Profiling Floats Research Articles

Detection of the 2012 Havre submarine eruption plume using Argo floats and its implications for ocean dynamics

More than 85% of the Earth's volcanism and geothermal heat release occurs underwater at mid-ocean ridges, intra-plate hotspots, and oceanic island arcs. However, we lack a clear understanding of how a submarine eruption interacts with the overlying water column, the structure of the submarine eruptive plume, and the transport of volcanic products in the ocean by these plumes. We describe here the detection of eruption-derived temperature increase and salinity decrease from the 2012 Havre submarine caldera eruption by an existing array of temperature/salinity profiling floats, known as Argo. The Argo floats observed the signal, significant at >3 sigma level with respect to the background ocean variability (noise), at ocean depths of ∼1750–2000 m deeper than the eruptive vent itself. In order to understand this signal, we develop a new conceptual submarine plume model which suggests that the sub-vent level temperature and salinity anomalies are caused by large-scale ocean mixing induced by the eruptive plume, rather than heating directly from the eruption. Using results from scaling analysis and a modified numerical plume-gravity current model, we show that submarine eruptions can efficiently advect water masses from the deep ocean closer to the surface and form multiple subsurface intrusions during the process. Consequently, the submarine eruptive plumes can initiate significant ocean mixing, a process with significant implications for both long- and short-term influence of submarine volcanism on ocean chemistry, dynamics, and ecology. Finally, our model confirms that a detectable anomaly would persist out to 100s of km from the eruption location, comparable to Argo's spatial sampling. Given the global ocean coverage and a decadal baseline, the Argo floats (and other similar datasets), in concert with hydrophone and seismic arrays, can provide significant new constraints on subaqueous volcanism, eruption dynamics, and the impact on Earth systems through enhanced ocean mixing and nutrient supply, e.g. during submarine Large Igneous Provinces.

The AlborEX dataset: sampling of sub-mesoscale features in the Alboran Sea

Abstract. The AlborEX (Alboran Sea Experiment) consisted of a multi-platform, multi-disciplinary experiment carried out in the Alboran Sea (western Mediterranean Sea) between 25 and 31 May 2014. The observational component of AlborEx aimed to sample the physical and biogeochemical properties of oceanographic features present along an intense frontal zone, with a particular interest in the vertical motions in its vicinity. To this end, the mission included 1 research vessel (66 profiles), 2 underwater gliders (adding up 552 profiles), 3 profiling floats, and 25 surface drifters.Near real-time ADCP velocities were collected nightly and during the CTD sections. All of the profiling floats acquired temperature and conductivity profiles, while the Provor-bio float also measured oxygen and chlorophyll a concentrations, coloured dissolved organic matter, backscattering at 700 nm, downwelling irradiance at 380, 410, and 490 nm, as well as photo-synthetically active radiation (PAR).In the context of mesoscale and sub-mesoscale interactions, the AlborEX dataset constitutes a particularly valuable source of information to infer mechanisms, evaluate vertical transport, and establish relationships between the thermal and haline structures and the biogeochemical variable evolution, in a region characterised by strong horizontal gradients provoked by the confluence of Atlantic and Mediterranean waters, thanks to its multi-platform, multi-disciplinary nature.The dataset presented in this paper can be used for the validation of high-resolution numerical models or for data assimilation experiment, thanks to the various scales of processes sampled during the cruise. All the data files that make up the dataset are available in the SOCIB data catalog at https://doi.org/10.25704/z5y2-qpye (Pascual et al., 2018). The nutrient concentrations are available at https://repository.socib.es:8643/repository/entry/show?entryid=07ebf505-bd27-4ae5-aa43-c4d1c85dd500 (last access: 24 December 2018).

Smartfloat: A Multimodal Underwater Vehicle Combining Float and Glider Capabilities

This paper proposes a novel hybrid underwater vehicle, the Smartfloat, which integrates the concept of buoyancy-driven underwater gliders and conventional profiling floats. The vehicle is presented to address the challenges in ocean monitoring, such as the multidisciplinary observations of long-range transport of the mesoscale features with high spatial-temporal resolution. The vehicle combines the mechanisms of Argo profiling float and the underwater glider, with the application of a special designed attitude control system and the ingenious general arrangement. The vehicle can switch the operating mode between drifting mode and gliding mode. Such a multimodal vehicle would merge the benefits of making measurements in a very energy-efficient way when drifting with the currents in Argo mode, and operating as an underwater glider in glider mode when it is needed to cross the ocean eddies, ocean fronts, filaments, or some stirring regions. In this paper, a proof-of-concept platform including its concept of operations, the main components and subsystems design, and the correlative mathematical analysis is introduced in detail. Experiments in field trials are presented to characterize and illustrate each mode of operation and repeated mode transitions. The results demonstrate the feasibility and the good performance of the proposed vehicle.

Lagrangian Geography of the Deep Gulf of Mexico

AbstractUsing trajectories from acoustically tracked (RAFOS) floats in the Gulf of Mexico, we construct a geography of its Lagrangian circulation within the 1500–2500-m layer. This is done by building a Markov-chain representation of the Lagrangian dynamics. The geography is composed of weakly interacting provinces that constrain the connectivity at depth. The main geography includes two provinces of near-equal areas separated by a roughly meridional boundary. The residence time is about 4.5 (3.5) years in the western (eastern) province. The exchange between these provinces is effected through a slow cyclonic circulation, which is well constrained in the western basin by preservation of f/H, where f is the Coriolis parameter and H is depth. Secondary provinces of varied shapes covering smaller areas are identified with residence times ranging from about 0.4 to 1.2 years or so. Except for the main provinces, the deep Lagrangian geography does not resemble the surface Lagrangian geography recently inferred from satellite-tracked drifter trajectories. This implies disparate connectivity characteristics with potential implications for pollutant (e.g., oil) dispersal at the surface and at depth. Support for our results is provided by a Markov-chain analysis of satellite-tracked profiling (Argo) floats, which, while forming a smaller dataset and having seemingly different water-following characteristics than the RAFOS floats, replicate the main aspects of the Lagrangian geography. Our results find further validation in independent results from a chemical tracer release experiment.

Depth Control Method of Profiling Float Based on an Improved Double PD Controller

A kinematic equation of profiling float is nonlinear and has time-varying parameters. Traditional PD controllers not only demonstrate an inconsistent response to different depth controls but also face problems of overshooting and high power consumption. To realize the goal of depth control of profiling buoy under low power consumption, an improved double PD control method was proposed in this paper. The real-time prediction of position and low-power running of the sensor were realized through sparse sampling and depth prediction. The combination control over position, speed, and flow was realized by introducing the speed and flow expectation function. Then, a MATLAB/Simulink simulation model was constructed, and the proposed controller was compared with a single PD controller and an improved single PD controller. Among ten depth control tests, the proposed method was superior given its short response time, small overshooting, small steady-state error, and low power consumption. Moreover, it achieved a consistent control effect on different target depths. The simulation results demonstrated that a nonlinear and time-varying floating system controlled by the proposed method has favorable robustness and stability. This system will consume minimal power simultaneously.

Water Mass Transformation in the Greenland Sea during the Period 1986–2016

AbstractHydrographic measurements from ships, autonomous profiling floats, and instrumented seals over the period 1986–2016 are used to examine the temporal variability in open-ocean convection in the Greenland Sea during winter. This process replenishes the deep ocean with oxygen and is central to maintaining its thermohaline properties. The deepest and densest mixed layers in the Greenland Sea were located within its cyclonic gyre and exhibited large interannual variability. Beginning in winter 1994, a transition to deeper (>500 m) mixed layers took place. This resulted in the formation of a new, less dense class of intermediate water that has since become the main product of convection in the Greenland Sea. In the preceding winters, convection was limited to <300-m depth, despite strong atmospheric forcing. Sensitivity studies, performed with a one-dimensional mixed layer model, suggest that the deeper convection was primarily the result of reduced water-column stability. While anomalously fresh conditions that increased the stability of the upper part of the water column had previously inhibited convection, the transition to deeper mixed layers was associated with increased near-surface salinities. Our analysis further suggests that the volume of the new class of intermediate water has expanded in line with generally increased depths of convection over the past 10–15 years. The mean export of this water mass from the Greenland Sea gyre from 1994 to present was estimated to be 0.9 ± 0.7 Sv (1 Sv ≡ 106m3s−1), although rates in excess of 1.5 Sv occurred in summers following winters with deep convection.

Temperature profiling measurements by sea turtles improve ocean state estimation in the Kuroshio-Oyashio Confluence region

We demonstrate that assimilation of water temperature measurements by sea turtles into an operational ocean nowcast/forecast system improves representation of mesoscale eddies and front variations in the Kuroshio-Oyashio Confluence region. For a period from August to December in 2009, vertical ranges of the measurements by six turtles covered from surface to maximum 150 m depth, and the number of the measurements in the region was comparable to that of usual sampling by research vehicles and profiling floats. Comparison of the turtle measurements and products of an operational ocean nowcast/forecast system JCOPE2M elucidated low-temperature bias in JCOPE2M due to assimilation of high-resolution satellite sea surface temperature data. Additional assimilation of the turtle data into a modified JCOPE2M system with correction of the low-temperature bias led to reasonable modification of horizontal temperature/salinity gradient associated with northward moving warm core rings separating from the Kuroshio Extension and southward moving the Oyashio water intrusion branches. Effects of the turtle data assimilation propagated to far east of the Kuroshio-Oyashio confluence region along the subarctic boundary and front through advection. Another experiment assimilating the in situ profile data excluding the traditional temperature/salinity profiles data but including only the turtle data showed that the turtle measurements captured the warm core rings better than the Oyashio intrusion branches, suggesting possible optimum design of future ocean observing systems composed of different kinds of animals and/or autonomous underwater vehicles.

Deep-float salinity data synthesis for deep ocean state estimation: method and impact

The importance of deep ocean observations has been recognized with regard to changes in the deep ocean such as global bottom-water warming. Therefore, sustainable deep ocean monitoring networks that use autonomous profiling floats have been widely proposed, and a number of deep-float deployment initiatives have begun around the world. Deployed floats promise to provide unprecedented deep ocean information. However, present deep-float data are known to have biases. In particular, a depth-dependent bias in salinity data is a major issue that prevents us from constructing global deep ocean monitoring networks. This paper proposes a new approach to utilize ongoing deep-float salinity data to reduce the bias in estimates of the global full-depth ocean state. It reports results from comparative experiments with and without deep-float data by using the proposed approach to examine the impact of data from currently operating deep floats on ocean state estimates. The results demonstrate that available float data possibly contribute local corrections to the modeled climate ocean state. Furthermore, we clarify how interannual basin-scale estimations are controlled by available deep-float salinity data in two specific regions of the Southern and Indian Oceans.

ProVal: A New Autonomous Profiling Float for High Quality Radiometric Measurements

An efficient system to produce in situ high quality radiometric measurements is compulsory to rigorously perform the vicarious calibration of satellite sensors dedicated to Ocean Color Radiometry (OCR) and to validate their derived products. This requirement is especially needed during the early stages of an OCR satellite activity or for remote areas poorly covered by oceanographic cruises with possible bio-optical anomalies. Taking advantage of Argo’s profiling float, we present a new autonomous profiling float dedicated to in situ radiometric measurements. The float is based on the Provor CTS5 (manufacturer NKE) with an added novel two protruding arm design allowing for sensor redundancies, shading mitigation and near-surface data. Equipped with two identical radiometers on each arm that measure downward irradiance and upwelling radiance at seven wavelengths, the ProVal float generates both redundant radiometric profiles as well as an estimate of Remote Sensing Reflectance. Results from 449 profiles sampled obtained in the NW Mediterranean Sea and in the Indian sector of the Southern Ocean are presented to illustrate the ProVal float technical maturity. Analysis of the behavior of the profiling float, including tilting and ascent speeds, is presented. The vertical stability of the ProVal exhibits 85% of surface data of the Mediterranean Sea with a tilt smaller than 10 degrees. This percentage is 45% in the Southern Ocean due to rougher seas. Redundant sensors provide a characterization of the relative drift between sensors over the deployment which is found to be less than 0.15% per month over a year. Post-cruise calibration of a recovered float revealed no significant drift. As an example of the utility of ProVal floats, a match-up of Remote Sensing Reflectance measured with the European Space Agency Ocean and Land Color Imager (OLCI onboard Sentinel-3A & 3B) is shown. It follows that profiling floats, such as ProVal, could provide a significant contribution to an upcoming global System Vicarious Calibration of space-based radiometers.

Observing the Ice‐Covered Weddell Gyre With Profiling Floats: Position Uncertainties and Correlation Statistics

AbstractArgo‐type profiling floats do not receive satellite positioning while under sea ice. Common practice is to approximate unknown positions by linearly interpolating latitude‐longitude between known positions before and after ice cover, although it has been suggested that some improvement may be obtained by interpolating along contours of planetary‐geostrophic potential vorticity. Profiles with linearly interpolated positions represent 16% of the Southern Ocean Argo data set; consequences arising from this approximation have not been quantified. Using three distinct data sets from the Weddell Gyre—10‐day satellite‐tracked Argo floats, daily‐tracked RAFOS‐enabled floats, and a particle release simulation in the Southern Ocean State Estimate—we perform a data withholding experiment to assess position uncertainty in latitude‐longitude and potential vorticity coordinates as a function of time since last fix. A spatial correlation analysis using the float data provides temperature and salinity uncertainty estimates as a function of distance error. Combining the spatial correlation scales and the position uncertainty, we estimate uncertainty in temperature and salinity as a function of duration of position loss. Maximum position uncertainty for interpolation during 8 months without position data is 116 ± 148 km for latitude‐longitude and 92 ± 121 km for potential vorticity coordinates. The estimated maximum uncertainty in local temperature and salinity over the entire 2,000‐m profiles during 8 months without position data is 0.66 ∘C and 0.15 psu in the upper 300 m and 0.16 ∘C and 0.01 psu below 300 m.

Estimation of the numerical modeling accuracy of the Black Sea thermohaline fields based on using ARGO profiling floats

The paper considers the matters of numerical modeling estimation accuracy of temperature and salinity three-dimensional fields in the monitoring and forecasting center of the Black Sea. Automatic system of analysis and forecast of the Black Sea state is run in the center in an operational mode. The data of in situ measurements from ARGO profiling floats regularly provided by the European Marine Forecasting Service – Copernicus – were used to solve the problem. Spatial and temporal mismatch between the model data and in situ measurements was eliminated to form a joint sample of these two data sources. Comparison is performed for the time period from 2012 to 2015. The results show quite good simulation accuracy of the ther-mohaline fields, however, the problems of modeling the temperature fields in the 5-30 m layer were detected where there is a fairly narrow seasonal thermocline in late spring, summer and early autumn.

Inferring and Removing a Spurious Response in the Optical Backscattering Signal from an Autonomous Profiling Float

AbstractDevelopment of autonomous profiling floats, allowing for long-term continuous measurement of bio-optical variables, promises to significantly increase our knowledge of the variability of the particulate optical backscattering coefficient bbp in marine environments. However, because autonomous floats are designed for unattended data collection and only rarely are recovered for analysis of the condition of the sensors in situ, the quality-control analysis of float data streams is of paramount importance in both a particular dataset and the larger understanding of the response of sensors over the lifetime of the floats. Anomalous data from a backscattering sensor (MCOMS) mounted on autonomous profiling floats are reported here. The observed sensor behavior, which presents itself as significant differences in the values observed at the parking depth between profiles, caused by a steady increase in the signal during the profiling time, is neither common to all sensors nor can it be a function of changes in the particle population. A simple quality-control procedure that is able to detect this spurious sensor response is proposed. Further characterization of this effect will require laboratory experimentation under controlled conditions of temperature and pressure.

A validation and comparison study of new, compact, versatile optodes for oxygen, pH and carbon dioxide in marine environments

Continuous monitoring of dissolved oxygen, pH and carbon dioxide are of great importance in oceanography. Sensors are the optimal tools for in situ measurements from mobile platforms, like Autonomous Underwater Vehicles (AUVs) or Argo profiling floats, and for shipboard deployments. A validation study of small, versatile, easy-to-use, stand-alone optodes is presented. Each analyte can be read out with the identical optoelectronics which greatly minimizes the costs of the hardware needed. Several deployments were performed to evaluate the applicability of the sensors. The deployments varied in terms of duration (profiling, long-term monitoring 5 days to 8 weeks) and environmental conditions (salinity: 6–33 PSS; temperature: 9–25 °C). A set of sensors was successfully deployed at a mooring buoy, in an aquaculture facility and in the Monterey Bay Aquarium Open Sea Exhibition. They were also integrated in an AUV and a profiling float. The performance of the optodes was evaluated in comparison with commercially available sensors for dissolved oxygen (Aanderaa Data Instruments AS, Sea-Bird Scientific, OxyGuard®), pH (Hach, Satlantic) and carbon dioxide (Turner design). The data collected by our optodes and the commercially available sensors is generally in good agreement showing that the new, compact sensor device in combination with sensor foils (pO2, pH, pCO2) can be a valuable tool for many applications in oceanography. The data also revealed the importance of the calibration strategy since inappropriate calibration resulted in an offset in the measured parameter. The efficiency of simple biofouling protection strategy (copper guard) for prolong measurements in highly dynamic environments was also demonstrated.

Biological and physical controls on the oxygen cycle in the Kuroshio Extension from an array of profiling floats

The Kuroshio Extension (KE) is a current associated with the largest CO2 flux into the Pacific Ocean, a broad region of uptake that extends across the Pacific basin between the subarctic and subtropical regions. The relative importance of the biological and physical processes controlling this sink is uncertain. Because oxygen is stoichiometrically linked to changes in dissolved inorganic carbon due to photosynthesis and respiration and subject to many of the same physical drivers as the CO2 flux, in situ oxygen measurements help to determine the processes driving this large CO2 flux. We analyzed data from eight Argo profiling floats equipped with oxygen sensors to estimate oxygen fluxes in the upper ocean of the KE region (approximate bounds: 25°N to 45°N, 135°E to 155°E). In situ air calibrations of these sensors allowed us to accurately measure air-sea oxygen differences, which largely control the flux of oxygen to and from the atmosphere. To characterize distinct biogeographical regions in the Kuroshio Extension and to accommodate seasonal north-south shifts in the location of the regional boundaries, we averaged oxygen measurements from different floats along isopycnal surfaces into 3 regions based on temperature-salinity relationships: North KE, Central KE, and South KE. Using these regional concentration time series, we determined the physical fluxes using an upper ocean layered model and calculated the residual oxygen flux, a combination of column-integrated net community production and physical processes unexplained by the model. The annual oxygen budget is largely a balance of air-sea exchange and the residual oxygen term. Residual oxygen fluxes are -5.4 ± 1.1, -5.9 ± 0.1, and 2.1 ± 2.2 mol O2 m-2 yr-1 (where negative is a loss from the upper ocean) for the North, Central, and South KE regions, respectively. The North and Central KE are regions of mode water formation, which balances the large air-sea fluxes into the ocean. The South KE oxygen residual indicates a biologically produced flux to the atmosphere in two out of three years that agrees with previous estimates of subtropical annual net community production (ANCP) but exhibits high interannual variability. This study suggests that physical processes are the primary drivers for the annual uptake of the gases oxygen and carbon dioxide in the Central KE region where the annual CO2 uptake is strongest.

Water masses in the far western equatorial Pacific during the winters of 2010 and 2012

Conductivity-temperature-depth (CTD) data obtained during the 2010 La Nina winter and the 2012 normal winter, combined with concurrent Argo profiling float data, provide a quasi-synoptic description of the water mass distributions and their variations in the far western equatorial Pacific Ocean. The water mass connection between the western Pacific and the east Indonesian seas is emphasized. Analysis indicates that the North Pacific Tropical Water (NPTW, S >34.9) carried by the Mindanao Current southward and the South Pacific Tropical Water (SPTW, S >35.1) from the southern hemisphere meet in the area. Observations suggest that the southward transport of the NPTW is stronger in 2010 than in 2012 due to enhanced advection of the Mindanao Current. The distribution of SPTW, which crosses the equator in the northwest direction and retroflects back to the interior Pacific Ocean, is found to retreat from 4°–5°N in 2012 to 2°–3°N in 2010 La Nina peak in the 130°E section. A relatively fresh tropical subsurface water is identified in between the NPTW and the SPTW, moving eastward with the North Equatorial Countercurrent into the equatorial Pacific Ocean. However, the salinity maximum of this subsurface fresh water is found to decrease eastward, suggesting that the salinity maximum is generated either by strong diapycnal mixing or by isopycnal mixing of temporally entrained Indonesian sea water into the area.

Hydrodynamic Analysis of a Marine Current Energy Converter for Profiling Floats

With the continuous improvement of people’s interest in ocean exploration, research on deep-water profiling floats has received more and more attention. Energy supply is the key factor that restricts the working hours of deep-water floats. For this consideration, a marine current energy converter for deep-water profiling floats is proposed in this paper. A spiral involute blade is designed so that energy can be captured in two directions. Specifically, in the shallow sea area, the energy of the radial current is captured, and in the deep-sea area, the axial relative flow energy of the floats’ autonomous up and down motions is captured. This captured energy is then converted into electrical energy to charge the battery and extend the working time of the floats. The novel spiral involute blade has unique hydrodynamic characteristics. The turbine’s self-starting performance and its capacity coefficient are the main research topics studied using the computational fluid dynamics technique. Through numerical analysis and simulation, the self-starting response range and energy capture were obtained. This paper verifies the feasibility of this innovative idea using a theory analysis and provides the basis for future prototype testing and further applied research.

Transport, properties, and life cycles of mesoscale eddies in the eastern tropical South Pacific

Abstract. The influence of mesoscale eddies on the flow field and the water masses, especially the oxygen distribution of the eastern tropical South Pacific, is investigated from a mooring, float, and satellite data set. Two anticyclonic (ACE1/2), one mode-water (MWE), and one cyclonic eddy (CE) are identified and followed in detail with satellite data on their westward transition with velocities of 3.2 to 6.0 cm s−1 from their generation region, the shelf of the Peruvian and Chilean upwelling regime, across the Stratus Ocean Reference Station (ORS; ∼20∘ S, 85∘ W) to their decaying region far west in the oligotrophic open ocean. The ORS is located in the transition zone between the oxygen minimum zone and the well oxygenated South Pacific subtropical gyre. Velocity, hydrographic, and oxygen measurements at the mooring show the impact of eddies on the weak flow region of the eastern tropical South Pacific. Strong anomalies are related to the passage of eddies and are not associated with a seasonal signal in the open ocean. The mass transport of the four observed eddies across 85∘ W is between 1.1 and 1.8 Sv. The eddy type-dependent available heat, salt, and oxygen anomalies are 8.1×1018 J (ACE2), 1.0×1018 J (MWE), and -8.9×1018 J (CE) for heat; 25.2×1010 kg (ACE2), -3.1×1010 kg (MWE), and -41.5×1010 kg (CE) for salt; and -3.6×1016 µmol (ACE2), -3.5×1016 µmol (MWE), and -6.5×1016 µmol (CE) for oxygen showing a strong imbalance between anticyclones and cyclones for salt transports probably due to seasonal variability in water mass properties in the formation region of the eddies. Heat, salt, and oxygen fluxes out of the coastal region across the ORS region in the oligotrophic open South Pacific are estimated based on these eddy anomalies and on eddy statistics (gained out of 23 years of satellite data). Furthermore, four profiling floats were trapped in the ACE2 during its westward propagation between the formation region and the open ocean, which allows for conclusions on lateral mixing of water mass properties with time between the core of the eddy and the surrounding water. The strongest lateral mixing was found between the seasonal thermocline and the eddy core during the first half of the eddy lifetime.

Autonomous profiling float observations reveal the dynamics of deep biomass distributions in the denitrifying oxygen minimum zone of the Arabian Sea

Data from 13 autonomous profiling BGC-Argo floats, equipped with biogeochemical and bio-optical sensors deployed between 2011 and 2016, were used to explore the potential of bio-optical methods to map deep biomass distribution in the Arabian Sea oxygen minimum zone (OMZ). Dissolved oxygen sensors revealed concentrations below 5 μmol kg −1 for much of the depth range between 200 and 400 m and below 1 μmol kg −1 in the centre of the OMZ, which is well below climatological values. Optical particle backscatter sensors revealed intensities within the upper OMZ that were nearly as high as within the euphotic zone. The distribution of these particulate scatterers was confined to oxygen concentrations below 1 μmol kg −1 , with vertical distributions that exhibited maxima just below the top of the OMZ and decreased downward with similar attenuation to that expected for sinking organic matter. These distributions were very similar to those of nitrate deficits (ΔNO 3 ) estimated from a float with an ultra-violet nitrate sensor (R 2 = 0.54, p < 0.01), suggesting backscatter may be a useful proxy to investigate the changing dynamics of denitrification. Weak correlations between the upper OMZ particulate backscatter signals and both backscatter and chlorophyll fluorescence in the overlying euphotic zone is consistent with previous suggestions that advection of organic matter from remote sources is likely to be an important control on denitrification in the Arabian Sea. These results offer a useful path for examining denitrification dynamics in OMZs, which can be augmented by additional sensors for pH to quantify carbon respiration and dissolved organic matter to examine its possible importance relative to particulate oxygen demand. They clearly demonstrate the powerful insights that can be gained from arrays of autonomous profiling floats equipped with biogeochemical sensors for understanding globally significant, large-scale biogeochemical patterns and processes. • BGC-Argo data were used to map deep biomass distribution in the Arabian Sea OMZ. • Oxygen concentration in the centre of the OMZ, which is below climatological values • Increased scattering layer was confined to oxygen concentrations below 1 μmol kg −1 . • Optical backscattering may be a useful proxy to investigate denitrification.

Profiling Floats in SOCCOM: Technical Capabilities for Studying the Southern Ocean

AbstractWe report on profiling float technology used in the Southern Ocean Carbon and Climate Observations and Models (SOCCOM) program, a 6 year study of the interaction of ocean physics and the carbon cycle in the Southern Ocean. A central part of this program is to produce and deploy 200 profiling floats equipped with CTD units and chemical sensors capable of measuring dissolved oxygen, nitrate, pH, chlorophyll fluorescence, and particulate backscatter. The performance of the first 63 floats deployed in SOCCOM is examined, and examples of the design criteria used in producing these floats are shown. Some of the sensors require surface measurements to be made in the dark at regular intervals, and the probability of ascending to the sea surface in the dark is estimated as a function of year‐day and latitude. An energy budget derived from laboratory measurements shows that only about 25% of the total energy stored in the batteries is used by the biogeochemical sensors, which bodes well for the long‐term survivability of the floats. The ice‐avoidance algorithm is discussed in detail, and it is shown that it is working as designed and allowing unprecedented numbers of profiles to be collected beneath the wintertime ice cover. The overall reliability of the first group of SOCCOM floats is compared with a much larger ensemble of Argo floats; the results show that the SOCCOM floats are surviving at a rate similar to the Argo floats, which have been shown to have lifetimes in excess of 5 years.

Assessment of Autonomous pH Measurements for Determining Surface Seawater Partial Pressure of CO2

AbstractThe Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) program currently operates &gt;80 profiling floats equipped with pH sensors in the Southern Ocean. Theoretically, these floats have the potential to provide unique year‐around estimates of pCO2 derived from pH measurements. Here, we evaluate this approach in the field by comparing pCO2 estimates from pH sensors to directly measured pCO2. We first discuss data from a ship's underway system which covered a large range in temperature (2–30°C) and salinity (33.6–36.5) over 43 days. This pH sensor utilizes the same sensing technology but with different packaging than those on SOCCOM floats. The mean residual varied between −4.6 ± 4.1 and 8.6 ± 4.0 (1σ) μatm, depending on how the sensor was calibrated. However, the standard deviation of the residual, interpreted as the ability to track spatiotemporal variability, was consistently &lt; 5 μatm and was independent of the calibration method. Second, we assessed the temporal stability of this approach by comparing pCO2 estimated from four floats over 3 years to the Hawaii Ocean Time‐series. Good agreement of −2.1 ± 10.4 (1σ) µatm was observed, with coherent seasonal cycles. These results demonstrate that pCO2 estimates derived from profiling float pH measurements appear capable of reproducing spatiotemporal variations in surface pCO2 measurements and should provide a powerful observational tool to complement current efforts to understand the seasonal to interannual variability of surface pCO2 in underobserved regions of the open ocean.