Which Triggers Produce the Most Erosive, Frequent, and Longest Runout Turbidity Currents on Deltas?

Subaerial rivers and turbidity currents are the two most voluminous sediment transport processes on our planet, and it is important to understand how they are linked offshore from river mouths. Previously, it was thought that slope failures or direct plunging of river floodwater (hyperpycnal flow) dominated the triggering of turbidity currents on delta fronts. Here we reanalyze the most detailed time‐lapse monitoring yet of a submerged delta; comprising 93 surveys of the Squamish Delta in British Columbia, Canada. We show that most turbidity currents are triggered by settling of sediment from dilute surface river plumes, rather than landslides or hyperpycnal flows. Turbidity currents triggered by settling plumes occur frequently, run out as far as landslide‐triggered events, and cause the greatest changes to delta and lobe morphology. For the first time, we show that settling from surface plumes can dominate the triggering of hazardous submarine flows and offshore sediment fluxes

Current-aligned dewatering sheets and ‘enhanced’ primary current lineation in turbidite sandstones of the Marnoso-arenacea Formation

Turbidite sandstones of the Miocene Marnoso-arenacea Formation (northern Apennines, Italy) display centimetre to decimetre long, straight to gently curved, 0.5 to 2.0 cm regularly spaced lineations on depositional (stratification) planes. Sometimes these lineations are the planform expression of sheet structures seen as millimetre to centimetre long vertical ‘pillars’ in profile. Both occur in the middle and upper parts of medium-grained and fine-grained sandstone beds composed of crude to well-defined stratified facies (including corrugated, hummocky-like, convolute, dish-structured and dune stratification) and are aligned sub-parallel to palaeoflow direction as determined from sole marks often in the same beds. Outcrops lack a tectonic-related fabric and therefore these structures may be confidently interpreted to be sedimentary in origin. Lineations resemble primary current lineation formed by the action of turbulence during bedload transport under upper stage plane bed conditions. However, they typically display a larger spacing and micro-topography compared to classic primary current lineation and are not associated with planar-parallel, finely-laminated sandstones. This type of ‘enhanced lineation’ is interpreted to develop by the same process as primary current lineation, but under relatively high near-bed sediment concentrations and suspended load fallout rates, as supported by laboratory experiments and host facies characteristics. Sheets are interpreted to be dewatering structures and their alignment to palaeoflow (only noted in several other outcrops previously) inferred to be a function of vertical water-escape following the primary depositional grain fabric. For the Marnoso-arenacea beds, sheet orientation may be genetically linked to the enhanced primary current lineation structures. Current-aligned lineation and sheet structures can be used as palaeoflow indicators, although the directional significance of sheets needs to be independently confirmed. These indicators also aid the interpretation of dewatered sandstones, suggesting sedimentation under a traction-dominated depositional flow – with a discrete interface between the aggrading deposit and the flow – as opposed to under higher-concentration grain or hindered settling dominated regimes

Mud-clast armoring and its implications for turbidite systems

Seafloor sediment density flows are the primary mechanism for transporting sediment to the deep sea. These flows are important because they pose a hazard to seafloor infrastructure and deposit the largest sediment accumulations on Earth. The cohesive sediment content of a flow (i.e., clay) is an important control on its rheological state (e.g., turbulent or laminar); however, how clay becomes incorporated into a flow is poorly understood. One mechanism is by the abrasion of (clay-rich) mud clasts. Such clasts are common in deep-water deposits, often thought to have traveled over large (more than tens of kilometers) distances. These long travel distances are at odds with previous experimental work that suggests that mud clasts should disintegrate rapidly through abrasion. To address this apparent contradiction, we conduct laboratory experiments using a counter rotating annular flume to simulate clast transport in sediment density flows. We find that as clay clasts roll along a sandy floor, surficial armoring develops and reduces clast abrasion and thus enhances travel distance. For the first time we show armoring to be a process of renewal and replenishment, rather than forming a permanent layer. As armoring reduces the rate of clast abrasion, it delays the release of clay into the parent flow, which can therefore delay flow transformation from turbidity current to debris flow. We conclude that armored mud clasts can form only within a sandy turbidity current; hence where armored clasts are found in debrite deposits, the parent flow must have undergone flow transformation farther up slope

Author Correction: Rapidly-migrating and internally-generated knickpoints can control submarine channel evolution (Nature Communications, (2020), 11, 1, (3129), 10.1038/s41467-020-16861-x)

© 2020, The Author(s). The original version of this Article contained an error in the labelling of the cross-section in Fig. 2g and the vertical axis in Fig. 2b. This has been corrected in both the PDF and HTML versions of the Article

Nurse-patient interaction and communication: a systematic literature review

Aim: The purpose of this review is to describe the use and definitions of the concepts of nurse-patient interaction and nurse-patient communication in nursing literature. Furthermore, empirical findings of nurse-patient communication research will be presented, and applied theories will be shown. Method: An integrative literature search was executed. The total number of relevant citations found was 97. The search results were reviewed, and key points were extracted in a standardized form. Extracts were then qualitatively summarized according to relevant aspects and categories for the review. Results: The relation of interaction and communication is not clearly defined in nursing literature. Often the terms are used interchangeably or synonymously, and a clear theoretical definition is avoided or rather implicit. Symbolic interactionism and classic sender-receiver models were by far the most referred to models. Compared to the use of theories of adjacent sciences, the use of original nursing theories related to communication is rather infrequent. The articles that try to clarify the relation of both concepts see communication as a special or subtype of interaction. Conclusion: The included citations all conclude that communication skills can be learned to a certain degree. Involvement of patients and their role in communication often is neglected by authors. Considering the mutual nature of communication, patients’ share in conversation should be taken more into consideration than it has been until now. Nursing science has to integrate its own theories of nursing care with theories of communication and interaction from other scientific disciplines like sociology

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Deposit structure and processes of sand deposition from a decelerating sediment suspension

Turbidity currents are notoriously difficult to monitor directly, therefore interpretation of their deposits forms the basis for much of our understanding of these flows. The deceleration rate of a flow is a potentially important yet poorly understood control on depositional processes. A series of experiments were conducted in an annular flume, in which fast (up to 3.5 m/s) and highly turbulent flows of sand (up to 250 µm) and water were decelerated at different rates and processes of deposition and deposit character analyzed. Previously poorly documented depositional processes were observed in the experiments. This is because the flows were initially unusually fast and of prolonged duration, with sustained periods of sediment fallout as the flow slowed down. The conditions in these flows are thus likely to be closer to those at the base of a waning turbidity current than is achieved in other relatively slow experimental flows. The collapse of high-concentration, moving, thin (&lt; 5 mm) near-bed layers (laminar sheared layers) were an important mechanism by which the bed aggraded beneath these unsteady flows. At bed aggradation rates in excess of 0.44 mm/s the sequential collapse of laminar sheared layers produced a structureless, poorly graded and poorly sorted deposit (Bouma Ta). When bed aggradation rates fell below 0.44 mm/s the collapsing laminar sheared layers were reworked by turbulence to form planar laminae (Bouma Tb). These laminae are formed in a very different manner than the planar laminae attributed to bedwaves in previous open-channel flow experiments. Collapse of laminar sheared layers is therefore an alternative process for generating the Bouma Tb division. Inverse grading developed at the base of the deposits of slowly decelerated flows. This inverse grading was probably a result of grain sorting in a high-concentration layer that persisted at the base of the flow for many minutes prior to the onset of deposition. <br/

Deposits of flows transitional between turbidity current and debris flow

The relationship between submarine sediment gravity flows and the character of their deposits is poorly understood. Annular flume experiments were used to investigate the depositional dynamics and deposits of waning sediment-laden flows. Decelerating fast (&gt;3 m/s) flows with fixed sand content (10 vol%) and variable mud content (0–17 vol%) resulted in only four deposit types. Clean sand with a mud cap that resembled a turbidity current deposit (turbidite) formed if the flow was turbulent when deposition began, or if the muddy fluid had insufficient strength to suspend the sand. The clean sand could contain structures if mud content was low (&lt;6%) and the deceleration period was &gt;300 s. Ungraded muddy sand with a mud cap that resembled a debris-flow deposit (debrite) formed if the flow became laminar before sand could deposit. Clean sand overlain by ungraded muddy sand and a mud cap formed either from a transitional flow or by late-stage settling of sand from a muddy suspension. These deposits resemble enigmatic submarine flow deposits called linked debrite-turbidites. The experiments provide a basis for inferring flow type from deposit character for submarine sediment-laden flows. <br/