a 4500 year proxy climate record from peatlands in the north of ireland the identification of widespread summer drought phases abstract mid to late holocene high resolution testate amoebae derived water table reconstructions from two peatlands in the north of ireland are presented the proxy climate records are dated and correlated using a combination of ams 14 c dating spheroidal carbonaceous particles and tephrochronology the reconstructions start prior to the hekla 4 tephra isochron 2395 2279 bc and thus span the last 4500 years the records are compiled by the process of tuning within chronological errors standardisation and stacking comparisons are made to existing palaeoclimate records from peatlands in northern britain and ireland and the compiled lake level record for mid latitude europe four coherent dry phases are identified in the records at ca 1150 800 bc 320 bc ad 150 ad 250 470 and ad 1850 2000 recent research has shown that peat derived water table reconstructions reflect summer water deficit and therefore the dry phases are interpreted as periods with a higher frequency and or greater magnitudes of summer drought these drought phases occur during periods of relatively low 14 c production which may add support to the hypothesis of persistent solar forcing of climate change during the holocene any relationship with the north atlantic stacked drift ice record is less clear

towards a holocene tephrochronology for the faroe islands north atlantic abstract the faroe islands hold a key position in the north atlantic region for tephra studies due to their relative proximity to iceland several tephras have been described over the last 50 years in peat and lake sediment sequences including the type sites for the saksunarvatn and mjauvotn tephras here we present a comprehensive overview of holocene tephras found on the faroe island in total 23 tephra layers are described including visible macrotephras such as the saksunarvatn and hekla 4 tephras and several cryptotephras the importance of tephras originally described from the faroe islands is highlighted and previously unpublished results are included in addition full datasets for several sites are published here for the first time the saksunarvatn ash now considered to be the result of several eruptions rather than one major eruption can be separated into two phases on the faroe islands one early phase with two precursor eruptions with lower mgo concentrations 4 5 5 0 wt than the main eruption and a later phase with higher mgo concentrations 5 5 6 0 wt including the visible saksunarvatn ash the tjornuvik tephra previously considered to be a primary deposit is now interpreted as a reworked tephra with material from at least two middle holocene eruptions of hekla several of the tephras identified on the faroe islands provide useful isochrons for climate events during the holocene

fine scale variability of isopycnal salinity in the california current system this paper examines the finescale structure and seasonal fluctuations of the isopycnal salinity of the california current system from 2007 to 2013 using temperature and salinity profiles obtained from a series of underwater glider surveys the seasonal mean distributions of the spectral power of the isopycnal salinity gradient averaged over submesoscale 12 30 km and mesoscale 30 60 km ranges along three survey lines off monterey bay point conception and dana point were obtained from 298 transects the mesoscale and submesoscale variance increased as coastal upwelling caused the isopycnal salinity gradient to steepen areas of elevated variance were clearly observed around the salinity front during the summer then spread offshore through the fall and winter the high finescale variances were observed typically above 25 8 kg m 3 and decreased with depth to a minimum at around 26 3 kg m 3 the mean spectral slope of the isopycnal salinity gradient with respect to wavenumber was 0 19 0 27 over the horizontal scale of 12 60 km and 31 to 35 of the spectra had significantly positive slopes in contrast the spectral slope over 12 30 km was mostly flat with mean values of 0 025 0 32 an increase in submesoscale variability accompanying the steepening of the spectral slope was often observed in inshore areas e g off monterey bay in winter where a sharp front developed between the california current and the california under current and the lower layers of the southern california bight where vigorous interaction between a synoptic current and bottom topography is to be expected

on sampling the ocean using underwater gliders surface to 1000 m and back took 5 6 h and covered 5 3 km resulting in a horizontal speed of 0 26 m s 1 seasoar undulated between the surface and 400 m completing a cycle in 11 min while covering 2 6 km for a speed of 3 9 m s 1 adjacent profiles of temperature and salinity are compared between the two platforms to prove that each is accurate spray and seasoar data are compared through sections isopycnal spatial series and wave number spectra the relative slowness of the glider results in the projection of high frequency oceanic variability such as internal waves onto spatial structure the projection is caused by doppler smearing because of finite speed and aliasing due to discrete sampling the projected variability is apparent in properties measured on depth surfaces or in isopycnal depth no projected variability is seen in observations of properties on constant density surfaces because internal waves are intrinsically filtered wave number spectra suggest that projected variability affects properties at constant depth at wavelengths shorter than 30 km these results imply that isobaric quantities like geostrophic shear are valid at wavelengths longer than 30 km while isopycnal quantities like spice may be analyzed for scales as small as a glider measures

holocene tephrostratigraphy of varved sediment records from lakes tiefer see ne germany and czechowskie n poland a detailed holocene tephrostratigraphic framework has been developed for two predominately varved lake sediment sequences from ne germany lake tiefer see and central n poland lake czechowskie a total of thirteen tephras and cryptotephras of icelandic provenance were detected and chemically fingerprinted in order to define correlatives and to integrate known tephra ages into the sediment chronologies out of these three cryptotephras askja ad1875 askja s and h asseldalen were identified in both records thus allowing a detailed synchronization of developing high resolution palaeoenvironmental proxy data the early holocene saksunarvatn ash layer and the middle holocene lairg b and hekla 4 cryptotephras in lake tiefer see are further important anchor points for the comparison with other high resolution palaeoclimate records in central and northern europe tentative correlations of cryptotephras have been made with a historical basaltic grimsv otn eruption ad890 e ad856 and three late holocene rhyolitic eruptions including the 2 1 ka glen garry and two unknown high silicic cryptotephras of probably icelandic provenance 1 9 cal ka bp

dates of holocene icelandic volcanic eruptions from tephra layers in irish peats tephra from historic and prehistoric eruptions of oraefajokull and hekla iceland have been found in irish peats using a series of stratigraphically related high precision radiocarbon measure ments the date of a known age eruption has been satisfactorily estimated based on the same techniques the calendrical date of the hekla 4 eruption has been estimated as 2310 20 bc

improving the geoid combining altimetry and mean dynamic topography in the california coastal ocean satellite gravity mapping missions altimeters and other platforms have allowed the earth s geoid to be mapped over the ocean to a horizontal resolution of approximately 100 km with an uncertainty of less than 10 cm at finer resolution this uncertainty increases to greater than 10 cm achieving greater accuracy requires accurate estimates of the dynamic ocean topography dot in this study two dot estimates for the california current system with uncertainties less than 10 cm are used to solve for a geoid correction field the derived field increases the consistency between the dots and along track altimetric observations suggesting it is a useful correction to the gravitational field the correction is large compared to the dynamic ocean topography with a magnitude of 15 cm and significant structure especially near the coast the results are evidence that modern high resolution dynamic ocean topography products can be used to improve estimates of the geoid

poleward flows in the southern california current system glider observations and numerical simulation 1 three years of continuous spray glider observations in the southern california current system ccs are combined with a numerical simulation to describe the mean and variability of poleward flows in the southern ccs gliders provide upper ocean observations with good across shore and temporal resolution along two across shore survey lines while the numerical simulation provides a dynamically consistent estimate of the ocean state persistent poleward flows are observed in three areas within 100 km of the coast at point conception within the southern california bight scb and offshore of the scb and the santa rosa ridge srr poleward transport by the flows within the scb and offshore of the srr exceeds the poleward transport off point conception suggesting that the poleward flows are not continuous over the 225 km between observation lines the numerical simulation shows offshore transport between the survey lines that is consistent with some of the poleward flow turning offshore before reaching point conception the poleward current offshore of the srr is unique in that it is strongest at depths greater than 350 m and it is observed to migrate westward away from the coast this westward propagation is tied to westward propagating density anomalies originating in the scb during the spring summer upwelling season when wind stress curl is most strongly positive the across shore wave number frequency and phase speed of the westward propagation and the lack of across shore transport of salinity along isopycnals are consistent with first mode baroclinic rossby dynamics

palaeoecology of human impact during the historic period palynology and geochemistry of a peat deposit at abbeyknockmoy co gaiway ireland understanding the present condition of the cultural landscape requires a palaeoecological perspective with a particular emphasis on the growing intensity of human impact over the last few centuries detailed palynological investigations of the uppermost metre of peat at abbeyknockmoy bog were supplemented by silicon and titanium analyses to give additional proxy records for the intensity of human impact on the local landscape the ams radiocarbon chronology for this profile is constrained by the presence of the hekla 1 tephra isochron of ad 1104 the palaeoenvironmental evidence correlates closely to the local historical and archaeological records the results indicate a late iron age lull in human impact in the early centuries ad which is followed by increasing agricultural activity during the early christian period the establishment of the cistercian monastery of abbeyknockmoy in the twelfth century ad had a significant impact upon the landscape a peak in deforestation and farming activity is registered in the seventeenth and eighteenth centuries ad the silicon and titanium records correlate strongly with the pollen indicators for increased human disturbance

characterizing the semidiurnal internal tide off tasmania using glider data the spatial structure of the semidiurnal internal tide in the vicinity of tasmania is characterized using temperature and salinity data from seaglider and slocum glider deployments wavelet analysis of isopycnal displacements measured by the gliders was used to isolate the semidiurnal internal tide with a solid signal observed both to the east and to the south of tasmania the signal south of tasmania was attributed to local forcing while that to the east of tasmania was found to have propagated from the south east to the north west a result which supports previous studies indicating the presence of an internal tidal beam originating over the macquarie ridge south of new zealand displacement amplitudes were observed to be amplified in the vicinity of the continental slope with the incoming tidal beam shown to be both reflected and scattered on the continental slope and shelf and energy transferred to higher modes

trapped diurnal internal tides propagating semidiurnal internal tides and mixing estimates in the california current system from sustained glider observations 2006 2012 abstract from 2006 2012 along 3 repeated cross shore transects california cooperative oceanic fisheries investigations lines 66 7 80 and 90 in the california current system 33 609 shear and 39 737 strain profiles from 66 glider missions are used to estimate mixing via finescale parameterizations from a dataset containing over 52 000 profiles elevated diffusivity estimates and energetic diurnal d1 and semidiurnal d2 internal tides are found a within 100 km of the coast on lines 66 7 and 80 and b over the santa rosa cortes ridge srcr in the southern california bight scb on line 90 while finding elevated mixing near topography and associated with internal tides is not novel the combination of resolution and extent in this ongoing data collection is unmatched in the coastal ocean to our knowledge both d1 and d2 internal tides are energy sources for mixing at these latitudes the d1 internal tide is subinertial on line 90 d1 and d2 tides are equally energetic over the srcr the main site of elevated mixing within the scb numerous sources of internal tides at the rough topography in the scb produce standing and or partially standing waves on lines 66 7 and 80 the dominant energy source below about 100 m for mixing is the d1 internal tide which has an energy density of the d2 internal tide on line 80 estimated diffusivity estimated dissipation and d1 energy density peak in summer the d1 energy density shows an increasing trend from 2006 to 2012 its amplitude and phase are mostly consistent with topographically trapped d1 internal tides traveling with the topography on their right the observed offshore decay of the diffusivity estimates is consistent with the exponential decay of a trapped wave with a mode 1 rossby radius of 20 30 km despite the variable mesoscale it is remarkable that coherent internal tidal phase is found

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

glider observations of the north equatorial current in the western tropical pacific the north equatorial current nec of the pacific ocean advects subtropical subpolar and tropical water masses repeat underwater glider observations of the nec from june 2009 to january 2014 along 134 3 e provide absolute zonal geostrophic velocity transport and water mass structure at length scales of 10 1000 km the nec is strongest near the surface and persistent eastward undercurrents are identified deeper than potential density surface 26 kg m 3 at 9 6 n and 13 1 n mean transport from the surface to 27 3 kg m 3 and 8 5 n 16 5 n is 37 6 sv 106 m3 s 1 with a standard deviation of 15 6 sv the transport variability is greatest deeper than 26 kg m 3 due to undercurrent variability wavelet analysis at scales of 10 80 km reveals extrema of fine scale salinity variance along isopycnals spice variance high spice variance is found in the north pacific tropical water nptw and the north pacific intermediate water npiw with a spice variance minimum between water masses at 25 5 kg m 3 a horizontal cox number ch relates salinity variance at fine scales 10 80 km to that at greater length scales 120 200 km as a function of density ch is nearly vertically uniform indicating that the stirring of mean salinity gradients enhances fine scale salinity variance nptw with an estimated horizontal eddy diffusivity of order 104 m s 2 is a useful tracer for the region and may be used to relate the fine scale salinity variance to an eddy diffusivity

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

seasonal evolution of upper ocean horizontal structure and the remnant mixed layer 1 we discuss the seasonal evolution of upper ocean thermohaline structure at small horizontal scales the upper 350 m of a 1000 km long section in the subtropical north pacific was observed in winter spring and summer with 3 14 km horizontal resolution four vertical regions had distinct density and salinity structure the mixed layer remnant mixed layer high stratification layer and permanent thermocline the remnant mixed layer consists of water from the winter mixed layer left over after restratification the remnant mixed layer was most similar to the mixed layer in winter and spring and most similar to the high stratification layer below in summer the high stratification layer had elevated stratification that varied seasonally the permanent thermocline varied little seasonally and was horizontally and vertically uniform in comparison in all seasons density ratios showed that mixed layer s differences tended to compensate in density with the strongest tendency toward compensation in winter density ratios were temperature dominated in the remnant mixed layer consistent with salt fingering salinity anomalies were largest at the surface and decayed with depth in all seasons spectra of isopycnal depth and s anomalies along isopycnals are compared between the three seasons and four vertical layers isopycnal depth variance at 30 46 km wavelengths decreased from winter to spring to summer by a factor of 2 10 in stratified regions by treating salinity anomalies as a tracer the effective isopycnal diffusivity in the remnant mixed layer was estimated to be 1 4 m2 s 1 over 30 46 km wavelengths

volcanic ash from the 1362 a d oraefajokull eruption iceland in the greenland ice sheet a continuous record of electrical conductivity measurements ecm was made on site during the drilling of a 200 m ice core at summit greenland and was used to identify horizons in the ice that might be linked to volcanic eruptions in one detailed section that we studied a large peak in the number of particles two orders of magnitude above the background was measured the particle peak was not associated with an ecm peak however the particles were identified as volcanic ash on the basis of both particle morphology and chemical composition the ash composition suggests an explosive rhyolitic eruption and is believed to have originatedfrom oraefajokull in iceland in 1362 a d

towards a tephrochronology for the holocene of the north of ireland discrete layers of tephra have been found in both raised and blanket bogs in the north of ireland some of the layers have been identified to an icelandic source and in two cases specific eruptions of known radiocarbon age are suggested nine layers spanning the holocene are replicated in three lowland raised bogs one of the major layers has also been identified at a number of sites in two separate upland blanket peat systems and in a lake sediment

varve microfacies and varve preservation record of climate change and human impact for the last 6000 years at lake tiefer see ne germany the holocene sediment record of lake tiefer see exhibits striking alternations between well varved and non varved intervals here we present a high resolution multi proxy record for the past 6000

thermohaline variability in the upper ocean the main goal of this exploratory study is to determine how the temperature salinity relationship changes with horizontal length scale and depth in the ocean temperature and salinity were measured on a range of scales from 4 m to 1000 km towing a seasoar along isobars and isopycnals in the subtropical gyre of the north pacific during the winter of 1997 the wavelet transform technique is used to compute the horizontal density ratio and thermohaline variability as a function of scale and location measurements along an isobar in the mixed layer show that the horizontal density ratio is 1 at all scales observed that is horizontal temperature and salinity gradients tend to cancel each other in their effect on density thermohaline variability at small scales is intermittent and clusters around large scale thermohaline anomalies below the base of the mixed layer horizontal gradients of temperature are only partially opposed by salinity and the density ratio is close to 2 in the thermocline the distribution of thermohaline variability is uniform along isobars but intermittent and colocated at different scales along isopycnals density compensated variability ubiquitous in the mixed layer is reduced along deeper isopycnals compensation of horizontal temperature and salinity gradients supports recent theoretical ideas that mixing in the winter mixed layer depends on horizontal density gradients

tephra geochemistry a discussion of some persistent analytical problems distal tephrochronological studies are reliant upon precise and accurate geochemical quantitation this quantitation can involve difficulties not often encountered in more conventional petrology solving these problems is of particular importance in the holocene and late quaternary of northwest europe where numerous tephra layers of icelandic origin have been detected in peat bogs and lake and marine sediments electron probe microanalysis epma has proved the most applicable analytical technique when insufficient quantities of tephra are available for bulk analysis standard epma techniques require fine tuning to the tephra problem as the geochemical instability of glass is a common feature in many previous studies geochemical data of avoidably low quality have been produced and little attention appears to have been directed to modification of epma methods it is suggested that the black box approach to geochemical analysis should be avoided by the consideration of several factors these include

tephra analysis in ombrotrophic peatlands a geochemical comparison of acid digestion and density separation techniques ombrotrophic peatlands often lack any substantial local mineral component and therefore present exceptional opportunities for the extraction and identification of tephra horizons following concerns of shard geochemistry alteration during isolation using acid digestion an alternative methodology using heavy liquids has been proposed however harsh basic and acidic digestions are rarely required in organic rich ombrotrophic peatlands consequently this study tested for geochemical differences between tephra shards from a known rhyolitic eruption isolated from the same stratigraphic depth of a peat sequence using density separation and an acid digestion methodology typically applied to ombrotrophic peat samples and analysed using electron probe microanalysis findings suggest that the two samples could not be geochemically distinguished using visual and statistical methods and that in the context of rhyolitic tephras in ombrotrophic peats acid digestion can be used without significant effects on the interpretation of results density separation may still be required in peatlands with high mineral input and further work is required to examine the effect of the acid digestion technique on tephra of non rhyolitic compositions copyright 2015 john wiley sons ltd

thermohaline structure in the california current system observations and modeling of spice variance 1 upper ocean thermohaline structure in the california current system is investigated using sustained observations from autonomous underwater gliders and a numerical state estimate both observations and the state estimate show layers distinguished by the temperature and salinity variability along isopycnals i e spice variance mesoscale and submesoscale spice variance is largest in the remnant mixed layer decreases to a minimum below the pycnocline near 26 3 kg m 3 and then increases again near 26 6 kg m 3 layers of high low meso and submesoscale spice variance are found on isopycnals where large scale spice gradients are large small consistent with stirring of large scale gradients to produce smaller scale thermohaline structure passive tracer adjoint calculations in the state estimate are used to investigate possible mechanisms for the formation of the layers of spice variance layers of high spice variance are found to have distinct origins and to be associated with named water masses high spice variance water in the remnant mixed layer has northerly origin and is identified as pacific subarctic water while the water in the deeper high spice variance layer has southerly origin and is identified as equatorial pacific water the layer of low spice variance near 26 3 kg m 3 lies between the named water masses and does not have a clear origin both effective horizontal diffusivity h and effective diapycnal diffusivity v are elevated relative to the diffusion coefficients set in the numerical simulation but changes in h and v with depth are not sufficient to explain the observed layering of thermohaline structure

mid holocene glacier peak and mount st helens we tephra layers detected in lake sediments from southern british columbia using high resolution techniques abstract a glacier peak tephra has been found in the mid holocene sediment records of two subalpine lakes frozen lake in the southern coast mountains and mount barr cirque lake in the north cascade mountains of british columbia canada the age depth relationship for each lake suggests an age of 5000 5080 14 c yr b p 5500 5900 cal yr b p for the eruption which closely approximates the estimated age 5100 5500 14 c yr b p of the dusty creek tephra assemblage found near glacier peak the tephra layer which has not been reported previously from distal sites and was not readily visible in the sediments was located using contiguous sampling magnetic susceptibility measurements wet sieving and light microscopy the composition of the glass in pumice fragments was determined by electron microprobe analysis and used to confirm the probable source of this mid holocene tephra layer using the same methods the a d 1481 1482 mount st helens we tephra layer was identified in sediments from dog lake in southeastern british columbia suggesting the plume drifted further north than previously thought this high resolution method for identifying tephra layers in lake sediments which has worldwide application in tephrachronologic paleoenvironmental studies has furthered our knowledge of the timing and airfall distribution of holocene tephras from two important cascade volcanoes

along isopycnal variability of spice in the north pacific two hydrographic surveys in the gulf of alaska and the north pacific subtropical gyre are presented both surveys are roughly perpendicular to lateral temperature gradients and were collected in the summer when there was a shallow mixed layer and a seasonal thermocline isopycnal displacements and horizontal velocities are dominated by internal waves spice anomalies along isopycnals are examined to diagnose lateral stirring mechanisms the spectra of spice anomaly gradients along near surface isopycnals roughly follow power laws of kx0 6 0 2 variance spectra power laws of kx 1 4 0 2 and in most cases the spectra become redder at depth the near surface spectra are possibly consistent with the predictions of quasi geostrophic turbulence theory when surface buoyancy effects are accounted for but the spectra at depth are inconsistent with any quasi geostrophic theory probability distributions of spice gradients exhibit a large peak at low gradients and long tails for large gradients symptomatic of fronts vertical coherence of the spice signal falls off with a decorrelation depth scale that has a maximum of about 80 m at 100 km wavelengths and depends on horizontal wavelength with a power law of approximately kx 1 2 lateral decorrelation length scales are 20 40 km close to the baroclinic rossby radius lateral stirring occurs over large scales with average lateral displacements of about 200 km in the upper 75 m decreasing to 100 km at greater depths the depth variation of the statistics indicates that time history of tracer stirring on each isopycnal is important or that there are unconsidered depth dependent stirring mechanisms

submesoscale water mass spectra in the sargasso sea submesoscale stirring contributes to the cascade of tracer variance from large to small scales multiple nested surveys in the summer sargasso sea with tow yo and autonomous platforms captured submesoscale water mass variability in the seasonal pycnocline at 20 60 m depths to filter out internal waves that dominate dynamic signals on these scales spectra for salinity anomalies on isopycnals were formed salinitygradient spectra are approximately flat with slopes of 20 2 6 0 2 over horizontal wavelengths of 0 03 10km while the two to three realizations presented here might be biased more representative measurements in the literature are consistent with a nearly flat submesoscale passive tracer gradient spectrum for horizontal wavelengths in excess of 1km a review of mechanisms that could be responsible for a flat passive tracer gradient spectrum rules out i quasigeostrophic eddy stirring ii atmospheric forcing through a relict submesoscale winter mixed layer structure or nocturnal mixed layer deepening iii a downscale vortical mode cascade and iv horizontal diffusion because of shear dispersion of diapycnal mixing internal wave horizontal strain appears to be able to explain horizontal wavenumbers of 0 1 7 cycles per kilometer cpkm but not the highest resolved wavenumbers 7 30cpkm submesoscale subduction cannot be ruled out at these depths though previous observations observe a flat spectrum well below subduction depths so this seems unlikely primitive equation numerical modeling suggests that nonquasigeostrophic subinertial horizontal stirring can produce a flat spectrum the last need not be limited to mode one interior or surface rossby wavenumbers of quasigeostrophic theory but may have a broaderband spectrum extending to smaller horizontal scales associated with frontogenesis and frontal instabilities as well as internal waves

dating the glen garry tephra a widespread late holocene marker horizon in the peatlands of northern britain the distal icelandic tephra known as the glen garry layer has been dated by ams 14c at eight ombrotrophic peat bogs from northern england and scotland the geochemistry of all the tephra layers is consistent with there being only one glen garry tephra rather than two or more from eruptions of the same volcanic source at seven of the sites all in scotland the tephra layer was bracketed by 1 cm contiguous samples below at and above the horizon at the one english site walton moss cumbria a suite of 16 ams dates was applied to a 116 cm section of a peat core containing the tephra the resulting dates were calibrated and wiggle matched using the bcal and bpeat programmes to give an estimated age for the glen garry tephra of 2176 cal bp with a 2 range of 2210 1966 cal bp this 244 year range is an improvement on the 410 years calibrated date range for the date without the wiggle match this age estimate will allow future work on peat profiles and other sediments containing the tephra to use the date as a pinning point in age depth models and obviate the need for radiocarbon dating at this period

subthermocline eddies over the washington continental slope as observed by seagliders 2003 09 abstractin the california current system subthermocline lenslike anticyclonic eddies generated within the california undercurrent cu are one mechanism for lateral transport of the warm saline waters of the cu garfield et al established the name cuddies for eddies of this type and hypothesized that they account for a significant fraction of the offshore transport of cu water this study presents observations of subthermocline eddies collected from a time series of seaglider surveys in the northern california current system gliders made 46 crossings of subthermocline anticyclones and 17 crossings of subthermocline cyclones over 5 5 yr close inspection grouped these into 20 distinct anticyclones and 10 distinct cyclones water properties at the core of anticyclonic eddies were similar to those in the core of the cu over the continental slope these anticyclones are examples of cuddies anticyclonic cyclonic eddies had average radii of 20 4 20 6 km peak azimuthal current speeds of 0 25 0 23

the spatial distribution and annual cycle of upper ocean thermohaline structure 1 observations of the spatial distribution and persistence of thermohaline structure are presented and show how advection and diffusion affect a passive tracer more than two years of underwater glider observations in the central subtropical north pacific showed thermohaline variability over horizontal scales from 5 to 1300 km thermohaline fluctuations along isopycnals spice fluctuations were elevated in layers throughout the water column with the largest fluctuations near the surface and subtropical frontal regions fluctuations were uncorrelated between the layers but stirred by the same velocity field spice variance had local extrema in the vertical because of differences in source water properties and the influence of neighboring water masses spice variance spanned about three orders of magnitude along deeper isopycnals with larger variance where different water masses met and where velocity and vorticity variance were elevated horizontal wave number spectra of spice had slopes of 2 everywhere in the upper 1000 m submesoscale spice fluctuations had slopes in physical space near the ratio of the coriolis parameter to the buoyancy frequency f n consistent with predictions of quasi geostrophic theory in the mixed layer thermohaline structure had a significant annual cycle with smaller interannual differences thermohaline fluctuations left behind during restratification and isolated from the mixed layer decayed with time because of diffusion along isopycnals horizontal diffusivity estimates in the remnant mixed layer were 0 4 m2 s 1 at 15 28 km wavelengths and 0 9 m2 s 1 at 35 45 km wavelengths

site specific sediment responses to climate change during the last 140 years in three varved lakes in northern poland accurate dating and unambiguous chronological correlation using cryptotephras provide a powerful tool to compare the varved sediment records of the lakes gleboczek jg czechowskie jc and jelone

the flow of the undercurrent over the continental borderland off southern california 1 iniroduction 2 background the bottom topography off southern california has been the cc a slow had equatornard flow is the eastern limb of termed a continental borderland to distinguish it from the ordinary the large scale anticyclonic gyre of the temperate north pacific shelf slope morphology found along most continental margins ocean the cc carries relatively cool low salinity waters of shepard and emuy 19411 islands shallow banks basins and subarctic origin to lower latitudes on average the core of the cc troughs form a complex bathymetric region extending from the has velocities of 0 10 to 0 15 m s and traces a path roughly coast to 200 lon offshore the southern california coastline has a parallel to the california baja california coastline localized concave curvature between the headland at point conception to measurements of flow can exceed 0 5 m s davis 19851 an the u s mexican border as a whole this region is referred to as instantaneous realization of the cc includes a tangle of meanders the california bight the geographic bathymetric dguration eddies and narrow jetlike flows and counterllows the cc lies at of the bight exm a pronounced influence upon the local circula varying distances off the coast and at the latitude of the tion patterns and heme upon the distributions of physical e u s mexican border there is a strong shoreward component to sverdrup and fleming 19411 and biological quantities e g the flow in most seasons especially summa the flow splits one allen 1945 owen 19801 during 1985 we conducted an oceano branch turns and flows northward into the california bight graphic survey off southern california the sampling grid was becoming the eastern limb of a cyclonic eddy centered about the designed to reveal the mumce of the geographic bathymetric offshore banks seasonally fall and winter a weak inshore features upon the circulation of the california current system countercurrent ic develops at the surface along various portion6 ccs especially the flow of the california undercurrent cu of the coastline reid et d 19581 at depth the cu cdes the survey grid also includes station lines mss the core of the waters of subtropical origin poleward along the continental slope california current cc and transects an offshore dipole eddy these waters are relatively warm and saline and have low mm simpson and lym this issue the station grid of this study trations of dissolved oxygen the cu also demonstrates a welldiffers considerably from that used by the california cooperative defined seasonality and at times opposes the overlying dace oceanic fisheries investigations calcofi surveys in both its flow maps and sections of the long term seasonal means of relaspatial resolution and depth of sampling the objectives of thic tive geostrophic velocity and distributions of ocean characteristics report are 1 to examine the spatial continuity of the cu through for the ccs are available in calcofi atlas 30 lym et d 19821 the complex bathymeny of the bight 2 to trace the poleward for a comprehensive review of the long term seasonal large scale paths and offshore spread of waters of southern origin transported description of the ccs the readex is referred to recent papas by by the cu 3 to contrast this subsurface flow with the surface hickey 1979 chelton 19841 and lynn andslnpsm 19871 and flow and 4 to compare these results with the long term calcofi to important references of pioneering work given therein mean conditions

snapshots in time precise correlations of peat based proxy climate records in scotland using mid holocene tephras mid holocene tephra layers have been located and geochemically analysed from seven ombrotrophic bogs in scotland the tephras found in these scottish peats occur as stratigraphically discrete horizons not visible to the naked eye and originate from volcanic activity in iceland identifying and geochemically typing the tephra layers can enable precise correlations between sites on regional scales depending on the spatial extent of the airfall events dispersal of both the glen garry and hekla 4 tephras is excellent over scotland enabling snapshot views of the past at the time of these tephra depositions palaeoecological analyses have also been undertaken on these bogs providing detailed reconstructions of past changes in bog vegetation and surface wetness a proxy for past climates correlations between the ombrotrophic bogs at the time of the glen garry tephra revealed significant differences between the proxy climate records in the north and the south of scotland suggesting asynchronous changes between northern scotland and the rest of great britain

mixing of a tracer in the pycnocline a patch of sulfur hexafluoride was released in may 1992 in the eastern north atlantic on an isopycnal surface near 300 m depth and was surveyed over a period of 30 months as it dispersed across and along isopycnal surfaces the diapycnal eddy diffusivity k estimated for the first 6 months was 0 12 0 02 cm2 s while for the subsequent 24 months it was 0 17 0 02 cm2 s the vertical tracer distribution remained very close to gaussian for the full 30 months as the root mean square rms dispersion grew from 5 to 50 m lateral dispersion was measured on several scales the growth of the rms width of the tracer streaks from less than 100 m to approximately 300 m within 2 weeks implies an isopycnal diffusivity of 0 07 m2 s at scales of 0 1 to 1 km larger than expected from the interaction between vertical shear of the internal waves and diapycnal mixing teasing of the overall patch initially about 25 km across into streaks with an overall length of 1800 km within 6 months supports predictions of exponential growth by the mesoscale strain field at a rate of 3 0 5 10 7 s 1 the rms width of these streaks estimated as 3 km and maintained in the face of the streak growth indicates an isopycnal diffusivity of 2 m2 s at scales of 1 to 10 km much greater than expected from internal wave shear dispersion the patch was painted in albeit streakily by 12 months confirming expectations from analytical and numerical models homogenization of the patch continued during the subsequent 18 months while the patch continued to spread with an effective isopycnal eddy diffusivity on the order of 1000 m2 s acting at scales of 30 to 300 km

estimation of exit velocity of volcanic plume from analysis of vortex structures abstract we propose a simple method for estimating the exit velocities of volcanic eruptions from the observation of volcanic plumes for this purpose we used a model of a vortex ring of an experimental jet which was developed in the engineering field to validate the model for the vortex structures of volcanic plumes we applied it to plumes generated in 3 d numerical simulations in 11 cases where exit velocity 66 8 200 5 m s is given as a boundary condition we successfully estimated it with 7 underestimation by analyzing the size and motion of the leading vortex ring that forms at the plume front using the same procedure we could also estimate the exit velocity by analyzing the trailing vortices that develop behind the vortex ring 14 underestimation from these results we conclude that i the model of the vortex ring proposed by the jet engineering studies is appropriate for the vortex ring at the front of simulated volcanic plumes and ii the model is also applicable to the trailing vortices of the plumes these conclusions indicate that we can estimate the time evolution of the exit velocity for a series of eruptions from observations of the vortex structures of the actual volcanic plumes by applying that method to an eruption of sakurajima volcano on february 15 2011 we found that following an increase during the first 10 s of the eruption the exit velocity remained constant at 40 m s up to 80 s after the onset of the eruption our method will be useful in understanding the time evolution of eruptive events such as the transitional behavior from stable column to column collapse from observations of volcanic plumes

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

underwater gliders reveal rapid arrival of el nino effects off california s coast 1 the 2009 2010 el nino marked the first occurrence of this climate phenomenon since the initiation of sustained autonomous glider surveillance in the california current system ccs spray glider observations reveal the subsurface effects of el nino in the ccs with spatial and temporal resolutions that could not have been obtained practically with any other observational method glider observations show that upper ocean waters in the ccs were unusually warm and isopycnals were abnormally deep during the el nino event but indicate no anomalous water masses in the region observed oceanic anomalies in the ccs are nearly in phase with an equatorial el nino index and local anomalies of atmospheric forcing these observations point toward an atmospheric teleconnection as an important mechanism for the 2009 2010 el nino s remote effect on the midlatitude ccs

observations of sound speed fluctuations in the western philippine sea in the spring of 2009 as an aid to understanding long range acoustic propagation in the philippine sea statistical and phenomenological descriptions of sound speed variations were developed two moorings of oceanographic sensors located in the western philippine sea in the spring of 2009 were used to track constant potential density surfaces isopycnals and constant potential temperature surfaces isotherms in the depth range 120 2000 m the vertical displacements of these surfaces are used to estimate sound speed fluctuations from internal waves while temperature salinity variability along isopycnals are used to estimate sound speed fluctuations from intrusive structure often termed spice frequency spectra and vertical covariance functions are used to describe the space time scales of the displacements and spiciness internal wave contributions from diurnal and semi diurnal internal tides and the diffuse internal wave field related to the garrett munk gm spectrum are found to dominate the sound speed variability spi

tephrochronological studies in northern england tephrostratigraphic investigations of two upland blanket bogs in northern england show that micro scopic layers of tephra are present their geochemistry shows that they are identical to two icelandic tephra layers of known age found at sites in scotland and the north of ireland the work extends the regional tephro chronology of the mid holocene for the british isles

zonal evolution of alaskan stream structure and transport quantified with argo data the alaskan stream as flows west southwestward along the south side of alaska and the aleutian island arc a western boundary current at the northern edge of the north pacific subpolar gyre the argo float array has improved sampling of the gulf of alaska allowing quantification of the as s zonal evolution from 140 w to 175 w geostrophic alongshore transport of the as in the upper 1000 dbar referenced to an assumed level of no motion at 1000 dbar shows little change from east to west however alongshore absolute geostrophic transports in the top 2000 dbar obtained by combining mean absolute 1000 dbar velocities from float displacements with the geostrophic velocity fields generally increase to the west we estimate full depth transports by fitting a barotropic and the first two baroclinic modes calculated from a climatology to the absolute geostrophic velocities in the upper 2000 dbar and applying the velocities from these fits from 2000 dbar to the seafloor flowing west from its formation region at 140 w 145 w the full depth as becomes stronger more barotropic and also narrower once it reaches 160 w with along shore transports increasing from 16 4 4 9 sv 1 sv 106 m3 s 1 at 140 w to 32 6 5 2 sv at 175 w mean concentrations of relatively warm salty oxygen poor and nutrient rich pacific equatorial water pew in the as decrease from 17 8 0 3 to 8 5 0 5 between 140 w and 175 w however the volume transport of pew by the as exhibits little change over the pew density range between these longitudes

first discovery of holocene alaskan and icelandic tephra in polish peatlands despite the discovery of cryptotephra layers in over 100 peatlands across northern europe holocene cryptotephra layers have not previously been reported from polish peatlands here we present the first holocene tephra findings from two peatlands in northern poland at bagno kusowo peatland we identify the most easterly occurrence of the ad 860 b tephra recently correlated to the white river ash wrae derived from mount churchill alaska a shorter core from linje peatland contains tephra from the askja 1875 eruption extending the spatial distribution and regional importance of this icelandic tephra in eastern europe our research indicates the potential of cryptotephra layers to date and correlate the growing number of palaeoenvironmental studies being conducted on polish peatlands and contributes towards the development of a regional holocene tephrostratigraphy for poland

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

the tephrochronology of iceland and the north atlantic region during the middle and late quaternary a review the tephrochronology of iceland and the north atlantic region is reviewed in order to construct a unified framework for the last 400 kyr bp nearly all of the tephra layers described are also characterised geochemically a number of new tephra layers are analysed for the first time for their geochemical signature and a number of pre holocene tephra layers have been given an informal denotation the tephrostratigraphy of ash zone ii is highlighted where possible the rhyolitic tephra layers found outside iceland have been correlated to known icelandic tephra layers or to the volcanic source area the application of tephra fallout in various depositional environments is described and discussed copyright 2000 john wiley sons ltd

icelandic volcanic ash and the mid holocene scots pine pinus sylvestris decline in the north of ireland no correlation tephra linked pollen and dendrochronological studies were performed on mid holocene subfossil peats and pines and two lowland raised bogs in the north of ireland the results demonstrated that at these sites contrary to recent findings in the north of scotland there was no temporal link between the decline in pine pollen and tephra from the eruption of the icelandic volcano hekla h4

geochemical stability of fine grained silicic holocene tephra in iceland and scotland this paper tests two assumptions fundamental to the use of fine grained silicic tephras from iceland for creating chronological frameworks in northwest europe it is shown firstly that glass shards can retain their overall chemical integrity on at least a four millennial time scale in contrasting depositional environments in iceland and scotland and secondly that an acid digestion process the most practical method for extracting tephra from peat does not significantly bias the results of major element analysis by electron microprobe the implication is that there is great potential and an appropriate method for developing both the resolution and the spatial coverage of chronologies based on silicic icelandic tephras in northwest europe