oceanic uptake rate of anthropogenic co2 in a subpolar marginal sea the sea of okhotsk 1 we proposed a new simple approach for estimating the oceanic rate of increase of anthropogenic co2 uanth in a subpolar marginal sea that produces ventilated water with the sea ice formation this approach was based only on the differences in dissolved inorganic carbon dic and apparent oxygen utilization aou between the ventilated water and the source water applying our approach to the sea of okhotsk for 1993 1999 and 2000 we estimated the averaged uanth transported into the intermediate water ui and in the surface water from spring to fall uss f and in the surface water in winter usw to be 1 1 0 9 mol kg 1 yr 1 0 70 0 01 mol kg 1 yr 1 and 1 1 0 9 mol kg 1 yr 1 respectively during the past 8 years the accumulation rate of anthropogenic carbon was estimated as 0 78 1012 g c yr 1 over the entire sea of okhotsk

formation of 26 8 26 9 σθ water in the kuril basin of the sea of okhotsk as a possible origin of north pacific intermediate water by using all japanese hydrographic data obtained south of 55 n in latitude in the sea of okhotsk we compile a data set for this study our investigations with these data show that a large quantity of relatively cold fresh oxygen rich homogeneous intermediate water with a density range of 26 8 to 26 9 exists in the kuril basin we name this intermediate water the kuril basin intermediate water kbiw results of isosteric analyses show that a possible origin of kbiw is located in a region off the hokkaido coast in the southwestern sea of okhotsk we suggest that kbiw is produced by the isopycnal mixing of relatively dense soya warm water which appears only in early spring with the colder fresher water which originates from the northwestern okhotsk finally we demonstrate that kbiw may be a source water of the north pacific intermediate water npiw because it has the same density range and water properties

foreshock occurrence before large earthquakes rates of foreshock occurrence involving shallow m 6 and m 7 mainshocks and m 5 foreshocks were measured in two worldwide catalogs over 20 year intervals the overall rates observed are similar to ones measured in previous worldwide and regional studies when they are normalized for the ranges of magnitude difference they each span the observed worldwide rates were compared to a generic model of earthquake clustering based on patterns of small and moderate aftershocks in california the aftershock model was extended to the case of moderate foreshocks preceding large mainshocks overall the observed worldwide foreshock rates exceed the extended california generic model by a factor of 2 significant differences in foreshock rate were found among subsets of earthquakes defined by their focal mechanism and tectonic region with the rate before thrust events higher and the rate before strike slip events lower than the worldwide average among the thrust events a large majority composed of events located in shallow subduction zones had a high foreshock rate while a minority located in continental thrust belts had a low rate these differences may explain why previous surveys have found low foreshock rates among thrust events in california especially southern california while the worldwide observations suggests the opposite california lacking an active subduction zone in most of its territory and including a region of mountain building thrusts in the south reflects the low rate apparently typical for continental thrusts while the worldwide observations dominated by shallow subduction zone events are foreshock rich if this is so then the california generic model may significantly underestimate the conditional probability for a very large m 8 earthquake following a potential m 7 foreshock in cascadia the magnitude differences among the identified foreshock mainshock pairs in the harvard catalog are consistent with a uniform distribution over the range of observation

provenance of intermediate waters in the western north pacific deduced from thermodynamic imprint on δ13c of dic 1 stable carbon isotopes of dissolved inorganic carbon 13cdic together with phosphate concentrations po43 of the western north pacific marginal area are presented although 13cdic controlled not only air sea exchange but also biological activities by subtracting po43 as a biological factor from the 13cdic the thermodynamic imprint on the carbon isotopic composition 13cas is used as a conservative tracer the linear relationship between 13cas and temperature with the 13cas temperature slope of 0 104 c is observed in the north pacific subtropical region this relationship can be extended to the weddell sea deep waters therefore oceanic dic is apparently in temperature dependent isotopic equilibrium with atmospheric co2 to characterize each water mass the isotopically labeled temperature tiso which is derived from 13cas temperature relationship obtained for the subtropical gyre water and weddell sea water is introduced in contrast the 13cas temperature relationship is not necessarily linear for the northern japan sea water the kuroshio oyashio mixed water and the okhotsk sea water this nonlinearity implies apparent air sea carbon isotopic disequilibria resulting from water cooling without accompanying air sea carbon isotope equilibrium by using the potential temperature tpot and the tiso the source waters constituting intermediate waters 26 8 have been estimated the results clearly indicate that 1 the intermediate water in the southern okhotsk sea contains up to 20 japan sea water and that 2 new north pacific intermediate water npiw consists of okhotsk sea water subarctic gyre water and old subtropical npiw

seismicity alert probabilities at parkfield california revisited for a decade the u s geological survey has used the parkfield earthquake prediction experiment scenario document to estimate the probability that earthquakes observed on the san andreas fault near parkfield will turn out to be foreshocks followed by the expected magnitude 6 mainshocks during this time we have learned much about the seismogenic process at parkfield about the long term probability of the parkfield mainshock and about the estimation of these types of probabilities the probabilities for potential foreshocks at parkfield are reexamined and revised in light of these advances as part of this process we have confirmed both the rate of foreshocks before strike slip earthquakes in the san andreas physiographic province and the uniform distribution of foreshocks with magnitude proposed by earlier studies compared to the earlier assessment these new estimates of the long term probability of the parkfield mainshock are lower our estimate of the rate of background seismicity is higher and we find that the assumption that foreshocks at parkfield occur in a unique way is not statistically significant at the 95 confidence level while the exact numbers vary depending on the assumptions that are made the new alert probabilities are lower than previously estimated considering the various assumptions and the statistical uncertainties in the input parameters we also compute a plausible range for the probabilities the range is large partly due to the extra knowledge that exists for the parkfield segment making us question the usefulness of these numbers

characteristics of the cold water belt formed off soya warm current 1 we examined the data obtained by acoustic doppler current profiler conductivity temperature depth profiler and expendable bathythermograph observations which were collected in the summers of 2000 2001 and 2002 to clarify the characteristics of the cold water belt cwb i e lower temperature water than the surrounding water extending from the southwest coast of sakhalin along the offshore side of soya warm current swc and to confirm one of the formation mechanisms of the cwb as suggested by our previous study i e the upwelling due to the convergence of bottom ekman transport off the swc region the cwb was observed at about 30 km off the coast having a thickness of 14 m and a minimum temperature of 12 c at the sea surface the cwb does not have the specific water mass but is constituted of three representative water types off the northeast coast of hokkaido in summer i e swc water fresh surface okhotsk sea water and okhotsk sea intermediate water in a comparison of the horizontal distributions of current and temperature the cwb region is found to be advected to the southeast at an average of 40 29 of the maximum current velocity of the swc the pumping speed due to the convergence of the bottom ekman transport is estimated as 1 5 3 0 10 4 m s 1 we examined the mixing ratio of the cwb and the results implied that the water mass of the cwb is advected southeastward and mixes with a water mass upwelling in a different region off swc

influence of riverine alkalinity on carbonate species in the okhotsk sea 1 comparing data set of carbonate species and other hydrographic chemical properties in 1999 2000 and 2006 in the okhotsk sea we found that salinity normalized alkalinity in the subsurface water has shown a rate of increase by 2 6 0 1 mol kg 1 y 1 while the increase in salinity normalized dissolved inorganic carbon corrected by aou was almost half of that in alkalinity therefore ph has increased by 0 013 0 001 ph unit y 1 in the subsurface water 26 5 27 3 which is the origin of the north pacific intermediate water this increase in ph could be explained by the increase in alkalinity in the amur river in the last decade suggesting a possibility that could mitigate one fifth of recent ocean acidification in the north pacific

foreshock rates from aftershock abundance the question whether foreshocks behave like mainshocks that happen to have larger aftershocks is important for the understanding of earthquake nucleation and the modeling of earthquake clustering many models including the short term earthquake probability step model for forecasting short term earthquake hazard in california and the epidemic type aftershock sequence etas model for the description of earthquake clustering imply that all earthquakes of magnitude m including foreshocks can trigger earthquakes according to a magnitude dependent triggering ability 10 m the magnitudes of the triggered earthquakes are proportional to 10 bm according to the gutenberg richter relation for the magnitude frequency distribution and therefore can be larger than the magnitude of the initiating event however numerous studies observe a lower foreshock occurrence than predicted from aftershock models in this article we show that for homogeneous earthquake catalogs and a consistent definition of foreshocks and aftershocks foreshock rates can be predicted from aftershock characteristics for southern california the probability that the initiating event of an earthquake cluster in the magnitude range 2 0 4 5 is followed by at least one larger event within one day is around 4 this agrees well with corresponding data from the global centroid moment tensor cmt catalog where the probability that the initiating earthquake of a cluster is followed by at least one larger event within 30 days is around 3 these foreshock rates are significantly lower than previously reported and we discuss possible reasons for this

the influence of air sea exchange on the isotopic composition of oceanic carbon observations and modeling although the carbon isotropic composition of ocean waters after they leave the surface ocean is determined by biological cycling air sea exchange affects the carbon isotopic composition of surface waters in two ways the equilibrium fractionation between oceanic and atmospheric carbon increases with decreasing temperature in southern ocean surface waters this isotopic equilibrium enriches delta sup 13 c relative to the delta sup 13 c expected from uptake and release of carbon by biological processes alone similarly surface waters in the subtropical gyres are depleted in delta sup 13 c due to extensive air sea exchange at warm temperatures countering the tendency toward isotopic equilibration with the atmosphere a relatively slow process are the effects of the equilibration of co sub 2 itself a much faster process in regions where there is a net transfer of isotopically light co sub 2 from the ocean to the atmosphere e g the equator surface waters become enriched in sup 13 c whereas in regions where isotopically light co sub 2 is entering the ocean e g the north atlantic surface waters become depleted in sup 13 c a compilation of high quality oceanic delta sup 13 c measurements along with experiments performed using a zonally averaged three basin dynamic ocean model are used to explore these processes 40 refs 14more figs 1 tab less

chlorofluorocarbons in the sea of okhotsk ventilation of the intermediate water 1 ventilation of the intermediate layer in the sea of okhotsk is studied with regard to the ventilation of north pacific intermediate water npiw measurements of chlorofluorocarbons cfcs from 1998 to 2000 reveal that the okhotsk intermediate water is ventilated in two ways the first consists of dense water formation in the polynyas that form on the northern shelves during winter measurements show that on the northwestern shelf because of atmospheric cooling and brine rejection the cold water that forms is dense enough to enter the intermediate layer the cfc concentration in this dense shelf water dsw is high and almost saturated with respect to atmospheric cfcs indicating that the dsw experiences active air water gas exchange during its formation away from the shelves the cfc distribution shows that the dsw directly ventilates the upper level of the okhotsk sea intermediate water osiw the second ventilation process is driven by the strong tidal mixing around the bussol strait the observed distribution of cfcs at the 27 4 level suggest that diapycnal mixing around the strait transports cfcs from the surface to this deeper layer ventilating the osiw combination of both processes means that the osiw is more ventilated than pacific water at the same density levels

earthquake hazard after a mainshock in california after a strong earthquake the possibility of the occurrence of either significant aftershocks or an even stronger mainshock is a continuing hazard that threatens the resumption of critical services and reoccupation of essential but partially damaged structures a stochastic parametric model allows determination of probabilities for aftershocks and larger mainshocks during intervals following the mainshock the probabilities depend strongly on the model parameters which are estimated with bayesian statistics from both the ongoing aftershock sequence and from a suite of historic california aftershock sequences probabilities for damaging aftershocks and greater mainshocks are typically well constrained after the first day of the sequence with accuracy increasing with time

differences between spontaneous and triggered earthquakes their influences on foreshock probabilities 1 in this study we investigate the foreshock probabilities calculated from earthquake catalogs from japan southern california and new zealand unlike conventional studies on foreshocks we use a probability based declustering method to separate each catalog into stochastic versions of family trees such that each event is classified as either having been triggered by a preceding event or being a spontaneous event the probabilities are determined from parameters that provide the best fit of the real catalogue using a space time epidemic type aftershock sequence etas model the model assumes that background and triggered earthquakes have the same magnitude dependent triggering capability a foreshock here is defined as a spontaneous event that has one or more larger descendants and a triggered foreshock is a triggered event that has one or more larger descendants the proportion of foreshocks in spontaneous events of each catalog is found to be lower than the proportion of triggered foreshocks in triggered events one possibility is that this is due to different triggering productivity in spontaneous versus triggered events i e a triggered event triggers more children than a spontaneous events of the same magnitude however further analysis on simulated data shows that such difference might be caused by the events triggered by smaller events below the magnitude threshold of the catalog even if the physical interpretation is unclear a clustering model where spontaneous events and triggered events have different triggering behaviors can be used to assess the risk of foreshocks and to avoid overpredicting

carbon isotopes and habitat of polar planktic foraminifera in the okhotsk sea the carbonate ion effect under natural conditions the upper 500 or 1000 m of the water column in the okhotsk sea was sampled for living planktic foraminifera the polar species neogloboquadrina pachyderma sinistral strongly dominates the foraminiferal assemblage the subpolar to temperate species globigerina bulloides accounts for 10 25 other species account for up to 3 only the shell 18o and 13c values of the species n pachyderma sin are compared to water 18o values and 13c values of dissolved inorganic carbon dic the strong gradient in 18o composition and temperature in the upper water column is reflected in the 18o of n pachyderma sin relative to the values expected for inorganic calcite precipitated under equilibrium conditions n pachyderma sin displays a vital effect of about 1 in 18o the 13c composition of n pachyderma sin is about constant with water depth and the reflection of 13cdic in the foraminiferal shell seems to be masked by other effects most foraminifera are found above or slightly below the thermocline and can be assumed to calcify in the upper 200 m of the water column the gradient of 13cdic extends well below this depth therefore the lack of correlation can partly be attributed to this fact the remaining discrepancy between 13c of n pachyderma sin and 13cdic correlates with the carbonate ion concentration in the water column this leads to the conclusion that the carbonate ion effect cie which has been derived from culturing experiments for other species spero et al 1997 nature 390 497 500 is found here under natural conditions when the magnitude of the cie derived for g bulloides is applied to n pachyderma sin cie corrected 13c of n pachyderma sin is a direct reflection of 13cdic in the water column with a constant offset of 1 2

structure and seasonal variability of the east sakhalin current abstract in order to clarify the structure and seasonal variability of the flow field near the western boundary of the sea of okhotsk long term mooring measurements were carried out from 1998 to 2000 in this region in most of the mooring period a persistent southward flow the east sakhalin current was observed which extends from the surface to a depth around 1000 m the speed of this southward flow clearly changed seasonally the peak monthly mean speed along 53 n at a depth of 200 m attained a maximum of 37 9 cm s 1 in january and a minimum of 10 8 cm s 1 in july three different cores of intense flow were identified in the southward flow the first core was centered over the continental slope and had rather large vertical extent reaching the bottom on the slope the second core was trapped over the shelf near the surface and was observed from october to november this core was associated with less saline surface water affected by the amur river discharge the third core was intensified toward

okhotsk sea intermediate water formation deduced from oxygen isotope systematics to clarify the mechanisms of the okhotsk sea intermediate water formation water samples collected in the okhotsk sea and neighboring western north pacific were analyzed for 18o as well as salinity and other routinely measured components the 18o salinity relation in the okhotsk sea was markedly different from that in the western subarctic pacific feeding the okhotsk sea the intermediate water of the okhotsk sea was less saline than that of the western subarctic water at the same density but was more saline at the same 18o value especially in the density range 26 5 27 0 this could be due to mixing of dense shelf water formed during sea ice formation with neighboring water the amount of fresh water removed by the sea ice formation was estimated from the salinity anomaly of the okhotsk sea intermediate water the calculated amounts of fresh water removed from the okhotsk sea intermediate water corresponded to the amount of sea ice formed for 0 6 3 8 years in the okhotsk sea this suggests that the residence time of the okhotsk sea intermediate water is a few years

foreshocks and time dependent earthquake hazard assessment in southern california the probability that an earthquake in southern california m 3 0 will be followed by an earthquake of larger magnitude within 5 days and 10 km i e will be a foreshock is 6 0 5 per cent 1 s d and is not significantly dependent on the magnitude of the possible foreshock between m 3 and m 5 the probability that an earthquake will be followed by an m 5 0 main shock however increases with magnitude of the foreshock from less than 1 per cent at m 3 to 6 5 2 5 per cent 1 s d at m 5 the main shock will most likely occur in the first hour after the foreshock and the probability that a main shock will occur decreases with elapsed time from the occurrence of the possible foreshock by approximately the inverse of time thus the occurrence of an earthquake of m 3 0 in southern california increases the earthquake hazard within a small space time window several orders of magnitude above the normal background level

impact of earthquake rupture extensions on parameter estimations of point process models abstract stochastic point processes are widely applied to model spatiotemporal earthquake occurrence in particular the epidemic type aftershock sequence etas model has been shown to successfully reproduce the short term clustering of earthquakes an important parameter of the model is the value describing the scaling of the aftershock productivity with magnitude of the triggering earthquake according to 10 m fitting of the space dependent etas model to empirical data yields values that are typically much smaller than the scaling inverted from more simple stacking of aftershock sequences we show by means of synthetic simulations that this is likely to result from assuming spatial isotropy of aftershock occurrence that in fact aligns along the mainshock rupture we fit the space dependent and space independent etas models to simulations where each earthquake is a line source with an empirical magnitude length relation although the space time model describes past activity quite well it overestimates the forecasted earthquake rate on the other hand the application of the space independent etas model predicts future seismicity well and can therefore be applied for forecasting purposes our test for the observed aftershock sequence following the 1992 m 7 3 landers earthquake supports these results

the influence of air and sea exchange on the carbon isotope distribution in the sea we explore here the influence of the temperature dependence of isotope fractionation between atmospheric co2and ocean co2 on the distribution of carbon isotopes in the ocean this is accomplished by an analysis of departures from the expected redfield tie between po4 and 13c we find that for the surface ocean the temperature influence largely compensates for the biologic influence in the deep ocean the temperature influence imprinted at the sites of deepwater formation reduces somewhat the biologically induced difference between the carbon isotope ratios for deep waters produced in the northern atlantic and in the antarctic these same features are reproduced in the hamburg ocean model in order to assess the impact of changes in the ratio of ocean mixing rate to wind speed we have made a model run in which co2 exchange rates between air and sea were everywhere doubled as expected the influence of the thermodynamic effect on the oceanic carbon isotope distribution is magnified

near surface circulation and tidal currents of the okhotsk sea observed with satellite tracked drifters 1 near surface circulation of the okhotsk sea was observed with argos drifters from august 1999 to february 2000 the drifters clearly revealed the existence of the southward boundary current the east sakhalin current off the east sakhalin this current is strongly controlled by bottom topography and confined to the region shallower than 1000 m the volume transport of this current is estimated to be in the range of 4 9 sv 1 sv 106m3 s 1 with the increase from summer to winter the current appears to consist of two cores one exists near the coast 50 150 m depths with typical speeds of 0 3 0 4 m s 1 and the other exists over the shelf slope 300 900 m depths with typical speeds of 0 2 0 3 m s 1 a part of this southward current continues as far as the southern tip of sakhalin island while another part turns to the east around terpeniya bay 48 n flowing eastward as far as bussol strait most of the drifters that survived in the okhotsk sea went out to the pacific through bussol strait by less than a half year suggesting that bussol strait is the main pathway for the surface water to flow out from the okhotsk sea mesoscale anticyclonic eddies with diameters of 100 200 km are dominant in the kuril basin diurnal shelf waves were identified over the shelf in the northern part of the east sakhalin shelf large amplification of diurnal tidal currents order of 1 0 m s 1 was observed over kashevarov bank along with the residual anticyclonic circulation both diurnal and semidiurnal tidal currents were found to be enhanced in and around bussol strait

transport of chemical components in sea ice and under ice water during melting in the seasonally ice covered saroma ko lagoon hokkaido japan abstract physico chemical properties in the brine and under ice water were measured in saroma ko lagoon on the northeastern coast of hokkaido japan which is connected to the sea of okhotsk during the period from mid february through mid march 2006 the brine within brine channels of the sea ice was collected with a new sampling method examined in this study salinity dissolved inorganic carbon dic total alkalinity ta dissolved oxygen do nutrients and oxygen isotopic ratio 18 o contained in the brine within brine channels of the sea ice and in the under ice water varied largely in both time and space during the ice melt period when discharge from saromabetsu river located on the southeast of the lagoon increased markedly due to the onset of snow melting the under ice plume expands as far as 4 5 km from the river mouth at mid march 2006 transporting chemical components supplied from the river into the lagoon the under ice river water was likely transported into the sea ice through well developed brine channels in the sea ice due to upward flushing of water through brine channels occurred by loading of snowfalls deposited over the sea ice these results suggest that the river water plume plays an important role in supplying chemical components into the sea ice which may be a key process influencing the biogeochemical cycle in the seasonally ice covered saroma ko lagoon

flux of low salinity water from aniva bay sakhalin island to the southern okhotsk sea abstract in this study we examined the relationship between the low salinity water in the shelf region of the southern okhotsk sea which was seasonally sampled 0 200 m and fluxes of low salinity water from aniva bay to express the source of freshwater mixing in the surface layer we applied normalized total alkalinity nta and stable isotopes of seawater as chemical tracers nta s diagrams indicate that nta of low salinity water in the upper 30 m layer just off the soya warm current is clearly higher than in the far offshore region in summer and autumn using nta s regression lines we could deduce that the low salinity and high nta water in the upper layer originates from aniva bay for convenience we defined this water as the aniva surface water asw with values s 2450 mol kg 1 formation and transport processes of asw are discussed using historical data the interaction between the maximum core of high nta water on the bottom slope of eastern aniva bay and an anticyclonic eddy at the mouth of aniva bay are concluded to control asw formation upwelling of the cold water belt water at the tip of cape krillion is considered to cause asw outflow from aniva bay

foreshock occurrence rates before large earthquakes worldwide global rates of foreshock occurrence involving shallow m 6 and m 7 mainshocks and m 5 foreshocks were measured using earthquakes listed in the harvard cmt catalog for the period 1978 1996 these rates are similar to rates ones measured in previous worldwide and regional studies when they are normalized for the ranges of magnitude difference they each span the observed worldwide rates were compared to a generic model of earthquake clustering which is based on patterns of small and moderate aftershocks in california and were found to exceed the california model by a factor of approximately 2 significant differences in foreshock rate were found among subsets of earthquakes defined by their focal mechanism and tectonic region with the rate before thrust events higher and the rate before strike slip events lower than the worldwide average among the thrust events a large majority composed of events located in shallow subduction zones registered a high foreshock rate while a minority located in continental thrust belts measured a low rate these differences may explain why previous surveys have revealed low foreshock rates among thrust events in california especially southern california while the worldwide observations suggest the opposite california lacking an active subduction zone in most of its territory and including a region of mountain building thrusts in the south reflects the low rate apparently typical for continental thrusts while the worldwide observations dominated by shallow subduction zone events are foreshock rich

variability in river runoff distribution in the eurasian basin of the arctic ocean 1 the distribution of freshwater within the arctic ocean and its export from it are intimately involved in climate and climate change processes both within and outside the arctic ocean river runoff in the arctic ocean constitutes a major part of the arctic ocean freshwater budget within the arctic ocean variability in the distribution of river runoff will be reflected in the location of the cold halocline that isolates the sea ice from the warm atlantic layer outside the arctic ocean such variability will impact on the salinity of north atlantic waters great salinity anomaly and on deep convection areas of the north atlantic ocean and thereby potentially on global thermohaline circulation rivers entering the arctic ocean have high levels of total alkalinity that contribute significantly to the total alkalinity of the surface polar mixed layer we exploit total alkalinity data to trace river runoff in the surface polar mixed layer and to observe variability in the river runoff distribution in the eurasian basin over the period 1987 2001 the river runoff front changed from a position over the gakkel ridge in 1987 and 1991 to over the lomonosov ridge in 1996 and returned to a midpoint between the two ridges in 2001 wind field changes as characterized by the arctic oscillation index are considered to be a major factor in determining ice and surface water flow we note a correlation with 4 6 years delay between changes in river runoff distribution and the arctic oscillation index we show that the delay can be inferred from a geostrophic flow calculation

extending earthquakes reach through cascading earthquakes whatever their size can trigger other earthquakes mainshocks cause aftershocks to occur which in turn activate their own local aftershock sequences resulting in a cascade of triggering that extends the reach of the initial mainshock a long lasting difficulty is to determine which earthquakes are connected either directly or indirectly here we show that this causal structure can be found probabilistically with no a priori model nor parameterization large regional earthquakes are found to have a short direct influence in comparison to the overall aftershock sequence duration relative to these large mainshocks small earthquakes collectively have a greater effect on triggering hence cascade triggering is a key component in earthquake interactions