Composite microbialites: Thrombolite, dendrolite, and stromatolite associations in a modern environment, Pozo Bravo lake, Salar de Antofalla, Catamarca Puna, Argentina

ABSTRACT Pozo Bravo is a high-altitude Andean lake that harbors modern microbialites thriving in hypersaline conditions in the Salar de Antofalla, one of the driest sites on Earth and located in the Puna region of Catamarca, northwest Argentine. Due to the lake physiography, microbialites are restricted to a narrow belt following Pozo Bravo lake variations. Microbialites exhibit a wide range of external morphologies including domal, discoidal, tabular, and horseshoe-like bioherms which vary considerably in size, as well as large biostromal terraces. As documented by other studies on modern microbialites, external morphology appears to be mainly the product of the environmental setting. In Pozo Bravo lake, high evaporation rates and hypersalinity (driven by high temperature and strong winds), water-level fluctuations, and lake-bottom topography are major controlling factors. The distinctive feature of Pozo Bravo microbialites is their internal structure, showing a gradual transition from a thrombolitic core to dendrolitic structures and to a sharply overlying stromatolitic layer within a single microbialite. We suggest that these various microbialite textures represent a gradual change within an environmental gradient based on lake-level variations, and the influence of these environmental factors on biological activity, mainly by cyanobacteria and diatoms. The study of this site is particularly relevant given that it represents an active system where progressive changes in microbialite type (from thrombolites to dendrolites and stromatolites) are recorded, providing an excellent natural laboratory to study these textural changes from a mechanistic perspective, and it may provide insights for better understanding of the microbialite geological record. In addition, given that these systems are threatened by human activities (mining of lithium-rich brines), its study and preservation are necessary.

Ice shelf internal reflection horizons reveal ice provenance, dynamics, surface accumulation and oceanic melt

<p>Ice shelves are widely known to slow the transfer of Antarctic grounded ice to the ocean, especially if their flow is decelerated by local pinning points. Their longevity is influenced by variations in ice dynamics, surface accumulation and oceanic conditions in the ice shelf cavity. This is reflected in the ice shelf structure, which can be characterized by the shape of internal radar reflection horizons.</p><p>We aim to map the internal ice shelf stratigraphy of ice shelves, starting with the narrow belt of ice-shelves in the Dronning Maud Land area. The final goal will be to evaluate these as a spatiotemporal archive of ice provenance and ice dynamics. The bulk of the data presented here were collected with AWI’s airborne multi frequency ultra-wideband radar and we combine these new observations with airborne and ground-based radar surveys from previous years. We present a consistent set of internal radar isochrones on a catchment scale for the Roi Baudoin area including the Ragnhild ice streams, the grounding-zone, the iceshelf and multiple ice rises.  Using pattern matching technique we can link isochrones across different ice rises in the area, and hence provide first observational constraints on how ice rises jointly react to changes in atmospheric and oceanographic forcings. We also find a number of interesting features including dynamically induced dips in shear zones, truncating layers at the ice-shelf base, and the development of a meteoric ice layer distinguishing advected from newly accumulated ice in the iceshelf. The time series provided by radar observations over the last 10 years also offers the potential to map temporal changes. We use ice-flow modelling to provide age constraints for some internal layers and delineate portions within the shelf as a function of their advection history, hence marking areas of differing rheologies within the shelf. Taken together, this case study on a catchment scale is a primer to unravel the information stored in the isochronal stratigraphy of coastal Antarctica and contributes to international efforts (e.g., SCAR AntArchitecture)  of mapping stratigraphy on ice sheet scales.</p>

Spatio-temporal patterns of the Red-footed Falcon’s hunting behavior during the nestling period suggest ad hoc conservation policies

The Red-footed Falcon (Falco vespertinus) is a species of high international conservation interest. We analyzed its hunting behavior at the two largest colonies in Italy during the nestling period. Using accurate data-loggers, we tracked three adult Red-footed Falcons in June and July, 2019 and collected 4703 GPS points. We detected clear patterns of hovering and perching activity (HPA) in both time and space. HPA occupied one-third of the Red-footed Falcons’ day, and showed two peaks just after sunrise (between 35 and 40% of the monitoring time) and just before sunset (50‒60%) in both June and July, and minimum (20‒30%) at night and during the hottest time interval (10:00 a.m.‒4:00 p.m.). Almost 40% of HPA occurred within 50 m from nests. Our findings, although preliminary, have important implications for the conservation of these two colonies that are located within two Natura 2000 sites. The detected spatio-temporal patterns of Red-footed Falcons’ hunting behavior suggests the creation of two nested protection belts: the inner one is a narrow belt (up to 50 m from the two rows of trees that host the two colonies) with integral conservation, and hopefully increase the alfalfa crops and fallow land, and the outer belt (50 m‒2 km) with optimized agricultural activities.

The unexpected narrowness of eccentric debris rings: a sign of eccentricity during the protoplanetary disc phase

This paper shows that the eccentric debris rings seen around the stars Fomalhaut and HD 202628 are narrower than expected in the standard eccentric planet perturbation scenario (sometimes referred to as ‘pericentre glow’). The standard scenario posits an initially circular and narrow belt of planetesimals at semi-major axis a , whose eccentricity is increased to e f after the gas disc has dispersed by secular perturbations from an eccentric planet, resulting in a belt of width 2 ae f . In a minor modification of this scenario, narrower belts can arise if the planetesimals are initially eccentric, which could result from earlier planet perturbations during the gas-rich protoplanetary disc phase. However, a primordial eccentricity could alternatively be caused by instabilities that increase the disc eccentricity, without the need for any planets. Whether these scenarios produce detectable eccentric rings within protoplanetary discs is unclear, but they nevertheless predict that narrow eccentric planetesimal rings should exist before the gas in protoplanetary discs is dispersed. PDS 70 is noted as a system hosting an asymmetric protoplanetary disc that may be a progenitor of eccentric debris ring systems.

Methodology for Carrying out Measurements of the Tombolo Geomorphic Landform Using Unmanned Aerial and Surface Vehicles near Sopot Pier, Poland

The human impact on the ecosystem has been particularly evident in the last century; it transforms the Earth’s surface on an unprecedented scale and brings about irreversible changes. One example is an oceanographic phenomenon known as a tombolo, i.e., a narrow belt connecting the mainland with an island lying near the shore formed as a result of sand and gravel being deposited by sea currents. The phenomenon contributes to an increase in the biogenic substance content in the littoral zone, which leads to increased cyanobacteria blooming in the summer period. Moreover, the debris accumulation in the littoral zone results in the mud formation, which makes the beach landscape less attractive. One of the main features of the tombolo phenomenon is its variability of shape, which includes the form of both the shore and the seabed adjacent to it. Therefore, to describe its size and spatio-temporal variability, it is necessary to apply methods for geodetic (the land) and hydrographic (the sea) measurements that can be carried out in different ways. The aim of the paper is to present the methodology for carrying out measurements of the tombolo oceanographic phenomenon using Unmanned Aerial Vehicles (UAV) and Unmanned Surface Vehicles (USV) on the example of a waterbody adjacent to the Sopot pier. It also presents the results of surveys carried out in November 2019 within this area. The study demonstrated that the integration of two measuring devices whose development began in the second decade of the 20th century, i.e., UAVs and USVs, enables accurate (even up to several centimeters) and reliable determination of the scale and variability of the phenomena occurring in the littoral zone.

Geospatial Modeling of the Tombolo Phenomenon in Sopot using Integrated Geodetic and Hydrographic Measurement Methods

A tombolo is a narrow belt connecting a mainland with an island lying near to the shore, formed as a result of sand and gravel being deposited by sea currents, most often created as a result of natural phenomena. However, it can also be caused by human activity, as is the case with the Sopot pier—a town located on the southern coast of the Baltic Sea in northern Poland (φ = 54°26’N, λ = 018°33’E). As a result, the seafloor rises constantly and the shoreline moves towards the sea. Moreover, there is the additional disturbing phenomenon consisting of the rising seafloor sand covering over the waterbody’s vegetation and threatening the city's spa character. Removal of the sand to another place has already been undertaken several times. There is a lack of precise geospatial data about the tombolo’s seafloor course, its size and spatial shape caused by only lowering the seafloor in random places, and the ongoing environmental degradation process. This article presents the results of extensive and integrated geodetic and hydrographic measurements, the purpose of which was to make a 3D model of the phenomena developing in Sopot. The measurements will help determine the size and speed of the geospatial changes. Most of the modern geodetic and hydrographic methods were used in the study of these phenomena. For the construction of the land part of geospatial model, the following were used: photos from the photogrammetric flight pass (unmanned aerial vehicle—UAV), laser scanning of the beach and piers, and satellite orthophotomaps for analysis of the coastline changes. In the sea part, bathymetric measurements were carried out with an unmanned surface vehicle (USV).

Accuracy Analysis of Measuring X-Y-Z Coordinates with Regard to the Investigation of the Tombolo Effect

Tombolo is a narrow belt connecting the mainland with an island lying near the shore. It is formed as a result of sand and gravel being deposited by sea currents. In consequence, the seabed constantly rises and the shoreline moves towards the sea. This paper deals with accuracy analysis of the undertaken tombolo effect investigation, namely estimation of uncertainty of the measurement results. The aforementioned analysis concerns two methods used for creating a 3D beach model: Firstly, based on geodetic laser scanning (TLS—terrestrial laser scanning) and secondly, using images from unmanned aerial vehicles (UAV). The presented exemplary estimation of uncertainty of the measurement of coordinates X-Y-Z is based on the Polish case study.

Morphotectonic aspects in a part of Naga-Schuppen belt, Assam-Nagaland region, Northeast India

The Belt of Schuppen is an important tectonic element of the Assam-Arakan basin. It is a narrow belt of thrust slices in southeastern boundary of the Assam valley. The Naga Schuppen Belt, consisting of eight or more imbricated thrusts, occurs between the Naga and Disang thrusts. This present study encompasses an area of 4,720 sq km along the Assam-Nagaland border. The Dikhow River, which is a seventh order basin, originates from Naga Hills flowing through a total length of 240 km in the Assam valley and reaches the Brahmaputra. In this study, the morphotectonic analysis of the Dikhow River was carried out to understand the role of active tectonics of the Naga Hills in Nazira-Naginimora areas of Assam and Nagaland respectively. The parameters such as asymmetric factor (AF), transverse topographic symmetric factor (T), and stream length gradient index (SL) were computed. Absolute AF values shows asymmetric to highly asymmetrical shape of the basins (range III-IV) which is also supported by T values. Anomalous SL values were obtained wherein major lineament and tectonic features are present. This indicates that the study area is tectonically active. Further, in the Assam valley it has been observed in the bank stratigraphy of Dikhow River that the Quaternary sediments are deformed. This deformation of the soft older alluvium indicates that the area is undergoing deformation during post Pliocene time. This evidence demands the morphotectonic evaluation of the aforesaid area to demarcate the tectonic activeness of the region in post Pliocene times.

Itinéraires et mutations urbaines dans le Mašriq islamique (ier/viie-iiie/ixe siècles)

In the 1st/7th and the early 2nd/8th centuries, the Arab-Muslim conquest united two immense territories, once separated by a shifting border joining the Black sea to the Persian Gulf. To the East, the Arab-Muslims dominated Central Asia and the long-held Asian empire of the Sassanids that reached as far as the Chinese and Indian borders. To the West, they controlled the southern part of the Eastern and Western Roman empires. In the 2nd/8th century, the area conquered thus formed a narrow belt of lands from the Atlantic to the Chinese borders and from Georgia to Yemen. The Middle East became a converging hub of merchants and commercial goods. The article aims to discuss the political and social mechanisms involved in redrawing the map of the routes in the Mašriq from the early Umayyads in 41/661 to the death of caliph al-Muktafī in 295/908. It investigates the impact the evolution of road networks had on settlement patterns and economic strategies. Au ier/viie et au début du iie/viiie siècle, la conquête arabo-musulmane réunit deux immenses territoires, jusqu’alors séparés par une frontière au tracé mouvant joignant la mer Noire au golfe Persique. À l’Est, les Arabo-musulmans dominent l’Asie centrale et l’ancien empire asiatique des Sassanides jusqu’aux confins chinois, et à l’Ouest, la partie méridionale des empires romains d’Orient et d’Occident. L’espace conquis forme au iie/viiie siècle une étroite ceinture de terres de l’Atlantique aux confins de la Chine et de la Géorgie au Yémen. Dans cet espace immense, jusque-là si divisé, le Proche-Orient devient le pôle de convergence des marchands et des biens. Cette reconfiguration géopolitique du Proche-Orient au début de l’Islam entraîne des changements décisifs. L’enjeu de cet article est d’appréhender par quels mécanismes politiques et sociaux la carte des réseaux routiers du Mašriq a été redessinée entre le début du règne des Omeyyades en 41/661 et le décès du calife al-Muktafī en 295/908. Il s’agit d’explorer quel impact l’évolution des trafics eut sur les dynamiques de peuplement et sur les échanges. This article is in French.