a nonlinear theory for el nino bursting abstract a new mechanism is proposed that explains two key features of the observed el nino southern oscillation enso phenomenon its irregularity and decadal amplitude changes using a low order enso model the authors show that the nonlinearities in the tropical heat budget can lead to bursting behavior characterized by decadal occurrences of strong el nino events la nina events are not affected a feature that is also seen in enso observations one key result of this analysis is that decadal variability in the tropics can be generated without invoking extratropical processes or stochastic forcing the el nino bursting behavior simulated by the low order enso model can be understood in terms of the concept of homoclinic and heteroclinic connections it is shown that this new model for enso amplitude modulations and irregularity although difficult to prove might explain some features of enso dynamics seen in more complex climate models and the observations

a role for scavenging in the marine biogeochemical cycling of zinc and zinc isotopes zinc zn and cadmium cd are important biologically active trace metals in the ocean to date the marine distributions of these elements have been understood primarily in terms of biological assimilation by growing phytoplankton and regeneration of sinking biological material initial studies of zn and cd concentrations and stable isotope ratios 66zn and 114cd have therefore focused on their use as simple tracers of assimilation and regeneration in the oceans however these two processes are insufficient to explain new data on the marine distribution of zn and 66zn here using the first high resolution paired marine depth profiles of zn cd 66zn and 114cd we suggest that scavenging of zn onto organic matter plays a major yet largely unconsidered role in the marine cycling of zn this hypothesis is supported by culture experiments which show that zn released from degrading phytoplankton is rapidly scavenged back onto organic matter and that adsorbed zn is isotopically heavier than the dissolved phase by 0 58 in contrast very little cd or phosphate was scavenged and cd isotopes were not significantly fractionated during degradation our hypothesis is further supported by one dimensional modeling which reproduces observed marine 66zn profiles with 1 of zn adsorbed to particles understanding how zn cycling in the oceans is a balance between assimilation scavenging and regeneration is necessary in order to investigate 66zn as a tracer of marine productivity we anticipate that paired analyses of 66zn and 114cd will prove to be valuable new tools in constraining patterns of global primary productivity providing key information for the marine carbon cycle during periods of past and present global climate change

southern hemisphere circulation features associated with el nino southern oscillation events abstract composite seasonal mean and anomaly fields prepared from operational numerical analyses have been used to describe the southern hemisphere sh circulation features associated with el nino southern oscillation enso events the period of analyses available 1972 83 has limited the composites to include only three enso events the reliability and stability of the composites has been tested using multiple permutation methods and by comparison with the results obtained using a longer period 1950 79 of sh rawinsonde station data in the sh winter a weak equivalent barotropic wavetrain pattern of anomalies extends over australia and the south pacific ocean to south america this wavetrain pattern is quite variable in amplitude and location between enso events although it is more stable over the subtropical pacific in the sh summer the circulation anomalies are more zonally symmetric with increased height at low and high latitudes and decreased height in middle latitudes the circulation anoma

stable strontium isotopes δ88 86sr in cold water corals a new proxy for reconstruction of intermediate ocean water temperatures abstract zooxanthellate scleractinian corals are known as archives for temporal variations of climate variables such as sea surface temperature salinity or productivity the use of azooxanthellate cold water corals as potential archives for intermediate water mass properties and climate variability was tested recently however the correlation of established proxies such as 18o and 13c with temperature is difficult since there is no direct temperature equation applicable as in shallow water corals other temperature proxies such as sr ca mg ca and u ca are influenced by the complex microstructure of the aragonite skeleton the rate of calcification and other vital effects observed for coral species for the first time we show that the stable strontium isotope ratio 88 86sr incorporated in the skeletons of the cold water coral species lophelia pertusa portrays the ambient seawater temperature the temperature sensitivity from live samples collected along the european continental margin covering a temperature range from 6 to 10 c is 0 026 0 003 c 2 standard error which is a sensitivity similar to the tropical shallow water coral record of pavona clavata this indicates a similar fractionation process of strontium for both zooxanthellate and azooxanthellate corals for coral aragonite the 88 86sr ratio may serve as a new paleo temperature proxy and introduces new perspectives in paleoceanography with respect to intermediate water dynamics

molybdenum isotopic composition of modern and carboniferous carbonates we investigate the redox sensitive isotope system of molybdenum mo in marine carbonates to evaluate their potential as archive of the mo isotopic composition of coeval seawater we present mo isotope data delta 98 95 mo of modern skeletal and non skeletal carbonates as well as a variety of precipitates from the mid and late carboniferous the external reproducibility is determined by repeated analyses of two commercially available carbonate standards the resulting uncertainty of the low concentration samples is 0 1 parts per thousand 2 sigma analysis of modern ooid sands from the bahamas shows a consistently heavy mo isotopic composition delta 98 95 mo between 2 and 2 2 parts per thousand approaching modern mean seawater values delta 98 95 mo 2 3 parts per thousand 0 1 parts per thousand 2 sigma this suggests that isotope fractionation during mo uptake into non skeletal carbonate precipitates is small in contrast modern skeletal carbonates show variable isotopic compositions 0 1 to 2 2 parts per thousand which suggests a biologically controlled fractionation process the varying mo signatures found in carboniferous cement phases point to a strong response to local changes in fluid composition from which they precipitated overall we recognized three important factors to cause an offset relative to ocean water mo derived from skeletal components input of detrital mo and admixture of light hydroxide derived mo via diagenetic fluids all of these factors cause a lighter mo isotopic composition relative to seawater due to the apparent small isotope fractionation during mo uptake into non skeletal carbonates their delta 98 95 mo closely reflects the ambient fluid composition from these results we conclude that carbonates represent a promising new tool to characterize the water mass mo isotopic composition of marine paleo environments

the influence of temperature and vital effects on magnesium isotope variability in porites and astrangia corals abstract the magnesium isotope composition 26 mg of sub annually and bulk sampled porites corals is presented and suggests that the coral seawater fractionation factor 26 mg is temperature dependent with a sensitivity of 0 03 c 1 although the apparent temperature dependence of 26 mg in porites corals could be used empirically to reconstruct paleoclimate its temperature sensitivity is about three times that of abiogenic aragonites which indicates that kinetic and or biologically induced processes collectively known as vital effects are also important comparison with data from abiogenic aragonite precipitation experiments suggests that 26 mg vital effects vary seasonally in porites the 26 mg of skeleton deposited in winter is within the analytical error of abiogenic aragonite but that of skeletal aragonite grown during summer exhibits significantly smaller fractionations that may be associated with light enhanced calcification the observed vital effect is consistent with 26 mg but cannot be evaluated with current data however the observed vital effect is not consistent with the isotope fractionation expected from rayleigh processes ion attachment detachment kinetics or diffusion furthermore the 26 mg of symbiotic and asymbiotic astrangia corals is within analytical error and indicates that vital effects cannot be attributed to the presence of photosymbionts some data suggest that the offset between coral and abiogenic aragonite 26 mg may be proportional to that for oxygen isotope fractionations raising the possibility that vital effects in both isotope systems may be influenced by a common mechanism although the presence of vital effects and analytical limitations will complicate the development of a 26 mg based paleothermometer it may still be a valuable tool for reconstructing seawater 26 mg or investigating biomineralization processes especially when applied as part of a multi proxy approach

tropical cyclone movement and surrounding flow relationships abstract this paper presents results of a comprehensive study of the relationship between the movement of tropical cyclones and the large scale circulation which surrounds them cyclones have been stratified by direction and speed of movement latitude intensity change and size as determined by the radius of the outermost closed surface isobar in three ocean basins the northwest pacific the west atlantic and the australian south pacific region twenty one different stratifications are available in the northwest pacific 13 in the west atlantic and 6 in the australian south pacific area cyclone movement and surrounding flow relationships were studied at different pressure levels and a variety of radii pressure weighted layer averages were also analyzed in search of such relationships results show an important relationship between surrounding large scale flow and tropical cyclone movement for all stratifications the winds in the mid troposphere 500 700 mb at 5 7 latitude radius from the cyclone

porites corals as recorders of mining and environmental impacts misima island papua new guinea abstract in 1989 open cut gold mining commenced on misima island in papua new guinea png open cut mining by its nature causes a significant increase in sedimentation via the exposure of soils to the erosive forces of rain and runoff this increased sedimentation affected the nearby fringing coral reef to varying degrees ranging from coral mortality smothering to relatively minor short term impacts the sediment associated with the mining operation consists of weathered quartz feldspar greenstone and schist these rocks have distinct chemical characteristics rare earth element patterns and high abundances of manganese zinc and lead and are entering the near shore environment in considerably higher than normal concentrations using laser ablation inductively coupled plasma mass spectrometry la icp ms we analyzed eight colonies two from high sedimentation two transitional two minor and two unaffected control sites for y la ce mn zn and pb all sites show low steady background levels prior to the commencement of mining in 1988 subsequently all sites apart from the control show dramatic increases of y la and ce associated with the increased sedimentation as well as rapid decreases following the cessation of mining the elements zn and pb exhibit a different behavior increasing in concentration after 1989 when ore processing began and one year after initial mining operations elevated levels of zn and pb in corals has continued well after the cessation of mining indicating ongoing transport into the reef of these metals via sulfate rich waters rare earth element ree abundance patterns measured in two corals show significant differences compared to coral sea seawater the corals display enrichments in the light and middle rees while the heavy rees are depleted relative to the seawater pattern this suggests that the nearshore seawater ree pattern is dominated by island sedimentation trace element abundances of misima island corals clearly record the dramatic changes in the environmental conditions at this site and provide a basis for identifying anthropogenic influences on corals reefs

mixed mode oscillations of el nino southern oscillation abstractvery strong el nino events occur sporadically every 10 20 yr the origin of this bursting behavior still remains elusive using a simplified three dimensional dynamical model of the tropical pacific climate system which captures el nino southern oscillation enso combined with recently developed mathematical tools for fast slow systems the authors show that decadal enso bursting behavior can be explained as a mixed mode oscillation mmo which also predicts a critical threshold for rapid amplitude growth it is hypothesized that the mmo dynamics of the low dimensional climate model can be linked to a saddle focus equilibrium point which mimics a tropical pacific ocean state without ocean circulation

tropical cyclone track characteristics as a function of large scale circulation anomalies abstract factors that contribute to intraseasonal variability in western north pacific tropical cyclone track types are investigated it is hypothesized that the 700 mb large scale circulation can affect tropical cyclone track characteristics by enhancing or excluding genesis in certain regions and concurrently prohibiting or favoring recurving versus straight tracks a track type climatology indicates that genesis location alone may explain some of the variability in track type although some genesis regions have no preference for straight moving or recurving tracks a formation north of 20 n or east of 150 e and north of 10 n favors a recurvature track these recurving storms are classified as recurving north and recurving storms that form in regions with nearly equal probability of straight or recurving tracks are classified as recurving south a compositing technique is used to define anomalous 700 mb large scale circulations that exist during the formation of tropical cyclones that subsequently fol

the biogeochemical cycling of zinc and zinc isotopes in the north atlantic ocean zinc zn is a marine micronutrient with an overall oceanic distribution mirroring the major macronutrients especially silicate seawater zn isotope ratios 66zn are a relatively new oceanographic parameter which may offer insights into the biogeochemical cycling of zn to date the handful of published studies of seawater 66zn show the global deep ocean to be both remarkably homogeneous approximately 0 5 and isotopically heavier than the marine sources of zn 0 1 to 0 3 here we present the first high resolution oceanic section of 66zn from the u s geotraces ga03 north atlantic transect from lisbon to woods hole throughout the surface ocean biological uptake and release of isotopically light zn together with scavenging of heavier zn leads to large variability in 66zn in the ocean below 1000 m 66zn is generally homogeneous 0 50 0 14 2 sd though deviations from 0 5 allow us to identify specific sources of zn the mediterranean outflow is characterized by 66zn of 0 1 to 0 3 while margin sediments are a source of isotopically light zn 0 5 to 0 8 which we attribute to release of nonregenerated biogenic zn mid atlantic ridge hydrothermal vents are also a source of light zn close to 0 5 though zn is not transported far from the vents understanding the biogeochemical cycling of zn in the modern ocean begins to address the imbalance between the light 66zn signature of marine sources and the globally homogeneous deep oceans 66zn of 0 5 on long timescales with overall patterns pointing to sediments as an important sink for isotopically light zn throughout the oceans

application of scale selective data assimilation to tropical cyclone track simulation tropical cyclone track is strongly controlled by the large scale environmental circulation in limited area models lams driven by global analyses or forecasts through a conventional lateral boundary nesting approach the global analyses are often distorted by the use of sponge zone or interpolation when they are passed into the lam in this study a dynamical downscaling approach based on scale selective data assimilation ssda is applied to a limited area numerical weather prediction model with emphasis on tropical cyclone track simulation the idea of the ssda approach is to drive the lam not only from the lateral boundary but also from the model domain interior the large scale flow from global analyses or forecasts is assimilated into the regional model using 3 d variational data assimilation the large scale features in the lam are thus constrained to follow the global analyses while allowing the regional model itself to develop the regional and small scale characteristics the results from the case study of hurricane katrina 2005 show that both large and small scale flows in the regional model benefited from the ssda approach leading to an improvement in the accuracy of storm track simulation when provided with an accurate large scale circulation from global analyses in addition the ssda procedure is shown to be an effective method to construct a nested grid regional modeling system that reduces model sensitivity to model domain geometry and location

the effect of regional climate model domain choice on the simulation of tropical cyclone like vortices in the southwestern indian ocean a regional climate model is tested for several domain configurations over the southwestern indian ocean to examine the ability of the model to reproduce observed cyclones and their landfalling tracks the interaction between large scale and local terrain forcing of tropical storms approaching and transiting the island landmass of madagascar makes the southwestern indian ocean a unique and interesting study area in addition tropical cyclones across the southern indian ocean are likely to be significantly affected by the large scale zonal flow therefore the effects of model domain size and the positioning of its lateral boundaries on the simulation of tropical cyclone like vortices and their tracks on a seasonal time scale are investigated four tropical cyclones which occurred over the southwestern indian ocean in january of the years 1995 97 are studied and four domains are tested the regional climate model is driven by atmospheric lateral boundary conditions that are derived from large scale meteorological analyses the use of analyzed boundary forcing enables comparison with observed cyclones in these tests simulations are performed using a 60 km horizontal resolution and for an extended time integration of about 6 weeks results show that the positioning of the eastern boundary of the regional model domain is of major importance in the life cycle of simulated tropical cyclone like vortices a vortex entering through the eastern boundary of the regional model is generally well simulated the size of the domain also has a bearing on the ability of the regional model to simulate vortices in the mozambique channel and the island landmass of madagascar additionally influences storm tracks these results show that the regional model can produce cyclonelike vortices and their tracks with some deficiencies given analyzed lateral boundary forcing statistical analyses of gcm driven nested model ensemble integrations are now required to further address predictive skill of cyclones in the southwestern indian ocean and to test if the model can realistically simulate tropical storm genesis as opposed to advecting existing tropical disturbances entering through the model boundaries

a simple model for the pacific cold tongue and enso abstract a conceptual model is constructed based upon the bjerknes hypothesis of tropical atmosphere ocean interaction it is shown that strong feedbacks among the trade winds equatorial zonal sea surface temperature contrast and upper ocean heat content occur in the tropical pacific basin coupled atmosphere ocean dynamics produce both the strong pacific cold tongue climate state and the el nino southern oscillation enso phenomenon the cold tongue climate state is unstable and gives rise to the self sustained enso which can be understood as an equatorial ocean recharge oscillator the small basin size and the influence of a wind system resulting from heating sources of its adjacent landmasses are responsible for a weak and stable atlantic cold tongue state that cannot support enso like interannual variability the presence of westerly wind associated with the walker circulation ascending at the western pacific warm pool disables the dynamical coupling processes in the equatorial indian ocean as a

biogeochemical cycling of zinc and its isotopes in the southern ocean abstract we report zn concentration and isotope data for seawater samples from the atlantic sector of the southern ocean collected during the ipy geotraces ant xxiv iii cruise along the greenwich zero meridian data are reported for the full depth range of the water column at three stations as well as a transect of surface samples using a new analytical approach that is presented in detail here zn concentrations increase with depth though due to proximity to upwelling sites surface concentrations are not as low as in some parts of the ocean such as further northward into the sub antarctic zone for two depth profiles south of the polar front zone the physical stratification of the upper water column is reflected in sudden near surface changes in zn concentration with depth in contrast beneath 100 300 m zn concentrations barely change with depth zn isotopic data beneath 1000 m for the southern ocean data presented here as well as published data from the north atlantic and north pacific are strikingly homogeneous with an average 66zn 0 53 0 14 2sd 2se 0 03 n 21 the surface southern ocean is more variable with 66zn ranging from 0 07 to 0 80 between the two is a thin horizon at 40 80 m which in the southern ocean as well as the north atlantic and north pacific is characterised by distinctly light isotopic signatures with 66zn about 0 3 lower than surface waters strong correlations between si and zn concentrations seen here and elsewhere coupled to the lack of any systematic relationship between si and zn isotopes in the southern ocean suggest that the removal of zn associated with diatom opal involves little or no isotopic fractionation regeneration of this zn also explains the homogeneous zn isotopic composition of the global deep ocean so far sampled however the low zn content of opal requires that deep ocean zn does not directly come from the opal phase itself but rather from associated organic material external to the diatom frustule during growth experimental data are consistent with little or no fractionation during incorporation of zn into this material on the other hand the light zinc at 40 80 m is most consistent with the regeneration of an intra cellular pool that both culturing experiments and field data suggest will be isotopically light the data thus imply two processes by which zn is taken up in the surface ocean that these pools have very different regeneration lengthscales and that physical mixing of the oceans cannot eradicate their isotopic signatures finally the deep 66zn ocean value is significantly higher than the current best estimate of the input to the oceans the most obvious candidate for the required light sink is the survival of some of the cellular zn to be buried in sediment

paleoprecipitation record from coral sr ca and δ18o during the mid holocene in the northern south china sea coupled high resolution sr ca and delta o 18 records of a modern and a mid holocene coral from sanya in the southern hainan island northern south china sea scs were reported and the residual delta o 18 delta delta o 18 were calculated to indicate precipitation change in this region unlike other paleoclimate studies this study focused on changes of precipitation time rather than precipitation amount as negative delta delta o 18 peaks in coral generally correspond to peak precipitations or rainy seasons in the surrounding region the time offsets between negative delta delta o 18 peaks and other seasonal indicators such as sea surface temperature sst can well indicate the time of rainy seasons and the precise time offsets can be estimated by the method of cross spectral analysis the results of the modern coral indicate that the variation of the coral delta delta o 18 lags that of the instrumental measured precipitation by about 2 months and about 3 months to the sst derived from coral sr ca ratios this agrees well with the modern observation that the salinity change in the southern coastal regions generally lags that of the precipitation in hianan island by about 2 months and the precipitation change lags about 1 month behind the sst in this region thus coral delta delta o 18 records can be a reliable proxy for the change of rainy seasons in this region the results of the mid holocene coral show about 2 5 months leading of the delta delta o 18 variation ahead of the sst by compensating the approximate 3 months lag of the delta delta o 18 variation behind the sst in modern time the occurrence of rainy seasons during the mid holocene may have advanced about 5 6 months in detail it may start around december and end around april to may with maximum occurring around february therefore rainy seasons mainly occur in winter through early spring during the mid holocene compared with that from may through october in modern times such precipitation patterns appear to agree with the mid holocene pollen records in this region variations of large scale circulation may possibly result in such a different precipitation pattern further studies in particular climate model studies collaborated with meteorologists are required for a better understanding of the mechanism

a high resolution sr ca and δ18o coral record from the great barrier reef australia and the 1982 1983 el nino abstract a high resolution near weekly sr ca and oxygen isotopic record is presented for a coral from the pandora reef in the great barrier reef gbr of australia during the period 1978 to 1984 the records are well correlated except for periods of high rainfall when river runoff has significantly modified the 18o value of seawater using the sr ca temperature calibration of de villiers et al 1994 the sr ca records exhibit seasonally controlled cyclical sst sea surface temperature variations of from 21 to 28 c during the very strong el nino of 1982 1983 the sr ca systematics indicate a sharp drop in the winter sst to 18 5 c this represents a temperature anomaly of 3 c which is approximately twice that given by the 18o variations suggesting an 2 amplification of the anomaly by the sr ca system possibly due to the increasing dominance of inorganically controlled aragoniteseawater fractionation the oxygen isotopic systematics show the combined effects of both temperature and changing seawater 18o values the latter reflecting the influx of 18o depleted runoff during periods of high rainfall due to the extremely low 10 3 sr and ca contents of river run off relative to seawater it is possible to use the sr ca thermometer to calculate temperatures independent of major floods and hence deconvolve the combined effects in the oxygen isotopic record of variable temperature and the 18o value of seawater using this approach it is possible to quantitatively reproduce the volume of runoff from the burdekin river during the periods of major flooding that occurred in early 1979 and 1981 the results of this study demonstrate that the combined use of high resolution sr ca and 18o systematics in scleractinian corals is a powerful tool for providing quantitative constraints on past climate

the effect of skeletal mass accumulation in porites on coral sr ca and δ18o paleothermometry 1 paleotemperature estimates based on coral sr ca have not been widely accepted because the reconstructed glacial holocene shift in tropical sea surface temperature 4 6 c is larger than that indicated by foraminiferal mg ca 2 4 c we show that corals over estimate changes in sea surface temperature sst because their records are attenuated during skeletogenesis within the living tissue layer to quantify this process we microprofiled skeletal mass accumulation within the tissue layer of porites from australasian coral reefs and laboratory culturing experiments the results show that the sensitivity of the sr ca and 18o thermometers in porites will be suppressed variable and dependent on the relationship between skeletal growth rate and mass accumulation within the tissue layer our findings help explain why 18o sst sensitivities for porites range from 0 08 c to 0 22 c and are always less than the value of 0 23 c established for biogenic aragonite based on this observation we recalibrated the coral sr ca thermometer to determine a revised sensitivity of 0 084 mmol mol c after rescaling most of the published sr ca sst estimates for the indo pacific region for the last 14 000 years 7 c to 2 c relative to modern fall within the 95 confidence envelope of the foraminiferal mg ca sst records we conclude that two types of calibration scales are required for coral paleothermometry an attenuated porites specific thermometer sensitivity for studies of seasonal to interannual change in sst and importantly the rescaled 0 084 mmol mol c sr ca sensitivity for studies of 20th century trends and millennial scale changes in mean sst the calibration scaling concept will apply to the development of transfer functions for all geochemical tracers in corals

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

spectral nudging to eliminate the effects of domain position and geometry in regional climate model simulations 1 it is well known that regional climate simulations are sensitive to the size and position of the domain chosen for calculations here we study the physical mechanisms of this sensitivity we conducted simulations with the regional atmospheric modeling system rams for june 2000 over north america at 50 km horizontal resolution using a 7500 km 5400 km grid and ncep ncar reanalysis as boundary conditions the position of the domain was displaced in several directions always maintaining the u s in the interior out of the buffer zone along the lateral boundaries circulation biases developed a large scale structure organized by the rocky mountains resulting from a systematic shifting of the synoptic wave trains that crossed the domain the distortion of the large scale circulation was produced by interaction of the modeled flow with the lateral boundaries of the nested domain and varied when the position of the grid was altered this changed the large scale environment among the different simulations and translated into diverse conditions for the development of the mesoscale processes that produce most of precipitation for the great plains in the summer season as a consequence precipitation results varied sometimes greatly among the experiments with the different grid positions to eliminate the dependence of results on the position of the domain we used spectral nudging of waves longer than 2500 km above the boundary layer moisture was not nudged at any level this constrained the synoptic scales to follow reanalysis while allowing the model to develop the small scale dynamics responsible for the rainfall nudging of the large scales successfully eliminated the variation of precipitation results when the grid was moved we suggest that this technique is necessary for all downscaling studies with regional models with domain sizes of a few thousand kilometers and larger embedded in global models