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Abstract Retreat of continental ice sheets exposes comminuted sediment in disequilibrium with non-glacial conditions. Weathering of this sediment may create climate feedbacks by altering exchange of greenhouse gases between atmosphere and landscapes. Here we show in a partially deglaciated watershed in southwest Greenland that glacial meltwater contains low concentrations of reactive dissolved organic carbon that enhances weathering of freshly comminuted sediment causing net sequestration of carbon dioxide. In contrast, soil water reactions enhance methanogenesis and carbon dioxide production and create greenhouse gas sources as organic carbon is remineralized. We suggest that a change from greenhouse gas sinks in glacial meltwater to greenhouse gas sources in soil water creates a switch from a negative to positive warming feedback during glacial-interglacial transitions, but a negative warming feedback may return with future anthropogenic warming, glacial retreat, and increased meltwater production. We anticipate changing weathering reactions following exposure also alter nutrient and radiogenic isotope exports. 

In this research, we present a study on the manner in which induced longitudinal (axial) and lateral (radial) shear flows differ experimentally when stimulated in a three-dimensional (3D) complex (dusty) plasma produced in the PlasmaKristal-4 (PK4- BU) at Baylor University. 

ABSTRACT Hard external armors have to defend against a lifetime of threats yet are traditionally understood by their ability to withstand a single attack. Survival of bivalve mollusks thus can depend on the ability to repair shell damage between encounters. We studied the capacity for repair in the intertidal mussel Mytilus californianus by compressing live mussels for 15 cycles at ∼79% of their predicted strength (critically fracturing 46% of shells), then allowing the survivors 0, 1, 2 or 4 weeks to repair. Immediately after fatigue loading, mussel shells were 20% weaker than control shells that had not experienced repetitive loading. However, mussels restored full shell strength within 1 week, and after 4 weeks shells that had experienced greater fatiguing forces were stronger than those repetitively loaded at lower forces. Microscopy supported the hypothesis that crack propagation is a mechanism of fatigue-caused weakening. However, the mechanism of repair was only partially explained, as epifluorescence microscopy of calcein staining for shell deposition showed that only half of the mussels that experienced repetitive loading had initiated direct repair via shell growth around fractures. Our findings document repair weeks to months faster than demonstrated in other mollusks. This rapid repair may be important for the mussels’ success contending with predatory and environmental threats in the harsh environment of wave-swept rocky coasts, allowing them to address non-critical but weakening damage and to initiate plastic changes to shell strength. We highlight the significant insight gained by studying biological armors not as static structures but, instead, as dynamic systems that accumulate, repair and respond to damage. 

Abstract Progress in gravitational-wave (GW) astronomy depends upon having sensitive detectors with good data quality. Since the end of the Laser Interferometer Gravitational-Wave Observatory-Virgo-KAGRA third Observing run in March 2020, detector-characterization efforts have lead to increased sensitivity of the detectors, swifter validation of GW candidates and improved tools used for data-quality products. In this article, we discuss these efforts in detail and their impact on our ability to detect and study GWs. These include the multiple instrumental investigations that led to reduction in transient noise, along with the work to improve software tools used to examine the detectors data-quality. We end with a brief discussion on the role and requirements of detector characterization as the sensitivity of our detectors further improves in the future Observing runs. 

The Heisenberg uncertainty principle dictates that the position and momentum of an object cannot be simultaneously measured with arbitrary precision, giving rise to an apparent limitation known as the standard quantum limit (SQL). Gravitational-wave detectors use photons to continuously measure the positions of freely falling mirrors and so are affected by the SQL. We investigated the performance of the Laser Interferometer Gravitational-Wave Observatory (LIGO) after the experimental realization of frequency-dependent squeezing designed to surpass the SQL. For the LIGO Livingston detector, we found that the upgrade reduces quantum noise below the SQL by a maximum of three decibels between 35 and 75 hertz while achieving a broadband sensitivity improvement, increasing the overall detector sensitivity during astrophysical observations.