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

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

nonuniform response of the major surface currents in the nordic seas to insolation forcing implications for the holocene climate variability 1 high resolution sediment cores from the voring plateau the north iceland shelf and the east greenland shelf have been studied to investigate the stability of major surface currents in the nordic seas during the holocene results from diatom assemblages and reconstructed sea surface temperatures ssts indicate a division of the holocene into three periods the holocene climate optimum 9500 6500 calendar cal years bp the holocene transition period 6500 3000 cal years bp and the cool late holocene period 3000 0 cal years bp the overall climate development is in step with the decreasing insolation on the northern hemisphere but regional differences occur regarding both timing and magnitude of sst changes sites under the direct influence of the norwegian atlantic current and the irminger current indicate sst cooling of 4 5 c from early holocene to present compared to 2 c recorded under the east greenland current superimposed on the general holocene cooling trend there is a high frequency sst variability which is in the order of 1 1 5 c for the voring plateau and the east greenland shelf and 2 5 3 c on the north iceland shelf

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

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

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

gisp2 oxygen isotope ratios the gisp2 oxygen isotope record with its high resolution detail yields crucial information on past climate change the glacial 18o oscillations of the gisp2 core with their very fast onsets are templates of a prototype oscillation of variable duration with an amplitude of 3 9 the halfway mark of the cold warm transition is reached in 2 years the top is reached in 50 years the 18o time gradient of the leading front is about 7 8 per 100 yr after reaching the top 18o slowly declines by 0 14 per 100 yr the duration of 18o decline varies from a couple of centuries for fast oscillations to about 4000 yr for slower ones the subsequent 18o downturn during the warm cold transition has a 18o time gradient of 3 2 per 100 yr and lasts about 80 yr

life on the periphery is tough vegetation in northwest iceland and its responses to early holocene warmth and later climate fluctuations long and short term climate variations in the north atlantic have been of sufficient magnitude to leave a discernible mark on the history of vegetation and landscape stability in iceland during the holocene a reconstruction of early and mid holocene vegetation around lake kaga arholl northwest iceland examines how climate fluctuations have affected the terrestrial ecosystem a thorough reconstruction has been made using pollen and plant macrofossil analyses combined with proxies for organic and inorganic matter the record shows the development from a period of pioneer vegetation towards a woodland ecosystem the deposition of the saksunarvatn tephra at c 10 300 cal yr bp caused a 100 year period of instability followed by a gradual trend of stabilization over several centuries while material left behind by retreating glaciers and tephra was being contained by expanding and developing vegetation early holocene warmth is indicated by high pollen production of juniperus communis around the lake by

is there evidence for solar forcing of climate in the gisp2 oxygen isotope record abstract changes in solar constant over an 11 yr cycle suggest a certain but limited degree of solar forcing of climate the high resolution climate oxygen isotope record of the greenland gisp2 greenland ice sheet project 2 ice core has been analyzed for solar and volcanic influences the atmospheric14c record is used as a proxy of solar change and compared to the oxygen isotope profile in the gisp2 ice core an annual oxygen isotope profile is derived from centimeter scale isotope measurements available for the post a d 818 interval associated extreme summer and winter isotope ratios were found to yield similar climate information over the last millennium the detailed record of volcanic aerosols converted to optical depth and volcanic explosivity change was also compared to the isotope record and the oxygen isotope response calibrated to short term volcanic influences on climate this calibration shows that century scale volcanic modulation of the gisp2 oxygen isotope record can be neglected in our analysis of solar forcing the timing estimated order of temperature change and phase lag of several maxima in14c and minima in18o are suggestive of a solar component to the forcing of greenland climate over the current millennium the fractional climate response of the cold interval associated with the maunder sunspot minimum and14c maximum as well as the medieval warm period and little ice age temperature trend of the past millennium are compatible with solar climate forcing with an order of magnitude of solar constant change of 0 3 even though solar forcing of climate for the current millennium is a reasonable hypothesis for the rest of the holocene the century scale events are more frequent in the oxygen isotope record than in the14c record and a significant correlation is absent for this interval oceanic atmospheric circulation forcing of climate may dominate solar forcing during the surprisingly strong 1470 yr climate cycle of the 11 000 75 000 yr b p interval is rather hypothetical

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

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

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

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

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

evidence for solar forcing of sea surface temperature on the north icelandic shelf during the late holocene diatom proxies from the modern position of the oceanographic polar front north of iceland record variability in sea surface temperatures ssts during the past 2 k y the sedimentary record is dated with tephrochronology alleviating marine 14c reservoir age uncertainties comparison of changes in ssts on the north icelandic shelf with variations in the atmospheric circulation above greenland north american atlantic coastal ssts and mean temperature anomalies for the northern hemisphere suggests synchronous north atlantic wide fluctuations which would seem to imply a common forcing factor a positive and significant correlation between our sst record from the north icelandic shelf and reconstructed solar irradiance together with modeling results supports the hypothesis that solar forcing is an important constituent of natural climate variability in the northern north atlantic region

the last 18 kyr fluctuations in norwegian sea surface conditions and implications for the magnitude of climatic change evidence from the north sea a combined record of three cores spanning the last 18 kyr from the northern north sea is investigated for content of benthic and planktonic foraminifera and stable oxygen isotopes the paleoenvironmental development through this time period shows an early deglaciation 18 14 4 ka and the younger dryas 12 7 11 5 ka characterized by arctic polar conditions and increased ice rafting in the norwegian channel during the bolling allerod period warm sea surface temperature 9 c conditions similar to present conditions are inferred while bottom waters stayed cold 0 1 c with normal salinity the bolling allerod period is interrupted twice at 13 9 13 6 ka older dryas and at 13 0 12 8 ka inter allerod cooling period by reductions in sea surface temperatures and increased sea ice cover the beginning of the holocene period is marked by increases in surface and bottom water temperature superimposed on the broad climatic changes through the holocene a series of short lived oscillations in the ocean circulation are recorded the amplitude of these holocene events appears larger in the early holocene prior to 8 ka than compared with the remaining part of the holocene this amplification can possibly be attributed to a general increased freshwater budget in the north atlantic at this time during the final stages of the deglaciation of the laurentide and scandinavian ice sheets

temperature reconstructions for sw and n iceland waters over the last 10 cal ka based on δ18o records from planktic and benthic foraminifera abstract we have obtained 18 o carb data from planktic n pachyderma s and benthic foraminifera c lobatulu s m barleeanu s from eight cores between 40 and 500 m water depth along the sw core b997 347 and n iceland margins cores b997 321 324 327 328 329 330 and 332 that span the last 10 cal ka sampling resolution varies between centuries to millennial scales over this time range changes in 18 o carb in foraminifera are the product of changes in the global ice volume and the temperature and salinity of the water at the level in which the foraminifera live in order to evaluate the relative roles of these variables we investigate 1 the salinity s and 18 o water values for present day waters off iceland and 2 the present day relationships between 18 o carb or calcite values of foraminifera and water column temperature and salinity data we estimate the average error in the temperature estimate to be 0 3 c based on a monto carlo simulation of the various error terms we argue that around iceland the variations in 18 o carb of both benthic and planktic species over the last 10 cal ka are principally controlled by temperature variations while salinity changes prove less important spatial and temporal changes are examined for both bottom water and 50 m water temperature reconstructions based on six and four cores respectively reconstructed temperatures for sites around sw n iceland indicate that surface and seafloor water temperatures were warmest in the early holocene 10 6 cal ka beginning at 6 cal ka surface and seafloor temperatures began to cool in n iceland and to become less stratified in sw iceland over the last 5000 yrs sea surface temperature variations have been 1 c for 50 of the observations with a maximum range of 2 5 c a profound decrease in temperature of 1 5 c is recorded in our fjord site b997 328 during the little ice age an abrupt earlier cold event is well expressed in at least three n iceland cores around 5 cal ka

temporal changes in holocene δ18o records from the northwest and central north iceland shelf the region of north iceland is highly sensitive climatically owing to its location with respect to atmospheric and oceanographic fronts in this study we present total carbonate and 18o records of benthic and planktic foraminifera from nine sediment cores from the north iceland shelf the results of this work indicate that the deglaciation of the vestfirdir peninsula was completed by 10 200 cal yr bp the 8200 cal yr bp cold event is present only as a minor isotopic event and seems not to have had much of a cooling effect on the bottom waters of the northwest iceland shelf the holocene maximum warmth attributed to a stronger north icelandic irminger current occurred between ca 7800 and 6200 cal yr bp over the past 4500 cal yr bp a general cooling trend has occurred on the north iceland shelf and superimposed on this overall cooling trend are a number of oscillations between periods when relatively warmer and cooler waters occupied the shelf relatively cooler waters were present at 4200 4000 cal yr bp 3200 2900 cal yr bp 2500 2350 cal yr bp and 600 200 cal yr bp whereas relatively warmer waters were present on the shelf at 3750 3450 cal yr bp 2800 2600 cal yr bp and 1700 1000 cal yr bp copyright 2004 john wiley sons ltd

a high resolution holocene sediment record from hunafloaall n iceland margin centuryto millennial scale varability since the vedde tephra md99 2269 is a 25 m long core from hunafloaall a deep trough which runs northward towards the shelf break from the narrow neck of land which joins the northwest peninsula of iceland with the main land the core was recovered from the thickest part of an elongate shelf sediment body underlain by glacial diainictons with ages 26 ka bp 3 5 khz profiles indicate the presence of a reflector ri which can be traced over long distances twelve ams radiocarbon dates and the presence of the saksunarvatn tephra which is the origin for the ri reflector at 21 m core depth define a linear depth age relation with an accumulation rate of 200 cm ky the date on the core top is modern x radiographs indicate that the sediments are principally massive bioturbated muds the data were measured at resolutions of between 5 and 40 yr sample our primary data represent aspects of a multisensor track measurements b colour c grain size d sediment properties and e sediment magnetic properties principal component analysis pca was used to simplify the analysis of these five data sets and resulted in nine significant axes compared to over 70 original variables the explained variance on the first axes varied between 47 and 96 these time series were reduced to a common 50 yr sample interval which were then also subject to pca using the resulting pc scores we present three primary axes of environmental variability in hunafloaall that have century scale quasi periodicities and demonstrate that these are highly correlated with specific raw variables we focus on variables linked to changes in grain size and productivity and show regional coherence cores b997 321 and 330 in the coercivity grain size measure armj 20 armj 0 which have a close similarity to the detrended 14 c series this provides a potential link to the vigour of the thermohaline circulation to the north of the iceland shelf in the iceland and greenland seas our data indicate increas

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

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

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

the 8k event cause and consequences of a major holocene abrupt climate change abstract a prominent abrupt climate event about 8200 years ago brought generally cold and dry conditions to broad northern hemisphere regions especially in wintertime in response to a very large outburst flood that freshened the north atlantic changes were much larger than typical climate variability before and after the event with anomalies up to many degrees contributing to major displacement of vegetative patterns this 8k event provides a clear case of cause and effect in the paleoclimatic realm and so offers an excellent opportunity for model testing the response to north atlantic freshening has the same general anomaly pattern as observed for older events associated with abrupt climate changes following north atlantic freshening and so greatly strengthens the case that those older events also reflect north atlantic changes the north atlantic involvement in the 8k event helps in estimating limits on climate anomalies that might result in the future if warming caused ice melt and hydrologic cycle intensification at high latitudes lead to major changes in north atlantic circulation few model experiments have directly addressed the 8k event and most studies of proxy records across this event lack the time resolution to fully characterize the anomalies so much work remains to be done

high resolution record of late glacial and deglacial sea ice changes in fram strait corroborates ice ocean interactions during abrupt climate shifts the transition from last glacial to deglacial and subsequently to modern interglacial climate conditions was accompanied by abrupt shifts in the palaeoceanographic setting in the subpolar north atlantic knowledge about the role that sea ice coverage played during these rapid climate reversals is limited since most marine sediment cores from the higher latitudes provide only a coarse temporal resolution and often poorly preserved microfossils here we present a highly resolved reconstruction of sea ice conditions that characterised the eastern fram strait a key area for water mass exchange between the arctic ocean and the north atlantic for the past 30 ka bp this reconstruction is based on the distribution of the sea ice biomarker ip25 and phytoplankton derived biomarkers in a sediment core from the continental slope of western svalbard during the late glacial 30 ka to 19 ka bp recurrent advances and retreats of sea ice characterised the study area and point to a hitherto less considered oceanic and or atmospheric variability a long lasting perennial sea ice coverage in eastern fram strait persisted only at the very end of the last glacial maximum i e from 19 2 to 17 6 ka bp and was abruptly reduced at the onset of heinrich event 1 coincident with or possibly even inducing the collapse of the atlantic meridional overturning circulation amoc further maximum sea ice conditions prevailed during the younger dryas cooling event and support the assumption of an amoc reduction due to increased formation and export of arctic sea ice through fram strait a significant retreat of sea ice and sea surface warming are observed for the early holocene

surface and sub surface multi proxy reconstruction of middle to late holocene palaeoceanographic changes in disko bugt west greenland we present new surface water proxy records of meltwater production alkenone derived relative sea surface temperature diatom alkenones and sea ice diatoms changes from the disko bugt area off central west greenland we combine these new surface water reconstructions with published proxy records benthic foraminifera bottom water proxy dinocyst assemblages surface water proxy along with atmospheric temperature from greenland ice core and greenland lake records this multi proxy approach allows us to reconstruct centennial scale middle to late holocene palaeoenvironmental evolution of disko bugt and the western greenland coastal region with more detail than previously available combining surface and bottom water proxies identifies the coupling between ocean circulation west greenland current conditions the atmosphere and the greenland ice sheet centennial to millennial scale changes in the wider north atlantic region were accompanied by variations in the west greenland current wgc during periods of relatively warm wgc increased surface air temperature over western greenland led to ice sheet retreat and significant meltwater flux in contrast during periods of cold wgc atmospheric cooling resulted in glacier advances we also identify potential linkages between the palaeoceanography of the disko bugt region and key changes in the history of human occupation cooler oceanographic conditions at 3 5 ka bp support the view that the saqqaq culture left disko bugt due to deteriorating climatic conditions the cause of the disappearance of the dorset culture is unclear but the new data presented here indicate that it may be linked to a significant increase in meltwater flux which caused cold and unstable coastal conditions at ca 2 ka bp the subsequent settlement of the norse occurred at the same time as climatic amelioration during the medieval climate anomaly and their disappearance may be related to harsher conditions at the beginning of the little ice age

millennial climate oscillations over the course of the ice ages the climate oscillated with a period of about 20 000 to 100 000 years superimposed on these variations were millennial oscillations of 1000 to 2000 years these oscillations also occurred in the holocene which began 11 000 years ago and has been thought to be a time of a relatively stable climate as shown on p 1257 of this issue by bond et al the perspective by oppo discusses these results obtained from marine sediments and the possible mechanisms underlying these relatively rapid changes in climate

sea surface conditions in the southern nordic seas during the holocene based on dinoflagellate cyst assemblages dinoflagellate cyst dinocyst records from the southern nordic seas were compiled in order to evaluate the evolution of upper ocean conditions on a millennial timescale and supported by a highly resolved record from the voring plateau after the transitional phase from the last deglaciation three main phases define the holocene the early holocene 7 5 ka bp features important numbers of cool temperate species dominated by nematosphaeropsis labyrinthus and impagidinium pallidum in the west the assemblage composition changes drastically at the transition from the early to the mid holocene from when on operculodinium centrocarpum dominates the changeover is dated between 6 1 and 7 5 ka bp perhaps earlier closer to the iceland scotland ridge and appears to be linked to the onset of a modern type of surface circulation warmest assemblages occur at the voring plateau shortly after the transition when atlantic waters also appear to have spread farthest westward the recurrence of colder elements can be linked to cooling from 2 4 ka bp at the voring plateau and presumably earlier in the west but is difficult to date there because of the low sedimentation rates this is a general issue in many areas of the nordic seas and appears to have an important effect on cyst concentrations and assemblage composition with the possible loss of oxygenation sensitive cysts in the older parts of the cores comparing dinocyst based quantitative reconstructions with those retrieved from other plankton reveals a significantly different trend between proxies linked to a differing autecological response to seasonal changes at their respective depth habitats

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

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

surface water dynamics in the reykjanes ridge area during the holocene as revealed by coccolith assemblages abstract the calcareous nannofossil assemblages from sediment core ds97 2p from the reykjanes ridge have been investigated to document oceanographic changes in surface water during the holocene the recorded variations in coccolithophore species assemblages and accumulation rates indicate that the region was subjected to rapid changes of surface water masses throughout the entire holocene coccolithophore assemblages generally are of low species diversity and consist mainly of emiliania huxleyi and coccolithus pelagicus ssp pelagicus two major events occurred at 8 5 7 ka and at 4 5 3 5 ka showing higher coccolith accumulation rates suggesting that the influence of relatively warm atlantic waters via the irminger current was strong in the investigated area the coccolithophore assemblages have been compared with diatom foraminifer and sedimentological records within the same core these data supported by a comparison with previously published proxy records add credit to the hypothesis that holocene changes did not occur uniformly across the north atlantic the results have highlighted the holocene pattern in the north atlantic as a period influenced by strong regionalism with discrepancies in the hydrographical trends and in the distribution of the planktonic proxies

radio occultation measurements of transient eddies in the northern hemisphere of mars 1 we have characterized the behavior of transient eddies in the northern hemisphere of mars through analysis of radio science rs occultation data from mars global surveyor mgs the weather in the lowest scale height above the surface at 55 n 80 n is dominated by shallow eastward moving baroclinic eddies distinguished by their intensity and coherence the vertical structure of these eddies is fully resolved by the rs measurements which also yield unique estimates of the near surface meridional winds implied by geostrophic balance we identified and characterized the most prominent eddies through space time analysis of rs measurements of geopotential height at 610 pa a few kilometers above the surface eddy activity appears as well defined modes with zonal wave numbers 1 3 and variations in the amplitudes of these modes tend to be anticorrelated so that a large amplitude in one mode is often accompanied by a small amplitude in the others the wave number and period of the dominant mode shift at intervals of 30 50 sols eddy winds near the surface vary distinctively with season in response to changes in eddy amplitude and zonal wave number the meridional winds peak sharply in two seasonal windows one in early to middle autumn and the other in middle to late winter separated by a lull around winter solstice comparisons with previous results reveal close connections with the transient eddies observed by the viking landers and with distinctive southward moving frontal dust storms observed by the mgs mars orbiter camera

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

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

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

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

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

a high resolution study of holocene paleoclimatic and paleoceanographic changes in the nordic seas 1 high resolution records from images core md95 2011 in the eastern norwegian sea provide evidence for relatively large and small scale high latitude climate variability throughout the holocene during the early and mid holocene a situation possibly driven by consistent stronger westerlies increased the eastward influence of arctic intermediate and near surface waters for the late holocene a relaxation of the atmospheric forcing resulted in increased influence of atlantic water the main changes in holocene climate show no obvious connection to changing solar irradiance and spectral analysis reveals no consistent signature for any periodic behavior of holocene climate at millennial or centennial timescales there are however indications of consistent multidecadal variability

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

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

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

distribution patterns of diatom surface sediment assemblages in the laptev sea arctic ocean abstract the modern diatom distribution in the laptev sea arctic ocean was investigated in 89 surface sediment samples diatom concentrations are relatively low showing values between 0 01 10 6 and 6 7 10 6 valves per gram dry sediment based on a factor analysis using seventeen taxa or taxa groups five diatom surface sediment assemblages can be defined the ice diatom assemblage of the central region of the laptev sea the chaetoceros assemblage of the eastern and southeastern shelf the thalassiosira antarctica assemblage of the continental slope and deep sea the freshwater diatom assemblage in the vicinity of river mouths and deltas and the thalassiosira nordenskioeldii assemblage which shows a patchy occurrence on the central laptev sea shelf the distribution pattern of diatom assemblages in surface sediment is significantly related to oceanographic conditions of surface water masses the main factors controlling the distribution of diatoms in the laptev sea are the riverine freshwater input during the summer which strongly affects the salinity conditions and the sea ice extent furthermore the composition of the thalassiosira antarctica assemblage of the continental slope is largely influenced by dissolution and lateral transport processes

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

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

multiproxy fossil comparison reveals contrasting surface ocean conditions in the western iceland sea for the last two interglacials abstract dinoflagellate cyst dinocyst coccolith and planktic foraminiferal assemblages from a core in the western iceland sea were used to reconstruct and compare the surface ocean developments of the holocene and the last interglacial marine isotopic stage or mis 5e while increasing subpolar planktic foraminifers from 10 ka indicate subsurface warming peaking around 7 5 ka the dinocyst data suggest that the uppermost ocean remained dominated by cold waters until 6 5 ka a reduced advection of cold polar waters through the east greenland east icelandic current thereafter entailed warmest and most saline holocene conditions between 6 5 and 5 ka in turn followed by a general cooling trend by contrast both planktic foraminifers and dinocysts show an increased presence of atlantic type waters from 122 ka onward resulting in a mis 5e thermal optimum around 120 5 ka nonetheless occasional freshwater input from melting drift ice created stratified but also seasonally variable conditions during this first half of mis 5e this stratification signature disappeared at 120 ka when a marked repositioning of the oceanographic fronts occurred slightly colder conditions are indicated by both phyto and zooplankton from there on until the end of mis 5e around 117 ka a late mis 5e cooling at the iceland plateau is opposite to a late mis 5e optimum observed in the eastern nordic seas this regional difference is likely explained by various feedback mechanisms following the major reorganisation of the oceanic fronts at 120 ka the holocene and mis 5e interglacial variability is not reflected in the quasi monospecific coccolith assemblages and illustrates the low sensitivity of living coccolithophore communities to subtle temperature changes in the low temperature regions of the nordic seas overall quite different surface water properties appear to have characterised both interglacial intervals with a higher share of warm atlantic elements in the planktic communities during mis 5e this suggests a higher contribution of atlantic waters in the southwestern nordic seas probably due to a more northward expansion of the irminger current under weakened polar east greenland east icelandic currents such a reduced influence of polar waters in the southwestern nordic seas may thus explain other evidence for relatively warm conditions in mis 5e all around southern greenland

radiolarian based sea surface temperatures and paleoceanographic changes during the late pleistocene holocene in the subantarctic southwest pacific abstract a high resolution record of radiolarian faunal changes from site y8 south of the subtropical front stf offshore eastern new zealand provides insight into the paleoceanographic history of the last 265 kyrs quantitative analysis of radiolarian paleotemperature indicators and radiolarian based sea surface temperature sst estimates reveal distinct shifts during glacial interglacial g i climate cycles encompassing marine isotope stages mis 8 1 faunas at site y8 are abundant and diverse and consist of a mixture of species typical of the subantarctic transitional and subtropical zones which is characteristic of subantarctic waters just south of the stf during interglacials diverse radiolarian faunas have increased numbers of warm water taxa 15 while cool water taxa decrease to 11 of the assemblage warmest climate conditions occurred during mis 5 5 and the early holocene climatic optimum hco at the onset of mis 1 where ssts reach maxima of 12 8 and 12 9 c respectively this suggests that temperatures during the hco were comparable to the eemian one of the warmest interglacial intervals of the late quaternary glacials are characterized by less diverse radiolarian faunas with cool water taxa increasing to 49 of the assemblage coolest climate conditions occurred in mis 4 and 2 where ssts are reduced to 5 4 c and 4 3 c respectively radiolarian faunal changes and sst estimates clearly identify major water masses and oceanic fronts in the offshore eastern new zealand area during warmest mis 5 5 and early mis 1 substantial influence of northern sourced subtropical surface water stw is evident at site y8 this implies southward incursions of stw around the eastern crest of chatham rise with the stf displaced towards higher latitudes and spinning off eddies as far south as campbell plateau additionally increased flow of the southland current sc might have enhanced the local occurrence of warm water radiolarians derived from the subtropical tasman sea coolest glacials are marked by a strong inflow of cool southern sourced waters at site y8 indicating a more vigorous flow along the subantarctic front saf

paleoceanographic implications of a 90 000 year long diatom record in piston core kh94 3 lm 8 off ne japan abstract q mode principal component analysis pca of a fossil diatom assemblage reveals the late quaternary paleoceanography of the nw pacific margin based on submarine core kh94 3 lm 8 recovered off the sanriku coast of ne japan 38 53 46 n 143 22 19 e overall diatoms were abundant during interglacials but low in abundance and poor in preservation during the last glacial with each oxygen isotope stage having its own characteristic assemblage the results of pca are principal component 1 pc1 is composed mainly of thalassionema nitzschioides which predominated during the coldest oxygen isotopic stages 4 75 58 ka and 2 25 11 ka and by allochthonous taxa the diatom tests are poorly preserved and the diatom mass accumulation rate dmar is the lowest in these stages pc2 is characterized by ice related diatoms that predominate in stage 3 the interstadial whereas pc3 which is characterized by neodenticula seminae and odontella aurita shows high values in stage 1 diatom assemblages exhibit drastic changes between oxygen isotopic stages 3 and 1 11 0 ka distinct increases of dmar occurred during both periods we infer an intensified advection of sea ice from the sea of okhotsk toward the area off sanriku during stage 3 this interpretation explains the high dmar in stage 3 owing to high productivity at the sea ice edge our study can contribute to marine environmental reconstruction since the last glaciation because fewer micropaleontological data exist in the nw pacific margin for these time intervals compared with other oceans

holocene centennial to millennial scale climatic variability evidence from high resolution magnetic analyses of the last 10 cal kyr off north iceland core md99 2275 abstract high resolution magnetic analysis has been performed on the top 25 m of core md99 2275 66 33 06 n 17 41 59 w 440 m water depth from the mid outer shelf off north iceland this is a key boundary region for climate changes related to atmospheric and oceanographic variations influenced by the moving limit between the cold and warm water masses at the polar front and the low depression track with its associated westerlies situated across iceland an age model based on tephrochronology was previously reported for this core and has allowed precise timing of significant variations in the magnetic mineral concentration and grain size over the last 10 cal kyr the holocene climatic optimum identified in north iceland between 10 and 6 cal kyr bp is characterized by minor variations in the magnetic record while there is a clear increase in oceanographic instability from 6 cal kyr bp to the present at large scale a decreasing trend in the magnetic mineral content toward the present is presumably associated with a change in the circulation pattern and coincides in time with decreasing north atlantic deep water formation short term intervals of decreased magnetic mineral content are also identified at 5 2 4 9 3 77 3 41 3 01 2 7 and 0 93 0 62 cal kyr bp the youngest one ad 1020 to 1330 corresponding in time to the medieval warm period these events are interpreted to reflect periods of increased activity of the relatively warm high salinity surface irminger current related to stronger input of north atlantic waters into the nordic seas in addition spectral analysis of selected magnetic parameters demonstrates centennial scale periodicities of 715 240 170 and 100 yr which are more clearly expressed in the last 6 cal kyr bp than in the previous period these periodicities might be attributed to intervals of persistence in the north atlantic oscillation nao mode at centennial timescales this record therefore indicates that the holocene climate was more unstable than is often assumed and it demonstrates the importance of high resolution climatic studies for this recent time period to improve climate model predictions

ice sheet and ocean interactions margin of the east greenland ice sheet 14 ka to present diatom evidence seven marine sediment cores were collected from the kangerdlugssuaq trough off the southeast coast of greenland the trough cuts across the continental shelf from the fjord mouth to the upper slope in denmark strait and provides a sedimentary environment sheltered from the east greenland current flowing along the shelf the cores have been 14c dated accelerator mass spectroscopy dates and analyzed for diatom accumulation rates and changes in floral composition it was found that the shelf probably was not glaciated by grounded ice but occupied by an ice shelf and or permanent sea ice between 14 000 years b p and the present average retreat rates of glacial permanent sea ice were circa 60 m yr between circa 13 500 and 11 000 years b p the retreat rates increased to about 150 m yr between 11 000 to 10 000 years b p the increase is unexpected because this correlates with fairbanks 1989 projected low glacial meltwater discharge for the same time which is coeval with the younger dryas several events of sea surface warming cooling took place on the outer shelf from 12 000 to 9000 years b p followed by cooling to the present with a possible warming between 3000 4000 years bp on the inner shelf pulses of warm cool surface water occurred from 9000 to 6000 years b p which was succeeded by surface water cooling until present

late quaternary sea surface conditions in the laurentian fan evidence from coccolith and dinocyst assemblages abstract the analyses of coccoliths and dinocysts from the images core md95 2033 collected on the laurentian fan 44 39 87n 55 37 21w water depth 1412 m in the northwest north atlantic provide a new dataset to assess the magnitude of climatic changes during the holocene with a millennial time resolution coccolith and dinocyst data were combined to reconstruct changes in past sea surface conditions in addition the dinocyst assemblages were used to reconstruct the sea surface temperature sst and salinity sss based on the modern analog technique the distribution of the coccolith and dinocyst assemblages suggests a succession of climatic events during the late quaternary and early holocene linked to change in the influence of the labrador current and or the st lawrence river discharge the dinocyst assemblages recorded a thermal optimum during the mid holocene in the late holocene coccolith concentrations show two peaks at 2 3 and 1 1 ky which coincide with the presence of species with different ecological properties likely due to the localized influence of the slope water jet swj current the presence of this current has played a role in the development of the coccolith and dinocyst assemblages and sst fluctuations especially in the last 2 ky overall the interaction between the st lawrence river the swj the lc and the nac has all controlled the sss ssts and the development of the coccolith and dinocyst assemblages confirming a significant regionalism of the entire area

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