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Deployment of Deep Argo regional pilot arrays is underway as a step toward a global array of 1250 surface-to-bottom profiling floats embedded in the upper-ocean (2000 m) Argo Program. Of the 80 active Deep Argo floats as of July 2019, 55 are Deep Sounding Oceanographic Lagrangian Observer (SOLO) 6000-m instruments, and the rest are composed of three additional models profiling to either 4000 or 6000 m. Early success of the Deep SOLO is owed partly to its evolution from the Core Argo SOLO-II. Here, Deep SOLO design choices are described, including the spherical glass pressure housing, the hydraulics system, and the passive bottom detection system. Operation of Deep SOLO is flexible, with the mission parameters being adjustable from shore via Iridium communications. Long lifetime is a key element in sustaining a global array, and Deep SOLO combines a long battery life of over 200 cycles to 6000 m with robust operation and a low failure rate. The scientific value of Deep SOLO is illustrated, including examples of its ability (i) to observe large-scale spatial and temporal variability in deep ocean temperature and salinity, (ii) to sample newly formed water masses year-round and within a few meters of the sea floor, and (iii) to explore the poorly known abyssal velocity field and deep circulation of the World Ocean. Deep SOLO’s full-depth range and its potential for global coverage are critical attributes for complementing the Core Argo Program and achieving these objectives.

The Solomon Sea carries the equatorward western boundary current of the South Pacific, a principal element of subtropical-equatorial communication. Eighty-seven glider transects across the mouth of the Sea over nine years describe the velocity structure and variability of this system. The time series spans two El Ninos and two La Ninas, which produced large transport anomalies, up to 50% of the mean. While transport increased during El Ninos and decreased during La Ninas, their signatures were inconsistent among the events. Separated glider tracks show the merging of two inflows, one from the tropics east of the Solomon Island chain, the other entering as a western boundary current generated by winds over the full subtropical gyre. A model of linear wind-driven dynamics, including western boundary currents, had skill in describing the variability of the two inflows, identifying the distinct wind forcing driving each. The model suggests that both the mean and low-frequency variability of flow entering the Solomon Sea are driven remotely by wind over the South Pacific, acting through long Rossby waves. The ultimate significance of in situ observations in this small sea will be to describe its role in subtropical-tropical heat exchange that is crucial to ENSO and longer-timescale climate variations along the equator. We take an initial step here, suggesting that temperature advection through the Solomon Sea is a first-order contribution to interannual temperature changes of the equatorial strip as a whole.

Author(s): Ohman, MD; Davis, RE; Sherman, JT; Grindley, KR; Whitmore, BM; Nickels, CF; Ellen, JS | Abstract: We present the design and preliminary results from ocean deployments of Zooglider, a new autonomous zooplankton-sensing glider. Zooglider is a modified Spray glider that includes a low-power camera (Zoocam) with telecentric lens and a custom dual frequency Zonar (200 and 1000 kHz). The Zoocam quantifies zooplankton and marine snow as they flow through a defined volume inside a sampling tunnel. Images are acquired on average every 5 cm from a maximum operating depth of ~ 400 m to the sea surface. Biofouling is mitigated using a dual approach: an ultraviolet light-emitting diode and a mechanical wiper. The Zonar permits differentiation of large and small acoustic backscatterers in larger volumes than can be sampled optically. Other sensors include a pumped conductivity, temperature, and depth unit and chlorophyll a fluorometer. Zooglider enables fully autonomous in situ measurements of mesozooplankton distributions, together with the three-dimensional orientation of organisms and marine snow in relation to other biotic and physical properties of the ocean water column. It is well suited to resolve thin layers and microscale ocean patchiness. Battery capacity supports 50 d of operations. Zooglider includes two-way communications via Iridium, permitting near-real–time transmission of data from each dive profile, as well as interactive instrument control from remote locations for adaptive sampling.

Autonomous underwater gliders offer the possibility of sustained observation of the coastal ocean. Since 2006 Spray underwater gliders in the California Underwater Glider Network (CUGN) have surveyed along California Cooperative Oceanic Fisheries Investigations (CalCOFI) lines 66.7, 80.0, and 90.0, constituting the world’s longest sustained glider network, to our knowledge. In this network, gliders dive between the surface and 500 m, completing a cycle in 3 h and covering 3 km in that time. Sections extend 350–500 km offshore and take 2–3 weeks to occupy. Measured variables include pressure, temperature, salinity, and depth-average velocity. The CUGN has amassed over 10,000 glider-days, covering over 210,000 km with over 95,000 dives. These data are used to produce a climatology whose products are for each variable a mean field, an annual cycle, and the anomaly from the annual cycle. The analysis includes a weighted least-squares fit to derive the mean and annual cycle, and an objective map to produce the anomaly. The final results are variables on rectangular grids in depth, distance offshore, and time. The mean fields are finely resolved sections across the main flows in the California Current System, including the poleward California Undercurrent and the equatorward California Current. The annual cycle shows a phase change from the surface to the thermocline, reflecting the effects of air/sea fluxes at the surface and upwelling in the thermocline. The interannual anomalies are examined with an emphasis on climate events of the last ten years including the 2009–2010 El Nino, the 2010–2011 La Nina, the warm anomaly of 2014–2015, and the 2015–2016 El Nino.

Neutral-buoyancy vehicles demand high-density energy sources and lithium is light with high oxidation energy. PolyPlus Battery Company has developed a prototype lithium-seawater battery that is attractive for powering long-duration autonomous oceanographic vehicles (floats and underwater gliders). These batteries were tested in the laboratory and at sea.PolyPlus batteries use “Protected Lithium Electrodes” with proprietary “windows” protecting the volatile lithium anode from water while passing lithium ions. The cathode reduces oxygen dissolved in seawater, or hydrolyzes seawater to produce hydrogen. Not requiring additional electrolyte, fuel, or pressure cases, these cells have impressive weight advantages. Good electrode–seawater mass transfer is required but can increase drag and be impeded by biofouling.Tests assessing robustness of the PolyPlus batteries in oceanographic use, evaluating mass transfer issues, and observing biofouling impacts are reported. In sea trials, two cells were tested for 69 days mounted on a Spray glider. Findings are as follows: 1) the cells were robust over 900 dives, most to 400 m; 2) without antifouling measures, the cells became substantially biofouled, but their performance was undiminished; and 3) performance was complex, depending on current density, oxygen concentration, and flow conditions. For dissolved oxygen concentration above 1 mL L−1, the cells delivered 9 W m−2 of electrode surface at 3 V. For low oxygen, the cell shifted to hydrolysis near 2.3 V, but mass transfer was less critical so current density could be increased and observed power reached 5 W m−2. This could be increased using a lower resistance load.

Operational statistics for the Spray underwater glider are presented to demonstrate capabilities for sustained observations. An underwater glider is an autonomous device that profiles vertically by changing buoyancy and flies horizontally on wings. The focus has been on sustained observations of boundary currents to take advantage of the glider’s small size, which allows it to be deployed and recovered from small vessels close to land, and the fine horizontal resolution delivered by the glider, which is scientifically desirable in boundary regions. Since 2004, Spray underwater gliders have been deployed for over 28 000 days, traveling over 560 000 km, and delivering over 190 000 profiles. More than 10 gliders, on average, have been in the water since 2012. Statistics are given in the form of histograms for 297 completed glider missions of longer than 5 days. The statistics include mission duration, number of dives, distance over ground, and horizontal and vertical distance through water. A discussion of problems, losses, and short missions includes a survival analysis. The most extensive work was conducted in the California Current system, where observations on three across-shorelines have been sustained, with 97% coverage since 2009. While the authors have certain advantages as developers and builders of the Spray underwater glider and Spray may have design and construction advantages, they believe these statistics are a sound basis for optimism about the widespread future of gliders in oceanographic observing.

The history of over 100 years of observing the ocean is reviewed. The evolution of particular classes of ocean measurements (e.g., shipboard hydrography, moorings, and drifting floats) are summarized along with some of the discoveries and dynamical understanding they made possible. By the 1970s, isolated and “expedition” observational approaches were evolving into experimental campaigns that covered large ocean areas and addressed multiscale phenomena using diverse instrumental suites and associated modeling and analysis teams. The Mid-Ocean Dynamics Experiment (MODE) addressed mesoscale “eddies” and their interaction with larger-scale currents using new ocean modeling and experiment design techniques and a suite of developing observational methods. Following MODE, new instrument networks were established to study processes that dominated ocean behavior in different regions. The Tropical Ocean Global Atmosphere program gathered multiyear time series in the tropical Pacific to understand, and eventually predict, evolution of coupled ocean–atmosphere phenomena like El Niño–Southern Oscillation (ENSO). The World Ocean Circulation Experiment (WOCE) sought to quantify ocean transport throughout the global ocean using temperature, salinity, and other tracer measurements along with fewer direct velocity measurements with floats and moorings. Western and eastern boundary currents attracted comprehensive measurements, and various coastal regions, each with its unique scientific and societally important phenomena, became home to regional observing systems. Today, the trend toward networked observing arrays of many instrument types continues to be a productive way to understand and predict large-scale ocean phenomena.

“Spray” gliders, most launched from small boats near shore, have established a sustainable time series of equatorward transport through the Solomon Sea. The first 3.5 years (mid-2007 through 2010) are analyzed. Coast-to-coast equatorward transport through the Solomon Sea fluctuates around a value of 15 Sv (1 Sv ≡ 106 m3 s−1) with variations approaching ±15 Sv. Transport variability is well correlated with El Niño indices like Niño-3.4, with strong equatorward flow during one El Niño and weak flow during two La Niñas. Mean transport is centered in an undercurrent focused in the western boundary current; variability has a two-layer structure with layers separated near 250 m (near the core of the undercurrent) that fluctuate independently. The largest variations are in midbasin, confined to the upper layer, and are well correlated with ENSO. Analysis of velocity and salinity on isopycnals shows that the western boundary current within the Solomon Sea consists of a deep core coming from the Coral Sea and a shallow core that enters the Solomon Sea in mid basin. Analysis of the structure of transport and its fluctuations is presented.

The recent proliferation of icebergs in the Southern Ocean and the chemical and biological enrichment recently identified in the surrounding water raise the question of whether these icebergs are major contributors to drawdown of CO2 and the export of organic carbon to the deep ocean. The Lagrangian sediment trap (LST) was developed to measure the carbon export associated with these free-drifting icebergs. The core of the LST is a neutrally buoyant Sounding Oceanographic Lagrangian Observer (SOLO) float ( Davis et al., 2001 ) that contains a variable-buoyancy engine, enabling it to sink to a set depth (600 m for the iceberg study), drift at that depth, then resurface on preset time intervals. Four sediment-trap funnels and opening/closing sample cups mounted around each SOLO float collect sinking particulate matter. Additionally, an upward-looking acoustic system mounted on the float detects the presence of ice cover above. In March/April 2009, three LSTs were deployed in the NW Weddell Sea for a total of five successful missions. Four of these LST deployments were made near or under a large iceberg. The fifth deployment was made at a control site 74 km from the nearest large iceberg. Sinking particulate matter was collected on each deployment. Despite the high-risk nature of the deployments, the LSTs successfully sampled particulate matter beneath drifting icebergs.

A novel hydrothermal field has been discovered at the base of Lōihi Seamount, Hawaii, at 5000 mbsl. Geochemical analyses demonstrate that ‘FeMO Deep', while only 0.2 °C above ambient seawater temperature, derives from a distal, ultra-diffuse hydrothermal source. FeMO Deep is expressed as regional seafloor seepage of gelatinous iron- and silica-rich deposits, pooling between and over basalt pillows, in places over a meter thick. The system is capped by mm to cm thick hydrothermally derived iron-oxyhydroxide- and manganese-oxide-layered crusts. We use molecular analyses (16S rDNA-based) of extant communities combined with fluorescent in situ hybridizations to demonstrate that FeMO Deep deposits contain living iron-oxidizing Zetaproteobacteria related to the recently isolated strain Mariprofundus ferroxydans. Bioenergetic calculations, based on in-situ electrochemical measurements and cell counts, indicate that reactions between iron and oxygen are important in supporting chemosynthesis in the mats, which we infer forms a trophic base of the mat ecosystem. We suggest that the biogenic FeMO Deep hydrothermal deposit represents a modern analog for one class of geological iron deposits known as ‘umbers' (for example, Troodos ophilolites, Cyprus) because of striking similarities in size, setting and internal structures.

Upper-ocean dynamics analyzed from mooring-array observations are contrasted between two storms of comparable magnitude. Particular emphasis is put on the role of the transition layer, the strongly stratified layer between the well-mixed upper layer, and the deeper more weakly stratified region. The midlatitude autumn storms occurred within 20 days of each other and were measured at five moorings. In the first storm, the mixed layer follows a classical slab-layer response, with a steady deepening during the course of the storm and little mixing of the thermocline beneath. In the second storm, rather than deepening, the mixed layer shoals while intense near-inertial waves are resonantly excited within the mixed layer. These create a large shear throughout the transition layer, generating turbulence that broadens the transition layer. Details of the space–time structure of the frequencies in both short waves and near-inertial waves are presented. Small-scale waves are excited within the transition layer. Their frequencies change with time and there are no clear peaks at harmonics of inertial or tidal frequencies. Wavelet transforms of the inertial oscillations show the evolution as a spreading in frequency, a deepening of the core into the transition layer, and a shift off the inertial frequency. A second near-inertial energy core appears below the transition layer at all moorings coincident with a rapid decay of mixed layer currents. An overall result is that direct wind-generated motions extend to the depth of the transition layer. The transition layer is a location of enhanced wave activity and enhanced shear-driven mixing.

A full-scale adaptive ocean sampling network was deployed throughout the month-long 2006 Adaptive Sampling and Prediction (ASAP) field experiment in Monterey Bay, California. One of the central goals of the field experiment was to test and demonstrate newly developed techniques for coordinated motion control of autonomous vehicles carrying environmental sensors to efficiently sample the ocean. We describe the field results for the heterogeneous fleet of autonomous underwater gliders that collected data continuously throughout the month-long experiment. Six of these gliders were coordinated autonomously for 24 days straight using feedback laws that scale with the number of vehicles. These feedback laws were systematically computed using recently developed methodology to produce desired collective motion patterns, tuned to the spatial and temporal scales in the sampled fields for the purpose of reducing statistical uncertainty in field estimates. The implementation was designed to allow for adaptation of coordinated sampling patterns using human-in-the-loop decision making, guided by optimization and prediction tools. The results demonstrate an innovative tool for ocean sampling and provide a proof of concept for an important field robotics endeavor that integrates coordinated motion control with adaptive sampling. (c) 2010 Wiley Periodicals, Inc.

Author Posting. © Oceanography Society, 2009. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 22 no. 2 (2009): 34-43.

The Autonomous Ocean Sampling Network Phase Two (AOSN-II) experiment was conducted in and offshore from the Monterey Bay on the central California coast during July 23–September 6, 2003. The objective of the experiment was to learn how to apply new tools, technologies, and analysis techniques to adaptively sample the coastal ocean in a manner demonstrably superior to traditional methodologies, and to use the information gathered to improve predictive skill for quantities of interest to end-users. The scientific goal was to study the upwelling/relaxation cycle near an open coastal bay in an eastern boundary current region, particularly as it developed and spread from a coastal headland. The suite of observational tools used included a low-flying aircraft, a fleet of underwater gliders, including several under adaptive autonomous control, and propeller-driven AUVs in addition to moorings, ships, and other more traditional hardware. The data were delivered in real time and assimilated into the Harvard Ocean Prediction System (HOPS), the Navy Coastal Ocean Model (NCOM), and the Jet Propulsion Laboratory implementation of the Regional Ocean Modeling System (JPL/ROMS). Two upwelling events and one relaxation event were sampled during the experiment. The upwelling in both cases began when a pool of cold water less than 13 °C appeared near Cape Ano Nuevo and subsequently spread offshore and southward across the bay as the equatorward wind stress continued. The primary difference between the events was that the first event spread offshore and southward, while the second event spread only southward and not offshore. The difference is attributed to the position and strength of meanders and eddies of the California Current System offshore, which blocked or steered the cold upwelled water. The space and time scales of the mesoscale variability were much shorter than have been previously observed in deep-water eddies offshore. Additional process studies are needed to elucidate the dynamics of the flow.

Gliders are autonomous underwater vehicles that achieve long operating range by moving at speeds comparable to those of, or slower than, typical ocean currents. This paper addresses routing gliders to rapidly reach a specified waypoint or to maximize the ability to map a measured field, both in the presence of significant currents. For rapid transit in a frozen velocity field, direct minimization of travel time provides a trajectory “ray” equation. A simpler routing algorithm that requires less information is also discussed. Two approaches are developed to maximize the mapping ability, as measured by objective mapping error, of arrays of vehicles. In order to produce data sets that are readily interpretable, both approaches focus sampling near predetermined “ideal tracks” by measuring mapping skill only on those tracks, which are laid out with overall mapping skill in mind. One approach directly selects each vehicle's headings to maximize instantaneous mapping skill integrated over the entire array. Because mapping skill decreases when measurements are clustered, this method automatically coordinates glider arrays to maintain spacing. A simpler method that relies on manual control for array coordination employs a first-order control loop to balance staying close to the ideal track and maintaining vehicle speed to maximize mapping skill. While the various techniques discussed help in dealing with the slow speed of gliders, nothing can keep performance from being degraded when current speeds are comparable to vehicle speed. This suggests that glider utility could be greatly enhanced by the ability to operate high speeds for short periods when currents are strong.

Glider observations were essential components of the observational program in the Autonomous Ocean Sampling Network (AOSN-II) experiment in the Monterey Bay area during summer of 2003. This paper is focused on the impact of the assimilation of glider temperature and salinity observations on the Navy Coastal Ocean Model (NCOM) predictions of surface and subsurface properties. The modeling system consists of an implementation of the NCOM model using a curvilinear, orthogonal grid with 1–4 km resolution, with finest resolution around the bay. The model receives open boundary conditions from a regional (9 km resolution) NCOM implementation for the California Current System, and surface fluxes from the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) atmospheric model at 3 km resolution. The data assimilation component of the system is a version of the Navy Coupled Ocean Data Assimilation (NCODA) system, which is used for assimilation of the glider data into the NCOM model of the Monterey Bay area. The NCODA is a fully 3D multivariate optimum interpolation system that produces simultaneous analyses of temperature, salinity, geopotential, and vector velocity. Assimilation of glider data improves the surface temperature at the mooring locations for the NCOM model hindcast and nowcasts, and for the short-range (1–1.5 days) forecasts. It is shown that it is critical to have accurate atmospheric forcing for more extended forecasts. Assimilation of glider data provided better agreement with independent observations (for example, with aircraft measured SSTs) of the model-predicted and observed spatial distributions of surface temperature and salinity. Mooring observations of subsurface temperature and salinity show sharp changes in the thermocline and halocline depths during transitions from upwelling to relaxation and vice versa. The non-assimilative run also shows these transitions in subsurface temperature; but they are not as well defined. For salinity, the non-assimilative run significantly differs from the observations. However, the glider data assimilating run is able to show comparable results with observations of thermocline as well as halocline depths during upwelling and relaxation events in the Monterey Bay area. It is also shown that during the relaxation of wind, the data assimilative run has higher value of subsurface velocity complex correlation with observations than the non-assimilative run.

We combined a Sounding Oceanographic Lagrangian Observer float with a Laser Optical Plankton Counter (LOPC) and a fluorometer to make an autonomous biological profiler, the SOLOPC. The instrument senses plankton and other particles over a size range of 100 µm to 1 cm in profiles to 300 m in depth and sends data ashore via satellite. Objects sensed by the LOPC include aggregates and zooplankton, the larger of which can be distinguished from one another by their transparency. We hypothesized that the diel production of particles and their loss by sinking and grazing are reflected in the change of the particle distribution. We present data from four deployments of the SOLOPC off California. Particle volume was maximal at the base of the surface mixed layer and correlated with chlorophyll a fluorescence. In a 3-d deployment in 2005, particle volume was greatest in the early evening and smallest in the morning, and average particle size increased with depth. Eigenvector analysis of the particle volume distribution as a function of diameter for each of the deployments yielded size peaks characteristic of planktonic crustaceans. Ship-based measurements showed that the abundance of opaque particles of 1.1-1.7 mm equivalent spherical diameter was positively correlated with copepods of this size and simultaneously collected in nets. This relationship was used with SOLOPC data to estimate the distribution of large copepods, which were most abundant beneath the depth of maximal particle flux, estimated from particle size and published sinking rates. Our data are consistent with a model with diel production of particles and their loss by sinking and grazing.

Since 2005, Spray underwater gliders have been used to sample sections across the southern California Current System (CCS). Properties measured are depth-averaged velocity and profiles of temperature, salinity, Acoustic Doppler Profiler shear, chlorophyll a fluorescence, and 750-kHz acoustic backscatter. Although slow and carrying a relatively small sensor suite, gliders observed multiple 350-700-km sections that reveal details of known elements of the CCS circulation like the California Current and Undercurrent as well as a previously undescribed undercurrent 100-200 km offshore. The long time series with high spatial resolution disclose the close link between fronts in physical and biological variables, both the main pycnocline front and secondary weaker but sharp fronts farther offshore. These fronts appear to organize chlorophyll and acoustic backscatter fields, particularly during spring. Much of the patchiness of chlorophyll is associated with vertical displacements of fields that are much smoother within potential density surfaces. The horizontal structure of both chlorophyll and spice (the dynamically passive variable formed from temperature and salinity) appear to be formed by mesoscale stirring. © 2008, by the American Society of Limnology and Oceanography, Inc.

The South Equatorial Current (SEC) entering the Coral Sea through the gap between New Caledonia and the Solomon Islands was observed by an autonomous underwater vehicle (Spray glider) and an overlapping oceanographic cruise during July–October 2005. The measurements of temperature, salinity, and absolute velocity included high-horizontal-resolution profiles to 600-m depth by the glider, and sparser, 2000-m-deep profiles from the cruise. These observations confirm the splitting of the SEC into a North Vanuatu Jet (NVJ) and North Caledonian Jet (NCJ), with transport above 600 m of about 20 and 12 Sv, respectively. While the 300-km-wide NVJ is associated with the slope of the main thermocline and is thus found primarily above 300 m, the NCJ is a narrow jet about 100 km wide just at the edge of the New Caledonian reef. It extends to at least a 1500-m depth with very little shear above 600 m and has speeds of more than 20 cm s−1 to at least 1000 m. An Argo float launched east of New Caledonia with a parking depth fixed at 1000 m became embedded in the NCJ and crossed the glider/cruise section at high speed about 3 months before the glider, suggesting that the jet is the continuation of a western boundary current along the east side of the island and extends across the Coral Sea to the coast of Australia. In the lee of New Caledonia, the glider passed through a region of eddies whose characteristics are poorly understood.

An increase in the circulation of the South Pacific Ocean subtropical gyre, extending from the sea surface to middepth, is observed over 12 years. Datasets used to quantify the decadal gyre spinup include satellite altimetric height, the World Ocean Circulation Experiment (WOCE) hydrographic and float survey of the South Pacific, a repeated hydrographic transect along 170°W, and profiling float data from the global Argo array. The signal in sea surface height is a 12-cm increase between 1993 and 2004, on large spatial scale centered at about 40°S, 170°W. The subsurface datasets show that this signal is predominantly due to density variations in the water column, that is, to deepening of isopycnal surfaces, extending to depths of at least 1800 m. The maximum increase in dynamic height is collocated with the deep center of the subtropical gyre, and the signal represents an increase in the total counterclockwise geostrophic circulation of the gyre, by at least 20% at 1000 m. A comparison of WOCE and Argo float trajectories at 1000 m confirms the gyre spinup during the 1990s. The signals in sea surface height, dynamic height, and velocity all peaked around 2003 and subsequently began to decline. The 1990s increase in wind-driven circulation resulted from decadal intensification of wind stress curl east of New Zealand—variability associated with an increase in the atmosphere’s Southern Hemisphere annular mode. It is suggested (based on altimetric height) that midlatitude gyres in all of the oceans have been affected by variability in the atmospheric annular modes on decadal time scales.

This paper addresses the design of mobile sensor networks for optimal data collection. The development is strongly motivated by the application to adaptive ocean sampling for an autonomous ocean observing and prediction system. A performance metric, used to derive optimal paths for the network of mobile sensors, defines the optimal data set as one which minimizes error in a model estimate of the sampled field. Feedback control laws are presented that stably coordinate sensors on structured tracks that have been optimized over a minimal set of parameters. Optimal, closed-loop solutions are computed in a number of low-dimensional cases to illustrate the methodology. Robustness of the performance to the influence of a steady flow field on relatively slow-moving mobile sensors is also explored

The multi-year mean, mid-depth circulation of the subpolar North Atlantic Ocean was estimated from direct velocity measurements obtained over a 7.5-year period by 211 neutrally-buoyant, profiling, subsurface floats. We present a statistical analysis of these drift velocity data, and describe the features of the circulation from 400–1500 m depth as measured by the floats. The time-lagged auto-covariances of velocity indicate a Lagrangian integral time scale of approximately 10 days at all drift depths and throughout the basin. Space–time averages of velocity and the associated error ellipses were constructed, and this information was used in an objective analysis to produce estimates of the multi-year mean flow. Estimates of eddy kinetic energy were also computed. The mapped flow depicts a basin-scale cyclonic gyre bounded in the south by the North Atlantic Current. The strongest currents are found along the coasts of Greenland and Labrador, where mean speeds exceed 10cms-1. Closed cyclonic recirculations appear just offshore of the boundary currents in the Labrador and Irminger Seas and in the Iceland basin, and also southwest of the Reykjanes Ridge. Topographic steering extends upwards to at least 400 m depth above bathymetry that is significantly deeper, and is most apparent in flow along basin boundaries, around the Reykjanes Ridge, and through gaps in the Mid-Atlantic Ridge. In the center of the basin-scale gyre and to the south of the North Atlantic Current flow is characteristically weak with few large-scale circulation features. There is no indication of a strong linkage along the western boundary from the subpolar to subtropical gyre at depths sampled by floats.

The large-scale context for oceanic subduction is examined in the region bounded by 10°N and 40°N and 10°W and 40°W using data collected from June 1991 to June 1993. In contrast to climatology, it was found that over the entire region the ocean gained heat, ranging from 10–30 W m –2 to the north to 40–50 W m –2 to the south. Steady tradewinds dominated the southeastern half of the region. To the northwest of the axis of these tradewinds was a broad region of downward Ekman pumping with a 2-yr mean of about 50 m yr –1 . Wind-driven surface currents and a seasonal cycle in mixed layer temperature and depth were found that reflected the influence of local forcing. The interior circulation was consistent with the clockwise circulation of the eastern end of the subtropical gyre, though eddy variability dominated the northern part of the region. Due to Ekman convergence the winter mixed layer in the central and southwestern parts of the region was as deep as to the north; however, it was also warm. This deep, warm mixed layer in the center of the region aided the subduction of water from the northeast by providing a protective cap; isopycnals that outcropped to the north passed well below the base of this mixed layer.

Autonomous floats profiling in high-nitrate low-silicate waters of the Southern Ocean observed carbon biomass variability and carbon exported to depths of 100 m during the 2002 Southern Ocean Iron Experiment (SOFeX) to detect the effects of iron fertilization of surface water there. Control and “in-patch” measurements documented a greater than fourfold enhancement of carbon biomass in the iron-amended waters. Carbon export through 100 m increased two- to sixfold as the patch subducted below a front. The molar ratio of iron added to carbon exported ranged between 10 4 and 10 5 . The biomass buildup and export were much higher than expected for iron-amended low-silicate waters.

During 1994–1996, 215 Autonomous Lagrangian Circulation Explorers (ALACE floats) were released at a nominal 900 m depth in the Indian Ocean as part of the World Ocean Circulation Experiment. Of these, 66 entered the region around Madagascar (2–30°S, 35–55°E), generally at a depth of 800–900 m. Floats approaching the island from the east were deflected either northward or southward depending on latitude, with the bifurcation point being near 20°S. Mean southward velocities in the western boundary current were 8.5 cm s-1 during each 25-day observation period, with mean northward velocities 7.7 cm s-1. Speeds past Cape Amber were about 11 cm s-1. These figures are comparable to those obtained from in situ current meter measurements. Floats rounding the island to the north frequently drifted north of the Comores for many months with no discernable pattern, before exiting the region either to the north in the East African Coastal Current and the equatorial current system or to the south via the Mozambique Channel. Flow rates in this region were highly skewed towards low (less than 5 cm s-1) velocities. Floats passing south of Madagascar showed little northward movement into the Mozambique Channel, but tended to move steadily westwards towards the African coast, becoming entrained in the Agulhas Current and its recirculation gyres near 28°S. Similarly, floats released within the southern portion of the Channel all tended to move to the south and west despite occasional entanglement with eddies. Mean flow in the Agulhas region was about 18 cm s-1, with maximum velocities over 25 days of up to about 35 cm s. All flows were extremely variable because of the ubiquity of eddies. In essence, the flow observed near 800 m resembled closely that seen at the surface from TOPEX/POSEIDON altimetry and at 845 m in the OCCAM global model. Temperature data collected by the floats were used to determine when a given float was being acted on by an anticyclonic eddy. Deviations, which were typically 0.5°C or more from the background temperature field, were found only in eddies south of 12°S and occurred in about 9% of float records within the Mozambique Channel. The results support the idea of a net southward flow of water through the Channel from the tropics to the Agulhas Current, with the eddies playing a major role in the transport in the southern part of the region. In the northern and eastern parts of the region, however, eddies were far less prevalent, and topographic steering by the Mascarene Ridge became important.

The analysis of interdecadal physical and biological variability is made challenging by the relative shortness of available time series. It has been suggested that rapid temporal changes of the most energetic empirical orthogonal function of North Pacific sea surface temperature (sometimes called the Pacific Decadal Oscillation or PDO) represents a ‘‘regime shift’’ between states with otherwise stable statistics. Using random independent time series generated to have the same frequency content as the PDO, we show that a composite analysis of climatic records recently used to identify regime shifts is likely to find them in Gaussian, red noise with stationary statistics. Detection of a shift by this procedure is not evidence of nonlinear processes leading to bi-stable behavior or any other meaningful regime shift. r 2003 Elsevier Science Ltd. All rights reserved.

Two autonomous robotic profiling floats deployed in the subarctic North Pacific on 10 April 2001 provided direct records of carbon biomass variability from surface to 1000 meters below surface at daily and diurnal time scales. Eight months of real-time data documented the marine biological response to natural events, including hydrographic changes, multiple storms, and the April 2001 dust event. High-frequency observations of upper ocean particulate organic carbon variability show a near doubling of biomass in the mixed layer over a 2-week period after the passage of a cloud of Gobi desert dust. The temporal evolution of particulate organic carbon enhancement and an increase in chlorophyll use efficiency after the dust storm suggest a biotic response to a natural iron fertilization by the dust.

The occurrence and extent of deep convection in the Labrador Sea in winters 1996/97 and 1997/98 is investigated from measurements of over 200 neutrally buoyant subsurface Profiling Autonomous Lagrangian Circulation Explorer (PALACE) and Sounding Oceanographic Lagrangian Observer (SOLO) floats. In addition to providing drift velocity data and vertical profiles of temperature and salinity, 55 floats are equipped with vertical current meters (VCMs). Time series of vertical velocity (derived from measured pressure and vertical flow past the float) and temperature are obtained from the VCM floats. Mixed layer depths estimated from profile measurements indicate that convection reached depths greater than 1300 m in 1997, but no deeper than 1000 m in 1998. Deep mixed layers were concentrated in the western basin, although a number of deep mixed layers were observed southwest of Cape Farewell and also north of 60°N. The highest variance in vertical velocity and the lowest mean temperatures were found in t...

The Southwest Pacific Ocean Circulation and Climate Experiment (SPICE) is an international research program under the auspices of CLIVAR. The key objectives are to understand the Southwest Pacific Ocean circulation and the South Pacific Convergence Zone (SPCZ) dynamics, as well as their influence on regional and basin‐scale climate patterns. South Pacific thermocline waters are transported in the westward flowing South Equatorial Current (SEC) toward Australia and Papua‐New Guinea. On its way, the SEC encounters the numerous islands and straits of the Southwest Pacific and forms boundary currents and jets that eventually redistribute water to the equator and high latitudes. The transit in the Coral, Solomon, and Tasman Seas is of great importance to the climate system because changes in either the temperature or the amount of water arriving at the equator have the capability to modulate the El Niño‐Southern Oscillation, while the southward transports influence the climate and biodiversity in the Tasman Sea. After 7 years of substantial in situ oceanic observational and modeling efforts, our understanding of the region has much improved. We have a refined description of the SPCZ behavior, boundary currents, pathways, and water mass transformation, including the previously undocumented Solomon Sea. The transports are large and vary substantially in a counter‐intuitive way, with asymmetries and gating effects that depend on time scales. This paper provides a review of recent advancements and discusses our current knowledge gaps and important emerging research directions. Por pares

Hydrographic data about latitudes 30°–32°S in the Pacific Ocean are presented and used together with direct velocity observations from floats and moorings to investigate the spatial distribution of meridional flow and its associated transports. An initial velocity scheme is developed with reference to the water property distributions that is subsequently adjusted to meet constraints on net mass and dissolved silica transports. The resulting circulation is found to be sensitive to a priori scaling assumptions and differs in detail from past estimates of the flow in this region. Additionally constraining the flow with directly measured time averaged estimates of the velocity from floats and a current meter array significantly reduces the uncertainty in the derived flow field and improves consistency between the velocity and the property distributions. The derived circulation includes a nearly closed bottom-to-deep-water overturning circulation of 16–20 Sv, below a subtropical gyre flow of thermocline and surface waters consisting of nearly distinct Tasman Sea (∼30 Sv) and basin interior (∼10 Sv) circulations and (a prescribed) ∼10±5 Sv of net northward flow to supply the Indonesian and Bering Strait throughflows. On the basis of this circulation scheme, the heat flux divergence for the Pacific north of the P6 line is estimated to be 0.75±0.56 pW (ocean gaining heat from the atmosphere) and the net freshwater divergence is estimated to be 0.1±0.1 Sv (ocean gains fresh water via air-sea exchange and runoff). The former is highly dependent on the strength of the Indonesian throughflow; the latter also depends on the intensity of the lateral subtropical gyre circulation, which is constrained by the float data. Combined with estimates from the Indian and Atlantic Oceans, we find the subtropical Southern Hemisphere oceans transport 0.46±0.38 PW poleward, less than half the poleward heat transport achieved by the subtropical oceans in the Northern Hemisphere.

Over the past decade more than 1200 autonomous floats have been deployed worldwide. In addition to velocity as marked by lateral movement, many of these floats measured quantities like profiles of temperature and salinity, temperature microstructure, and time series of vertical velocity. The authors' laboratory's implementation of profile measurements in what is called a Profiling Autonomous Lagrangian Circulation Explorer is described. Biofouling and degradation of antifouling coatings on the conductivity sensor both cause drifts that mean accurate salinity measurements will depend on corrections based on known temperature–salinity relations. A second generation autonomous float called the Sounding Oceanographic Lagrangian Observer (SOLO) has been developed to provide enhanced reliability and to provide complete two-way depth control. A dual hydraulic-pneumatic buoyancy system reduces the energy cost of vertical cycling and buoyancy generation at the surface. A SOLO Vertical Current Meter has be...

A small (50-kg, 2-m long) underwater vehicle with operating speeds of 20-30 cm/s and ranges up to 6000 km has been developed and field tested. The vehicle is essentially an autonomous profiling float that uses a buoyancy engine to cycle vertically and wings to glide horizontally while moving up and down. Operational control and data relay is provided by GPS navigation and two-way communication through ORBCOMM low-Earth-orbit satellites. Missions are envisioned with profile measurements repeated at a station or spaced along a transect. The initial instrument complement of temperature, conductivity, and pressure sensors was used to observe internal waves and tides in the Monterey underwater canyon.

he ocean is changing vigorously on a wide range of time and space scales. This variability leads to substantial problems in observing and modeling (simulating) the rapidly changing flow field, the ocean's temperature distribution, and more generally the consequences of those changes on a wide variety of scientific, military, and societal problems, including climate research, fisheries management, coastal pollution (spill) predictions, or ship routing. As an example, the ocean carries roughly 50% of the heat from the low latitudes to mid and high latitudes, where it is released to the atmosphere and moderates our climate. Any significant variation in this heat transport will necessarily lead to a perturbation of the climate system. Among the goals of the present ocean research are therefore to measure, understand, and eventually predict these variations by combining ocean data and ocean models.

Phase 1 (9/99 - 9/02) and Phase 2 (7/00 - 6/02) of US Argo provided a total of 187 CTD profiling floats in the Pacific, Atlantic and Indian Oceans. Objectives were to demonstrate technological capabilities for fabrication and for deployment of float arrays in remote ocean locations (Phase 1) and to demonstrate the capability for manufacture and deployment of large float arrays (Phase 2). Recent technology developments in profiling floats were also implemented, including new generation salinity sensors, improved depth capability, and deployment techniques using fast ships and aircraft. Development of the U.S. Argo Data System was part of Phase 1, on a collaborative basis with international partners. Objectives are to make all Argo data publicly available within a day of collection, applying automated quality control procedures consistent with international Argo practices. Data appropriate for research applications and for comparison with climate change models are not available for several months since they need quality control by salinity experts and evaluation of data over many (10 day) float cycles. Phase 3 is a 5-year project (8/01 - 6/06) including full implementation of the US component of Argo. This report includes Phase 3/Year 2, which deployed 290 CTD profiling floats during CY2003 plus support for these deployments, data management activities and for national and international coordination of Argo. Float deployments targeted the Atlantic, Pacific, Indian, and Southern Oceans. Priorities for US float deployment are set by the US Argo Advisory Panel.

The subsurface oceanic circulation is an important part of the Earth climate system. Subsurface currents traditionally are inferred indirectly from distributions of temperature and dissolved substances, occasionally supplemented by current meter measurements. Neutrally-buoyant floats however, now enable us to obtain for the first time directly measured intermediate depth velocity fields over large areas such as the western South Atlantic. Here, our combined data set provides unprecedented observations and quantification of key flow patterns, such as the Subtropical Gyre return flow (12 Sv; 1 Sverdrup = 10(6)m(3)s(-1)), its bifurcation near the Santos Plateau and the resulting continuous narrow and swift northward intermediate western boundary current (4 Sv). This northward flowing water passes through complex equatorial flows and finally enters into the North Atlantic.

Coarse-resolution numerical models of ocean circulation rely on parameterizations of unresolved mesoscale eddy effects. In order to investigate the role of eddy-flux divergences in the density equation, the GFDL Modular Ocean Model (MOM) has been configured as a simple flat-bottomed channel model with sufficient resolution to represent mesoscale eddies. Eady-type baroclinic instability and a wind-forced channel have been considered. As an analog to the large-scale components addressed by low-resolution models, the influence of eddy fluxes on the zonal-mean density field was evaluated. Results show that eddy-flux divergences are larger than meanflux divergences. The effect of mesoscale eddies on the mean density field is often hypothesized to take an advective form that conserves mean density so that eddy effects are adiabatic in the zonal mean. However, in both of the examples studied a significant component of the mesoscale eddy effect on the zonal mean is diabatic and makes mean density nonconservative. The associated diapycnal fluxes result from zonally averaging terms representing processes that are locally adiabatic. Subgrid-scale parameterizations (such as eddy diffusion) represent the unresolved eddy-flux divergence as a function of the resolved density field. The authors computed optimal coefficients for a variety of parameterizations and evaluated their skill. When the model output is time-averaged, quasi-adiabatic parameterizations, such as the one proposed by Gent and McWilliams, are able to explain as much as 43% of the mean-squared eddy-flux divergence. However, for shorter averaging periods or instantaneous snapshots, even for the spatially averaged model fields, parameterization skill drops.

As part of the World Ocean Circulation Experiment, 300 Autonomous Lagrangian Circulation Explorer floats were deployed in the tropical and South Pacific to measure the general circulation at 900 m depth. Most floats measured average currents over 25 submerged days between ascents to the surface for locating and data relay. By the end of 1997, over 12,500 observations spanning 840 float years were obtained. Accuracy of the average velocity is limited by variability, some of which is found to arise from steady flows with spatial variations smaller than averaging scales. Observed 25-day velocities are serially uncorrelated except near the equator where energetic zonal variability has seasonal timescales and appears to be described by a data-assimilating ocean circulation model run by the National Centers for Environmental Prediction. Space-time averages of float velocities disclose a general pattern of middepth flow that resembles the surface circulation with the strongest flows of O (3 cm/s) in the deep Antarctic Circumpolar Current and East Australian Current. The weaker elements of the flow, including an interior subtropical circulation with O (millimeters per second) flows, are described by an objective analysis whose accuracy is limited by sampling noise rather than uncertainty of the analysis parameters. The subtropical circulation has a gyres-within-a-gyre structure including boundary currents along Australia and east of New Zealand and a concentrated equatorial limb with surprising strength in the western basin. This current is also involved in a tropical gyre with generally eastward flow along the equator in the western basin at least. Because of strong seasonal-scale variability, the equatorial zonal currents are not well measured yet but data are still being accumulated. Comparison with Reid's [1997] absolute circulation shows more areas of agreement than of disagreement.

Our overall goal is to increase the capabilities of today s Unmanned Underwater Vehicles (UUVs) and Unmanned Underwater Gliders (UUGs) by using high energy-density lithium-seawater batteries. Specific objectives are (1) to test in the laboratory and ocean new lithium-seawater batteries developed and manufactured by the PolyPlus Battery Company, (2) to discover how to mount and operate these cells to maximize their mass transfer with the ambient seawater and to minimize the adverse impacts of bio-fouling, and (3) to develop a long-range underwater UUV or UUG to exploit this energy source. Our target is to double the range/duration of long-range neutrally buoyant underwater vehicles.

Recently it has been argued that in many regions of the ocean the Osborn–Cox model accurately determines the total long-term diapycnal flux of a tracer θ if the mean gradient and dissipation in the model are long-time averages. The mean gradient is easily determined, but averaging the scalar dissipation χ = 2κ|∇θ′|2 is notoriously difficult because of its highly intermittent distribution. The distribution of χ has long been known to be approximately lognormal, and Baker and Gibson suggest estimating (χ) by fitting observations to a lognormal probability distribution. There are four reasons why this does not apply to the observations needed to find long-term averages of χ. First, the theoretical arguments for the lognormal distribution apply to dissipation under a single set of local macroscopic factors (shear, stability, etc.) and low-frequency modulation of macroscopic factors is likely to cause slow changes of the parameters of the local lognormal distribution, leading to a different distributi...

The motions of eight Autonomous Lagrangian Circulation Explorer (ALACE) floats released near 750 m depth in Drake Passage and followed through the South Atlantic are described and compared with emulations made by advecting model floats through 12 monthly snapshots of velocity from the fine resolution Antarctic model (FRAM). Both ALACEs and FRAM reproduce the major features of the general circulation as follows: strong intermediate depth flow in Drake Passage, bifurcation of the Antarctic Circumpolar Current (ACC) passing over the Falkland Plateau, a strong Falkland Current, its confluence with the Brazil Current, and moderate zonal flow across the South Atlantic. FRAM versus ALACE comparisons are made in both the Eulerian frame and using observed and modeled trajectories. In Drake Passage, where float velocities agree with earlier observations, FRAM velocities are about twice too big. Both FRAM and ALACE velocities are consistent with an O(100 Sv) Falkland Current. In the central South Atlantic the few available float observations indicate the ACC and South Atlantic Current (SAC) to be more localized than in the model. Eddy kinetic energy is much stronger in the observations than in FRAM. Float dispersion in both the model and observations is due primarily to mean shear. Initial RMS particle separation of 100 km grows to nearly 1000 km after 1 year, but most of this is associated with floats that take different paths of the general circulation. The observations indicate that eddy effects are particularly important near the Falkland-Brazil Current confluence in allowing Antarctic Intermediate Water to transfer from the ACC to the SAC, from which they may enter the subtropical gyre.

A new autonomous instrument collected 76 profiles of temperature microstructure over a ten-day period in the eastern subtropical North Atlantic as part of the North Atlantic Tracer Release Experiment. The data between 200-m and 350-m depth was used to determine the mean rate of temperature variance dissipation 〈χ〉. The estimated diapycnal diffusivity is Ky = 1.4×10−5 m2 s−1. The distribution of χ is approximately lognormal, suggesting that the 95% confidence limits on 〈χ〉 are ±4%. This uncertainty is less than that caused by the imperfectly known probe response, possible noise spikes on the probes, and variability in the degree of microstructure anisotropy; the latter two effects were estimated from a pair of closely spaced probes. Each of these uncertainties is about ±15%. Statistically significant low-frequency variability of χ is observed with 〈χ〉 decreasing by a factor of 2 between the first and second half of the observation. This low-frequency variability is likely the largest cause of erro...

The Osborn-Cox model is a simplified tracer variance budget that is a basis for direct estimates of the diapycnal Kv. diffusivity When used to interpret temperature variance dissipation measurements, it indicates Kv to be O(10−5 m2 s−1) in the thermocline–much smaller than the diffusivities found by matching large-scale observations to models or budgets. It is argued that, if the Osborn-Cox model is to describe fluxes in the general circulation, it must describe the variance budget of all fluctuations around the long-term average used to define the general circulation. Within this framework, the simplifications leading to the Osborn-Cox model are re-examined to find if they still hold and which is most likely to cause Kv errors. Factors examined (and the importance found) are approximations in the Fourier and Ficks diffusion laws (unimportant), accumulation and advection of tracer variance (unimportant except in regions of strong upwelling), variance production by lateral fluxes (dominant at high...

The Osborn–Cox model is the basis for the most direct estimates of the diapycnal diffusivity Kv for tracers. When used to interpret temperature variance dissipation measurements, it leads to Kv of O (10−5 m2 s−1) or less in the main thermocline. Large-scale diagnostic models typically match observations best using Kv of O (10−4 m2 s−1). The framework for describing diapycnal fluxes of tracers like temperature or density from large-scale property distributions is reexamined in an attempt to discover possible causes for this disagreement. Starting from basic thermodynamics principles, suitable tracer conservation equations are developed and the simplifications leading to conventional mean-field and variance balances are examined. It is argued that separation of mean and eddy fields is best based on long but finite time averages rather than the usual space-scale separation. Because this separation leads to a more vigorous eddy field than the usual procedure it is necessary to reexamine all conventio...

[1] Three years of continuous Spray glider observations in the southern California Current System (CCS) are combined with a numerical simulation to describe the mean and variability of poleward flows in the southern CCS. Gliders provide upper ocean observations with good across-shore and temporal resolution along two across-shore survey lines while the numerical simulation provides a dynamically consistent estimate of the ocean state. Persistent poleward flows are observed in three areas: within 100 km of the coast at Point Conception, within the Southern California Bight (SCB), and offshore of the SCB and the Santa Rosa Ridge (SRR). Poleward transport by the flows within the SCB and offshore of the SRR exceeds the poleward transport off Point Conception, suggesting that the poleward flows are not continuous over the 225 km between observation lines. The numerical simulation shows offshore transport between the survey lines that is consistent with some of the poleward flow turning offshore before reaching Point Conception. The poleward current offshore of the SRR is unique in that it is strongest at depths greater than 350 m and it is observed to migrate westward away from the coast. This westward propagation is tied to westward propagating density anomalies originating in the SCB during the spring-summer upwelling season when wind stress curl is most strongly positive. The across-shore wave number, frequency, and phase speed of the westward propagation and the lack of across-shore transport of salinity along isopycnals are consistent with first-mode baroclinic Rossby dynamics.

[1] The 2009–2010 El Nino marked the first occurrence of this climate phenomenon since the initiation of sustained autonomous glider surveillance in the California Current System (CCS). Spray glider observations reveal the subsurface effects of El Nino in the CCS with spatial and temporal resolutions that could not have been obtained practically with any other observational method. Glider observations show that upper ocean waters in the CCS were unusually warm and isopycnals were abnormally deep during the El Nino event, but indicate no anomalous water masses in the region. Observed oceanic anomalies in the CCS are nearly in phase with an equatorial El Nino index and local anomalies of atmospheric forcing. These observations point toward an atmospheric teleconnection as an important mechanism for the 2009–2010 El Nino's remote effect on the midlatitude CCS.