Lessons learned from monitoring of turbidity currents and guidance for future platform designs

Turbidity currents transport globally significant volumes of sediment and organic carbon into the deep-sea and pose a hazard to critical infrastructure. Despite advances in technology, their powerful nature often damages expensive instruments placed in their path. These challenges mean that turbidity currents have only been measured in a few locations worldwide, in relatively shallow water depths (≪2 km). Here, we share lessons from recent field deployments about how to design the platforms on which instruments are deployed. First, we show how monitoring platforms have been affected by turbidity currents including instability, displacement, tumbling and damage. Second, we relate these issues to specifics of the platform design, such as exposure of large surface area instruments within a flow and inadequate anchoring or seafloor support. Third, we provide recommended improvements to improve design by simplifying mooring configurations, minimising surface area, and enhancing seafloor stability. Finally we highlight novel multi-point moorings that avoid interaction between the instruments and the flow, and flow-resilient seafloor platforms with innovative engineering design features, such as ejectable feet and ballast. Our experience will provide guidance for future deployments, so that more detailed insights can be provided into turbidity current behaviour, and in a wider range of settings

Upwelling rebound, ephemeral secondary pycnoclines, and the creation of a near-bottom wave guide over the Monterey Bay continental shelf

The article of record as published may be found at http://dx.doi.org/10.1002/2014GL061897The USGS data sets presented herein can be obtained by sending a written request to the corresponding author.Several sequential upwelling events were observed in fall 2012, using measurements from the outer half of the continental shelf in Monterey Bay, during which the infiltration of dense water onto the shelf created a secondary, near-bottom pycnocline. This deep pycnocline existed in concert with the near-surface pycnocline and enabled the propagation of near-bottom, cold, semidiurnal internal tidal bores, as well as energetic, high-frequency, nonlinear internal waves of elevation (IWOE). The IWOE occurred within 20m of the bottom, had amplitudes of 8–24 m, periods of 6–45 min, and depth-integrated energy fluxes up to 200Wm 1. Iribarren numbers (<0.03) indicate that these IWOE were nonbreaking in this region of the shelf. These observations further demonstrate how regional upwelling dynamics and the resulting bulk, cross-margin hydrography is a first-order control on the ability of internal waves, at tidal and higher frequencies, to propagate through continental shelf waters.U.S. Geological Survey’s Coastal and Marine Geology Program.National Science FoundationNational Science Foundation grant OCE096181

Jedem Tier (s)einen Namen geben? : Die Individualität des Tieres und ihre Relevanz für die Wissenschaften

Michael ROSENBERGER: Jedem Tier (s)einen Namen geben? Eine Einführung; Carola OTTERSTEDT: Grußwort; Kurt KOTRSCHAL: Mit System unterschiedlich. Zur bio-psychologischen Basis von Persönlichkeit bei Menschen und anderen Tieren; Diskussion im Anschluss an den Vortrag; Jessica ULLRICH: Vom Präparat zum Individuum. Das Nachleben der Eisbären in der Installation nanoq. flat out and bluesome von Bryndís Snæbjörnsdóttir und Mark Wilson; Diskussion im Anschluss an den Vortrag; Roland BORGARDS: Herzi-Lampi-Schatzis Tod und Bobbys Vertreibung. Tierliche Eigennamen bei Friedrich Hebbel und Emmanuel Levinas; Diskussion im Anschluss an den Vortrag; Judith BENZ-SCHWARZBURG und Herwig GRIMM: Tierliche Individuen in der Forschung. Tiere zwischen Modell und einzigartiger Persönlichkeit; Diskussion im Anschluss an den Vortrag; Michael ROSENBERGER: Einzigartige Berufung. Überlegungen zu einer „Existenzialethik des Tieres“; Diskussion im Anschluss an den Vortrag; Die Relevanz tierlicher Individualität für die Wissenschaften; Die Autorinnen und Autoren; Die Teilnehmerinnen und Teilnehmer; Profil der Linzer WiEGe-Reihe. Beiträge zu Wirtschaft – Ethik – Gesellschaft

Preconditioning by sediment accumulation can produce powerful turbidity currents without major external triggers

Turbidity currents dominate sediment transfer into the deep ocean, and can damage critical seabed infrastructure. It is commonly inferred that powerful turbidity currents are triggered by major external events, such as storms, river floods, or earthquakes. However, basic models for turbidity current triggering remain poorly tested, with few studies accurately recording precise flow timing. Here, we analyse the most detailed series of measurements yet made of powerful (up to 7.2 m s−1) turbidity currents, within Monterey Canyon, offshore California. During 18-months of instrument deployment, fourteen turbidity currents were directly monitored. No consistent triggering mechanism was observed, though flows did cluster around enhanced seasonal sediment supply. We compare turbidity current timing at Monterey Canyon (a sandy canyon-head fed by longshore drift) to the only other systems where numerous (>10-100) flows have been measured precisely via direct monitoring; the Squamish Delta (a sandy fjord-head delta), and the Congo Canyon (connected to the mud-dominated mouth of the Congo River). A common seasonal pattern emerges, leading to a new model for preconditioning and triggering of turbidity currents initiating through slope failure in areas of sediment accumulation, such as canyon heads or river mouths. In this model, rapid or sustained sediment supply alone can produce elevated pore pressures, which may persist, thereby predisposing slopes to fail. Once preconditioned, a range of minor external perturbations, such as moderate storm-waves, result in local pore pressure variation, and thus become effective triggers. Major external triggers are therefore not always a prerequisite for triggering of powerful turbidity currents

Sediment and organic carbon transport and deposition driven by internal tides along Monterey Canyon, offshore California

Submarine canyons are globally important conduits for sediment and organic carbon transport into the deep sea. Using a novel dataset from Monterey Canyon, offshore central California, that includes an extensive array of water column sampling devices, we address how fine-grained sediment and organic carbon are transported, mixed, fractionated, and buried along a submarine canyon. Anderson-type sediment traps were deployed 10–300 m above the seafloor on a suite of moorings anchored between 278 and 1849 m water depths along the axial channel of Monterey Canyon during three consecutive 6-month deployments (2015–2017). Tidal currents within the canyon suspended and transported fine-grained sediment and organic carbon that were captured in sediment traps, which record the composition of sediment and organic carbon transport along the canyon. High sediment accumulation rates in traps increased up-canyon and near the seafloor, where fine-scale (<1 cm) layering was increasingly distinctive in CT scans. There was no along-canyon trend in the organic carbon composition (percent modern carbon and isotopic signatures) among trap locations, suggesting effective mixing. Organic carbon content (weight percent total organic carbon) and excess 210Pb activities (dpm/g) increased down-canyon, reflecting reduced flux of sediment and organic carbon into deeper water, more distal traps. Differing organic carbon signatures in traps compared with previous measurements of seabed deposits along Monterey Canyon suggest that organic carbon transported through the canyon with internal tides may not be consistently recorded in seafloor deposits. First-order estimates from comparing organic carbon content of core and trap samples results in low organic carbon specific burial efficiency (ranging from ~26% to ~0.1%) and suggests that the modern upper Monterey Canyon may not be an effective sink for carbon. Organic carbon isotopic signatures from sediment traps in the water column show more marine influence than seafloor sediment cores; this is likely due to the deposition and reworking of seafloor deposits by sediment density flows and preferential consumption of fresh marine organic carbon on the seafloor, which is better preserved in the traps. Sediment and remaining organic carbon in canyon floor and lower flank deposits preferentially reflect episodic sediment density flow events that are unrelated to internal tides. This study provides a quantified example and conceptual model for internal-tide-related sediment and organic carbon transport, mixing, and burial trends along a submarine canyon that are likely to be similar in many canyons worldwide