delimiting oceanographic provinces to determine drivers of mesoscale patterns in benthic megafauna a case study in the barents sea abstract communities of benthic megafauna in the deep waters of continental shelves 100 m are important components of marine ecosystems in high latitude ecosystems this fauna is increasingly impacted by human activities and climate variability in this study we provide baseline knowledge on the oceanographic conditions affecting its distribution in the barents sea in the vicinity of the polar front an oceanic front occurring at the transition zone between the atlantic and arctic water masses we used fields of temperature and currents from an ocean circulation model regional ocean modelling system roms to derive variables divided into 3 groups relevant to bottom fauna temperature water column structure and bottom currents expressing either mean conditions or temporal variability over 10 years 2001 2010 benthic megafauna was surveyed in summer 2011 at 139 sites to analyze the relationship between spatial variability in the composition of benthic megafauna i e diversity and oceanographic conditions we 1 used generalized dissimilarity modelling gdm and 2 delimited oceanographic provinces i e regions of similar conditions for each group of variables using principal component analysis pca followed by cluster analysis turnover in benthic megafauna was explained by 7 oceanographic variables temperature 4 water column structure 2 bottom currents 1 depth and geographic distance 56 7 of total deviance explained concurrently patterns in oceanographic provinces among the 3 groups of variables coincided with results from the gdm where provinces derived from temperature were sharply delimited relative to the other groups we concluded that the spatial structure of the environment is important in the relationship between spatial variability of benthic megafauna and oceanographic conditions in shelf deep waters ocean models are powerful tools to study this relationship but the way in which their inherent uncertainty affects the conclusions of ecological models should be assessed more thoroughly

the mjauvotn tephra and other holocene tephra horizons from the faroe islands a link between the icelandic source region the nordic seas and the european continent six different tephra horizons were found in peat and lacustrine sediments on the faroe islands in the north atlantic their geochemistry showed that they were of icelandic origin three of these can be correlated with previously described tephra horizons from the faroe islands the saksunarvatn tephra c 9000 bp the hekla 4 c 3800 bp and hekla selsund c 3600 bp a previously unrecorded basaltic tephra dated to c 5700 5300 bp was found in two lacustrine successions this horizon is named the mjauvotn tephra after mjauvotn lake on the island of streymoy two further tephras were recorded the basaltic phase of the landnam tephra viia c ad 870s and the rhyolitic tjornuvk tephra these were found in sediments deposited shortly after the first phase of human settlement at tjornuvik which is ams dated to ad 675 861 calibrated age the faroe islands are an important link between the volcanic sources on iceland and the established tephrochronological frameworks on the british isles scandinavia and germany their position within a sensitive region of the northeastern branch of the north atlantic drift make the faroe islands ideal for registering climate changes during the holocene the establishment of a modern tephrochronology may provide a tool for more precisely dating and correlating regional climate events in and around the nordic seas

on the role of the mesoscale circulation on an idealized coastal upwelling ecosystem 1 an idealized circulation model of coastal upwelling coupled to an ecosystem model has been built to address the impact of features such as eddies and filaments emerging from mesoscale dynamics on a marine ecosystem the model mimics coastal upwelling along an infinite straight coast with north south cyclic boundary conditions thanks to the parametrization of the geostrophic onshore flow in the thermocline the circulation captures the typical characteristics of a coastal upwelling region an equatorward coastal jet a poleward undercurrent along the continental slope and mesoscale eddies and filaments this eddying three dimensional simulation is compared to a two dimensional simulation using the averaged velocity field of the first simulation as velocity field this approach allows us to compare simulations having similar upwelling and nutrient input but differing in the nature of the flow an offshore spreading of the phytoplankton bloom is found in the eddying simulation the width of the productive coastal band is increased from 80 km to 200 km by the mesoscale activity a biogeochemical budget carried out in a 300 km wide coastal band provides evidence that mesoscale activity decreases the total phytoplankton content mainly by exporting a significant part of the surface phytoplankton below the euphotic layer in presence of mesoscale activity the downward and offshore export of phytoplankton zooplankton and detritus significantly contributes to total export of organic matter out of the surface coastal ocean whereas their contribution to export is weak in the two dimensional case

a detrital heavy mineral viewpoint on sediment provenance and tropical weathering in se asia abstract understanding heavy mineral preservation is important for interpreting generation pathways provenance and geochemistry of sediments despite this many assumptions about heavy mineral stability are based on ancient strata and few studies consider modern sediments particularly those in tectonically active tropical areas such as se asia we report new heavy mineral data on 69 river sand samples from the malay peninsula and sumatra in which one aim was to find provenance indicators specific to these areas identifications were performed using optical microscopy and confirmed with sem eds in the malay peninsula heavy minerals record granitic and contact metamorphic provenance variable amounts of zircon tourmaline hornblende andalusite epidote monazite rutile and titanite and minor amounts of pyroxene apatite anatase garnet diaspore colourless spinel cassiterite and allanite are typical of this source area the composition of assemblages from sumatra indicates contributions from two major sources the modern volcanic arc i and the basement ii abundant pyroxene particularly hypersthene up to 70 is diagnostic of the volcanic arc source vesuvianite garnet andalusite tourmaline chrome spinel rutile anatase and corundum are present only in small amounts

origin of the torlesse terrane and coeval rocks south island new zealand the carboniferous to lower cretaceous torlesse terrane and haast schist derivatives constitute the major part of the complexly deformed facies of the eastern province of new zealand strata consist mainly of quartzofeldspathic graywacke and mudstone intercalated with minor but widely distributed conglomerate and volcanics with associated chert and limestone clastic rocks were deposited largely by sediment gravity flow mechanisms in a deep marine environment also present are a few highly fossiliferous shallow marine and terrestrial deposits of limited areal extent which rest unconformably on or in fault contact with torlesse flysch several periods of deformation are recognized and melange is present on both local and regional scales metamorphism ranges from zeolite to greenschist facies the bulk of the rocks fall into five areally extensive and mutually exclusive fossil zones of the following ages permian atomodesma middle triassic early late triassic torlessia late triassic monotis and late jurassic early cretaceous contacts between major fossil zones are mainly tectonic petrographic analysis permits subdivision of torlesse sandstones into five major petrofacies that correspond in age to the five major fossil zones the sandstone petrofacies mainly arkosic together with the composition of conglomerate clasts mainly indurated torlesse rocks indicate that the source terrane was a continental volcano plutonic arc probably part of gondwanaland coupled with autocannibalistic reworking of older uplifted torlesse rocks in contrast to the quartzofeldspathic nature of the torlesse coeval sedimentary rocks of the eastern province are volcanogenic they are thought to represent related forearc basin maitai murihiku terranes and trench complex caples terrane deposits derived from a volcanic island arc brook street terrane three petrofacies are established for maitai murihiku and caples sandstones the petrofacies indicate a common evolving immature to submature volcanic island arc source for these terranes a reconstruction of new zealand s eastern and western provinces is proposed in permian and triassic times the torlesse was deposited in trench slope or borderland basins along a trench transform margin fronting a continental volcano plutonic arc source western province gondwanaland deposition was spasmodic but voluminous and was accompanied by concurrent deformation and accretion resulting in parallel belts of torlesse rock younging outward from the gondwanaland margin at the same time the brook street terrane volcanic arc and associated terranes were forming to the west of the torlesse site separated from gondwanaland by a marginal sea in latest triassic or early jurassic times the torlesse was rafted into the volcanic arc system via transform faulting approximately parallel to the gondwana margin the collision event resulted in tectonic thickening of torlesse and caples rocks at the plate interface and metamorphism to haast schist the source was then dominated by older partly metamorphosed torlesse terrane newly uplifted along the collision front closing of the marginal sea behind the brook street terrane in late jurassic early cretaceous times resulted in juxtapositioning with the western province gondwanaland along the median tectonic line

structure of a near polar latitude forest from the new zealand jurassic a tidal platform at curio bay near the southernmost point of the south island new zealand preserves the petrified remains of an in situ middle jurassic forest the forest grew close to the palaeo polar circle but data are not precise enough to tell on which side it lay a mapped portion of the forest floor provides data on tree density and population structure allowing comparison with recent forests and with records of other fossil forests the forest has tree densities similar to many forests growing in low to mid latitudes today it appears to have had emergents projecting through a low canopy and a well developed undergrowth of smaller gymnosperms and osmundaceous ferns no aspect of the forest structure uniquely distinguishes it from that of non polar latitude forests an extended discussion is given on reconstructing tree height from stump diameter on the basis of this a reinterpretation of the structure of an early cretaceous fossil forest from alexander island antarctica is offered

eastern boundary currents and coastal upwelling abstract the adjustment of the eastern coastal zone of an inviscid ocean with vertical walls to a change in wind conditions occurs in two stages after the propagation of a kelvin wave across the forced region in a time tk which is of the order of a day or two the coastal upwelling zone is temporarily in equilibrium with the wind further adjustment occurs after a time tr which is of the order of a few mouths when westward rossby dispersion of the coastal jet becomes important these time scales define three frequency ranges that characterize the response to fluctuating winds with period p 1 at high frequencies p tk short kelvin waves can destroy coherence between the forcing and response alonshore coherence of oceanic variables is small and the spectrum of the response is red even if that of the forcing is white the offshore wale of the response is the radius of deformation poleward phase propagation at kelvin wave speed c in unforced regions and at speed 2c in the forced region is prominent

mesoscale sst wind stress coupling in the peru chile current system which mechanisms drive its seasonal variability satellite observations and a high resolution regional ocean atmosphere coupled model are used to study the air sea interactions at the oceanic mesoscale in the peru chile upwelling current system coupling between mesoscale sea surface temperature sst and wind stress ws intensity is evidenced and characterized by correlations and regression coefficients both the model and the observations display similar spatial and seasonal variability of the coupling characteristics that are stronger off peru than off northern chile in relation with stronger wind mean speed and steadiness the coupling is also more intense during winter than during summer in both regions it is shown that ws intensity anomalies due to sst anomalies are mainly forced by mixing coefficient anomalies and partially compensated by wind shear anomalies a momentum balance analysis shows that wind speed anomalies are created by stress shear anomalies near surface pressure gradient anomalies have a negligible contribution because of the back pressure effect related to the air temperature inversion as mixing coefficients are mainly unchanged between summer and winter the stronger coupling in winter is due to the enhanced large scale wind shear that enables a more efficient action of the turbulent stress perturbations this mechanism is robust as it does not depend on the choice of planetary boundary layer parameterization

tephrostratigraphy of an loch mor inis oirr western ireland implications for holocene tephrochronology in the northeastern atlantic region twelve definable cryptotephra layers younger than c 8600cal bp are reported from lacustrine core material taken from an loch mor inis oirr aran islands western ireland the geochemistry of these shard layers which represent more holocene tephras than previously geochemically characterized from any european site outside the proximal volcanic influence of italy or iceland is presented of these tephras four may correlate with known iceland derived tephra horizons vo 1477 hi lairg a and h5 one appears to have two possible named correlatives hoy lairg b at sluggan bog n ireland another has a plausible correlative ad 860a but two others represent icelandic tephras apparently not previously reported on iceland itself including a tephra that has geochemistry very similar to hl ad 1104 but which dates to c cal ad 840 four tephras that date from the period c ad 40 1400 have a distinct geochemical signature that relates to jan mayen 750km to the northeast of iceland and some 1800km distant from an loch mor the results contribute substantially to the chronology of the sediments from an loch mor and at the international level to the tephrostratigraphy of the northeast atlantic region the well attested icelandic h4 tephra from a hekla eruption of c 4260cal bp was not recorded it is suggested that an loch mor lies south of its recordable distribution in this part of the northeast atlantic region taken together with work at other sites the findings point to a wealth of potential tephra isochrons in holocene deposits of the northeast atlantic seaboard it is clear also that calcareous lake sediments can be as fruitful a source of tephras as peats potential problems relating to dating and geochemical fingerprinting of tephra layers in individual sites are highlighted with reference to the lairg tephras as recorded in scotland and northern ireland and to the hoy tephra that has been described from orkney

seven tephra isochrones in scotland this paper reports the presence and geochemical characteristics of seven separate tephras in scotland that fell in ad 1510 and about 450 bp 2100 bp 3600 bp 3830 bp 5600 bp and around 6000 bp the results come from 14 peat bogs spread throughout the highlands and islands where 26 tephra deposits have been characterized using over 400 grain discrete electron probe micro analysis firstly tephras are identified and defined by major element characteristics at a reference site secondly tephras are linked between sites on the basis of geochemistry and dated informal names based on british sites are suggested for tephras not yet linked to precise sources in iceland despite some apparent variation in colour all analysed grains in these seven deposits are silicic or intermediate in composition sio2 57 this phenomenon does not appear to be an artifact of preservation for two reasons first small 40 m basic glass shards in peat bogs in northern iceland are found to have undergone minimal alte

uranium lead ages from the dun mountain ophiolite belt and brook street terrane south island new zealand the dun mountain ophiolite and overlying maitai group is discontinuously exposed for 480 km in south island new zealand zircon u pb dates from plagiogranite are presented for relatively intact ophiolite ophiolitic melanges and for more silicic volcanic plutonic assemblages in the southern part of the belt where a typical ophiolite association is lacking step wise dissolution experiments on slightly discordant plagiogranite zircon produce more concordant residues that indicate the zircons have lost from 1 to more than 5 of their radiogenic pb relatively recently high precision 207 pb 206 pb dates establish the age of ophiolite formation for at least 350 km along strike to a narrow interval between about 275 and 285 ma the zircon u pb data confirm correlation of petrologically distinct segments of the dun mountain ophiolite and show that mafic ultramafic ophiolite assemblages and moderately potassic high level granitoids developed within a short time interval probably during the extension of a volcanic arc marginal basin thick lenses of polymictic breccia and bio clastic limestone of the maitai group locally rest in depositional contact on relatively intact ophiolite within the dun mountain ophiolite comparison of inferred biostratigraphic ages from the limestone with the 280 ma ages from the plagiogranites indicate a gap of 20 m y following ophiolite formation a granite clast from conglomerate higher in the maitai group yielded a near concordant u pb date of 265 ma and provides a maximum age for this part of the sequence attenuation of the dun mountain ophiolite by extensional faulting and erosion may have occurred during the interval between ophiolite formation and maitai group sedimentation the dun mountain ophiolite and overlying maitai group are bounded to the west by triassic and jurassic volcanogenic sedimentary rocks of the murihiku terrane and in turn by the brook street terrane which is interpreted as remnants of an early permian oceanic arc a hornblende gabbronorite associated with a layered mafic ultramafic intrusion in the brook street terrane yielded a date of 265 ma significantly younger than dun mountain ophiolite such intrusions may represent the plutonic roots for ankaramitic volcanic rocks that comprise a conspicuous component of the brook street terrane but which are not represented by detritus in the maitai group biotite granite occurs locally in the brook street terrane and is dated at 260 ma the absence of any clear stratigraphic correlation or provenance linkage between the brook street terrane and dun mountain maitai terrane suggests strike slip displacements on intervening terrane boundary faults

provenance of the murihiku terrane new zealand evidence from the jurassic conglomerates and sandstones in southland abstract sedimentary petrological geochemical and geochronological studies were carried out to reveal the provenance of the murihiku terrane southland new zealand the murihiku terrane comprises late permian to early cretaceous volcaniclastic sediments that were deposited at the fore arc or back arc basin of the eastern gondwana margin the strata in the waikawa district southland are middle or early late jurassic and comprise sandstones interbedded with conglomerates and mudstones the sediments can be petrologically classified into two groups one dominated by intermediate mafic volcanic detritus type a and the other more quartz bearing 15 20 in qfl dominated by felsic volcanic and plutonic detritus type b the chemistry of detrital clinopyroxene in type a sediments is compatible with their derivation from island arc volcanics whole rock major and trace element analyses suggest that granitoid and gabbroid clasts associated with type b sediments are also of volcanic arc origin geochemical characteristics of the plutonic clasts can be compared closely with the median batholith median tectonic zone whole rock k ar ages of the clasts 156 8 and 177 9 ma for gabbroid clasts and 156 8 and 212 11 ma for alkali feldspar granite clasts are consistent with the median batholith magma cooling small quantities of grandite and pyrope bearing garnet grains in type b sediments might be derived from metamorphosed intermediate mafic volcanic rocks to amphibolite facies granitic cataclasite and hornfels are also compatible with derivation from the median batholith that was accreted to the brook street terrane

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

investigation of the environmental impact of remote volcanic activity on north mayo ireland during the mid holocene seven layers of microscopic tephra have been detected in ombrotrophic peat from western ireland a radiocarbon chronology suggests that two of the tephra layers were deposited around 4000 bp pollen fungal spores and testate amoebae have been analyzed from the peat immediately above and below the tephra layers these analyses provide information of changes in the landscape surrounding the bog and as well as conditions on the bog surface analysis of rates of change in these data has been employed to investigate the relative magnitude of environmental changes at the time of tephra deposition tephra deposition occurred at least 100 years after a major decline in pinus pollen and coincides with fairly stable conditions in the terrestrial environ ment more significant changes on the bog surface indicative of wetter conditions are associated with the timing of tephra deposition

evidence for the occurrence of vedde ash in sweden radiocarbon and calendar age estimates a tephra layer of rhyolitic composition has been recorded in sediments from lake madtjarn southwestern sweden geochemical analyses have shown that the tephra is identical to the rhyolitic component of the middle younger dryas vedde ash a series of ams radiocarbon measurements places the radiocarbon age of the tephra within a 14c plateau at 10 400 10 300 14c y bp based on a linear younger dryas sedimentation rate and assumptions about the apparent synchroneity of changes in lake sediments tree rings and ice core records the calendar year age of the tephra concentrations is estimated at 12 045 11 975 yr bp which accords well with the age of the equivalent tephra in the grip core 1998 john wiley sons ltd

the formation of a subsurface anticyclonic eddy in the peru chile undercurrent and its impact on the near coastal salinity oxygen and nutrient distributions the formation of a subsurface anticyclonic eddy in the peru chile undercurrent pcuc in january and february 2013 is investigated using a multi platform four dimensional observational approach research vessel multiple glider and mooring based measurements were conducted in the peruvian upwelling regime near 12 30 s the dataset consists of 10000 glider profiles and repeated vessel based hydrography and velocity transects it allows a detailed description of the eddy formation and its impact on the near coastal salinity oxygen and nutrient distributions in early january a strong pcuc with maximum poleward velocities of 0 25 m s at 100 to 200 m depth was observed starting on january 20 a subsurface anticyclonic eddy developed in the pcuc downstream of a topographic bend suggesting flow separation as the eddy formation mechanism the eddy core waters exhibited oxygen concentrations 1 mol kg an elevated nitrogen deficit of 17 mol l and potential vorticity close to zero which seemed to originate from the bottom boundary layer of the continental slope the eddy induced across shelf velocities resulted in an elevated exchange of water masses between the upper continental slope and the open ocean small scale salinity and oxygen structures were formed by along isopycnal stirring and indications of eddy driven oxygen ventilation of the upper oxygen minimum zone were observed it is concluded that mesoscale stirring of solutes and the offshore transport of eddy core properties could provide an important coastal open ocean exchange mechanism with potentially large implications for nutrient budgets and biogeochemical cycling in the oxygen minimum zone off peru

thermochronology of northern murihiku terrane new zealand derived from apatite ft analysis murihiku terrane is the least deformed of a series of tectonostratigraphic terranes that have been amalgamated to form the basement underlying new zealand apatite fission track ft thermochronology has been applied to the youngest beds late jurassic hettangian tithonian stages of this terrane located at port waikato in western north island which are broadly folded the apatite ft ages are partially annealed are younger than their stratigraphic ages and remarkably decrease in age upsection interpretation and modelling of the maximum palaeotemperatures experienced by the sample horizons and the timing of cooling requires a wedge of cretaceous sedimentary rocks to have accumulated within the axis of the major fold kawhia syncline deposition of murihiku terrane sequences continued therefore into the cretaceous and probably until c 100 ma deposition may have ended as late as 85 10 ma when cooling via denudation started the upper parts of the former succession probably accumulated during folding in addition interpretation of the ft data require a marked increase in palaeogeothermal gradient from a subnormal value of 15 c km 1 during the late jurassic up to c 30 c km 1 at 85 10 ma this is attributed to the termination of subduction along the pacific margin of gondwanaland and a transition to a rift transform tectonic setting in western new zealand during tasman sea spreading the latest cretaceous palaeocene eastward tilting of the murihiku basement at port waikato may have been accommodated on the taranaki fault or another coast parallel fault the waikato fault probably acted as a transfer fault at that time accumulating a significant amount of throw

calendar year ages of three mid holocene tephra layers identified in varved lake sediments in west central sweden three intermediate to rhyolitic icelandic holocene tephra horizons hekla 3 kebister and hekla 4 have been identified in annually laminated varved lake sediments in the province of varmland west central sweden calendar year ages were obtained from varve counts and are supported by additional c 14 dating based on terrestrial plant macrofossils the varve ages of the three tephras are 3295 95 cal bp hekla 3 4030 103 cal bp kebister and 4390 107 cal bp hekla 4 the varve age of hekla 3 refines the former calibrated 14 c age based on studies in the british isles and germany considering the age error estimates associated with the varve chronology and calibrated c 14 ages the ages of kebister and hekla 4 are in agreement with former studies thus the age difference between kebister and hekla 4 is estimated to be ca 400 40 varve years formally estimated to ca 200 c 14 years between hekla 3 and hekla 4 to ca 1135 55 varve years formally estimated to ca 1100 calibrated c 14 years and between hekla 3 and kebister 708 20 varve years less

repeated flood events and fossil forests at curio bay middle jurassic new zealand during the middle jurassic the regional environment of curio bay southeast south island new zealand was a fluvial plain marginal to volcanic uplands intermittent flashy poorly confined flood events buried successive conifer forests with the termination of each flood soils developed and vegetation was reestablished in most cases this developed into coniferous forest in approximately 40 m of vertical section 10 fossil forest horizons can be distinguished highlighting a type of fluvial architecture which is poorly documented flood basin material is minimal but a short lived floodbasin lake is inferred to have developed within the interval of study paleocurrent indicators suggest enclosure of the basin on more than one side sedimentation style suggests a relatively dry less than humid but not arid climate with seasonal rainfall c 2001 elsevier science b v all rights reserved

sedimentation and volcanism in a permian arc related basin southern new zealand an exceptionally well exposed ancient intra arc basin in the permian takitimu group of new zealand contains 14 km of interbedded primary volcanic and marine volcaniclastic rocks of basaltic to rhyodacitic composition these are the products of subaerial and submarine arc volcanism and closely associated turbidite sedimentation the takitimu oceanic arc basin setting formed a dynamic closed sedimentary system in which large volumes of volcaniclastic material generated at the arc was rapidly redeposited in marine basins flanking the eruptive centres volcanism probably included 1 moderate to deep water extrusion of lava and deposition of hyaloclastite 2 extrusive and explosive eruptions from shallow marine to marginally emergent volcanoes in or on the margin of the basin and 3 plinian and phreato plinian eruptions from more distant subaerial vents along the arc much of the newly erupted material was rapidly transported to the adjacent marine basin by debris flows slumping and sliding hemipelagic sedimentation predominated on the outer margin of the basin infrequently interrupted by deposition of ash from the most explosive arc volcanism and the arrival of extremely dilute turbidites turbidite sedimentation prevailed in the remainder of the basin producing a thick prograding volcaniclastic apron adjacent to the arc the volcaniclastic strata closely resemble classic turbidite deposits and show similar lateral facies variations to submarine fan deposits study of such sequences provides insight into poorly understood processes in modern arc related basins

carbon and oxygen cycles sensitivity to changes in environmental forcing in a coastal upwelling system 1 biogeochemical cycles in the coastal ocean are changing and will continue to change in response to a changing climate effects on the oxygen and carbon cycles are particularly important as either episodic or permanent shifts toward lower oxygen and or higher inorganic carbon conditions can impact coastal ecosystems negatively here we study the sensitivity of these cycles to changes that may occur in the coastal ocean focusing on a summer wind driven upwelling region off southern vancouver island shelf we use a quasi 2 d configuration of the regional ocean modeling system roms to perform six sensitivity experiments results indicate that carbon and oxygen cycles in this region may be significantly affected by an altered upwelling season a shallower offshore oxygen minimum zone and a carbon enriched environment combinations of these scenarios suggest a potentially increasing risk for the development of coastal hypoxia and corrosive conditions in the region

physical characteristics and dynamics of the coastal latex09 eddy derived from in situ data and numerical modeling 1 we investigate the dynamics of a coastal anticyclonic eddy in the western part of the gulf of lion gol in the northwestern mediterranean sea during the latex campaign in the summer 2009 latex09 the sampling strategy combines sea surface temperature satellite imagery hull mounted acoustic doppler current profiler data conductivity temperature depth casts and drifter trajectories our measurements reveal an anticyclonic eddy latex09 eddy with a diameter of 23 km and maximum depth of 31 m centered at 3 34 e 42 33 n we use a high resolution three dimensional primitive equation numerical model to investigate its generation process and evolution the model is able to reproduce the observed eddy in particular its size and position the model results suggest that the latex09 eddy is induced by a large anticyclonic circulation in the northwestern part of the gol pushed and squeezed toward the coast by a meander of the northern current this represents a new generation mechanism that has not been reported before the post generation dynamics of the eddy is also captured by the model the collision of the latex09 eddy with cape creus results in a transient structure which is depicted by the trajectories of two lagrangian drifters during latex09 the transient structure and its advection lead to a transfer of mass and vorticity from the gol to the catalan shelf indicating the importance of mesoscale structures in modulating such exchanges in the region

diagenesis and very low grade metamorphism of volcaniclastic sandstones from contrasting geodynamic environments north island new zealand the murihiku and waipapa terranes the mesozoic murihiku and waipapa terranes are two accretionary wedges of linked forearc and trench sediments respectively that were juxtaposed in the early cretaceous late triassic to late jurassic murihiku terrane volcaniclastic sediments are folded into a regional syncline and have been diagenetically altered there is a general relationship between zeolite occurrence clay mineralogy vitrinite reflectance and stratigraphic position youngest jurassic sediments contain heulandite analcime and stilbite whereas late triassic to mid jurassic sediments have laumontite and heulandite in detail the zeolite distribution is complicated tuffaceous horizons on the eastern limb of the syncline are calcitized rather than zeolitized post diagenetic fractures associated with uplift are laumontite filled the inferred geothermal gradient is c 15 c km 1 the waipapa terrane is an accretionary complex dominated by imbricated terrigenous sediments of triassic and jurassic age with enclosed permian to jurassic pelagic sediments and basalts late jurassic sediments are massive volaniclastic sandstones the sediments are non foliated and metamorphic minerals in the massive sandstones have crystallized in specific domains the observed metamorphic succession of prehnite pumpellyite and pumpellyite actinolite facies assemblages was overprinted in the imbricated rocks during a thermal event that was late in the deformation sequence and broadly coincident with hydraulic fracturing and veining the metamorphic successions in the two terranes and their relationships to structural features are in excellent accord with accretionary complex models

the volcanic eruption on jan mayen january 1985 interaction between a volcanic island and a fracture zone abstract an eruption started on jan mayen on 6 january 1985 it lasted only 35 40 hours and discharged about 7 million m3 of magma an earthquake swarm accompanied the eruption with individual quakes reaching magnitude 5 the volcanic fissure that opened strikes about midway between the strike of the jan mayen fracture zone 25 n of w and the general trend of the island and its volcanic features sw ne this fact the strong earthquakes and compositional features all suggest that it was an eruption from a leaky fracture zone rather than from the jan mayen magma system proper

detrital heavy mineral constraints on the triassic tectonic evolution of the west qinling terrane nw china implications for understanding subduction of the paleotethyan ocean we have examined the triassic sediments in the west qinling terrane northeastern tibet these sediments consist mainly of flysch and shallow sea and fluvial deposits with abundant lithic and heavy mineral detritus sandwiched between and overlying late paleozoic and early middle triassic ophiolitic melanges volcanic and metamorphic detritus dominates the lithic component of lower triassic sandstones accompanied by high cr spinel pyroxene and magnetite contents indicating a mixed ophiolite and metamorphic source detrital mineral geochemistry further suggests that ophiolitic high grade metamorphic basic and intermediate acidic igneous rocks must have been exposed and deeply eroded in their source area abundances of zircon rutile garnet tourmaline and epidote are greater in the middle triassic samples and granitic and volcanic sources are the major contributors of detrital clasts considering these new observations on sedimentary petrography and detrital heavy mineral geochemistry along with published data on paleocurrents detrital zircon u pb ages sedimentary facies and regional magmatism we suggest that these triassic sediments represent the sedimentary fill of a forearc basin that overlies a late paleozoic ophiolitic complex a south facing andean type convergent continental margin system developed along the southern margin of the north china block during the triassic in response to northward subduction of the paleotethyan ocean

horizontal transport and the distribution of nutrients in the coastal transition zone off northern california effects on primary production phytoplankton biomass and species composition conductivity temperature depth surveys during 1988 encountered strong baroclinic jets that were evident in acoustic doppler current profiler and hydrographic data during june and july 1988 a filament with high surface nitrate high chlorophyll abundant populations of neritic centric diatoms and higher rates of primary production was evident perpendicular to the coast between point arena and point reyes however the high nutrient and phytoplankton regions were not in the baroclinic jets but were south and inshore of them surface water transported offshore by the strong baroclinic jets was found to have relatively low nutrient content suggesting that the jets themselves do not carry significant levels of coastally upwelled high nutrient water to the ocean interior the low nutrient and salinity content of the jet suggests that the water originated several hundred kilometers upstream although the jets themselves do not appear to transport significant levels of nutrients directly from the coastal regime to the oceanic regime dynamic processes associated with a meandering jet are likely responsible for high surface nutrients found several hundred kilometers offshore processes such as upwelling along the southern edge of the seaward jet result in significant enrichment of the coastal transition zone and in large blooms of neritic diatoms during 1988 the high nutrient high phytoplankton filament was present when the survey sequence began but then decayed after a month the surface and subsurface nitrate fields were coherent with the dynamic topography field throughout the survey sequence however the surface and integrated chlorophyll fields were coherent only through the first two surveys a decrease in phytoplankton biomass began during the third survey coincident with physical changes which occurred in that time frame 1 an intensification of the undercurrent and 2 changes in the surface circulation from predominantly offshore to predominantly longshore understanding the processes responsible for the uncoupling between biology and physics is paramount for realistic biological models of this region

linking the north atlantic to central europe a high resolution holocene tephrochronological record from northern germany a high resolution holocene tephrochronology for northern germany has been established based on systematic tephrostratigraphical analysis of three peat bogs microscopic volcanic ash layers have been traced and characterised petrographically and by the chemical composition of the glass shards at least 37 ash horizons representing 16 different explosive volcanic eruptions have been identified and many can be correlated between the three sites up to 100 km apart the tephra layers can be related to icelandic volcanic sources and some correlated to the eruptions of askja 1875 hekla 3 hekla selsund hekla 4 and hekla 5 as well as to unspecified eruptions of icelandic volcanic systems e g torfajokull the source volcanoes for some tephra layers remain unidentified some tephra layers were known previously from the north atlantic region e g sluggan glen garry others have not been recorded previously in the literature e g microlite tephra this study provides the first comprehensive holocene tephrostratigraphical record for northern germany complementing the north atlantic tephrostratigraphical dating framework effectively extending it into central europe the study shows that icelandic ash layers are even more widespread than hitherto thought copyright 2002 john wiley sons ltd

equilibrium structure and dynamics of the california current system this paper addresses the structure and dynamical mechanisms of regional and mesoscale physical variability in the subtropical northeast pacific ocean using the regional oceanic modeling system roms the model is configured with a u s west coast domain that spans the california current system ccs with a mesoscale horizontal resolution up to as fine as 3 5 km its mean seasonal forcing is by momentum heat and water fluxes at the surface and adaptive nudging to gyre scale fields at the open water boundaries its equilibrium solutions show realistic mean and seasonal states and vigorous mesoscale eddies fronts and filaments the level of eddy kinetic energy eke in the model is comparable to drifter and altimeter estimates in the solutions with sufficiently fine resolution because the model lacks nonseasonal transient forcing the authors conclude that the dominant mesoscale variability in the ccs is intrinsic rather than transiently forced the primary eddy generation mechanism is the baroclinic instability of upwelling alongshore currents there is progressive movement of meanseasonal currents and eddy energy offshore and downward into the oceanic interior in an annually recurrent cycle the associated offshore eddy heat fluxes provide the principal balance against nearshore cooling by mean ekman transport and upwelling the currents are highly nonuniform along the coast with important influences by capes and ridges in both maintaining mean standing eddies and launching transient filaments and fronts

production regimes in the northeast atlantic a study based on sea viewing wide field of view sensor seawifs chlorophyll and ocean general circulation model mixed layer depth 1 a 5 year time series of sea viewing wide field of view sensor seawifs ocean color images schl is compared with mixed layer depths mld and atmospheric forcings from the clipper model of the north atlantic 1998 2002 this comparison is done over the region 16 22 w 30 50 n where subpolar mode waters are formed and which overlaps the region of the 2001 programme ocean multidisciplinaire meso echelle pomme experiment at sea three production regimes are identified on the basis of the seasonal cycling of schl and mld the well known subpolar and subtropical regimes and a midlatitude regime the midlatitude regime is characterized by a single broad bloom weaker than the subpolar spring bloom and stronger than the subtropical fall bloom which starts in fall as an entrainment bloom and peaks in spring as a restratification bloom this specific regime is found between 35 n and 40 n 2 in the northeast atlantic it corresponds to winter mlds between ze the depth of the euphotic layer and 2ze i e it lays between the region where the winter mld is greater than sverdrup s critical depth subpolar regime and the region where the mixing is never deeper than the well lit layer subtropical regime the very specific characteristics of the midlatitude regime strengthen the biological carbon pump since production is active in winter within the waters to be subducted the midlatitude regime also may provide an explanation for the unexpectedly low f ratios sometimes observed during the bloom in the region north atlantic bloom experiment pomme a large interannual variability is observed for the three regimes in terms of the timing and the intensity of the blooms and of the geographical boundaries of the regimes these variabilities appear to be mainly driven by the synoptic and the low frequency atmospheric variabilities it is also shown that in addition to the northward propagation of the subpolar spring bloom from 41 n 1 3 to 50 n the fall entrainment bloom propagates southward over the whole latitudinal range 35 50 n

front eddy influence on water column properties phytoplankton community structure and cross shelf exchange of diatom taxa in the shelf slope area off concepcion 36 37 s in eastern boundary current systems ebcss submesoscale to mesocale variability contributes to cross shore exchanges of water properties nutrients and plankton data from a short term summer survey and satellite time series january february 2014 were used to characterize submesoscale variability in oceanographic conditions and phytoplankton distribution across the coastal upwelling and coastal transition zones north of punta lavapie and to explore cross shelf exchanges of diatom taxa a thermo haline front frn 1 flanked by a mesoscale anticyclonic intrathermocline eddy ite 1 or mode water eddy persisted during the study period and the survey was undertaken during a wind relaxation event at the survey time ite 1 contributed to an onshore intrusion of warm oceanic waters southern section and an offshore advection of cold coastal waters northern section with the latter forming a cold high chlorophyll a filament in situ phytoplankton and diatom biomasses were highest at the surface in frn 1 and at the subsurface in ite 1 whereas values in the coastal zone were lower and dominated by smaller cells diatom species typical of the coastal zone and species dominant in oceanic waters were both found in the frn 1 and ite 1 interaction area suggesting that this mixture was the result of both offshore and onshore advection overall front eddy interactions in ebcss could enhance cross shelf exchanges of coastal and oceanic plankton as well as sustain phytoplankton growth in the slope area through localized upward injections of nutrients in the frontal zone combined with ite induced advection and vertical nutrient inputs to the surface layer

an eddy permitting model of the atlantic circulation evaluating open boundary conditions as part of the french clipper project an eddy permitting model of the atlantic circulation has been run for 22 years the domain has open boundaries at drake passage and at 30 e from africa to antarctica the simulated mean circulation as well as the eddy activity is satisfactory for a 1 3 model resolution and the meridional heat transport at 30 s is within the range estimated from observations we use the mixed open boundary algorithm of barnier et al 1998 which has both a radiation condition and a relaxation to climatology the climatological boundary forcing strongly constrains the solution in the whole domain the model heat balance adjusts through the surface heat flux retroaction term more than the open boundaries the radiation phase velocities calculated within the algorithm are analyzed this shows quite surprisingly that both the eastern and western boundaries have a similar behavior regardless of the preferred directions for advection mainly eastward and wave propagation mainly westward our results confirm that open boundary algorithms behave differently according to the dynamics of the region considered the passive boundary condition that penduff et al 2000 applied successfully in the north eastern atlantic does not work in the present south atlantic model we emphasize the need for a careful prescription of the climatology at the open boundary for which a new approach based on synoptic sections is implemented

do submesoscale frontal processes ventilate the oxygen minimum zone off peru the peruvian upwelling system encompasses the most intense and shallowest oxygen minimum zone omz in the ocean this system shows pronounced submesoscale activity like filaments and fronts we carried out glider based observations off peru during austral summer 2013 to investigate whether submesoscale frontal processes ventilate the peruvian omz we present observational evidence for the subduction of highly oxygenated surface water in a submesoscale cold filament the subduction event ventilates the oxycline but does not reach omz core waters in a regional submesoscale permitting model we study the pathways of newly upwelled water about 50 of upwelled virtual floats are subducted below the mixed layer within 5 days emphasizing a hitherto unrecognized importance of subduction for the ventilation of the peruvian oxycline

whole rock geochemical variations and evolution of the arc derived murihiku terrane new zealand arc flank volcaniclastic sedimentation in the murihiku terrane of new zealand lasted about 120 million years from late permian to early cretaceous time despite the effects of pervasive zeolite facies alteration whole rock geochemical parameters for sandstones siltstones and tuffs record changes in source rock composition both in time and along the length of the depositional basin sandstones are considered to give a more reliable indication of the state of evolution of the source volcanic arc than do the siltstones the siltstones commonly contain detrital white mica flakes that are generally lacking in the sandstones and are possibly of distal continental origin some also contain very fine felsic ash particles average abundances and normalized multi element diagrams are used to estimate proportions of three model end member source constituents average upper continen tal crust ucc high k rhyolite rhy and basaltic andesite and sandstone provenance for the southland syncline sector changed from a predominantly basaltic andesite source in late permian to early middle triassic time for example ucc rhy and 0 17 83 in the early to early middle triassic to highly felsic in the middle to late triassic reaching ucc rhy and 2 74 24 in the late triassic oretian stage a ucc component became increasing significant from latest triassic upward and the proportion of mafic to felsic volcanism increased again with ucc rhy and 15 30 35 in the middle jurassic temaikan stage mix modelling suggests that along arc source propor tions varied with greater mafic and upper continental crust contributions in the northern kawhia seg ment than in the southland segment these patterns may be explained by deposition at an oceanic aleutian type arc margin with transition to a continental oceanic arc character induced either by arc evolution and dissection forearc sliver translation or underplating of rafted microcontinental fragments

mesoscale to submesoscale transition in the california current system part i flow structure eddy flux and observational tests in computational simulations of an idealized subtropical eastern boundary upwelling current system similar to the california current a submesoscale transition occurs in the eddy variability as the horizontal grid scale is reduced to o 1 km this first paper in a series of three describes the transition in terms of the emergent flow structure and the associated time averaged eddy fluxes in addition to the mesoscale eddies that arise from a primary instability of the alongshore wind driven currents significant energy is transferred into submesoscale fronts and vortices in the upper ocean the submesoscale arises through surface frontogenesis growing off upwelled cold filaments that are pulled offshore and strained in between the mesoscale eddy centers in turn some submesoscale fronts become unstable and develop submesoscale meanders and fragment into roll up vortices associated with this phenomenon are a large vertical vorticity and rossby number a large vertical velocity relatively flat horizontal spectra contrary to the prevailing view of mesoscale dynamics a large vertical buoyancy flux acting to restratify the upper ocean a submesoscale energy conversion from potential to kinetic a significant spatial and temporal intermittency in the upper ocean and material exchanges between the surface boundary layer and pycnocline comparison with available observations indicates that submesoscale fronts and instabilities occur widely in the upper ocean with characteristics similar to the simulations

detrital zircon age constraints on depositional history and provenance of the murihiku supergroup murihiku terrane north island new zealand abstract in the murihiku terrane of new zealand u pb detrital zircon ages in murihiku supergroup sandstones of late triassic jurassic and possibly earliest cretaceous age have a marked youngest age component that is close to and sometimes coincident with established biostratigraphic ages thus reflecting contemporary volcanism however youngest huriwai group samples yield 137 142 ma zircon age components earliest early cretaceous in conflict with palynofloras that suggest only a latest jurassic age this is resolved if the age of the jurassic cretaceous boundary is lowered to ca 140 ma older reworked zircons are mainly early jurassic late triassic and late permian reflecting an enduring exhumed magmatic arc source nearby this might be in the adjacent median batholith but as a murihiku sediment source its jurassic triassic and permian elements are not well matched in terms of extent age and bulk compositions a connection between the murihiku proximal forearc and waipapa composite distal accretionary wedge terranes is probable with a common magmatic arc speculatively situated in the new england orogen eastern australia

icelandic volcanic ash and the mid holocene scots pine pinus sylvestris pollen decline in northern scotland a volcanic ash layer in peat from northern scotland has been identified and coincides exactly with an abrupt decline in pinus sylvestris l scots pine pollen frequencies this provides an isochrone time equivalent marker horizon with which to investigate the timing of the holocene pine decline furthermore two possible causes of the southward shift of the range of pinus in scotland c 4000 bp are suggested a direct effect of acid pollution by chemicals produced by the eruption of hekla h 4 or a volcanically induced climatic perturbation these possibilities have wider implications for the influence of volcanism on postglacial environmental change

coastal trapped waves alongshore pressure gradients and the california undercurrent abstractthe california undercurrent cuc a poleward flowing feature over the continental slope is a key transport pathway along the west coast of north america and an important component of regional upwelling dynamics this study examines the poleward undercurrent and alongshore pressure gradients in the northern california current system ccs where local wind stress forcing is relatively weak the dynamics of the undercurrent are compared in the primitive equation navy coastal ocean model and a linear coastal trapped wave model both models are validated using hydrographic data and current meter observations in the core of the undercurrent in the northern ccs in the linear model variability in the predominantly equatorward wind stress along the u s west coast produces episodic reversals to poleward flow over the northern ccs slope during summer however reproducing the persistence of the undercurrent during late summer requires additional incoming energy from sea level variability applied south

finite amplitude evolution of instabilities associated with the coastal upwelling front abstract a primitive equation model is used to study the finite amplitude evolution of instabilities associated with the coastal upwelling front simulations of increasing complexity are examined that represent idealizations of summer conditions off the oregon coast including cases with steady and with time variable wind in a domain with alongshore uniform bathymetry and with time variable wind in a domain with realistic oregon coast bathymetry the numerical results indicate that the fastest growing mode in this system has approximately an 8 10 km alongshore wavelength but that once the disturbances grow to finite amplitude the predominant alongfront scale increases rapidly because of nonlinear effects separation of the total kinetic energy into contributions from the alongshore average flow and perturbation about that average shows that the initial growth of the perturbation kinetic energy is due to potential energy conversion but transfer of energy from the kinetic energy of the alongshore average

radiating instability of a meridional boundary current a linear stability analysis of a meridional boundary current on the beta plane is presented the boundary current is idealized as a constant speed meridional jet adjacent to a semi infinite motionless far field the far field region can be situated either on the eastern or the western side of the jet representing a western or an eastern boundary current respectively it is found that when unstable the meridional boundary current generates temporally growing propagating waves that transport energy away from the locally unstable region toward the neutral far field this is the so called radiating instability and is found in both barotropic and two layer baroclinic configurations a second but important conclusion concerns the differences in the stability properties of eastern and western boundary currents an eastern boundary current supports a greater number of radiating modes over a wider range of meridional wavenumbers it generates waves with amplitude envelopes that decay slowly with distance from the current the radiating waves tend to have an asymmetrical horizontal structure they are much longer in the zonal direction than in the meridional a consequence of which is that unstable eastern boundary currents unlike western boundary currents have the potential to act as a source of zonal jets for the interior of the ocean

impacts of the mesoscale ocean atmosphere coupling on the peru chile ocean dynamics the current induced wind stress modulation the ocean dynamical responses to the surface current wind stress interaction at mesoscale are investigated in the south east pacific using a high resolution regional ocean atmosphere coupled model two simulations are compared one includes the surface current in the wind stress computation while the other does not in the coastal region absolute wind velocities are different between the two simulations but the wind stress remains very similar as a consequence the mean regional oceanic circulation is almost unchanged on the contrary the mesoscale activity is strongly reduced when taking into account the effect of the surface current on the wind stress this is caused by a weakening of the eddy kinetic energy generation near the coast by the wind work and to intensified offshore eddy damping we show that above coherent eddies the current stress interaction generates eddy damping through ekman pumping and eddy kinetic energy dissipation through wind work this alters significantly the coherent eddy vertical structures weakening the temperature and vorticity anomalies and increasing strongly the vertical velocity anomalies associated to eddies

anomalous chlorofluorocarbon uptake by mesoscale eddies in the drake passage region the role of mesoscale eddies in the uptake of anthropogenic chlorofluorocarbon 11 cfc 11 gas is investigated with a 1 20 eddy resolving numerical ocean model of a region of the southern ocean with a relatively fast air sea equilibrium time scale about a month the air sea cfc 11 flux quickly responds to the changes in the mixed layer cfc 11 partial pressure pcfc 11 at the mesoscale significant correlations are observed between pcfc 11 anomaly anomalies in sea surface temperature sst net heat flux and mixed layer depth an eddy centric analysis of the simulated cfc 11 field suggests that anticyclonic warm core eddies generate negative pcfc 11 anomalies and cyclonic cold core eddies generate positive anomalies of pcfc 11 surface pcfc 11 is modulated by mixed layer dynamics in addition to cfc 11 air sea fluxes a negative cross correlation between mixed layer depth and surface pcfc 11 anomalies is linked to higher cfc 11 uptake in anticyclones and lower cfc 11 uptake in cyclones especially in winter an almost exact asymmetry in the air sea cfc 11 flux between cyclones and anticyclones is found

an outline tephrochronology for the holocene of the north of ireland geochemically typed thin layers of icelandic holocene tephras form a tephrochronology for the north of ireland tephrochronology construction is based on geochemical linkage with dated historic icelandic eruptions and high precision multisample radiocarbon dating comparison with geochemically typed holocene layers at sites throughout scotland and northern england shows that some layers are widespread throughout much of the northern british isles other layers of known historic date have so far been detected only in ireland

average circulation seasonal cycle and mesoscale dynamics of the peru current system a modeling approach h isolines the pccc appears to be directly forced by the cyclonic wind stress curl the model is able to produce the upwelling front the cold water tongue which extends toward the equator and the equatorial front as described in the literature model seasonal changes in sst and ssh are compared to measurements for the central pcs model eke is 10 to 30 lower than the observations the model eddy diameters follow a strong equatorward increase the injection length scales derived from the energy spectra strongly correlate to the rossby radius of deformation confirming the predominant role of baroclinic instability at 3 s the model solution appears to switch from a turbulent oceanic regime to an equatorial regime dominated by zonal currents

late quaternary icelandic tephras in ireland and great britain detection characterization and usefulness microscopic studies of late quaternary tephras from iceland yield a detailed tephrochronology in deposits of the british isles where the quantities of volcanic glass employed are much less than those used to construct almost any other late quatemary tephrochronology we summarize improved methods of isolating extremely sparse glass shards for light microscope and electron microprobe analysis and provide major element geochemistry for 20 volcanic glass layers detected in ireland including those which comprise an outline historic tephrochronology for ireland the paper highlights possible limitations of chronology construction when attempting to separate dated tephras whose major element geochemistries are almost identical tephras in other parts of the british isles and europe are used with those in ireland to demonstrate further applications of tephrochronology especially for dating deposits where other dating methods e g radiocarbon have proved difficult