i pallidum and nematosphaeropsis labyrinthus are mainly restricted to the oceanic environment whereas the other species have also been reported from neritic environments in previous studies due to the limited knowledge of the ecological and sedimentological factors influencing the occurrence of dinoflagellate cysts in oceanic environments their distribution in recent sediments can be only related to surface water masses in a broad sense although the distribution of assemblages correlates with specific surface water masses comparison with assemblages recovered from sediment traps deployed basinwide in the norwegian greenland sea dale and dale 1992 revealed some major discrepancies in species composition and percentage abundances the differences cannot be explained with certainty at the moment although there is some evidence that transport of dinoflagellate cysts and other fossilizable microplankton in water masses by currents in sea ice and sediments may modify the assemblages found in recent oceanic surface sediments from the norwegian greenland sea

the circulation water masses and sea ice of baffin bay abstract the oceanographic meteorological and sea ice conditions in baffin bay are studied using historical hydrographic satellite and meteorological data and a set of current meter data from a mooring program of the bedford institute of oceanography baffin bay is partially covered by sea ice all year except august and september the interannual variation of the ice extent is shown to be correlated with winter air temperature available hydrographic data were used to study the water masses and the horizontal and vertical distribution of temperature salinity three water masses can be identified arctic water in the upper 100 300 m of all regions except the southeast west greenland intermediate water at 300 800 m in most of the interior of baffin bay and deep baffin bay water in all regions below 1200 m the temperature and salinity in baffin bay have limited seasonal variability except in the upper 300 m of eastern davis strait northern baffin bay and the mouth of lancaster sound summer data have a temperature minimum at 100 m which suggests winter convection does not penetrate deeper than this depth current meter data and results of a circulation model indicate that the mean circulation is cyclonic the seasonal variation of the currents is complex overall summer and fall tend to have stronger currents than winter and spring at all depths among the different regions the largest seasonal variation occurs at the mouth of lancaster sound and the baffin island slope model generated velocity fields show a basic agreement with the observed currents and indicate strong topographic control in the vicinity of davis strait and on the greenland shelves the model also produces a southward counter current on the greenland slope which may explain the observed high horizontal shears over the greenland slope estimates of the volume and fresh water transports through lancaster jones and smith sounds are reviewed transports through davis strait are computed from the current meter data the balance of freshwater budget and sensitivity of the thermohaline circulation to freshwater transport are discussed

evolution of major and trace element composition during melt migration through crystalline mush implications for chemical differentiation in the crust we present the first quantitative model of heat mass and both major and trace element transport in a mush undergoing compaction that accounts for component transport and chemical reaction during melt migration and which is applicable to crustal systems the model describes the phase behavior of binary systems both eutectic and solid solution with melt and solid compositions deter mined from phase diagrams using the local temperature and bulk composition trace element concentration is also determined the results demonstrate that component transport and chemical reaction generate compositional variation in both major and trace elements that is not captured by existing geochemical models in particular we find that even for the simplest case of a homogenous insulated column that is instantaneously melted then allowed to compact component transport and reaction leads to spatial variations in major element composition that in this case produces melt that is more enriched in incompatible elements than predicted by batch melting in deep crustal hot zones dchz created by the repeated intrusion of hot mantle derived magmas buoyant melt migrating upwards accumulates in high porosity layers but has a composition corresponding to only a small fraction of batch melting because it has locally equilibrated with mush at low temperature moreover melt migration and chemical reaction in a layered protolith may lead to the rapid formation of high porosity melt layers at the interface between different rock compositions in both of these cases the melt in the high porosity layer s is less enriched in incompatible trace elements than predicted if it is assumed that melt with the same major element composition was produced by batch melting this distinctive decoupling of major and trace element fractionation may be characteristic of magmas that originate in dchz application of the model to a number of crustal systems including the ivrea verbano zone the rum layered intrusion and the holyoke flood basalt suggests that composi tional heterogeneity can be explained by buoyancy driven melt migration and compo nent transport through a reactive crystalline mush

chemical differentiation cold storage and remobilization of magma in the earth s crust the formation storage and chemical differentiation of magma in the earth s crust is of fundamental importance in igneous geology and volcanology recent data are challenging the high melt fraction magma chamber paradigm that has underpinned models of crustal magmatism for over a century suggesting instead that magma is normally stored in low melt fraction mush reservoirs 1 9 a mush reservoir comprises a porous and permeable framework of closely packed crystals with melt present in the pore space1 10 however many common features of crustal magmatism have not yet been explained by either the chamber or mush reservoir concepts1 11 here we show that reactive melt flow is a critical but hitherto neglected process in crustal mush reservoirs caused by buoyant melt percolating upwards through and reacting with the crystals10 reactive melt flow in mush reservoirs produces the low crystallinity chemically differentiated silicic magmas that ascend to form shallower intrusions or erupt to the surface11 13 these magmas can host much older crystals stored at low and even sub solidus temperatures consistent with crystal chemistry data6 9 changes in local bulk composition caused by reactive melt flow rather than large increases in temperature produce the rapid increase in melt fraction that remobilizes these cool or cold stored crystals reactive flow can also produce bimodality in magma compositions sourced from mid to lower crustal reservoirs14 15 trace element profiles generated by reactive flow are similar to those observed in a well studied reservoir now exposed at the surface16 we propose that magma storage and differentiation primarily occurs by reactive melt flow in long lived mush reservoirs rather than by the commonly invoked process of fractional crystallization in magma chambers14 magma storage and differentiation in the earth s crust mainly occurs by reactive melt flow in long lived mush reservoirs rather than by fractional crystallization in magma chambers as previously thought

deposition models for chronological records abstract long term sedimentary sequences provide a wealth of useful information for research into the palaeo environment especially in relation to past climate change shorter records provide similar information in many archaeological contexts however if such records are to be used to provide precise timing of events and more critically the relative timing between different records methods are needed to provide accurate and precise age depth models for these sequences given the imprecision of individual calibrated radiocarbon determinations it is necessary to use the information we have about the deposition process to refine our chronologies and also to provide interpolation between dated levels in any sequence even with layer counted chronologies the uncertainties are sometimes hard to quantify this paper outlines a range of bayesian models for deposition which have been implemented in the computer programme oxcal these models can be used to combine information from the sediments themselves with radiocarbon or other direct dating information such models have the potential to integrate information between different records and provide a coherent chronology on which to base environmental or archaeological research