multidecadal oceanographic changes in the western pacific detected through high resolution bomb derived radiocarbon measurements on corals high resolution measurements of radiocarbon 14c in corals can be used to reconstruct past variability in ocean conditions here we report seasonal 14c changes in coral from ishigaki island japan and compare with previously reported data from palau and guam our data clearly indicate a significant increase in 14c from 1947 to 1998 related to atmospheric nuclear bomb testing the three early 14c spikes related to the atmospheric nuclear bomb tests in the us proving grounds at bikini and enewerak atoll conducted in 1954 1956 and 1958 were detected from the ishigaki coral after 1976 variability in the mindanao dome region related to north equatorial current nec bifurcation latitude migration affected the 14c difference between palau and guam whereas the difference between ishigaki and guam was not correlated with the bifurcation latitude the 14c difference between ishigaki and guam may be due to mesoscale eddies in the kuroshio area on the decadal scale the northward shift of nec bifurcation latitude after 1976 the year as known as pacific decadal oscillation regime shift from negative to positive was concurrent with the abundant westward propagating mesoscale eddies in the subtropical countercurrent region and stronger kuroshio transport off the east taiwan which may be represented by a smaller 14c difference between ishigaki and guam after 1976

precise zircon u pb and molybdenite re os dating of the shuikoushan granodiorite related pb zn mineralization southern hunan south china abstract the shuikoushan ore district located in southern hunan province south china contains pb zn au mineralization hosted in the devonian to triassic strata and mesozoic granodiorite intrusions ore minerals are mainly pyrite sphalerite galena and minor molybdenite molybdenite usually intergrown with pyrite formed during pb zn hydrothermal mineralization in order to determine the precise age of pb zn mineralization and further understand the relationship between magma emplacement and hydrothermal mineralization in the ore district molybdenite re os dating and zircon sims u pb dating were undertaken the zircon u pb dating reveals that the granodiorite intrusion was emplaced at 158 8 1 8 ma mswd 0 40 re os isotopic age of seven molybdenite samples yields model ages ranging from 157 5 2 5 ma to 161 0 2 4 ma and gives a well defined 187re 187os isochron age of 157 8 1 4 ma 2 mswd 1 3 indicating the timing of pb zn mineralization in the shuikoushan ore district at about 158 ma this date coincides well with the zircon sims u pb age of the granodiorite revealing a genetic association between the pb zn mineralization and the granitic magmatism combined with geochronological data published for other pb zn cu deposits in southern hunan it can be concluded that the granodiorite related pb zn mineralization throughout southern hunan mainly occurred at 160 156 ma rather than 180 170 ma or 170 160 ma as considered previously the pb zn mineralization and major w sn mineralization in southern hunan are coeval and may be related to the same geological event

the northeastward current southeast of the ryukyu islands in late fall of 2000 estimated by an inverse technique 1 the northeastward current nc southeast of the ryukyu islands is estimated using an inverse technique with hydrographic section data collected in december 2000 the inversion results show the nc flowing over the continental slope with a subsurface maximum velocity of 34 cm s 1 at 270 dbar depth southeast of okinawa and 67 cm s 1 at 400 dbar depth east of amami ohshima the nc volume transports are nearly equal at the two lines 15 sv and their vertical profiles exhibit similar subsurface maximum structure at both lines these results strongly suggest that the nc off amami ohshima originates from the nc off okinawa during our observation period

comment on current system east of the ryukyu islands by a nagano et al 1 in a recent paper nagano et al 2007 hereafter n2007 discussed the variation of current structure and volume transport of the ryukyu current system rcs east of the ryukyu islands using an inverse technique with hydrographic section data collected from three cruises their paper appears to be important for understanding this western boundary current since it is based on repeated hydrographic surveys in the region east of the ryukyu islands but acquiring meaningful results from inverse calculations requires great care fiadeiro and veronis 1982 p 160 say because inverse analysis always supplies a solution it appeared that the assumed reference level matters less in inverse theory than in the hydrographer s level of no motion approach actual computations have shown that is not true a bad assumption leads to bad results the advantage of inverse theory is that one sees how bad the results are the inverse technique minimizes the velocity at the reference level and that point is indeed raised in the final paragraph of n2007 which used the reference level of 100 dbar to determine whether this shallow reference level is an appropriate condition or not one should investigate the effect of choosing other reference levels in particular deeper levels in this note we perform two inverse calculations to calculate the current east of the ryukyu islands from the same data as one of the n2007 cruises but using a reference level of 2000 dbar the resulting rcs circulation field is we believe more realistic than that of n2007 2 three hydrographic surveys were carried out during may june september and october 2002 along three lines ae e os east of the ryukyu islands figure 1 may june and september cruises used xctd xbt casts along the e line but the october cruise collected ctd casts along all three lines surprisingly absolute geostrophic velocity sections determined by n2007 with a 100 dbar reference level revealed large values up to 30 40 cm s 1 at 1000 dbar the deepest level shown figures 2 3b and 4c in n2007 we have calculated full depth absolute geostrophic velocity sections using the inverse results of n2007 and plotted them to 3000 dbar figures 2a 2b 3a 3b 4a and 4b figures 2b 3b and 4b show strong deep currents with maximum speeds of 20 50 cm s 1 on each line in each case note the contour lines of velocity are nearly vertical and strong currents extend to the bottom for example a current velocity of 57 cm s 1 touches the bottom near 3100 dbar in the ae section is the computed strong deepcurrent field real or is it an artifact of the shallow reference level we address this question by carrying out the inverse calculation using a reference level of 2000 dbar instead of 100 dbar and compare results using the two reference levels we present results for the october cruise data only because the xbt xctd casts reached only 1000 dbar also the ctd measurements provide more accuracy in the inverse calculations

petrogenesis of late jurassic two mica granites and associated diorites and syenite porphyries in guangzhou se china abstract the south china block scb is considered to have undergone extensive reworking of continental crust however the mechanisms of this crustal reworking are unclear here we report on late jurassic 162 155 ma two mica granites and associated diorites and syenite porphyries from the huolushan longyandong area of guangzhou city southeastern china the two mica granites have high sio2 contents 69 6 73 6 wt and weakly peraluminous to strongly peraluminous compositions these rocks have enriched sr nd hf isotopic compositions 87sr 86sr i 0 7094 0 7145 end t 10 5 to 9 3 ehf t 12 7 to 4 2 the huolushan two mica granites have variable zircon o isotopic compositions 18o 6 8 10 4 whereas the longyandong two mica granites have homogeneous compositions 18o 8 6 9 9 the huolushan syenite porphyries have moderate sio2 59 6 60 1 wt and high alkaline k2o na2o 9 4 9 8 wt contents their sr nd hf o isotopic compositions 87sr 86sr i 0 7105 0 7119 end t 9 9 to 9 8 ehf t 14 1 to 5 9 18o 6 5 10 6 are similar to those of the huolushan two mica granites the huolushan diorites have moderate sio2 contents 59 9 60 4 wt and are high k calc alkaline and metaluminous with mg values of 43 2 43 8 their sr nd isotopic compositions 87sr 86sr i 0 7106 0 7109 end t 8 8 to 8 6 are less enriched than those of the two mica granites and syenite porphyries in addition the diorites have high zircon 18o values 7 8 8 9 and a wide range of zircon ehf t values 13 4 to 5 6 we propose that the huolushan two mica granites were derived from a metagreywacke dominated hybridized source with minor juvenile crustal rocks and that the longyandong two mica granites were generated by partial melting of metagreywackes the huolushan syenite porphyries were formed by the mixing of metasedimentary rock derived felsic magmas and minor enriched mantle derived alkaline magmas the huolushan diorites were most likely derived by partial melting of mafic lower crust with the dioritic magmas undergoing assimilation and fractional crystallization afc during ascent all of these intrusive rocks were likely formed in an extensional intraplate setting the mantle derived magmas which could have been triggered by lithospheric extension underplated the middle lower crust and provided heat for crustal reworking and materials for late mesozoic crustal growth

speleothem evidence for holocene fluctuations of the prairie forest ecotone north central usa carbon and oxygen isotopic trends from seven midwestern speleothems record significant offsets in the timing of middle holocene vegetation change interactions of dry pacific and moist gulf of mexico air masses maintained a sharp moisture gradient across iowa minnesota and wisconsin such that the arrival of prairie was offset by 2000 years between caves and pollen sites located only 50 km apart oxygen isotopes shift concomitantly with carbon in most cases although these changes are believed to represent increased evaporative enrichment of 18o prior to infiltration during the prairie period

energetics of eddy mean flow interactions along the western boundary currents in the north pacific abstractthe energetics of eddy mean flow interactions along two western boundary currents of the north pacific the kuroshio and ryukyu currents are systematically investigated using 22 years of n

observations of flow variability through the kerama gap between the east china sea and the northwestern pacific the kerama gap near the middle of the ryukyu island chain is the deepest channel with a sill depth of 1050 m connecting the east china sea ecs to the northwestern pacific we measured the flow through the kerama gap from june 2009 to june 2011 the 2 year mean transport 2 0 0 7 sv is into the ecs from the northwestern pacific it contributes about 11 of the mean kuroshio transport in the ecs at the pn line subtidal standard deviation of the transport through the kerama gap is 3 2 sv comparable to that of the pn line kuroshio transport 4 0 sv suggesting a significant effect of kerama gap transport on temporal variability of the kuroshio transport in the ecs comparison with time series of satellite measured sea surface height maps reveals that temporal variability of the kerama gap transport is related to the arrival of mesoscale eddies from the east high low transport into the ecs is associated with the presence of a cyclonic anticyclonic eddy south of the kerama gap

satellite altimeter monitoring the kuroshio transport south of japan in 1993 1995 we carried out observations of the kuroshio south of japan including direct current measurements and repeated hydrographic surveys along a satellite track of the topex poseidon altimeter the velocity field of the kuroshio is determined by geostrophic calculation using the repeated hydrographic survey data referenced to velocities observed at mid and abyssal depths the volume transport of the kuroshio is estimated from this velocity field the estimated transports of the kuroshio have a high correlation with sea surface height differences across the kuroshio having this relationship and using the altimeter data we obtained a time series of the kuroshio transport over seven years at ten day intervals the kuroshio transport excluding contributions by local recirculations is estimated to be 42 106 m sec on average the correlation between sea surface height difference and transport provides a practical method of long term monitoring of the kuroshio transport using satellite altimetry

extraordinary subsurface mesoscale eddy detected in the southeast of okinawa in february 2002 1 in february 2002 a subsurface mesoscale eddy with extraordinary features was detected at a depth of about 300 dbar in the southeast of okinawa a part of the ryukyu islands the water mass occupying this subsurface eddy is characterized as the north pacific subtropical mode water npstmw with salinity maximum and thick thermostad its temperature salinity and potential density at the core of the eddy are 18 4 c 34 81 and 25 06 respectively thickness and width of the eddy are about 300 m and 100 km respectively mixing between the eddy and the surrounding water mass is also found such eddy with the npstmw has never been detected during ten years

structure and variability of the kuroshio current in tokara strait four years of mooring array measurements in tokara strait south of kyushu japan from 1992 to 1996 are used to analyze the structure and temporal variability of the kuroshio current the mean kuroshio current in tokara strait shows a nearly permanent subsurface double core structure possibly due to topographic blockage effects the dominant variations of the kuroshio in tokara strait are separated into long term variability typically 100 day period and short term variability 10 days to 1 month according to spectrum and wavelet analysis the long term variability has a large horizontal scale across the strait with a striking twofold banded structure in spatial correlations this is due to the north south kuroshio axis shift that advects the double core structure of the mean current the axis shift can be indexed with the northeastward current velocity at the northernmost station a composite analysis using this index shows well defined northward and southward axis shift structures of the kuroshio current from the composite of the topex poseidon sea level anomaly in terms of this index the kuroshio axis shift and the current structure change are associated with a dipole shape sea level anomaly east of tokara strait on the other hand the short term variability of high kinetic energy only has a small horizontal scale within the northern part of the current which is related to frontal variability there exists a deep southwestward undercurrent below 600 m in the northern part of tokara strait flowing along the isobaths the undercurrent becomes stronger during the northward shift of the kuroshio axis while it almost disappears during the southward shift

annual variation of the kuroshio transport in a two layer numerical model with a ridge abstract a two layer numerical model driven by the wind stress is used to explain the observed annual variation of the kuroshio transport south of japan special attention is given to the effect of a ridge representing the izu ogasawara ridge on the generation of the baroclinic activity through the coupling of the barotropic and baroclinic modes of motion for annual variation lower layer motion is found in areas surrounding the ridge because isostasy a state of no motion in the lower layer is not achieved within such a short timescale thus the lower layer flow impinges on the bottom slope this impinging process generates anomalies of the upper layer thickness especially on the eastern side of the ridge thereafter anomalies move westward with characteristic velocities composed of the vertically averaged flow and westward propagation of the long baroclinic rossby wave forced above the ridge as anomalies of the upper layer thickness move westward above the ridge isostasy is accomplished with res

energetics of a global ocean circulation model compared to observations 1 the majority of the eddy kinetic energy eke in the ocean is found on scales of 50 km to 500 km encompassed by mesoscale eddies and the meanders and rings of the boundary currents mesoscale eddies play a critical role in the dynamics of the ocean circulation with instabilities of the strong mean currents generating eddies in the upper ocean interactions between eddies transfer energy from the upper ocean to the deep ocean where eddies interact with bottom topography to generate abyssal mean flows and eddies transfer momentum back to the mean currents the kinetic energy in a global hybrid coordinate ocean circulation model hycom is compared with long term observations from surface drifters geostrophic currents from satellite altimetry subsurface floats and deep current meter moorings hycom configured at 1 12 5 9 km typical of the present generation of high resolution models is deficient in eke in both the upper and abyssal ocean depths greater than 3000 m by 21 and 24 respectively compared to surface drifting buoys and deep current meters increasing the model resolution to 1 25 4 4 km or injecting mesoscale eddies through the assimilation of surface observations in a 1 12 5 model increases the surface and the abyssal eke to levels consistent with the observations in these models the surface abyssal eke is increased by 23 51 and 15 46 for the higher resolution or data assimilative models respectively compared to the 1 12 5 non assimilative model while data assimilation increases the eke in both the upper and abyssal ocean the kinetic energy of the mean flow in the upper ocean is decreased in the data assimilative hindcast

current system east of the ryukyu islands 1 the ryukyu current system rcs is a northeastward current southeast of the ryukyu islands the variation of current structure in the rcs region was investigated on the basis of the absolute geostrophic velocity estimated by inverse calculation using hydrographic data three realizations of the rcs are examined from cruises in may september and october 2002 it was found that the current structure in the rcs region is divided into upper and lower layers by an isopycnal surface of 26 the currents in both layers proceed northeastward along the eastern slope east of the ryukyu islands the current in the upper layer merges with the inflow from the interior region resulting in larger northeastward volume transport southeast of amami oshima island than southeast of okinawa island the volume transport from the east reaches more than 40 of that southeast of amami oshima island on the other hand the current in the lower layer is not affected by inflow from the east it is also found that the upper rcs gains heat mainly through the advection of warm water from the east resulting in an increase in the downstream temperature by about 0 5 c on average

tidal and residual currents across the northern ryukyu island chain observed by ferryboat adcp ferryboat acoustic doppler current profiler adcp data from 2003 to 2012 are used to estimate the tidal and residual currents across the northern ryukyu island chain ric between the islands of okinawa and amamioshima in this region the m2 tide current is the strongest tidal component and the k1 tide current is the strongest diurnal tidal component the corresponding maximum amplitudes are 40 and 34 cm s 1 respectively after removal of the tidal currents the mean volume transport 1 5 2 7 sv flows into the east china sea ecs from the western north pacific through four channels in this area in an empirical orthogonal function eof analysis performed to clarify the temporal and spatial variability of currents through the four channels the first two eof modes account for 71 and 18 of the total variance respectively the eof1 mode shows a clear bottom intensified mode through the deep channel which is likely to be formed by the propagation of bottom trapped long topographic rossby wave caused by the impingement of westward propagating mesoscale eddies upon the eastern slope of the northern ric the eof2 mode has significant seasonal variability and may be driven by the wind stress prevailing over the kuroshio flow region around the northern ric in october to november this study provides observational evidence of the water exchanges across the northern ric which is essential for constructing a circulation scheme in the north pacific subtropical western boundary region

a reconstruction of subtropical western north pacific sst variability back to 1578 based on a porites coral sr ca record from the northern ryukyus japan we present a seasonal reconstruction of sea surface temperature sst from 1578 to 2008 based on a porites coral sr ca record from the northern ryukyus within the kuroshio southern recirculation gyre interannual sst anomalies are generally 0 5 c making sr ca derived sst reconstructions a challenging task replicate measurements along adjacent coral growth axes enabled by the laser ablation inductively coupled plasma mass spectrometry technique used here give evidence of rather large uncertainties nonetheless derived winter sst anomalies are significantly correlated with the western pacific atmospheric pattern which has a dominant influence on winter temperature in east asia annual mean ssts show interdecadal variations notably cold intervals between 1670 and 1700 during the maunder minimum mm and between 1766 and 1788 characterized by a negative phase of the north atlantic oscillation cold summers in 1783 and 1784 coincide with the long lasting laki eruption that had a profound impact on the northern hemisphere climate including the severe tenmei famine in japan the decades between 1855 and 1900 are significantly cooler than the first half of the twentieth century while those between 1700 and 1765 following the mm are warmer than average sst variability in the ryukyus is only marginally influenced by the pacific decadal oscillation so that external forcing remains the main driver of low frequency temperature changes however the close connection between the kuroshio extension ke and its recirculation gyre suggests that decadal sst anomalies associated with the ke front also impact the ryukyus and there is a possible additional role for feedback of the kuroshio oyashio variability to the large scale atmosphere at decadal timescale

the current system east of the ryukyu islands as revealed by a global ocean reanalysis abstract the structure and variability of the ryukyu current system rcs which forms the western boundary current along the eastern slope of the ryukyu islands are studied using results from a 32 layer 1 12 5 global hybrid coordinate ocean model hycom and navy coupled ocean data assimilation ncoda reanalysis for the period 1993 2012 it is confirmed that the reanalysis realistically reproduces salient features of the observed currents at three sections southeast of miyakojima okinawa and amami ohshima the mean velocity sections show well developed subsurface velocity maxima between 700 and 900 m the current core southeast of amami ohshima shows year to year variations with cyclonic anticyclonic circulation east of amami ohshima generating weak strong velocity cores interaction of the rcs with an anticyclonic eddy often produces a two core velocity structure with a surface core in the upper 300 m and a deeper core near 700 900 m the horizontal structure of the rcs at 15 m depth shows a well developed northeastward current northeast of okinawa which is partly fed by the southwestward extension of the anticyclonic recirculation gyre the rcs forms a continuous northeastward current from miyakojima to amami ohshima below 500 m with shoreward intensification the circulation at 2000 m shows a seasonal flow reversal which is northeastward from december to june and southwestward from august to october with july and november being the transition months the volume transports across these three sections have respective mean values of 0 6 6 2 and 12 4 sv 1 sv 106 m3 s 1 and standard deviations of 10 2 7 1 and 11 3 sv they have dominant seasonal variations with the maximum in winter and spring and the minimum in summer the interannual variation of the transport anomaly which co varies with the rcs core results from westward propagating mesoscale eddies arriving from the pacific interior

the kuroshio east of taiwan moored transport observations from the woce pcm 1 array observations from the woce pcm 1 moored current meter array east of taiwan for the period september 1994 to may 1996 are used to derive estimates of the kuroshio transport at the entrance to the east china sea three different methods of calculating the kuroshio transport are employed and compared these methods include 1 a direct method that uses conventional interpolation of the measured currents and extrapolation to the surface and bottom to estimate the current structure 2 a dynamic height method in which moored temperature measurements from moorings on opposite sides of the channel are used to estimate dynamic height differences across the current and spatially averaged baroclinic transport profiles and 3 an adjusted geostrophic method in which all moored temperature measurements within the array are used to estimate a relative geostrophic velocity field that is referenced and adjusted by the available direct current measurements the first two methods are largely independent and are shown to produce very similar transport results the latter two methods are particularly useful in situations where direct current measurements may have marginal resolution for accurate transport estimates these methods should be generally applicable in other settings and illustrate the benefits of including a dynamic height measuring capability as a backup for conventional direct transport calculations the mean transport of the kuroshio over the 20 month duration of the experiment ranges from 20 7 to 22 1 sv 1 sv 106 m3 s 1 for the three methods or within 1 3 sv of each other the overall mean transport for the kuroshio is estimated to be 21 5 sv with an uncertainty of 2 5 sv all methods show a similar range of variability of 10 sv with dominant timescales of several months fluctuations in the transport are shown to have a robust vertical structure with over 90 of the transport variance explained by a single vertical mode the moored transports are used to determine the relationship between kuroshio transport and sea level difference between taiwan and the southern ryukyu islands allowing for long term monitoring of the kuroshio inflow to the east china sea

effects of mesoscale eddies on the volume transport and branch pattern of the kuroshio east of taiwan using satellite altimeter data and a long term altimetric transport index for the kuroshio inflow northeast of taiwan the effects of mesoscale eddies on the kuroshio volume transport kvt at the east taiwan channel and the branching pattern of the kuroshio east of taiwan are investigated at scales from those of individual events to interannual timescales both anticyclonic and cyclonic eddies are found to be able either to strengthen or weaken the kvt depending on the relative strength of mass convergence and divergence produced upstream and downstream of the eddies the major factor influencing the intensity of the kuroshio inflow is the meridional location of the eddies for single eddy events the kvt is significantly correlated with the latitude of the eddy s center the correlations being 0 44 and 0 48 for anticyclonic and cyclonic eddies respectively for dipole eddy events when the direction angle falls in the interval 40 150 240 300 the kvt anomaly tends to be positive negative furthermore low kvt events generally correspond to the formation of the ryukyu current branch which is also generated from strong mass divergence produced by the eddies in addition on interannual time scales the variation of kvt is closely related to the relative number of anticyclonic to cyclonic eddies west of 125 e with a correlation of 0 5 this article is protected by copyright all rights reserved

the northeastward current southeast of okinawa island observed during november 2000 to august 2001 1 in order to estimate the variability of current structure and mean geostrophic volume transport in the southeast of okinawa island the round trip acoustic travel times between sea bottom and surface at nine sites were measured by inverted echo sounder with pressure gauge pies from november 2000 to august 2001 vertical sections of geostrophic velocity are calculated by using vertical profiles of specific volume anomaly derived by the gravest empirical mode method from the pies data in the upper 500 m layer over a slope shallower than 1000 m depth the northeastward current reached up to 60 cm s 1 during the occupation of an anticyclonic eddy and decreased to 15 cm s 1 during the occupation of a cyclonic eddy around the mean of 20 cm s 1 the temporal mean geostrophic volume transport relative to the 2000 dbar level was estimated to be 6 1 sv 1 sv 106 m3 s 1 northeastward in the west of 128 85 e