Error determination in the photogrammetric assessment of shoreline changes

The evaluation of error or uncertainty in shoreline change studies is an issue of prime importance for providing an adequate framework for calculated rates of change and to allow the establishment of threshold values above which the rates would be significant. In this note, a practical, easy-to-use method is presented to estimate error involved in the calculation of shoreline changes on aerial photographs, including the three most used types of shoreline indicators: high water line, dune/cliff toe and cliff top. This approach takes into account the specific characteristics of each shoreline proxy, such as relief in the case of the cliff top or tidal oscillations in the case of the high water line. At the same time it includes the error components that are independent from the proxy, basically related to the technical aspects of the process such as photo scanning and georeferencing. A practical example of application of the method is provided for several types of data inputs, based on shoreline changes around the Bay of Cádiz (SW Spain)

Mitochondrial phylogeography of baboons (Papio spp.) – Indication for introgressive hybridization?

<p>Abstract</p> <p>Background</p> <p>Baboons of the genus <it>Papio </it>are distributed over wide ranges of Africa and even colonized parts of the Arabian Peninsula. Traditionally, five phenotypically distinct species are recognized, but recent molecular studies were not able to resolve their phylogenetic relationships. Moreover, these studies revealed para- and polyphyletic (hereafter paraphyletic) mitochondrial clades for baboons from eastern Africa, and it was hypothesized that introgressive hybridization might have contributed substantially to their evolutionary history. To further elucidate the phylogenetic relationships among baboons, we extended earlier studies by analysing the complete mitochondrial cytochrome <it>b </it>gene and the 'Brown region' from 67 specimens collected at 53 sites, which represent all species and which cover most of the baboons' range.</p> <p>Results</p> <p>Based on phylogenetic tree reconstructions seven well supported major haplogroups were detected, which reflect geographic populations and discordance between mitochondrial phylogeny and baboon morphology. Our divergence age estimates indicate an initial separation into southern and northern baboon clades 2.09 (1.54–2.71) million years ago (mya). We found deep divergences between haplogroups within several species (~2 mya, northern and southern yellow baboons, western and eastern olive baboons and northern and southern chacma baboons), but also recent divergence ages among species (< 0.7 mya, yellow, olive and hamadryas baboons in eastern Africa).</p> <p>Conclusion</p> <p>Our study confirms earlier findings for eastern Africa, but shows that baboon species from other parts of the continent are also mitochondrially paraphyletic. The phylogenetic patterns suggest a complex evolutionary history with multiple phases of isolation and reconnection of populations. Most likely all these biogeographic events were triggered by multiple cycles of expansion and retreat of savannah biomes during Pleistocene glacial and inter-glacial periods. During contact phases of populations reticulate events (i.e. introgressive hybridization) were highly likely, similar to ongoing hybridization, which is observed between East African baboon populations. Defining the extent of the introgressive hybridization will require further molecular studies that incorporate additional sampling sites and nuclear loci.</p

Formation of gullies on Mars by debris flows triggered by CO_2 sublimation

Martian gully landforms resemble terrestrial debris flows formed by the action of liquid water and have thus been interpreted as evidence for potential habitable environments on Mars within the past few millennia. However, ongoing gully formation has been detected under surface conditions much too cold for liquid water, but at times in the martian year when a thin layer of seasonal CO_2 frost is present and defrosting above the regolith. These observations suggest that the CO_2 condensation–sublimation cycle could play a role in gully formation. Here we use a thermo-physical numerical model of the martian regolith underlying a CO_2 ice layer and atmosphere to show that the pores beneath the ice layer can be filled with CO_2 ice and subjected to extreme pressure variations during the defrosting season. The subsequent gas fluxes can destabilize the regolith material and induce gas-lubricated debris flows with geomorphic characteristics similar to martian gullies. Moreover, we find that subsurface CO_2 ice condensation, sublimation and pressurization occurs at conditions found at latitudes and slope orientations where gullies are observed. We conclude that martian gullies can result from geologic dry ice processes that have no terrestrial analogues and do not require liquid water. Such dry ice processes may have helped shape the evolution of landforms elsewhere on the martian surface

Nearshore Sediment Transport in a Changing Climate

The impact of changing wave climate on the most important nearshore process, longshore sediment transport (LST), along the central west coast of India is investigated. The main purpose of this study is to provide a better understanding of the meteo-marine climate of the central west coast of India, which is highly influenced by the Arabian Sea and the Indian Ocean. To understand the contemporary evolution of the coastline, hindcast wave climate from ERA-Interim wave data (1979–2016) is used. The annual average significant wave height (Hs), wave period (Tp) and wave direction (α0) are obtained and used to estimate annual LST. This region receives oblique waves from the W-SW direction which induces a huge gross northerly transport. It experiences two types of waves, swell waves (remotely generated waves that travel thousands of kilometres before hitting the coastline) and wind waves (also known as seas, which are locally generated), both of which are responsible for coastal sediment transport. The swell waves are the major component of a total wave system. It has more strength than the locally generated wind waves and dictates the wave direction and significant wave height at any given point of time. Therefore, the swell wave-induced LST is an order of magnitude higher than the wind wave-induced LST. It was observed that the sediment transport has a seasonal nature due to the influence of monsoonal winds in this region. The total LST in the central west coast of India shows a decreasing trend due to the reduced swell generation in the lower latitudes of the Arabian Sea and the Indian Ocean

Chk1 deficiency in the mouse small intestine results in p53-independent crypt death and subsequent intestinal compensation

Chk1 is a serine/threonine protein kinase which is activated by a wide range of DNA damaging agents in order to slow the cell cycle during S phase and G2/M. Abrogation of these cell cycle checkpoints using Chk1 inhibitors results in hypersensitivity to DNA damaging agents in vitro and may provide a potential therapeutic tool to sensitize tumour cells in vivo. We have generated a Cre-Lox based mouse model, where Chkl can be inducibly deleted from somatic epithelial cells in the adult mouse small intestine and liver. Loss of Chk1 in the liver is tolerated with no apparent phenotype. In contrast, loss of Chk1 within the small intestine results in immediate DNA damage, and high levels of p53-independent apoptosis leading to crypt death. However, the intestine is able to compensate for this death by undergoing complete repopulation with Chk1 proficient cells. This data therefore shows that Chk1 deficiency is cell lethal, but the intestine can tolerate such lethality at the organ level