Subtropical Ocean Research Articles

A new global coupled atmosphere-ocean wavenumber-4 pattern in Southern mid–latitudes during austral summer and its climate linkage

A new pattern referred to as the coupled ocean-atmosphere wavenumber-4 (COAW4) pattern has been identified in the Southern mid-latitudes during austral summer. This pattern consists of a wavenumber-4 pattern in the anomalous 200-hPa meridional wind and a wavenumber-4 pattern of the anomalous sea surface temperature (SST). The SST component of the COAW4 pattern, which includes the Indian Ocean Subtropical Dipole (IOSD), the South Atlantic Subtropical Dipole (SASD) and the South Pacific Subtropical Dipole (SPSD), develops through air-sea interactions involving surface turbulent heat flux, surface wind, and ocean mixed-layer depth. The atmospheric component displays a barotropic structure. The sources for COAW4 pattern include not only the wavenumber-4 pattern of the anomalous SST over Southern oceans, but also the anomalous convective activities over Southern land areas. The COAW4 pattern is associated with increased precipitation over land in southern mid-latitudes, particularly in central Australia. Furthermore, the COAW4 pattern is linked to Antarctic sea ice cover in the Weddell, Amundsen, and northern Ross Seas. Plain language summary In the southern mid-latitudes, there exists a wavenumber 4 pattern in the anomalous 200-hPa meridional wind and a wavenumber-4 pattern of the anomalous sea surface temperature (SST). Previous studies have examined the two wavenumber-4 patterns separately, but their potential linkage remains largely unknown. Through statistical analyses of SST and atmospheric global data, we demonstrated that the two wavenumber 4 patterns could be integrated into a coupled ocean-atmosphere wavenumber-4 (COAW4) pattern in Southern mid-latitudes in austral summer. Additionally, we have investigated the sources of this pattern as well as its effect on precipitation over southern lands and on Antarctic sea ice.

Satellite-observed strong subtropical ocean warming as an early signature of global warming

Satellite observations covering the last four decades reveal an ocean warming pattern resembling the negative phase of the Pacific Decadal Oscillation. This pattern has therefore been widely interpreted as a manifestation of natural climate variability. Here, we re-examine the observed warming pattern and find that the predominant warming over the subtropical oceans, while mild warming or even cooling over the subpolar ocean, is dynamically consistent with the convergence and divergence of surface water. By comparison of observations, paleo-reconstructions, and model simulations, we propose that the observed warming pattern is likely a short-term transient response to the increased CO2 forcing, which only emerges during the early stage of anthropogenic warming. On centennial to millennial timescales, the subpolar ocean warming is expected to exceed the temporally dominant warming of the subtropical ocean. This delayed but amplified subpolar ocean warming has the potential to reshape the ocean-atmosphere circulation and threaten the stability of marine-terminating ice sheets.

Spatial and temporal occurrence of preformed nitrate anomalies in the subtropical North Pacific and North Atlantic oceans

Preformed nitrate (PreNO3) was formulated to act as a conservative tracer of ocean circulation after accounting for the stoichiometry of marine biochemical reactions involving oxygen and nitrate. However, PreNO3 anomalies (e.g. negative values) have been identified within the shallow subsurface of the subtropical ocean which still have yet to be fully explained. The mechanisms proposed to drive the formation of PreNO3 anomalies include: vertical export and remineralization of N-poor dissolved organic matter (DOM) or transparent exopolymer particles (TEP), and the actions of vertically migrating phytoplankton. In this study we use observations from the subtropical Pacific and Atlantic Oceans taken by twenty Biogeochemical Argo profiling floats to assess the spatiotemporal variability of negative subsurface and positive euphotic zone PreNO3 anomalies and their formation rates. After explicitly accounting for the magnitude of DOM cycling, residual euphotic zone positive PreNO3 anomalies and subsurface negative PreNO3 anomalies are consistently observed between 40°S and 40°N. The seasonal timing of euphotic zone positive residual PreNO3 anomaly formation in relation to subsurface negative residual PreNO3 anomalies suggests that both vertically migrating phytoplankton and the remineralization of N-deficient TEP likely contribute to the formation of residual PreNO3 anomalies, but with regional variance suggesting a potentially larger role for migrating phytoplankton in the North Pacific and TEP processes in the North Atlantic. Since migrators include large diatoms that produce ballasted organic matter while TEP may only sink shallowly before remineralization, further investigation into the mechanisms generating PreNO3 anomalies and their quantitative significance is needed to assess the future trajectory of the biological carbon pump in an expanding subtropical ocean ecosystem.

Observational Constraints on the Submesoscale Sea Surface Height Variance of Balanced Motion

Abstract A combination of in situ and remotely sensed observations are used to constrain the imprint of submesoscale turbulence in the sea surface height (SSH) field. The distribution of SSH variance across frequencies and wavenumbers is estimated by comparing an empirical model spectrum to two sets of observations. First, submesoscale SSH variance is constrained using a pair of GPS buoys spaced at about 10 km. From these data, one can estimate frequency spectra not only of SSH variance but also of the variance in the SSH difference between the buoys. The ratio between these two spectral estimates is sensitive to how much SSH variance is present in the submesoscale range and thus constrains the spectral roll-off of SSH variance in wavenumber space. Second, a combination of moored current meters and nadir altimetry is used to obtain an independent constraint. This constraint is enabled by geostrophy and the nonseparability of the wavenumber–frequency spectrum of SSH variance revealed by the GPS data. The frequency spectra of kinetic energy and SSH variance follow different power laws, and the difference constrains the spectral content in wavenumber space, allowing for a constraint without the need to actually resolve the submesoscales in space. In all four locations studied, spanning the midlatitude and subtropical ocean, these constraints indicate that the wavenumber spectral roll-off of submesoscale SSH variance is between about k−4 and k−5, where k is the wavenumber. These estimates are consistent with previous observations, model results, and theoretical predictions. They provide for a strong prior for the interpretation of upcoming high-resolution satellite data.

PAHs in the monsoonal open ocean: Homogeneous spatial pattern and wind-driven significant seasonal variations

PAHs enter the ocean via surface runoff and atmospheric transport pathways, and the distribution of PAHs is highly variable in coastal seas due to the influence of direct human activities, inputs of surface runoff, and strong biological activities. However, highly temporal variability of PAHs has also been widely observed in the open oligotrophic tropical and subtropical oceans without the influence of three types of factors mentioned above. This study developed a method to quantify the variability of oceanic PAHs based on wind frequency and wind-speed-weighted wind frequency using in-situ survey data from three cruises in the Philippine Sea, and tested the validity of this method using publicly available data from other monsoonal open oceans. The result showed that the wind frequency could better explain the variation of dissolved PAHs and particulate PAHs in the surface ocean, while the wind-speed-weighted wind frequency could better explain the variation of particulate PAHs. This study suggests that the influence of seasonal atmospheric transport cannot be ignored when describing and interpreting the distribution patterns of PAHs in the monsoon-influenced low and mid-latitude open oceans and also provides a reference method for a better understanding of the global-scale distribution patterns of PAHs in the ocean.

Variability of tintinnid ciliate communities with water masses in the western Pacific Ocean

Abstract Tintinnids play a pivotal role in the marine plankton ecosystem and are model organisms in plankton studies. However, the biogeographic distribution type and community variation of tintinnids from coastal to open waters in the western Pacific have never been studied before. In the present study, 42 surface tintinnid samples were collected from coastal water to the western Pacific warm pool. A total of 84 tintinnid species were identified. The Kuroshio intrusion has obvious influence on tintinnid distribution and community structure. Fifty-two tintinnid species with relatively high occurrence frequency were classified into neritic, transitional, Kuroshio, warm-pool and cosmopolitan species. We verified the existence of tintinnid transitional species and community in Mixed Water between Neritic and Kuroshio Waters (KW). Tintinnid species richness, abundance, Shannon-Wiener index and Pielou index were higher in the KW than in the Warm-pool Water. The community complexity and stability was highest in the KW. Our findings provide a profound understanding of planktonic biogeography and community variation from nearshore to open waters in tropical and subtropical oceans.

Exchange of Pb from Indian to Atlantic Ocean is driven by Agulhas current and atmospheric Pb input from South Africa

Using a spatiotemporal dataset of dissolved lead (dPb) from the subtropical oceans surrounding South Africa, this study quantifies the exchange of dPb between the Indian and Atlantic Oceans. Despite the absence of a major Pb source within the South Atlantic sector and the complete phase-out of leaded petroleum in Southern Africa, the ecologically important southeast Cape Basin shows an elevated surface dPb concentration (21–30 pmol kg−1). We estimated up to 90% of the measured dPb in surface waters of the Cape Basin was delivered from the Indian Ocean via the Agulhas Current (AC). Eddy dynamics and leakage at Agulhas retroflection result in an increased Pb flux from winter to summer, while a long-term (2008–2019) temporal change in dPb in the AC-derived water of Cape Basin was contemporaneous to a change in atmospheric Pb emissions from South Africa. The South African-origin atmospheric Pb, however, contributes first to the Agulhas waters in the West Indian Ocean, which is then transported to the South Atlantic, thereby regulating the dPb inventory of the Cape Basin. This indirect mechanism of Pb transfer emphasizes the importance of regulating Pb emissions from Southern Africa to protect rich fishing grounds associated with the Benguela marine ecosystem.

Records and palaeoenvironmental conditions of Early Miocene scleractinian corals from the Fırat formation (Diyarbakır, Turkey)

Miocene scleractinian corals were documented for the first time in the Fırat Formation of Sarıca village, Eğil district of Diyarbakır, SE Turkey. The fauna consists of four hermatypic species belonging to three families: Diploastrea taurinensis (d’Achiardi, 1868), Tarbellastraea reussiana (Milne-Edwards and Haime, 1850), Echinopora gemmacea (Lamarck, 1816) and Montastraea pelouaensis (Chevalier, 1954). The morphospecies described here are typical of the early Miocene (Aquitanian-Burdigalian) and show that the Fırat Formation coral community was composed of shallow and subtropical reefs of Mediterranean Tethys palaeobiogeographical affinity. The examined species are reef components found in tropical and subtropical oceans, as are the majority of zooxanthellae. The species were upper photic zone related, had massive colonial growth morphology, and lived in a shallow tropical-subtropical marine palaeoenvironment at a depth of up to 50m. They grew on hard ground, clean water, and normal salinity and required a minimum seawater temperature of 18̊C; however, they were most abundant at water temperatures ranging from 22 to 26̊C in high-moderate water energy. Consequently, this fossil assemblage will not only improve our knowledge of scleractinian coral diversity and morphological variation in SE Turkey but will also provide an important background for future studies of coral taxonomy, diversity and biogeography of the region.

An environmental DNA metabarcoding survey reveals generic-level occurrence of scleractinian corals at reef slopes of Okinawa Island.

Coral reefs have the highest biodiversity of all marine ecosystems in tropical and subtropical oceans. However, scleractinian corals, keystone organisms of reef productivity, are facing a crisis due to climate change and anthropogenic activities. A broad survey of reef-building corals is essential for worldwide reef preservation. To this end, direct observations made by coral-specialist divers might be supported by another robust method. We improved a recently devised environmental DNA (eDNA) metabarcoding method to identify more than 43 scleractinian genera by sampling 2 l of surface seawater above reefs. Together with direct observations by divers, we assessed the utility of eDNA at 63 locations spanning approximately 250 km near Okinawa Island. Slopes of these islands are populated by diverse coral genera, whereas shallow 'moats' sustain fewer and less varied coral taxa. Major genera recorded by divers included Acropora, Pocillopora, Porites and Montipora, the presence of which was confirmed by eDNA analyses. In addition, eDNA identified more genera than direct observations and documented the presence of previously unrecorded species. This scleractinian coral-specific eDNA method promises to be a powerful tool to survey coral reefs broadly, deeply and robustly.

Atmospheric Input and Seasonal Inventory of Dissolved Iron in the Sargasso Sea: Implications for Iron Dynamics in Surface Waters of the Subtropical Ocean

AbstractConstraining the role of dust deposition in regulating the concentration of the essential micronutrient iron in surface ocean waters requires knowledge of the flux of seawater‐soluble iron in aerosols and the replacement time of dissolved iron (DFe) in the euphotic zone. Here we estimate these quantities using seasonally resolved DFe data from the Bermuda Atlantic Time‐series Study region and weekly‐scale measurements of iron in aerosols and rain from Bermuda during 2019. In response to seasonal changes in vertical mixing, primary production and dust deposition, surface DFe concentrations vary from ∼0.2 nM in early spring to >1 nM in late summer, with DFe inventories ranging from ∼30 to ∼80 μmol/m2, respectively, over the upper 200 m. Assuming the upper ocean approximates steady state for DFe on an annual basis, our aerosol and rainwater data require a mean euphotic‐zone residence time of ∼0.8–1.9 years for DFe with respect to aeolian input.

Cetaceans of the oceanic northern Gulf of Mexico: Distributions, group sizes and interspecific associations

The Gulf of Mexico is a subtropical ocean basin with a diverse oceanic cetacean community. Cetacean research in the Gulf of Mexico has been driven by mandates of the US Marine Mammal Protection Act as well as concerns over the rapidly expanding oil and natural gas industry and related potential threats (e.g. seismic surveys, increased ship traffic, oil spills). Previously, cetacean distribution and abundances for specific Gulf of Mexico areas or species have been described based on work over periods of several years, and recently abundance estimates were made for the entire oceanic northern Gulf of Mexico (1996-2001). For each cetacean species, the paper describes distribution, group size, associated sea surface temperature and water depth and interspecific associations based on surveys conducted over 11 years that span the entire northern Gulf of Mexico. This dataset is the most comprehensive to date for the oceanic northern Gulf. Nine ship surveys totalling 45,462km of effort were conducted during spring seasons (1991-2001) in continental shelf-edge and oceanic waters ( 100m) of the northern Gulf of Mexico. Eighteen species were identified from 1,868 sightings. Cetaceans were found throughout the area although some species had localised distributions or occurred in restricted ranges of water depths. Spinner dolphins (Stenella longirostris) had the largest mean group size (n = 40, x – = 151.5, SE = 30.90), followed by melon-headed whales (Peponocephala electra), clymene dolphins (S. clymene), pantropical spotted dolphins (S. attenuata), Fraser’s dolphins (Lagenodelphis hosei) and striped dolphins (S. coeruleoalba) (range of means 46.1-99.6). Beaked whales (Ziphiidae), Bryde’s whales (Balaenoptera edeni/brydei), sperm whales (Physeter macrocephalus) and pygmy/dwarf sperm whales (Kogia spp.) were found in the smallest groups (x – < 3). Twenty-seven sightings (1.4% of all sightings) were composed of two cetacean species. Common bottlenose dolphins (Tursiops truncatus) were recorded in mixedspecies groups with more species than any other cetacean. Forty-five cetacean sightings (2.4% of all sightings) were associated with at least one bird species, and 21 (1.1% of all sightings) were associated with schools of fish. Contrary to previous reports, pantropical spotted dolphins were observed in association with both fish (including surface tunas) and seabirds, although to a lesser extent than for other tropical oceans. No mixed pantropical spotted and spinner dolphin groups were sighted despite their regular co-occurrence in other tropical oceans.

The effect of temperature and salinity on DMSP production in Gephyrocapsa oceanica (Isochrysidales, Coccolithophyceae)

ABSTRACT A subtropical clone of Gephyrocapsa oceanica was grown over the temperature and salinity range 10–30°C and 20‰–45‰ respectively. Cellular DMSP increased with increasing salinity, compatible with the hypothesis that DMSP is a compatible osmolyte. Cellular DMSP content was highest at colder temperatures and decreased as temperature increased. Net DMSP production rate also depended on cell size and growth rate was greatest about 2°C below the optimum growth temperature of 20°C for this clone. This resulted in a unimodal response of net DMSP production to increasing temperature: net DMSP production increased with increasing temperature when the cells were growing at temperatures below optimum for growth. At and above optimum growth temperature, further warming decreased net DMSP production. For the effect of temperature alone, in the subtropical oceans, where G. oceanica is growing at or above its optimum, further warming due to climate change will result in decreased net DMSP production and so a probable decrease in the flux of DMS to the atmosphere and sulphate aerosol production. Inasmuch as these aerosols modulate cloud albedo and longevity then these too will both decrease, resulting in a positive feedback response for temperature. The reverse effect may occur in higher latitude oceans where growth temperature is below optimum. The exact response in both regions is complicated because warming will also enhance water column stratification and may reduce mixed layer depths, affecting both nutrient and light regimes, as well as possible species succession effects. Further work is required to investigate these other indirect temperature effects.

Marine Boundary Layer Heights in the Tropical and Subtropical Oceans Derived from COSMIC-2 Radio Occultation Data

Marine Boundary Layer Heights in the Tropical and Subtropical Oceans Derived from COSMIC-2 Radio Occultation Data

Chromosome-Level Genome Assembly of the Rough-Toothed Dolphin (Steno bredanensis)

The rough-toothed dolphin (Steno bredanensis), the single extant species of the genus Steno, inhabits tropical and subtropical oceans. It is an attractive species for studying aquatic adaptation and evolution. The latest advances in high-throughput sequencing are transforming the study of marine mammals and contributing to understanding various phenomena at the species and population level by determining high-quality genomes. Here, to comprehensively understand the genetic features and explore the molecular basis of aquatic adaption, the chromosome-level genome assembly and comparative genomics analyses of S. bredanensis were performed. The 2.30 Gb final genome assembly of S. bredanensis (scaffold N50 length of 105.53 Mb) was obtained using single-tube long fragment read (stLFR) and Hi-C technologies. The genome assembly clearly revealed the preservation of large chromosomal fragments between S. bredanensis and the melon-headed whale (Peponocephala electra). The S. bredanensis genome contained 19,451 predicted protein-coding genes, of which about 92.33% have functional annotations. The genome assembly and gene sets showed high completeness, with a BUSCO score of 90.6% and 97.3%, respectively. We also identified several positively selected genes specific to S. bredanensis, which may be related to fat cell differentiation, tooth morphogenesis, and immunoregulatory activity. Finally, the demographic dynamics of S. bredanensis were estimated by the pairwise sequentially Markovian coalescent (PSMC) model and found that the population was affected by the climate at the time. We demonstrated that improved continuity and accuracy of the assembled sequence warranted the adoption of this chromosome-level genome as the reference genome and advanced the understanding of genetic features of the rough-toothed dolphin, which will be essential for future evolutionary studies and the protection of this species.

Distinct regional meteorological influences on low-cloud albedo susceptibility over global marine stratocumulus regions

Abstract. Marine stratocumuli cool the Earth effectively due to their high reflectance of incoming solar radiation and persistent occurrence. The susceptibility of cloud albedo to droplet number concentration perturbations depends strongly on large-scale meteorological conditions. Studies focused on the meteorological dependence of cloud adjustments often overlook the covariability among meteorological factors and their geographical and temporal variability. We use 8 years of satellite observations sorted by day and geographical location to show the global distribution of marine low-cloud albedo susceptibility. We find an overall cloud brightening potential for most marine warm clouds, which is more pronounced over subtropical coastal regions. A weak cloud darkening potential in the annual mean is evident over the remote SE Pacific and SE Atlantic. We show that large-scale meteorological fields from the ERA5 reanalysis data, including lower-tropospheric stability, free-tropospheric relative humidity, sea surface temperature, and boundary layer depth, have distinct covariabilities over each of the eastern subtropical ocean basins where marine stratocumuli prevail. This leads to a markedly different annual cycle in albedo susceptibility over each basin. Moreover, we find that basin-specific regional relationships between key meteorological factors and albedo susceptibilities are absent in a global analysis. Our results stress the importance of considering the geographical distinctiveness of temporal meteorological covariability when scaling up the local-to-global response of cloud albedo to aerosol perturbations.

Composite Analysis-Based Machine Learning for Prediction of Tropical Cyclone-Induced Sea Surface Height Anomaly

Sea surface height anomaly (SSHA) induced by tropical cyclones (TCs) is closely associated with oscillations and is a crucial proxy for thermocline structure and ocean heat content in the upper ocean. The prediction of TC-induced SSHA, however, has been rarely investigated. This study presents a new composite analysis-based random forest (RF) approach to predict daily TC-induced SSHA. The proposed method utilizes TC's characteristics and pre-storm upper oceanic parameters as input features to predict TC-induced SSHA up to 30 days after TC passage. Simulation results suggest that the proposed method is skillful at inferring both the amplitude and temporal evolution of SSHA induced by TCs of different intensity groups. Using a TC-centered 5°×5° box, the proposed method achieves highly accurate prediction of TC-induced SSHA over the Western North Pacific with root mean square error of 0.024m, outperforming alternative machine learning methods and the numerical model. Moreover, the proposed method also demonstrated good prediction performance in different geographical regions, i.e., the South China Sea and the Western North Pacific subtropical ocean. The study provides insight into the application of machine learning in improving the prediction of SSHA influenced by extreme weather conditions. Accurate prediction of TC-induced SSHA allows for better preparedness and response, reducing the impact of extreme events (e.g., storm surge) on people and property.

Nutrient uptake plasticity in phytoplankton sustains future ocean net primary production.

Annually, marine phytoplankton convert approximately 50 billion tons of dissolved inorganic carbon to particulate and dissolved organic carbon, a portion of which is exported to depth via the biological carbon pump. Despite its important roles in regulating atmospheric carbon dioxide via carbon sequestration and in sustaining marine ecosystems, model-projected future changes in marine net primary production are highly uncertain even in the sign of the change. Here, using an Earth system model, we show that frugal utilization of phosphorus by phytoplankton under phosphate-stressed conditions can overcompensate the previously projected 21st century declines due to ocean warming and enhanced stratification. Our results, which are supported by observations from the Hawaii Ocean Time-series program, suggest that nutrient uptake plasticity in the subtropical ocean plays a key role in sustaining phytoplankton productivity and carbon export production in a warmer world.

Epipelagic nitrous oxide production offsets carbon sequestration by the biological pump

The removal of carbon dioxide from the atmosphere by the marine biological pump is a key regulator of Earth’s climate; however, the ocean also serves as a large source of nitrous oxide, a potent greenhouse gas and ozone-depleting substance. Although biological carbon sequestration and nitrous oxide production have been individually studied in the ocean, their combined impacts on net greenhouse forcing remain uncertain. Here we show that the magnitude of nitrous oxide production in the epipelagic zone of the subtropical ocean covaries with remineralization processes and thus acts antagonistically to weaken the radiative benefit of carbon removal by the marine biological pump. Carbon and nitrogen isotope tracer incubation experiments and nitrogen isotope natural abundance data indicate enhanced biological activity promotes nitrogen recycling, leading to substantial nitrous oxide production via both oxidative and reductive pathways. These shallow-water nitrous oxide sources account for nearly half of the air–sea flux and counteract 6–27% (median 9%) of the greenhouse warming mitigation achieved by carbon export via the biological pump.

Global precipitation system scale increased from 2001 to 2020

How precipitation responds to global warming has drawn much interest from the scientific community. However, as one of the important properties of precipitation, changes in the precipitation system scale have rarely been studied. The latest retrospective merged satellite precipitation product has provided a great opportunity to investigate quasi-global precipitation system scale changes. This study uses the Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (IMERG) data during 2001–2020 to investigate quasi-global precipitation system scale changes. Our results indicate that, generally, quasi-global precipitation system scales exhibit a significant increasing trend, which is more significant in winter and spring than that in summer and autumn over both hemispheres. The scale of nearly all precipitation systems over land regions has increased over the last two decades. In oceanic regions, precipitation system scales increase over tropical oceans but decrease over subtropical oceans. Medium-scale precipitation systems (100–1000 km) significantly increase in scale and decrease in frequency, while large-scale precipitation systems significantly increase in frequency, which both lead to a quasi-global increase in the precipitation system scale. Diagnostic investigation based on atmospheric analysis reveals that an increase in atmospheric stability tends to suppress local convective precipitation, while an increase in the total column water vapor could help maintain and enhance precipitation system scale, which jointly contribute to quasi-global precipitation system scale increase.

Glider observations of thermohaline staircases in the tropical North Atlantic using an automated classifier

Abstract. Thermohaline staircases are stepped structures of alternating thick mixed layers and thin high-gradient interfaces. These structures can be up to several tens of metres thick and are associated with double-diffusive mixing. Thermohaline staircases occur across broad swathes of the Arctic and tropical and subtropical oceans and can increase rates of diapycnal mixing by up to 5 times the background rate, driving substantial nutrient fluxes to the upper ocean. In this study, we present an improved classification algorithm to detect thermohaline staircases in ocean glider profiles. We use a dataset of 1162 glider profiles from the tropical North Atlantic collected in early 2020 at the edge of a known thermohaline staircase region. The algorithm identifies thermohaline staircases in 97.7 % of profiles that extend deeper than 300 m. We validate our algorithm against previous results obtained from algorithmic classification of Argo float profiles. Using fine-resolution temperature data from a fast-response thermistor on one of the gliders, we explore the effect of varying vertical bin sizes on detected thermohaline staircases. Our algorithm builds on previous work by adding improved flexibility and the ability to classify staircases from profiles with noisy salinity data. Using our results, we propose that the incidence of thermohaline staircases is limited by strong background vertical gradients in conservative temperature and absolute salinity.