the pribilof islands temperature salinity and nitrate during summer 2004 abstract the pribilofs comprised of st paul and st george islands and two smaller islands are a highly productive area on the western edge of the eastern bering sea shelf proximity to both the slope and more shallow shelf waters and the confluence of multiple physical domains differentiates conditions in this region from those in other areas on this shelf this is a unique domain in the bering sea that we refer to as the pribilof domain hydrographic and biological data were collected during a 2004 summer research cruise in this region the study undertook testing the hypothesis that on shelf intrusion of slope waters supplies nutrients to this multi domain area thereby seasonally influencing new primary production and consequently the entire marine ecosystem the pribilof domain is characterized by enhanced mixing particularly the area between st paul and st george islands organized anti cyclonic flow around st paul island around st george island and around the island group strong tidal currents and is a location where nutrient rich water from the bottom layer of the middle shelf and deeper water from the slope are vertically mixed to sustain production throughout the summer

interannual variability of summer biochemical enhancement in relation to mesoscale eddies at the shelf break in the vicinity of the pribilof islands bering sea abstract this study examined variability of the eddy field and primary production over the bering sea s eastern shelf break area during summer using a satellite multi sensor data set the eddy field and on shelf nutrient flux below 50 m water depth were also investigated using a numerical model the satellite altimeter data analysis and numerical experiments indicated that the eddy field was induced by perturbations of the bering slope current system and or instabilities in the bering sea basin via flow through the aleutian passes the distribution of high primary production roughly coincided with the high variability area of the eddy field numerical experiments showed a 70 increase in net on shelf flux and 54 increase in net on shelf transport by the generation propagation of eddies along the shelf break at pribilof canyon towed ctd fluorometer measurements during the summer of 2003 revealed a stable water column and high fluorescence 10 g l 1 in the area between the 200 and 1000 m isobaths at a time when there was a low level of on shelf flux regardless of the eddy field conversely the eddy induced on shelf flux and stable water column can enhance primary production from spring to summer at the shelf break moreover the eddy induced on shelf nutrient flux probably contributes to the primary productivity at the western shelf of the pribilof islands where the bering sea ecosystem is very dynamic this eddy related shelf break process can be applied to not only the bering sea shelf break but also all shelf break areas in which propagating eddies are found

slow spreading ridge axis tectonics evidence from the lizard complex uk abstract the east coast section of the lizard ophiolite complex cornwall u k preserves a series of interrelated extensional faults and dyke sets which indicate that the formation of this section of obducted oceanic lithosphere resulted from a combination of contemporaneous structural and magmatic events three dolerite dyke sets are evident the first two sets 1 and 2 are cut by and rotated on a series of ridge parallel extensional faults and shear zones later dykes set 3 cross cut the extensional faults these data indicate that both rotation and significant thinning in the region of 40 of this part of the oceanic lithosphere occurred prior to the final period of dyke injection the thinning of the lithosphere was the result of extension along the normal faults all of the dolerite dykes show morb characteristics although the late dykes set 3 are more primitive tending to be aphyric to sparse olivine phyric and show higher cr ni and lower zr values than the typically plagioclase phyric dolerite dykes sets 1 and 2 intruded prior to the ductile shearing event the more primitive dolerites post date the tectonism and indicate the lack of a significant magma chamber following a period of amagmatic extension the data are consistent with observations at present day slow spreading ridge axes and some mafic ultramafic ophiolite sequences and provide insight into the nature of ridge related structures and the interrelationships between tectonism and geochemical evolution of the dykes and record a mechanism listric faulting to account for the presence of peridotites and gabbros commonly dredged at slow spreading centres

geochemistry of the start complex greenschists rhenohercynian morb the meta igneous greenschists of the start complex southdevon are composed of a mineralogically uniform but texturally variable actinolite epidote albite assemblage with retrogressed variants containing chlorite muscovite sphene carbonate and oxidized opaque minerals geochemically they represent a suite of relatively primitive tholeiites exhibiting mild differentiation depleted incompatible element abundances and variable light rare earth element depletion patterns comparable to modern basalts from normal spreading ridge segments n morb as the start greenschistsexhibit a number of chemical similarities to the nearby upper palaeozoic lizard ophiolite and morb type clasts within the rhenohercynian zone generally they may also represent local variscan ocean crust which floored smalloceanic basins that separated the old red sandstone continent from the armorican microplate to the south the start complex could thus represent a previously unrecognized oceanic component to the variscan orogenic belt rhenohercynian zone of northwest europe

impact of climate warming on upper layer of the bering sea the impact of climate warming on the upper layer of the bering sea is investigated by using a high resolution coupled global climate model the model is forced by increasing atmospheric co2 at a rate of 1 per year until co2 reaches double its initial value after 70 years after which it is held constant in response to this forcing the upper layer of the bering sea warms by about 2 c in the southeastern shelf and by a little more than 1 c in the western basin the wintertime ventilation to the permanent thermocline weakens in the western bering sea after co2 doubling the southeastern shelf of the bering sea becomes almost ice free in march and the stratification of the upper layer strengthens in may and june changes of physical condition due to the climate warming would impact the pre condition of spring bio productivity in the southeastern shelf

on the bering sea ice edge front an oceanographic field program was carried out along the bering sea ice edge in winter 1982 83 to investigate the temperature salinity front associated with and paralleling the winter ice edge currents were measured using taut wire moorings that were in place over winter and an intensive ctd survey was carried out of the frontal structure in midwinter february march the midwinter front separated cold 0 c more saline 32 5 outer shelf water the front had northwestward baroclinic currents paralleling the front ice edge with near surface speeds of 5 6 cm s and an associated transport of about 0 3 106 m3 s these baroclinic currents were superimposed on a regional barotropic along isobath flow resulting in north westward midwinter upper layer flows with monthly mean speeds exceeding 10 cm s an upper layer flow component was directed beneath the ice and provided heat adequate to melt the ice and limit advance of the edge the resulting low salinity meltwater was mixed vertically to maintain the front by wind acting across a highly mobile hydrodynamically rough ice cover subtidal fluctuations were not significantly affected by the front or the ice cover and local winds accounted for less than one quarter of the observed current variability the remainder being probably due to regional variations in the barotropic flow

foraging habitats of lactating northern fur seals are structured by thermocline depths and submesoscale fronts in the eastern bering sea the relationships between fine scale oceanographic features prey aggregations and the foraging behavior of top predators are poorly understood we investigated whether foraging patterns of lactating northern fur seals callorhinus ursinus from two breeding colonies located in different oceanographic domains of the eastern bering sea st paul island shelf bogoslof island oceanic were a function of submesoscale oceanographic features we tested this by tracking 87 lactating fur seals instrumented with bio logging tags 44 st paul island 43 bogoslof island during july september 2009 we identified probable foraging hotspots using first passage time analysis and statistically linked individual areas of high use to fine scale oceanographic features using mixed effects cox proportional hazard models we found no overlap in foraging areas used by fur seals from the two islands but a difference in the duration of their foraging trips trips from st paul island were twice as long 7 9 d average and covered 3 times the distance 600 km average compared to trips from bogoslof island st paul fur seals also foraged at twice the scale mean radius 12 km of bogoslof fur seals 6 km which suggests that prey were more diffuse near st paul island than prey near bogoslof island comparing first passage times with oceanographic covariates revealed that foraging hotspots were linked to thermocline depth and occurred near submesoscale surface fronts eddies and filaments st paul fur seals that mixed epipelagic night and benthic day dives primarily foraged on shelf in areas with deeper thermoclines that may have concentrated prey closer to the ocean floor while strictly epipelagic night foragers tended to use waters with shallower thermoclines that may have aggregated prey closer to the surface fur seals from bogoslof island foraged almost exclusively over the bering sea basin and appeared to hunt intensively along submesoscale fronts that may have converged prey within narrow bands near the surface bogoslof fur seals also foraged closer to their island which was surrounded by strong surface fronts while fur seals from st paul island traveled4100 km and extended some trips off shelf to the basin to forage at similar oceanographic features the relative distribution and accessibility of prey concentrating oceanographic features can account for the observed inter island foraging patterns which may in turn have population level consequence sf or the two fur seal colonies

multi year meanders and eddies in the alaskan stream as observed by topex poseidon altimeter the birth life and decay of long lived anticyclonic eddies or meanders in the alaskan stream are observed from topex poseidon t p satellite their surface height anomalies approach 72 cm average diameter is about 160km and they live for 1 to 3 years propagating along the stream with mean speed of 2 5 km d 1 of the six observed the last three were formed after the first t p observations in september 1992 of these two evolved from eddies near alaskan panhandle in winter drifting across the northern gulf of alaska before entering the alaskan stream while another formed in the stream west of shelikof strait

upper palaeozoic ophiolite generation and obduction in south cornwall the gramscatho flysch sequence of south cornwall including the melanges of the meneage formation and the lizard ophiolite are described in relation to the development of the gramscatho basin the timing and geotectonic evolution of this feature are considered in its regional context within the rhenohercynian zone of northwest europe this zone is interpreted as an intracontinental dextral transform system that developed during the devonian closure of the so called massif central ocean a basin and rise topography is attributed to extension and compression at offsets on major faults e w extension of the gramscatho pull apart basin in middle and upper devonian times is believed to have caused rifting and the development of ocean crust from which the lizard ophiolite was assembled in an oceanic setting at a ridge transform junction the meneage formation was generated as a result of intrabasinal uplift on transcurrent faults a major change of plate motions took place when the massif central ocean finally closed at the end of the devonian and the weak rhenohercynian zone became a site of crustal convergence from which thrust nappes were transported northwards foreland basins were sequentially developed and deformed by thin skinned tectonics as the system advanced northwards during the carboniferous

mercury cratering record viewed from messenger s first flyby morphologies and size frequency distributions of impact craters on mercury imaged during messenger s first flyby elucidate the planet s geological history plains interior to the caloris basin displaying color and albedo contrasts have comparable crater densities and therefore similar ages smooth plains exterior to caloris exhibit a crater density 40 less than on interior plains and are thus volcanic and not caloris impact ejecta the size distribution of smooth plains craters matches that of lunar craters postdating the late heavy bombardment implying that the plains formed no earlier than 3 8 billion years ago ga at diameters less than or equal to 8 to 10 kilometers secondary impact craters on mercury are more abundant than primaries this transition diameter is much larger than that on the moon or mars a low density of craters on the peak ring basin raditladi implies that it may be younger than 1 ga

cold halocline in the northern california current an invasion of subarctic water 1 subsurface upper ocean waters off oregon and vancouver island were about 1 c cooler in july 2002 than in july 2001 the anomalously cool layer coincides with the permanent halocline which has salinities of 32 2 to 33 8 suggesting an invasion of nutrient rich subarctic waters the anomalously cool layer lies at 30 150 m the cool anomaly is likely caused by stronger southward flow in the california current and weaker northward flow in the alaska and davidson currents during spring 2002 other factors may include reduced coastal downwelling in late winter and early spring 2002 enhanced eastward flow in the subarctic current and enhanced winter mixing offshore

geochemistry and u pb and 40ar 39ar geochronology of the man of war gneiss lizard complex sw england pre hercynian arc type crust with a sudeten iberian connection the man of war gneiss is a variably deformed meta igneous body that ranges in composition from gabbro to tonalite and comprises part of the basal structural slice of the lizard ophiolite complex sw england u pb dating of zircon demonstrates that the parental magmas crystallized in the earliest ordovician 499t s 3 ma but 40 ar 39 ar step heating analysis of amphiboles suggests that at least the northernmost zone of the gneiss was subjected to an amphibolite grade metamorphic event at c 374 ma probably associated with thrust emplacement of the ophiolite the gneiss exhibits major trace and rare earth element variations in conformity with an origin through partial melting of an amphibolitic source containing hornblende and plagioclase probably with minor garnet and zircon the elemental abundances and variations are characteristic of granitoids formed in supra subduction zone environments a granitoid sill within the adjacent old lizard head series schists previously inferred to be related to the man of war gneiss is trondhjemitic and exhibits higher sio 2 tio 2 and mgo but lower zr v ba and sr contents and therefore is probably not genetically related to the latter the sill may record local melting during ophiolite emplacement the man of war gneiss probably represents a structural inlier of pre hercynian basement incorporated in the hercynian nappes of sw england during nnw directed thrusting we emphasize the geological and geochronological similarities between variably deformed granitoid units of the lizard complex the sudeten massif of southern poland and the allochthonous complexes of northern portugal and nw spain these granitoid rocks may represent dispersed remnants of tremadoc arcs that formed oceanward from the northern margin of gondwana this is further convincing evidence that at this time eastern avalonia was separated from northern gondwana by an ocean basin that may have been connected with the tornquist sea

the evolution and depth structure of shelf and slope temperatures and velocities during the 1997 1998 el nino near point conception california abstract moored survey and drifter observations are used to describe the evolution of temperature sea level velocity and salinity from 1997 to 1998 over the california shelf between san luis obispo bay and the eastern entrance to the santa barbara channel the dominant event during this time was the 1997 1998 el nino its relation to background seasonal and interannual variability depended on which property is considered subsurface temperature and local sea level showed extreme anomalies between march 1997 and october 1998 three distinct peaks occurred the first two are associated with the regional response to el nino while the cause of the third remains unclear the first peaked in june 1997 and decayed until august the main el nino peak reached maximum amplitude between november 1997 and january 1998 after the collapse of the regional el nino anomaly in february 1998 a final peak occurred locally during the summer of 1998 the central result presented here concerns the spatial structure of temperature during these events the initial peak was surface intensified and was barely detectable at 45 m its amplitude varied with position along the coast decaying with distance north the main peak showed a strong signal down to at least 200 m the amplitude and timing of temperature anomalies during this event were depth dependent the largest absolute amplitudes relative to seasonal cycles were in excess of 4 c and occurred between 45 and 65 m depth the anomalies reached their maximum values at later time with increasing depth between october 1997 and january 1998 the amplitude of this main peak was comparable at all mooring sites the final peak in august 1998 had a comparable amplitude at all mooring sites to a depth of 100 m temperature increases during the three events were accompanied by a corresponding rise in sea level the el nino signals in currents and salinity are more difficult to distinguish from background variability than those in temperatures and sea level however stronger than average poleward flow was observed at the eastern entrance to the santa barbara channel between 5 and 100 m depth for most of 1997 and there are indications for greater than usual poleward flow over the santa maria basin in fall 1997 surface drifter evidence although qualitative also suggests greater than usual poleward displacement in november 1997 relative to other years along with increased temperature survey observations of salinity suggest changes to the regional temperature salinity relation during november 1997 with greater than usual salinity at temperatures below 12 c

possible lizard derived material in the underlying meneage formation the lizard complex rests tectonically on the meneage formation within the top of the flysch dominated gramscatho group of sediments the meneage formation is a middle to upper devonian sedimentary melange sequence with interbedded rudites the possibility that one or both of these lithologies include lizard derived debris is examined in detail the rudaceous debris is characterized by a range of meta psammitic pelitic and basic lithologies which cannot be matched with a lizard source parts of this suite notably granite gneiss and amphibolitic material are found to be quite different from superficially similar possible lizard source rocks a cratonic source is required the only widespread type of melange phacoid with a possible lizard source is greenstone geochemically these have ocean floor tholeiite affinities gabbro and amphibolite occur within and serpentinite near one particularly large greenstone phacoid however no precise geochemical comparison can be made between greenstones and lizard dykes autochthonous oceanic tholeiites in the gramscatho group sequence and the absence of varied and widespread possible lizard derived material suggest that the lizard complex is an unlikely source for the allochthonous greenstones a separate local development of oceanic crust now no longer exposed and autochthonous volcanics are postulated as more likely sources

observations from a yakutat eddy in the northern gulf of alaska 1 the impingement of deep basin eddies on the shelf in the gulf of alaska has been implicated as an important mechanism for cross shelf exchange the influence of eddies on biological processes has been confirmed with data from the sea viewing wide field of view sensor showing elevated chlorophyll associated with eddies altimetry data suggest that an eddy formed in the winter of 2003 near yakutat alaska and propagated along the shelf break reaching the head of the gulf by spring this eddy was sampled during may and september of 2003 the eddy core water was warm salty and high in nitrate relative to basin water of the same density but was similar to historical water properties from the shelf near yakutat this suggests a shelf origin for the eddy core water

trapped motion around the pribilof islands in the bering sea observations in the region of the pribilof islands and canyon pic reveal a clockwise circulation around the group of islands and around each of the two largest islands st paul and st george six current meters deployed around st paul island revealed a steady clockwise flow around the island which was strongest south of the island and weakest to the east we use a high resolution tidal model in the pic region to show that this flow pattern results from tidal rectification over the shallow topography tides tidal residual currents of 10 15 cm s were predicted by the model compared to mean currents of 5 20 cm s observed at the mooring sites both diurnal and semidiurnal tidal oscillations contribute to the clockwise circulation around the islands in the diurnal band the enhanced currents occur also at the shelf slope where a tidal wave generates a shelf wave due to resonance with topography in the pic region the main shelf wave occurs in the pribilof canyon where both observations and measurements show enhancement of the diurnal tidal currents

physical forcing and nutrient conditions associated with patterns of chl a and phytoplankton productivity in the southeastern bering sea during summer abstract measurements of nutrients primary 14 c productivity and new nitrate productivity collected in the southeastern bering sea in july and august 2004 together with measurements from july 1981 are used to characterize the regional production system during summer and to analyze the major physical and nutrient factors controlling biological patterns the patterns of surface productivity suggested by the two different summers were remarkably similar in the regions of data overlap and agree with recent compilations of summer conditions from remotely sensed data summer was characterized by low production in the middle and outer shelf associated with surface mixed layers that were stabilized by heat elevated productivity was restricted to regions associated with the surface expression of thermohaline fronts as well as to tidally mixed regions adjacent to and between the pribilof islands based on chl a and productivity measurements the biological impact of the shelf break front of the southeastern bering sea extends at least as far inshore as the pribilof islands the existence of elevated summer productivity associated with a recently identified shelf partition front between the pribilof domain and the middle shelf domain east of st paul island was confirmed and its thermohaline nature resulting from cumulative intrusions of slope derived water is described yearly estimates of new and primary productivity compiled for the various biophysical regimes range from 1800 mmol n m 2 yr 1 and 170 g c m 2 yr 1 at the shelf break front to less than 700 mmol n m 2 yr 1 and 100 g c m 2 yr 1 in oceanic and coastal waters we hypothesize that trace metals rather than macronutrients or grazing likely restrict the seaward extent of elevated production at the shelf break front iron may be supplied to the front by isopycnal mixing from deeper shelf waters that were in contact with sediments by extending elevated production throughout the summer the thermohaline and tidal fronts enhance the coupling of primary production to epipelagic food webs for the large populations of fish birds and mammals in the region changes in the intensity or location of these frontal systems may impact populations that forage in them from the nearby pribilof islands

how thick are mercury s polar water ice deposits an estimate is made of the thickness of the radar bright deposits in craters near to mercury s north pole to construct an objective set of craters for this measurement an automated crater finding algorithm is developed and applied to a digital elevation model based on data from the mercury laser altimeter onboard the messenger spacecraft this produces a catalogue of 663 craters with diameters exceeding 4 km northwards of latitude 55 a subset of 12 larger well sampled and fresh polar craters are selected to search for correlations between topography and radar same sense backscatter cross section it is found that the typical excess height associated with the radar bright regions within these fresh polar craters is 50 35 m this puts an approximate upper limit on the total polar water ice deposits on mercury of 3 1015 kg

the importance of freshwater to spatial variability of aragonite saturation state in the gulf of alaska high latitude and subpolar regions like the gulf of alaska goa are more vulnerable than equatorial regions to rising carbon dioxide co2 levels in part due to local processes that amplify the global signal recent field observations have shown that the shelf of the goa is currently experiencing seasonal corrosive events carbonate mineral saturation states 1 including suppressed in response to ocean acidification as well as local processes like increased low alkalinity glacial melt water discharge while the glacial discharge mainly influences the inner shelf on the outer shelf upwelling brings corrosive waters from the deep goa in this work we develop a high resolution model for carbon dynamics in the goa identify regions of high variability of and test the sensitivity of those regions to changes in the chemistry of glacial melt water discharge results indicate the importance of this climatically sensitive and relatively unconstrained regional freshwater forcing for variability in the nearshore the increase was nearly linear at 0 002 per 100 mol kg increase in alkalinity in the freshwater runoff we find that the local winds biological processes and freshwater forcing all contribute to the spatial distribution of and identify which of these three is highly correlated to the variability in given that the timing and magnitude of these processes will likely change during the next few decades it is critical to elucidate the effect of local processes on the background ocean acidification signal using robust models such as the one described here

observations of the aleutian north slope current bering sea 1996 2001 1 cyclonic circulation dominates flow in the bering sea basin the eastward flowing aleutian north slope current ansc flows along the north slope of the aleutian islands turning northwestward in the southeast corner of the basin to form the bering slope current bsc during the period 1997 to 2007 a pair of hydrographic lines was occupied 14 times in the southeastern portion of the basin one transect was across the ansc and the second was across the bsc in addition a series of five yearlong moorings was deployed in a water depth of 1000 m in the ansc and a single yearlong mooring was deployed to the northeast in a water depth of 2200 m at the primary mooring site strong variability in temperature and salinity occurred at fortnightly and annual periods while strong variability in the currents occurred at fortnightly and semiannual periods the mean geostrophic flow relative to 1500 m calculated from the 14 occupations of the hydrographic lines was 3 1 106 m3 s 1 in the ansc and 3 3 106 m3 s 1 in the bsc a significant barotropic component measured by the current meters adds 3 106 m3 s 1 to the transport

currents and transport on the eastern bering sea shelf an integration of over 20 years of data abstract more than 20 years of data from moorings satellite tracked drifters and hydrographic surveys are integrated to provide a comprehensive view of currents and transport on the eastern bering sea shelf the major sources of water onto the eastern bering sea shelf are north pacific water flowing through unimak pass and bering slope water flowing onto the shelf usually via the canyons that intersect the shelf break absolute geostrophic transport through unimak pass varies from an average of 0 25 106 m3 s 1 sv in the warm months to 0 43 sv in the cold months flow along the 50 m isobath is weak with a transport of 13 months and from amukta pass to bering strait via the bering slope current is 8 months consequently the source of most of the heat transported into the arctic through bering strait is a result of air sea interactions local to the northern bering sea analysis of the currents and water properties on the southern shelf indicates that 50 of the shelf water is exchanged with slope water during october january each year this exchange elevates the october mid shelf average nitrate level from 6 m to 14 16 m by the end of january

on the recent warming of the southeastern bering sea shelf abstract during the last decade the southeastern bering sea shelf has undergone a warming of 3 c that is closely associated with a marked decrease of sea ice over the area this shift in the physical environment of the shelf can be attributed to a combination of mechanisms including the presence over the eastern bering sea shelf of a relatively mild air mass during the winter especially from 2000 to 2005 a shorter ice season caused by a later fall transition and or an earlier spring transition increased flow through unimak pass during winter which introduces warm gulf of alaska water onto the southeastern shelf and the feedback mechanism whereby warmer ocean temperatures during the summer delay the southward advection of sea ice during winter while the relative importance of these four mechanisms is difficult to quantify it is evident that for sea ice to form cold arctic winds must cool the water column sea ice is then formed in the polynyas during periods of cold north winds and this ice is advected southward over the eastern shelf the other three mechanisms can modify ice formation and melt and hence its extent in combination these four mechanisms have served to temporally and spatially limit ice during the 5 year period 2001 2005 warming of the eastern bering sea shelf could have profound influences on the ecosystem of the bering sea from modification of the timing of the spring phytoplankton bloom to the northward advance of subarctic species and the northward retreat of arctic species

satellite and hydrographic observations of the bering sea green belt abstract green belt is the aptly named region of high productivity occurring principally along and above the shelf slope boundary in the bering sea topex altimeter measurements of sea surface topography seawifs imagery of chlorophyll a concentration and shipboard measurements of salinity and fluorescence are used to describe the surface structure of the green belt and its relationship to the bering slope current eddy field during the 2000 2001 and 2002 spring blooms during spring 2000 high surface chlorophyll a concentrations 10 mg m 3 were observed within a 200 km wide band adjacent to and seaward of the shelf break in the northwest bering sea this high concentration chlorophyll band was associated with an anticyclonic eddy group that propagated along isobaths above the continental slope and entrained chlorophyll from the shelf slope front during spring 2001 anticyclonic eddies in the northwest bering sea had propagated off slope prior to the onset of the spring bloom and were too far from the shelf slope front to entrain frontal chlorophyll during the bloom a second chlorophyll front associated with the leading edge of the off slope eddies was observed between these two fronts was a region of relatively low chlorophyll a concentration 1 mg m 3 the eddy field during the 2002 spring bloom was observed to propagate northwestward adjacent to the shelf break and entrain chlorophyll from the shelf slope region in a manner similar to what was observed during the 2000 spring bloom these observations suggest that eddies are important if not the principal agents that cause variability in the distribution of chlorophyll during the spring bloom in the central bering sea

the petrology and geochemistry of dykes of the lizard ophiolite complex cornwall dykes from the coastal section of the lizard ophiolite sw england have been analysed for both major and trace elements the dykes vary from fresh olivine dolerites to lower amphibolite grade metadolerites all are basaltic and tholeiitic and possess broadly oceanic characteristics three magma groupings can be defined geochemically on the basis of trace element contents particularly rare earth elements and p y ratios these magma groupings are thought to have been generated by differing degrees of partial melting and from differing source rocks each group is thought to have undergone fractional crystallization the spatial and suggested temporal separation of these groups supports a pulsatory magma chamber model for the spreading centre at which the lizard ophiolite developed

hollows on mercury materials and mechanisms involved in their formation recent images of the surface of mercury have revealed an unusual and intriguing landform sub kilometre scale shallow flat floored steep sided rimless depressions typically surrounded by bright deposits and generally occurring in impact craters these hollows appear to form by the loss of a moderately volatile substance from the planet s surface and their fresh morphology and lack of superposed craters suggest that this process has continued until relatively recently and may be on going hypotheses to explain the volatile loss have included sublimation and space weathering and it has been suggested that hollow forming volatiles are endogenic and are exposed at the surface during impact cratering however detailed verification of these hypotheses has hitherto been lacking in this study we have conducted a comprehensive survey of all messenger images obtained up to the end of its fourth solar day in orbit in order to identify hollowed areas we have studied how their location relates to both exogenic processes insolation impact cratering and solar wind and endogenic processes explosive volcanism and flood lavas on local and regional scales we find that there is a weak correlation between hollow formation and insolation intensity suggesting formation may occur by an insolation related process such as sublimation the vast majority of hollow formation is in localised or regional low reflectance material within impact craters suggesting that this low reflectance material is a volatile bearing unit present below the surface that becomes exposed as a result of impacts in many cases hollow occurrence is consistent with formation in volatile bearing material exhumed and exposed during crater formation while in other cases volatiles may have accessed the surface later through re exposure and possibly in association with explosive volcanism hollows occur at the surface of thick flood lavas only where a lower reflectance substrate has been exhumed from beneath them indicating that this form of flood volcanism on mercury lacks significant concentrations of hollow forming volatiles

multi scale modeling of the north pacific ocean assessment and analysis of simulated basin scale variability 1996 2003 1 a primitive equation ocean general circulation model is used to investigate climate impacts in the north pacific ocean in the 1996 to 2003 period the objective is to assess the model ability to reproduce observed modes of variability and study their impact in the northeast pacific this work is done within the framework of the u s global ecosystem globec northeast pacific program studying the links between climate variability and ecosystem dynamics three large scale events are considered the 1997 1998 el nino the 1999 regime shift and the 2002 cold fresh subsurface anomalous water mass that was observed in the gulf of alaska and off the coast of oregon the circulation model is shown to generate the correct seasonal to interannual large scale variability and is able to represent the climatic signals of interest in the eastern pacific we show that the influence of the 1997 1998 el nino reached the coastal gulf of alaska and induced an increase in the upper ocean heat content along the coast of north america an analysis of the sea surface temperature for the model years shows agreement between model and data in the representation of the 1999 shift to a cold phase in the eastern and northern north pacific finally using the model results we speculate that the origin of the 2002 cold fresh anomaly in the northeast pacific was due to enhanced mixing during the preceding winter in the center of the alaska gyre owing to anomalous changes in the density structure of the upper ocean this water was able to move geostrophically toward the coast and it persisted in the northeast pacific below the mixed layer the following year

moon mars mercury basin formation ages and implications for the maximum surface age and the migration of gaseous planets abstract basin formation ages for moon mars and mercury are determined by cratering statistics compared and evaluated with respect to their maximum surface ages and available isotope ages and two possible solar system evolution models both mars and mercury appear to have undergone significant resurfacing so that at least the first 200 400 million years are not recorded on their surfaces basin frequency and crater frequencies below 150 km indicate that the moon has the oldest surface mercury has an intermediate age and mars has the youngest preserved terrain an offset between the basin size frequency distribution the smaller crater size frequency distribution and the main belt asteroid size frequency distribution is observed in all three cases suggesting an age difference of about 150 ma between basin and smaller crater distribution based ages i interpreted this in terms of lack of understanding of the basin formation process and suggest that one possible explanation for the apparently under representative basin frequency could be a different lower average impact velocity compatible with the nice flux model the basin formation pattern derived with the standard monotonically decaying or the sawtooth like nice model flux does not reveal a coherent picture according to the late heavy bombardment idea this is here attributed to an incomplete understanding of the cratering rate ratios between the planetary bodies considered here because of the moon s unique formation history i also suggest that it is questionable whether the moon is a suitable analogue for the formation evolution and cratering record of the other terrestrial bodies

evolution of oceanographic conditions off baja california 1997 1999 abstract this paper examines the oceanic response off baja california mexico to the 1997 1998 el nino and the transition to la nina conditions the data presented were gathered during seven cruises over a grid based on the calcofi station plan from lines 100 130 out to station 80 t s diagrams with data obtained during the peak phase of el nino demonstrate that warmer and saltier spicier than normal conditions prevailed in the upper 600 m over this region temperature and salinity anomalies calculated for calcofi line 120 revealed waters near the coast at 50 m depth to be up to 8 7 c warmer and s 0 8 saltier than the climatology during october 1997 these large anomalies persisted through january 1998 with some slight diminution in the magnitudes near the surface this study suggests that anomalously warm and salty waters were fed from a source of spicy water to the southwest identified as subtropical surface water stsw and that low salinity tropical surface waters tsw were blocked to the southeast in the vicinity of the tip of the peninsula subsurface waters associated with the california undercurrent cu fed from the eastern tropical pacific etp were also warmer and saltier than normal and indicate a significant expansion in volume of the cu presumably a result of intensification of poleward flow at depth we postulate that the well defined near surface and deep poleward flows in the study area reflect anomalous large scale cyclonic circulation affecting the flow in the southeastern region of the north pacific subtropical gyre east of 125 w following the el nino event warm and salty upper waters retreated to latitudes south of punta eugenia with the return to normal and cooler conditions equatorward flow over the sampling grid predominated with an increased meandering and mesoscale activity transition to la nina conditions would have been associated with re establishment of normal anticyclonic flow in the southeastern quadrant of the pacific subtropical gyre

an examination of the physical variability around the pribilof islands in 2004 the pribilof islands form a unique ecosystem an anti cyclonic oceanic flow exists around the islands nutrients are introduced into this circulation from two sources 1 the flow along the 100 m isobath with intrusions of nutrient rich water in pribilof canyon and 2 the westward transport and vertical mixing of middle shelf water which contains nutrient rich bottom water enhanced tidal mixing around the pribilofs introduces this deeper nutrient rich water into the euphotic zone and thus supports prolonged production around the islands further the middle shelf water that is advected into the region causes the upper 50 m of the water column around the islands to freshen throughout the summer this enhances the frontal structure and strengthens the baroclinic flow along the 100 m isobath the strengthening of the frontal structure can moderate ecosystem productivity by limiting the intrusion of slope water rich in nutrients and oceanic copepods

transport through unimak pass alaska we examined inflow through unimak pass 200 m deep which is the only major connection between the shelves of the north pacific ocean and the eastern bering sea geostrophic transport was generally northward from the gulf of alaska into the bering sea the flow through the pass appeared to be modulated by the seasonal cycle of freshwater discharge on shorter time scales transport also was affected by semi daily variations in tidal mixing this effect was significant and not anticipated near bottom currents measured from moorings were maximum during winter and significantly correlated r 0 7 with the alongshore winds although the flow through unimak pass transported some nutrients from the north pacific ocean the gulf of alaska shelf is not the major source of nutrients to the bering sea shelf

stratification on the eastern bering sea shelf revisited abstract the timing and magnitude of stratification can have profound influences on the marine ecosystem on the eastern bering sea shelf in the absence of strong wind mixing stratification can be initiated by the melting of seasonal sea ice or by springtime warming of the surface temperature and salinity both influence the stratification of the eastern bering sea shelf with their relative importance varying spatially and temporally in the northern middle shelf domain north of 60 n salinity stratification is often as important as temperature stratification on the southern middle shelf while the influence of temperature on stratification dominates during summer the influence of salinity stratification plays a role in the interannual variability mooring 2 m2 56 9 n 164 1 w has been deployed at 70 m depth in the southern middle shelf domain since 1995 data from this mooring show that stratification typically begins to set up in may and to break down in september october but these dates can vary by 30 d while no trend is found in the timing of the spring setup the fall stratification breakdown exhibited a trend toward later breakdown 2 d later per year from 1996 to 2009 results suggest that it may be difficult to forecast stratification on the eastern bering sea shelf from climate models as simple indices of wind mixing or heat fluxes are not correlated with stratification contrary to intuition the strength of summer stratification is not correlated with depth averaged temperature warm years such as 2000 and 2001 can have low stratification and cold years such as 2007 can have very high stratification this decoupling of stratification and temperature has implications for forecasting the ecosystem in the face of climate change as we cannot assume that projections of a warmer climate simply imply higher stratification in the future

circulation in the eastern bering sea inferences from a 2 km resolution model abstract a 2 km resolution model of the eastern bering sea is developed to capture dynamical processes on the scale of the rossby radius of deformation on tidal to seasonal time scales the model spans the region from 178 e to the alaskan coast and from roughly 50 to 66 n including the aleutian islands in the south and the bering strait in the north the high resolution throughout ensures that the mesoscale dynamics of significant subregions of the domain such as the aleutian island passes bering sea slope and the shelf canyons are captured simultaneously without the concern for loss of interconnectivity between regions simulations are performed for the ice free season june october of 2009 with tidal and atmospheric forcing the model compares favorably with observations from avhrr and envisat satellites argo drifters and bering sea shelf moorings the mesoscale dynamics of the mixing and exchange flow through the eastern aleutian island passes which exhibit strong diurnal and two week variability are well represented the two week oscillation in volume flux through the largest of these passes amukta pass is found to be out of phase with the transport through the neighboring passes e g seguam and samalga passes mesoscale structure is also found to be ubiquitous along the mixing front of the cold pool structures at the scale of o 20 km persist and play a role in determining the pattern of erosion of the water mass as the shelf warms and mixes on the bering sea shelf tidal motions are dominant and variability on the horizontal scale of the first mode internal tide develops o 30 km from the shelf break to the onshore edge of the bering shelf cold pool

the proportion of remineralized nitrate on the ice covered eastern bering sea shelf evidenced from the oxygen isotope ratio of nitrate 1 we present measurements of nitrate and its natural abundance oxygen isotope composition 18o 16o in the water column of the broad and shallow eastern bering sea shelf in the late winter and early spring of 2007 and 2008 in both years nitrate concentrations showed a characteristic decrease from 25 m at the slope to 5 m inshore the 18o 16o ratio of nitrate 18ono3 versus smow also decreased from 3 2 at the slope to 1 5 inshore in 2007 and to as low as 1 inshore in 2008 indicating that nitrate inshore was nitrified at least once since having been entrained as nitrate from the slope the shoreward decrease was less pronounced in 2007 due to 18o enrichment of nitrate from incident phytoplankton assimilation in the ice covered water column whereas little to no algal growth in the water column was evident in 2008 by comparing the 18o of nitrate to that of ambient water in spring 2008 we estimate the fraction of nitrate that was remineralized in situ rather than recently advected from the slope these estimates indicate that 20 100 of the nitrate in winter water of the middle and inner shelves derives from regeneration directly on the shelf rather than from the seasonal entrainment of slope waters with recycling being the dominant mode of seasonal nitrate recharge from the 70 m isobath shoreward these observations indicate substantial nutrient recycling on the shallow shelf which has direct implications for the extent of fixed n loss to benthic denitrification and the fertility of the eastern shelf

496 my age of plagiogranites in the chamrousse ophiolite complex external crystalline massifs in the french alps evidence of a lower paleozoic oceanization genuine ophiolitic series are extremely rare in the variscan orogenic belt and the chamrousse formation appears as an exception the main lithological and geochemical characters of the ophiolite are summarized and a special attention is paid to the field relationships and the magmatic filiation of the leucocratic rocks the time evolution of the mafic magmas is considered to express the transition of attenuated continental lithosphere to oceanic lithosphere the silicic rocks represents the final products from a multisequence fractional crystallization of a tholeiitic lil enriched magma and their compositional diversity results from the local increase of the h2o partial pressure during syn accretion tectonics dating the plagiogranites using theup b method on zircons also give the date of the oceanization the resulting age of496 6ma is closely comparable 1 to the accretion age of ophiolites from peri atlantic paleozoic belts and 2 to the protolith crystallization age of the leptyno amphibolitic groups lags from western europe but these relics ophiolites and lags of the cambro ordovician distensional event later undergo very different tectonometamorphic evolution the distinct post magmatic evolutions may be related to their rather distinct original geodynamic significance and to their primitive location with respect to the subsequent zonation of the hercynian belt

changes in the distribution and abundance of albatrosses in the eastern bering sea 1975 2010 abstract a number of marine species are showing poleward shifts in their distributions in response to climate warming three albatross species frequent the bering sea the laysan phoebastria immutabilis the black footed phoebastria nigripes and the endangered short tailed albatross phoebastria albatrus to determine if albatrosses changed their distribution or abundance in the eastern bering sea between 1975 and 2010 we examined at sea survey data using the north pacific pelagic seabird database within our study area all three species of albatross occurred most frequently in the waters of the aleutian islands in the eastern bering sea all three species were most abundant near the shelf break and in particular in the vicinity of the major submarine canyons in the shelf slope starting in the 1990s population densities increased for all three albatross species with a marked increase in the 2000s in the 2000s there was also an increase in the frequency at which albatrosses were recorded in the central and northern bering sea both black footed and short tailed albatrosses shifted the centers of their bering sea distributions northward the laysan albatross center of distribution shifted southward due to increased numbers along the southern shelf break but densities also increased northward we suggest that the observed changes in distribution and abundance of the three albatross species in the eastern bering sea may have been responses to an increase in the availability of squid their primary prey there additionally the expansion of the distribution of the short tailed albatross in the eastern bering sea may represent the reclamation of its previous range now that the population is beginning to recover from near extinction caused by over harvesting we suggest that predicted increases in ocean temperatures and northward movement of prey could result in albatrosses and other marine apex predators foraging farther north along the bering sea shelf and staying later in fall

a mariner messenger global catalog of mercurian craters abstract using messenger and mariner 10 flyby images we have compiled a global catalog of impact structures with diameters d 10 km the distribution of impact structures shows a factor of 10 range in areal crater density most regions of low crater density are located within large impact basins consistent with the idea that these were low lying areas that have been filled by subsequent volcanism over an extended period

circulation in the bering sea basin observed by satellite tracked drifters 1986 1993 abstract from 1986 through april 1993 86 satellite tracked buoys were deployed in the north pacific and bering sea most of the buoys were drogued at 40 m a composite current pattern is derived using these data the two principal currents the alaskan stream and kamchatka current are clearly evident eddy kinetic mean kinetic energy ratios are low in the stream and along the western bering sea basin an eastward flowing current occurred along the north flank of the aleutian islands this flow was modified by inflow at the passes westward flow occurred north of 56 n its source was the bering slope current the kamchatka current originated near 175 e along the russian coast numerous eddies and meanders were observed in the kamchatka current eddies were also present on the eastern side of the basin

the global population of large craters on mercury and comparison with the moon 1 we have compiled a near global catalog of impact craters on mercury for diameters 20 km from images obtained during the flybys of the mariner 10 and messenger spacecraft the observed variations in crater density suggest that the smooth plains within and around the caloris basin are the most prominent contiguous comparatively young regions on mercury no other comparably large area appears as young in more heavily cratered terrain even the most densely cratered regions on mercury are deficient in craters between 20 km and 100 km in diameter compared with the moon a result that extends an observation made from mariner 10 images of a smaller fraction of mercury s surface this deficit is interpreted to reflect crustal resurfacing of mercury early in its history most likely by volcanic processes for craters larger than 100 km in diameter the density of craters on mercury in a given size range is similar to that of the moon because such larger craters are less easily removed by volcanic resurfacing we interpret this similarity to be the result of impact saturation effects on both bodies

the signature of el nino off oregon 1982 1983 national science foundation through grants oce 8026131 oce 8405232 oce 8014943 and oce 8315014

origins of the subsurface ammonium maximum in the southeast bering sea abstract in the bering sea it has long been argued that ammonium rich bottom water from the middle shelf of bristol bay is tidally diffused seaward resulting in a mid depth ammonium tongue over the outer shelf weak horizontal mean flows in the region relative to an especially strong tidal component support this contention we examined the distribution of ammonium further north in the vicinity of the pribilof islands on the middle shelf bottom waters had concentrations of 4 7 mol kg 1 and over the outer shelf there was a mid depth ammonium tongue optimal multiparameter analysis of hydrographic data suggested that bottom waters from the middle shelf were prevalent across the outer shelf and could account for this ammonium tongue drifter tracks demonstrated that middle shelf water was incorporated into a westward flow along the shelf break south of st george island and mean flows derived from several decades of drifter tracks also show prominent cross shelf advection in the region this was consistent with a scalar argument suggesting that in the vicinity of the pribilof islands the seaward movement of middle shelf water and loss of nitrogen over the middle shelf was the result of advection rather than tidally driven lateral diffusion

the kennack gneiss of the lizard peninsula cornwall sw england commingling and mixing of mafic and felsic magmas accompanying givetian continental incorporation of the lizard ophiolite the kennack gneiss comprises a suite of interlayered mafic and felsic igneous rocks that intruded the 397 ma lizard ophiolite complex cornwall at 376 4 1 7 ma u pb single zircon date and were shortly thereafter c 370 ma metamorphosed to the amphibolite facies weakly deformed examples at the type locality of kennack sands reveal net veining of the mafic by the felsic component dispersed enclaves of the former in the latter and flame like interfingering of the two features indicative of magmatic commingling and mixing the silicic components of the kennack gneiss range from granodiorite to syenogranite and from metaluminous to peraluminous the least silicic rocks being the most peraluminous they were generated through anatexis of a predominantly metasedimentary crustal source having trace element and isotopic compositions comparable to those of the devonian gramscatho group of south cornwall the mafic component of the gneiss includes members group 1 which are weakly enriched in light ree have minor negative ta nb p and ti anomalies in extended trace element plots and display primitive time corrected 143 nd 144 nd and 87 sr 86 sr values and others group 2 which are more strongly enriched in all incompatible trace elements exhibit more prominent negative ta nb p and ti anomalies and have isotopic ratios intermediate between group 1 mafic components and the associated felsic gneiss group 2 represents mixtures of group 1 and granitic melts whereas group 1 rocks are comparable to emorb and were probably generated through partial melting of a weakly enriched mantle source emplacement of two commingled magmas into the base of the lizard ophiolite one representing the products of crustal anatexis implies that the ophiolite was removed from its oceanic setting and was in the process of obduction in the givetian

a numerical model of the ventilated thermocline abstract a steady state numerical solution is found for an idealized rectangular ocean basin driven by wind and surface buoyancy flux a three dimensional primitive equation model is used in agreement with recent analytical modeling the thermocline in the numerical solution consists of three regions quite distinct in their ventilation characteristics forming the greater part of the subtropical thermocline is an unventilated pool zone located in the core of the subtropical gyre and a ventilated zone to the east the unventilated shadow zone lies farther east and toward the equator analysis of potential vorticity on constant density surfaces is used to study the structure of the thermocline a small but intense zone of convection located in the western boundary outflow caused by rapid heat loss to the atmosphere produces source water for the ventilated zone this water of extremely low potential vorticity mode water is distributed widely into the subtropical thermocline the pool forms equ

results from a three dimensional nested biological physical model of the california current system and comparisons with statistics from satellite imagery 1 a three dimensional model of the california current system ccs from 35 n to 48 n extending offshore to 134 w is coupled with a four component trophic model the model reproduces many conspicuous characteristics in the ccs including complex filamentary mesoscale surface features seen in the pigment and temperature from satellite imagery wind driven coastal upwelling at appropriate spatial and temporal scales and the close correlation between prominent features seen in pigment and those in temperature observed by satellites abbott and zion 1985 statistical estimates of the characteristic spatial scales of variability as calculated from the coupled nested model agree with those previously estimated from satellite images for both surface temperature and pigment denman and abbott 1988 1994 model estimates of the characteristic temporal scales of variability from decorrelation times agree with those previously estimated from satellite images typical model decorrelation times lie between 2 and 4 days in agreement with calculations from earlier sequences of coastal zone color scanner czcs and advanced very high resolution radiometer avhrr satellite images denman and abbott 1988 1994

effects of seasonal and interannual variability in along shelf and cross shelf transport on groundfish recruitment in the eastern bering sea the bering sea responds rapidly to atmospheric perturbations and over the past several decades has experienced extreme variability in both its physical and biological characteristics these changes can impact organisms that inhabit the region particularly marine fishes as normal current patterns to which reproductive habits are tuned can be disrupted which in turn may influence recruitment and population dynamics to understand the influence of ocean circulation on groundfish recruitment in the eastern bering sea we examined transport along and across the bering slope derived from 23 years 1982 2004 of simulations from a regional ocean modeling system roms ocean circulation model we expected that changes in the strength and position of the bering slope current bsc would affect recruitment in selected species pacific cod walleye pollock greenland halibut pacific halibut and arrowtooth flounder and that circulation features along and across the shelf edge would be strongly influenced by atmospheric forcing variability in along shelf transport at three transects along the path of the bsc cross shelf transport across the 100 and 200 m isobaths and transport through unimak pass were examined strong seasonal and interannual variations in flow were observed with transport typically highest during fall and winter months coinciding with timing of spawning activity in the five species significant correlations were found between transport bsc position and groundfish recruitment pacific cod in particular benefitted from decreased along shelf and on shelf flow while pacific halibut recruitment increased in relation to increased on shelf transport through southern canyons the results of this study improve our understanding of variability in circulation and associated effects on groundfish recruitment in the eastern bering sea

nutrient and phytoplankton dynamics on the inner shelf of the eastern bering sea the nitrogen cycle on the inner shelf of the southeastern bering sea is complicated due to limited nutrient replenishment across this broad shelf and substantial nitrogen loss through sedimentary processes while diffusion at the inner front may periodically support new production the shelf is generally hypothesized to be a regenerative system this study uses a combination of hydrographic surveys and measurements of nitrogen assimilation and benthic fluxes to examine nitrogen cycling on the inner shelf and connectivity between the middle and inner shelves of the southern and central bering sea results establish the inner shelf as primarily a regenerative system even in spring although new production can occur at the inner front results also identify key processes that influence nutrient supply to the inner shelf and reveal coupling between the middle shelf nutrient pool and production on the inner shelf this article is protected by copyright all rights reserved

numerical treatment of cross shelf open boundaries in a barotropic coastal ocean model abstract using a barotropic coastal ocean model with a straight coastline and uniform cross shelf bottom slope seven different cross shelf open boundary conditions four of which are applied in either implicit or explicit form are compared in three numerical experiments 1 a mound of water is allowed to collapse and radiate waves toward the open boundaries 2 a uniform alongshelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment 3 a uniform cross shelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment the boundary condition which is most transparent to waves consists of a sponge at the outer edge of the model domain with an orlanski radiation condition at the outer edge of the sponge several open boundary conditions perform adequately in the wind stress experiments but the orlanski radiation condition alone without a sponge appears to give the best total performance of thes

a revised control network for mercury an improved control net for mercury has been completed by utilizing images acquired during the three mariner 10 flybys in 1974 1975 relative positional errors within the net are 1 km on average and absolute locations are estimated to be better than 25 km the analytical triangulation resulted in new values for focal lengths camera a 1493 6 mm camera b 1500 1 mm w0 329 548 and camera orientation angles for 811 images acquired during all three flybys of mercury

crater size frequency distributions and a revised martian relative chronology a revised martian relative chronology is determined which dates geologic units with respect to the end of the period of heavy bombardment this analysis differs from previous studies by using viking 1 2m photomosaics to map all 25 826 craters 8km diameter which postdate the lithologic units making up the martian surface the relative plotting technique is used because it shows changes in the shape and density of the crater size frequency distribution curves more clearly than cumulative plots the changes in shapes of the distribution curves are interpreted to be due to two different impacting populations one dominating during the heavy bombardment period and the other emplaced during the post heavy bombardment period the 8 km diameter limit was chosen to exclude the majority of secondary craters and to minimize obliteration effects acting over the age of the planet the results obtained are average ages valid for units with typical thicknesses between about 1 and 3 km and extending over an area of about 105 km2 the shapes and densities of the crater distribution curves indicate that approximately 60 of the martian lithologic units in which these craters occur formed during the period of heavy bombardment many of the small volcanoes those generally less than 200 km diameter including most in the tharsis and elysium regions date from this period the hellas and argyre impacts bracket the average age of the intercrater plains in the highlands the ridged plains distribution curves indicate formation during the period of heavy bombardment but their lower crater density indicates that they are the last geologic unit to retain the scars from this population of impactors they therefore likely formed near the end of heavy bombardment the remaining 40 of martian terrain units show distribution curves indicative of emplacement since the end of heavy bombardment the wide range in crater densities among different regions of plains indicate a range in formation ages although the general view of martian geologic evolution does not differ significantly from previous studies the present analysis explicitly states the relationship of numerous geologic units to the period of heavy bombardment and has revised the relative ages of localized regions across mars

altimeter derived surface circulation in the large scale ne pacific gyres part 2 1997 1998 el nino anomalies abstract changes in the sea surface heights ssh and geostrophic transports in the ne pacific are examined during the 1997 1998 el nino using altimeter data sea level pressure slp fields proxy winds and satellite sea surface temperature sst most of the signal occurs along the boundaries of the basin from panama to the alaska peninsula changes in the ssh and alongshore transports along the boundaries are caused both by propagation of signals from the south stronger between the equator and the gulf of california and by local and basin scale winds stronger between the pacific northwest and the alaska peninsula two periods of high ssh occur at the equator may july 1997 and october 1997 january 1998 the first coastal ssh signal moved quickly polewards to approximately 24 n in early june then stalled and moved farther north during transient events in july september large scale wind forcing combined with the equatorial signals during the second period of high equatorial ssh fall 1997 to move the high ssh and poleward transports quickly around the alaska gyre a connection between the boundary currents and the interior north pacific developed as part of the large scale response to the basin scale winds after changes in the boundaries decreases in anomalies of ssh and poleward transports began in january 1998 south of 40 n and in february 1998 farther north

the coastal ocean off oregon and northern california during the 1997 8 el nino abstract the evolution and decay of el nino 1997 8 was observed in coastal waters off oregon in a sequence of cruises along 44 6 n from the coast to more than 150 km offshore hydrographic observations were made during eleven cruises between july 1997 and april 1999 at stations on the newport hydrographic line which had been occupied regularly from 1961 to 1971 the data from the earlier decade provide a basis for defining normal conditions and allow comparisons with the recent el nino in terms of t s spiciness and geostrophic velocity independent of el nino the ocean in july 1997 was already anomalously warm offshore of 50 km and above 100 m by september 1997 there were unambiguous indications of el nino isotherms and isohalines sloped down toward the coast indicating poleward flow over shelf and slope and anomalously spicy water was present at the shelf break in november 1997 and february 1998 shelf break waters were even warmer and there was strong poleward flow inshore of 100 km extending to depths greater than 200 m the april 1998 section closely resembled that of april 1983 another el nino year but by june 1998 the anomalies were mostly gone november 1998 was near normal and the sections from subsequent cruises resemble the mean sections from 1961 1971 four cruises between november 1997 and november 1998 included sampling at several latitudes between 38 and 45 n as expected these sections show significant alongshore gradients but also a surprising degree of homogeneity in the anomalous features associated with el nino in the temperature salinity spiciness and geostrophic velocity fields the anomalous signature of el nino was stronger at its winter peak in 1998 than in 1983 but the signature in the temperature and spiciness fields and in coastal sea level did not persist as long as in 1983 by april 1999 the coastal ocean from 38 n to 45 n was significantly colder than it had been in april 1984

characteristics and variability of the inner front of the southeastern bering sea the inner front of the southeastern bering sea shows marked spatial variability in frontal characteristics created by regional differences in forcing mechanisms differences in forcing mechanisms sea ice advance retreat and storm strength and timing and early spring water properties result in strong interannual variability in biological chemical and physical features near the front we have developed a simple model based on surface heat flux and water column mixing to explain the existence of cold belts cont shelf res 19 14 1999 1833 associated with such fronts hydrography fluorescence and nutrient observations show that pumping of nutrients into the euphotic zone occurs and this can prolong primary production at the inner front the effectiveness of this process depends on two factors the existence of a reservoir of nutrients in the lower layer on the middle shelf and the occurrence of sufficient wind and tidal energy to mix the water column

correlations between seabirds and ocenic fronts around the pribilof islands alaska abstract located on the extensive continental shelf of the bering sea the pribilof islands alaska are the site of one of the largest breeding colonies of seabirds in the northern hemisphere during summer these islands are surrounded by a front that separates vertically homogeneous waters from well stratified waters farther seaward we studied the front with hydrographic data and the bird distributions with concurrent counts during summer 1977 and spring summer and fall 1978 murres uria lomvia and u aalge sitting on the water aggregated near the front during summer 1977 and probably during summer 1978 other species such as northern fulmars fulmarus glacialis and auklets aethia pusilla and a cristatella were unaffected by the front we hypothesize that the aggregation of the murres was related to an enhanced availability of their food near the front