Fluvial organic carbon cycling regulated by sediment transit time and mineral protection

Rivers transfer terrestrial organic carbon (OC) from mountains to ocean basins, playing a key role in the global carbon cycle. During fluvial transit, OC may be oxidized and emitted to the atmosphere as CO2 or preserved and transported to downstream depositional sinks. The balance between oxidation and preservation determines the amount of particulate OC (POC) that can be buried long term, but the factors regulating this balance are poorly constrained. Here, we quantify the effects of fluvial transit on POC fluxes along an ~1,300 km lowland channel with no tributaries. We show that sediment transit time and mineral protection regulate the magnitude and rate of POC oxidation, respectively. Using a simple turnover model, we estimate that annual POC oxidation is a small percentage of the POC delivered to the river. Modelling shows that lateral erosion into POC-rich floodplains can increase POC fluxes to downstream basins, thereby offsetting POC oxidation. Consequently, rivers with high channel mobility can enhance CO2 drawdown while management practices that stabilize river channels may reduce the potential for CO2 drawdown.

Evidence for enhanced fluvial channel mobility and fine sediment export due to precipitation seasonality during the Paleocene-Eocene thermal maximum

The Paleocene-Eocene thermal maximum (PETM) was the most extreme example of an abrupt global warming event in the Cenozoic, and it is widely discussed as a past analog for contemporary climate change. Anomalous accumulation of terrigenous mud in marginal shelf environments and concentration of sand in terrestrial deposits during the PETM have both been inferred to represent an increase in fluvial sediment flux. A corresponding increase in water discharge or river slope would have been required to transport this additional sediment. However, in many locations, evidence for changes in fluvial slope is weak, and geochemical proxies and climate models indicate that while runoff variability may have increased, mean annual precipitation was unaffected or potentially decreased. Here, we explored whether changes in river morphodynamics under variable-discharge conditions could have contributed to increased fluvial sand concentration during the PETM. Using field observations, we reconstructed channel paleohydraulics, mobility, and avulsion behavior for the Wasatch Formation (Piceance Basin, Colorado, USA). Our data provide no evidence for changes in fluvial slope during the PETM, and thus no evidence for enhanced sediment discharge. However, our data do show evidence of increased fluvial bar reworking and advection of sediment to floodplains during channel avulsion, consistent with experimental studies of alluvial systems subjected to variable discharge. High discharge variability increases channel mobility and floodplain reworking, which retains coarse sediment while remobilizing and exporting fine sediment through the alluvial system. This mechanism can explain anomalous fine sediment accumulation on continental shelves without invoking sustained increases in fluvial sediment and water discharge.

Supplemental Material: Evidence for enhanced fluvial channel mobility and fine sediment export due to precipitation seasonality during the Paleocene-Eocene thermal maximum

A more-detailed explanation of the field methods used to collect the data for this study, and the statistical tools used to analyze the data, in addition to a description of how the data file is organized. This information should be applied in conjunction with the data and code if readers are interested in using these data for future work.<br>

Supplemental Material: Evidence for enhanced fluvial channel mobility and fine sediment export due to precipitation seasonality during the Paleocene-Eocene thermal maximum

A more-detailed explanation of the field methods used to collect the data for this study, and the statistical tools used to analyze the data, in addition to a description of how the data file is organized. This information should be applied in conjunction with the data and code if readers are interested in using these data for future work.<br>

Denotational semantics of channel mobility in UTP-CSP

In this paper, we present the denotational semantics for channel mobility in the Unifying Theories of Programming (UTP) semantics framework. The basis for the model is the UTP theory of reactive processes, precisely, the UTP semantics for Communicating Sequential Processes (CSP), which is extended to allow the mobility of channels—the set of channels that a process can use for communication (its interface), originally static or constant (set during the process's definition), is now made dynamic or variable: it can change during the process's execution. A channel is thus moved around by communicating it via other channels and then allowing the receiving process to extend its interface with the received channel. We introduce a new concept, the capability of a process, which allows separating the ownership of channels from the knowledge of their existence. Mobile processes are then defined as having a static capability and a dynamic interface. Operations of a mobile telecommunications network, e.g., handover, load balancing, are used to illustrate the semantics. We redefine CSP operators and in particular provide the first semantics for the renaming and hiding operators in the context of channel mobility.

Molecular Mobility in Oriented and Unoriented Membranes Based on Poly[2-(Aziridin-1-yl)ethanol]

Unoriented and oriented membranes based on dendronized polymers and copolymers obtained by chemical modification of poly[2-(aziridin-1-yl) ethanol] (PAZE) with the dendron 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]benzoate were considered. DSC, XRD, CP-MAS NMR and DETA, contribute to characterize the tendency to crystallize, the molecular mobility of the benzyloxy substituent, the dendritic liquid crystalline group and the clearing transition. The orientation of the mesogenic chain somewhat hindered this molecular motion, especially in the full substituted PAZE. The fragility, free volume and thermal expansion coefficients of these membranes near the glass transition are related to the orientation and the addition of the dendritic groups. PAZE-based membranes combine both order and mobility on a supramolecular and macroscopic level, controlled by the dendritic group and the thermal orientation, and open the possibility of preparing membranes with proper channel mobility that promotes selective ionic transport.