physical dynamics and biological implications of a mesoscale eddy in the lee of hawai i cyclone opal observations during e flux iii abstract e flux iii march 10 28 2005 was the third and last field experiment of the e flux project the main goal of the project was to investigate the physical biological and chemical characteristics of mesoscale eddies that form in the lee of maui and the island of hawai i focusing on the physical biogeochemical interactions the primary focus of e flux iii was the cyclonic cold core eddy opal which first appeared in the noaa goes sea surface temperature sst imagery during the second half of february 2005 during the experiment cyclone opal moved over 160 km generally southward thus the sampling design had to be constantly adjusted in order to obtain quasi synoptic observations of the eddy analyses of ship transect depth profiles of ctd optical and acoustic doppler current profiler adcp data revealed a well developed feature characterized by a fairly symmetric circular shape with a radius of about 80 km depth profiles of temperature salinity and density were characterized by an intense doming of isothermal isohaline and isopycnal surfaces isopleths of nutrient concentrations were roughly parallel to isopycnals indicating the upwelling of deep nutrient rich water the deep chlorophyll maximum layer dcml shoaled from a depth of about 130 m in the outer regions of the eddy to about 60 m in the center chlorophyll concentrations reached their maximum values in opal s core region about 40 km in diameter where nutrients were upwelled into the euphotic layer adcp velocity data clearly showed the cyclonic circulation associated with opal vertical sections of tangential velocities were characterized by values that increased linearly with radial distance from near zero close to the center to a maximum of about 60 cm s 1 at roughly 25 km from the center and then slowly decayed the vertical extent of the cyclonic circulation was primarily limited to the upper mixed layer as tangential velocities decayed quite rapidly within a depth range of 90 130 m potential vorticity analysis suggests that only a relatively small about 50 km in diameter and shallow to a depth of approximately 70 m portion of the eddy is isolated from the surrounding waters radial movements of water can occur between the center of the eddy and the outer regions along density surfaces within an isopycnal range of t 23 6 t 23 6 kg m 3 and t 24 4 t 24 4 kg m 3 thus the biogeochemistry of the system might have been greatly influenced by these lateral exchanges of water at depth especially during opal s southward migration while the eddy was translating deep water in front of the eddy might have been upwelled into the core region leading to an additional injection of nutrients into the euphotic zone at the same time part of the chlorophyll rich waters in the core region might have remained behind the translating eddy and thus contributed to the formation of an eddy wake characterized by relatively high chlorophyll concentrations

accumulation of mineral ballast on organic aggregates 1 to address whether the incorporation of suspended minerals drives the sedimentation of particulate organic carbon in the ocean or vice versa incubations of phytoplankton detritus aggregates were set up in rolling tanks containing seawater and suspended clay illite or calcium carbonate at concentrations ranging between 10 and 50 000 g l 1 the suspended minerals were efficiently scavenged by and incorporated into the organic aggregates the volume and porosity of aggregates decreased with increasing mineral concentrations and at suspended mineral concentrations higher than 500 g l 1 the initially medium sized aggregates were fragmented into thousands of tiny dense aggregates because radius and density have opposite effects on aggregate sinking rates the relationship between aggregate particulate organic carbon poc to mineral ratio and sinking rate is not a straightforward one that necessarily results in higher sinking rates with increased mineral content in these experiments the saturating capacity of organic aggregates for mineral particles appeared to be 97 to 98 weight percent mineral i e a poc to dry weight ratio of 0 02 to 0 03 g c g 1 this parallels the values of 0 05 g c g 1 observed for sinking particles in the deep sea and suggests that it is the flux of poc that determines the flux of minerals to the deep and not the other way around

the early environment and its evolution on mars implication for life there is considerable evidence that the early climate of mars was very different from the inhospitable conditions there today this early climate was characterized by liquid water on the surface and a dense atmosphere composed predominantly of co2 the duration of these warm initial conditions on the surface of mars is uncertain but theoretical models suggest that they could have persisted for hundreds of millions up to a billion years from studies of the earth s earliest biosphere we know that by 3 5 gyr ago life had originated on earth and reached a fair degree of biological sophistication surface activity and erosion on earth make it difficult to trace the history of life before the 3 5 gyr time frame if mars did maintain a clement environment for longer than it took for life to originate on earth then the question of the origin of life on mars follows naturally the fossil evidence of early life on earth provides clues as to what form fossils on mars might take of particular interest are stromatolites macroscopic layered structures that result from the anchoring of sediments by microorganisms living in the photic zone since over two thirds of the martian surface is more than 3 5 gyr old the possibility exists that mars may hold the best record of the events that led to the origin of life even though there may be no life there today

subtidal response of scotian shelf circulation to local and remote forcing part i observations abstract data collected during the canadian atlantic storms program casp suggest that two primary current regimes exist on the scotian shelf during winter moorings inside the 100 m isobath feature currents that are parallel to the general bathymetry and have small eastward mean velocities the time varying part of the flow is nearly rectilinear alongshelf at typical maximum velocities of 0 2 0 3 m s 1 and oscillates on 2 5 day periods in response to meteorological forcing the current at locations beyond the 100 m isobath exhibits a persistent westward flow of about 0 3 m s 1 denoting the dominance of the nova scotian current although smaller magnitude along and cross shelf fluctuations occur at synoptic frequencies flow in both regions is largely uniform with depth at this time of year the velocity response to local and remote sources of forcing was examined using a frequency dependent multiple regression model flow is dominated by nonlocal forcing at 0 2 cpd alongshelf wind stress is t

the kinematic and hydrographic structure of the gulf of maine coastal current the gulf of maine coastal current gmcc which extends from southern nova scotia to cape cod massachusetts was investigated from 1998 to 2001 by means of extensive hydrographic surveys current meter moorings tracked drifters and satellite derived thermal imagery the study focused on two principal branches of the gmcc the eastern maine coastal current emcc that extends along the eastern coast of maine to penobscot bay and the western maine coastal current wmcc that extends westward from penobscot bay to massachusetts bay results confirm that gmcc is primarily a pressure gradient driven system with both principal branches increasing their transport in the spring and summer due to fresh water inflows and flowing southwestward against the mean wind forcing during this period in the spring and summer the subtidal surface currents in the emcc range from 0 15 to 0 30 ms 1 while subtidal wmcc currents range from 0 05 to 0 15 ms 1 the reduction of southwestward transport near penobscot bay is accomplished via an offshore veering of a variable portion of the emcc some of which recirculates cyclonically within the eastern gulf of maine the degree of summer offshore veering versus leakage into the wmcc varied strongly over the three study years from nearly complete disruption in 1998 to nearly continuous through flow in 2000 observations show strong seasonal and interannual variability in both the strength of the gmcc and the degree of connectivity of its principal branches r 2005 elsevier ltd all rights reserved

satellite remote sensing reveals coastal upwelling events in the san matias gulf northern patagonia abstract coastal upwelling events are effective in fluxing nutrients upward to the euphotic layer thus promoting the growth of marine phytoplankton satellite data may provide useful information to detect and characterize upwelling events in regions of sparse in situ observations we analyze the coastal upwelling process on the western san matias gulf on the northern continental shelf of argentina based on the analysis of remote sensing and in situ data upwelling events are characterized by their frequency of occurrence and magnitude during the austral summer we found roughly 6 upwelling favorable wind events per year satellite derived sea surface temperature sst data provide evidence of upwelling in 85 of the cases between 2000 and 2008 analysis of specific events provides clues on the wind forcing characteristics required to generate upwelling and on characteristic space and time scales of the process on february 2005 sst data reveal a narrow coastal band 10 km of relative cold water extending 100 km along the west coast of smg the sst in this band was 1 5 c lower than further offshore near bottom temperature fluctuations from in situ daily observations collected at two near shore locations are significantly correlated with along shore wind stress suggesting that coastal upwelling is a dominant process controlling high frequency temperature fluctuations near shore a simple quantitative estimate reveals a volume of upwelled water reaching the sea surface of about 10 10 m 3 during one relatively intense upwelling event

mesozooplankton biomass and grazing responses to cyclone opal a subtropical mesoscale eddy as part of e flux iii cruise studies in march 2005 plankton net collections were made to assess the effects of a cyclonic cold core eddy cyclone opal on the biomass and grazing of mesozooplankton mesozooplankton biomass in the central region of cyclone opal an area of uplifted nutricline and a subsurface diatom bloom averaged 0 8070 24 and 1 5170 59 g dw m 2 for day and night tows respectively these biomass estimates were about 80 higher than control out stations with increases more or less proportionately distributed among size classes from 0 2 to 45 mm though elevated relative to surrounding waters south of the hawaiian islands hawai i lee total biomass and size distribution in cyclone opal were almost exactly the same as contemporary measurements made at stn aloha 100 km north of the islands by the hot hawaii ocean time series program mesozooplankton biomass and community composition at the out stations were also similar to aloha values from 1994 to 1996 preceding a recent decadal increase these comparisons may therefore provide insight into production characteristics or biomass gradients associated with decadal changes at stn aloha gut fluorescence estimates were higher in opal than in ambient waters

coupled north atlantic slope water forcing on gulf of maine temperatures over the past millennium to investigate ocean variability during the last millennium in the western gulf of maine gom we collected a 142 year old living bivalve arctica islandica l in 2004 and three fossil a islandica shells calibrated 14cams 1030 78 ad 1320 45 ad 1357 40 ad for stable isotope and growth increment analysis a statistically significant relationship exists between modern gom temperature records shell isotope derived 30 m r 0 79 p 0 007 prince 5 50 m r 0 72 p 0 019 boothbay harbor sst r 0 76 p 0 011 and labrador current lc transport data from the eastern newfoundland slope during 1993 2003 in all cases as lc transport increased gom water temperatures decreased the following year decadal trends in the north atlantic oscillation nao and the atlantic multidecadal oscillation amo influence gom water temperatures in the most recent period with water temperatures decreasing during nao and amo negative modes most likely linked to lc transport and gulf stream interaction mean shell derived isotopic changes 18oc during the last 1 000 years were 0 47 and likely reflect a 1 2 c cooling from 1000 ad to present based on these results we suggest that observed cooling in the gom during the last millennium was due to increased transport and or cooling of the lc and decreased gulf stream influence on the gom

association of sinking organic matter with various types of mineral ballast in the deep sea implications for the rain ratio 1 we compiled and standardized sediment trap data below 1000 m depth from 52 locations around the globe to infer the implications of the armstrong et al 2002 ballast model to the ratio of organic carbon to calcium carbonate in the deep sea the rain ratio we distinguished three forms of mineral ballast calcium carbonate opal and lithogenic material we concur with armstrong et al 2002 that organic carbon sinking fluxes correlate tightly with mineral fluxes based on the correlations seen in the trap data we conclude that most of the organic carbon rain in the deep sea is carried by calcium carbonate because it is denser than opal and more abundant than terrigenous material this analysis explains the constancy of the organic carbon to calcium carbonate rain ratio in the deep sea today and argues against large changes in the mean value of this ratio in the past however sediment trap data show variability in the ratio in areas of high relative calcium carbonate export mass caco3 mass ratio 0 4 unexplainable by the model leaving open the possibility of regional variations in the rain ratio in the past

the influence of warm core rings on slope water entering the gulf of maine the seasonal baroclinic circulation in the gulf of maine is partly determined by the distribution of dense water that enters from the continental slope and spreads over sills into the deep basins of the gulf the slope water enters the gulf as an intermittent deep flow through the northeast channel which provides the principal connection with the atlantic ocean warm core rings from the gulf stream occasionally approach the mouth of the northeast channel and at times ring water contributes to or modifies the inflowing slope water for example sequential surveys in june and july of 1986 showed that a ring streamer crowded against georges bank and brushed obliquely across the channel mouth the resulting inflow in july flooded the channel mouth with streamer modified slope water which overwhelmed the more usual maine intermediate water outflow noted 1 month earlier compared to previous years relatively little slope water was found inside the gulf in june 1986 and it is tempting to speculate that a delayed spin up of the interior baroclinic circulation began with the major inflow episode observed in july warm core rings from the gulf stream may influence the timing intensity and structure of the circulation and dependent processes that develop each year in the gulf of maine a test of this hypothesis will require long term monitoring of the northeast channel region coupled with seasonal hydrographic surveys and current measurements at strategic locations inside the gulf of maine

martian gases in an antarctic meteorite significant abundances of trapped argon krypton and xenon have been measured in shock altered phases of the achondritic meteorite elephant moraine 79001 from antarctica the relative elemental abundances the high ratios of argon 40 to argon 36 2000 and the high ratios of xenon 129 to xenon 132 2 0 of the trapped gas more closely resemble viking data for the martian atmosphere than data for noble gas components typically found in meteorites these findings support earlier suggestions made on the basis of geochemical evidence that shergottites and related rare meteorites may have originated from the planet mars

the circulation of eastern canadian seas abstract the eastern canadian seas including baffin bay the labrador sea and shelf the n e newfoundland shelf the scotian shelf and the gulf of st lawrence form an integrated hydro dynamical system the circulation is investigated using current meter data and a high resolution three dimensional coupled ice ocean circulation model cecom canadian east coast ocean model covering the entire area the model is forced with realistic atmosphere fluxes and the results are compared to the current meter data collected in four selected periods between 1987 and 2008 many features of the model current fields are similar to those from the previous regional circulation models for the shelves new findings from cecom include seasonal differences of the circulation around davis strait the detailed structure of the labrador current re circulation two cross shelf currents on the scotian shelf and strong currents in halibut channel which connects the waters of the western grand banks and scotian shelf the annual variation of the circulation is investigated both the model and data show the labrador current is strong in fall and weak in spring the outflow from the gulf of st lawrence through cabot strait and the currents on the inner scotian shelf are strong in winter and fall and weak in spring and are in phase with the labrador current the model currents are compared to observations using a qualitative method of visual comparison and a quantitative method based on statistical analysis the comparisons indicate that the main features of the current fields from the observations are successfully reproduced by the model the quantitative analysis indicates that the model currents are in reasonable agreement with the observations specifically a good agreement is found in the labrador shelf newfoundland shelf and flemish pass a fair agreement is found in davis strait the inner scotian shelf and sable bank however the agreement for cabot strait and the scotian shelf break is less satisfactory an analysis of the spatial variability of the current field suggests that the degree of agreement is closely related to the spatial variability of the current field the regions with low spatial variability generally have good agreements the volume and freshwater transports through several sections from the model are in good agreement with available estimates based on data

the earliest atmosphere of the earth walker j c g 1982 the earliest atmosphere of the earth precambrian res 17 147 171 this paper examines from the point of view of atmospheric physics the possibility that the initial complement of volatiles in the material that formed the earth was very much larger than that remaining the escape of large amounts of hydrogen into an interplanetary vacuum is possible only if the heat source in the upper levels of the atmosphere provided by solar extreme ultraviolet and particle emissions was much larger than it is today rapid escape of hydrogen would have swept heavy minor gases along with it if the rate of escape declined due to a decreasing upper atmospheric energy source minor gases would have been selectively retained by the earth beginning with the heaviest rotation would not have facilitated escape significantly because a rapidlyescaping atmosphere would have tended to conserve angular momentum if earth accreted in the presence of a gaseous nebula it would have acquired a dense hot atmosphere of nebular composition this primary atmosphere would probably have been convective and adiabatic at lower levels with the upper atmosphere approximately isothermal and devoid of turbulence planetary rotation would have imposed a global circulation on the upper atmosphere and overlying nebula with downwelling over the poles and upwelling over the equator this circulation would have carried away into the nebula any gases released from the solid phase during the course of accretion the primary atmosphere may not have dissipated completely after the disappearance of the nebula heavy gases particularly may have been retained by the earth to contribute to the present volatile inventory

an offshore study in the california current system preface l etude d un tourbillon de mesoechelle quasi permanent et quasi stationnaire dans le systeme du courant de californie comprend quatre parties dynamique au sein du systeme manifestations a la surface structure chimique et distribution du plancton

volatile inventories of the terrestrial planets the past few years have seen continuing application of classical theories of thermal and nonthermal atmospheric escape to problems involving the compositional and isotopic evolution of planetary volatile reservoirs a new emphasis on a previously underappreciated thermal process hydrodynamic escape has appeared in interpretations of hydrogen and noble gas fractionation patterns in terrestrial planet atmospheres other mechanisms for loss of atmospheric mass notably by impact induced erosion at various scales have been discussed and roughly modeled direct spacecraft exploration of halley s comet in 1986 has rekindled interest in cometary matter as a possible early source of planetary volatiles particularly for venus

morphology and composition of submarine barchan dunes on the scotian shelf canadian atlantic margin abstract submarine barchan dunes have been mapped on browns bank scotian shelf using multibeam sonar bathymetry and backscatter strength the morphology of subaerial barchans has been studied for almost a century but the advent of multibeam sonar technology now enables a quantitative investigation of their submarine counterparts the browns bank submarine barchans occur at a depth of 60 70 m and are crescentic in planform reaching almost 700 m in horn width and 5 m in height the barchans are convex to the se with steep lee faces to the nw indicating a dominant nw flowing current the barchans overlie a widespread gravel lag covered elsewhere with little or no sand obstacle marks emanate from the lee faces of the barchans and represent a lack of sand deposition and exposure of gravel lag on the sea floor the browns bank submarine barchan sediment texture is gravelly sand or sandy gravel and is primarily composed of subrounded to well rounded quartz grains the allometric relationship between submarine barchan slip face height and distance between horns is markedly different from that of subaerial barchans for the same dune height barchan horn width is about ten times greater in the marine environment the superimposition of megaripples on the stoss slopes of the submarine barchans suggests that the barchans are active and therefore represent an engineering risk to sea floor infrastructure current observations and models indicate that seasonal mean current strength is less than the critical velocity required for barchan migration however the barchans may be active under higher velocity storm induced currents repetitive multibeam sonar mapping is required to detect if barchan migration is occurring over longer time scales

structure and variability of the western maine coastal current abstract analyses of ctd and moored current meter data from 1998 and 2000 reveal a number of mechanisms influencing the flow along the western coast of maine on occasions the eastern maine coastal current extends into the western gulf of maine where it takes the form of a deep order 100 m deep and broad order 20 km wide southwestward flow with geostrophic velocities exceeding 20 cm s 1 this is not a coastally trapped flow however in fields of geostrophic velocity computed from shipboard ctd data the core of this current is roughly centered at the 100 m isobath and its onshore edge is no closer than 10 km from the coast geostrophic velocity fields also reveal a relatively shallow order 10 m deep baroclinic flow adjacent to the coast this flow is also directed to the southwest and appears to be principally comprised of local river discharge analyses of moored current meter data reveal wind driven modulations of the coastal flow that are consistent with expectations from simple theoretical models however a large fraction of the near shore current variance does not appear to be directly related to wind forcing sea surface temperature imagery combined with analysis of the moored current meter data suggests that eddies and meanders within the coastal flow may at times dominate the near shore current variance

the supply and accumulation of silica in the marine environment rivers and submarine hydrothermal emanations supply 6 1 1014g sio2 yr to the marine environment approximately two thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep sea deposits siliceous deep sea sediments located beneath the antarctic polar front convergence account for over a fourth 1 6 1014g sio2 yr of the silica supplied to the oceans deep sea sediment accumulation rates beneath the polar front are highest in the south atlantic with values as large as 53cm kyr during the last 18 000 yr siliceous sediments in the bering sea sea of okhotsk and subarctic north pacific accumulate 0 6 1014g sio2 yr or 10 of the dissolved silica input to the oceans the accumulation of biogenic silica in estuarine deposits removes a maximum of 0 8 1014g sio2 yr although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters siliceous sediments from continental margin upwelling areas e g gulf of california walvis bay or peru chile coast have the highest biogenic silica accumulation rates in the marine environment 69 g sio2 cm2 kyr despite the rapid accumulation of biogenic silica upwelling areas account for less than 5 of the silica supplied to the marine environment because they are confined laterally to such small areas

new martian paradigms several interrelated paradigms concerning the nature and the evolution of mars are discussed these include an impact origin of the northern lowland mars as a water rich planet former oceans in the northern lowlands a warm wet climate on early mars and the possibility of ancient life on mars locations on mars suggested for the search of possible ancient life include the heavily cratered terrain dissected by valley networks possible lacustrine deposits in valles marineris the oxidizing layer below the surface sites along the fringes of the hypothetical northern circumpolar ocean and in evaporite deposits

tidal and buoyancy driven currents in chignecto bay bay of fundy circulations in the chignecto bay system upper part of the bay of fundy were studied using current meter moorings tidal and diagnostic models and salinity and suspended sediment concentration measurements the current meter observations revealed that 1 the tides behaved basically as standing waves tidal current leads tidal elevation by about 90 2 tidal currents were typically of the order of 1 m s 1 and were almost rectilinear 3 residual currents were up to 0 17 m s 1 and the circulation pattern was quite complex and 4 a two layer residual circulation with inflow in the upper layer and outflow in the lower layer existed at the entrance to the bay most of the residual currents in the upper part of the bay were driven by tidal rectification the two layer residual circulation at the bay entrance was examined using a diagnostic model it was found that the circulation was probably induced by horizontal density variations near the entrance to cumberland basin shepody bay and chignecto bay the cross channel variation of surface suspended sediment concentration was consistent with the observed residual currents from current meter moorings and the estimated currents from the diagnostic model the cross channel variation of salinity near the entrance to chignecto bay was also consistent with the observed and computed residual currents

wind induced interannual variability of sea level slope along shelf flow and surface salinity on the northwest atlantic shelf in this study we examine the importance of regional wind forcing in modulating advective processes and hydrographic properties along the northwest atlantic shelf with a focus on the nova scotian shelf nss gulf of maine gom region long term observational data of alongshore wind stress sea level slope and along shelf flow are analyzed to quantify the relationship between wind forcing and hydrodynamic responses on interannual time scales additionally a simplified momentum balance model is used to examine the underlying mechanisms our results show significant correlation among the observed interannual variability of sea level slope along shelf flow and alongshore wind stress in the nss gom region a mechanism is suggested to elucidate the role of wind in modulating the sea level slope and along shelf flow stronger southwesterly northeastward winds tend to weaken the prevailing southwestward flow over the shelf building sea level in the upstream newfoundland shelf region whereas weaker southwesterly winds allow stronger southwestward flow to develop raising sea level in the gom region the wind induced flow variability can influence the transport of low salinity water from the gulf of st lawrence to the gom explaining interannual variations in surface salinity distributions within the region hence our results offer a viable mechanism besides the freshening of remote upstream sources to explain interannual patterns of freshening in the gom

the case for a martian origin of the shergottites nitrogen and noble gases in eeta 79001 abstract nitrogen and noble gases were measured in samples of a glass inclusion and the surrounding basaltic matrix from the antarctic shergottite eeta 79001 a nitrogen component trapped in the glass but not present in the matrix has a 15n value at least as high as 190 ratios of40ar 14n and15n 14n in the glass are consistent with dilution of a martian atmospheric component 15n 620 160 40ar 14n 0 33 0 03 by either terrestrial atmosphere adsorbed on the samples or by indigenous nitrogen from the minerals of the rock trapped noble gases in the glass reproduce within error the elemental and isotopic compositions measured in mars atmosphere by viking and are in general agreement with previous measurements except for much lower abundances of neutron generated krypton and xenon isotopes the most reasonable explanation at the present time for the noble gas pattern and the isotopically heavy nitrogen is that a sample of martian atmosphere has been trapped in the eeta 79001 glass and that this meteorite and thus the shergottites and probably the nakhlites and chassignites as well originated on mars nitrogen in the non glassy matrix of eeta 79001 amounts to less than 0 5 ppm and has a spallation corrected 15n value in the range 0 to 20 it may reflect indigenous nitrogen in the basalt or a mixture of indigenous and adsorbed terrestrial nitrogen spallogenic noble gases yield single stage exposure ages between 400 000 and 900 000 years depending on irradiation geometry trapped argon may have an unusually low36ar 38ar ratio trapped krypton except for a small excess at80kr is smoothly mass fractionated with respect to either terrestrial or chondritic kr the trapped xenon composition is consistent with addition of neutron capture radiogenic and fissiogenic isotopes to a base composition resembling terrestrial atmospheric xe the elemental84kr 132xe ratio of 25 is close to the terrestrial value and very different from the chondritic ratio

coastal upwelling and eddy development off nova scotia satellite photos during the summer of 1984 show the development of a band of cool water along the seaward coast of nova scotia during a month long period of upwelling favorable winds the timing of the appearance of the cool water band the rate at which it broadened and the bottom temperature evolution at several representative points along the coast are shown to be in good agreement with an idealized two layer model of the wind driven shelf circulation the presence of the cool water is clearly attributable to upwelling after the temperature front moves offshore wavelike features develop rapidly with alongshore wavelengths of 50 75 km and similar maximum cross shore displacement amplitudes the associated alongshore propagation speed is at most 0 02 m s 1 to the northeast the length and time scales of these features are shown to be consistent with results from simple linear instability models which allow for both potential and kinetic energy release from the mean state by perturbations results suggest that the wavelike features are primarily due to baroclinic instability of the upwelling associated base state rough estimates suggest that upwelling and subsequent eddy development can play an important role in the supply of nutrients to the surface waters of the shelf

seasonal variability of sea surface temperature fronts on georges bank abstract sea surface temperature sst fronts extracted from archived 1985 1996 advanced very high resolution radiometer avhrr data are determined in the georges bank region resulting frontal locations clearly show the tidal mixing front on georges bank the probability of detecting an sst front at an individual pixel on georges bank is presented as a monthly climatology variations in the probability position and associated water depth of sst fronts in the georges bank region show the development of the tidal mixing front during the summer as well as the presence of a persistent front near the shelfbreak from the 12 yr time series of fronts 144 individual monthly frontal probability images are decomposed into the mean frontal position and empirical orthogonal functions eof using singular value decomposition svd spatial and temporal information from the first eof mode reveals the seasonal development of the tidal mixing front spatial patterns associated with the first mode also reveal the winter occurrence of fronts on the northeast peak area of georges bank which is most likely associated with scotian shelf water flow across the northeast channel the second mode also indicates the development of the hot spot often observed over georges bank during the late summer and early fall further evidence indicates that the mean position of detected sst fronts on southern georges bank changes approximately 10 km on bank from late spring to mid summer monthly mean positions are also compared to the distribution of simpson and hunter s 1974 tidal mixing parameter with resultant positions compared to historical stratification at those locations comparison of detected sst fronts to historical hydrographic data on georges bank points to the fronts being located in increasingly stratified water from may through august

spatial and temporal structure of the barotropic response of the scotian shelf and gulf of maine to surface wind stress a model based study the barotropic current and pressure field responses of the scotian shelf and gulf of maine region to spatially uniform wind stress are examined using a three dimensional finite element numerical model the model is linear and harmonic with spatially varying eddy viscosity and bottom friction coefficients obtained from a nonlinear m2 tidal solution the solutions for low frequency 20 day period wind stress and upstream boundary forcing are generally consistent with previous depth averaged model results showing a substantially stronger response for along shelf compared to cross shelf stress and strong topographic shaping of the associated arrested topographic waves with their expanded domain and dimensionality the present solutions reveal important additional features of the responses such as the northeast channel being the primary conduit for cross shelf subsurface flow compensating the cross shelf ekman transport over the scotian shelf widespread areas of near bottom upwelling and downwelling along the coast and shelf break and leakage of the response across the shelf break model solutions for stress forcing with periods in the storm band 2 5 days show similar structures and elevation current gains to those in the low frequency solutions with the primary exception that the large northeast channel transport for along shelf stress excites a topographic wave over the continental slope south of georges bank the strength of bottom stress dependent on the magnitudes of both the bottom friction coefficient and near bottom viscosity in the model has a significant quantitative influence on the inner shelf response coastal elevation amplitudes and cross shelf decay scales in particular the implications of the model solutions for the interpretation of various observational features of the region s response to wind stress are discussed including coastal elevations offshore bottom pressures currents transports upwelling zones frequency dependences and seasonal and frictional influences

hydrographic and transport variability on the halifax section 1 archived data and geostrophic computations are used to examine variability in hydrographic properties and along shelf transport on the scotian shelf with focus on the halifax section and a decadal scale hydrographic anomaly during the late 1950s and early mid 1960s the long term annual cycle shows strong seasonal variations in baroclinic transport on the inner shelf and at the shelf edge and an associated steric change in adjusted sea level asl at halifax regional wind forcing and barotropic currents make smaller contributions to the annual cycle in asl in contrast regional wind forcing contributes about 40 of the asl variability for periods of 6 30 days hydrographic sections indicate that the 1950s 1960s anomaly arose from episodic extensions of labrador slope water along the shelf edge followed by on shelf intrusions primarily during the fall spring periods of 1958 1959 and 1963 1964 it ended with excursions of warm slope water into the region in 1967 1968 an analysis of monthly temperature anomalies indicates that slope temperatures can account for 50 of the variance of deep shelf temperatures 3 6 months later correlations between the hydrographic and baroclinic transport variations indicate increased southwestward flow associated with lower temperatures and salinities but no evidence was found for large local current events at the onset and termination times of the 1950s 1960s anomaly positive correlations between wind adjusted asl and steric anomalies point to the potential for sea level being helpful in monitoring baroclinic transport variability

comparison of coccolith and dinocyst assemblages in the northern north atlantic how well do they relate with surface hydrography abstract coccolith and dinoflagellate cyst or dinocyst population counts were compiled from existing surface sediment databases as well as new counts in order to establish an 87 sample database for which assemblages of both microfossil groups are known this database allowed a direct comparison of the distribution of coccolith and dinocyst assemblages in the subtropical to subpolar north atlantic in addition the relationship between these assemblages and sea surface environmental parameters was addressed in order to identify possible differences in the ecology of the two plankton groups the comparison highlights an excellent correspondence between dinocyst assemblages coccolith assemblages and the distribution of the surface water masses represented in our database notably in the subtropical and temperate domains in the subpolar domain coccolith assemblages are much less diversified than dinocyst assemblages in terms of species as a result the discrimination between the subpolar water masses based on coccolith assemblages is not as clear as in the subtropical temperate regions whereas dinocyst assemblages show a distribution pattern closely related with surface hydrography canonical correspondence analyses performed on coccolith and dinocyst assemblages show that sea surface temperature is the primary environmental parameter influencing the distribution of both groups dinocyst assemblages also seem to respond to the distance to the coast and may therefore bring additional information compared with coccolith assemblages other significant environmental factors include sea surface salinity and productivity but their relative importance changes depending on the inclusion of samples from extreme environmental settings in the database results suggest that the complexity of the interrelationships between the various environmental parameters makes it difficult to adequately bring to light all the different environments and their associated coccolith dinocyst assemblages in multivariate analyses however each surface water mass represented in our database is characterized by a unique combination of environmental parameters as well as by distinct associations of coccolith and dinocyst assemblages thus showing that these microfossil groups closely relate to sea surface conditions including temperature salinity and productivity

carbon abundance and isotopic studies of shergotty and other shergottite meteorites consortium samples of the shergotty meteorite have been measured for c abundance and isotopic composition by stepped combustion and the results compared to different samples of the same meteorite and the other known shergottites clearly the shergottite meteorites have a complex c chemistry and contain components of both low and high thermal stability two components labile at low temperature can be tentatively identified one which is enriched in 13c and may be related to the carbonate thought to be produced by pre terrestrial weathering in nakhla the other which is isotopically light is presently of unknown origin but we speculate that it may be related to shock effects at high temperatures two of the samples examined show evidence for a component of co2 trapped from the martian atmosphere possibly indicating that shock produced glass is heterogeneously distributed throughout the shergottite group this interpretation is corroborated by n isotope measurements made on one of the specimens all samples appear to contain evidence of a high temperature magmatic component of c

quaternary geology and surficial sediment processes browns bank scotian shelf based on multibeam bathymetry abstract browns bank is located on the glaciated continental shelf off southern nova scotia geological mapping of browns bank is based on interpretation of multibeam bathymetric and backscatter data in conjunction with 220 line km of seismic reflection profiles and sidescan sonograms sea floor sediment samples and bottom photographs the fundian moraine part of the previously identified end moraine system on the continental shelf off nova scotia is a prominent west east flat topped multi lobate ridge identifiable in the multibeam bathymetric data and in geophysical records the fundian moraine was subjected to erosion in the surf zone during sea level rise in depths less than 100 m a series of north south roughly parallel till ridges continuous in the subsurface with the fundian moraine is interpreted as interlobate moraines suggesting formation by a tidewater glacier the browns bank moraine connected to the fundian moraine is evidence of a newly identified grounded ice position farther seaward than the latter bedforms including obstacle marks comet marks sand waves and megaripples are evidence of a vigorous anticyclonic current pattern on browns bank the combination of multibeam bathymetric imagery with high resolution geoscientific information represents a powerful technique for sea floor geological investigations

a 250 year decadally resolved radiocarbon time history in the gulf of maine reveals a hydrographic regime shift at the end of the little ice age

an offshore eddy in the california current system part iv plankton distributions abstract the distribution of plankton across a warm core eddy system in the california current 400 km off point conception california was studied in january 1981 the eddy system about 150 km in diameter at the 7 c isotherm was made up of a 75 m thick surface layer a cold core region extending from 75 m to about 200 m and a warm core eddy below 200 m extending to at least 1450 m casts for the vertical distribution of chlorophyll phaeophytin and integrating zooplankton net tows were taken at 37 stations located about 20 km apart on two orthogonal transects across the eddy system vertical distributions of microplankton were determined on one section from the eddy center to beyond the eastern edge integrated chlorophyll phaeophytin values were highest to the north and east of the eddy system across the system itself there was only a small increase of values near the center asymmetrical distributions of maximum concen current water was being entrained into the center of the eddy system from the northeast dinoflagellates were numerically the most important member of the microplankton especially in the deep chlorophyll maximum zooplankton distributions indicated the intermingling of warm and cool water species throughout at least the upper 200 m of the eddy system some cold water species were as abundant inside the system as outside to the north and east their numbers were much reduced in a band surrounding the system where warm water species were most abundant the presence of species characteristic of different water types throughout the region of the eddy system provides an indication of the mixing that had occurred since the system originally formed the biological data together with the physical and chemical results indicate the importance of frontal boundary processes and lateral entrainment of surrounding water into the eddy system in determining the character and productivity of such systems

comment on the paper on the influx of small comets into the earth s upper atmosphere ii interpretation by l a frank j b sigwarth and j d graven the suggestion that the earth is being bombarded by cometoids that subject it to an influx of 3 1011 water molecules cm sec encounters severe aeronomical problems there is a serious disposal problem for water molecules deposited near 100 km the implications for venus and mars also present serious problems it is argued that the proposable is untenable

the influence of a mature cyclonic eddy on particle export in the lee of hawaii abstract mesoscale eddies may enhance primary production pp in the open ocean by bringing nutrient rich deep waters into the euphotic zone potentially leading to increased transport of particles to depth this hypothesis remains controversial however due to a paucity of direct particle export measurements in this study we investigated particle dynamics using 234 th 238 u disequilibria within a mesoscale cold core eddy cyclone opal which formed in the lee of the hawaiian islands 234 th samples were collected along two transects across cyclone opal as well as during a time series within the eddy core during a decaying diatom bloom particulate carbon pc particulate nitrogen pn and biogenic silica bsio 2 fluxes at 150 m varied spatially and temporally within the eddy and strongly depended on the 234 th model formulation used e g steady state versus non steady state inclusion of upwelling etc particle fluxes estimated from a steady state model assuming an upwelling rate of 2 m day 1 yielded the best fit to sediment trap data these 234 th derived particle fluxes ranged from 332 14 to 1719 53 mol c m 2 day 1 27 3 to 114 12 mol n m 2 day 1 and 33 20 to 309 73 mol si m 2 day 1 although pp rates within cyclone opal were elevated by a factor of 2 3 pc and pn fluxes were the same within error inside and outside of cyclone opal the ratio of pc export to pp remained surprisingly low at 2 fluxes within the eddy core were three times higher detailed analyses of 234 th depth profiles consistently showed excess 234 th at 100 175 m associated with the remineralization and possible accumulation of suspended and dissolved organic matter from the surface we suggest that strong microzooplankton grazing facilitated particulate organic matter recycling and resulted in the export of empty diatom frustules thus while eddies may increase pp they do not necessarily increase pc and pn export to deep waters this may be a general characteristic of wind driven cyclonic eddies of the north pacific subtropical gyre and suggests that eddies may preferentially act as a silica pump thereby playing an important role in promoting silicic acid limitation in the region

current response at the shelf break to transient wind forcing an analysis of current meter and hydrographic data collected from an array of moorings situated at the shelf break off nova scotia is presented in particular the focus is on the ocean response to moderate 10 to 20m s 1 transient winds of two or more days duration blowing parallel to the local bathymetry under these conditions upwelling occurs at the shelf break from depths of 400 m and with peak vertical velocities of about 2 mm s 1 the upwelling appears to be confined to within 10 km of the slope acceleration coriolis and pressure gradient terms are important for the along and cross slope momentum balances local topographic variations contribute to the anomalously large bottom currents on the shoreward side of the shelf break both coastal sea level and the shelf break circulation respond coherently to synoptic wind forcing but quantitative agreement with two layer shelf models is poor

seasonal circulation on the western and central scotian shelf abstract a realistic representation of 3d seasonal circulation and hydrography on the western and central scotian shelf has been obtained from historical observations and a combination of diagnostic and prognostic numerical models with forcing by tides wind stress and baroclinic and barotropic pressure gradients the major current features the southwestward nova scotian and shelf edge currents and partial gyres around browns and sable island banks are found to persist year round but with significant seasonal changes comparison with current meter observations shows good agreement for the browns bank southwest nova scotia and inner shelf regions and poorer agreement in the sable island bank and shelf edge regions where current and density observations are sparser and tidal influences weaker there is significant spatial structure in the seasonal circulation and hydrography and in the underlying dynamical processes on the shelf scale there are substantial changes in stratification potential energy

physical and bio optical observations of oceanic cyclones west of the island of hawai i abstract interdisciplinary observations of mesoscale eddies were made to the west of the island of hawai i a central goal of the studies is to improve our understanding of the coupling of physical biological and biogeochemical processes that occur within these eddies a specific objective was to test the hypothesis that the physical mechanisms of mesoscale eddies result in increases in nutrient availability to the euphotic layer increases in primary production changes in biological community compositions and size distributions and increases in carbon flux to the deep sea data were obtained from ships surface drifters and satellite sensors during three separate field experiments variability was associated with two well developed cyclonic cold core mesoscale eddies cyclone noah and cyclone opal which were observed during the e flux i survey november 6 20 2004 and e flux iii survey march 10 27 2005 field campaigns respectively no mesoscale eddies were found during e flux ii survey january 10 19 when winds were erratic in magnitude and direction supporting the hypothesis that persistent trade winds drive the production of cold core mesoscale eddies in the lee of the hawaiian islands cold core eddies were present in the e flux study area for about 2 3 of a year beginning may 1 2004 and trade winds prevailed for about 3 4 of the same year both cyclone noah and cyclone opal were generated during strong persistent northeasterly trade wind conditions and appeared downwind of the alenuihaha channel separating the islands of maui and hawai i the likely production mechanism for both mesoscale cold core eddies involves localized wind stress curl induced upwelling produced by trade wind forcing cyclone noah was likely spun up by strong trade winds just to the southwest of the alenuihaha channel 20 10 n 156 40 w between august 13 and 21 2004 based on modis satellite sea surface temperature sst imagery and quikscat satellite wind data and apparently began to dissipate by mid december 2004 cyclone opal was likely spun up by strong trade winds between february 2 and 18 2005 southwest of the alenuihaha channel 20 30 n 156 30 w but was no longer evident in april 2005 both cyclone noah and cyclone opal had strong physical chemical and biological expressions and displayed similar maximum tangential current speeds of 60 cm s 1 however cyclone opal was more symmetric and larger in scale roughly 180 200 km in diameter compared to 160 km in horizontal scale for cyclone noah both mesoscale eddies displayed significant doming in their centers and in some cases outcroppings of isothermal isopycnal nutrient and chlorophyll a isopleths after formation and a slow drift southward cyclone noah remained in nearly the same location roughly 19 60 n 156 50 w during the 3 week in situ sampling period whereas cyclone opal drifted southward by 165 km over a similar time span of sampling interestingly the physical manifestations of both features were relatively unchanged during the ship based surveys however the biology appears to have evolved within cyclone opal the present report sets the context for several other e flux studies

numerical simulation of coastal upwelling and inerfacial instability of a rotaion and stratified fluid the evolution of the coastal upwelling and interfacial instability of a stratified and rotating fluid is studied numerically by using large eddy simulation upwelling is generated near the sidewall of a rotating annulus by the shear at the top the fluid initially consists of a stably stratified two layer structure with a narrow interface separating the two layers the large scale motion of the flow is simulated by solving the time dependent non hydrostatic incompressible navier stokes and scalar transport equations while the small scale motion is represented by a dynamic subgrid scale model the upwelling process contains both stable and unstable stratification the vertical structure of upwelling consists of a persistent primary front a trailing mixing zone on the shore side of the front and a temporary secondary front which leads a top inversion layer the longshore velocity profile has two maxima which occur at the edge of the sidewall boundary layer and at the density front the upwelled density front is unstable to azimuthal perturbations and baroclinic waves develop and grow to large amplitude pairs of cyclonic and anticyclonic waves appear at the front which form jet streams the secondary front is unstable to azimuthal perturbations its instability and the associated drop of the top inversion layer take the form of radial bands which subsequently break up into isolated patches and eventually sink the computed values of various upwelling time and length scales are compared to and are in good agreement with past experimental data

tidal influence on particulate organic carbon export fluxes around a tall seamount as tall seamounts may be stepping stones for dispersion and migration of deep open ocean fauna an improved understanding of the productivity at and food supply to such systems needs to be formed here the 234th 238u approach for tracing settling particulate matter was applied to senghor seamount a tall sub marine mountain near the tropical cape verde archipelago in order to elucidate the effects of topographically influenced physical flow regimes on the export flux of particulate organic carbon poc from the near surface topmost 100 m into deeper waters the comparison of a suitable reference site and the seamount sites revealed that poc export at the seamount sites was 2 4 times higher than at the reference site for three out of five seamount sites the calculated poc export fluxes are likely to be underestimates if this is taken into account it can be concluded that poc export fluxes increase while the passing waters are advected around and over the seamount with the highest export fluxes occurring on the downstream side of the seamount this supports the view that biogeochemical and biological effects of tall seamounts in surface ocean waters might be strongest at some downstream distance from rather than centred around the seamount summit based on measured vessel mounted adcp and modelled regional flow field aviso internal tides at senghor mitgcm flow dynamics it is proposed that tidally generated internal waves result in a screen of increased rates of energy dissipation that runs across the seamount and leads to a combination of two factors that caused the increased poc export above the seamount 1 sudden increased upward transport of nutrients into the euphotic zone driving brief pulses of primary production of new particulate matter followed by the particles export into deeper waters and 2 pulses of increased shear driven aggregation of smaller slower settling into larger faster settling particles this study shows that under certain conditions there can be an effect of a tall seamount on aspects of surface ocean biogeochemistry with tidal dynamics playing a prominent role it is speculated that these effects can control the spatiotemporal distribution of magnitude and nutritional quality of the flux of food particles to the benthic and benthic pelagic communities at and near tall seamounts

the influence of bays on adjusted sea level over adjacent shelves with application to the labrador shelf we examine how low frequency variations in adjusted sea level over a continental shelf are influenced by an inland sea connected to the shelf through a strait an analytical model shows that free continental shelf waves propagating by the mouth of the strait are strongly modified at a period corresponding to a helmholtz like resonance of the inland sea and strait also near this period atmospheric pressure variations over the inland sea result in relatively strong flow through the strait and the resulting cross isobath flow over the exterior shelf efficiently generates continental shelf waves in the region forward of the strait calculations using a fully nonlinear numerical model with more realistic although still idealized topography verify the predictions of the simpler analytical model we apply this theory to the hudson bay labrador shelf system where we find that this mechanism of shelf wave generation strongly influences the shelf response in the energetic meteorological band 2 6 days data from nain labrador are analyzed using multiple linear regression models and lend further support to the theory

the carbon dioxide system and net community production within a cyclonic eddy in the lee of hawaii abstract the dynamics of dissolved inorganic carbon dic and processes controlling net community production ncp were investigated within a mature cyclonic eddy cyclone opal which formed in the lee of the main hawaiian islands in the subtropical north pacific gyre within the eddy core physical and biogeochemical properties suggested that nutrient and dic rich deep waters were uplifted by 80 m relative to surrounding waters enhancing biological production a salt budget indicates that the eddy core was a mixture of deep water 68 and surface water 32 ncp was estimated from mass balances of dic nitrate nitrite total organic carbon and dissolved organic nitrogen making rational inferences about the unobserved initial conditions at the time of eddy formation results consistently suggest that ncp in the center of the eddy was substantially enhanced relative to the surrounding waters ranging from 14 1 10 6 0 110 m within the euphotic zone to 14 2 9 2 0 50 m within the mixed layer to 18 5 10 7 0 75 m within the deep chlorophyll maximum layer mmol c m 2 d 1 depending on the depth of integration ncp in the ambient waters outside the eddy averaged about 2 37 4 24 mmol c m 2 d 1 in the mixed layer 0 95 m most of the enhanced ncp inside the eddy appears to have accumulated as dissolved organic carbon doc rather than exported as particulate organic carbon poc to the mesopelagic our results also suggest that the upper euphotic zone 0 75 m above the deep chlorophyll maximum is characterized by positive ncp while ncp in the lower layer 75 m is close to zero or negative

palynological records of red tide producing species in canada past trends and implications for the future abstract increases in red tides and other harmful algal blooms habs during the past 50 yr on both the atlantic and pacific coasts of canada suggest that global scale factors such as climate change and increased international shipping trade are the driving forces because the historical record is too short to understand the long term dynamics of habs the holocene history of harmful phytoplankton species was examined using ultra high resolution studies annual to decadal scale of dinoflagellate cysts as a proxy for red tide production paleoecological transfer functions were then applied to the cyst assemblage data to determine correlations with changes in sea surface temperature and salinity pacific records were obtained from varved marine sediments in saanich inlet british columbia and in the santa barbara basin off california comparison of annual cyst production and historical plankton data provides cyst theca ratios from which the magnitude of past bloom size can be evaluated the 10 500 yr pacific record clearly shows that the largest blooms correspond to cysts of protoceratium reticulatum and gonyaulax spinifera during the early holocene sporadic blooms of potentially toxic alexandrium spp lingulodinium polyedrum and gymnodinium spp also occurred from ca 7000 to 5000 yr bp and more frequently from ca 2000 to 3000 yr bp individual holocene blooms were up to 10 times larger than in the historical record but they almost always occurred sequentially without overlap of red tide species in pre historical times the bloom cycles started and stopped abruptly in 10 yr or less and they persisted for about 100 1000 yr in contrast the variability and near concurrence of species blooms in the modern past 60 yr record is unmatched in the past and suggests disequilibrium of the natural ecosystem structure atlantic records from la have and emerald basins on the scotian shelf are less precise because bioturbation limits time resolution to ca 25 yr however cyst abundances of cf alexandrium protoceratium reticulatum gonyaulax spinifera and lingulodinium polyedrum were also an order of magnitude larger in the early holocene where they correspond to a summer sea surface warming of 2 5 c lesser peaks also appear during the past 2000 yr where they apparently correspond to a slight increase in winter temperature there is no evidence of much lower salinity that would support stronger stratification the similarity of pre industrial age cyst records of red tide histories in the oceanographically different pacific and atlantic regions of canada indicates that climate change including surface temperature and storminess is the main driving force stimulating blooms this implies that habs will reoccur regardless of efforts to limit spreading however reduced pollution may decrease the hab diversity thereby stabilizing the population dynamics and increasing the predictability of bloom occurrences

influence of diurnal heating on stratification and residual circulation of georges bank 1 the influence of the diurnal heat flux on summer stratification and residual circulation over georges bank was examined using a three dimensional primitive equation numerical circulation model for a given spatially uniform and time varying heat flux the model results show that the surface water is heated much faster on the southern flank than on the northern flank and much faster in the stratified region than in the mixed region heating significantly strengthens the tidal mixing front and intensifies the frontward convergence near the surface as seasonal stratification develops the location of the tidal mixing front gradually shifts on bank on the southern flank while remaining almost unchanged on the northern flank response of the tidal currents to the diurnal variation in the heat flux varies across georges bank it changes periodically with tidal cycles on the southern flank but is locked to the phase of the eastward tidal current on the northern flank this phase lock feature directly contributes to the intensification of the along bank residual current jet on the northern flank diagnostic analysis suggests that this intensification is mainly caused by the heat enhanced cross bank momentum flux modelcomputed variations of near surface temperature and residual currents are in good agreement with satellite derived sea surface temperature data and drifter measurements index terms 4219 oceanography general continental shelf processes 4227 oceanography general diurnal seasonal and annual cycles 4255 oceanography general numerical modeling 4279 oceanography general upwelling and convergences 4528 oceanography physical fronts and jets keywords heat flux tidal mixing front residual current stratification frontward convergence

an optical study of the water masses of the gulf of maine optical studies of the suspended load in the gulf of maine have been performed in conjunction with hydrographic and biological analyses between late winter and early fall major particle sources are coastal runoff benthic resuspension and biological activity analysis of the optical efficiencies of the particles suggests that runoff and resuspension sources are restricted to the nearshore and shallow regions the variabilities in the coupling and discoupling of the optical and hydrographic features of the gulf demonstrate that advection is primarily responsible for the distribution of clear water masses while settling vertical mixing and productivity are the processes behind the distribution of particles

model simulations of the bay of fundy gyre 1 climatological results 1 the characteristics of a persistent gyre in the mouth of the bay of fundy are studied using model simulations a set of climatological runs are conducted to evaluate the relative importance of the different forcing mechanisms affecting the gyre the main mechanisms are tidal rectification and density driven circulation stronger circulation of the gyre occurs during the later part of the stratified season july august and september october the density driven flow around the gyre is set up by weak tidal mixing in the deep basin in the central bay of fundy and strong tidal mixing on the shallow flanks around grand manan island and western nova scotia spring river discharge has an important influence on near surface circulation but only a small effect when averaged over the entire water column retention of particles in the gyre is controlled by the residual tidal circulation increased frontal retention during stratified periods wind stress and interactions with the adjacent circulation of the gulf of maine residence times longer than 30 days are predicted for particles released in the proximity of the gyre

high resolution holocene palynological record from the scotian shelf abstract because of their location at the confluence of polar and subtropical airmasses and near a transition zone between the cold labrador current and the gulf stream the atlantic provinces experience some of the most dynamic climate conditions in canada major climate changes occurred during the holocene as shown by pollen records from lakes but previous paleoceanographic studies based on low resolution proxy data records do not show major changes during the past 8000 years therefore the holocene history of canada s atlantic region was examined using a high resolution palynological record from the scotian shelf la have basin sea surface conditions were reconstructed using proxy data from dinoflagellate cysts and paleobioclimatic transfer functions ocean atmosphere interactions are determined by onshore offshore correlation of marine and pollen records from nova scotia results show a succession of major paleoceanographic events sea surface temperatures sst february and august up to 5 c higher than today s average and slightly higher salinity are reconstructed between 10 5 and 8 5 ka the last pulse of meltwater from the residual ice sheet affected the shelf waters between 8 5 and 6 5 ka by lowering the sst in february and the salinity most previous studies failed to record this event since 6 5 ka august temperature generally remained around today s value while february temperature was generally 2 c above it except for recurring colder and lower salinity intervals these cold intervals have a recurrence of about 1000 years a slight cooling of summer sst is recorded in the last 500 years comparison with climatic reconstructions from nova scotia pollen records shows a difference in timing between ocean and atmosphere the onset of the climatic optimum hypsithermal in nova scotia lags by about 2000 years until 8 ka relative to the ocean but it lasted longer the neoglacial cooling in atlantic canada however started earlier 2 ka than the late holocene ocean cooling la have basin s holocene paleoceanography presents some differences from most other studies from the region 1 the hypsithermal started earlier 2 the last pulse of meltwater is recorded 3 the last 6500 years are punctuated by colder intervals increased productivity and blooms of toxic algae in the early holocene are probably due to a combination of factors increased nutrients and a greater stability of the water column because of meltwaters higher sst and increased upwelling or storm activity

interaction between the tidal and seasonal variability of the gulf of maine and scotian shelf region abstractas part of a broader study of ocean downscaling the seasonal and tidal variability of the gulf of maine and scotian shelf and their dynamical interaction are investigated using a high resolution 1 36 circulation model the model s seasonal hydrography and circulation and its tidal elevations and currents are compared with an observed seasonal climatology local observations and results from previous studies numerical experiments with and without density stratification demonstrate the influence of stratification on the tides the model is then used to interpret the physical mechanisms responsible for the largest seasonal variations in the m2 surface current that occur over and to the north of georges bank the model generates a striation pattern of alternating highs and lows aligned with georges bank in the m2 surface summer maximum speed in the gulf of maine the striations are consistent with observations by a high frequency coastal radar system and can be explained in terms of a li

the adjustment of a shelfbreak jet to cross shelf topography abstract a rigid lid finite difference numerical model is used to study the adjustment of inviscid along shelf barotropic shelfbreak jets to cross shelf channel topography the channel is embedded in the shelf topography perpendicularly to the shelfbreak the shelfbreak jet flows with the direction of propagation of long wavelength topographic rossby waves and the coast is sufficiently distant so as not to affect the flow three models are used that vary the strength of the channel topography s f hd uh where f is the coriolis parameter h is the difference between the shelf depth and the channel depth d is the width of the slope into the channel u is the maximum speed of the jet at the inflow and h is the depth of the shelf estimation of the path of the jet from the inflow parameters and the geometry of the channel is possible in some cases generally for large s the flow follows the topography of the channel and for small s the flow crosses the channel the motivation for this study is the episodic flow of scotian shelf water from the scotian shelf across the northeast channel to georges bank the steady inviscid non linear barotropic dynamics studied here do not allow such a flow for a channel of similar dimensions to the northeast channel and for flow speeds within the oceanographic range other factors such as stratification wind stress and time variability need to be introduced to account for this phenomenon

historical and recent evidence of scotian shelf water on southern georges bank abstract historical data from 1912 1987 indicate that low salinity less than 32 0 psu near surface water occurs occasionally on southern georges bank during may while none occurs during april composite monthly plots of historical near surface salinity and estimated advection rates show that the southwestern scotian shelf is the immediate upstream source of this low salinity water optimally interpolated satellite derived sst and hydrographic data reveal that very cold less than 2 0 c low salinity less than 32 0 psu scotian shelf water ssw initially located south of the 200 m isobath off southern georges bank in early march 1992 moved north onto southern georges bank during april 1992 ssw was not as extensive during the same period in 1993 as evidence by significantly higher temperatures and salinities these differences show large interannual variability in the transport and or properties of ssw flowing onto georges bank lower higher salinities measured during spring 1992 1993 on southern georges bank are consistent with higher lower st lawrence river discharge noted during spring 1991 1992 and the nine month lag between annual discharge maxima from rivers located upstream and minimum salinity at cape sable in february however comparisons between historical occurrences of low salinity less than 32 0 psu ssw on southern georges bank noted for may 1966 1971 and 1978 and cumulative st lawrence river discharge from the spring prior to each occurrence show no relationship this suggests that the occurrence of low salinity water on southern georges bank is not directly related to variations in upstream river discharge although an idealized model of wind forcing on a bank trapped density front shows that near surface flow is related to superposition of an ekman layer and the along bank gyral circulation evidence from late winter spring 1992 and 1993 on georges bank shows that except for on bank movement of the shelf slope front during late spring 1992 simple ekman theory does not explain on bank movement of the ssw plume during 1992 nor the immobile nature of the shelf slope front during late winter 1992 and late winter spring 1993 surface heat flux and satellite derived sst from georges bank and the scotian shelf together with a slab mixed layer model allows estimation of the advective heat flux and transport of ssw flowing onto georges bank from the scotian shelf during late winter spring 1992 mean advective heat flux onto georges bank during march may 1992 is 14 5 mw cm 2 with an estimated error of 3 5 mw cm 2 demonstrating that advection of cold ssw onto georges bank is required mean velocity and transport of ssw flowing onto georges bank during march may 1992 are 13 4 cm s 1 and 0 21 sv assuming a ssw depth width of 40 m 40 km demonstrating that flow of ssw onto georges bank was robust during the period at this time the dynamics that control the flow of ssw across northeast channel are unknown

observations of the eastern maine coastal current and its offshore extensions in 1994 cold surface temperatures reflecting scotian shelf origins and local tidal mixing serve as a tracer of the eastern maine coastal current and its offshore extensions which appear episodically as cold plumes erupting from the eastern maine shelf a cold water plume emanating from the eastern maine coastal current in may 1994 was investigated using advanced very high resolution radiometer avhrr imagery shipboard surveys of physical and biochemical properties and satellite tracked drifters evidence is presented that suggests that some of the plume waters were entrained within the cyclonic circulation over jordan basin while the major portion participated in an anticyclonic eddy at the distal end of the plume calculations of the nitrate transported offshore by the plume show that this feature can episodically export significant quantities of nutrients from the eastern maine coastal current to offshore regions that are generally nutrient depleted during spring summer a series of avhrr images is used to document the seasonal along shelf progression of the coastal plume separation point we speculate on potential causes and consequences of plume separation from the coastal current and suggest that this feature may be an important factor influencing the patterns and overall biological productivity of the eastern gulf of maine

fast deep sinking in mediterranean eddies i large up to 0 03 m s 1 downward vertical water velocities w are observed using yearlong moored adcp at 2400 m in the deep mediterranean sea s algerian basin once every 2 3 months w rapidly increases to o 0 01 0 002 m s 1 before slowly decreasing during a few weeks in association with the passage of mesoscale eddies formed nearby these amplitudes of negative w are o 100 times larger than those commonly linked to mesoscale eddies near the surface subduction and o 10 times larger than settling velocities for marine snow our observations suggest that mesoscale eddies which are important for biological productivity near the surface can also convect nearly fresh material down to the bottom 3000 m there within a few days

currents at lindenkohl sill in the southern gulf of maine from june 22 to september 3 1986 current speeds and directions were measured at depths of 76 127 and 212 m over lindenkohl sill 225 m which controls an important deepwater spreading path from georges basin into wilkinson basin in the gulf of maine most 70 of the low frequency subtidal variability occurred in a barotropiclike mode in which the inward currents were coherent with alongshore wind stress for 5 day periods early in the record and for 3 day periods late in the record the coherence weakened during the central part of the record when dense atlantic slope water from georges basin moved over the mooring site most of the remaining variance appeared in a baroclinic mode that added constructively to produce surprisingly large 1 m s 1 near bottom currents during the wind coherent intervals at other times the modes interfered to produce near zero currents over the sill while middepth and upper level currents were intensified the relationship between the wind stress and the currents suggests the action of a density modulated coastal upwelling mechanism in which the deep inward currents over the sill respond directly to northeastward alongshore wind stress at times of weak stratification increased density stratification caused by water mass adjustments or seasonal heating produces a more complex baroclinic response it is suggested that the springtime onset of northeastward winds over the gulf of maine may play an indirect but important role in the yearly intensification of the baroclinic circulation in the gulf by controlling or modulating the indraft of slope water into the inner basins

234th in different size classes of sediment trap collected particles from the northwestern pacific ocean abstract 234 th a surface area specific particle reactive radionuclide has been used to estimate particulate organic carbon poc export fluxes based on the poc 234 th ratio of sinking particles and the 234 th flux in the ocean the poc 234 th ratios from large particles 50 m are conventionally considered to represent sinking particles collected by sediment traps but this assumption has not been thoroughly tested more recently hung and gong 2010 separated sinking particles from the northern south china sea where diatoms are the most dominant group using different nitex screens and found that small 234 th and poc flux however the size distribution of sinking particles has seldom been measured in picoplankton dominated oligotrophic and upwelling conditions here we used nitex screens to separate sinking particles in oligotrophic and upwelling regions additionally images of selected bulk sinking particles not subject to sequential filtration were directly taken by scanning electron microscopy sem to determine the size distribution of sinking particles within the trap collected 234 th pool in the upwelling area the 1 10 and 10 50 m fractions had on average the highest amounts of 234 th while poc did not show significant variations among the different size fractions in the oligotrophic region the 10 50 and 1 10 m fractions had on average the highest amounts of 234 th while the 150 and 10 50 m had elevated shares of poc results thus demonstrate that 234 th was mainly carried by the smaller 234 th flux can be a major fraction of the total sinking flux of this isotope and thus particles smaller than 50 m cannot be ignored because the poc 234 th ratio that is often used is that of large 50 m particles obtained from pump systems not traps

surface heat flux horizontal advection and the seasonal evolution of water temperature on the scotian shelf seasonal temperature variations on the scotian shelf penetrate to a depth of about 75 m the net surface heat flux q can explain about 85 of the annual cycle in the rate of change of mean temperature over this depth range the long term mean heat budget for a midshelf location shows that horizontal advection 40 w m 2 is almost exactly balanced by the combined contributions of q 25 w m 2 horizontal mixing 11 w m 2 and vertical diffusion 6 w m 2 the seasonal evolution of temperature structure on the mid scotian shelf is modeled with a one dimensional vertical diffusion equation modified to include the effect of horizontal advection the model features a vertical eddy diffusivity k that varies with the background density stratification n according to the parameterization k k0 1 np 1 the three free parameters k0 and p are estimated by best fitting in a least squares sense the predicted temperatures to observations at standard depths between the surface and 100 m typical values of k lie in the range 0 2 20 10 4 m2 s 1 with the highest values found in winter and close to the surface as expected the root mean square of the differences between observed and predicted monthly temperatures is small and equal to 1 0 c the root mean square of the errors increases significantly from 1 0 c to 3 1 c on fitting with a constant k highlighting the importance of allowing k to vary with depth and time the diffusion model is finally used to examine the role of q and horizontal advection in the seasonal evolution of the temperature profile on the scotian shelf and in particular the cold intermediate layer which is a prominent feature of the hydrography on the midshelf

impact induced dehydration of serpentine and the evolution of planetary atmospheres shock recovery experiments in the 25 to 45 gpa range on antigorite serpentine determine the amount of shock induced loss of structural water as a function of shock pressure infrared absorption spectra of shock recovered samples demonstrate systematic changes in the amount of structural water and molecular surface adsorbed water these yield qualitative estimates of shock induced water loss and demonstrate that a portion of the shock released structural water is readsorbed on interfacial grain surfaces determination of the post shock water content of the shocked samples relates shock induced water loss and shock pressure based on the present results and theoretical predictions we conclude that shock pressures of from 20 to 60 gpa induce incipient to complete water loss respectively this result agrees closely with theoretical estimates for total dehydration the dehydration interval and the activation energies for dehydration in shocked samples decrease systematically with increasing shock pressure as experienced by the sample we believe the present experiments are applicable to describing dehydration processes of serpentine like minerals in the accretional environment of the terrestrial planets we conclude that complete loss of structural water in serpentine could have occurred from accretional impacts of 3 km sec when earth and venus have grown to about 50 of their final size accreting planetesimals impacting mars never reached velocities sufficient for complete dehydration of serpentine our results support a model in which an impact generated atmosphere hydrosphere forms while the earth is accreting

the steady state barotropic response of the gulf of maine and adjacent regions to surface wind stress abstract the response of the gulf of maine region to steady spatially uniform wind stress is examined using a linearized numerical model with the influence of the strong tidal currents in the region included in the bottom stress formulation the sensitivity of the model results to various idealizations is investigated including the assumption of linearity the bottom steam formulation cross shelf structure in the large scale alongshelf wind stress and the cross shelf boundary conditions the model solutions for the gulf are found to be sensitive to the backward boundary condition on the scotian shelf but not to the forward boundary condition in the middle atlantic bight for alongshelf stress the former is estimated using csanady s arrested topographic wave model and observed coastal sea level gains at halifax the model has a spinup time of about one day comparable to previous estimates for the region the alongshelf component of wind stress is generally much more effective than the cross s

cobalt manganese and iron near the hawaiian islands a potential concentrating mechanism for cobalt within a cyclonic eddy and implications for the hybrid type trace metals abstract the vertical distributions of cobalt iron and manganese in the water column were studied during the e flux program e flux ii and iii which focused on the biogeochemistry of cold core cyclonic eddies that form in the lee of the hawaiian islands during e flux ii january 2005 and e flux iii march 2005 17 stations were sampled for cobalt n 147 all of which demonstrated nutrient like depletion in surface waters during e flux iii two depth profiles collected from within a mesoscale cold core eddy cyclone opal revealed small distinct maxima in cobalt at 100 m depth and a larger inventory of cobalt within the eddy we hypothesize that this was due to a cobalt concentrating effect within the eddy where upwelled cobalt was subsequently associated with sinking particulate organic carbon poc via biological activity and was released at a depth coincident with nearly complete poc remineralization benitez nelson c bidigare r r dickey t d landry m r leonard c l brown s l nencioli f rii y m maiti k becker j w bibby t s black w cai w j carlson c a chen f kuwahara v s mahaffey c mcandrew p m quay p d rappe m s selph k e simmons m p yang e j 2007 mesoscale eddies drive increased silica export in the subtropical pacific ocean science 316 1017 1020 there is also evidence for the formation of a correlation between cobalt and soluble reactive phosphorus during e flux iii relative to the e flux ii cruise that we suggest is due to increased productivity implying a minimum threshold of primary production below which cobalt phosphate coupling does not occur dissolved iron was measured in e flux ii and found in somewhat elevated concentrations 0 5 nm in surface waters relative to the iron depleted waters of the surrounding pacific fitzwater s e coale k h gordon m r johnson k s ondrusek m e 1996 iron deficiency and phytoplankton growth in the equatorial pacific deep sea research ii 43 4 6 995 1015 possibly due to island effects associated with the iron rich volcanic soil from the hawaiian islands and or anthropogenic inputs distinct depth maxima in total dissolved cobalt were observed at 400 600 m depth suggestive of the release of metals from the shelf area of comparable depth that surrounds these islands

subtidal circulation on the scotian shelf assessing the hindcast skill of a linear barotropic model currents measured during the winter of 1985 1986 by four moorings on the inner scotian shelf are used to assess the hindcast skill of a three dimensional circulation model forced by local wind stress and coastal sea level the model is linear and barotropic the integration scheme is based on the modification of the galerkin spectral method proposed recently by sheng and thompson 1993 the skill of the model is measured by the variance of the hindcast errors divided by the variance of the observations henceforth 2 the model is most effective within 30 km of shore 0 51 2 0 66 at the mooring in the nova scotia current a surface intensified southwestward jet with its center approximately 50 km from shore the model fails to capture the bulk of the variance at current meters within 70 m of the surface 0 81 2 0 87 the skill of the model is lowest at the mooring 65 km from shore 0 92 2 0 94 to put these measures of skill into perspective the currents are hindcast using a linear statistical model with the same inputs as the circulation model the statistical model is optimal in the sense no other linear model with these inputs can achieve a lower hindcast error variance for half of the current meters within 30 km of shore and two in the nova scotia current the skill of the circulation model is not significantly lower than that of the statistical model the largest discrepancies in the skill of the two models are found at the offshore mooring we show that the suboptimal performance of the circulation model is due in part to the assumption of a spatially uniform wind field we speculate that another contributing factor is the assumed form of the sea level profile along the open boundary that is upstream in the sense of coastal trapped wave propagation finally the statistical model is used to estimate the increase in skill of the circulation model that may result from the assimilation of hydrographic data and additional coastal sea levels

temperature and salinity variability on the scotian shelf and in the gulf of maine 1945 1990 examination of temperature and salinity data from the scotian shelf gulf of maine gulf of st lawrence and the adjacent continental slope has shown that the dominant low frequency event over the last 45 years was a cooling and subsurface freshening of the water masses from 1952 to 1967 followed by a rapid reversal of these trends the largest temperature and salinity changes 1952 1967 were 4 6 c and 0 7 respectively and occurred at about 100 m over the slope exchanges with shelf waters and vertical mixing gave rise to the surface manifestation of this variability the westward transport of the labrador current was found to have similar variability increasing from about 1 106 m3 s 1 in the early 1950s to about 4 106 m3 s 1 in the mid 1960s a simple model that accounts for this variation of transport and has a constant entrainment of north atlantic water indicates that changes of the westward flow of the labrador current could contribute significantly to the t s fluctuations

seasonal variation of the three dimensional mean circulation over the scotian shelf the seasonal mean circulation over the scotian shelf is studied numerically by computing mean and tidal current fields for winter spring and summer using a three dimensional nonlinear diagnostic model the mean current fields are forced by seasonal mean baroclinic pressure gradients tidal rectification uniform wind stresses and associated barotropic pressure gradients a historical hydrographic database is used to determine the climatological mean baroclinic forcing upstream open boundary conditions are estimated from the density fields to give no normal geostrophic bottom flow and are specified as either along boundary elevation gradients or depth integrated normal velocities the numerical solutions for nominal bimonthly periods january february april may and july august reveal the dominant southwestward nearshore and shelf break flows of relatively cool and fresh shelf water from the gulf of st lawrence and newfoundland shelf with speeds up to about 20 cm s the seasonal intensification of the southwestward flows is reproduced by the model with the transport increasing from 0 3 sv in summer to 0 9 sv in winter on the inner halifax section there are also pronounced topographic scale influences of submarine banks basins and cross shelf channels on the circulation such as anticyclonic gyres over banks and cyclonic gyres over basins baroclinicity is the dominant forcing throughout the domain but tidal rectification is comparable on the southwestern scotian shelf e g about 0 2 sv recirculating transport around browns bank for all the periods the mean wind stress generates offshore surface drift in winter the solutions are in approximate agreement with observed currents and transports over the scotian shelf although there are local discrepancies

wind generation of the costa rica dome upwelling in the costa rica dome is seasonal and the result of the localized cyclonic wind stress curl fluctuations in the wind stress curl in the fall release the upwelled region as a rossby wave similar low latitude domes are hypothesized to be ubiquitous to those oceans where a localized cyclonic wind stress curl is associated with an intertropical convergence zone

the mean and seasonal circulation off southwest nova scotia abstract long term measurements off southwest nova scotia reveal the following features of the mean circulation a a westward longshore coastal current 4 10 cm s 1 b an anticyclonic gyre around brown bank 5 15 cm s 1 and c an upwelling circulation off cape sable 1 2 cm s 1 at bottom the gyre circulation appears permanent but the coastal current and upwelling exhibit annual variations of the same order as the means there is a distinct annual signal in the longshore transport at cape sable maximum westward in winter whereas the mean transport 0 14 106 m4 s 1 is consistent with both geostrophic estimates and budget requirements in the gulf of marine strong seasonal cycles are also found in the salinity and density fields at cape sable which appear to be controlled both by buoyancy input from the coastal current and local mixing effects a linear diagnostic model indicates that the primary dynamical balance for the circulation is between a longshore pressure gradient and longshore mean

snc meteorites clues to martian petrologic evolution the shergottites nakhlites and chassigny snc meteorites are apparently cumulate mafic and ultramafic rocks that crystallized at shallow levels in the crust of their parent body the mineralogy and chemistry of these meteorites are remarkably like equivalent terrestrial rocks although their ratios of fe fe mg and certain incompatible elements and their oxygen isotopic compositions are distinctive all have crystallization ages of 1 3 b y or younger and formed from magmas produced by partial melting of previously fractionated source regions isotope systematics suggest that the snc parent body had a complex and protracted thermal history spanning most of geologic time some meteorites have been severely shock metamorphosed and all were ejected from their parent body at relatively recent times possibly in several impact events late crystallization ages complex petrogenesis and possible evidence for a large gravitational field suggest that these meteorites are derived from a large planet trapped gases in shergottite shock melts have compositions similar to the composition measured in the martian atmosphere ejection of martian meteorites may have been accomplished by acceleration of near surface spalls or other mechanisms not fully understood if snc meteorites are of martian origin they provide important information on planetary composition and evolution the bulk composition and redox state of the martian mantle as constrained by shergottite phase equilibria must be more earthlike than most current models planetary thermal models should benefit from data on the abundances of radioactive heat sources the melting behavior of the mantle and the timing of planetary differentiation calculated depletion of chalcophile elements in source regions indicates a core dominated by sulfides and paleomagnetic measurements suggest the presence of a weak magnetic field within the last several hundred thousand years concentrations of volatile elements indicate that the snc parent body was not volatile depleted and trapped atmospheric components measured in shock melts may be useful in understanding planetary degassing by providing comparisons for spectral reflectance data and viking soil analyses these meteorites may also constrain surface mineralogy and weathering mechanisms

apparent enhancement of 234th based particle export associated with anticyclonic eddies national basic research program of china 973 program 2009cb421200 national natural science foundation of china nsfc 41121091 41130857

vernal circulation in the gulf of maine the circulation in the gulf of maine has an important baroclinic component it appears to be driven mostly by the density contrast between high salinity slope water which enters from the atlantic and fresher waters which are formed in the gulf or which enter from the scotian shelf hydrographie surveys in three successive spring seasons suggest that slope water accumulates in georges basin driving a counterclockwise surface circulation which brings scotian shelf water westward into the gulf and contributes to the eastward jet along the inner edge of georges bank the slope water also crosses a sill and enters jordan basin where it provides a potential energy source which may enhance a counterclockwise gyre partly driven by nearshore buoyancy sources and perhaps the wind the coastal limb of the gyre turns offshore east of penobscot bay part of the separated coastal current recirculates in jordan basin and part of it continues into wilkinson basin generating a clockwise eddy as it passes over jeffreys bank there is little evidence for recirculating surface flow in wilkinson basin instead the surface water appears to split into branches feeding the jordan basin gyre the georges bank jet and an export path to nantucket shoals the jordan and georges branches seem to be divided by the denser slope water in georges basin and this may be the central process controlling the vernal intensification of the circulation in the gulf a more complete dynamical understanding awaits models which include the baroclinic influence of boundary waters