Impedance matching to axion dark matter: considerations of the photon-electron interaction

We introduce the concept of impedance matching to axion dark matter by posing the question of why axion detection is difficult, even though there is enough power in each square meter of incident dark-matter flux to energize a LED light bulb. By quantifying backreaction on the axion field, we show that a small axion-photon coupling does not by itself prevent an order-unity fraction of the dark matter from being absorbed through optimal impedance match. We further show, in contrast, that the electromagnetic charges and the self-impedance of their coupling to photons provide the principal constraint on power absorption integrated across a search band. Using the equations of axion electrodynamics, we demonstrate stringent limitations on absorbed power in linear, time-invariant, passive receivers. Our results yield fundamental constraints, arising from the photon-electron interaction, on improving integrated power absorption beyond the cavity haloscope technique. The analysis also has significant practical implications, showing apparent tension with the sensitivity projections for a number of planned axion searches. We additionally provide a basis for more accurate signal power calculations and calibration models, especially for receivers using multi-wavelength open configurations such as dish antennas and dielectric haloscopes.

Benthic Foraminiferal Response to the Millennial-Scale Variations in Monsoon-Driven Productivity and Deep-Water Oxygenation in the Western Bay of Bengal During the Last 45 ka

In this study, we presented a high-resolution benthic foraminiferal assemblage record from the western Bay of Bengal (BoB) (off Krishna–Godavari Basin) showing millennial-scale variations during the last 45 ka. We studied temporal variations in benthic foraminiferal assemblages (relative abundances of ecologically sensitive groups/species, microhabitat categories, and morphogroups) to infer past changes in sea bottom environment and to understand how monsoon induced primary productivity-driven organic matter export flux and externally sourced deep-water masses impacted the deep-sea environment at the core site. Our records reveal a strong coupling between surface productivity and benthic environment on glacial/interglacial and millennial scale in concert with Northern Hemisphere climate events. Faunal data suggest a relatively oxic environment when the organic matter flux to the sea floor was low due to low primary production during intensified summer monsoon attributing surface water stratification and less nutrient availability in the mixed layer. Furthermore, records of oxygen-sensitive benthic taxa (low-oxygen vs. high-oxygen benthics) indicate that changes in deep-water circulation combined with the primary productivity-driven organic matter flux modulated the sea bottom oxygen condition over the last 45 ka. We suggest that the bottom water at the core site was well-ventilated during the Holocene (except for the period since 3 ka) compared with the late glacial period. At the millennial timescale, our faunal proxy records suggest relatively oxygen-poor condition at the sea floor during the intervals corresponding to the cold stadials and North Atlantic Heinrich events (H1, H2, H3, and H4) compared with the Dansgaard/Oeschger (D-O) warm interstadials. The study further reveals oxygen-poor bottom waters during the last glacial maximum (LGM, 19–22 ka) which is more pronounced during 21–22 ka. A major shift in sea bottom condition from an oxygenated bottom water during the warm Bølling–Allerød (B/A) (between 13 and 15 ka) to the oxygen-depleted condition during the cold Younger Dryas (YD) period (between 10.5 and 13 ka) is noticed. It is likely that the enhanced inflow of North Atlantic Deep Water (NADW) to BoB would have ventilated bottom waters at the core site during the Holocene, B/A event, and probably during the D-O interstadials of marine isotope stage (MIS) 3.

Ammonia-oxidizing archaea have similar power requirements in diverse marine oxic sediments

Energy/power availability is regarded as one of the ultimate controlling factors of microbial abundance in the deep biosphere, where fewer cells are found in habitats of lower energy availability. A critical assumption driving the proportional relationship between total cell abundance and power availability is that the cell-specific power requirement keeps constant or varies over smaller ranges than other variables, which has yet to be validated. Here we present a quantitative framework to determine the cell-specific power requirement of the omnipresent ammonia-oxidizing archaea (AOA) in eight sediment cores with 3–4 orders of magnitude variations of organic matter flux and oxygen penetration depth. Our results show that despite the six orders of magnitude variations in the rates and power supply of nitrification and AOA abundances across these eight cores, the cell-specific power requirement of AOA from different cores and depths overlaps within the narrow range of 10−19–10−17 W cell−1, where the lower end may represent the basal power requirement of microorganisms persisting in subseafloor sediments. In individual cores, AOA also exhibit similar cell-specific power requirements, regardless of the AOA population size or sediment depth/age. Such quantitative insights establish a relationship between the power supply and the total abundance of AOA, and therefore lay a foundation for a first-order estimate of the standing stock of AOA in global marine oxic sediments.

Surface- and deep-water response to the Early Aptian OAE 1a in the western Tethys

<p>The Cretaceous was punctuated by interludes of widespread deposition of organic-rich sediments (black shales) in the oceans and epicontinental seas, named Oceanic Anoxic Events (OAE)s, representing major alterations in the global carbon budget. The early Aptian OAE 1a (ca. 120 Ma) coincided with a global paleoclimatic and paleoenvironmental perturbation which lasted for ca. 1.1 Myrs probably triggered by volcanogenic CO<sub>2 </sub>emissions associated with the emplacement of the Ontong Java Plateau. To date, there is a comprehensive characterization of OAE 1a paleoceanographic conditions and paleoecology of surface-waters while less information is available for bottom-water evolution. In this regard, benthic foraminifera are ideal to characterize deep-water oxygen levels and the organic carbon flux. We present a high-resolution study of benthic foraminiferal assemblages across OAE 1a in the Cismon Core (western Tethys, Lombardy Basin, Northern Italy). Contrarily to many sites, the Cismon Core yields benthic foraminifera also in the Selli Level thus providing information about deep-water conditions during OAE 1a. Our data are indicative of fluctuations in bottom-water oxygenation and organic-matter flux to the sea-floor prior to, during and after OAE 1a. The integration of the new benthic foraminiferal data with calcareous nannofossil and planktonic foraminiferal datasets is here used to produce a model of surface- to bottom-water paleowater evolution through the latest Barremian-early late Aptian. In particular, the new data show coeval changes in bottom- and surface-waters conditions prior to and at the onset of OAE 1a. Anoxia was reached during the core of the negative carbon isotope anomaly, under maximum warming and higher surface-water fertility. Conversely, the repopulation of benthic foraminifera postponed the plankton recovery. Benthic foraminifera data at Cismon show, for the first time, evidence of a repopulation event during the OAE 1a suggestive for a slight increase in the supply of oxygen to the seafloor during the Selli Level deposition.</p>

The evolution of the Carpathian Foredeep Basin during the latest Badenian and Sarmatian (Middle Miocene): inferences from micropalaeontological data

Seven Middle Miocene (Upper Badenian to Lower Sarmatian) sedimentary sections of the Central Paratethys, two from the Polish Carpathian Foredeep Basin (PCFB) and five from the Eastern Carpathian Foreland Basin (ECFB) of Romania and the Republic of Moldova have been analysed micropalaeontologically to better constrain the Badenian-Sarmatian Extinction Event, characterized by significant taxonomic impoverishment of both foraminifers and ostracods. Our studies show significant palaeoenvironmental changes in the basin including depth, salinity, oxygenation, and organic matter flux. The occurrence of moderately diverse planktonic foraminifera (Globigerina, Globigerinita, Globorotalia, Trilobatus, Orbulina, Velapertina) in the Upper Badenian deposits of the PCFB as well as in the ECFB and their rarity in the lowermost Sarmatian indicate an almost fully marine environment during the latest Badenian, followed by a significant regression and possible appearance of much more restricted marine conditions across the boundary. The taxonomic composition of the Sarmatian foraminifera, ostracoda and calcareous nannofossils indicate that during this interval the salinity fluctuated strongly, with the water regime varying from brackish to normal marine. In addition, the identified micropalaeontological assemblages identified show palaeoenvironmental similarity across different basins of the Central Paratethys. This supports a hypothesis of possible connections during the latest Badenian between different areas of the Central Paratethys, as well as of the existence of a gateway between the Central Paratethys and the Mediterranean realm

Two-dimensional area and matter flux in the theory of causal fermion systems

The notions of two-dimensional area, Killing fields and matter flux are introduced in the setting of causal fermion systems. It is shown that for critical points of the causal action, the area change of two-dimensional surfaces under a Killing flow in null directions is proportional to the matter flux through these surfaces. This relation generalizes an equation in classical general relativity due to Ted Jacobson setting of causal fermion systems.

Summer rainfall dissolved organic carbon, solute, and sediment fluxes in a small Arctic coastal catchment on Herschel Island (Yukon Territory, Canada)

Coastal ecosystems in the Arctic are affected by climate change. As summer rainfall frequency and intensity are projected to increase in the future, more organic matter, nutrients and sediment could be mobilized and transported into the coastal nearshore zones. However, knowledge of current processes and future changes is limited. We investigated streamflow dynamics and the impacts of summer rainfall on lateral fluxes in a small coastal catchment on Herschel Island in the western Canadian Arctic. For the summer monitoring periods of 2014–2016, mean dissolved organic matter flux over 17 days amounted to 82.7 ± 30.7 kg km−2 and mean total dissolved solids flux to 5252 ± 1224 kg km−2. Flux of suspended sediment was 7245 kg km−2 in 2015, and 369 kg km−2 in 2016. We found that 2.0% of suspended sediment was composed of particulate organic carbon. Data and hysteresis analysis suggest a limited supply of sediments; their interannual variability is most likely caused by short-lived localized disturbances. In contrast, our results imply that dissolved organic carbon is widely available throughout the catchment and exhibits positive linear relationship with runoff. We hypothesize that increased projected rainfall in the future will result in a similar increase of dissolved organic carbon fluxes.