enhanced turbulence and energy dissipation at ocean fronts the ocean surface boundary layer mediates air sea exchange in the classical paradigm and in current climate models its turbulence is driven by atmospheric forcing observations at a 1 kilometer wide front within the kuroshio current indicate that the rate of energy dissipation within the boundary layer is enhanced by one to two orders of magnitude suggesting that the front rather than the atmospheric forcing supplied the energy for the turbulence the data quantitatively support the hypothesis that winds aligned with the frontal velocity catalyzed a release of energy from the front to the turbulence the resulting boundary layer is stratified in contrast to the classically well mixed layer these effects will be strongest at the intense fronts found in the kuroshio current the gulf stream and the antarctic circumpolar current all of which are key players in the climate system

response of diatom and silicoflagellate assemblages in the central gulf of california to regional climate change during the past 55 kyrs abstract high resolution studies of diatoms and silicoflagellates of the past 55 kyrs in cores md02 2517 2515 from the central gulf of california goc reveal profound changes in goc surface waters roperia tesselata a diatom proxy for late winter early spring upwelling and dictyocha stapedia a subtropical silicoflagellate indicative of goc sea surface temperatures ssts 24 c are common during the holocene but rare during marine isotope stage mis 2 and most of mis 3 a relationship that likely reflects a more northerly position of the north pacific high nph during the holocene in contrast during most of mis 2 27 15 ka the persistent presence of distephanus speculum a silicoflagellate associated with ssts during mis 3 55 27 ka increased dominance of azpeitia nodulifera diatom implies that stratified tropical waters were present year round whereas silicoflagellate assemblages suggest that stratified tropical conditions alternated with more productive upwelling conditions on millennial timescales reduced biosiliceous productivity during heinrich events likely reflected a reduction in both surface water nutrient levels and in the strength of northwest winds due to a weakened and more southerly nph conversely enhanced biosiliceous productivity during mis 3 interstadials was probably linked to heightened nutrient levels and a strengthened nph abrupt relative abundance increases of the silicoflagellate dictyocha aculeata approximate the termination of mis3 heinrich events and may signal times when nutrient rich deep waters associated with the resumption of enhanced atlantic meridional overturning circulation penetrated into the central gulf

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

late quaternary oceanography of the mouth of the gulf of california the polycystine connection the mouth of the gulf of california is a region where three principal water masses converge the equatorial water the water associated with the california current and the water from the gulf itself these water masses exhibit a complex interaction which has been recorded by the polycystine radiolarian distribution patterns defined in the underlying sediments the occurrence in the gulf of water associated with the california current is indicated by the distribution of cycladophora davisiana ehrenberg while the occurrence of the equatorial water is characterized by high abundance of tetrapyle octacantha muller where the california current meets the equatorial water a water mass boundary is formed and this is depicted by the distribution of druppatractus cf pyriformis bailey micropaleontological analysis of six sedimentary gravity cores located along the mouth of the gulf of california correlated through 18o stratigraphy show that from approximately 33 000 to 15 500 years ago the california current frequently invaded the mouth of the gulf displacing the water mass boundary system and the equatorial water southward these oceanographic events preceded the global climatic changes indicated by the 18o stratigraphy occurring first in the surface and subsurface water in the mouth of the gulf and then in the deep waters

cycles steps and co2 paleoceanography in the united states from 1983 1986 the field of paleoceanography experienced continued growth during the last three years the first international conference on paleoceanography was held in zurich switzerland in july 1983 and a new journal devoted to the topic paleoceanography american geophysical union washington d c began publication in spring 1986 edited by dr james kennett of the university of rhode island nine legs of the r v glomar challenger concentrated upon paleoceanographic topics legs 71 75 in the south atlantic leg 81 in the north atlantic leg 85 in the equatorial pacific leg 86 in the northwest pacific and leg 90 in the southwest pacific several special symposia and conferences resulted in volumes of collected papers dealing with topics such as climate variability hansen and takahashi 1984 the global carbon cycle sundquist and broecker 1985 catastrophes and earth history berggren and van couvering 1984 orbital insolation and periodicity berger et al 1984 and coastal upwelling suess and thiede 1983 some very useful books have been published which summarize existing information on radiolaria anderson 1983 neogene planktonic foraminifera kennett and srinivasan 1983 calcareous nannofossils haq 1983 1984 and biostratigraphy bolli et al 1983

the vertical structure of turbulent dissipation in shelf seas abstract the free fall fly profiler has been used to determine the variation in energy dissipation in the water column over a tidal cycle at mixed and stratified sites in the irish sea it was found that exhibits a strong m4 variation with a pronounced phase lag that increases with height above the bed in mixed conditions this m4 signal which extends throughout the water column is reasonably well reproduced by turbulent closure models of the vertical exchange in the summer stratified situation the m4 signal in is confined to about 40 m above the seabed with phase delays of more than 4 h relative to the seabed the lowest levels of dissipation 10 5 w m 3 measured in the pycnocline are significantly above the system noise level and much higher than predicted by a model using the mellor yamada level 2 closure scheme my2 0 however when allowance is made for the diffusion of tke the model my2 2 simulates the depth time distribution of dissipation in the stratified case satisfactorily if

planktonic foraminiferal faunal and stable isotopic indices of upwelling a sediment trap study in the san pedro basin southern california bight

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

variation of upwelling oceanic conditions during the latest pleistocene through holocene off the central peruvian coast a diatom record diatoms are well preserved in partly laminated holocene and late pleistocene sediments on the upper continental slope of central peru accumulation rates of diatom species previously recognized as tropical oceanic warm water and subtropical neritic cooler water upwelling changed markedly downcore in kasten cores obtained at 11 15 s 12 58 s and 13 37 s latitude subtropical species e g thalassiosira eccentrica group thalassiothrix frauenfeldii chaetoceros spp resting spores delphineis spp predominated in late pleistocene sediments of the two southern cores a mix of tropical and subtropical diatom assemblages occurred in latest pleistocene sediments while tropical species e g coscinodiscus nodulifer radiatus pseudoeunotia doliolus thalassionema nitzschioides var parva predominated in the late holocene sediments in the northern core latest pleistocene sediments also contained a mix of tropical and subtropical species similarly late holocene sediments contained predominately tropical species of diatoms neoglacial periods 200 400 yr b p 2000 2700 yr b p however were sometimes characterized by a greater abundance of subtropical species and punctuated periodically with blooms of skeletonema costatum and rhizosolenia shrubsolei it is proposed that during times of southern hemisphere cooling peruvian coastal waters north of 12 s were subjected to episodic mixing with warmer water masses before being overwhelmed by tropical waters that may have either passed southward across a weakened equatorial front or arose from intensified offshore countercurrents coastal waters south of 12 s latitude were probably unaffected by the tropical influence rather these waters may have undergone intensified upwelling during the last glacial epoch

high resolution paleoceanography of the guaymas basin gulf of california during the past 15 000 years abstract deep sea drilling project site 480 27 54 10 n 111 39 34 w 655 m water depth contains a high resolution record of paleoceanographic change of the past 15 000 years for the guaymas basin a region of very high diatom productivity within the central gulf of california analyses of diatoms and silicoflagellates were completed on samples spaced every 40 50 yr whereas icp aes geochemical analyses were completed on alternate samples sample spacing 80 100 yr the bolling allerod interval 14 6 12 9 ka note ka refers to 1000 calendar years bp throughout this report is characterized by an increase in biogenic silica and a decline in calcium carbonate relative to surrounding intervals suggesting conditions somewhat similar to those of today the younger dryas event 12 9 11 6 ka is marked by a major drop in biogenic silica and an increase in calcium carbonate increasing relative percentage contributions of azpeitia nodulifera and dictyocha perlaevis a tropical diatom and silicoflagellate respectively and reduced numbers of the silicoflagellate octactis pulchra are supportive of reduced upwelling of nutrient rich waters between 10 6 and 10 0 ka calcium carbonate and a nodulifera abruptly decline at dsdp 480 while roperia tesselata a diatom indicative of winter upwelling in the modern day gulf increases sharply in numbers a nearly coincident increase in the silicoflagellate dictyocha stapedia suggests that waters above dsdp 480 were more similar to the cooler and slightly more saline waters of the northern gulf during much of the early and middle parts of the holocene 10 to 3 2 ka at about 6 2 ka a stepwise increase in biogenic silica and the reappearance of the tropical diatom a nodulifera marks a major change in oceanographic conditions in the gulf a winter shift to more northwesterly winds may have occurred at this time along with the onset of periodic northward excursions el nino driven of the north equatorial countercurrent during the summer beginning between 2 8 and 2 4 ka the amplitude of biogenic silica and wt fe al and ti proxies of terrigenous input increase possibly reflecting intensification of enso cycles and the establishment of modern oceanographic conditions in the gulf increased numbers of o pulchra after 2 8 ka suggest enhanced spring upwelling

a 20 year varve record of siliceous phytoplankton variability in the central gulf of california abstract year to year variability in the structure of the preserved siliceous phytoplankton assemblage is reconstructed from a box core retrieved from the varved sediments along the guaymas slope of the gulf of california a 20 year record from 1953 through 1972 is obtained from interpretation of the varve stratigraphy supported by 210 pb and 228 th dating ecological time series derived from microfossil analysis show a strong coherence with interannual sea level anomalies indicating a response to large scale climatic variability associated with the el nino southern oscillation phenomenon el nino periods are generally marked by increases in preserved abundances of the total siliceous assemblage and in particular by greater numbers of individuals within species whose distribution is limited to tropical and subtropical waters

paleoceanographic history of the guaymas basin gulf of california during the past 15 000 years based on diatoms silicoflagellates and biogenic sediments high resolution records of calcium carbonate biogenic opal diatoms and silicoflagellates from western guaymas basin gravity core ggc55 and piston core jpc56 and eastern guaymas basin dsdp site 480 reveal a complex paleoceanographic history of the central gulf of california during the past 15 000 years prior to 6 2 ka the eastern and western guaymas basin proxy records were remarkably similar after conditions similar to those of today during the bolling allerod the younger dryas yd saw a major drop in diatom production coincident with increased calcium carbonate and tropical microfossils suggestive of el nino like conditions biosiliceous productivity began increasing during the latter part of the yd but it was only during the earliest holocene 11 6 to 11 0 ka that conditions similar to those of the bolling allerod returned to the central gulf between around 11 0 and 6 2 ka tropical diatoms and silicoflagellates were virtually absent from the central gulf as relatively cooler and fresher surface waters resembling those of the modern northern gulf were present in the central gulf beginning at about 6 2 ka tropical diatoms and silicoflagellates began increasing in the central gulf and coccoliths returned to western gulf sediments the onset of modern day monsoon conditions in the american southwest required the presence of warm ssts in the northern gulf which probably did not occur until after about 5 4 ka when tropical diatoms and silicoflagellates became relatively common in the central gulf modern east west contrasts which arise from late winter early spring coastal upwelling on the mainland side and lower diatom productivity on the western side of the gulf commenced between 6 2 and 5 4 ka possibly due to a shift in the direction of late winter early spring winds more towards the southeast or down the axis of the gulf this proposed wind shift might have ultimately been due to a late holocene strengthening of enso like conditions in the eastern equatorial pacific published by elsevier b v

variations of upwelling intensity recorded in varved sediment from the gulf of california during the past 3 000 years circulation in the pacific ocean is periodically affected by el nino events which are a direct response to intensity changes in trade winds1 2 the appearance of anomalously warm surface water in the eastern equatorial pacific ocean is one of the most spectacular manifestations of this event warm surface water anomalies are also observed in the northern hemisphere along the californian coast and in the gulf of california in the gulf strengthened trade winds induce upwelling during the winter whereas in the summer prevailing southerly winds provoke an input of warm water from the south3 we have sampled laminated sediments from the slopes of guaymas basin to reconstruct with high resolution variations of the hydrology of surface waters in the central part of the gulf of california sedimentation rate is of the order of 4 mm yr 1 at the top and 1 2 mm yr 1 down core by analysing the oxygen isotope ratio of biogenic silica of diatoms4 we have recorded the surface water temperature variations in the guaymas basin the comparison of these fluctuations and variations of silicoflagellate abundance has allowed us to reconstruct changes in upwelling intensity during the past three thousand years the present conditions of low upwelling activity are seen to be abnormal in comparison with those prevailing in the past

radiolarian distribution in the water column southern gulf of california and its implication in thanatocoenose constitution abstract the geographical and depth distributions of five radiolarian plankton assemblages defined through q mode factor analysis of 24 plankton samples demonstrate a direct correspondence to the distribution of oceanographic water masses in the southern gulf of california two assemblages are associated exclusively with water masses of the mixed layer two represent only subsurface water masses and one is important in both surface and subsurface environments the lithomelissa thoracites group and peridium spinipes are predominant species in water that is formed at the surface of the guaymas basin and subsequently is subducted southward into the carmen basin plagiocantha panarium is the predominant species in upwelled surface water at the carmen basin while tetrapyle octhacanta and botryostrobus scutum follow the incursion of the subtropical water mass into the gulf of california through the pescadero and farallon basins druppatractus variabilis and porodiscus sp b occur conspicuously in the upper layer of the pacific intermediate water between approximately 400 and 700 m water depth statistical correlation between plankton and sediment assemblages supports previous evidence that the radiolarian thanatocoenose in the gulf of california is composed primarily of species from the surface mixed layer two exceptions to this are observed in the data first the upwelling plankton assemblage was not well correlated to the sediment assemblage and second input to the sediment during glacial stages appears to be dominated by subsurface forms

an idealized model of weddell gyre export variability recent observations suggest that the export of antarctic bottom water aabw from the weddell sea has a seasonal cycle in its temperature and salinity that is correlated with annual wind stress variations this variability has been attributed to annual vertical excursions of the isopycnals in the weddell gyre modifying the water properties at the depth of the orkney passage recent studies attribute these variations to locally wind driven barotropic dynamics in the northern weddell sea boundary current this paper explores an alternative mechanism in which the isopycnals respond directly to surface ekman pumping which is coupled to rapidly responding mesoscale eddy buoyancy fluxes near the gyre boundary a conceptual model of the interface that separates weddell sea deep water from circumpolar deep water is described in which the bounding isopycnal responds to a seasonal oscillation in the surface wind stress different parameterizations of the mesoscale eddy diffusivity are tested the model accurately predicts the observed phases of the temperature and salinity variability in relationship to the surface wind stress the model despite its heavy idealization also accounts for more than 50 of the observed oscillation amplitude which depends on the strength of the seasonal wind variability and the parameterized eddy diffusivity these results highlight theimportanceofmesoscaleeddiesinmodulatingtheexportofaabwinnarrowboundarylayersaroundthe antarctic margins

mesoscale to submesoscale transition in the california current system part ii frontal processes this is the second of three papers investigating the regime transition that occurs in numerical simulations for an idealized equilibrium subtropical eastern boundary upwelling current system similar to the california current the emergent upper ocean submesoscale fronts are analyzed from phenomenological and dynamical perspectives using a combination of composite averaging and separation of distinctive subregions of the flow the initiating dynamical process for the transition is near surface frontogenesis the frontal behavior is similar to both observed meteorological surface fronts and solutions of the approximate dynamical model called surface dynamics i e uniform interior potential vorticity q and diagnostic force balance in the intensification of surface density gradients and secondary circulations in response to a mesoscale strain field however there are significant behavioral differences compared to the surface dynamics model wind stress acts on fronts through nonlinear ekman transport and creation and destruction of potential vorticity the strain induced frontogenesis is disrupted by vigorous submesoscale frontal instabilities that in turn lead to secondary frontogenesis events submesoscale vortices and excitation of even smaller scale flows intermittent submesoscale breakdown of geostrophic and gradient wind force balance occurs during the intense frontogenesis and frontal instability events

the effects of shear flow on propagation of rossby waves in the equatorial oceans abstract the effects of strong meridional shear of mean flow on propagation of long waves having a wavelength of about 1000 km and period of 25 days observed in the equatorial pacific and atlantic oceans are analyzed in this paper information from the weekly multichannel sea surface temperature images derived from the advanced very high resolution radiometer on board the noaa series satellites from january 1986 to march 1992 is used for the statistics of the visual parameters of the waves the characteristic scales of the waves are estimated based on the results by previous investigators and the statistical results of the present study solving a potential vorticity equation the authors obtain a dispersion relation with an additional term depending on the flow shear strength compared with that of the free rossby wave the theoretical model provides a good explanation for the variable behavior of long wave propagation

satellite altimetry the marine geoid and the oceanic general circulation for technical reasons the general circulation of the ocean has historically been treated as a steady laminar flow field the recent availability of extremely highaccuracy and high precision satellite altimetry has provided a graphic demonstration that the ocean is actually a rapidly time evolving turbulent flow field to render the observations quantitatively useful for oceanographic purposes has required order of magnitude improvements in a number of fields including orbit dynamics gravity field estimation and atmospheric variability with five years of very high quality data now available the nature of oceanic variability on all space and time scales is emerging including new findings about such diverse and important phenomena as mixing coefficients the frequency wavenumber spectrum and turbulent cascades because the surface elevation is both a cause and consequence of motions deep within the water column oceanographers soon will be able to provide general circulation numerical models tested against and then combined with the altimeter data these will be complete three dimensional timeevolving estimates of the ocean circulation permitting greatly improved estimates of oceanic heat carbon and other property fluxes

wave induced mixing in the upper ocean distribution and application to a global ocean circulation model 1 from the reynolds stress expression the wave induced vertical viscosity or diffusivity bv is defined which can be used as a parameter to estimate the strength of wave induced mixing in addition a parameter d5 is introduced to represent a wave induced mixing penetration depth the global distribution of bv averaged over the upper 20 m is calculated and its latitudinal transects in boreal summer and winter is discussed the results show that in summer the wave induced mixing is strong in the southern oceans south of 30 s and in winter it is strong in the north pacific and the north atlantic north of 30 n as well as in the southern oceans south of 40 s adding bv to the vertical diffusivity in a global ocean circulation model yields a temperature structure in the upper 100 m that is closer to the observed climatology than a model without the wave induced mixing

eddy mean flow interaction in the decadally modulating kuroshio extension system abstract satellite altimeter sea surface height ssh data of the past 16 years are used to investigate the decadal changes of the kuroshio extension ke system that oscillated between a stable and an unstable dynamic state during the stable state of 10 1992 06 1995 and 01 2002 12 2004 the ke jet was intense and had a northerly zonal mean path and a well defined southern recirculation gyre during the unstable state of 07 1995 12 2001 and 01 2005 present the ke jet had a reduced eastward transport and a more southerly flow path transitions between the two dynamic states are caused by the basin scale wind stress curl forcing in the eastern north pacific related to the pacific decadal oscillations pdos or the north pacific gyre oscillations npgos during the positive pdo or negative npgo phase the intensified aleutian low generates negative ssh anomalies in the eastern north pacific through ekman divergence as these wind induced negative ssh anomalies propagate to the west as baroclinic rossby waves they weaken the zonal ke jet and shift its path southward as its path is pushed southward 32 n the deep reaching ke jet has to ride over the shallow shatsky rise generating localized disturbances that lead to their subsequent development along the ke jet west of the shatsky rise the sequence opposite to that listed above occurs when the pdo npgo changes to its negative positive phase after the ke system transitions from a stable to unstable state the enhanced eddy interaction is found to strengthen both the southern recirculation gyre and quasi stationary meanders along the ke s upstream path this nonlinear eddy interaction is important in determining the amplitude of the observed decadal ke variability

oceanographic variability in the south pacific convergence zone region over the last 210 years from multi site coral sr ca records 1 in the south pacific convergence zone spcz the variability in a sub seasonally resolved microatoll porites colony sr ca record from tonga and a previously published high resolution record from fiji are strongly influenced by sea surface temperature sst over the calibration period from 1981 to 2004 r2 0 67 0 68 however the sr ca derived sst correlation to instrumental sst decreases back in time the lower frequency secular trend 1 c and decadal scale 2 3 c modes in sr ca derived sst are almost two times larger than that observed in instrumental sst the coral sr ca records suggest that local effects on sst generate larger amplitude variability than gridded sst products indicate reconstructed 18o of seawater 18osw at these sites correlate with instrumental sea surface salinity sss r 0 64 0 67 but not local precipitation r 0 10 to 0 22 demonstrating that the advection and mixing of different salinity water masses may be the predominant control on 18osw in this region the sr ca records indicate sst warming over the last 100 years and appears to be related to the expansion of the western pacific warm pool wpwp including an increasing rate of expansion in the last 20 years the reconstructed 18osw over the last 100 years also shows surface water freshening across the spcz the warming and freshening of the surface ocean in our study area suggests that the spcz has been shifting expanding southeast possibly related to the southward shift and intensification of the south pacific gyre over the last 50 years in response to strengthened westerly winds

biogenic and abiogenic components of laminated hemipelagic sediments in the central gulf of california abstract alternating light and dark submillimeter to millimeter thick layered sediments rhythmites are found along the slopes of the central and southern gulf of california where a strong oxygen minimum zone intersects the sediment water interface two short intervals of distinct alternations were sampled lamina by lamina from two cores in the central gulf both cores are from the slope of the guaymas basin one core is from the mainland side the other core is from the baja side each lamina sample was analyzed for its opal micro floral assemblage textural character trace metal and bulk chemical cu mn fe ni zn ca k al sio2 and c org content and mineralogy on both sides of the gulf the light laminae contain more diatom frustules up to 90 and less terrigenous and organic material than the dark laminae the sediment is predominantly silt sized the dark laminae contain more terrigenous material which is primarily clay size on both sides of the gulf the light laminae apparently represent sedimentation during the dry winter season of northwesterly winds whereas the dark laminae represent the wet summer season of southeasterly winds

diatom taphocoenoses in the coastal upwelling area off south west africa abstract the diatom floral composition of 124 sediment samples from the south east atlantic records the influence of coastal upwelling on sediment composition off south west africa inner shelf samples between 19 and 24 s are rich in diatom valves and the patterns of diatom species distribution in these samples are related to the coastal upwelling process comparison with recent phytoplankton data shows that the sediment assemblages preserve many of the important species of the diatom biocoenoses including chaetoceros resting spores delphineis karstenii thalassiosira eccentrica and thalassionema nitzschioides delphineis karstenii a pioneer species in enriched coastal water occurs nearshore and chaetoreros resting spores are widespread with highest relative abundance values in some more offshore samples the abundance of the thalassiosira eccentrica group and of thalassionema nitzschioides in sediment samples in and near walvis bay reflects the recurrence of intense upwelling off this part of the coast an abundance of large centric species has been reported in hydrological conditions characteristic of newly upwelled waters and correspondingly actinocyclus octonarius and some large coscinodiscus species occur in the sediments in nearshore patches or belts

distribution of silicoflagellates in plankton and core top samples from the gulf of california plankton and surface sediment samples from the gulf of california were examined to determine the present geographic distribution of silicoflagellate species in this area variations in the species composition of the silicoflagellate assemblage were found to be related to water mass distributions eight species were identified in these samples octactis pulchra is associated with high levels of primary productivity in the surface waters and is found in greatest abundance in the central gulf of california dictyocha messanensis dominates the silicoflagellate assemblage in stations outside the gulf of california and increases in relative abundance with decreasing amounts of octactis pulchra dictyocha calida dictyocha sp a and dictyocha sp b are associated with equatorial waters and have the highest relative abundance near the mouth of the gulf dictyocha epiodon and distephanus speculum are associated with cold california current water and dictyocha epiodon is present in minor abundance in gulf samples dictyocha sp 2 has a patchy distribution with low relative abundance

radiolarian and silicoflagellate response to oceanographic changes associated with the 1983 el nino strong seasonal signals in fluxes and composition of siliceous microfossils have been recorded in sediment traps from two sites in the equatorial pacific deployed from december 1982 to march 1984 during the early part of the sampling period the 1982 83 el nino event had a profound effect on the radiolaria and silico flagellates within these two areas during the el nino the radio larian trap assemblages at site c 1 n 139 w most resembled faunal assemblages in western equatorial pacific sediments whereas the trap assemblages resembled equatorial divergence sediments in the latter half of the period at site s 11 n 140 w the radiolaria and silicoflagellate species can be correlated with organic carbon fluxes in general silicoflagellate shell fluxes are correlated to total opal fluxes where radiolarian fluxes do not exhibit this relationship approximately 20 25 of the total count of radiolaria in traps are not present in underlying sediments with a significant loss of the weakly silicified forms however the comparison of trap sample assemblages with underlying sediments reported here shows that dissolution does not alter relative abundances of the fossil species used in palaeoclimatic reconstructions a significant difference is observed between the silicoflagellate trap assemblage and the underlying sediment assemblage

solar forcing of gulf of california climate during the past 2000 yr suggested by diatoms and silicoflagellates abstract high resolution records of the past 2000 yr are compared in a north south transect 28 n to 24 n of three cores from the eastern slopes of the guaymas carmen and pescadero basins of the gulf of california hereafter referred to as the gulf evenly spaced samples from the varved sediments in each core allow sample resolution ranging from 16 to 37 yr diatoms and silicoflagellates capture the seasonal variation between a late fall to early spring period of high biosiliceous productivity that is driven by northwest winds and a summer period of warmer more stratified waters during which these winds slacken and or reverse direction monsoonal flow as these winds decrease tropical waters enter the gulf and spread northward individual samples represent a composite of 7 to 23 yr of deposition and are assumed to record the relative dominance of the winter vs summer floral components intervals of enhanced summer incursion of tropical waters alternating with periods of increased late fall to early spring biosiliceous productivity are recorded in all three cores regularly spaced cycles 100 yr duration of octactis pulchra a silicoflagellate proxy for lower sst and high productivity and azpeitia nodulifera a tropical diatom occur between a d 400 and 1700 in the more nearshore carmen basin core nh01 21 26 3 n suggesting a possible solar influence on coastal upwelling cores bam80 e 17 27 9 n and nh01 26 24 3 n contain longer duration cycles of diatoms and silicoflagellates the early part of medieval climate anomaly a d 900 to 1200 is characterized by two periods of reduced productivity warmer sst with an intervening high productivity cool interval centered at a d 1050 reduced productivity and higher sst also characterize the record of the last 100 to 200 yr in these cores solar variability appears to be driving productivity cycles as intervals of increased radiocarbon production sunspot minima correlate with intervals of enhanced productivity it is proposed that increased winter cooling of the atmosphere above southwest u s during sunspot minima causes intensification of the northwest winds that blow down the gulf during the late fall to early spring leading to intensified overturn of surface waters and enhanced productivity a new silicoflagellate species dictyocha franshepardii bukry is described and illustrated

coastal ocean wind fields gauged against the performance of an ocean circulation model 1 atmosphere model derived flux fields are used to force coastal ocean models coarse resolution and incomplete boundary layer dynamics limit the accuracy of these forcing fields and hence the performance of the ocean models we address this limitation for the west florida shelf using optimal interpolation to blend winds measured in situ with winds produced by model analyses by improving the coastal wind field we improve the fidelity between currents modeled and currents observed comparisons between momentum analyses performed independently from the model and the data demonstrate the fidelity to be of a correct dynamical basis we conclude that the primary limitation to coastal ocean model performance lies with the boundary conditions

diatoms in the gulf of california seasonal flux patterns and the sediment record for the last 15 000 years flux and taxonomic composition of the diatom assemblage was determined for biweekly sediment traps in the central gulf of california over a 2 year period fluxes and relative abundance of taxa are not significantly different in traps from the eastern side of the guaymas basin and the western side of the carmen basin indicating that patterns of diatom production are uniform across the central gulf at all seasons of the year the annual maximum in diatom flux occurred during the winter season of both years either as a sustained event over many weeks 1990 or as a series of short blooms 1991 1992 of the most abundant taxa only hyalochaete chaetoceros species showed a clear seasonal cycle with a flux maximum in the spring of both years factor analysis defines five assemblages representing 1 summer and fall conditions of surface stratification and nutrient limitation 2 winter bloom triggered by onset of strong northwesterly winds 3 late spring to summer production probably related to sporadic events during periods of weak southeasterly winds 4 spring 1991 inferred to reflect the distal edge of a coastal upwelling phase 5 lateral advection of resuspended sediments from the continental shelf possibly resulting from trapped coastal waves during summer hurricanes and from storms during the 1991 1992 el nino southern oscillation enso the diatom data support the inference that subtropical pacific water penetrates deeper into the gulf during enso events in order to compare the sediment trap record to a sediment core a second factor analysis was done using only the taxa which are preserved in the sediment and omitting the most abundant taxa which showed little downcore variation this produces five factors representing 1 summer fall low production 2 early winter bloom 3 late winter spring upwelling 4 enso conditions and 5 a late spring summer assemblage of uncertain significance variation of species characterisic of each factor was examined in piston core atlantis ii 125 8 56jpc taken from the oxygen minimum zone in guaymas basin correlation to nearby deep sea drilling project hole 480 indicates that the core penetrates to about 15 ka with laminated sediments in the holocene 0 10 ka and late deglacial 11 13 ka and massive nonlaminated sediments around younger dryas time 10 11 ka and before 13 ka downcore variations in the diatom assemblage do not correspond directly to presence of laminations implying that the processes controlling bottom water oxygen content are not determined by conditions of surface water production presence of calcareous nannofossils downcore correlates inversely with two diatom assemblages enso and winter bloom indicators and not with occurrence of laminations suggesting that occurrence of calcareous nannofossils in the sediment is at least partly a function of surface water production prior to 12 ka production was lower than at present during all seasons implying weaker winds throughout the year subtropical waters extended to the midgulf as they do today during enso events between 11 and 12 ka conditions were similar to those of the present with relatively high winter and spring production resulting from northwesterly winds enso events were still common although less so than during the preceding period younger dryas time was one of transition with intermediate conditions a slackening of winter spring northwesterly winds and reduction of total annual production and increased occurrence of enso conditions in the early to middle holocene winter northwesterlies increased to a maximum resulting in very high production but apparently did not persist into spring subtropical waters mostly disappeared from the gulf in the late holocene northwesterly winds have supported high production during both winter and spring seasons

seasonal occurrence of silicoflagellate morphologies in different environments of the eastern pacific ocean data on weekly to bimonthly particle flux collected by sediment traps in three environments show that forms of silicoflagellates do not have a simple and consistent relationship to either temperature or productivity of the overlying water column sites were located in the fjords of british columbia along a transect off the coast of southern oregon and in san pedro basin of the southern california bight either the cool distephanus speculum or the warm dictyocha messanensis may dominate at temperatures over a range from 10 19 c d speculum dominated high productivity periods off oregon whiled messanensis dominated during coastal upwelling events in the san pedro basin regardless of surface temperature octactis pulchra showed no distinctive trend in the san pedro basin the only locality where it was observed the isolated presence ofd speculum in the fjords where mixed zone salinity may be as low as 11 indicates a tolerance for hyposaline waters but no other trends could be defined with respect to surface salinity

nitrogen isotopic variations in the gulf of california since the last deglaciation response to global climate change high resolution records of the nitrogen isotopic composition of organic matter 15norg opal content and opal accumulation rates from the central gulf of california reveal large and abrupt variations during deglaciation and gradual holocene changes coincident with climatic changes recorded in the north atlantic homogenous sediments with relatively low 15norg values and low opal content were deposited at the end of the last glacial period during the younger dryas event and during the middle to late holocene in contrast laminated sediments deposited in the two deglacial stages are characterized by very high 15norg values 14 and opal accumulation rates 29 41 mg cm 2 yr 1 abrupt shifts in 15norg were driven by widespread changes in the extent of suboxic subsurface waters supporting denitrification and were amplified in the central gulf record due to variations in upwelling vertical mixing and or the latitudinal position of the intertropical convergence zone