Glider Data Research Articles

Erosion of the Subsurface Salinity Maximum of the Loop Current Eddies From Glider Observations and a Numerical Model

AbstractThe erosion of the subsurface salinity maximum, signature of the Caribbean Subtropical UnderWater (SUW), within the Loop Current Eddy (LCE) Poseidon (August 2016 to July 2017) in the Gulf of Mexico (GoM) and the formation of the Gulf Common Water (GCW) during its journey westward, was observed using glider data. Most of the dilution of the SUW high‐salinity core within Poseidon occurs during late autumn and winter associated with Northern winds and mixed‐layer deepening. The physical processes that contribute to salt dilution of the SUW inside the LCEs' core are investigated using a numerical regional model. The analysis of the salt budget in a long‐lasting numerical LCE and a composite analysis of sixteen LCEs reveal that the salinity trend is mostly explained by the vertical salinity diffusion. Cold and dry Northern winds during the first winter drive strong negative net heat fluxes that trigger turbulent flux of salt into the LCEs' thermostad and dilution of the SUW high‐salinity core below. The vertical salinity diffusion continues homogenizing the salinity in the upper ocean until the vertical gradient of salinity is negligible. As a result, SUW is transformed to precursor of GCW that is ultimately diffused to surrounding waters in the western GoM. Although the contribution of advection to the salinity trend above the isopycnal of 1,026 kg m−3 is of second order, below is the most important process driving loss of salinity, presumably due to, eddy‐eddy interactions during LCEs' westward propagation and eddy pumping (upwelling) during the LCEs' decaying phase along the western slope.

Near-Automatic Routine Field Calibration/Correction of Glider Salinity Data Using Whitespace Maximization Image Analysis of Theta/S Data

Glider vehicles are now perhaps some of the most prolific providers of real-time and near real-time operational oceanographic data. However the data from these vehicles can and should be considered to have a long term legacy value capable of playing a critical role in understanding and separating inter-annual, inter-decadal and long term global change. To achieve this we have to go further than simply assuming the manufacturers calibrations; and field correct glider data in a more traditional way, for example, by careful comparison to water bottle calibrated lowered CTD datasets and/or ‘gold’ standard recent climatologies. In this manuscript we bring into the 21st century an historical technique that has been used manually by oceanographers for many years/decades for field correction, thermal lag correction and adjustment for biological fouling. The technique has now been made semi-automatic for machine processing of oceanographic glider data, although it’s future and indeed its origins have far wider scope. The subject of this manuscript is drawn from the original Description of Work (DoW) for a key task in the recently completed JERICO-NEXT (Joint European Research Infrastructure Network for Coastal observatories) EU funded program, but goes on to consider future application and the suitability for integration with machine learning.

Occurrence and seasonal variability of Dense Shelf Water Cascades along Australian continental shelves

Transport of water between the coast and the deeper ocean, across the continental shelf, is an important process for the distribution of biota, nutrients, suspended and dissolved material on the shelf. Presence of denser water on the inner continental shelf results in a cross-shelf density gradient that drives a gravitational circulation with offshore transport of denser water along the sea bed that is defined as Dense Shelf Water Cascade (DSWC). Analysis of field data, collected from multiple ocean glider data missions around Australia, confirmed that under a range of wind and tidal conditions, DSWC was a regular occurrence during autumn and winter months over a coastline spanning > 10,000 km. It is shown that even in the presence of relatively high wind- and tidal-induced vertical mixing, DSWCs were present due to the strength of the cross-shelf density gradient. The occurrence of DSWC around Australia is unique with continental scale forcing through air-sea fluxes that overcome local wind and tidal forcing. It is shown that DSWC acts as a conduit to transport suspended material across the continental shelf and is a critical process that influences water quality on the inner continental shelf.

Long duration underwater glider dataset: Indian Ocean from Perth, Australia to Mirissa, Sri Lanka.

This data was collected using an underwater research vehicle, Slocum glider. The glider is an autonomous robot that is able to measure several water properties from surface to 1000 m depth. The duration of missions for underwater gliders are on the order of 1 month to over a year. Detailed here is the live satellite telemetered dataset as transmitted during mission.Dataset includes positional data, vehicle engineering, attitude, temperature, salinity, and depth averaged currents. Raw data as well as some derived variables from the raw data are included in this dataset. This data is transmitted every couple hours and comprises of a subset of the data stored on the vehicle's internal memory.The data is returned in segmented files which comprises of an underwater segment bookended by GPS positions. Because most analysis require longer time series, effort has been taken to conglomerate the segment datasets into a single continuous dataset stitching together the segments. The platform chosen for this is currently MATLAB.This data can provide the community with an example dataset of underwater glider data pertinent to a long duration and low energy glider mission. It also includes ocean measurements of temperature, salinity, and ocean currents. Built into the dataset object are various functions designed to help the user navigate and display a glider's collected data.The effort is being made to serve future datasets, 2017 and onward, via ERDAPP at the following location: http://slocum-data.marine.rutgers.edu/erddap/index.htmlAnalyzed by the Applied Ocean Research article: Modeling for the Performance of Navigation, Control and Data Post-Processing of Underwater Gliders where it is used for flight efficiency analysis as well as ocean model comparisons.

Real-time quality control of data from Sea-Wing underwater glider installed with Glider Payload CTD sensor

Profiles observed by Sea-Wing underwater gliders are widely applied in scientific research. However, the quality control (QC) of these data has received little attention. The mismatch between the temperature probe and conductivity cell response times generates erroneous salinities, especially across a strong thermocline. A sensor drift may occur owing to biofouling and biocide leakage into the conductivity cell when a glider has operated for several months. It is therefore critical to design a mature real-time QC procedure and develop a toolbox for the QC of Sea-Wing glider data. On the basis of temperature and salinity profiles observed by several Sea-Wing gliders each installed with a Sea-Bird Glider Payload CTD sensor, a real-time QC method including a thermal lag correction, Argo-equivalent real-time QC tests, and a simple post-processing procedure is proposed. The method can also be adopted for Petrel gliders.

Comparison of fin whale 20 Hz call detections by deep-water mobile autonomous and stationary recorders.

Acoustically equipped deep-water mobile autonomous platforms can be used to survey for marine mammals over intermediate spatiotemporal scales. Direct comparisons to fixed recorders are necessary to evaluate these tools as passive acoustic monitoring platforms. One glider and two drifting deep-water floats were simultaneously deployed within a deep-water cabled hydrophone array to quantitatively assess their survey capabilities. The glider was able to follow a pre-defined track while float movement was somewhat unpredictable. Fin whale (Balaenoptera physalus) 20 Hz pulses were recorded by all hydrophones throughout the two-week deployment. Calls were identified using a template detector, which performed similarly across recorder types. The glider data contained up to 78% fewer detections per hour due to increased low-frequency flow noise present during glider descents. The glider performed comparably to the floats and fixed recorders at coarser temporal scales; hourly and daily presence of detections did not vary by recorder type. Flow noise was related to glider speed through water and dive state. Glider speeds through water of 25 cm/s or less are suggested to minimize flow noise and the importance of glider ballasting, detector characterization, and normalization by effort when interpreting glider-collected data and applying it to marine mammal density estimation are discussed.

GliderTools: A Python Toolbox for Processing Underwater Glider Data

Underwater gliders have become widely used in the last decade. This has led to a proliferation of data and the concomitant development of tools to process the data. These tools are focused primarily on converting the data from its raw form to more accessible formats and often rely on proprietary programming languages. This has left a gap in the processing chain for glider data, specifically academics, who often need to perform secondary quality control, calibrate, correct, interpolate and visualise data. Here, we present GliderTools, an open-source Python package that addresses these needs of the glider user community. The tool is designed to change the focus from the processing to the data. In this paper, we present a set of tools, that includes: secondary cleaning and calibration, calibration procedures for bottle samples, fluorescence quenching correction, photosynthetically available radiation corrections and data interpolation in the vertical and horizontal dimensions. Many of these processes have been described in several other studies, but do not exist in a collated package designed for underwater glider data. Importantly, we provide potential users with guidelines on how these tools are used so that they can be easily and rapidly accessible to a wide range of users that span the student to the experienced researcher. We recognise that this package may not be all-encompassing for every user and we thus welcome community contributions and promote GliderTools as a community-driven project for scientists.

Observations of Layering under a Warm-Core Ring in the Gulf of Mexico

AbstractTwo glider transects in the Gulf of Mexico reveal fine-vertical-scale thermohaline structures within a Loop Current eddy (LCE). Partially compensating temperature and salinity anomalies are shown to organize as thin layers below the eddy and near its edges. The anomalies have vertical scales ranging from 2 to 60 m and extend laterally over distances up to 120 km. These structures are evident in synthetic acoustic reflectivity derived from the glider data and are reminiscent of the intense layering observed in seismic imagery around meddies, Agulhas rings, and warm-core Kuroshio rings. The observed layers are aligned with the geostrophic streamfunction rather than isopycnals and develop preferentially in zones of intense vertical shear. These observations suggest that tracer stirring by the eddy’s vertically sheared azimuthal flow might be an important process for their generation. In an attempt to rationalize this process, high-resolution quasigeostrophic simulations were performed using an idealized anticyclonic ring for the initial conditions. As the vortex destabilizes, layering rapidly develops in the model, resulting in structures similar to those found in the observation data. Passive tracer experiments also suggest that the layers form through differential advection of the tracer field by the vertically sheared flow associated with the LCE.

Constructing the Three-Dimensional Structure of an Anticyclonic Eddy in the South China Sea Using Multiple Underwater Gliders

AbstractMesoscale eddies have great influence on heat and material transport in the ocean and thus play an important role in modulating the global climate variability. However, our understanding of their fine three-dimensional (3D) thermohaline and biogeochemical structure remains incomplete because of the scarcity of high-resolution measurements. This research aims to construct the fine 3D structure of an anticyclonic eddy in the northern South China Sea (NSCS) to validate the effectiveness of a glider network for observing mesoscale eddies. Twelve Petrel gliders were deployed in NSCS during August 2017 to gather fine information of an anticyclonic eddy. By combining the high-resolution in situ glider data and the sea level anomaly data, we have constructed a detailed 3D structure of the eddy. The analysis results of the absolute dynamic topography map and the water mass comparison imply that the anticyclonic eddy may generate from eddy shedding of the Kuroshio loop current. The maximum potential temperature anomaly (over 3°C) appears at the thermocline, and the maximum salinity anomaly (~0.8 psu) exists at ~50 m. The maximum value of the dissolved oxygen concentration (~7.5 mg L−1) appears at 50–80 m. The maximum chlorophyll concentration (~1.2 μg L−1) lies at 80–120 m, just below that of the dissolved oxygen concentration. The colored dissolved organic matter concentration increases with depth, with the mean value being less than 1.23 ppb above 50 m and beyond 2.2 ppb at 500–800 m. The results verify the capability of the glider network to observe a fine-scaled 3D structure of mesoscale eddies and will provide a useful guide for future eddy observations.

Internal tide energy flux over a ridge measured by a co-located ocean glider and moored acoustic Doppler current profiler

Abstract. Internal tide energy flux is an important diagnostic for the study of energy pathways in the ocean, from large-scale input by the surface tide to small-scale dissipation by turbulent mixing. Accurate calculation of energy flux requires repeated full-depth measurements of both potential density (ρ) and horizontal current velocity (u) over at least a tidal cycle and over several weeks to resolve the internal spring–neap cycle. Typically, these observations are made using full-depth oceanographic moorings that are vulnerable to being “fished out” by commercial trawlers when deployed on continental shelves and slopes. Here we test an alternative approach to minimize these risks, with u measured by a low-frequency acoustic Doppler current profiler (ADCP) moored near the seabed and ρ measured by an autonomous ocean glider holding station by the ADCP. The method is used to measure the semidiurnal internal tide radiating from the Wyville Thomson Ridge in the North Atlantic. The observed energy flux (4.2±0.2 kW m−1) compares favourably with historic observations and a previous numerical model study. Error in the energy flux calculation due to imperfect co-location of the glider and ADCP is estimated by subsampling potential density in an idealized internal tide field along pseudorandomly distributed glider paths. The error is considered acceptable (<10 %) if all the glider data are contained within a “watch circle” with a diameter smaller than 1∕8 the mode-1 horizontal wavelength of the internal tide. Energy flux is biased low because the glider samples density with a broad range of phase shifts, resulting in underestimation of vertical isopycnal displacement and available potential energy. The negative bias increases with increasing watch circle diameter. If watch circle diameter is larger than 1∕8 the mode-1 horizontal wavelength, the negative bias is more than 3 % and all realizations within the 95 % confidence interval are underestimates. Over the Wyville Thomson Ridge, where the semidiurnal mode-1 horizontal wavelength is ≈100 km and all the glider dives are within a 5 km diameter watch circle, the observed energy flux is estimated to have a negative bias of only 0.4 % and an error of less than 3 % at the 95 % confidence limit. With typical glider performance, we expect energy flux error due to imperfect co-location to be <10 % in most mid-latitude shelf slope regions.

OceanGliders: A Component of the Integrated GOOS

The OceanGliders program started in 2016 to support active coordination and enhancement of global glider activity. OceanGliders contributes to the international efforts of the Global Ocean Observation System (GOOS) for Climate, Ocean Health, and Operational Services. It brings together marine scientists and engineers operating gliders around the world: (1) to observe the long-term physical, biogeochemical, and biological ocean processes and phenomena that are relevant for societal applications; and, (2) to contribute to the GOOS through real-time and delayed mode data dissemination. The OceanGliders program is distributed across national and regional observing systems and significantly contributes to integrated, multi-scale and multi-platform sampling strategies. OceanGliders shares best practices, requirements, and scientific knowledge needed for glider operations, data collection and analysis. It also monitors global glider activity and supports the dissemination of glider data through regional and global databases, in real-time and delayed modes, facilitating data access to the wider community. OceanGliders currently supports national, regional and global initiatives to maintain and expand the capabilities and application of gliders to meet key global challenges such as improved measurement of ocean boundary currents, water transformation and storm forecast.

Operational assimilation of glider temperature and salinity for an improved description of the Cyprus eddy

The authors demonstrate how assimilation of hydrographic data from a single ocean glider can significantly improve short-term regional forecasts. An operational data assimilation system for the Eastern Mediterranean is described and evaluated for a six-month numerical experiment consisting of two nearly-identical hydrodynamic model runs. In the assimilative run, glider profiles of temperature and salinity were assimilated daily into a high-resolution ocean forecast, after an initial spin up of one week. In the control run, the same initial and boundary conditions were used to produce an operational forecast, but without assimilation of in situ data. While both runs were similar for most of the time and most of the domain, significant differences were found mostly near the region of assimilation, particularly when the glider passed through the anticyclonic Cyprus eddy, but also far away. The spatial scale at which the assimilation of the glider data improved the forecast is up to 40–50 km around the glider. Root mean square differences of the misfits between the temperature and salinity observations and the model background field at those locations were approximately 15% lower in the assimilative run. Improvements in the forecasting capability of surface currents were found and would provide a significant improvement of predictive capacity for applications such as pollutant spreading or offshore operational safety.

Temporal and Spatial Hydrodynamic Variability in the Mallorca Channel (Western Mediterranean Sea) From 8 Years of Underwater Glider Data

AbstractEight years of glider data are used to characterize the temporal and spatial variability of a region in the western Mediterranean that will constitute one of the targets for the calibration phase of the Surface Water and Ocean Topography (SWOT) satellite mission. The characteristic horizontal dimension of mesoscale instabilities in the Mallorca channel is 6.0 km. The temporal evolution of intermediate water masses is dominated by an increase over time of the characteristic temperature values. Western Mediterranean and Levantine Intermediate waters display an increase of the temperature extrema of 0.064 ± 0.002 and 0.044 ± 0.002 °C/year between 2011 and 2018, respectively. At the layer of Levantine Intermediate water the salinity temporal regression reveals a mean trend of 0.010 year−1. Temperature annual cycle shows an averaged temperature gradient of ∼6 °C in 6 months at the upper layer, with a disconnection with the annual cycle at 100‐m depth. The circulation across the channel is dominated by high‐frequency variability. The signature of eddies with radius ranging from 5 to 18 km is apparent in 16% of the transects analyzed and mainly in spring and summer, with a dominance of subsurface cyclonic eddies. Two‐way flow controls the annual cycle of the water transport through the channel with prevalence of the inflow of Atlantic water. Variations of water transport over timescales of weeks to months can be similar to those identifiable as seasonal changes.

Southern Ocean Seasonal Restratification Delayed by Submesoscale Wind–Front Interactions

AbstractOcean stratification and the vertical extent of the mixed layer influence the rate at which the ocean and atmosphere exchange properties. This process has direct impacts for anthropogenic heat and carbon uptake in the Southern Ocean. Submesoscale instabilities that evolve over space (1–10 km) and time (from hours to days) scales directly influence mixed layer variability and are ubiquitous in the Southern Ocean. Mixed layer eddies contribute to mixed layer restratification, while down-front winds, enhanced by strong synoptic storms, can erode stratification by a cross-frontal Ekman buoyancy flux. This study investigates the role of these submesoscale processes on the subseasonal and interannual variability of the mixed layer stratification using four years of high-resolution glider data in the Southern Ocean. An increase of stratification from winter to summer occurs due to a seasonal warming of the mixed layer. However, we observe transient decreases in stratification lasting from days to weeks, which can arrest the seasonal restratification by up to two months after surface heat flux becomes positive. This leads to interannual differences in the timing of seasonal restratification by up to 36 days. Parameterizing the Ekman buoyancy flux in a one-dimensional mixed layer model reduces the magnitude of stratification compared to when the model is run using heat and freshwater fluxes alone. Importantly, the reduced stratification occurs during the spring restratification period, thereby holding important implications for mixed layer dynamics in climate models as well as physical–biological coupling in the Southern Ocean.

Remote and local drivers of oxygen and nitrate variability in the shallow oxygen minimum zone off Mauritania in June 2014

Abstract. Upwelling systems play a key role in the global carbon and nitrogen cycles and are also of local relevance due to their high productivity and fish resources. To capture and understand the high spatial and temporal variability in physical and biogeochemical parameters found in these regions, novel measurement techniques have to be combined in an interdisciplinary manner. Here we use high-resolution glider-based physical–biogeochemical observations in combination with ship-based underwater vision profiler, sensor and bottle data to investigate the drivers of oxygen and nitrate variability across the shelf break off Mauritania in June 2014. Distinct oxygen and nitrate variability shows up in our glider data. High-oxygen and low-nitrate anomalies were clearly related to water mass variability and probably linked to ocean transport. Low-oxygen and high-nitrate patches co-occurred with enhanced turbidity signals close to the seabed, which suggests locally high microbial respiration rates of resuspended organic matter near the sea floor. This interpretation is supported by high particle abundance observed by the underwater vision profiler and enhanced particle-based respiration rate estimates close to the seabed. Discrete in situ measurements of dissolved organic carbon and amino acids suggest the formation of dissolved organic carbon due to particle dissolution near the seabed fueling additional microbial respiration. During June an increase in the oxygen concentration on the shelf break of about 15 µmol kg−1 was observed. These changes go along with meridional circulation changes but cannot be explained by typical water mass property changes. Thus our high-resolution interdisciplinary observations highlight the complex interplay of remote and local physical–biogeochemical drivers of oxygen and nitrate variability off Mauritania, which cannot be captured by classical shipboard observations alone.

Glider data collected during the Algerian Basin Circulation Unmanned Survey

Abstract. We present data collected in the framework of the Algerian BAsin Circulation Unmanned Survey (ABACUS) project. The main objective of ABACUS is the monitoring of the basin circulation and of the surface and intermediate water masses' physical and biological properties in a key region of the Mediterranean Sea circulation. Data presented here have been collected through deep glider cruises in the Western Mediterranean Sea during the autumns of 2014, 2015 and 2016; activities at sea are expected to be repeated during the coming years, so that the dataset will be extended. Glider missions were conducted in the Algerian Basin, between the island of Mallorca and the Algerian coast. Across the three glider missions, eight repeated transects were completed which enabled us to investigate the basin-scale circulation and the presence of mesoscale structures, utilising both the adaptive sampling capabilities of the gliders and the higher resolution of the data. After collection, all data passed a quality control procedure and were then made available through an unrestricted repository host by the SOCIB Data Centre at https://doi.org/10.25704/b200-3vf5. The actual dataset spans three autumn seasons, providing an important contribution to the data collection in the chronically undersampled Algerian Basin. Temperature and salinity data collected in the first 975 m of the water column allowed us to identify the main water masses and describe their characteristics, improving the understanding of the dynamics of the region. On the timescale of the project, data show a large variability in the surface layer and reduced variability in the intermediate and deep layers. Our measurements have been successfully compared to data previously collected in the area from 1909 to 2011. Results showed similar overall distribution, ranges and variability to the historical data, with no outliers in the surface or deep layers.

Why Gliders Appreciate Good Company: Glider Assimilation in the Oregon‐Washington Coastal Ocean 4DVAR System With and Without Surface Observations

AbstractGliders are low‐power autonomous underwater vehicles used to obtain oceanic measurements in vertical sections. Assimilation of glider temperature and salinity into coastal ocean circulation models holds the potential to improve the ocean subsurface structure estimate. In this study, the impact of assimilation of glider observations is studied using a four‐dimensional variational (4DVAR) data assimilation and forecast system set offshore of Oregon and Washington on the U.S. West Coast. Four test cases are compared: (1) no assimilation, (2) assimilation of glider temperature and salinity data alone, (3) assimilation of the glider data in combination with the surface observations including satellite sea surface temperature, sea surface height, and high‐frequency radar surface velocities, and (4) assimilation of the surface data alone. It is found that the assimilation of glider observations alone creates unphysical eddies in the vicinity of the glider transect. As a consequence, the forecast errors in the surface velocity and temperature increase compared to the case without data assimilation. Assimilation of surface and subsurface observations in combination prevents these features from forming and reduces the errors in the forecasts for the subsurface fields compared to the other three experiments. These improvements persisted in 21‐day forecasts run after the last data assimilation cycle.

Closing the Gap Between the Coral Sea and the Equator: Direct Observations of the North Australian Western Boundary Currents

AbstractBoundary currents along northeastern Australia provide source waters for the East Australian Current and redistribute water to the equator within the Gulf of Papua Current (GPC). These currents are formed following the bifurcation of two Coral Sea westward jets, the North Vanuatu Jet (NVJ) and the North Caledonian Jet. While the existence of the boundary currents has been inferred from limited geostrophic sections, gridded climatological analyses, and modeling studies, no direct measurements have been collected. This study synthesizes current and water property measurements from a 7‐year record at Lizard Island and multiple Seaglider deployments between 2010 and 2014. Both repeat glider transects at 14.5 and 18°S and deployments spanning latitudes between 18 and 11°S are included. Cross‐track velocities of these currents show their vertical structure, seasonal changes, and the spatial translation of the bifurcation latitude. The NVJ bifurcation varies seasonally about a mean latitude between 14.4 and 14.7°S. It has a peak northward extent in summer, when the East Australian Current and GPC exhibit maximum and minimum transports, respectively. The deeper GPC originates from the North Caledonian Jet south of 18°S and varies seasonally by 4 Sv. When the westward flow of the NVJ reaches the boundary, the GPC's northward transport grows by ~13 Sv. The salinity signature of the glider data confirms that up to 6 Sv of this influx is sourced from the base of the NVJ. The observed seasonal cycle of current strength and changes in along boundary transport are consistent with the results from an ocean general circulation model.

Annual and Interannual Variability in the California Current System: Comparison of an Ocean State Estimate with a Network of Underwater Gliders

AbstractA data-constrained state estimate of the southern California Current System (CCS) is presented and compared with withheld California Cooperative Oceanic Fisheries Investigations (CalCOFI) data and assimilated glider data over 2007–17. The objective of this comparison is to assess the ability of the California State Estimate (CASE) to reproduce the key physical features of the CCS mean state, annual cycles, and interannual variability along the three sections of the California Underwater Glider Network (CUGN). The assessment focuses on several oceanic metrics deemed most important for characterizing physical variability in the CCS: 50-m potential temperature, 80-m salinity, and 26 kg m−3 isopycnal depth and salinity. In the time mean, the CASE reproduces large-scale thermohaline and circulation structures, including observed temperature gradients, shoaling isopycnals, and the locations and magnitudes of the equatorward California Current and poleward California Undercurrent. With respect to the annual cycle, the CASE captures the phase and, to a lesser extent, the magnitude of upper-ocean warming and stratification from late summer to early fall and of isopycnal heave during springtime upwelling. The CASE also realistically captures near-surface diapycnal mixing during upwelling season and the semiannual cycle of the California Undercurrent. In terms of interannual variability, the most pronounced signals are the persistent warming and downwelling anomalies of 2014–16 and a positive isopycnal salinity anomaly that peaked with the 2015–16 El Niño.

Contextualizing time-series data: quantification of short-term regional variability in the San Pedro Channel using high-resolution in situ glider data

Abstract. Oceanic time series have been instrumental in providing an understanding of biological, physical, and chemical dynamics in the oceans and how these processes change over time. However, the extrapolation of these results to larger oceanographic regions requires an understanding and characterization of local versus regional drivers of variability. Here we use high-frequency spatial and temporal glider data to quantify variability at the coastal San Pedro Ocean Time-series (SPOT) site in the San Pedro Channel (SPC) and provide insight into the underlying oceanographic dynamics for the site. The dataset could be described by a combination of four water column profile types that typified active upwelling, a surface bloom, warm-stratified low-nutrient conditions, and a subsurface chlorophyll maximum. On weekly timescales, the SPOT station was on average representative of 64 % of profiles taken within the SPC. In general, shifts in water column profile characteristics at SPOT were also observed across the entire channel. On average, waters across the SPC were most similar to offshore profiles, suggesting that SPOT time series data would be more impacted by regional changes in circulation than local coastal events. These results indicate that high-resolution in situ glider deployments can be used to quantify major modes of variability and provide context for interpreting time series data, allowing for broader application of these datasets and greater integration into modeling efforts.