inferring circulation and lateral eddy fluxes in the arctic ocean s deep canada basin using an inverse method abstractthe deep waters in the canada basin display a complex temperature and salinity structure the evolution of which is poorly understood the fundamental physical processes driving changes in

the fertilization of the bahamas by saharan dust a trigger for carbonate precipitation the enigma of the bahamas is that this highly productive carbonate system has existed for at least 100 m y building a vast edifice of carbonates thousands of meters thick in an essentially nutrientpoor environment based on measurements of the insoluble material the fe and mn in the carbonate fraction and the d 15 n of the sedimentary organic matter we suggest a paradigm shift in order to explain the formation of the bahamas and possibly other similar platforms we propose that the great bahama bank is currently and may in the past have been fertilized by atmospheric dust promoting the fixation of atmospheric n 2 by cyanobacteria these cyanobacteria provided a source of nitrogen to the rest of the community in this nutrient poor environment the fixation of n has imparted a characteristic d 15 n signal and has been responsible through the drawdown of co 2 for initiating the precipitation of carbonate in the shallow waters this phenomenon might be responsible for the formation of vast amounts of sediments in the oceans not only within recent times but throughout geological history particularly in the early history of the earth prior to the existence of calcium carbonate secr eting organisms

dynamics in the deep canada basin arctic ocean inferred by thermistor chain time series abstract a 50 day time series of high resolution temperature in the deepest layers of the canada basin in the arctic ocean indicates that the deep canada basin is a dynamically active environment not the quiet stable basin often assumed vertical motions at the near inertial tidal frequency have amplitudes of 10 20 m these vertical displacements are surprisingly large considering the downward near inertial internal wave energy flux typically observed in the canada basin in addition to motion in the internal wave frequency band the measurements indicate distinctive subinertial temperature fluctuations possibly due to intrusions of new water masses

joint effects of boundary currents and thermohaline intrusions on the warming of atlantic water in the canada basin 1993 2007 1 the 1990 1991 influx of atlantic water both anomalously warm and in greater volume than in the past enveloped the chukchi borderland in the western canada basin by 2002 and spread across the southeastern canada basin by 2007 warmer younger more ventilated and less dense fram strait branch waters have replaced colder older and denser waters increasing the temperature of the fram strait branch core from a 50 year or more mean of 0 45 c to 0 7 c physical and geochemical data collected from 1993 to 2007 show that the two main transport mechanisms are the boundary current and thermohaline intrusions established by large thermal gradients the boundary current operates in a cyclonic direction whereas the thermohaline intrusions operate in an anticyclonic direction because of the influence of the beaufort gyre this shows that the beaufort gyre s effect on ocean circulation extends into the fram strait branch of the atlantic layer the boundary current a fully pan arctic structure is much slower in the canada basin than in basins upstream with an effective speed of 0 5 cm s the effective spreading rate of the thermohaline intrusions relative to the core is 0 2 cm s thermohaline intrusions show signs of dissipation near the northwind ridge in 2007 suggesting that as temperature gradients between inflowing and resident waters decrease they will disappear from the canada basin

the arctic ocean warms from below 1 the old 450 year isolation age and near homogenous deep waters of the canada basin cbdw that are found below 2700 m warmed at a rate of 0 0004 c yr 1 between 1993 and 2010 this rate is slightly less than expected from the reported geothermal heat flux fg 50 mw m 2 a deep temperature minimum tmin layer overlies cbdw within the basin and is also warming at approximately the same rate suggesting that some geothermal heat escapes vertically through a multi stepped 300 m thick deep transitional layer double diffusive convection and thermobaric instabilities are identified as possible mechanisms governing this vertical heat transfer the cbdw found above the lower continental slope of the deep basin maintains higher temperatures than those in the basin interior consistent with geothermal heat being distributed through a shallower water column and suggests that heat from the basin interior does not diffuse laterally and escape at the edges

evolution of the deep water in the canadian basin in the arctic ocean abstract an overflow of magnitude 0 25 sv sv 106 m 3 s 1 has been predicted to enter the makarov basin part of the canadian basin in the arctic ocean from the eurasian basin via a deep gap in the dividing lomonosov ridge the authors argue that this overflow does not ventilate the deep makarov basin below 2400 m where the water is too warm and salty to be compatible with such a large cold fresh inflow however complete isolation of the homogeneous bottom layer of the makarov basin must be ruled out because changes there are too small to arise from more than a small fraction of the measured geothermal heat flux into the basin a small cold fresh inflow of about 0 01 sv from the amundsen basin seems to be required this could occur if the gap in the dividing lomonosov ridge is shallower than previously thought it could also occur if there is active mixing and dilution of the predicted overflow in the gap leaving only a small fraction to descend into the deep makarov basin hydraulic theory and hy

does rotation influence double diffusive fluxes in polar oceans abstractthe diffusive or semiconvection regime of double diffusive convection ddc is widespread in the polar oceans generating staircases consisting of high gradient interfaces of temperature and salinity separated by convectively mixed layers using two dimensional direct numerical simulations support is provided for a previous theory that rotation can influence ddc heat fluxes when the thickness of the thermal interface sufficiently exceeds that of the ekman layer this study finds therefore that the earth s rotation places constraints on small scale vertical heat fluxes through double diffusive layers this leads to departures from laboratory based parameterizations that can significantly change estimates of arctic ocean heat fluxes in certain regions although most of the upper arctic ocean thermocline is not expected to be dominated by rotation

rapid climate change and conditional instability of the glacial deep ocean from the thermobaric effect and geothermal heating previous results from deep sea pore fluid data demonstrate that the glacial deep ocean was filled with salty cold water from the south this salinity stratification of the ocean allows for the possible accumulation of geothermal heat in the deep sea and could result in a water column with cold fresh water on top of warm salty water and with a corresponding increase in potential energy for an idealized 4000 dbar two layer water column we calculate that there are 10 6j m 2 0 2j kg of potential energy available when a 0 4 psu salinity contrast is balanced by a 2 c temperature difference this salt based storage of heat at depth is analogous to convectively available potential energy cape in the atmosphere the thermobaric effect in the seawater equation of state can cause this potential energy to be released catastrophically because deep ocean stratification was dominated by salinity at the last glacial maximum lgm the glacial climate is more sensitive to charging this thermobaric capacitor and can plausibly explain many aspects of the record of rapid climate change our mechanism could account for the grouping of dansgaard oeschger events into bond cycles and for the different patterns of warming observed in ice cores from separate hemispheres

thermobaricity in the transition zones between alpha and beta oceans abstractthe role of the ocean in earth s climate is fundamentally influenced by the locally dominant stratifying property heat or salt which in turn can be used to categorize the ocean into three classes alpha beta and transition zone oceans alpha and beta oceans are regions where the stratification is permanently set by heat and salt respectively transition zone oceans exist between alpha and beta oceans and are regions where the stratification is seasonally or intermittently set by heat or salt despite their large ranges of temperature and salinity transition zone oceans are the most weakly stratified regions of the upper oceans making them ideal locations for thermobaric effects arising from the nonlinear equation of state of seawater here a novel definition and quantification of alpha beta and transition zone oceans is presented and used to analyze 4 years 2010 13 of hydrographic data developed from the argo profiling float array two types of thermobaric instabilities are defined and

cam3 bias over the arctic region during northern winter studied with a linear stationary model this study builds upon two prior papers which examine arctic region bias of cam3 ncar community atmosphere model version 3 simulations during winter cam3 output is compared with ecmwf european centre for medium range weather forecasts 40 year reanalysis era 40 data our prior papers considered the temperature and the vorticity equation terms and demonstrated that diabatic transient and linear terms dominate nonlinear bias terms over most areas of interest accordingly this paper uses a linearized form of the model s dynamical core equations to study aspects of the forcing that lead to the cam3 biases we treat the model s long term winter bias as a solution to a linear stationary wave model lswm key features of the bias in the vorticity temperature and ln of surface pressure q fields are shown at medium resolution the important features found at medium resolution are captured at the much lower lswm resolution the arctic q bias has two key features excess q over the barents sea and a missing beaufort high negative maximum q bias to the north of alaska and eastern siberia the forcing fields are calculated by the lswm horizontal advection tends to create multi polar combinations of negative and positive extrema in the forcing the positive and negative areas of forcing approximately match corresponding areas in the bias there is a broad relation between cold bias with elevated q bias as expected from classical theory forcing in related quantities near surface vorticity and surface pressure combine to produce the sea level pressure bias

production of lime mud by breakdown of foraminiferal tests abstract many sources of lime mud have been discussed in the literature however foraminifers despite their abundance and importance in recent as well as in ancient sediments have been generally disregarded this study is based on stereo microscope observations and on a detailed sem study of modern carbonate sediments from new caledonia and french polynesia and of foraminiferal tests many particles of the mud fraction have a morphology and composition similar to particles observed in benthic foraminiferal tests the particles are calcitic or mg calcitic needles or are columns composed of crystallites less than 0 5 m in size in tropical environments foraminifers can produce as much as 1 kg m 2 of carbonate annually and their tests may form more than 80 of the sediment these observations show the genetic link from mud back to foraminiferal tests and show that at least a noticeable part of the carbonate mud can result from the breakdown of foraminiferal tests the role of foraminifers for the production of calcitic mud may be as important as the role of halimeda for the production of biogenic aragonite

thermohaline circulation in the arctic mediterranean seas the renewal of the deep north atlantic by the various overflows of the greenland scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north the arctic ocean and the greenland iceland and norwegian seas collectively called the arctic mediterranean the traditional site of deep ventilation for these basins is the greenland sea but a growing body of evidence also points to the arctic ocean as a major source of deep water this deep water is relatively warm and saline and it appears to be a mixture of dense brine enriched shelf water with intermediate strata in the arctic ocean the deep water exits the arctic ocean along the greenland slope to mix with the greenland sea deep water conversely very cold low salinity deep water from the greenland sea enters the arctic ocean west of spitsbergen within the arctic ocean the lomonosov ridge excludes the greenland sea deep water from the canadian basin leaving the latter warm saline and rich in silica in general the entire deep water sphere of the arctic mediterranean is constrained by the greenland scotland ridges to circulate internally therefore it is certain of the intermediate waters formed in the greenland and iceland seas which ventilate the north atlantic these waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface induced signals into the deep north atlantic

mooring based observations of double diffusive staircases over the laptev sea slope abstracta yearlong time series from mooring based high resolution profiles of water temperature and salinity from the laptev sea slope 2003 04 2686 m depth 78 26 n 125 37 e shows six remarkably persistent staircase layers in the depth range of 140 350 m encompassing the upper atlantic water aw and lower halocline despite frequent displacement of isopycnal surfaces by internal waves and eddies and two strong aw warming pulses that passed through the mooring location in february and late august 2004 the layers preserved their properties using laboratory derived flux laws for diffusive convection the authors estimate the time averaged diapycnal heat fluxes across the four shallower layers overlying the aw core to be 8 w m 2 temporal variability of these fluxes is strong with standard deviations of 3 7 w m 2 these fluxes provide a means for effective transfer of aw heat upward over more than a 100 m depth range toward the upper halocline these findings suggest that double diffusion is an imp

waters of the makarov and canada basins abstract hydrographic measurements from the 1994 arctic ocean section show how the makarov and canada basins of the arctic ocean are related and demonstrate their oceanographic connections to the eurasian basin the inflow into the makarov basin consists largely of well ventilated water within a broad band of densities from a boundary flow over the siberian end of the lomonosov ridge the boundary flow contains a significant component of dense shelf water likely originating in the barents kara and laptev seas earlier ice camp data show that the canada basin is relatively more isolated from this ventilation source in the canada basin shelf sources influenced by bering sea water appear to add cold waters with high silicate concentrations to the halocline and deeper in 1994 the halocline silicate maximum over the central makarov basin was absent evidence of the recent displacement of the upper s 33 1 halocline water from the chukchi east siberian sea region by water from the eurasian basin much of the makarov basin water in and below the halocline is in fact from the eurasian basin with admixture of waters from the canada basin suggested by their higher silicate concentrations mid depth eddies may transport anomalous properties into the central arctic and create property gradients or fronts in mid depth and deep waters the complex topography of the mendeleyev ridge chukchi plateau region also may assist spreading of water from the boundary into the interior atlantic layer characteristics in 1994 differed from previous general depictions in particular the core temperatures at the chukchi mendeleyev boundary were at least 0 2 c warmer on average than indicated in earlier work the recent warming at intermediate depth has resulted from inflow of atlantic waters that have been cooled relatively little during their transit of the norwegian sea

calcite mud in a holocene back barrier lagoon lake reeve victoria australia abstract lake reeve is a coastal back barrier lagoon that has been deprived of significant amounts terrigenous sediment for up to 4000 yr during most of this period there has been no significant tidal or marine influence and the lagoon is now schizohaline rainfall is seasonal more than 50 is during june august annual evaporation is 2 5 times precipitation causing the lagoon to be intermittent drying up during the summer these conditions plus the abundance of photosynthetic organisms lead to widespread carbonate mud accumulation throughout most of the lagoon this mud up to 30 cm thick in some parts of the lagoon is typically in the form of 2 m crystals unlike other carbonate accumulating back barrier lagoons most of the caco3 is low mg calcite with some sk letal aragonite high mg calcite is present in two small lakes within the pleistocene barrier immediately landward of lake reeve and no dolomite was detected we interpret the carbonate mud to have resulted from the activities of cyanobacteria which are abundant through much of lake reeve

origin of sr rich magnesian calcite mud in a holocene pond basin lee stocking island bahamas abstract magnesian calcite represents about 90 of carbonate mud that has accumulated in a holocene 30 c hypersaline pond waters at times exceeding gypsum saturation elevated sr content is likely a product of changing sr cafluid ratios in pond water related to gypsum formation by incorporating carbon and oxygen isotope stratigraphies of indigenous biota the foraminifer ammonia beccarii and gastropod cerithidea sp with that of pond mud this sedimentary basin preserves a record of high order environmental changes over the last 1500 years that likely influenced mud precipitation and its accumulation these changes reflect variation in water residence time temperature likely bacterial productivity and bicarbonate sources

characterization of double diffusive convection steps and heat budget in the deep arctic ocean 1 in this paper we explore the hydrographic structure and heat budget in the deep canada basin by using data measured with mclane moored profilers mmp bottom pressure recorders bpr and conductivity temperature depth ctd profilers upward from the bottom a homogeneous bottom layer and its overlaying double diffusive convection ddc steps are well identified at mooring a 75 n 150 w we find that the deep water is in weak diapycnal mixing because the effective diffusivity of the bottom layer is 1 8 10 5 m2s 1 while that of the other steps is 10 6 m2s 1 the vertical heat flux through the ddc steps is evaluated by using different methods we find that the heat flux 0 1 11 mwm 2 is much smaller than geothermal heating 50 mwm 2 this suggests that the stack of ddc steps acts as a thermal barrier in the deep basin moreover the temporal distributions of temperature and salinity differences across the interface are exponential whereas those of heat flux and effective diffusivity are found to be approximately lognormal both are the result of strong intermittency between 2003 and 2011 temperature fluctuations close to the sea floor were distributed asymmetrically and skewed toward positive values which provide a direct observation that geothermal heating was transferred into the ocean both bpr and ctd data suggest that geothermal heating and not the warming of the upper ocean is the dominant mechanism responsible for the warming of deep water as the ddc steps prevent vertical heat transfer geothermal heating is unlikely to have a significant effect on the middle and upper arctic ocean

beaufort gyre freshwater reservoir state and variability from observations 1 we investigate basin scale mechanisms regulating anomalies in freshwater content fwc in the beaufort gyre bg of the arctic ocean using historical observations and data collected in 2003 2007 specifically the mean annual cycle and interannual and decadal fwc variability are explored the major cause of the large fwc in the bg is the process of ekman pumping ep due to the arctic high anticyclonic circulation centered in the bg the mean seasonal cycle of liquid fwc is a result of interplay between the mechanical ep and thermal ice transformations factors and has two peaks one peak occurs around june july when the sea ice thickness reaches its minimum maximum ice melt the second maximum is observed in november january when wind curl is strongest maximum ep and the salt input from the growing ice has not yet reached its maximum interannual changes in fwc during 2003 2007 are characterized by a strong positive trend in the region varying by location with a maximum of approximately 170 cm a 1 in the center of ep influenced region decadal fwc variability in the period 1950 2000 is dominated by a significant change in the 1990s forced by an atmospheric circulation regime change the center of maximum fwc shifted to the southeast and appeared to contract in area relative to the pre 1990s climatology in spite of the areal reduction the spatially integrated fwc increased by over 1000 km 3 relative to climatology

double diffusion in saline powell lake british columbia powell lake contains a deep layer of relic seawater separated from the ocean since the last ice age permanently stratified and geothermally heated from below this deep layer is an isolated geophysical domain suitable for studying double diffusive convection high resolution ctd and microstructure measurements showseveraldouble diffusivestaircases rr 51 6to6 inthedeepwater separatedverticallybysmoothhighgradientregionswithmuchlargerdensityratios theloweststaircasecontainsstepsthatarelaterallycoherent on the basin scale and have a well defined vertical structure on average temperature steps in this staircase are 4mk salinity steps are 2mgkg 21 and mixed layer heights are 70cm the ctd is capable of measuring bulk characteristics of the staircase in both temperature and salinity microstructure measurements are limited to temperature alone but resolve the maximum temperature gradients in the center of selected laminar interfaces two different algorithms for characterizing the staircase are compared consistent estimates of the steady state heat flux 27mwm 22 are obtained from measurements above and below the staircase as well as from microstructure measurements in the center of smooth interfaces estimates obtained from bulk interface gradients underestimate the steady state flux by nearly a factor of 2 the mean flux calculated using a standard 4 3 flux law parameterization agrees well with the independent estimates but inconsistencies between the parameterization and the observations remain these inconsistencies are examined by comparing the underlying scaling relationship to the measurements