an 15 000 year record of el nino driven alluviation in southwestern ecuador debris flows have deposited inorganic laminae in an alpine lake that is 75 kilometers east of the pacific ocean in ecuador these storm induced events were dated by radiocarbon and the age of laminae that are less than 200 years old matches the historic record of el nino events from about 15 000 to about 7000 calendar years before the present the periodicity of clastic deposition is greater than or equal to 15 years thereafter there is a progressive increase in frequency to periodicities of 2 to 8 5 years this is the modern el nino periodicity which was established about 5000 calendar years before the present this may reflect the onset of a steeper zonal sea surface temperature gradient which was driven by enhanced trade winds

variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

measurements of shoaling internal waves and turbulence in an estuary 1 the shoaling of horizontally propagating internal waves may represent an important source of mixing and transport in estuaries and coastal seas including such effects in numerical models demands improvements in the understanding of several aspects of the energetics especially those relating to turbulence generation and observations are needed to build this understanding to address some of these issues in the estuarine context we undertook an intensive field program for 10 days in the summer of 2008 in the st lawrence estuary the sampling involved shore based photogrammetry ship based surveys and an array of moorings in the shoaling region that held both conventional and turbulence resolving sensors the measurements shed light on many aspects of the wave shoaling process wave arrivals were generally phase locked with the m2 tide providing hints about far field forcing in the deeper part of the study domain the waves propagated according to the predictions of linear theory in intermediate depth waters the waves traversed the field site perpendicularly to isobaths a pattern that continued as the waves transformed nonlinearly acoustic doppler velocimeters permitted inference of the turbulent energetics and two main features were studied first during a period of shoaling internal waves turbulence dissipation rates exceeded values associated with tidal shear by an order of magnitude second the evolving spectral signatures associated with a particular wave shoaling event suggest that the turbulence is at least partly locally generated overall the results of this study suggest that parameterizations of wave induced mixing could employ relatively simple dynamics in deep water but may have to handle a wide suite of turbulence generation and transport mechanisms in inshore regions

origin of limestone conglomerates in the choson supergroup cambro ordovician mid east korea abstract the choson supergroup cambro ordovician of mid east korea consists mainly of shallow marine carbonates and contains a variety of limestone conglomerates these conglomerates are largely comprised of oligomictic rounded lime mudstone clasts of various size and shape equant oval discoidal tabular and irregular and dolomitic shale matrices most clasts are characterized by jigsaw fit mosaic disorganized or edgewise fabric and autoclastic lithology each conglomerate layer is commonly interbedded with limestone dolomitic shale couplets and occasionally underlain by fractured limestone layer capped by calcareous shale limestone conglomerates in the choson supergroup consist of 1 disorganized polymictic conglomerate cd 2 horizontally stratified conglomerate cs 3 mosaic conglomerate cm and 4 disorganized edgewise oligomictic conglomerate cd e these conglomerates are either depositional cd and cs or diagenetic cm and cd e in origin diagenetic conglomerates formed under the conditions of 1 alternating deposition and preservation of carbonate rich and carbonate poor layers and 2 early differential cementation of carbonate rich layers in situ fragmentation may result from brittle fracturing and ductile deformation due to compaction and dewatering enhanced by dissolution processes fluidization is promoted by the overlying impermeable calcareous shale beds and has probably reinforced in situ fragmentation of the underlying limestone beds in situ fragmentation and rounding process is important whereby earlier semiconsolidated portions of limestone are incorporated into the still fluid portion which can be termed autoconglomeration process a synthesis of 145 beds of limestone conglomerates in the choson supergroup suggests that less than about 7 of the conglomerate layers 10 145 are depositional whereas the rest more than 93 135 145 are identified as diagenetic conglomerates the common occurrence of diagenetic conglomerates warrants further study on limestone conglomerates elsewhere in the world

compound specific d h ratios of the marine lakes of palau as proxies for west pacific warm pool hydrologic variability abstract we tested the use of hydrogen isotopic ratios d of lipids in marine lake sediments from the micronesian republic of palau against the instrumental record of the last century to assess their capacity to record past hydrological changes of the western pacific warm pool d values of the algal lipid biomarker dinosterol d dino and the more generic palmitic acid d pa were found to be sensitive indicators of the intensity of regional precipitation as recorded by the southern oscillation index soi the observed sensitivity is caused by the combined effect of 1 the amount effect in tropical precipitation 2 dilution of the isotopically heavy saline surface waters with light precipitation 3 a salinity effect on the biosynthetic d h fractionation between lipid and lake water both lake water d d lake and d dino could be expressed as a quadratic function of either precipitation or lake water salinity d dino values were used to reconstruct past hydrological changes of the region long term variations in the strength and sign of the el nino southern oscillation enso since the little ice age lia 1450 1850 a d and during the early holocene 7 9 kyr bp appeared to dominate decadal variability and indicate very dry conditions during the lia early holocene d dino values were on average 10 higher than those of recent centuries which we interpret as a result of millennial scale hydrologic and water mass changes on a global level the similar 35 range of d changes during the early holocene and last several centuries imply a similar range of decadal centennial hydrologic variability during those two climate regimes our results indicate that a correlation exists between solar irradiance levels and tropical pacific climate

quantification of holocene asian monsoon rainfall from spatially separated cave records abstract a reconstruction of holocene rainfall is presented for southwest china an area prone to drought and flooding due to variability in the east asian monsoon the reconstruction is derived by comparing a new high resolution stalagmite 18 o record with an existing record from the same moisture transport pathway the new record is from heshang cave 30 27 n 110 25 e 294 m and shows no sign of kinetic or evaporative effects so can be reliably interpreted as a record of local rainfall composition and temperature heshang lies 600 km downwind from dongge cave which has a published high resolution 18 o record wang y j cheng h edwards r l he y q kong x g an z s wu j y kelly m j dykoski c a li x d 2005 the holocene asian monsoon links to solar changes and north atlantic climate science 308 854 857 by differencing co eval 18 o values for the two caves secondary controls on 18 o e g moisture source moisture transport non local rainfall temperature are circumvented and the resulting 18 o signal is controlled directly by the amount of rain falling between the two sites this is confirmed by comparison with rainfall data from the instrumental record which also allows a calibration of the 18 o proxy the calibrated 18 o record provides a quantitative history of rainfall in southwest china which demonstrates that rainfall was 8 higher than today during the holocene climatic optimum 6 ka but only 3 higher during the early holocene significant multi centennial variability also occurred with notable dry periods at 8 2 ka 4 8 4 1 ka 3 7 3 1 ka 1 4 1 0 ka and during the little ice age this holocene rainfall record provides a good target with which to test climate models the approach used here of combining stalagmite records from more than one location will also allow quantification of rainfall patterns for past times in other regions

direct observations of microscale turbulence and thermohaline structure in the kuroshio front 1 direct observations of microstructure near the kuroshio front were conducted in august 2008 and october 2009 these show negative potential vorticity pv in the mixed layer south of the front where directly measured turbulent kinetic energy dissipation rates are an order magnitude larger than predicted by wind scaling these elevated dissipation rates scale better with an empirical scaling which considers local wind and ekman buoyancy flux driven by downfront wind near zero pv in the thermocline under the kuroshio mainstream is observed at 200 300 m depth with dissipation exceeding open ocean thermocline values by factors of 10 100 overall the large turbulent dissipation rates measured in the kuroshio can be categorized into two groups one characterized by low richardson number along the kuroshio front thermocline and the other characterized by high stratification away from the kuroshio mainstream the former is attributed to mixing by unbalanced frontal ageostrophic flows and the latter is attributed to internal wave breaking on average both groups appear in regions of large horizontal density gradients observed thermohaline structure shows low salinity tongues from the surface to over 300 m depth and deep cold tongues extending upward from 500 to 100 m depth in a narrow 20 km zone suggesting down and upwelling driven by geostrophic straining which is confirmed by quasigeostrophic omega equation solutions this implies that adiabatic along isopycnal subduction and diabatic diapycnal turbulent mixing acting in tandem at the kuroshio front likely contribute to npiw formation

hydraulic control of flow over the sill in observatory inlet observations of density velocity and acoustic backscatter obtained over the sill in observatory inlet british columbia during the ebb tide illustrate several features of internal hydraulic control in a tidally forced stratified flow following high water slack the flow field was initially determined by critical control of the second internal mode at the sill crest as the flow speed increased a transition occurred and control changed to an approach control of the second internal mode located upstream of the sill crest whereas the critical control represents a minimum energy condition at the crest the approach control corresponds to a maximum energy condition upstream of the sill crest later when the ebb currents were just past their maximum values the control condition changed to critical control of the first internal mode the concept of approach control of flow over topography has not previously been discussed in the literature the data described here are believed to represent the first field observations of this phenomenon the changing hydraulic conditions are analyzed in terms of two and three layer hydraulic models model results are consistent with the evolution of the flow patterns although the model cannot reproduce the apparent hysteresis in the response after maximum ebb the concept of an approach control is demonstrated with a simple two layer laboratory model

a 25 ka indian ocean monsoon variability record from the andaman sea recent paleoclimatic work on terrestrial and marine deposits from asia and the indian ocean has indicated abrupt changes in the strength of the asian monsoon during the last deglaciation comparison of marine paleoclimate records that track salinity changes from asian rivers can help evaluate the coherence of the indian ocean monsoon iom with the larger asian monsoon here we present paired mg ca and d 18 o data on the planktic foraminifer globigerinoides ruber white from andaman sea core rc12 344 that provide records of sea surface temperature sst and d 18 o of seawater d 18 osw over the past 25 000 years ka before present bp age control is based on nine accelerator mass spectrometry ams dates on mixed planktic foraminifera mg ca sst data indicate that sst was 31c cooler during the last glacial maximum lgm than the late holocene andaman sea d 18 osw exhibited higher than present values during the lateglacial interval ca 19 15 ka bp and briefly during the younger dryas ca 12 ka bp lower than present d 18 osw values during the bolling allerod ca 14 5 12 6 ka bp and during the early holocene ca 10 8 5 5 ka bp are interpreted to indicate lower salinity reflect some combination of decreased evaporation precipitation e p over the andaman sea and increased irrawaddy river outflow our results are consistent with the suggestion that iom intensity was stronger than present during the bolling allerod and early holocene and weaker during the late glaciation younger dryas and the late holocene these findings support the hypothesis that rapid climate change during the last deglaciation and holocene included substantial hydrologic changes in the iom system that were coherent with the larger asian monsoon r 2007 elsevier ltd all rights reserved

equatorial undercurrents associated with indian ocean dipole events during contrasting summer monsoons 1 positive indian ocean dipole iod events generally tend to be accompanied by intensified summer monsoon flows and above normal precipitation over the sub continent although strong monsoons have not always coincided with positive iod events numerical simulation experiments and supplementary data diagnostics are performed to understand the iod sub surface dynamics in relation to the monsoon strength the model experiments when forced by iod winds during strong monsoon periods generated a strong subsurface zonal pressure gradient along the equator and an eastward equatorial undercurrent euc leading to supply of cold subsurface waters to the upwelling regions in the eastern equatorial indian ocean however the simulations when forced with iod winds during weak monsoon periods were unable to set up the subsurface pressure gradients and the euc thus resulting in weak sst cooling in the east these results raise the possibility that iod monsoon interactions during strong monsoon years might favor intensification of the iod

diagenesis and geochemistry of porites corals from papua new guinea implications for paleoclimate reconstruction coral proxy records of sea surface temperature sst and hydrological balance have become important tools in the field of tropical paleoclimatology however coral aragonite is subject to post depositional diagenetic alteration in both the marine and vadose environments to understand the impact of diagenesis on coral climate proxies two mid holocene porites corals from raised reefs on muschu island papua new guinea were analysed for sr ca 18 o and 13 c along transects from 100 aragonite to 100 calcite thin section analysis showed a characteristic vadose zone diagenetic sequence beginning with leaching of primary aragonite and fine calcite overgrowths transitional to calcite void filling and neomorphic fabric selective replacement of the coral skeleton average calcite sr ca and 18 o values were lower than those for coral aragonite decreasing from 0 0088 to 0 0021 and 5 2 to 8 1 respectively the relatively low sr ca of the secondary calcite reflects the sr ca of dissolving phases and the large difference between aragonite and calcite sr ca partition coefficients the decrease in 18 o of calcite relative to coral aragonite is a function of the 18 o of precipitation carbon isotope ratios in secondary calcite are variable though generally lower relative to aragonite ranging from 2 5 to 10 4 the variability of 13 c in secondary calcite reflects the amount of soil co 2 contributing 13 c depleted carbon to the precipitating fluids diagenesis has a greater impact on sr ca than on 18 o the calcite compositions reported here convert to sst anomalies of 115 c and 14 c respectively based on calcite sr ca compositions in this study and in the literature the sensitivity of coral sr ca sst to vadose zone calcite diagenesis is 1 1 to 1 5 c per percent calcite in contrast the rate of change in coral 18 o sst is relatively small 0 2 to 0 2 c per percent calcite we show that large shifts in 18 o reported for mid holocene and last interglacial corals with warmer than present sr ca ssts cannot be caused by calcite diagenesis low level calcite diagenesis can be detected through x ray diffraction techniques thin section analysis and high spatial resolution sampling of the coral skeleton and thus should not impede the production of accurate coral paleoclimate reconstructions copyright 2003 elsevier science ltd

on the evolution of the southern oscillation abstract the evolution of the southern oscillation so is examined in the time domain by computing lagged cross correlations between sea level pressures at darwin and sea level or surface pressures at selected stations also in the northern hemisphere the historical and u s navy sea level pressure analyses are used all monthly time series are low pass filtered to retain periodicities greater than 20 months in order to highlight the interannual fluctuations which are primarily associated with the so a detailed analysis of the post 1941 period results in plotted maps of the phase lead or lag and magnitude of the maximum cross correlations with darwin in a manner analogous to a broadband coherence and phase spectrum the relationships within the so are further examined where possible back to 1882 using time series of running decadal cross covariances the dominant pattern reveals the two poles of the traditional standing oscillation or seesaw of the so with centers of opposite sign over indonesia

comment on a snapshot of climate variability at tahiti at 9 5 ka using a fossil coral from iodp expedition 310 by kristine l delong terrence m quinn chuan chou shen and ke lin 1 the integrated ocean drilling program iodp expedition 310 recovered drill cores from the drowned reefs around the island of tahiti 17 40 s 149 30 w many of which contained samples of massive corals from the genus porites herein we report on one well preserved fossil coral sample a 13 6 cm long porites sp dated by uranium series techniques at 9523 33 years monthly 18o and sr ca determinations reveal nine clear and robust annual cycles coral 18o and sr ca determinations estimate a mean temperature of 24 3 c 3 2 c colder than modern for tahiti at 9 5 ka however this estimate is viewed with caution since potential sources of cold bias in coral geochemistry remain to be resolved the interannual variability in coral 18o is similar between the 9 5 ka coral record and a modern record from nearby moorea the seasonal cycle in coral sr ca is approximately the same or greater in the 9 5 ka coral record than in modern coral records from tahiti paired analysis of coral 18o and sr ca indicates cold wet warm dry interannual anomalies opposite from those observed in the modern instrumental record

pressure solution in carbonate source rocks and its control on petroleum generation and migration abstract based on detailed geochemical and petrographic studies of conventional cores of a triassic age carbonate source rock formation from three well sites at increasing maturity stages it is shown that the effects of carbonate diagenesis especially pressure solution during relatively shallow burial stages exercise major controls on the processes of petroleum generation and migration during deeper burial pressure solution leads to an internal redistribution of organic matter within this source rock formation in the form of local concentrations as solution seams and stylolites they provide very favourable conditions for effective petroleum generation and migration due to their internal structure and composition three dimensional arrangement of kerogen surrounded by carbonate cemented rims as tight seals the geochemical and petrographic effects of petroleum generation and expulsion are documented e g the expulsion of petroleum occurred as a separate phase fluid at high efficiencies 60 80 for the normal and isoprenoid alkanes and was facilitated by fractures presumably resulting from pore fluid overpressuring a five stage conceptual model is proposed to explain how the effects of pressure solution achieved during relatively shallow burial stages exercised controls on the extent and efficiency of petroleum generation and expulsion during deeper burial stages

strong internal waves generated by the interaction of the kuroshio and tides over a shallow ridge abstractthe kuroshio and tides significantly influence the oceanic environment off the japanese mainland and promote mass heat transport however the interaction between the kuroshio and tides int

oscillations in the southern extent of the indo pacific warm pool during the mid holocene the indo pacific warm pool ipwp is thought to play a key role in the propagation and amplification of climate changes through its influence on the global distribution of heat and water vapour however little is known about past changes in the size and position of the ipwp in this study we use a total of 48 modern and fossil coral records from the mentawai islands sumatra indonesia and muschu koil islands papua new guinea to reconstruct oscillations in the extent of the ipwp since the mid holocene we show that reliable estimates of mean sea surface temperature sst can be obtained from fossil corals by using low resolution sr ca analysis of a suite of corals to overcome the large uncertainties associated with mean sr ca sst estimates from individual coral colonies the coral records indicate that the southeastern and southwestern margins of the ipwp were cooler than at present between similar to 5500 and 4300 years bp similar to 1 2 degrees c 0 3 degrees c and were similarly cool before similar to 6800 years bp this mid holocene cooling was punctuated by an abrupt short lived shift to mean ssts that were warmer than at present between similar to 6600 and 6300 years bp similar to 1 3 degrees c 0 3 degrees c while similarly warm conditions may have also existed after similar to 4300 years bp we suggest that mid holocene cooling at our study sites was related to contractions of the southeastern and southwestern margins of the ipwp associated with the more northerly position of the inter tropical convergence zone itcz that accompanied mid holocene strengthening of the asian summer monsoon conversely intervals of abrupt warming appear to correspond with widespread episodes of monsoon weakening and accompanying southward migrations of the itcz that caused the ipwp to expand beyond our coral sites intervals of a strengthened asian monsoon and cooling in the southwestern ipwp during the mid holocene appear to correspond with a more positive indian ocean dipole iod like mean configuration across the tropical indian ocean suggesting that the asian monsoon iod interaction that exists at interannual time scales also persists over centennial to millennial scales associated mean changes in the pacific enso modes may have also occurred during the mid holocene the dynamic and inter connected behaviour of the ipwp with tropical climate systems during the mid holocene highlights the fundamental importance of the warm pool region for understanding climate change throughout the tropics and beyond c 2009 elsevier ltd all rights reserved

three dimensional nonhydrostatic numerical simulation of nonlinear internal wave generation and propagation in the south china sea 1 we present the results of three dimensional nonhydrostatic simulations of internal tides and waves in the south china sea scs using the suntans model model results accurately predict the observed wave arrival times at two mooring locations in the scs internal wave amplitudes are underpredicted which causes underprediction of internal wave speeds due to a lack of amplitude dispersion we show that the well known a and b waves arise from the steepening of semidiurnal internal tides that are generated due to strong barotropic flow over ridges in the luzon strait a wave generation is stronger in the southern portion of the luzon strait because diurnal internal tidal beams augment the amplitude of the semidiurnal a waves b wave generation is stronger in the northern portion where the distance between the eastern and western ridges is approximately equal to one internal tidal wavelength and leads to semidiurnal internal tidal resonance the orientation of the ridges produces large a waves that propagate into the northern portion of the western scs basin and stronger b waves that propagate into the southern portion when traced back in time along linear characteristics a waves consistently line up close to peak ebb eastward barotropic currents while b waves consistently line up with peak flood westward barotropic currents this reinforces the notion that the lee wave mechanism and associated hydraulic or nonlinear effects are weak as demonstrated by a simple linear model relating the amplitude of the simulated waves to the excursion parameter at the ridges

limestone pseudoconglomerates in the late cambrian gushan and chaomidian formations shandong province china soft sediment deformation induced by storm wave loading this paper focuses on the formative processes of limestone pseudoconglomerates in the gushan and chaomidian formations late cambrian of the north china platform shandong province china the gushan and chaomidian formations consist mainly of limestone and shale marlstone interlayers wackestone to packstone grainstone and microbialite as well as numerous limestone conglomerates seventy three beds of limestone pseudoconglomerate in the gushan and chaomidian formations were analysed based on clast and matrix compositions internal fabric sedimentary structures and bed geometry these pseudoconglomerates are characterized by oligomictic to polymictic limestone clasts of various shapes i e flat to undulatory disc blade and sheet marlstone and or grainstone matrix and various internal fabrics i e intact thrusted edgewise and disorganized as well as transitional boundaries limestone pseudoconglomerates formed as a result of soft sediment deformation of carbonate and argillaceous interlayers at a shallow burial depth differential early cementation of carbonate and argillaceous sediments provided the requisite conditions for the formation of pseudoconglomerates initial deformation i e burial fragmentation liquefaction and injection and subsequent mobilization and disruption of fragmented clasts are two important processes for the formation of pseudoconglomerates burial fragmentation resulted from mechanical rupture of cohesive carbonate mud whereas subsequent mobilization of fragmented clasts was due to the injection of fluid materials liquefied carbonate sand and water saturated argillaceous mud under increased stress storm wave loading was the most probable deformation mechanism as an external triggering force subsequent re orientation and rounding of clasts were probably prolonged under normal compactional stress eventually disrupted clasts along with matrix materials were transformed into pseudoconglomerates by progressive lithification soft sediment deformation is prevalent in alternate layers of limestone and mud marl stone and or grainstone regardless of their depositional environments

internal tidal mixing as a control on continental margin ecosystems we show that a breaking internal tide at a shelf edge is a fundamental control on the structural and functional properties of ecosystems contrasts in vertical mixing of nitrate between the shelf and the open ocean correspond with horizontal and vertical changes in phytoplankton communities with largest cells found in surface waters at the shelf edge intense fishing activity is commonly seen at continental shelf edges targeting spawning fish stocks we suggest that the internal tide a globally ubiquitous physical process at steep shelf edge bathymetry supports shelf edge fisheries by providing large celled phytoplankton for first feeding fish larvae the repeatability of the internal tide removes fish from the need to time spawning with a spring bloom also with large phytoplankton cells dominating particulate organic carbon export the internal tides could be an important influence on spatial and temporal variability in patterns of global carbon sequestration in deep water and sediments citation sharples j c m moore a e hickman p m holligan j f tweddle m r palmer and j h simpson 2009 internal tidal mixing as a control on continental margin ecosystems geophys res lett 36 l23603 doi 10 1029 2009gl040683

individual and combined influences of enso and the indian ocean dipole on the indian summer monsoon the relative influences of the enso and indian ocean dipole iod events on the indian summer rainfall were studied using observational data and an atmospheric general circulation model agcm the composite analysis of rainfall anomalies demonstrates that the iod while significantly influencing the indian summer monsoon rainfall also significantly reduces the impact of enso on the indian summer rainfall whenever these events with the same phase co occur the agcm experiments have shown that during an el nino event the walker circulation over the tropical indo pacific region is modulated a low level anomalous divergence center over the western pacific and an anomalous convergence zone over the equatorial indian ocean are induced furthermore an anomalous zone of convergence over the myanmar and south china regions is induced during an el nino event these zones of anomalous convergence are complemented by anomalous divergence over the indian region causing anomalous subsidence and weakened rainfall when a strong positive iod event simultaneously occurs with el nino the latter s influence on the indian monsoon is reduced by both poles of the iod through the following mechanism an anomalous divergence center as compared to the summers when an el nino alone occurs is introduced in the eastern tropical indian ocean from this center the anomalous divergent flow crosses the equator and this air while weakening the el nino induced divergence over the western pacific also leads to convergence over the indian monsoon region this results in the reduction of the enso induced subsidence and the related rainfall deficit over the eastern flank of the indian monsoon trough region and adjoining regions to the east on the other hand over the western part of the tropical indian ocean sector part of the anomalous ascending motion from the warm pole of the positive iod event subsides just to the north of the equator moves northward ascends and causes surplus rainfall this reduces the enso induced rainfall deficit over western india the western part of the monsoon trough and parts of pakistan the agcm experiments also demonstrate that positive iod events amplify the enso induced dryness over the indonesian region

images of diagenetic textures in porites corals from papua new guinea and indonesia diagenesis is now recognized as a potentially major source of error in paleoclimatic reconstructions from fossil and modern coral geochemical records key to avoiding spurious results caused by diagenesis is thorough screening of coral material prior to geochemical analysis in this data brief we present color images from thin sections of fossil and modern porites corals and demonstrate the effectiveness of thin sections in detecting low levels of diagenesis the images presented here cover a range of coral preservation levels from pristine aragonite to 100 calcite we particularly focus on samples containing around 1 diagenetic material a level known to create artifacts in key climate parameters such as sea surface temperature and close to the detection limits of other screening methods such as x ray diffraction xrd a qualitative scheme is also presented to rate the degree of diagenesis in a coral where xrd results are not available or where secondary aragonite is present overall this collection of images is designed as a starting point in combination with other techniques to assist in identifying and screening corals for diagenesis

high resolution isotopic records from corals using ocean temperature and mass spawning chronometers abstract we present a 6 year long 1978 1984 18 o and 13 c record from a great barrier reef pandora reef porites lutea coral based on near weekly sample intervals a sampling technique was designed to minimise any smoothing or distortion of the isotopic record due to complex coral growth calyx architecture and calcification at depth within the tissue layer the arrival time of the mid winter minimum sea surface temperature is very consistent 2 weeks near pandora reef and provides an annual time marker offering more precision than the traditional density band chronometer the improved chronology and high resolution record demonstrate that signal distortion in porites due to calcification within the tissue layer and variable intra annual coral extension is generally negligible also confirmed is that the arrival time of monsoonal floods is precisely preserved 1 week within the skeleton of porites the sensitivity of weekly sampling allows the detection of a subtle warm to cool sea surface temperature anomaly which preceded by more than one year a similar temperature anomaly associated with the 1982 83 el nin o in the east pacific sharply higher 13 c values coincide with the time of the annual coral mass spawning event in the great barrier reef recognition of this mass spawning signal should simplify the interpretation of coral 13 c records and provides an additional precise time marker with which to adjust chronologies when intra annual coral extension is not constant

global ocean response to orbital forcing in the holocene 1 global upper ocean evolution in the holocene is studied in two coupled ocean atmosphere models under orbital forcing conditions at 3 6 8 and 11 ka the annual mean sea surface temperature sst changes in the early to mid holocene are found to be forced mainly by the annual mean insolation forcing with an overall symmetric response of colder equator 1 c in the arctic this sst change is consistent with a synthesis of mid holocene paleo sst records in contrast the temperature response in the thermocline is dominated by an antisymmetric pattern with a cooling warming in the northern southern hemisphere midlatitudes the thermocline response is determined predominantly by surface water subduction and ultimately the insolation forcing in local late winter

the shaping of continental slopes by internal tides the angles of energy propagation of semidiurnal internal tides may determine the average gradient of continental slopes in ocean basins 2 to 4 degrees intensification of near bottom water velocities and bottom shear stresses caused by reflection of semi diurnal internal tides affects sedimentation patterns and bottom gradients as indicated by recent studies of continental slopes off northern california and new jersey estimates of bottom shear velocities caused by semi diurnal internal tides are high enough to inhibit deposition of fine grained sediment onto the slopes

energetics of barotropic and baroclinic tides in the monterey bay area abstracta detailed energy analysis of the barotropic and baroclinic m2 tides in the monterey bay area is performed the authors first derive a theoretical framework for analyzing internal tide energetics based on the complete form of the barotropic and baroclinic energy equations which include the full nonlinear and nonhydrostatic energy flux contributions as well as an improved evaluation of the available potential energy this approach is implemented in the stanford unstructured nonhydrostatic terrain following adaptive navier stokes simulator suntans results from three dimensional high resolution suntans simulations are analyzed to estimate the tidal energy partitioning among generation radiation and dissipation a 200 km 230 km domain including all typical topographic features in this region is used to represent the monterey bay area of the 152 mw energy lost from the barotropic tide approximately 133 mw 88 is converted into baroclinic energy through internal tide generation and 42 56

from tides to mixing along the hawaiian ridge the cascade from tides to turbulence has been hypothesized to serve as a major energy pathway for ocean mixing we investigated this cascade along the hawaiian ridge using observations and numerical models a divergence of internal tidal energy flux observed at the ridge agrees with the predictions of internal tide models large internal tidal waves with peak to peak amplitudes of up to 300 meters occur on the ridge internal wave energy is enhanced and turbulent dissipation in the region near the ridge is 10 times larger than open ocean values given these major elements in the tides to turbulence cascade an energy budget approaches closure

abrupt changes in early holocene tropical sea surface temperature derived from coral records for many high latitude regions of the globe it is now clear that the transition to modern climate following the last glacial maximum was punctuated by a number of rapid and substantial climate oscillations1 2 in contrast relatively little is known about how the tropics responded to the deglaciation because few high resolution records are available from lower latitudes corals have recently been shown to provide an important source of tropical climate records because they can be easily and accurately dated using either 14c or 230th and because past sea surface temperatures can be recovered from the sr ca ratios in coral skeletons here we use this technique to derive several early holocene sea surface temperature records from a coral drill core recovered from espiritu santo vanuatu in the tropical southwest pacific ocean these records indicate that sea surface temperatures in this region were depressed by as much as 6 5 c below modern values at 10 350 calendar years bp but rose very abruptly during the following 1 500 years this temperature increase lags the post younger dryas increase observed in a coral record from the tropical atlantic ocean3by about 3 000 years an unexpected phase shift that may ultimately shed light on the mechanisms of deglacial climate change

evolution of the enso signal over the indo pacific domain abstract the evolution of the el nino southern oscillation enso in the indian and western pacific oceans is investigated observations of sea surface temperature sst heat storage in the upper 400 m hs zonal surface wind stress zsws and meridional surface wind stress msws are mapped monthly onto a 2 latitude longitude grid over as much of the indian and western pacific oceans i e 40 s 50 n 40 e 180 as possible for a 13 year period 1979 91 this grid resolution allows upper ocean temperature variability to be resolved in the eastern indian ocean i e timor sea and the western pacific ocean i e philippine sea time sequences of these variables at each grid node are band passed filtered to yield the enso period scales of 3 to 6 years extended empirical orthogonal functions analysis is applied to the filtered time sequences yielding an animation of the enso development in indian and western pacific oceans for the first modes of the four variables sst hs zsws and msws peak a

western pacific coral δ18o records of anomalous holocene variability in the el nino southern oscillation 1 skeletal oxygen isotope ratios in holocene porites corals from northern papua new guinea record decreases in sea surface temperature sst and rainfall during el nino events threshold analysis of seven fossil coral 18o records spanning the period 7 6 5 4 ka thousand years ago shows 8 12 el nino events century significantly less than the 23 events century recorded by the nino3 4 index the coral reconstructions also show a 15 reduction in el nino event amplitude for 7 6 5 4 ka compared to today which is greater than the suppression given by model studies in contrast large and protracted el nino events are identified for 2 5 1 7 ka taken together the results indicate a non linear atmospheric response to holocene changes in el nino sst anomalies we propose that small changes in tropical sst gradients the positioning of the intertropical convergence zone and the pacific tradewind climatology modify the impact of el nino events on western pacific rainfall

the generation and trapping of solitary waves over topography observations of tidal flow over a sill show that upstream solitary wave generation occurred in conjunction with the downstream movement of a streamline bifurcation over the obstacle crest solitary waves appeared upstream of the bifurcation riding on the surface stratification shear flow instabilities on the plunging interface were also evident and may contribute to wave generation through subharmonic interaction nonlinear waves generated downstream of an internal control became trapped in the supercritical flow

modes of climate variability synthesis and review of proxy based reconstructions through the holocene abstract modes of climate variability affect global and regional climates on different spatio temporal scales and they have important impacts on human activities and ecosystems as these modes are a useful tool for simplifying the understanding of the climate system it is crucial that we gain improved knowledge of their long term past evolution and interactions over time to contextualise their present and future behaviour we review the literature focused on proxy based reconstructions of modes of climate variability during the holocene i e the last 11 7 thousand years with a special emphasis on i proxy based reconstruction methods ii available proxy based reconstructions of the main modes of variability i e el nino southern oscillation pacific decadal variability atlantic multidecadal variability the north atlantic oscillation the southern annular mode and the indian ocean dipole iii major interactions between these modes and iv external forcing mechanisms related to the evolution of these modes this review shows that modes of variability can be reconstructed using proxy based records from a wide range of natural archives but these reconstructions are scarce beyond the last millennium partly due to the lack of robust chronologies with reduced dating uncertainties technical issues related to proxy calibration and difficulty elucidating their stationary impact or not on regional climates over time while for each mode the available reconstructions tend to agree at mutidecadal timescales they show notable disagreement on shorter timescales beyond the instrumental period the reviewed evidence suggests that the intrinsic variability of modes can be modulated by external forcing such as orbital solar volcanic and anthropogenic forcing the review also highlights some modes experience higher variability over the instrumental period which is partly ascribed to anthropogenic forcing these features stress the paramount importance of further studying their past variations using long climate proxy records for the progress of climate science

dynamics and energetics of trapped diurnal internal kelvin waves around a midlatitude island abstractthe generation of trapped and radiating internal tides around izu oshima island located off sagami bay japan is investigated using the three dimensional stanford unstructured nonhydrostatic terrain following adaptive navier stokes simulator suntans that is validated with observations of isotherm displacements in shallow water the model is forced by barotropic tides which generate strong baroclinic internal tides in the study region model results showed that when diurnal k1 barotropic tides dominate resonance of a trapped internal kelvin wave leads to large amplitude internal tides in shallow waters on the coast this resonance produces diurnal motions that are much stronger than the semidiurnal motions the weaker freely propagating semidiurnal internal tides are generated on the western side of the island where the m2 internal tide beam angle matches the topographic slope the internal wave energy flux due to the diurnal internal tides is much higher than that of the semidiurnal tides

intercomparison of coral oxygen isotope data and historical sea surface temperature sst potential for coral based sst field reconstructions we examine the extent to which the large scale features of the sea surface temperature sst anomaly field are represented by a sparse observational network of coral oxygen isotope 18o time series regression of annually averaged 18o data against gridded estimates of local sst anomaly within the period 1856 1990 confirm the literature regression of 18o anomaly on sst anomaly for indo pacific corals however while interannual sst variability is generally well represented by individual coral time series observed decadal and secular variability does not always display a linear relationship to local sst anomaly instead many records appear to better recover nonlocal large scale phenomena which in turn are related to either the coral local sst or sst covariant changes in seawater 18o we employ empirical orthogonal function eof analysis to identify common patterns of variability in the coral data we find two significant patterns which are interpretable as the oceanographic signature of the el nino southern oscillation enso and as a near global warming in which the eastern equatorial pacific cools a third pattern weakly resembles the pacific decadal oscillation these modes are seen more clearly in a singular vector decomposition svd of the covariance between the coral data and the dominant patterns of large scale historical sst variability the results are consistent with those found in eof and svd analyses of sst data from the coral locations as additional coral based proxy estimates become available they will improve the resolution of the patterns recovered these results suggest that a sparse network of coral data may be used to reconstruct interannual secular and decadal sst variability for preinstrumental periods albeit with large uncertainty

modeling climate shift of el nino variability in the holocene a coupled ocean atmosphere general circulation model is used to investigate climatic shift of el nino in the holocene the model simulates a reduced enso intensity in the early and mid holocene in agreement with paleoclimate record the enso reduction is proposed to be caused by both an intensified asian summer monsoon and a warm water subduction from the south pacific into the equatorial thermocline

extremes of the indian summer monsoon rainfall enso and equatorial indian ocean oscillation it is well known that anomalies of the indian summer monsoon rainfall ismr are linked to el nino and southern oscillation enso we show that large anomalies of the ismr are also linked to the equatorial indian ocean oscillation equinoo between states with enhancement suppression of atmospheric convection over the western part of the equatorial indian ocean with suppression enhancement over the eastern part and associated changes in the anomaly of the zonal wind along the equator equinoo is the atmospheric component of the coupled indian ocean dipole mode there is a strong relation between the large anomalies of ismr and a composite index which is a linear combination of the indices for enso and equinoo with all seasons with large deficits excess characterized by small large values of the index however the variation of ismr within one standard deviation is more complex and does not appear to be related to the composite index

model estimates of m2 internal tide generation over mid atlantic ridge topography abstract the conversion of barotropic to baroclinic m2 tidal energy is examined for a section of the mid atlantic ridge in the brazil basin using a primitive equation model model runs are made with different horizontal smoothing 1 5 6 and 15 km applied to a 192 km 183 km section of multibeam bathymetry to characterize the influence of topographic resolution on the model conversion rates in all model simulations barotropic to baroclinic conversion is highest over near and supercritical slopes on the flanks of abyssal hills and discordant zones from these generation sites internal tides propagate upward and downward as tidal beams the most energetic internal tide mode generated is mode 2 consistent with the dominant length scales of the topographic slope spectrum 50 km the topographic smoothing significantly affects the model conversion amplitudes with the domain averaged conversion rate from the 1 5 km run 15 1 mw m 2 4 and 19 higher than for the 6 km 14 5 mw m 2 and 15 km runs 12

effects of western boundary current dynamics on the internal wave field of the southeast florida shelf 1 shelf sea internal wave fields are typically highly variable and dominated by wind and tidal forces however this is not necessarily true for outer shelf regions or very narrow shelves where remote physical processes originating over the slope or deep ocean may exert a strong influence on the internal wave climate during the summers of 2003 and 2004 observational studies were conducted to examine the effects of a western boundary current the florida current tides and wind on the mean currents and internal wave field on the outer southeast florida shelf wavelet analyses of nonstationary shelf currents coupled with altimetry images of the straits of florida reveal the strong influence of florida current fluctuations on outer shelf flows local winds were found to be a small factor in flows on the outer shelf region and tidal forcing diurnal and semidiurnal accounted for less than a third of the total barotropic variance high frequency internal waves dominate the internal wave field and result in bottom intensified currents and strong shoreward mass transport we present evidence that suggests that the florida current plays as large a role in the determination of the high frequency internal wave field as tidal forces these observations and analyses show that it is necessary to include the forcing from the florida current meanders and instabilities in order to predict accurately the episodic nature of the internal wave field on the southeast florida shelf

model estimates of m2 internal tide energetics at the hawaiian ridge 1 a primitive equation model is used to examine the structure and energetics of m 2 internal tides generated at the hawaiian ridge recent estimates based on altimeter data suggest that 20 gw of barotropic tidal dissipation occurs at the ridge with conversion to internal tides believed to be the dominant dissipation mechanism the model simulates an internal tide that accounts for 9 7 gw of radiated energy away from the ridge in the northeast and southwest directions the strongest generation occurs at three sites where enhanced barotropic currents flow across elongated topographic features the depth integrated baroclinic energy flux and energy densities at these sites are on the order of 10 4 w m 1 and 10 4 j m 2 respectively a modal decomposition indicates that 62 of the outgoing energy flux is accounted for by the first internal mode 15 is accounted for by the second mode and less than 5 is accounted for by each subsequent higher mode the tidal dissipation due to bottom friction along the ridge is estimated to be 0 1 gw the level of turbulent dissipation near the ridge owing to tidal energy conversion remains to be determined to assess fully the barotropic baroclinic energy budget

the formation and fate of internal waves in the south china sea internal oceanic waves are subsurface gravity waves that can be enormous and travel thousands of kilometres before breaking but they are difficult to study here observations of such waves in the south china sea reveal their formation mechanism extreme turbulence relationship to the kuroshio current and energy budget internal waves are the underwater version of more familiar surface waves they can be enormous and travel thousands of kilometres before breaking the south china sea is known to be home to the largest internal waves in the world s oceans but their size generation mechanisms and role in the regional energy budget are unknown matthew alford and colleagues now present the results from the iwise observational campaign and reveal that internal waves more than 200 metres high break in the south china sea and create turbulence that is orders of magnitude larger than in the open ocean and that wave formation is influenced by the kuroshio current these results now allow for a complete energy budget of the south china sea and for a more accurate incorporation of internal waves into climate models internal gravity waves the subsurface analogue of the familiar surface gravity waves that break on beaches are ubiquitous in the ocean because of their strong vertical and horizontal currents and the turbulent mixing caused by their breaking they affect a panoply of ocean processes such as the supply of nutrients for photosynthesis1 sediment and pollutant transport2 and acoustic transmission3 they also pose hazards for man made structures in the ocean4 generated primarily by the wind and the tides internal waves can travel thousands of kilometres from their sources before breaking5 making it challenging to observe them and to include them in numerical climate models which are sensitive to their effects6 7 for over a decade studies8 9 10 11 have targeted the south china sea where the oceans most powerful known internal waves are generated in the luzon strait and steepen dramatically as they propagate west confusion has persisted regarding their mechanism of generation variability and energy budget however owing to the lack of in situ data from the luzon strait where extreme flow conditions make measurements difficult here we use new observations and numerical models to 1 show that the waves begin as sinusoidal disturbances rather than arising from sharp hydraulic phenomena 2 reveal the existence of 200 metre high breaking internal waves in the region of generation that give rise to turbulence levels 10 000 times that in the open ocean 3 determine that the kuroshio western boundary current noticeably refracts the internal wave field emanating from the luzon strait and 4 demonstrate a factor of two agreement between modelled and observed energy fluxes which allows us to produce an observationally supported energy budget of the region together these findings give a cradle to grave picture of internal waves on a basin scale which will support further improvements of their representation in numerical climate predictions

transport by breaking internal gravity waves on slopes we use the results of a direct numerical simulation dns with a particle tracking model to investigate three dimensional transport by breaking internal gravity waves on slopes onshore transport occurs within an upslope surge of dense fluid after breaking offshore transport occurs due to an intrusion of mixed fluid that propagates offshore and resembles an intermediate nepheloid layer inl entrainment of particles into the inl is related to irreversible mixing of the density field during wave breaking maximum onshore and offshore transport are calculated as a function of initial particle position and can be of the order of the initial wave length scale for particles initialized within the breaking region an effective cross shore dispersion coefficient is also calculated and is roughly three orders of magnitude larger than the molecular diffusivity within the breaking region particles are transported laterally due to turbulence that develops during wave breaking and this lateral spreading is quantified with a lateral turbulent diffusivity lateral turbulent diffusivity values calculated using particles are elevated by more than one order of magnitude above the molecular diffusivity and are shown to agree well with turbulent diffusivities estimated using a generic length scale turbulence closure model based on a favourable comparison of dns results with those of a similar two dimensional case we use two dimensional simulations to extend our cross shore transport results to additional wave amplitude and bathymetric slope conditions

holocene itcz and indian monsoon dynamics recorded in stalagmites from oman and yemen socotra abstract high resolution oxygen isotope 18o profiles of holocene stalagmites from four caves in northern and southern oman and yemen socotra provide detailed information on fluctuations in precipitation along a latitudinal transect from 12 n to 23 n 18o values reflect the amount of precipitation which is primarily controlled by the mean latitudinal position of the itcz and dynamics of the indian summer monsoon ism during the early holocene rapidly decreasing 18o values indicate a rapid northward displacement in the mean latitudinal position of the summer itcz and the associated ism rainfall belt with decadal to centennial scale changes in monsoon precipitation correlating well with high latitude temperature variations recorded in greenland ice cores during the middle to late holocene the summer itcz continuously migrated southward and monsoon precipitation decreased gradually in response to decreasing solar insolation a trend which is also recorded in other monsoon records from the indian and east asian monsoon domains importantly there is no evidence for an abrupt middle holocene weakening in monsoon precipitation although abrupt monsoon events are apparent in all monsoon records they are short lived and clearly superimposed on the long term trend of decreasing monsoon precipitation for the late holocene there is an anti correlation between ism precipitation in oman and inter monsoon spring autumn precipitation on socotra revealing a possible long term change in the duration of the summer monsoon season since at least 4 5 ka bp together with the progressive shortening of the ism season gradual southward retreat of the mean summer itcz and weakening of the ism the total amount of precipitation decreased in those areas located at the northern fringe of the indian and asian monsoon domains but increased in areas closer to the equator

sea surface temperature and salinity reconstruction from coral geochemical tracers massive scleractinian corals secrete an aragonitic skeleton which incorporates a large array of chemical tracers corals present several advantages for palaeoclimate research they grow continuously and can live up to 1000 years they are easy to date and they can be sampled at high resolution weekly to monthly resolution both live and fossil corals can be collected in the field in the past two decades significant efforts have been made to identify robust tracers of sea surface temperature sst and salinity sss in corals to date sr ca and 18o are considered to be the most reliable sst tracers although changes in seawater 18o can significantly alter sst reconstructed from coralline 18o because these variations in seawater 18o can be linked to sss changes this initial problem can in fact be turned into an advantage and provide us with an sss tracer the sst component in the coral 18o signal can either be evaluated through sr ca measurements or in some case simply filtered out however there is still much uncertainty concerning the exact mode of incorporation of trace elements and stable isotopes into the coral skeleton the effects of growth rate light intensity feeding habits ph and water chemistry are still poorly documented a review of the strength and weaknesses of sr ca and 18o is presented together with some examples of sst and sss reconstructions other potential sst tracers are also reviewed it is expected that the ability to grow corals in aquarium under controlled conditions and that the development of sophisticated analytical techniques at the micrometric level should help us understand better the robustness of each tracers and the factors controlling their incorporation in coral aragonite

two hundred fifty years of reconstructed and modeled tropical temperatures 1 recent large scale palaeoclimate reconstructions of past temperature have been essentially biased to the extratropics owing to a paucity of proxy data in tropical regions herein we describe the first coral based reconstruction of sea surface temperatures ssts for the whole of the tropics 30 n 30 s it was developed from 14 disparate coral records located in the indian and pacific oceans over the most replicated period the reconstruction explains 57 of the tropical sst variance however the strength of this signal weakens markedly as the number of coral records decreases the reconstruction is robust between 1850 and 1993 but some fidelity is indicated back as far as the mid 18th century these results suggest that ambiguities in the low frequency domain of 18o measurements can be partially overcome by pooling together multiple time series from different locations around the tropics agreement with simulations from two general circulation models indicates that the late 20th century is likely the warmest period in the tropics for the last 250 years and that this recent warming can only be explained by anthropogenic forcing the high frequency variability is dominated by the el nino southern oscillation the reconstruction owing to the small number of coral records is unfortunately restricted both in time and space therefore we hope that this study will spur the palaeoclimate community to develop new and longer proxy series to improve the current meager data base of temperature sensitive series in the tropics

high resolution windows into early holocene climate srca coral records from the huon peninsula high precision measurements of srca ratios are reported for porites corals from the uplifted holocene coral terraces at huon peninsula papua new guinea the early holocene porites have u th mass spectrometric ages of 8920 60 yr and 7370 50 yr and 234u t values of 145 2 similar to modern seawater the srca coral records provide 5 6 year high resolution near weekly time windows into early holocene sea surface temperatures seasonal temperature fluctuations are generally in the range of 1 c with occasional excursions of 2 c which may indicate the more frequent recurrence of very strong enso el nino southern oscillation events mean annual srca temperatures of 24 2 1 1 c and 22 9 0 8 c have been obtained which are 2 3 c cooler than that exhibited by a modern porites these results indicate that during the early holocene the equatorial western pacific ocean was at least several degrees cooler than present day temperatures this is consistent with late glacial coral records from the caribbean that indicate lower 6 c sea surface temperatures for the equatorial oceans the huon peninsula corals also indicate that ssts were several degrees cooler than those in the caribbean during the early holocene thus although the northern hemisphere summer radiation maximum occurred at 10 ka there appears to have been a significant lag in the response of the equatorial western pacific ocean to this warming cooler early holocene sea surface temperatures in the western pacific may have been due to changing patterns of ocean atmosphere circulation resulting from the exposure of large areas of continental shelf in the southeast asia region a consequence of lower glacial sea levels it is likely that ocean temperatures in the huon peninsula were influenced by the opening at 7 ka of the torres strait that now separates new guinea from the australian mainland

tracking the extent of the south pacific convergence zone since the early 1600s 1 the south pacific convergence zone spcz is the largest and most persistent spur of the intertropical convergence zone at the southeastern edge of the spcz near 170 w and 15 20 s a surface ocean salinity frontal zone exists that separates fresher western pacific warm pool water from saltier and cooler waters in the east this salinity front is known to shift east and west with the phase of the el nino southern oscillation we have generated subannually resolved and replicated coral oxygen isotopic time series from fiji 17 s 179 e and rarotonga 21 5 s 160 w that have recorded interannual displacements of the salinity front over the last 380 years and also indicate that at lower frequencies the decadal mean position of the salinity front and eastern extent of the spcz has shifted east west through 10 to 20 of longitude three times during this interval the most recent and largest shift began in the mid 1800s as the salinity front progressively moved eastward and salinity decreased at both sites our results suggest that sea surface salinity at these sites is now at the lowest levels recorded and is evidence for an unprecedented expansion of the spcz since the mid 1800s the expansion of the spcz implies a gradual change in the south pacific to more la nina like long term mean conditions this observation is consistent with the ocean thermostat mechanism for the pacific coupled ocean atmosphere system whereby exogenous heating of the atmosphere would result in greater warming in the western pacific and a greater east west surface temperature gradient components 8034 words 7 figures 2 tables

increased seasonality in middle east temperatures during the last interglacial period the last interglacial period about 125 000 years ago is thought to have been at least as warm as the present climate owing to changes in the earth s orbit around the sun it is thought that insolation in the northern hemisphere varied more strongly than today on seasonal timescales which would have led to corresponding changes in the seasonal temperature cycle here we present seasonally resolved proxy records using corals from the northernmost red sea which record climate during the last interglacial period the late holocene epoch and the present we find an increased seasonality in the temperature recorded in the last interglacial coral today climate in the northern red sea is sensitive to the north atlantic oscillation a climate oscillation that strongly influences winter temperatures and precipitation in the north atlantic region from our coral records and simulations with a coupled atmosphere ocean circulation model we conclude that a tendency towards the high index state of the north atlantic oscillation during the last interglacial period which is consistent with european proxy records contributed to the larger amplitude of the seasonal cycle in the middle east

palaeoenvironmental change in tropical australasia over the last 30 000 years a synthesis by the oz intimate group the tropics are the major source of heat and moisture for the australasian region determining the tropics response over time to changes in climate forcing mechanisms such as summer insolation and the effects of relative sea level on exposed continental shelves during the last glacial period is an ongoing process of re evaluation we present a synthesis of climate proxy data from tropical australasia spanning the last 30 000 years that incorporates deep sea core coral speleothem pollen charcoal and terrestrial sedimentary records today seasonal variability is governed largely by the annual migration of the inter tropical convergence zone itcz influencing this region most strongly during the austral summer however the position of the itcz has varied through time towards the end of marine isotope stage mis 3 conditions were far wetter throughout the region becoming drier first in the south universally cooler land and sea surface temperature sst were characteristic of the last glacial maximum with drier conditions than previously although episodic wet periods are noted in the fluvial records of northern australia the deglacial period saw warming first in the coral sea and then the indonesian seas with a pause in this trend around the time of the antarctic cold reversal c 14 5 ka coincident with the flooding of the sunda shelf wetter conditions occurred first in indonesia around 17 ka and northern australia after 14 ka the early holocene saw a peak in marine sst to the northwest and northeast of australia modern vegetation was first established on indonesia then progressively south and eastward to ne australia flores and the atherton tablelands show a dry period around 11 6 ka steadily becoming wetter through the early holocene the mid late holocene was punctuated by millennial scale variability associated with the el nino southern oscillation this is evident in the marine coral speleothem and pollen records of the region

millennial scale trends in west pacific warm pool hydrology since the last glacial maximum models and palaeoclimate data suggest that the tropical pacific climate system plays a key part in the mechanisms underlying orbital scale and abrupt climate change atmospheric convection over the western tropical pacific is a major source of heat and moisture to extratropical regions and may therefore influence the global climate response to a variety of forcing factors the response of tropical pacific convection to changes in global climate boundary conditions abrupt climate changes and radiative forcing remains uncertain however here we present three absolutely dated oxygen isotope records from stalagmites in northern borneo that reflect changes in west pacific warm pool hydrology over the past 27 000 years our results suggest that convection over the western tropical pacific weakened 18 000 20 000 years ago as tropical pacific and antarctic temperatures began to rise during the early stages of deglaciation convective activity as inferred from oxygen isotopes reached a minimum during heinrich event 1 ref 10 when the atlantic meridional overturning circulation was weak pointing to feedbacks between the strength of the overturning circulation and tropical pacific hydrology there is no evidence of the younger dryas event in the stalagmite records however suggesting that different mechanisms operated during these two abrupt deglacial climate events during the holocene epoch convective activity appears to track changes in spring and autumn insolation highlighting the sensitivity of tropical pacific convection to external radiative forcing together these findings demonstrate that the tropical pacific hydrological cycle is sensitive to high latitude climate processes in both hemispheres as well as to external radiative forcing and that it may have a central role in abrupt climate change events

a review of internal solitary wave dynamics in the northern south china sea abstract the current research into internal solitary waves isws and the related dynamic processes in the northern south china sea scs are reviewed in this paper this unique wave phenomenon did not draw much interest until about one decade ago and is now one of the hot topics in the field of wave dynamics three methods of investigation are summarized in the paper namely remote sensing images in situ measurements and numerical simulations previous works have primarily been based on one or two of these methods and have provided great insights into such wave phenomena the lifetime of an isw in the northern scs from its origin in the luzon strait ls through to its formation and evolution in the deep basin and its transformation near the shelf break up until its dissipation on the continental shelf is summarized with the illustration of different investigation approaches various factors that can affect the wave generation processes are summed up as well such factors as are barotropic tides in the ls kuroshio intrusion temporal and spatial variation of stratification and the modulation of the western ridge in the ls can significantly alter the wave fields and are extensively discussed

el nino modoki and its possible teleconnection 1 using observed data sets mainly for the period 1979 2005 we find that anomalous warming events different from conventional el nino events occur in the central equatorial pacific this unique warming in the central equatorial pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly ssta on both sides along the equator empirical orthogonal function eof analysis of monthly tropical pacific ssta shows that these events are represented by the second mode that explains 12 of the variance since a majority of such events are not part of el nino evolution the phenomenon is named as el nino modoki pseudo el nino modoki is a classical japanese word which means a similar but different thing the el nino modoki involves ocean atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution analogous to the southern oscillation in the case of el nino hence the total entity is named as el nino southern oscillation enso modoki the enso modoki events significantly influence the temperature and precipitation over many parts of the globe depending on the season the impacts over regions such as the far east including japan new zealand western coast of united states etc are opposite to those of the conventional enso the difference maps between the two periods of 1979 2004 and 1958 1978 for various oceanic atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline this appears to be a cause of more frequent and persistent occurrence of the enso modoki event during recent decades

radiation and dissipation of internal waves generated by geostrophic motions impinging on small scale topography theory abstract observations and inverse models suggest that small scale turbulent mixing is enhanced in the southern ocean in regions above rough topography the enhancement extends o 1 km above the topography suggesting that mixing is supported by the breaking of gravity waves radiated from the ocean bottom in this study it is shown that the observed mixing rates can be sustained by internal waves generated by geostrophic motions flowing over bottom topography weakly nonlinear theory is used to describe the internal wave generation and the feedback of the waves on the zonally averaged flow vigorous inertial oscillations are driven at the ocean bottom by waves generated at steep topography the wave radiation and dissipation at equilibrium is therefore the result of both geostrophic flow and inertial oscillations differing substantially from the classical lee wave problem the theoretical predictions are tested versus two dimensional high resolution numerical simulations with parameters representative of

el nino like pattern in ice age tropical pacific sea surface temperature sea surface temperatures ssts in the cold tongue of the eastern equatorial pacific exert powerful controls on global atmospheric circulation patterns we examined climate variability in this region from the last glacial maximum lgm to the present using a sst record reconstructed from magnesium calcium ratios in foraminifera from sea floor sediments near the galapagos islands cold tongue sst varied coherently with precession induced changes in seasonality during the past 30 000 years observed lgm cooling of just 1 2 c implies a relaxation of tropical temperature gradients weakened hadley and walker circulation southward shift of the intertropical convergence zone and a persistent el nino like pattern in the tropical pacific this is contrasted with mid holocene cooling suggestive of a la nina like pattern with enhanced sst gradients and strengthened trade winds our results support a potent role for altered tropical pacific sst gradients in global climate variations

modeling el nino and its tropical teleconnections during the last glacial interglacial cycle 1 simulations with the ncar climate system model csm a global coupled ocean atmosphere sea ice model for the last glacial interglacial cycle reproduce recent estimates based on alkenones and mg ca ratios of sea surface temperature sst changes and gradients in the tropical pacific and predict weaker el ninos la ninas compared to present for the holocene and stronger el ninos la ninas for the last glacial maximum lgm changes for the lgm holocene are traced to a weakening strengthening of the tropical pacific zonal sst gradient wind stresses and upwelling and a sharpening weakening of the tropical thermocline results suggest that proxy evidence of weaker precipitation variability in new guinea and ecuador are explained not only by changes in el nino la nina but also changes in the atmospheric circulation and hydrologic cycle index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4267 oceanography general paleoceanography 4522 oceanography physical el nino 3337 meteorology and atmospheric dynamics numerical modeling and data assimilation 9604 information related to geologic time cenozoic citation otto bliesner b l e c brady s i shin z liu and c shields modeling el nino and its tropical teleconnections during the last glacial interglacial cycle geophys res lett 30 23 2198 doi 10 1029 2003gl018553 2003

climate change at the 4 2 ka bp termination of the indus valley civilization and holocene south asian monsoon variability 1 planktonic oxygen isotope ratios off the indus delta reveal climate changes with a multi centennial pacing during the last 6 ka with the most prominent change recorded at 4 2 ka bp opposing isotopic trends across the northern arabian sea surface at that time indicate a reduction in indus river discharge and suggest that later cycles also reflect variations in total annual rainfall over south asia the 4 2 ka event is coherent with the termination of urban harappan civilization in the indus valley thus drought may have initiated southeastward habitat tracking within the harappan cultural domain the late holocene drought cycles following the 4 2 ka bp event vary between 200 and 800 years and are coherent with the evolution of cosmogenic 14c production rates this suggests that solar variability is one fundamental cause behind holocene rainfall changes over south asia

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

holocene changes in eastern tropical pacific climate inferred from a galapagos lake sediment record abstract paleoclimate records from the tropical pacific suggest the early to mid holocene was a period of reduced el nino southern oscillation enso variability with a transition to modern increased enso frequency occurring some time in the last few thousand years however the nature and timing of this shift remains uncertain due to the discontinuous nature and or coarse resolution of many enso proxies as well as a lack of agreement between previously published records a new continuous climate record from el junco crater lake in the galapagos islands reveals several abrupt changes in lake level and precipitation through the holocene hydroclimatic model simulations suggest that el junco lake level responds sensitively to increases in precipitation associated with el nino events rising during wet el nino events and falling during the intervening dry periods grain size data from el junco sediment cores indicate past lake level variability likely associated with changing seasonal precipitation and enso frequency the grain size data suggest increased precipitation intensity prior to 9000 120 cal years bp and after 4200 130 cal years bp as well as a two step increase in precipitation at 3200 160 and 2000 100 cal years bp maximum holocene precipitation and inferred enso variability occurred between 2000 100 and 1500 70 cal years bp during the same period that six other independent proxy records suggest higher enso frequency and longer stronger el nino events decreasing sediment carbon nitrogen c n ratios in el junco sediments indicate rising lake levels from the early holocene to present corroborating the grain size data the inferred increase in precipitation at 4200 130 cal years bp and at 2000 100 cal years bp coincides with decreasing southwest asian and east asian monsoon intensity suggesting tropical pacific climate and the asian monsoon were interconnected systems at centennial to millennial timescales during the holocene a weakening trend in the asian monsoon and the trend toward wetter conditions at el junco also coincide with a trend toward cooler and drier conditions inferred from cariaco basin sediment proxies from the mid holocene to present suggesting the migration of the intertropical convergence zone itcz likely influenced hydrological changes in both the eastern tropical pacific and the asian monsoon region during the holocene

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

mid holocene enso issues in quantitative model proxy data comparisons 1 evaluation of climate model simulations using observed data contributes to the assessment of confidence in model predictions of future climate change the mid holocene represents an opportunity to evaluate model simulations of el nino southern oscillation enso in comparison with coral proxy evidence of reduced enso amplitude quantitative comparisons between coral records and model output have been limited by 1 the use of different measures of enso amplitude 2 possible sampling of natural variability in short records and 3 uncertainty about the stationarity of the relationship between central pacific sea surface temperature sst variability and enso signals at the coral site we examine these issues using modern and fossil coral records from the western pacific and model simulations of preindustrial and mid holocene climate as a measure of enso amplitude the standard deviation is found to be preferable to event frequency or size as event based measures are highly dependent on the choice of threshold and may be unreliable for a small number of events model enso amplitude is found to be strongly dependent on the choice of averaging period with calendar year averages smoothing the seasonal enso signal a relatively robust relationship between sst variability in the nino3 4 region and the enso sst and precipitation anomalies archived in corals is demonstrated for the instrumental period and for a set of model simulations remaining uncertainty about changes in enso teleconnections under paleoclimate conditions implies the need for additional proxy records from enso sensitive regions before quantitative reconstructions of enso amplitude can be used to evaluate model sensitivity

post glacial evolution of the indo pacific warm pool and el nino southern oscillation recent research has revealed new insights into the temperature size and variability of the indo pacific warm pool ipwp and the nature of the el nino southern oscillation enso since the last glacial maximum lgm sea surface temperature sst reconstructions from foraminiferal mg ca alkenone and revised coral sr ca palaeothermometry agree that ssts in the ipwp during the lgm were similar to 3degreesc cooler than at present in the central portion of the ipwf the rapid post glacial rise in sst led the deglaciation by similar to 3000 years to produce near modern ssts by the early holocene in contrast further west and north post glacial shifts in ssts in the south china and sulu seas are synchronous with abrupt climate changes in the north atlantic new evidence for the nature of the little ice age in the tropics has been obtained from a 420 year record of coral sr ca and 6180 from the great barrier reef australia this indicates that ssts and salinity were higher in the 18th century than in the 20th century the results suggest that the tropical pacific played a role as a source region of water vapour during the global expansion of little ice age glaciers the onset of modern enso periodicities is identified by palaeo enso records throughout the tropical pacific region similar to 5000 years ago with an abrupt increase in enso magnitude similar to 3000 years ago individual enso events recorded by corals reveal that the precipitation response to el nino temperature anomalies was subdued in the mid holocene the apparent non linear onset of enso in the late holocene appears to reflect abruptly enhanced interaction between the southern oscillation and the pacific intertropical convergence zone comparisons of precipitation variability recorded by great barrier reef corals with enso indices for the last 350 years confirms that non stationarity of enso teleconnections is a natural characteristic of modern climate c 2003 elsevier ltd and inqua all rights reserved

climate change and the collapse of the akkadian empire evidence from the deep sea the akkadian empire ruled mesopotamia from the headwaters of the tigris euphrates rivers to the persian gulf during the late third millennium b c archeological evidence has shown that this highly developed civilization collapsed abruptly near 4170 150 calendar yr b p perhaps related to a shift to more arid conditions detailed paleoclimate records to test this assertion from mesopotamia are rare but changes in regional aridity are preserved in adjacent ocean basins we document holocene changes in regional aridity using mineralogic and geochemical analyses of a marine sediment core from the gulf of oman which is directly downwind of mesopotamian dust source areas and archeological sites our results document a very abrupt increase in eolian dust and mesopotamian aridity accelerator mass spectrometer radiocarbon dated to 4025 125 calendar yr b p which persisted for 300 yr radiogenic nd and sr isotope analyses confirm that the observed increase in mineral dust was derived from mesopotamian source areas geochemical correlation of volcanic ash shards between the archeological site and marine sediment record establishes a direct temporal link between mesopotamian aridification and social collapse implicating a sudden shift to more arid conditions as a key factor contributing to the collapse of the akkadian empire