application of tephrochronology to the timing and correlation of palaeoceanographic events recorded in holocene and late glacial shelf sediments off north iceland abstract the north icelandic shelf is partly distinguished by the tjornes fracture zone featuring numerous active basins in a mud dominated shelf environment late glacial and holocene high resolution sedimentary records from this area have been studied with tephrochronology as the main tool for correlation and for exact timing of palaeoceanographic events in the area data from three new piston cores from the shelf demonstrate the importance of tephra markers for the first chronological evaluation and correlation of the cores the correlation is extended with lithological logs and with magnetic susceptibility records a detailed multidisciplinary study including biostratigraphy and tephrochronology of a late holocene record of predominantly muddy sediments at the same location demonstrates that marked variations in the distribution of water masses occurred repeatedly through the last 4500 cal yr of special interest is the exact timing of a marked drop in sea surface temperature in the area indicated by ice rafting debris concentration to about 50 years before the hekla 3 eruption which occurred at 2980 cal yr bp this appears to predate most records of a general cooling event in nw europe by a couple of centuries two different possible age models one based on 14c dates combined with tephra markers and one based on tephra markers alone are discussed in context with the problem of different marine reservoir ages of the water masses in the area

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

late holocene ca 4 ka marine and terrestrial environmental change in reykjarfjordur north iceland climate and or settlement core b997 328pc is from the landward side of a 100 m deep basin in reykjarfjordur a small fjord on the north coast of the northwest peninsula of iceland this is an area that can be severely affected by incursions of polar sea ice but has not suffered marked land erosion during the settlement period the core is 422 cm in length and consists principally of fine grained muds with in situ molluscs eleven ams 14c dates on molluscs indicate a constant sediment accumulation rate of ca 1 cm 10 yr 1 for the last 4280 50 yr bp we measured and derived a variety of proxies for indications of changes in the nearshore environment these included physical properties and grain size mass accumulation rates micropalaeontology pollen and foraminifera multivariate analysis and constrained clustering were used to define major changes in the proxies in several parameters the major change in the fjord environment occurred close to 1000 14c yr ago thus approximately coincident with the onset of the settlement of iceland other changes are noted at around 1600 and 3400 14c yr ago betula pollen disappears from the record ca 1500 yr bp and there are peaks in marine productivity occurring ca 2 and 3 4 ka a major decline in carbonate accumulation and a sharp increase in the cold water benthic foraminifer elphidium excavatum forma clavata 400 yr ago represents the local marine signature of the little ice age none of the changes in our data can be explained adequately by a simple call to land use practices and an increase in land to sea transport but both the pollen and foraminiferal records indicate a decrease and even loss of warm elements in both flora and fauna over the past 4 kyr copyright 2001 john wiley sons ltd

multi proxy records showing significant holocene environmental variability the inner n iceland shelf hunafloi abstract over the last 50 yr the n iceland margin has seen dramatic changes in temperature and salinity associated with the relative dominance of warm atlantic water versus cold arctic or polar waters we report a study of holocene environmental changes to assess the sensitivity of this area on a longer timescale we present sedimentologic isotopic and biotic coccolith proxies from a 5 5 m piston core b997 330pc that was retrieved from a small basin on the inner n iceland shelf seven ams dates indicate a relatively constant rate of sediment accumulation which averaged 55 cm kyr sampling resolution of our proxies varied between 16 and 90 yr sample our data indicate substantial variability in environmental conditions over the last 10 000 cal yr total carbonate content and coccolith concentrations track each other and indicate that the early holocene was a time of low net carbonate accumulation net accumulation of carbonate reached maximum values in the mid to late holocene 4 2 cal ka but there has since been a substantial decrease with a minima during the little ice age north atlantic drift coccolith species show peaks in accumulation rates at 2 and 8 cal ka and low influx between 3 5 and 6 cal ka reworked neogene coccoliths occur also 8 ka and coincide with light 18 o values in the epifaunal foraminifera cibicides lobatulus principal component analysis indicates considerable covariance between biotic isotopic and sedimentological parameters three axes explain 84 of the variance in the data set and define three groups of interrelated variables a major change occurs ca 5 cal ka after which conditions become more variable with a 1 5 kyr cyclicity

ash layers from iceland in the greenland grip ice core correlated with oceanic and land sediments four previously known ash layers ash zones i and ii saksunarvatn and the settlement layer all originating in iceland have been identified in the central greenland ice core grip this correlation of the ash between the different environments is achieved by comparison of the chemical composition of glass shards from the ash this establishes and confirms detailed correlations between the different types of depositional records and the absolute dating of the younger part of the ice core by counting annual layers dates the eruptions accurately a precise connection with dates obtained by14c beyond the range of dendrochronology is established which provides an excellent confirmation of230th 234u dates from corals four additional icelandic ash layers have also been identified in the core but not yet correlated with known ash deposits

sensitivity of vatnajokull ice cap hydrology and dynamics to climate warming over the next 2 centuries 1 the sensitivity of vatnajokull ice cap to future climate change is examined using spatially distributed coupled models of ice dynamics and hydrology we simulate the evolving ice cap geometry mass balance velocity structure subglacial water pressures and fluxes and basin runoff in response to perturbations to a 1961 1990 reference climatology for a prescribed warming rate of 2 c per century simulated ice cap area and volume are reduced by 12 15 and 18 25 within 100 years respectively individual outlet glaciers experience 3 6 km of retreat in the first 100 years and a total retreat of 10 30 km over 200 years for the same applied warming our results suggest a maximum increase in glacier derived runoff of 25 after 130 years ice cap thinning and retreat alters vatnajokull s subglacial hydraulic catchment structure in the simulations with up to several kilometers of local hydraulic divide migration this serves to redistribute water among the major outlet rivers and in extreme cases to isolate river basins from glacially derived runoff glacier discharge from northern and northwestern vatnajokull distal from the coast appears to be the most robust to climate warming while discharge from vatnajokull s southern margin proximal to the coast is particularly vulnerable the latter reflects pronounced changes in the geometry of the southern outlet glaciers and has implications for glacier flood routing and frequency

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

glacier fluctuation and inferred climatology of langjokull ice cap through the little ice age abstract emerging paleoclimate records from proglacial lake hvitarvatn central iceland suggest that langjokull ice cap attained its maximum holocene extent within the last 400 years with the aim of constructing glaciological models and appropriate model inputs for holocene simulations of langjokull we begin by simulating the evolution of langjokull through the little ice age to present a period for which we have some constraint on ice cap geometry using modern measured mass balance distributions 1997 2003 and meteorological data from nearby hveravellir we derive a reference precipitation field for the period 1961 1990 over the ice cap our simulations suggest langjokull attained its maximum little ice age volume around 1840 with a second local maximum around 1890 the two outlet glaciers terminating in hvitarvatn nor urjokull and su urjokull advance slowly into the lake occupying their maximum lake area in the late 19th century and retreat comparatively rapidly in the mid to late 20th century simulations of nor urjokull are much more faithful to the geomorphic evidence than are simulations of su urjokull potentially suggesting a difference in dynamics between these two glaciers while only 35 of the hvitarvatn catchment area is ice covered meltwater from langjokull comprises 70 of the water input to the lake two thirds of this input from the ice cap is transported as groundwater simulated glacier derived discharge to the lake through the little ice age suggests that a sediment concentration of 1 5 kg m 3 would have resulted in the transport of 1 5 10 11 kg of material to the lake over the last 300 years comparable to the estimated mass of sediment in the most recently deposited sedimentary unit in the lake

historic volcanism european dry fogs and greenland acid precipitation 1500 b c to a d 1500 historic dry fogs in europe acid precipitation in greenland and major explosive volcanic eruptions correlate well with each other between 1500 b c and a d 1500 european mediterranean and icelandic volcanic eruptions appear to be the source of at least five of the nine largest acidity signals found in greenland ice for this period between 152 b c and a d 43 eruptions of sulfur rich mount etna probably supplied about 15 percent of the smaller acidity signals

persistent positive north atlantic oscillation mode dominated the medieval climate anomaly the medieval climate anomaly mca was the most recent pre industrial era warm interval of european climate yet its driving mechanisms remain uncertain we present here a 947 year long multidecadal north atlantic oscillation nao reconstruction and find a persistent positive nao during the mca supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker nao conditions into the little ice age lia globally distributed proxy data suggest that this nao shift is one aspect of a global mca lia climate transition that probably was coupled to prevailing la nina like conditions amplified by an intensified atlantic meridional overturning circulation during the mca

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

stabilization of glaciers terminating in closed water bodies evidence and broader implications 1 the behavior of glaciers terminating in deep water is determined by the interaction of buoyancy iceberg production and the sensitivity of ice flow to subtle changes in resistance at the glacier bed modeling efforts assume rapid evacuation of icebergs but some glaciers terminate in closed basins where icebergs may accumulate multibeam bathymetric survey of a glacial lake in iceland that received outlet glaciers during the little ice age document near parallel flow of narrow ice fingers that extended up to 1 km beyond the grounding line these previously unseen features apparently occurred when iceberg production exceeded iceberg melt resulting in iceberg buttressing of the ice margin similar stabilization of ice flow may resolve long standing debates about past continental ice sheet behavior including the rapid readvance of the laurentide ice sheet into lake superior ca 11 ka and the genesis of glacial flutes observed in the central arctic ocean basin

volcanic forcing of climate over the past 1500 years an improved ice core based index for climate models 1 understanding natural causes of climate change is vital to evaluate the relative impacts of human pollution and land surface modification on climate we have investigated one of the most important natural causes of climate change volcanic eruptions by using 54 ice core records from both the arctic and antarctica our recently collected suite of ice core data more than double the number of cores ever used before reduces errors inherent in reconstructions based on a single or small number of cores which enables us to obtain much higher accuracy in both detection of events and quantification of the radiative effects we extracted volcanic deposition signals from each ice core record by applying a high pass loess filter to the time series and examining peaks that exceed twice the 31 year running median absolute deviation we then studied the spatial pattern of volcanic sulfate deposition on greenland and antarctica and combined this knowledge with a new understanding of stratospheric transport of volcanic aerosols to produce a forcing data set as a function of month latitude and altitude for the past 1500 years we estimated the uncertainties associated with the choice of volcanic signal extraction criteria ice core sulfate deposition to stratospheric loading calibration factor and the season for the eruptions without a recorded month we forced an energy balance climate model with this new volcanic forcing data set together with solar and anthropogenic forcing to simulate the large scale temperature response the results agree well with instrumental observations for the past 150 years and with proxy records for the entire period through better characterization of the natural causes of climate change this new data set will lead to improved prediction of anthropogenic impacts on climate the new data set of stratospheric sulfate injections from volcanic eruptions for the past 1500 years as a function of latitude altitude and month is available for download in a format suitable for forcing general circulation models of the climate system

high resolution alkenone sea surface temperature variability on the north icelandic shelf implications for nordic seas palaeoclimatic development during the holocene the palaeoceanography of the northern icelandic shelf for the holocene period was reconstructed from alkenone indices measured in core jr51 gc35 this contains a continuous record of holocene sedimentation spanning 0 10 2 cal kyr bp with a resolution of 20 yr cm we have identified a general holocene cooling trend that has superimposed millennial scale oscillations of 28c their timing is in close agreement with the timing of glacier advances in northern iceland for the later half of the holocene the alkenone sea surface temperature sst record from jr51 gc35 correlates with proxy data for the strength of nadw formation recorded in cores south of iceland this is interpreted as evidence of a close connection existing between north icelandic sea surface temperatures and the north atlantic meridonal overturning circulation the timing of the millennial scale sst variability in our core off north iceland is found to be out of phase or anti phased with the sst variability of a record in the eastern nordic seas md952011 this suggests that the evolution of holocene climate in the nordic seas was more complex than previously proposed and it is likely to be caused by differential responses of the irminger and norwegian currents and modulated by changes in atmospheric circulation analogous to the north atlantic oscillation

a highly unstable holocene climate in the subpolar north atlantic evidence from diatoms a composite record lo09 14 of three sediment cores from the subpolar north atlantic reykjanes ridge was investigated in order to assess surface ocean variability during the last 11 kyr the core site is today partly under the influence of the irminger current ic a branch of the north atlantic drift continuing northwestward around iceland however it is also proximal to the sub arctic front saf that may cause extra dynamic hydrographic conditions we used statistical methods applied to the fossil assemblages of diatoms to reconstruct quantitative sea surface temperatures ssts our investigations give evidence for different regional signatures of holocene surface oceanographic changes in the north atlantic core lo09 14 reveal relatively low and highly variable ssts during the early holocene indicating a weak ic and increased advection of subpolar water over the site a mid holocene thermal optimum with a strong ic occurs from 7 5 to 5 kyr and is followed by cooler and more stable late holocene surface conditions several intervals throughout the holocene are dominated by the diatom species rhizosolenia borealis which we suggest indicates proximity to a strongly defined convergence front most likely the saf several coolings reflecting southeastward advection of cold and ice bearing waters occur at 10 4 9 8 8 3 7 9 6 4 4 7 4 3 and 2 8 kyr the cooling events recorded in the lo09 14 ssts correlate well with both other surface records from the area and the nadw reductions observed at odp site 980 indicating a surface deepwater linkage through the holocene

geochemical and climatic effects of increased marine organic carbon burial at the cenomanian turonian boundary perhaps the most significant event in the cretaceous record of the carbon isotope composition of carbonate1 2 other than the 1 2 5 negative shift in the carbon isotope composition of calcareous plankton at the cretaceous tertiary boundary3 is the rapid global positive excursion of 2 13c enrichment which took place between 91 5 myr and 90 3 myr late cenomanian to earliest turonian c t boundary event 1 4 5 this excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon tdc reservoir resulting from an increase in rate of burial of 13c depleted organic carbon which coincided with a major global rise in sea level5 during the so called c t oceanic anoxic event oae 6 here we present new data from nine localities which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the c t boundary7 8 is nearly synchronous with that for carbonate and is widespread throughout the tethys and atlantic basins fig 1 as well as in more high latitude epicontinental seas the postulated increase in the rate of burial of organic carbon may have had a significant effect on co2 and o2 concentrations in the oceans and atmosphere and consequent effects on global climate and sedimentary facies

responses of mountain ice caps in central iceland to holocene climate change abstract a chronology of holocene fluctuations of small outlet glaciers from the regnabu ajokull ice cap on hrutfell central iceland allows comparison of their sensitivity with the margin of the nearby langjokull icefield to ascertain which frequencies of climatic variability are recorded by adjacent glaciers of different size dating utilised tephra layers in aeolian soils lying on between and beneath moraine ridges key marker isochrones dating from the hekla 4 tephra c 3 8 ka bp to katla a d 1918 provide unequivocal bracketing ages the stratigraphy and geochemical fingerprinting of tephras on younger moraines allows subdivision of little ice age moraines five groups of moraines are identified at c 4 5 5 0 c 3 0 3 5 ka bp c 2 0 2 5 ka bp and from the little ice age at c a d 1700 and in the late 19th early 20th century these represent a neoglacial sequence in which steep small glaciers readvanced to similar positions during what are here termed little ice age type periods liatps in contrast the nearby margins of langjokull show evidence of a late nineteenth century advance only suggesting that this was the holocene maximum for this glacier the contrasting responses of local glaciers and the large icefield are explained by their different sizes and response times so that the preserved moraine record is largely pre conditioned by the glacier type in general the forefields of steep fast responding glaciers contain more complete archives of holocene climatic changes than do the margins of the large icefields

latest pleistocene and holocene alpine glacier fluctuations in scandinavia abstract during the early holocene abrupt decadal to centennial scale climate variations caused significant glacier variations in norway increased freshwater inflow to the north atlantic and arctic oceans has been suggested as one of the most likely mechanisms to explain the abrupt and significant lateglacial and early holocene climatic events in nw europe the largest early holocene glacier readvances occurred 11 200 10 500 10 100 9700 9200 and 8400 8000 cal yr bp the studied norwegian glaciers apparently melted away at least once during the early mid holocene the period with the most contracted glaciers in scandinavia was between 6600 and 6000 cal yr bp subsequent to 6000 cal yr bp the glaciers started to advance and the most extensive glaciers existed at about 5600 4400 3300 2300 1600 cal yr bp and during the little ice age times with overall less glacier activity were apparently around 5000 4000 3000 2000 and 1200 cal yr bp it has been proposed that several glacier advances occurred in scandinavia including northern sweden at 8500 7900 7400 7200 6300 6100 5900 5800 5600 5300 5100 4800 4600 4200 3400 3200 3000 2800 2700 2000 1900 1600 1200 1000 and 700 200 cal yr bp glaciers in northern sweden probably reached their greatest little ice age extent between the 17th and the beginning of the 18th centuries evidence for early holocene glacier advances in northern scandinavia however has been questioned by more recent multi disciplinary studies the early to mid holocene glacier episodes in northern sweden may therefore be questioned most norwegian glaciers attained their maximum little ice age extent during the mid 18th century cumulative glacier length variations in southern norway based on marginal moraines dated by lichenometry and historic evidence show an overall retreat from the mid 18th century until the 1930s 40s subsequently most norwegian glaciers retreated significantly maritime outlet glaciers with short frontal time lags 15 20 years continued their retreat to the 1970s and 1980s however maritime glaciers started to advance as a response to higher winter accumulation during the first part of the 1990s after 2000 several of the observed glaciers have retreated remarkably fast annual frontal retreat 100 m mainly due to high summer temperatures the general glacier retreat during the early holocene and the neoglacial advances after 6000 cal yr bp are in line with orbital forcing due to the decrease of northern hemisphere summer solar insolation and the increase in winter insolation in addition regional weather modes such as the north atlantic oscillation nao and the arctic oscillation ao play a significant role with respect to decadal and multi decadal climate variability

two millennia of north atlantic seasonality and implications for norse colonies 18o values of mollusks recovered from near shore marine cores in northwest iceland quantify significant variation in seasonal temperature over the period from 360 b c to a d 1660 twenty six aragonitic bivalve specimens were selected to represent intervals of climatic interest by using core sedimentological characteristics carbonate powder was sequentially micromilled from shell surfaces concordant with growth banding and analyzed for stable oxygen 18o and carbon 13c isotope values because 18o values record subseasonal temperature variation over the lifetime of the bivalves these data provide the first 2 000 year secular record of north atlantic seasonality from ca 360 cal yr b c to cal yr a d 1660 notable cold periods 360 b c to 240 b c a d 410 and a d 1380 to 1420 and warm periods 230 b c to a d 140 and a d 640 to 760 are resolved in terms of contrast between summer and winter temperatures and seasonal temperature variability literature from the viking age ca 790 to 1070 during the establishment of norse colonies and later in iceland and greenland permits comparisons between the 18o temperature record and historical records thereby demonstrating the impact of seasonal climatic extremes on the establishment development and in some cases collapse of societies in the north atlantic

holocene variability of the north atlantic irminger current on the south and northwest shelf of iceland abstract the irminger current ic transports heat and nutrients to the icelandic shelf and its fluctuations are strongly linked to variations in the strength of the north atlantic surface flow from the south by using benthic foraminiferal assemblages and their stable isotopic composition in two marine sediment cores located in the pathway of the ic on the west iceland shelf we were able to derive bottom water temperature estimates at a 100 year resolution and define the temperature difference between the core sites throughout the holocene these are the first transfer function bottom water temperatures presented from the icelandic shelf based on benthic foraminiferal assemblages our findings demonstrate a delayed holocene thermal maximum in the marine current system around iceland compared to the northern hemisphere summer insolation receipts the maximum heat transport in the ic occurred between 8 and 4 ka years later than some previous records report a reconstruction of the ambient seawater 18o based on paired samples of c2 transfer function temperature estimates and oxygen isotopic composition indicates repeated freshwater input to the n atlantic inflow in the early holocene impacting the current system before 8 ka two fundamental regime shifts are evident in the paleoceanography and foraminiferal properties during the holocene occurring around 8 ka towards more stable conditions and again around 4 ka towards more unstable conditions increasing fluctuation with similarities to the great salinity anomaly in the 1970s occur after 4 ka

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

thermal characteristics and impact of climate change on mountain permafrost in iceland 1 this study contains the first quantitative description of mountain permafrost in iceland obtained through analysis of four ground temperature time series from recently established shallow boreholes at high altitude 900 m above sea level in central and eastern iceland permafrost is present at three of the four boreholes where temperatures range from 2 to 0 c during the data logging period 2004 2006 the thickness of the active layer at the individual sites varied between less than 2 m and more than 5 m mainly owing to differences in near surface ice content the ground temperature profiles are nonlinear with near surface temperature perturbations considered to be related to a recent warming of the ground surface at the one nonpermafrost site the insulating influence of winter snow cover is more pronounced a one dimensional heat conduction model was calibrated using ground temperature measurements and driven by surface temperature time series the model results reproduce the measured ground temperature pattern well this simplified model simulating the results of possible future climate scenarios indicates that permafrost degradation will occur at these sites within decades depending on climate scenarios chosen and subsurface ice content

varve studies at hector lake alberta canada and the relationship between glacial activity and sedimentation glacial lake sedimentary records from hector lake in banff national park alberta are examined with the aim of clarifying the relationship between glacial activity and outwash sedimentation rhythmic couplets in lake bottom sediments provide a method for accurate documentation and dating of recent sedimentation chronology as analysis of 137cs content indicates that the couplets are of annual periodicity i e varves a comparison of sedimentation rate records with recent regional glacial history indicates that high sedimentation rates of one to a few decades duration occur either during and immediately following periods of moraine deposition ie maximum ice stands or during periods of rapid ice recession comparison of sedimentary records with somewhat longer term glacial and vegetation records indicates that sedimentation rate variations of several centuries duration closely parallel changes in upvalley ice extent over this time scale high sedimentation rates occur during periods of relatively increased ice extent low rates during periods of reduced ice extent within this general pattern however sedimentation rates may remain very high for nearly a century following maximum ice stands due to the exposure of unstable glaciogenic deposits to fluvial reworking during ice recession

a robust multisite holocene history of drift ice off northern iceland implications for north atlantic climate an important indicator of holocene climate change is provided by evidence for variations in the extent of drift ice a proxy for drift ice in iceland waters is provided by the presence of quartz q

geochemical and isotopic constraints on the age and origin of the nidar ophiolitic complex ladakh india implications for the neo tethyan subduction along the indus suture zone abstract the nidar ophiolite complex is exposed within the indus suture zone in eastern ladakh india the suture zone is considered to represent remnant neo tethyan ocean that closed via subduction as the indian plate moved northward with respect to the asian plate the two plates ultimately collided during the middle eocene the nidar ophiolite complex comprises a sequence of ultra mafic rocks at the base gabbroic rocks in the middle and volcano sedimentary assemblage on the top earlier studies considered the nidar ophiolite complex to represent an oceanic floor sequence based on lithological assemblage however present study based on new mineral and whole rock geochemical and isotopic data on bulk rocks and mineral separates indicate their generation and emplacement in an intra oceanic subduction environment the plutonic and volcanic rocks have nearly flat to slightly depleted rare earth element ree patterns the gabbroic rocks in particular show strong positive sr and eu anomalies in their ree and spidergram patterns probably indicating plagioclase accumulation depletion in high field strength elements hfse in the spidergram patterns may be related to stabilization of phases retaining the hfse in the subducting slab and or fractional crystallization of titano magnetite phases the high radiogenic nd and low radiogenic sr isotopic ratios for these rocks exclude any influence of continental material in their genesis implying an intra oceanic environment nine point mineral whole rock sm nd isochron corresponds to an age of 140 32 ma with an initial 143nd 144nd of 0 513835 0 000053 end t 7 4 this age is consistent with the precise early cretaceous age of hauterivian 132 2 to 127 1 6 ma to aptian 121 1 4 to 112 1 1 ma for the overlying volcano sedimentary radiolarian bearing chert sequences based on well preserved radiolarian fossils kojima s ahmad t tanaka t bagati t n mishra m kumar r islam r khanna p p 2001 early cretaceous radiolarians from the indus suture zone ladakh northern india in news of osaka micropaleontologists nom spec vol 12 257 270 and cooling ages of 110 130 ma based on 39ar 40ar for nidar spontang ophiolitic rocks maheo g berttrand h guillot s villa i m keller f capiez p 2004 the south ladakh ophiolites nw himalaya india an intra oceanic tholeiitic arc origin with implications for the closure of the neo tethys chem geol 203 273 303 as these gabbroic and volcanic rocks are interpreted to be arc related the new sm nd age data may indicate that intra ocean subduction in the neo tethyan ocean may have started much before 140 32 ma as this date is interpreted as the age of crystallization of the arc magma present and published age data on the arc magmatic rocks from the indus suture zone may collectively indicate episodic magmatism with increasing maturity of the arc from more basic during 140 32 ma when the arc was immature through intermediate andesitic granodioritic at 100 ma to more felsic rhyolitic dioritic magmatism at 50 45 ma when the indian and the asian plates collided

evolution of the irminger and east icelandic current systems through the holocene revealed by diatom based sea surface temperature reconstructions abstract sediment core md99 2269 from the northern shelf of iceland has been studied to assess the stability of the east icelandic irminger current system during the holocene the 25 4 m long holocene section was studied with a 40 years average resolution the chronology is based on the combination of 24 14c ams dates and two tephra layers diatoms are utilized to quantify the development and variability of the august sea surface temperature sst for the last 11 5 cal kyr bp three different transfer function methods have been used to reconstruct august sst at the site weighted average partial least squares wa pls maximum likelihood ml and imbrie and kipp i k the combined use of the three methods allows the august sst reconstruction with a higher confidence level than with using only one statistical technique these three reconstructions generate very similar august sst trends through the holocene the onset of the holocene climate optimum is characterized at the site by a rapid august sst increase at 10 4 cal kyr bp of almost 4 c the holocene climate optimum is recorded between 10 4 and 4 7 cal kyr bp the august ssts were around 2 c warmer during the major part of the holocene compared with the august ssts for the later half of the holocene combining the diatom record with the benthic foraminifera records from the same core enables us to reconstruct the evolution of both surface and bottom water masses during the holocene this reconstruction shows dominance of the arctic waters throughout the water column at the onset of the holocene and subsequent increase of the influence of the atlantic water especially during the holocene climate optimum this strong dominance of atlantic water tends to decrease between 4 7 and 2 2 cal kyr bp especially in the upper part of the water column since 2 2 cal kyr bp the trend is reversed suggesting an increased influence of atlantic water at least in the upper water column

high resolution palaeoclimatology of the last millennium a review of current status and future prospects this review of late holocene palaeoclimatology represents the results from a pages clivar intersection panel meeting that took place in june 2006 the review is in three parts the principal high resolution proxy disciplines trees corals ice cores and documentary evidence emphasizing current issues in their use for climate reconstruction the various approaches that have been adopted to combine multiple climate proxy records to provide estimates of past annual to decadal timescale northern hemisphere surface temperatures and other climate variables such as large scale circulation indices and the forcing histories used in climate model simulations of the past millennium we discuss the need to develop a framework through which current and new approaches to interpreting these proxy data may be rigorously assessed using pseudo proxies derived from climate model runs where the answer is known the article concludes with a list of recommendations first more raw proxy data are required from the diverse disciplines and from more locations as well as replication for all proxy sources of the basic raw measurements to improve absolute dating and to better distinguish the proxy climate signal from noise second more effort is required to improve the understanding of what individual proxies respond to supported by more site measurements and process studies these activities should also be mindful of the correlation structure of instrumental data indicating which adjacent proxy records ought to be in agreement and which not third large scale climate reconstructions should be attempted using a wide variety of techniques emphasizing those for which quantified errors can be estimated at specified timescales fourth a greater use of climate model simulations is needed to guide the choice of reconstruction techniques the pseudo proxy concept and possibly help determine where given limited resources future sampling should be concentrated

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

chronology of late holocene climatic events in the northern north atlantic based on ams 14c dates and tephra markers from the volcano hekla iceland a combination of ams14c dating and tephrochronology has been used to date late holocene oceanographic events in a 335 cm marine record covering about 4600 cal yr with sedimentation rates exceeding 80 cm 1000 yr 1 the core site is located 50 km offshore on the northern icelandic shelf tephra markers from iceland serve to correlate the marine and terrestrial records especially notable is the presence of three geochemically correlated tephra markers from the icelandic volcano hekla hekla 4 hekla 3 and hekla 1104 benthic and planktonic foraminiferal abundance and distribution as well as the petrography of the sand fraction of the muddy shelf sediments are used as palaeoceanographic proxies the foraminiferal assemblages reflect a general cooling trend during the last 4600 yr a marked drop in sea surface temperatures is registered at about 3000 cal yr bp corresponding to the level of the hekla 3 tephra there is faunal indication of temperature amelioration during the medieval warm period and a cooling again during the little ice age periods of ice rafting events are indicated by ice rafted debris ird concentrations e g at around 3000 cal yr bp and during the little ice age the former event occurred just prior to the deposition of the hekla 3 tephra marker the largest holocene hekla eruption a correlation with terrestrial climatic events in iceland is presented a standard marine reservoir correction of 400 14c yr appears to be reasonable at least during periods with high influence of water masses from the irminger current on the northern icelandic shelf an increase to ca 530 14c yr may have occurred however when water masses derived from the east greenland current were dominant in the area copyright 2000 john wiley sons ltd

recent volcanic history of the veidivotn fissure swarm southern iceland an approach to volcanic risk assessment abstract the recent volcanic history of the southwestern part of the veidivotn fissure swarm southern iceland provides a basis for assessment of volcanic risk in an area of large hydropower potential local tephrastratigraphy and regional tephrochronology provide relative and absolute dating of individual eruptions as well as information on the volume and distribution of the products formed in each eruption three large eruptions took place in this area in 1480 a d 900 a d and 150 a d respectively each eruption produced approx 1 km3 dre of basaltic and minor amounts of silicic lava and tephra on fissures up to 42 km long no evidence is found of smaller eruptions during this period the estimated eruption frequency one eruption every 600 800 years implies that this part of the veidivotn fissure swarm is inactive for long periods between relatively large volcanic events a change in the mode of eruption from effusive to explosive took place during this period the hazards posed by this area include far reaching lava flows widespread heavy tephra fall with thicknesses in excess of 2 m at distances of 10 km and damming of a large glacial river with the consequent formation of unstable lakes a volcano tectonic model which explains the observed eruption frequency and provides a basis for a long term monitoring program is proposed eruptions on the veidivotn fissure swarm are interpreted as corollaries of rifting episodes initiated in the bardarbunga central volcano volcano tectonic episodes affect the fissure swarm at an average interval of 100 years minor episodes are limited to the central volcano and adjacents parts of the fissure swarm during the less frequent major episodes rifting and volcanic activity extends to the extreme southwestern part of the fissure swarm seismic monitoring of the bardarbunga central volcano could provide an early warning of renewed activity on the veidivotn fissure swarm a major rifting episode resulting in eruption on its southwestern part can be expected during the next 100 to 300 years

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

a 4500 year reconstruction of sea surface temperature variability at decadal time scales off north iceland marine paleo records acquired at high temporal resolution provide critical data for testing numerical climate models and help to understand processes underlying ocean variability this study presents a unique 4500 year reconstruction of sea surface temperature sst obtained from alkenones in the north atlantic polar front area off north iceland at an average temporal resolution of 4 5 years spectral analysis of this signal shows dominant multidecadal oscillations which occurred with a stronger amplitude between 2500 and 4200 years bp hand in hand with fluctuations of bottom currents indicated by paleomagnetic proxies contemporaneous large excursions of the inter tropical convergence zone itcz are also recorded by the distant cariaco titanium time series suggesting a link with low latitude atlantic climate we speculate that the oscillations reflect changes of the meridional overturning circulation moc induced by increased enso activity

testing the fidelity of sediment chronology comparison of varve and paleomagnetic results from holocene lake sediments from central finland abstract a careful construction of independent varve and paleomagnetic chronologies from three varved lake sediment records from central finland resulted in detailed and continuous age depth profiles cumulative varve calculation errors were estimated to be 3 for lake alimmainen savijarvi 10 295 340 varve years and 1 for lakes nautajarvi 9898 97 varve years and korttajarvi 9590 103 varve years paleomagnetic secular variation psv curves demonstrate good consistency between these sites and within a margin of varve chronology error they show similar declination and inclination features commonly described in the uk and sweden the timing of psv patterns from finnish varved sites agree well with uk curves between the present and 2000 bc and in pre 6000 bc deposits and with swedish data between the present and 5000 bc combined inclination records from three independently dated finnish varved sites possess an opportunity for accurate paleomagnetic comparisons within the margin of varve chronology errors and throughout the last 10 000 years

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

holocene temperature history of northern iceland inferred from subfossil midges abstract the holocene temperature history of iceland is not well known despite iceland s climatically strategic location at the intersection of major surface currents in the high latitude north atlantic existing terrestrial records reveal spatially heterogeneous changes in iceland s glacier extent vegetation cover and climate over the holocene but these records are temporally discontinuous and mostly qualitative this paper presents the first quantitative estimates of temperatures throughout the entire holocene on iceland mean july temperatures are inferred based upon subfossil midge chironomidae assemblages from three coastal lakes in northern iceland midge data from each of the three lakes indicate broadly similar temperature trends and suggest that the north icelandic coast experienced relatively cool early holocene summers and gradual warming throughout the holocene until after 3 ka this contrasts with many sites on iceland and around the high latitude northern hemisphere that experienced an early to mid holocene thermal maximum in response to enhanced summer insolation forcing our results suggest a heightened temperature gradient across iceland in the early holocene with suppressed terrestrial temperatures along the northern coastal fringe possibly as a result of sea surface conditions on the north iceland shelf

marine reservoir age variability and water mass distribution in the iceland sea abstract lateglacial and holocene tephra markers from icelandic source volcanoes have been identified in five sediment cores from the north icelandic shelf and correlated with tephra layers in reference soil sections in north iceland and the grip ice core land sea correlation of tephra markers that have been radiocarbon dated with terrestrial material or dated by documentary evidence provides a tool for monitoring reservoir age variability in the region age models developed for the shelf sediments north of iceland based on offshore tephrochronology on one hand and on calibrated ams 14c datings of marine molluscs on the other display major deviations during the last 4500 years the inferred temporal variability in the reservoir age of the regional water masses exceeds by far the variability expected from the marine model calculations the observed reservoir ages are generally considerably higher by up to 450 years than the standard model ocean it is postulated that the intervals with increased and variable marine reservoir age reflect incursions of arctic water masses derived from the east greenland current to the iceland sea and the north icelandic shelf

holocene and latest pleistocene climate and glacier fluctuations in iceland abstract multiproxy climate records from iceland document complex changes in terrestrial climate and glacier fluctuations through the holocene revealing some coherent patterns of change as well as significant spatial variability most studies on the last glacial maximum and subsequent deglaciation reveal a dynamic iceland ice sheet iis that responded abruptly to changes in ocean currents and sea level the iis broke up catastrophically around 15 ka as the polar front migrated northward and sea level rose indications of regional advance or halt of the glaciers are seen in late allerod early younger dryas time and again in preboreal time due to the apparent rise of relative sea level in iceland during this time most sites contain evidence for fluctuating tidewater glacier termini occupying paleo fjords and bays the time between the end of the younger dryas and the preboreal was characterized by repeated jokulhlaups that eroded glacial deposits by 10 3 ka the main ice sheet was in rapid retreat across the highlands of iceland the holocene thermal maximum htm was reached after 8 ka with land temperatures estimated to be 3 c higher than the 1961 1990 reference and net precipitation similar to modern such temperatures imply largely ice free conditions across iceland in the early to mid holocene several marine and lacustrine sediment climate proxies record substantial summer temperature depression between 8 5 and 8 ka but no moraines have been detected from that time termination of the htm and onset of neoglacial cooling took place sometime after 6 ka with increased glacier activity between 4 5 and 4 0 ka intensifying between 3 0 and 2 5 ka although a distinct warming during the medieval warm period is not dramatically apparent in icelandic records the interval from ca ad 0 to 1200 is commonly characterized by relative stability with slow rates of change the literature most commonly describes little ice age moraines ca ad 1250 1900 as representing the most extensive ice margins since early holocene deglaciation with temperature depressions of 1 2 c compared to the ad 1961 1990 average steep north south and west east temperature gradients are reconstructed in the holocene records of iceland suggesting a strong maritime influence on the terrestrial climate of iceland

a review of the holocene environmental history of iceland abstract the purpose of this paper is to review the present knowledge of the holocene environmental history of iceland focusing on glacier fluctuations the ideas of the holocene being a relatively flat epoch in terms of environmental changes have been superseded by new studies reflecting active fluctuations the present paper promotes a revised model of the holocene glacier fluctuation history of iceland and recognises a long period of neoglaciation present data suggests an onset of glacier expansion in iceland around 5 ka bp which can be roughly correlated between different parts of the country and coincides with wider environmental changes specific glacier advances have been bracketed to 5 4 5 ka bp ca 4 2 ka bp ca 3 ka bp 2 ka bp and 1 5 1 2 ka bp during the little ice age lia glaciers in iceland begun to advance in the late 18th century and were biggest in the late 19th century

two tephra layers bracketing late holocene paleoecological changes in northern germany paleoecological records from two holocene peat bogs in northern germany are linked by two microscopic volcanic ash layers correlated by petrology and geochemistry to explosive volcanism on iceland the younger microlite tephra cannot be correlated to any known eruption while the older tephra layer is identified as a deposit of the hekla 3 eruption the tephra layers are dated by an age depth regression of accelerator mass spectrometry 14c ages that have been calibrated and combined in probability distributions this procedure gives an age of 730 664 cal yr b c for the microlite tephra event and 1087 1006 cal yr b c for the hekla 3 event accordingly the tephra layers were deposited during the late bronze age at this time human settlement slowly increased pressure on the environment as indicated by changes in woodland pollen composition at the two bogs the tephra marker horizons further show that the palynologically defined transition from the subboreal to the subatlantic period is synchronous in the investigated area however the macroscopic visible marker in peat the change from fibrous to sapric peat the schwarztorf weistorf kontakt is asynchronous bog vegetation did not immediately react in unison to a climatic change at this pollen zone boundary instead the timing of vegetation change depended on the location within the bog

timing and significance of mid holocene glacier advances in northern and central iceland tephrochronology is used to date mid holocene moraines in iceland in the granavatn cirque trollaskagi peninsula the h 4 tephra ca 3830 yr bp lies within sediment accumulated against the distal slope of a lateral moraine providing a minimum age for glaciation and the absence of h 5 ca 5950 yr bp provides a maximum age by implication the cirque was glaciated in the early neoglacial period a large rock glacier the development of which post dates the moraine probably formed within the little ice age lia of the sixteenth to nineteenth centuries ad at eystri lo mundarjokull in central iceland frozen colluvium containing the h 3 ca 2900 yr bp and h 4 tephras provides a minimum age of ca 3830 yr bp for two terminal moraines and a maximum age of ca 2900 yr bp for a third the older moraines are correlated with the vatnsdalur i drangagil advances ca 4700 yr bp and 4500 yr bp respectively and the begisardalur i advance ca 4200 yr bp they imply that early neoglacial advances throughout iceland were locally more extensive than those of the lia the apparent lia holocene glacial maximum may reflect i selective sampling of large ice cap outlet glaciers where the preservation potential of pre lia deposits is low and ii reliance on lichenometric dating which has a restriced temporal range copyright 2001 john wiley sons ltd

global surface temperatures over the past two millennia 1 we present reconstructions of northern and southern hemisphere mean surface temperature over the past two millennia based on high resolution proxy temperature data which retain millennial scale variability these reconstructions indicate that late 20th century warmth is unprecedented for at least roughly the past two millennia for the northern hemisphere conclusions for the southern hemisphere and global mean temperature are limited by the sparseness of available proxy data in the southern hemisphere at present

abrupt climate changes for iceland during the last millennium evidence from high resolution sea ice reconstructions a high resolution account of icelandic sea ice over the last millennium has been constructed using a novel proxy based on the presence in sediments of a biomarker ip25 produced by sea ice algae comparison with historical sea ice records demonstrates a strong correlation between documented sea ice occurrences and the ip25 proxy an excellent agreement is also observed between the ip25 record and a diatom based sea surface temperature reconstruction obtained from the same core and the crowley and lowery northern hemisphere temperature reconstruction using this approach we provide new historical sea ice data for periods where records are scarce or absent and evidence for abrupt changes to sea ice and or climate conditions around iceland during the little ice age

a 3000 year varved record of glacier activity and climate change from the proglacial lake hvitarvatn iceland a suite of environmental proxies in annually laminated sediments from hvitarvatn a proglacial lake in the central highlands of iceland are used to reconstruct regional climate variability and glacial activity for the past 3000 years sedimentological analysis is supported by tephrostratigraphy to confirm the continuous annual nature of the laminae and a master varve chronology places proxies from multiple lake cores in a secure geochronology varve thickness is controlled by the rate of glacial erosion and efficiency of subglacial discharge from the adjacent langjokull ice cap the continuous presence of glacially derived clastic varves in the sediment fill confirms that the ice cap has occupied the lake catchment for the duration of the record varve thickness varve thickness variance ice rafted debris total organic carbon mass flux and bulk concentration and c n of sedimentary organic matter reveal a dynamic late holocene climate with abrupt and large scale changes in ice cap size and landscape stability a first order trend toward cooler summers and ice cap expansion is punctuated by notable periods of rapid ice cap growth and or landscape instability at ca 1000 bc 600 bc 550 ad and 1250 ad the largest perturbation began ca 1250 ad signaling the onset of the little ice age and the termination of three centuries of relative warmth during medieval times consistent deposition of ice rafted debris in hvitarvatn is restricted to the last 250 years demonstrating that langjokull only advanced into hvitarvatn during the coldest centuries of the little ice age beginning in the mid eighteenth century this advance represents the glacial maximum for at least the last 3 ka and likely since regional deglaciation 10 ka the multi centennial response of biological proxies to the hekla 3 tephra deposition illustrates the significant impact of large explosive eruptions on local environments and catchment sensitivity to perturbations

palaeo oceanography deepwater variability in the holocene epoch the conversion of surface water to deep water in the north atlantic results in the release of heat from the ocean to the atmosphere which may have amplified millennial scale climate variability during glacial times1 and could even have contributed to the past 11 700 years of relatively mild climate known as the holocene epoch 2 3 4 here we investigate changes in the carbon isotope composition of benthic foraminifera throughout the holocene and find that deep water production varied on a centennial millennial timescale these variations may be linked to surface and atmospheric events that hint at a contribution to climate change over this period