intertropical latitudes and precessional and half precessional cycles a mcintyre and b molfino in their report about the forcing of atlantic equatorial and subpolar millennial cycles by precession suggest that climatic changes in high polar latitudes which are related to heinrich iceberg surges may be caused by events that occur in low latitudes 1 1 this

uisge meinne mine water hydrogeology in the celtic lands from kernow cornwall uk to ceap breattain cape breton canada

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

precession forced changes in south west african vegetation during marine isotope stages 101 100 2 56 2 51 ma the intensification of northern hemisphere glaciation inhg is one of the critical climate thresholds in the cenozoic this study focuses on marine sediments recovered from marine isotope stages 101 100 at the ocean drilling program site 1083 to assesses the impact of the inhg on continental southern african vegetation through n alkane straight chain hydrocarbon abundance and delta 13 c values the n alkane abundance data yield a convoluted signal due to the number of controlling factors such as the source area transportation routes and vegetation type the c 31 n alkane delta 13 c values however exhibit a cyclic pattern with a periodicity of c 20 ka and are not correlated to the abundance data it is inferred that the signal does not represent a change in the geographical source of n alkanes instead we suggest that the variations are caused by water stress induced changes in either carbon isotope fractionation during c 3 photosynthesis or subtle changes in the proportion of c 3 and c 4 plants these changes unlike variations in oceanographic proxies closely track precessional forcing factors and are independent of the prevailing obliquity forced glacial interglacial cycles we conclude that the varying monsoon strength rather than pco 2 or temperature change forced changes in southern african vegetation during this period c 2005 elsevier b v all rights reserved

the difference in chemical composition of the 1962 lava from miyakezima magma reservoir in japan many examples of mixed magmas in banded lavas have been studied another type of mixed magmas or inhomogeneity of magma reservoir found in the 1962 lava flows of miyake zima volcano erupted from fissures is reported

magma plumbing system of the 2000 eruption of miyakejima volcano japan during the 2000 eruption at miyakejima volcano two magmas with different compositions erupted successively from different craters magma erupted as spatter from the submarine craters on 27 june is aphyric basaltic andesite 5 vol phenocrysts 51 4 52 2 wt sio2 whereas magma issued as volcanic bombs from the summit caldera on 18 august is plagioclase phyric basalt 20 vol phenocrysts 50 8 51 3 wt sio2 the submarine spatter contains two types of crystal clots a type and a type andesitic type the phenocryst assemblages plagioclase pyroxenes and magnetite and compositions of clinopyroxene in these clots are nearly the same but only a type clots contain ca poor plagioclase an 70 we consider that the a type clots could have crystallized from a more differentiated andesitic magma than the a type clots because feo mgo is not strongly influenced during shallow andesitic differentiation the summit bombs contain only b type basaltic type crystal clots of ca rich plagioclase olivine and clinopyroxene the a type and b type clots have often coexisted in miyakejima lavas of the period 1469 1983 suggesting that the magma storage system consists of independent batches of andesitic and basaltic magmas according to the temporal variations of mineral compositions in crystal clots the andesitic magma became less evolved and the basaltic magma more evolved over the past 500 years we conclude that gradually differentiating basaltic magma has been repeatedly injected into the shallower andesitic magma over this period causing the andesitic magma to become less evolved with time the mineral chemistries in crystal clots of the submarine spatter and 18 august summit bombs of the 2000 eruption fall on the evolution trends of the a type and b type clots respectively suggesting that the shallow andesitic and deeper basaltic magmas existing since 1469 had successively erupted from different craters the 2000 summit collapse occurred due to drainage of the andesitic magma from the shallower chamber as the collapse occurred it may have caused disruption of crustal cumulates which then contaminated the ascending deeper basalt thus porphyritic basaltic magma could erupt alone without mixing with the andesitic magma from the summit caldera the historical magma plumbing system of miyakejima was probably destroyed during the 2000 eruption and a new one may now form

millennial scale fluctuations in north atlantic heat flux during the last 150 000 years abstract surface water and deep ocean palaeoclimate records obtained from north atlantic core su90 03 40 n 32 w exhibit pronounced fluctuations at sub orbital time scales surface temperature variability in the mid latitude atlantic over the last 150 kyr is dominated by forcing at precession 21 kyr and semi precession harmonics 11 kyr abrupt changes in sea surface temperatures show that the northward transport of heat by the north atlantic current was curtailed during ice rafting events sea surface temperatures were about 12 c colder than modern values during the most intense cooling episodes associated with major ice rafting events heinrich events 1 4 6 and 11 and 10 c below modern values during the later part of isotope stage 3 40 30 ka during these cold intervals the north atlantic current was displaced to south of 40 n as the cold meltwaters penetrated southwards into what is now the subtropical ocean these changes in surface ocean heat exchange were most probably allied to a latitudinal migration and increase in zonality of atmospheric circulation patterns concurrent shifts in ird concentration sea surface temperatures and benthic 13 c values provide evidence of coupling between sea surface processes and the deep water circulation and suggest that decreases in surface temperature and salinity during ice rafting events culminated in a significant reorganisation of north atlantic deep water production

fluorine and chlorine contents in the lavas and ejecta of the 1986 eruption of izu oshima volcano abstract fluorine and chlorine in 61 rock samples effused by the 1986 eruption of izu oshima volcano were determined to make clear the behavior of volatiles in the magma their f cl variation patterns differ from each other according to the features of the eruption the rocks erupted from the central cone crater a group have very uniform f contents 82 90 g g while cl contents are variable 200 300 g g due to selective degassing of cl after effusion the lavas and ejecta of fissure eruptions on the caldera floor b group have distinctly higher f 92 136 g g and cl 290 400 g g contents than the a group rocks with larger variations strong correlations are seen among their f cl and sio 2 contents these facts can be explained by separation of volatile free and silica poor minerals from the magma forming the a group rocks the products of fissure eruptions on the outer slope of the somma c group have intermediate f 70 126 g g and cl 240 390 g g contents between those of the a and b group but their variations are as large as the b group rocks contrary to the b group samples no correlations are seen among f sio 2 or cl sio 2 only f cl correlation is significant this indicates that the loss of volatiles during magma migration is predominant andesitic to dacitic pumices ejected from the b craters generally have high f contents 148 179 g g but they can be subdivided into two classes according to the cl content the high cl samples 490 560 g g might be derived from the a magma by strong crystallization fractionation on the other hand the low cl samples 40 160 g g must have another origin e g the basement rocks

glacial water mass geometry and the distribution of δ13c of σco2 in the western atlantic ocean 1 oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa cibicidoides and planulina from 25 new piston cores gravity cores and multicores from the brazil margin the cores span water depths from about 400 to 3000 m and intersect the major water masses in this region these new data fill a critical gap in the south atlantic ocean and provide the motivation for updating the classic glacial western atlantic 13c transect of duplessy et al 1988 the distribution of 13c of co2 requires the presence of three distinct water masses in the glacial atlantic ocean a shallow 1000 m southern source water mass with an end member 13c value of about 0 3 0 5 vpdb a middepth 1500 m northern source water mass with an end member value of about 1 5 and a deep 2000 m southern source water with an end member value of less than 0 2 and perhaps as low as the 0 9 values observed in the south atlantic sector of the southern ocean ninnemann and charles 2002 the origins of the water masses are supported by the meridional gradients in benthic foraminiferal 18o a revised glacial section of deep water 13c documents the positions and gradients among these end member intermediate and deep water masses the large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation

sensitivity of the thermohaline circulation to tropical and high latitude freshwater forcing during the last glacial interglacial cycle recent studies indicate that the tropical freshwater budget of the atlantic is modulated by changes in el nine southern oscillation enso if anomalies of the atlantic freshwater balance persist on the order of decades these might have a large influence on the north atlantic thermohaline circulation thc here we present a sensitivity study in which we use a model scenario for enso behavior during the last 120 kyr to force a simplified model of the thc with corresponding freshwater exchange between the tropical atlantic and pacific if the steady state strength of the north atlantic thc is similar to the present day its response to the forcing is of the order of 1 3 sv 1 sv 10 6 m 3 s 1 no mode changes of the thc are simulated for reasonable values of the coupling constant between freshwater exchange and enso if on the other hand the steady state overturning is significantly weaker a collapse of the thc occurs due to forcing from the tropics the modeled thc variation due to tropical freshwater perturbations are compared to those resulting from middle and high latitude freshwater forcing due to long term growth and decay of northern hemisphere ice sheets it is found that both forcings are of similar amplitude except during the deglaciation when high latitude forcing dominates a possible out of phase relationship between deep water formation in the north pacific and north atlantic is also explored

124 000 year periodicity in terrestrial vegetation change during the late pliocene epoch the late pliocene 3 2 6 million years ago is an interval of exceptional interest for understanding the earth s climate system it was a time of progressive global cooling resulting in the growth of large terrestrial ice sheets and the initiation of extensive northern hemisphere glaciation1 12 the build up of the ice sheets was cyclical and apparently paced by the orbitally driven oscillations in incoming solar radiation milankovitch cycles at periods of approximately 41 kyr obliquity and 23 19 kyr precession here we present a high resolution continental record of late pliocene climate change detailing the response of terrestrial vegetation to this interval of dramatic global environmental change the annually laminated sequence of lake sediments from pula maar in hungary represents approximately 320 kyr of accumulation between 3 0 and 2 6 million years ago spectral analyses of the record indicate terrestrial responses to incoming solar radiation at obliquity and precession periodicities but the strongest response appears at a period of 124 kyr calculations indicate that variations in insolation forcing at this periodicity were negligible at this time the pula record thus demonstrates that internally driven nonlinear responses of the climate system at a period of 124 kyr were at least as important as external forcing at the orbital frequencies of precession and obliquity in driving late pliocene large scale environmental change

the onset of major northern hemisphere glaciations and their impact on dinoflagellate cysts and acritarchs from the singa section calabria southern italy and dsdp holes 607 607a north atlantic abstract the climatic deterioration related to the onset of northern hemisphere glaciations circa 2 52 ma b p must have lead to reorganization and relocation of species associations and may have enhanced species turnover the present study investigates how this deterioration affects the dinoflagellate cyst and acritarch assemblages from two locations dsdp site 607 north atlantic and the singa section southern italy the records from these locations cover the interval from 2 8 to 2 2 ma with at least a 5 ka resolution and they have been correlated to the milankovitch periodicities on a cycle to cycle basis by means of integrated high resolution stable isotope calcium carbonate foraminiferal palynological and magnetostratigraphical datasets in the present study this high resolution stratigraphic framework is used for a detailed correlation of events occurring in each of the depositional sequences it also enables further assessment of the palaeoenvironmental preferences of some dinoflagellate cyst forms comparison of the two palynological records reveals a close correspondence in the timing of major assemblage changes and extinction events confirming their milankovitch cycle based correlation a close link between periods of northern hemisphere cooling at oxygen isotope stages 110 104 and 100 96 and increased dinoflagellate cyst turnover appears to be present for both dsdp site 607 and the singa section the turnover events can also be recognized in the records of planktic foraminifera and calcareous nannoplankton comparison of the singa section with site 607 and with other time equivalent marine palynological data sets shows that some oceanic taxa respond similarly over a large area the biostratigraphical implications are discussed notably the last occurrence of invertocysta lacrymosa appears to be a valuable marker for isotope stage 110 in the mediterranean and north atlantic

rapid changes in the mechanism of ocean convection during the last glacial period high amplitude rapid climate fluctuations are common features of glacial times the prominent changes in air temperature recorded in the greenland ice cores1 2 are coherent with shifts in the magnitude of the northward heat flux carried by the north atlantic surface ocean3 4 changes in the ocean s thermohaline circulation are a key component in many explanations of this climate flickering5 here we use stable isotope and other sedimentological data to reveal specific oceanic reorganizations during these rapid climate change events deep water was generated more or less continuously in the nordic seas during the latter part of the last glacial period 60 to 10 thousand years ago but by two different mechanisms the deep water formation occurred by convection in the open ocean during warmer periods interstadials but during colder phases stadials a freshening of the surface ocean reduced or stopped open ocean convection and deep water formation was instead driven by brine release during sea ice freezing these shifting magnitudes and modes nested within the overall continuity of deep water formation were probably important for the structuring and rapidity of the prevailing climate changes

high frequency climate linkages between the north atlantic and the mediterranean during marine oxygen isotope stage 100 mis100 high resolution records of mediterranean and north atlantic deep sea sediments indicate that rapid changes in hydrology and climate occurred during marine oxygen isotope stage 100 mis100 at 2 52 ma which exhibits characteristics similar to late pleistocene dansgaard oeschger bond cycles and heinrich events as in the late pleistocene north atlantic oceanographic and atmospheric changes were probably transmitted into the mediterranean by some combination of surface water inflow and atlantic mediterranean atmospheric pressure gradients our data suggest that the mechanism s responsible for sub milankovitch and millennial scale climate oscillations were the same over at least the past 2 6 ma notwithstanding the transition from the 41 kyr dominated glacial cycles of the late pliocene to the 100 kyr cycles of the late pleistocene

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

millennial scale climate instability during the early pleistocene epoch climate proxy records of the past 100 000 years show that the earth s climate has varied significantly and continuously on timescales as short as a few thousand years 1 7 similar variability has also recently been observed for the interval 340 500 thousand years ago8 these dramatic climate shifts expressed most strongly in the north atlantic region may be linked to and possibly amplified by alterations in the mode of ocean thermohaline circulation4 5 6 7 8 9 here we use sediment records of past iceberg discharge and deep water chemistry to show that such millennial scale oscillations in climate occurred over one million years ago this was a time of significantly different climate boundary conditions not only was the early pleistocene epoch generally warmer but global climate variations were governed largely by changes in earth s orbital obliguity our results suggest that such millennial scale climate instability may be a pervasive and long term characteristic of earth s climate rather than just a feature of the strong glacial interglacial cycles of the past 800 000 years

evolution of the norwegian current and the scandinavian ice sheets during the past 2 6 m y evidence from odp leg 104 biogenic carbonate and terrigenous records abstract records of biogenic and terrigenous components have been obtained from the interval corresponding to the last 2 6 m y of odp sites 643 and 644 in order to reconstruct surface and deep water regimes in the norwegian sea surface water regimes record long lasting moderate glacial conditions during the interval 2 6 1 0 ma small intrusions of atlantic water episodically penetrated into the norwegian sea forming a narrow tongue along the eastern margin which is documented at site 644 the polar front was most probably situated between the site 644 and 643 locations on the outer voring plateau during these time intervals deep water regimes reflect long term persistent corrosive bottom waters most probably due to a weakly undersaturated water column and a low rate of carbonate shell production in surface waters deep water production in the norwegian greenland sea may have operated in a different way e g brine formation during winter sea ice growth bottom waters were oxygenated throughout the entire period and deep water was exchanged persistently with the north atlantic increased glacial interglacial environmental contrasts are documented reflecting a strengthening of the norwegian current and intensified glaciations on the surrounding land masses during the interval 1 0 0 6 ma during this time a major shift in the mode of deep water production occurred the onset of large amplitudes in glacial interglacial environmental conditions with maximum contrasts in surface water regimes different modes of deep water production and intensified exchange with the north atlantic marks the last 0 6 ma a broad development of the norwegian current is observed during peak interglacials while during glacials seasonally variable sea ice cover and iceberg drift dominate surface water conditions

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

climate stability during the pliocene warm period 1 we present a high resolution climate record from a sediment core spanning an 80 kyr interval of time during the mid pliocene epoch when warmer conditions and lower global ice volume prevailed worldwide oxygen and carbon isotope analyses were made on benthic and planktonic foraminifera from odp site 981 in the north atlantic the amplitude and approximate recurrence interval of suborbital variations in these records are comparable to those of holocene and marine isotope stage 11 mis 11 records from the north atlantic we conclude that the mid pliocene warm interval was a time of relative climatic stability these results suggest that warmer climatic conditions alone may not necessarily enhance variability in the climate system a finding that may facilitate predictions of 21st century climatic response to anthropogenic warming

east asian monsoon forcing of suborbital variability in the sulu sea during marine isotope stage 3 link to northern hemisphere climate 1 we have generated a new high resolution record of variations in planktonic foraminiferal oxygen isotopes 18o and mg ca from a sediment core images 97 2141 in the sulu sea located in the philippine archipelago of western tropical pacific this record reveals distinct suborbital scale 18o changes most notably during marine isotope stage 3 mis3 30 000 to 60 000 years b p the amplitudes of these 18o fluctuations 0 4 to 0 7 exceed that which can be attributed to sea level changes and must be due to changes in sea surface conditions in the same interval variations in planktonic foraminifera mg ca suggest that suborbital surface ocean temperature variations of 1 to 1 5 c in the sulu sea were not in phase with 18o combined this evidence indicates that the mis3 millennial 18o events in the sulu sea were primarily the result of changes in surface water salinity which today is directly related to the east asian monsoon eam and its influence on the balance between surface water contributions from the south china sea and western pacific warm pool wpwp within dating uncertainties the mis3 sulu sea 18o suborbital variability indicates that times of fresher surface conditions in the sulu sea coincide with similar conditions in the wpwp stott et al 2002 and also with intensifications of the summer eam as recorded in the u th dated chinese hulu cave speleothem 18o record wang et al 2001 and thus by inference with interstadials in the greenland ice core records combined these results indicate that pronounced suborbital variability in the summer eam and intertropical convergence zone itcz during mis3 was tightly coupled with climate conditions in the northern high latitudes