an abrupt weakening of the subpolar gyre as trigger of little ice age type episodes we investigate the mechanism of a decadal scale weakening shift in the strength of the subpolar gyre spg that is found in one among three last millennium simulations with a state of the art earth system model the spg shift triggers multicentennial anomalies in the north atlantic climate driven by long lasting internal feedbacks relating anomalous oceanic and atmospheric circulation sea ice extent and upper ocean salinity in the labrador sea yet changes throughout or after the shift are not associated with a persistent weakening of the atlantic meridional overturning circulation or shifts in the north atlantic oscillation the anomalous climate state of the north atlantic simulated after the shift agrees well with climate reconstructions from within the area which describe a transition between a stronger and weaker spg during the relatively warm medieval climate and the cold little ice age respectively however model and data differ in the timing of the onset the simulated spg shift is caused by a rapid increase in the freshwater export from the arctic and associated freshening in the upper labrador sea such freshwater anomaly relates to prominent thickening of the arctic sea ice following the cluster of relatively small magnitude volcanic eruptions by 1600 ce sensitivity experiments without volcanic forcing can nonetheless produce similar abrupt events a necessary causal link between the volcanic cluster and the spg shift can therefore be excluded instead preconditioning by internal variability explains discrepancies in the timing between the simulated spg shift and the reconstructed estimates for the little ice age onset

northern europe climate variations during late holocene evidence from marine skagerrak abstract granulometric and stable oxygen isotope analyses of four sediment cores from two high accumulation areas in the skagerrak ne north sea were carried out in order to reconstruct climate fluctuations and to evaluate climate impact during the upper holocene extremely high sedimentation rates especially in the eastern skagerrak are explained by increased current activity which is responsible for the transport and deposition of high quantities of suspension load during periods of stormy zonal atmospheric circulation patterns these were most frequent during colder periods while warmer phases are characterized by calmer meridional to zonal atmospheric circulation patterns while the subatlantic climate deterioration and the subboreal climate optimum left only indistinct traces in the sediments the roman climate optimum and a colder period between ca 400 and 700 ad are well documented the following medieval warm period is characterized by a clear temperature increase of the waterbody in connection with less frequent advances of atlantic water masses into the skagerak deep and a decrease in bottom current strength a mode of sedimentation prevails similar to that of recent summer conditions suggesting short and mild winters during that period the onset of the little ice age around 1350 ad however shows an intensified bottom current circulation most probably due to amplifying westerly winds and a decrease in water temperatures in connection with more frequent advances of higher saline atlantic waters the little ice age can be divided into 3 phases a stormy zonal onset a calm meridional maximum and a stormy zonal end the stormy phases are characterized by a sedimentation mode similar to that of recent winter conditions while the little ice age maximum shows conditions comparable to exceptional cold modern winters from 1900 ad at the onset of the modern climate optimum the winter type sedimentation decreases and conditions change again to a level comparable to the medieval warm period

distribution of terrigenous lipids in marine sediments off northeastern taiwan surface sediments on the continental margin off northeastern taiwan have been analyzed for terrigenous lipids including n alkanes n fatty alcohols and sterols marine input to the sediments is particularly low based on the average n c17 n c29 alkane and n c16 n c28 fatty alcohol ratios 0 15 0 13 and 0 13 0 06 respectively this may be due to the fact that marine lipids are more prone to degradation than terrestrial ones the study area has the highest plant wax n alkane contribution average carbon preference index 3 9 1 2 among the coastal marine areas surrounding taiwan lateral particle transport from the southern east china sea shelf and river runoff from the east taiwan coast are considered to be the major contributors the distributions of plant wax n alkane and n alkanol concentrations normalized to total organic carbon toc in the study area generally show maximum values on the upper slope of the southernmost okinawa trough but not for phytosterols linear regression of toc versus plant wax n alkane concentrations show a weak relationship r 0 64 p 0 001 and an even weaker relationship r 0 42 p 0 05 between toc and plant wax n fatty alcohol concentrations is found this could be attributed to several factors 1 a complex input not a point source of terrigenous organic matter to the study area 2 toc also including marine organic matter 3 temporal variations in river flow due to flooding and 4 different rates of degradation for toc and individual biomarkers however in spite of those factors toc and phytosterol concentrations are positively linearly correlated r 0 85 p 0 001 implying that the dilution of phytosterols in terrigenous organic carbon with marine organic carbon with or without the phytosterols follows a nearly constant ratio which is remarkable in addition the predominant source of diploptene in the sediments does not appear to be of higher plant origin

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

a numerical study on the formation of upwelling off northeast taiwan 1 we examined the spatial and temporal variations of upwelling off northeast taiwan using a fine resolution numerical model with realistic bathymetry the zonally running shelf break in the area deflects the kuroshio seaward and produces upwelling on its on shelf edge the upwelling in turn manifests a cold dome or a cyclonic eddy in depths below 150 m or so the upwelling and hence the cyclonic eddy exist year round above this depth the eddy waxes and wanes as the upper portion of the kuroshio migrates seaward and shoreward respectively the eddy event fluctuates in a wide range of timescales seasonally the occurrence heavily favors summer rather than winter because the mean kuroshio axis migrates seaward in summer intraseasonally the fluctuation contains two dominant periods centered at 70 days and 30 days local wind forcing and channeling by two local canyons do not affect the eddy statistics significantly

seasonal exchanges of the kuroshio and shelf waters and their impacts on the shelf currents of the east china sea previous in situ observations and modeling studies have indicated that through mass and momentum exchanges across the shelf edge the kuroshio can significantly influence the shelf currents of the east china sea ecs here instead of localized observations this study uses 25yr of drifter data supported by satellite and other data to identify seasonal cross shelf exchanges along the entire shelf edge the authors show that kuroshiomeandersonshorefromfalltowinterandoffshorefromspringtosummer withthelargestamplitude northeast of taiwan the influence is limited to the shelf edge when the kuroshio meanders offshore in spring and summer by contrast strong onshelf intrusions and cross shelf exchanges occur when the kuroshio meanders onshore in fall and winter drifters intrude onshelf northeast of taiwan and spread as far north as 308n against the strong northeasterly wind the forcing on the shelf is identified as a northward downsloping of the sea level that is steepest north of taiwan at 258 288n but which is 3 times weaker farther north the vorticity budget computed from a numerical model indicates that intrusion during fall andwinter is primarily a result of balancebetweenonshelfadvectionofambientpotentialvorticityandvorticityproductionbythealong isobath pressure gradient acting on the changing mass of water column across the continental slope

8000 year marine record of climate variability and fjord dynamics from southern greenland abstract holocene sediment records of glacio marine environmental and climatic changes from ikersuaq fjord and narsaq sound in southern greenland have been studied the ikersuaq fjord record representing the last c 500 years is dominated by turbidite sedimentation and very high sedimentations rates of up to 1 cm yr the adjacent narsaq sound site on the other hand represents a continuous and more slowly accumulating sedimentation record of the last c 8000 years the narsaq record reveals changes in position and melting rates of glacier termini of the nearby greenland ice sheet from the holocene thermal optimum period terminating at about 5 0 ka to the neoglaciation period during the late holocene from 8 0 ka to 4 8 ka ice rafted debris ird influx progressively became reduced supporting a landward retraction of glacier termini neoglaciation of the region appears to have been initiated at about 4 8 ka with a culmination of ird rain at about 4 6 ka 3 6 ka 2 2 ka 1 0 ka 0 7 ka and 0 5 ka and onward some of these ird events appear to be associated with enhanced melting and glacier instability during warming episodes however at the transition to the little ice age at about 1450 years ad a marked increase in ird influx took place the bottom water of narsaq sound appears to have been dominated by modified irminger water atlantic during most of the holocene bottom current flow was quite sluggish before 3 2 ka whereas the late holocene period appears to have been characterised by three pronounced episodes of increased bottom current velocity and increased calcareous benthic foraminifera productivity the long term climate pattern in the narsaq sound record follows climate changes consistent with patterns of east greenland current variability which is partly related to dominant north atlantic oscillation forcing of wind and ice drift patterns

upper ocean currents around taiwan abstract current velocity measured by shipboard acoustic doppler current profiler sb adcp during 1991 2000 was used to study the upper ocean the composite and moored currents revealed a branch of the kuroshio that intruded steadily and persistently into the south china sea part of the intruded kuroshio flowed out of the south china sea through the northern luzon strait and re united with the main stream kuroshio the kuroshio had two velocity maximum cores southeast of taiwan but gradually combined into one as the kuroshio flowed north the kuroshio was deflected by the i lan ridge east of taiwan and the zonal running shelf break northeast of taiwan at the shelf break the kuroshio split with one branch intruding onto the shelf west of the luzon strait the kuroshio intruded into the south china sea some water flowed northward into the taiwan strait and re joined the kuroshio currents in the taiwan strait flowed primarily in a northward direction except for the southward current near the coast of mainland china north of the taiwan strait a branch of the northward flow followed the northern coast of taiwan to join the kuroshio the composite current varied consistently from season to season there was generally poor correlation between currents and local winds especially in the deep water regime remote forces were important in the currents around taiwan

sedimentation in the southern okinawa trough rates turbidites and a sediment budget forty seven box cores collected from the westernmost part of the southern okinawa trough were analyzed for fallout radionuclides 210 pb and 137 cs and sedimentary properties to study sedimentation rates and dynamics the results indicate steady hemipelagic sedimentation in the lower slope and deep basin at water depths below ca 1000 m with sedimentation rates generally decreasing with increasing water depth or distance offshore barring a localized depression below the 1400 m isobath where sediment deposition is enhanced by episodic inputs of turbidites the time of deposition of various turbidite layers can be dated circa 2002 1986 1966 1959 1947 and 1922 ad which can be correlated not only spatially among sites but also temporally with the history of major submarine earthquakes in and around the region based on the distribution of sedimentation rates at 52 sites including five with sediment trap measured rates a finite element approach was used to calculate the budget of sediment although the study area in the southern okinawa trough occupies less than 10 of the okinawa trough s area it receives more sediment than the rest of the okinawa trough however sediment deposited in the study area approximately 14 mt annually accounts for only 5 of the sediment discharged from taiwanese rivers and barely matches the annual load discharged from the nearby lanyang river thus the southern okinawa trough as a sink for sediment in the continental margin accretion wedge is not as important as generally speculated

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

modern distribution of diatoms in sediments from the george v coast antarctica abstract currently little information exists concerning high frequency climate change in the antarctic data that are essential to gaining a more complete understanding of global climate change sediments from the george v coast continental margin potentially contain a high resolution record of the late holocene the relatively high rate of sedimentation 3 mm year and the presence of laminated intervals which contain undisturbed sequences make these sediments valuable for future downcore work in order to utilize diatom assemblages as proxies of paleoclimatic and paleoceanographic parameters a preliminary study of the surface sediment distribution of diatoms from the george v coast continental margin was completed nitzschia curta van heurck hasle and nitzschia kerguelensis o meara hasle present great potential for tracking the holocene retreat of ice across the continental shelf of this region concentrations of n curta an ice related form decreases in an offshore direction whereas n kerguelensis an oceanic species associated with circumpolar flow displays an increase in sediments offshore the genus thalassiosira cleve displays a clear association with areas of open water primary production as has been noted in others parts of the antarctic downcore variability in relative abundance of this genus will be useful in understanding the history of sea ice versus open water production on the george v coast shelf in contrast the distribution of chaetoceros ehrenberg resting spores appears to be more complex but may be related to the position of the stationary ice edge associated with the annual minimal extent of sea ice finally an understanding of the downcore variability of thalassiothrix antarctica schimper ex karsten a species which is very abundant in the laminated sections of the sediment cores will have to rely on studies of its distribution in other areas of the antarctic as it is sparsely distributed along the george v coast today

late quaternary paleohydrology of the gulf of st lawrence quebec canada based on diatom analysis abstract postglacial sediments from three cores raised from the gulf of st lawrence along the path of the laurentian channel were analyzed for diatoms a sequence of four distinct zones was defined from oldest to youngest 1 characterized by low diatom concentrations this zone is mainly represented by heavily silicified species delphineis surirella stephanopyxis turris coscinodiscus radiatus and paralia ornata that were probably deposited by glacial drift in a glaciomarine environment from about 18 000 to 14 000 years bp 2 this postglacial sedimentation zone deposited around 13 000 years bp is marked by high diatom concentrations with cold water marine species thalassiosira antarctica resting spores and porosira glacialis the upper part of the zone suggests a gradual warming with the appearance of temperate water species bacterosira bathyomphala and chaetoceros spp both resting spores and vegetative cells 3 an important cooling of surface temperatures is noticed by the resurgence of cold species porosira glacialis thalassiosira antarctica resting spores and thalassiosira hyalina this zone is associated with the younger dryas chronozone dated from 10 800 to 10 300 years bp this interval is also characterized by two marked freshwater pulses coming from the outflow of laurentide ice sheet meltwater on the surface layer of the goldthwait sea although well defined in the northwestern gulf area core 90 031 015 the influence of this meltwater decreases considerably or even disappears in cabot strait core 89 007 111 and offshore core 90 031 044 evidence of reduced postglacial glacial runoff on surface water supports the conclusion that it could not have generated the younger dryas cooling episode 4 the diatom assemblages from 10 000 years bp through recent correspond to the progressive establishment of modern like surface water conditions

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

continental slope flow northeast of taiwan abstract hydrographic observations and current measurements with a shipboard acoustic doppler current profiler over the continental shelf slope junction northeast of taiwan during 10 17 august 1994 allow the construction of the mesoscale flow pattern generated by the collision of the kuroshio and a stretch of the continental shelf that has turned to run nearly east west the pattern is made up of a deflected kuroshio mainstream to the east an intrusion of kuroshio water onto the continental shelf region a counterclockwise circulation over mien hwa canyon mhc immediately northeast of taiwan a deep southwestward countercurrent along the northern wall of mhc and a seaward outflow of continental shelf water around the northern coast of taiwan the hydrography features a cold dome over the west side of mhc that consisted of subsurface kuroshio water a temperature salinity plot of all the station data shows the incorporation in the neighborhood of taiwan of continental shelf water into the kuroshio

late holocene diatom inferred reconstruction of temperature variations of the west greenland current from disko bugt central west greenland the diatom flora from a high resolution core collected from disko bugt central west greenland records variations in surface water temperature for the late holocene 1600 300 cal bp our data support the existence of a previously identified anti phase relationship between the surface water temperature from west greenland and climate events recorded in the ne atlantic and between surface and subsurface waters identified from benthic foraminifera of the west greenland current wgc the diatom flora record relatively cool surface water conditions during the end of the roman warm period and medieval warm period mwp and relatively warmer surface water conditions during the dark ages cold period and little ice age lia this is particularly pronounced during the mwp experiencing the coldest conditions and the lia experiencing the warmest conditions through the whole sequence studied the most likely explanation for this anti phase relationship is linked to the flux of meltwater delivered to the wgc from sea ice and the greenland ice sheet off the west greenland margin the generally warmer conditions of the mwp resulted in increased melting of sea ice and the greenland ice sheet producing an increased meltwater flux and cooling of the surface waters of the wgc in contrast reduced meltwater flux during the relatively cold lia resulted in reduced meltwater flux to the wgc producing a relative warming of the surface waters recorded by the diatom flora

acoustic transmission in the cold eddy in the southern east china sea 1 an acoustic transmission experiment with the hydrological observation was carried out in the southern east china sea ecs in summer 2003 the experiment site was located at a northwestern position of a cold eddy the comb structure of multipath signals a feature of the acoustic transmission in the typical shallow water with thermocline is received by the receiver positioned in the mixed layer the formation of the comb structure is explained with the normal modes in a depth mode number space combined with modal group velocities gvs the cold eddy has influence on the mode patterns and the modal gvs and the multipath structure of received signals

comparative study of sterols in shelf and slope sediments off northeastern taiwan abstract bottom sediments and suspended matter from the shelf and slope areas off northeastern taiwan were analyzed for sterol n alkanol and n alkane compositions the algal sterols cholesterol ratios mean 1 were 1 00 0 31 n 7 for the shelf sediments 3 29 0 61 n 7 for the slope sediments and 1 54 0 19 n 3 for the suspended matter the much higher proportion of cholesterol in the shelf sediments is most likely derived from mollusks in the relict sediments an additional sterol source for the shelf sediments probably is suspended matter in the water column although the shelf has no apparent sedimentation results from phytol and n alkanols suggest recent inputs of lipids from the water column to the shelf the stanol stenol ratios are lower for the older shelf sediments than for the younger slope sediments

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

separation of tidal and subtidal currents in ship mounted acoustic doppler current profiler observations a simple method is developed to analyze current measurements obtained from a moving platform the need for this is motivated by the now common use of the ship mounted acoustic doppler current profiler adcp to acquire absolute velocity data during an oceanographic survey of a given region the full potential of this new measurement technique is severely hindered when the presence of high frequency phenomena e g tidal or inertial motions prevents a clear visualization of the lower frequency current structure of interest our analysis method is based on a spatial interpolation scheme using arbitrary functions that allows for the tidal current time variability which then permits the tide induced motions to be subtracted from the adcp data to yield the subtidal current field the method also allows nearby moored and drifter current measurements if available to be combined with the shipboard adcp observations in a single analysis to obtain the best description of the tidal and subtidal currents to illustrate this method we present results from the analysis of adcp data taken during oceanographic surveys in two different continental shelf regions the east china sea and the amazon shelf a 5 day conductivity temperature depth ctd and adcp survey was made in the east china sea near the mouth of the yellow sea during january 1986 there the currents were essentially barotropic and dominated by the semidiurnal tide the adcp derived cotidal chart for the m2 12 42 hours component agrees well with existing charts derived empirically from sea level observations or from regional numerical models the adcp derived steady flow is also consistent with the observed density field and indicates little flow in or out of the yellow sea and a transport of about 1 sv toward the tsushima strait two ctd adcp surveys lasting 21 and 23 days were conducted over the amazon shelf during march and may 1990 simultaneously moored current observations were also obtained at three locations along a cross shelf array 200 km north of the amazon river mouth for a common period of at least 2 months february 12 to april 13 over the shelf tidal and subtidal currents were comparable in magnitude our analysis indicates that the tidal currents were essentially barotropic semidiurnal and polarized in the cross shelf direction increasing in magnitude toward the inner shelf where current values of more than 2 m s are common the adcp derived steady currents were aligned in the along shelf direction and strongly influenced by the north brazil current nbc during both adcp surveys the northwestward flowing nbc was transporting more than 2 sv over the shelf at depths shallower than 100 m

a comparison of sedimentary aliphatic hydrocarbon distribution between the southern okinawa trough and a nearby river with high sediment discharge twelve surface sediments from the southern okinawa trough ot and nine surface sediments from a nearby river the lanyang river lr with high sediment discharge were analyzed for comparison of their aliphatic hydrocarbon distributions performing cluster analysis on all hydrocarbon data of lr and ot sediments showed that the two areas had a similarity level of only 0 15 meaning that they were quite dissimilar the average ratio of terrigenous to aquatic n alkanes was 0 99 for lr sediments and 9 64 for ot sediments indicating that the concentrations of n alkanes in lr and ot sediments were quite different furthermore the mean pristane phytane ratios for lr and ot sediments were 1 01 and 2 57 respectively the difference between them was significant student s t test at the 99 significance level the carbon preference index cpi of c25ec33 n alkanes averaged 3 26 range 2 16e4 59 for lr sediments and 2 92 range 2 35e5 24 for ot sediments no significant difference was found between the two cpi averages student s t test at the 99 confidence level however higher plant n alkanes generally maximized at c29 for lr sediments but maximized at c31 for all ot sediments strongly indicating significant differences in the origins of the hydrocarbons in these two areas all present results appear to suggest that lr sediments are not a major hydrocarbon source for ot sediments in addition there was no positive linear correlation between diploptene hop 22 29 ene and terrestrial higher plant n alkanes for lr and ot sediments

interannual variability of the kuroshio onshore intrusion along the east china sea shelf break effect of the kuroshio volume transport the interannual variability of the kuroshio onshore intrusion koi across the east china sea ecs shelf break and its response to the ecs kuroshio volume transport kvt during 1993 approximate to 2010 are studied based on a high resolution real time and global ocean general circulation model since variability of kvt is mainly determined in the interior pacific it is rather a remote than a local factor for the local ecs koi on interannual time scales kvt affects koi not only in the net volume transport across the entire shelf break but also in the spatial pattern along the shelf break when kvt increases the intrusion decreases increases upstream downstream of the major intrusion region northeast of taiwan the retreating increases decreases upstream downstream of the main veering region southwest of kyushu these patterns are caused by cyclonic eddies induced by the seaward deflection of the kuroshio axis from the shelf break which ultimately results from the kvt increase a diagnostic mechanism of koi approximate to msin delta h 1 is proposed where h is the bottom depth is the angle between isobaths and the vertically averaged current and m is the absolute volume transport at the shelf break is large in the major intrusion retreating regions and stable on interannual time scales while m changes with opposite signs between upstream and downstream of the major intrusion retreating regions the mechanism explains well the relation of local kvt and the spatial pattern of koi along the shelf break in both the mean state and the interannual variations

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

geochemical and diatom signatures of bottom water renewal events in effingham inlet british columbia canada abstract sediments from effingham inlet vancouver island british columbia hold a valuable high resolution holocene record of paleoclimatic and paleoceanographic conditions in the northeast pacific ocean accurate interpretation of this record requires that the depositional environment be well understood in order to assess deposition within the fjord over the last 1500 years two cores a soutar box core and a kasten core were analyzed for fossil diatoms and biogeochemical properties the cores contain varved sequences intercalated with homogeneous mud layers and a seismite we show that homogeneous mud units related to periods of bottom water renewal are geochemically distinct from the seismite and that these bottom renewal events are favored when brackish rather than marine surface water conditions are present the seismite deposited in ad 1946 has lower opal and higher organic carbon concentrations and higher organic carbon nitrogen ratios reflecting greater terrestrial material input in contrast homogeneous mud units are marked by a lower organic c n and more isotopically heavy 13 c values suggesting a stronger marine influence major metals and trace element data also confirm that the source material of these units differs from that of the ad 1946 seismite fossil diatom assemblages within the homogeneous mud units are characterized by a decreased abundance of typical marine spring bloom taxa skeletonema costatum chaetoceros spp thalassiosira spp coupled with an increased abundance of the brackish water taxon cyclotella choctawhatcheeana reduced surface salinity enhances stratification of the water column which in turn favors an intensified two layer estuarine exchange across the shallow sills and associated bottom water renewal the homogeneous mud units are produced through transport of sediment into the fjord coupled with a reworking of the upper layers of the sediment column therefore these units represent a recorder of past changes in regional oceanography and climate

lagrangian observations of surface flow patterns in the vicinity of taiwan two satellite tracked surface drifters were launched off the southwestern coast of taiwan on october 7 1997 both traveled northward along the taiwan strait ts and into the seas north of taiwan lasting 20 and 53 days respectively from the drifter trajectories their rotary spectra and satellite infrared imagery several oceanic features have been detected and are discussed in this paper our results indicate that in the southern and central portions of the ts the floats followed a northward flow with a mean speed of 30 50 cm s upon reaching the northwestern taiwan coast the trajectories were strongly affected by the semidiurnal tides and interacted with the kuroshio water in the southern east china sea the onset of the strong northeastern winter monsoon in early november decelerated the northward movement and eventually reversed the direction this process was accompanied by wind generated near inertial motion one drifter was then captured by a counterclockwise circulation of a cold dome at the continental shelf break northeast of taiwan finally the drifter was entrained by the mainstream of the kuroshio and flowed towards the northeast

seasonal circulation patterns of the yellow and east china seas derived from satellite tracked drifter trajectories and hydrographic observations abstract we investigated seasonal circulation patterns of the yellow and east china seas yecs by reviewing previous works on the circulation and its dominant currents and taking into account newly compiled trajectories of satellite tracked drifters collected between the 1980s and 2000s the circulation patterns suggested before the 1990s can be categorized into two groups depending on the identified origin of the tsushima warm current in the korea tsushima straits i branching from the kuroshio southwest of kyushu or ii northeastward continuation of the taiwan strait throughflow the branching of the kuroshio southwest of kyushu and northeast of taiwan was clearly evidenced by current measurements and concurrent hydrographic surveys however there is still no clear evidence for the northeastward pathway of taiwan strait throughflow across the mid shelf area of the east china sea target oriented surveys in the 1990s and 2000s employing advanced instruments such as drifter tracking and acoustic doppler current profiler measurements now provide decisive proof of the clockwise rounding of the cheju warm current around jeju do throughout the year of the northeastward extension of changjiang discharge in summer and of the presence of the yellow sea warm current only in winter thus both coastal currents in shallow water and secondary branch currents of the kuroshio such as the yellow sea warm current are found to significantly change from winter to summer to better present the basic pattern of yecs circulation and its seasonality we have constructed seasonal circulations patterns based on review results on the newly compiled drifter trajectories and on hydrographic observations further investigations should be carried out in future with support of comprehensive current measurements on shelf areas and through elaborate numerical modeling

late holocene climatic changes as detected by the growth and decay of ice wedges on the southern shore of hudson strait northern quebec canada the dating of cryoturbated palaeosols associated with past ice wedge activity on late holocene sandy fluvial terraces in a region of continuous permafrost leads to an interpretation of periods of ice wedge growth and active cracking that alternated with periods of decay dormancy and active layer deepening the reconstruc tion corresponds with palaeoclimatic information obtained from existing arctic wide and regional proxy rec ords the little ice age stands out as a period of intense ice wedge activity in the study area it was followed by a warm thawing interval during the first half of the twentieth century from ad 1946 to 1991 a well documented cooling of the climate took place which reactivated 94 of the studied ice wedges the pyramidal shape of ice wedge tops and the depths of the upgrowth features could be correlated between sites several kilometres apart clearly indicating a regional climatic response the mean annual air temperature dropped from about 7 8 c in 1946 to 8 9 c in 1991 the t

paleoceanographical development off sisimiut west greenland during the mid and late holocene a multiproxy study abstract a multiproxy study of paleoceanographic and climatic changes in holsteinsborg dyb on the west greenland shelf shows that the area is sensitive to variations in the mixing between the two components of the west greenland current i e the atlantic water of the irminger current and the polar water from the east greenland current a seismic profile illustrates the general development in the area since the deglaciation and analyses of benthic foraminifera stable isotopes 18 o and 13 c and x ray fluorescence elemental counts in two cores covering ca 6650 and 1100 years respectively provide details on the oceanographic changes during the mid and late holocene the chronology is based on 210 pb and ams 14 c age determinations during the time interval of 6650 1600 cal yr bp the bottom waters are characterized by the presence of modified atlantic water with some influence of meltwater either local or regional depleted 18 o values and relatively high si fe ratio suggest warmer conditions from 6650 to 3800 cal yr bp corresponding in time to part of the holocene thermal maximum followed by a general slight cooling with some fluctuation after 3800 cal yr bp at 1600 cal yr bp there is an abrupt change in almost all investigated proxies the foraminiferal assemblage and the 18 o values suggest cold low salinity bottom water conditions and there is indication of seasonal sea ice cover between 1400 and 1200 cal yr bp corresponding in time to the dark ages cold period and to a minimum in solar irradiance from ca 1150 to 580 cal yr bp a time interval equivalent to the historical medieval warm period mwp the foraminiferal fauna remains indicative of cold low salinity bottom waters but without any indication of sea ice cover the influence of polar water meltwater at the sea floor during the mwp is thought to be a result of enhanced mixing of the two components of the west greenland current caused by an increase in wind activity during generally positive north atlantic oscillation conditions maybe combined with a displacement of the irminger current pathway to the outer shelf during the little ice age lia there is a strong influence of modified atlantic water at the sea floor related to sea ice formation and stratification of the water column after ad 1900 the benthic foraminiferal assemblage suggests a slight increase in polar water influence and thereby mixing even though the environment is not much different from that during the lia

driving mechanism of band structure of mean current over the continental shelf abstract a two layer numerical model is used to investigate the continental shelf circulation forced by western boundary currents along shelf edges emphasis is placed on an effect by frontal eddies or frontal waves which are reproduced in the model with the shelf edge along which a western boundary current is imposed after long term integration the model reaches the equilibrium state in which alternating bands of long term mean currents are found over the continental shelf the generation of the band structure is consistent with the observational results obtained by acoustic doppler current profilers on the shelf of the east china sea the western boundary current is accompanied by frontal waves and so vertical momentum transfer occurs because of the diffusive stretching topographic rossby waves are excited on the shelf slope by the vertical momentum transfer thereafter energy of the waves proceeds to flow toward the lower frequency limit by resonant interactions the along shelf wavenumber also

numerical study on the pattern and origins of kuroshio branches in the bottom water of southern east china sea in summer pattern and origins of kuroshio branches in the bottom water of southern east china sea ecs were carefully examined by numerical simulations based on the regional ocean modeling system roms together with observations model results show that in the bottom water of ecs the intrusion pattern of kuroshio is mainly composed of an offshore kuroshio branch current okbc which bifurcated from the kuroshio northeast of taiwan flows nearly along the isobath of similar to 100 m and a nearshore kuroshio branch current nkbc which originated from the kuroshio northeast of taiwan upwells northwestward gradually from similar to 250 m to similar to 60 m then turns to northeast around 27 5 degrees n 122 e thereafter flows northeastward along the isobath of similar to 60 m and finally reaches at 30 5 degrees n where it turns to east furthermore we found that the nkbc mostly originated in the kuroshio subsurface water 120 250 m east of taiwan whereas the okbc mainly stemmed from the kuroshio water 60 120 m east of taiwan this pattern and origins of okbc and nkbc well addressed the observational phenomena that off the coast of zhejiang province china there were colder less saline and more phosphate rich bottom water near the isobath of similar to 60 m rather than near the isobath of similar to 100 m in august 2009 finally it is proposed that on southern ecs continental shelf kuroshio exhibits its intrusion branches by an anticyclonical stair structure bottom stair nkbc middle stair okbc and top stair kuroshio surface branch kbc

a diatom based reconstruction of summer sea surface salinity in the southern okinawa trough east china sea over the last millennium a high resolution diatom record from site md05 2908 in the southern okinawa trough east china sea reveals pronounced multidecadal to centennial scale palaeoceanographic changes throughout the last millennium summer sea surface salinity sss was reconstructed using a weighted averaging partial least squares diatom based training set the reconstructed sss shows slightly decreasing values during the period ad 9051930 with considerable fluctuations superimposed on this general trend relatively high salinity conditions during the interval ad 9051450 probably suggest a low flood frequency in north eastern taiwan furthermore the high sss values are associated with a strong and stable influence of the kuroshio current on the southern okinawa trough during the medieval climate anomaly the period ad 14501930 is characterized by three low salinity intervals ad 14501500 ad 16251725 and ad 17701880 separated by periods of relatively high salinity the low sss intervals indicate increased freshwater discharge into the southern okinawa trough during the little ice age probably as a result of higher flood frequencies in north eastern taiwan spectral and wavelet analyses suggest that this pattern was linked to multidecadal variations in summer sss presumably associated with the pacific decadal oscillation copyright c 2012 john wiley sons ltd

organic carbon and nitrogen contents and their isotopic compositions in surficial sediments from the east china sea shelf and the southern okinawa trough abstract the southern okinawa trough has been noted as an important depocenter for the particulate organic matter from the east china sea shelf in order to determine the major sources of sedimentary organic matter in the southern okinawa trough we analyzed surficial sediments from the east china sea shelf and the southern okinawa trough for organic carbon and nitrogen contents and their isotopic compositions in the decarbonated fraction distributions of total organic carbon content 13corg and nitrogen content all show a similar spatial pattern resembling the distribution of fine grained sediments the coastal belt of elevated organic carbon content extends southward from the changjiang mouth and veers offshore towards the southern okinawa trough just north of taiwan implying a pathway for channeling fine grained sediments from the inner shelf to the depocenter this distribution pattern is consistent with the shelf circulation the isotope compositions 13corg 15n of sediments from the southern okinawa trough fall between those of riverine particulate organic matter and the mid outer shelf sediments but overlap with those of the inner shelf sediments in addition the previously reported 13corg values of sinking particles collected by sediment traps in the southern okinawa trough are also close to those of the inner shelf sediments especially during high flux conditions therefore the isotopic evidence strongly supports the notion that a major fraction of the sedimentary organic matter in the southern okinawa trough may originate from the inner shelf

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

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

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

the onshore intrusion of kuroshio subsurface water from february to july and a mechanism for the intrusion variation abstract to examine the variation of kuroshio subsurface water kssw off the coast of zhejiang province china we carried out six monthly cruises from february to july 2015 observations show that the kssw appears in a frequently reported algal bloom area near the coast as early as in april and persists until july however the kssw was absent in february we set up a fine resolution 4 km model which can reproduce most of the observed features model results and cruise data suggest that a nearshore kuroshio branch current nkbc originated from the kssw northeast of taiwan can emerge as early as in april which is responsible for the observed kssw from april to july however in february nkbc turns seaward before reaching this algal bloom area and thus the kssw is absent in addition to the traditional mechanisms of wind bottom stress and cooling we suggest a new mechanism of this nkbc variation in the origin area of the nkbc the kssw is more shoreward squeezed and flows more westward flowing northward in february while northwestward in april in april than february the change of flow direction caused different meeting point between the shelf break and the kuroshio current according to topographic beta spiral different meeting points will induce different upwelling velocity and then contribute to the different intrusion pattern of nkbc this direction change is one of the essential ingredients which enable nkbc to reach as far as the algal bloom area hence algal blooms in april may be potentially influenced by this nkbc whose water properties are significantly different to the coastal water

labrador current variability over the last 2000 years the ice loaded labrador current lc is an important component of the western north atlantic circulation that influences the position and strength of the northern limb of the north atlantic current nac this flow of cold and fresh polar waters originating from the arctic has a marked impact on the north atlantic climate yet little is known about its variability beyond the instrumental period in this study we present the first sub decadal alkenone based 2000 year long sea surface temperature sst records from the western labrador sea a climatically crucial region at the boundary between the lc and the nac our results show a clear link between the lc strength and the northern annular mode nam with a stronger nam and a more vigorous lc during the medieval climate anomaly mca this suggests enhanced lc activity upon future global warming with implications for the atlantic meridional overturning circulation amoc

continuum of earthquake rupture speeds enabled by oblique slip earthquake rupture speed can affect ground shaking and thus seismic hazard seismological observations show that large earthquakes span a continuum of rupture speeds from slower than rayleigh waves up to p wave speed and include speeds that are predicted to be unstable by 2d theory this discrepancy between observations and theory has not yet been reconciled by a quantitative model here we present numerical simulations that show that long ruptures with oblique slip both strike slip and dip slip components can propagate steadily at various speeds including those previously suggested to be unstable the obliqueness of slip and the ratio of fracture energy to static energy release rate primarily control the propagation speed of long ruptures we find that the effects of these controls on rupture speed can be predicted by extending the 3d theory of fracture mechanics to long ruptures with oblique slip we propose that this model provides a quantitative framework to interpret supershear earthquakes to constrain the energy ratio of faults based on observed rupture speed and rake angle and to relate the potential rupture speed and size of future earthquakes to the observed slip deficit along faults

intrusion of the kuroshio subsurface water in the southern east china sea and its variation in 2014 and 2015 traced by dissolved inorganic iodine species abstract the circulation systems and ecological environment of the east china sea ecs are greatly influenced by the kuroshio the nutrient rich kuroshio subsurface water kssw has been subject to considerable research attention but the intrusion pathway extent and variation of the kssw over the entire southern ecs shelf are still debated in june 2015 the dissolved inorganic iodine species diis were determined and hydrographic data were collected and analyzed in the southern ecs analysis of the collected data suggests that the kssw mainly intrudes onto the ecs shelf from northeast of taiwan and bifurcates into a nearshore branch and an offshore branch the nearshore branch ultimately appears in the subsurface layer within the 50 m isobath off the zhejiang coast north of 30 n and the offshore branch flows along the 100 m isobath and covers the area outside the 80 m isobath another kssw intrusion along the shelf edge is located at 28 n this additional kssw intrusion is weaker and the offshore area in the southern ecs is mainly influenced by the kssw intrusion northeast of taiwan compared with the kssw intrusion on the ecs continental shelf depth

holocene glacier variations in central jotunheimen southern norway based on distal glaciolacustrine sediment cores abstract sediment cores from two glacier fed lakes are used to reconstruct a continuous record of glacier variations since about 10 000 cal bp in the smorstabbtinden massif of central jotunheimen southern norway particular attention is paid to the century to millennial scale pre little ice age glacial signal based on an estimated temporal resolution of 55 and 25 yr cm 1 for bovertunsvatnet and dalsvatnet respectively visible lithostratigraphic variations organic content loss on ignition calcium carbonate content magnetic susceptibility and grain size fractions especially the fine silt are used as proxy indicators of glacier presence and extent in the lake catchments following deglaciation the early holocene was characterized by generally small glaciers until a major advance the finse event peaking at approximately 8200 cal bp from 7900 to at least 5300 cal bp glaciers appear to have been absent from central jotunheimen there is evidence of glacier expansion between about 2400 and 1600 cal bp the bovertun i event and between about 1400 and 800 cal bp the bovertun ii event before reduced glacier extent during the mediaeval warm period finally the most extensive neoglacial maximum occurred during the little ice age after 500 cal bp in addition to providing a record of the broad pattern of climatically forced holocene glacier variations periodicities at 110 140 200 285 and about 500 yr have been identified uncertainties remain concerning the precise timing of events glacierization and deglacierization detection thresholds a possible mid to late holocene 5300 2500 cal bp neoglacial build up of small glaciers and shorter term decadal to century scale variations in glacier size for which more proximal sites are required

distribution of chaetoceros resting spores in modern peri antarctic sediments abstract one hundred and sixty five surface sediment samples from the southern ocean were examined for distribution and relative abundance of chaetoceros resting spores the contribution of resting spores to the total diatom assemblage ranges from 0 in the subantarctic zone to 95 in the antarctic peninsula sector on the basis of both absolute and relative abundances four biogeographic zones are distinguished 1 the antarctic peninsula sector 2 the embayment systems ross sea and weddell sea 3 the continental shelf zone water depth 2000 m chaetoceros resting spores abundance reaches up to 900 10 6 valves g of dry sediment in the gerlache strait southwest of the antarctic peninsula the hydrology of this region is characterized by an intense stratification of the water column due to sea ice meltwater inputs continental glacial runoffs and thermal warming of the surface water layer the availability of nutrients the lack of vertical mixing in those surface waters having low salinity 2 4 c is thought to be the main pre condition for development of large chaetoceros species blooms we propose that increased relative abundances of chaetoceros resting spores in fossil diatom assemblages from the southern ocean can therefore be used as tracers of water column stratification due to glacial melt water

diatom evidence of climatic change in holsteinsborg dyb west of greenland during the last 1200 years diatom assemblages from holsteinsborg dyb on the west greenland shelf were analysed with high temporal resolution for the last 1200 years a high degree of consistency between changes in frequency

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

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

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

modeling iceberg rafted sedimentation in high latitude fjord environments 1 an iceberg model sedberg has been developed to simulate sedimentation in high latitude glaciated fjords sediments deposited in fjords provide an important record of glaciological response to changing climatic conditions the model simulates the formation drift and melt of a population of icebergs utilizing monte carlo based techniques with a number of underlying parametric probability distributions to describe the stochastic behavior of iceberg formation and dynamics the model captures iceberg dynamics and melt in fjord environments and has been applied to kangerdlugssuaq fjord in east greenland as an example of an iceberg dominated sedimentary environment sedimentation has been simulated over the past 1500 years encompassing the climatic intervals of the medieval warm period mwp and the little ice age lia model results have been compared with the observed sedimentary record the model demonstrates that the glaciological regime e g basal debris thickness mean annual calving rate mean iceberg size plays a more important role than the direct influence of climate ocean and air temperatures on iceberg sedimentation rate although often changes in climate result in changes to the glaciological regime

paleoceanographic changes in the disko bugt area west greenland during the holocene micropaleontological analyses of a sediment core raised in disko bugt west of greenland were undertaken in order to document paleoceanographical changes in the eastern baffin bay during the holoc

kuroshio subsurface water feeds the wintertime taiwan warm current on the inner east china sea shelf the taiwan warm current twc has an overwhelming influence on the heat salt and nutrients balance on one of the broadest shelf in the world the east china sea shelf in winter the twc flows in an unusual upwind direction and reaches the changjiang yangtze river estuary but its origin and pathway are intensely debated here combined evidences from current measurement hydrographic and stable isotopic data all suggest that the wintertime twc intrusion off the changjiang estuary mainly originates from the kuroshio subsurface water northeast of taiwan rather than from the taiwan strait warm water the kuroshio branched water northeast of taiwan can intrude into the inner shelf near the zhe min coast via bottom layer manifesting by a pronounced boundary at 50 m isobath around 28 n and thereby feeds the twc intrusion into the changjiang estuary the intrusion complicates the hydrological process in the estuary and shelf sea and its impact on marine environment deserves more research attentions

variabilities of particulate flux and 210pb in the southern east china sea and western south okinawa trough abstract variabilities of the particulate mass flux and associated 210 pb activity were examined on samples collected from time series sediment traps deployed in the continental slope area of the east china sea off northeast taiwan and in the western south okinawa trough sot as a part of the keep program the particulate flux decreases laterally from the continental slope toward the trough increases vertically toward the bottom at most of the mooring sites and shows fairly synchronous temporal variations among the traps in each mooring for most of the deployments the temporal variation of 210 pb is generally smaller than that of the particulate flux in terms of relative change as expressed in standard deviation of the mean of each trap in the lower slope area the mean particulate flux varies between 9 5 and 79 g m 2 d and the mean 210 pb varies between about 44 and 81 dpm g in the trough the mean particulate flux has the smallest values from 0 06 to 5 7 g m 2 d while the mean 210 pb has the highest from 82 to 192 dpm g the particulate flux decreases while the 210 pb activity increases from the slope toward the trough in the trough 210 pb increases with depth while the particulate flux may show a mid depth maximum of a nepheloid layer although the 210 pb activity increases from the slope toward the trough the 210 pb flux decreases toward the trough because of much greater particulate flux in the slope area within the trough the 210 pb flux as determined from the traps is comparable to that determined from the underlying sediments but on the lower slope the 210 pb flux determined from the traps is much higher than that obtained from the underlying sediments thus a large portion of the particulates and the associated 210 pb may have been transported laterally from elsewhere to the slope area in transit without depositing onto the underlying sediments plots of the mean 210 pb flux versus the mean mass flux for each of the traps show positive linear correlation with four distinctive slopes each representing a mean 210 pb activity of a particular area or a group of traps in the mien hua canyon the mean activity is about 40 dpm g in the sot the mean value is about 130 dpm g on the lower slope the mean values fall in between those of the canyon and the trough in the middle traps where the mass flux is higher in a nepheloid layer the mean activity is about 47 dpm g while the remaining traps yield a mean of about 65 dpm g taking the mean activity of the canyon and that of the trough as the two end member values the slope with a nepheloid layer is a mixture of about 90 canyon and 10 trough materials indicating the canyon as the major particulate provider for the nepheloid layer the slope without a nepheloid layer is a mixture of about 70 canyon and 30 trough materials

the reconstruction of late quaternary antarctic sea ice distribution the use of diatoms as a proxy for sea ice the study of annual diatom transfer from the southern ocean surface to the sea floor using time series sediment traps combined with the mapping of diatom assemblages from surface sediments results in the definition of a proxy for past variations of sea ice extent the application and robustness of the proposed proxy are demonstrated by the study of late pleistocene sediment cores recovered from different environmental regimes in the southern ocean relative amounts of the sea ice indicator diatoms fragilariopsis cylindrus and fragilariopsis curta of 3 in diatom assemblages preserved in sediments are representative of the presence of seasonal winter sea ice summer sea ice occurrence is signalled by a distinct drop in biogenic sedimentation rate as a result of strongly reduced biogenic export in the presence 3 of diatom assemblage of the deep temperature diatom fragilariopsis obliquecostata the spatial and temporal distribution pattern of the sea ice proxy indicates significant sea ice variations during marine isotope stages 1 and 5 in the present antarctic zone of the southern ocean during glacial maxima the antarctic winter sea ice was extended into the present polar front zone while the antarctic summer sea ice was most probably expanded into the area of the present winter sea ice edge during the short climatic optima at the onset of interglacial periods the winter sea ice extent was distinctly reduced

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

little ice age nivation activity in northeast greenland during the little ice age lia the periglacial landscape in northeast greenland responded rela tively quickly to the climatic deterioration with increased nivation activity resulting nivation landforms and associated sediment basins are used as palaeoclimatic archives documenting the significant geomorphological effect of nivation during the lia period in the zackenberg area a nival basin studied in detail showed the onset and dominance of niveo fluvial sedimentation in the period ad 1250 1420 followed by increasing niveo aeolian sedimentation between ad 1420 1500 1580 finally very rapid niveo aeolian sedimentation prevailed during the period ad 1500 1580 1690 in the same period some large nival fans accumulated in the zackenberg lowland as a result of increased niveo fluvial activity and niveo fluvial sediments were also deposited in pre existing fluvial valleys demonstrating the large areal extension of the nivation activity the chronology is based on nine ams 14c determinations the inte

bi polar ocean linkages evidence from late holocene antarctic marine and greenland ice core records a continuous 14c dated palaeoenvironmental 4000 year proxy from the antarctic peninsula glacial marine record demonstrates pronounced cycles of elevated palaeoproductivity warm events that rec

a multi proxy reconstruction of oceanographic conditions around the younger dryas holocene transition in placentia bay newfoundland abstract a marine sediment core from placentia bay off the south coast of newfoundland was studied to reconstruct past oceanographic conditions based on a multiproxy approach including diatoms benthic foraminifera grain size analysis ip25 x ray fluorescence calcium carbonate and total organic carbon content based on 6 radiocarbon dates the 513 5 cm long core spans the age interval from ca 13 to 10 cal kyrs bp and thus captures the transition from the younger dryas stadial into the holocene at sub decadal resolution the younger dryas was characterized by cold arctic water taxa of diatoms and benthic foraminifera and a stratified water column with high sea ice cover and low productivity due to strong influence of the labrador current during the second half of the younger dryas after ca 12 2 cal kyrs bp the influence of the labrador current gradually decreased and sea ice conditions became more variable the transition towards the holocene is characterized by a sequence of events starting with turnovers in the biogenic proxies followed by an abrupt retreat of sea ice and a rise in productivity these events are believed to be related to a northward migration of the gulf stream labrador current oceanic front the younger dryas termination is directly followed by a detrital carbonate layer associated with the final phase of the heinrich 0 event linked to laurentide ice sheet dynamics during the early holocene productivity remained high with minimal sea ice cover reduced stratification and stronger influence of warmer gulf stream derived waters

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