A methodology for Thorpe scaling 512 Hz fast thermistor data from buoyancy-driven gliders to estimate turbulent kinetic energy dissipation rate in the ocean

A Kongsberg Seaglider with a microstructure package was deployed in the Faroe-Shetland Channel in 2017 as part of the 4th Marine Autonomous Systems in Support of Marine Observations (MASSMO4). Using the FP07 fast thermistor (512 Hz), the standard Seaglider thermistor (0.2 Hz) and potential density calculated from Seaglider conductivity-temperature sail (0.2 Hz) a comparison of the Thorpe Scale method has been made. Through this method turbulent kinetic energy (TKE) dissipation rates are inferred from the length-scale of a turbulent overturn. Comparison of the three physical quantities show that overturns with a comparable length-scale also have a comparable TKE dissipation rate. The range of estimated TKE dissipation rates from the 0.2 Hz data is also comparable to those inferred using the same method applied to potential density calculated from a ship mounted CTD

INVESTIGATING TURBULENT MIXING PROCESSES USING HIGH-RESOLUTION TEMPERATURE SENSORS ON AUTONOMOUS OCEAN GLIDERS

Turbulent processes play a key role in ocean mixing. However, lack of spatial and temporal data collection limits our understanding of these processes, especially in the deep ocean away from boundaries. In this thesis we investigate the suitability of using the Thorpe scale method on high resolution temperature data from buoyancy driven gliders and vertical microstructure profilers to improve provision of estimates of turbulent kinetic dissipation rates. Using three datasets a robust methodology was developed to estimate dissipation rates from Thorpe length scales using both a vertical microstructure profiler and Seagliders. Three distinct regions were investigated; open ocean over the Mid-Atlantic Ridge using a vertical microstructure profiler, open ocean in the Subtropical North Atlantic away from boundaries using a Seaglider, and the flank of a submarine ridge in the Faroe-Shetland channel using a Seaglider. All regions showed dissipations ((O)10−11 to (O)10−6 W kg−1 ) and diffusivities ((O)10−6 to (O)10−4 m−2 s −1 ) within expected global ranges, although the latter two showed up to an order of magnitude difference to other studies from the same region. Over the Mid-Atlantic Ridge, Thorpe scale matched the structure and tidal cycle provided by shear data from the same platform. In contrast, in the Faroe-Shetland channel the method performed poorer, not showing the elevated values of dissipation expected in an internal tide generating region. Additionally, Thorpe scaling showed elevated levels of diapycnal mixing in the Subtropical North Atlantic associated with Thermohaline staircases even though this is non-mechanical process. The benefits, drawbacks and relevance of Thorpe scaling high resolution temperature are discussed and compared with other finescale parametrisations, leading to suggestions as to where the method is most applicable within the oceans for further study

Turbulent kinetic energy dissipation rate and associated fluxes in the western tropical Atlantic estimated from ocean glider observations

Ocean gliders enable us to collect the high-resolution microstructure observations necessary to calculate the dissipation rate of turbulent kinetic energy, ε, on timescales of weeks to months: far longer than is normally possible using traditional ship-based platforms. Slocum gliders have previously been used to this end; here, we report the first detailed estimates of ε calculated using the Batchelor spectrum method on observations collected by a FP07 fast thermistor mounted on a Seaglider. We use these same fast thermistor observations to calculate ε following the Thorpe scale method and find very good agreement between the two methods. The Thorpe scale method yields larger values of ε, but the average difference, which is less than an order of magnitude, is smaller than reported elsewhere. The spatio-temporal distribution of ε is comparable for both methods. Maximum values of ε (10−7 W kg−1) are observed in the surface mixed layer; values of approximately 10−9 W kg−1 are observed between approximately 200 and 500 m depth. These two layers are separated by a 100 m thick layer of low ε (10−10 W kg−1), which is co-located with a high-salinity layer of Subtropical Underwater and a peak in the strength of stratification. We calculate the turbulent heat and salt fluxes associated with the observed turbulence. Between 200 and 500 m, ε induces downward fluxes of both properties that, if typical of the annual average, would have a very small influence on the heat and salt content of the overlying salinity-maximum layer. We compare these turbulent fluxes with two estimates of double-diffusive fluxes that occur in regions susceptible to salt fingers, such as the western tropical Atlantic. We find that the double-diffusive fluxes of both heat and salt are larger than the corresponding turbulent fluxes

Western boundary circulation and coastal sea-level variability in Northern Hemisphere oceans

The northwest basins of the Atlantic and Pacific oceans are regions of intense western boundary currents (WBCs): the Gulf Stream and the Kuroshio. The variability of these poleward currents and their extensions in the open ocean is of major importance to the climate system. It is largely dominated by in-phase meridional shifts downstream of the points at which they separate from the coast. Tide gauges on the adjacent coastlines have measured the inshore sea level for many decades and provide a unique window on the past of the oceanic circulation. The relationship between coastal sea level and the variability of the western boundary currents has been previously studied in each basin separately, but comparison between the two basins is missing. Here we show for each basin that the inshore sea level upstream of the separation points is in sustained agreement with the meridional shifts of the western boundary current extension over the period studied, i.e. the past 7 (5) decades in the Atlantic (Pacific). Decomposition of the coastal sea level into principal components allows us to discriminate this variability in the upstream sea level from other sources of variability such as the influence of large meanders in the Pacific. Our result extends previous findings limited to the altimetry era and suggests that prediction of inshore sea-level changes could be improved by the inclusion of meridional shifts of the western boundary current extensions as predictors. Long-duration tide gauges, such as Key West, Fernandina Beach or Hosojima, could be used as proxies for the past meridional shifts of the western boundary current extensions

Effect of remote ischaemic conditioning on clinical outcomes in patients with acute myocardial infarction (CONDI-2/ERIC-PPCI): a single-blind randomised controlled trial.

BACKGROUND: Remote ischaemic conditioning with transient ischaemia and reperfusion applied to the arm has been shown to reduce myocardial infarct size in patients with ST-elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PPCI). We investigated whether remote ischaemic conditioning could reduce the incidence of cardiac death and hospitalisation for heart failure at 12 months. METHODS: We did an international investigator-initiated, prospective, single-blind, randomised controlled trial (CONDI-2/ERIC-PPCI) at 33 centres across the UK, Denmark, Spain, and Serbia. Patients (age >18 years) with suspected STEMI and who were eligible for PPCI were randomly allocated (1:1, stratified by centre with a permuted block method) to receive standard treatment (including a sham simulated remote ischaemic conditioning intervention at UK sites only) or remote ischaemic conditioning treatment (intermittent ischaemia and reperfusion applied to the arm through four cycles of 5-min inflation and 5-min deflation of an automated cuff device) before PPCI. Investigators responsible for data collection and outcome assessment were masked to treatment allocation. The primary combined endpoint was cardiac death or hospitalisation for heart failure at 12 months in the intention-to-treat population. This trial is registered with ClinicalTrials.gov (NCT02342522) and is completed. FINDINGS: Between Nov 6, 2013, and March 31, 2018, 5401 patients were randomly allocated to either the control group (n=2701) or the remote ischaemic conditioning group (n=2700). After exclusion of patients upon hospital arrival or loss to follow-up, 2569 patients in the control group and 2546 in the intervention group were included in the intention-to-treat analysis. At 12 months post-PPCI, the Kaplan-Meier-estimated frequencies of cardiac death or hospitalisation for heart failure (the primary endpoint) were 220 (8·6%) patients in the control group and 239 (9·4%) in the remote ischaemic conditioning group (hazard ratio 1·10 [95% CI 0·91-1·32], p=0·32 for intervention versus control). No important unexpected adverse events or side effects of remote ischaemic conditioning were observed. INTERPRETATION: Remote ischaemic conditioning does not improve clinical outcomes (cardiac death or hospitalisation for heart failure) at 12 months in patients with STEMI undergoing PPCI. FUNDING: British Heart Foundation, University College London Hospitals/University College London Biomedical Research Centre, Danish Innovation Foundation, Novo Nordisk Foundation, TrygFonden

Investigating turbulent mixing processes using high-resolution temperature sensors on autonomous ocean gliders

Turbulent processes play a key role in ocean mixing. However, lack of spatial and temporal data collection limits our understanding of these processes, especially in the deep ocean away from boundaries. In this thesis we investigate the suitability of using the Thorpe scale method on high resolution temperature data from buoyancy driven gliders and vertical microstructure profilers to improve provision of estimates of turbulent kinetic dissipation rates.Using three datasets a robust methodology was developed to estimate dissipation rates from Thorpe length scales using both a vertical microstructure profiler and Seagliders.Three distinct regions were investigated; open ocean over the Mid-Atlantic Ridge using a vertical microstructure profiler, open ocean in the Subtropical North Atlantic away from boundaries using a Seaglider, and the flank of a submarine ridge in the Faroe-Shetland channel using a Seaglider. All regions showed dissipations ((O)10−11 to (O)10−6 W kg−1 ) and diffusivities ((O)10−6 to (O)10−4 m−2 s −1 ) within expected global ranges, although the latter two showed up to an order of magnitude difference to other studies from the same region.Over the Mid-Atlantic Ridge, Thorpe scale matched the structure and tidal cycle provided by shear data from the same platform. In contrast, in the Faroe-Shetland channel the method performed poorer, not showing the elevated values of dissipation expected in an internal tide generating region. Additionally, Thorpe scaling showed elevated levels of diapycnal mixing in the Subtropical North Atlantic associated with Thermohaline staircases even though this is non-mechanical process.The benefits, drawbacks and relevance of Thorpe scaling high resolution temperature are discussed and compared with other finescale parametrisations, leading to suggestions as to where the method is most applicable within the oceans for further study

A methodology for Thorpe scaling 512 Hz fast thermistor data from buoyancy-driven gliders to estimate turbulent kinetic energy dissipation rate in the ocean

A Kongsberg Seaglider with a microstructure package was deployed in the Faroe-Shetland Channel in 2017 as part of the 4th Marine Autonomous Systems in Support of Marine Observations (MASSMO4). Using the FP07 fast thermistor (512 Hz), the standard Seaglider thermistor (0.2 Hz) and potential density calculated from Seaglider conductivity-temperature sail (0.2 Hz) a comparison of the Thorpe Scale method has been made. Through this method turbulent kinetic energy (TKE) dissipation rates are inferred from the length-scale of a turbulent overturn. Comparison of the three physical quantities show that overturns with a comparable length-scale also have a comparable TKE dissipation rate. The range of estimated TKE dissipation rates from the 0.2 Hz data is also comparable to those inferred using the same method applied to potential density calculated from a ship mounted CTD

Spreadsheets for GSNW, KEI and tide gauge derived sea-level modes

A set of CSV files containing different timeseries presented in Ocean Science paper &#39;Western boundary circulation and coastal sea-level variability in northern hemisphere oceans&#39;, from Samuel Ti&eacute;folo Diabat&eacute; and Coauthors (submitted). - Atlantic_PCs.csv: contains the two leading principal components of the tide gauge obtained sea-level anomalies for the Atlantic set of tide gauges. - Pacific_PCs.csv: same as previous, but for the Pacific set of tide gauges. - GSNW.csv: contains our Gulf Stream North Wall index, as defined in the paper. - KEI.csv: contains our Kuroshio Extension Index, as defined in the paper.</span