ALBERT

Description: High-resolution topographic data greatly facilitate the remote identification of geomorphic features, furnishing valuable information concerning surface processes and characterization of reference markers for quantifying tectonic deformation. Marine terraces have been used as long baseline geodetic markers of relative past sea-level positions, reflecting the interplay between vertical crustal movements and sea-level oscillations. Uplift rates may be determined from the terrace age and the elevation of its shoreline angle, a geomorphic feature that can be correlated with past sea-levels positions. A precise definition of the shoreline angle in time and space is essential to obtain reliable uplift rates with coherent spatial correlation. To improve our ability to rapidly assess and map shoreline angles at regional and local scales, we have developed TerraceM, a MATLAB® graphical user interface that allows the shoreline angle and its associated error to be estimated using high-resolution topography. TerraceM uses topographic swath profiles oriented orthogonally to the terrace riser. Four functions are included to analyze the swath profiles and extract the shoreline angle, from both staircase sequences of multiple terraces and rough coasts characterized by eroded remnants of emerged terrace surfaces. The former are measured by outlining the paleocliffs and paleoplatforms and finding their intersection by extrapolating linear regressions, whereas the latter are assessed by automatically detecting peaks of sea-stack tops and back-projecting them to the modern sea cliff. In the absence of rigorous absolute age determinations of marine terraces, their geomorphic age may be estimated using previously published diffusion models. Postprocessing functions are included to obtain first-order statistics of shoreline-angle elevations and their spatial distribution. TerraceM has the ability to process series of profiles from several sites in an efficient and structured workflow. Results may be exported in Google Earth and ESRI shapefile formats. The precision and accuracy of the method have been estimated from a case study at Santa Cruz, California, by comparing TerraceM results with published field measurements. The repeatability was evaluated using multiple measurements made by inexperienced users. TerraceM will improve the efficiency and precision of estimating shoreline-angle elevations in wave-cut terraces in both marine and lacustrine environments.

Description: In species with separate sexes, social systems can differ in the relative variances of male versus female reproductive success. Papionin monkeys (macaques, mangabeys, mandrills, drills, baboons, and geladas) exhibit hallmarks of a high variance in male reproductive success, including a female-biased adult sex ratio and prominent sexual dimorphism. To explore the potential genomic consequences of such sex differences, we used a reduced representation genome sequencing approach to quantifying polymorphism at sites on autosomes and sex chromosomes of the tonkean macaque ( Macaca tonkeana ), a species endemic to the Indonesian island of Sulawesi. The ratio of nucleotide diversity of the X chromosome to that of the autosomes was less than the value (0.75) expected with a 1:1 sex ratio and no sex differences in the variance in reproductive success. However, the significance of this difference was dependent on which outgroup was used to standardize diversity levels. Using a new model that includes the effects of varying population size, sex differences in mutation rate between the autosomes and X chromosome, and GC-biased gene conversion (gBGC) or selection on GC content, we found that the maximum-likelihood estimate of the ratio of effective population size of the X chromosome to that of the autosomes was 0.68, which did not differ significantly from 0.75. We also found evidence for 1) a higher level of purifying selection on genic than nongenic regions, 2) gBGC or natural selection favoring increased GC content, 3) a dynamic demography characterized by population growth and contraction, 4) a higher mutation rate in males than females, and 5) a very low polymorphism level on the Y chromosome. These findings shed light on the population genomic consequences of sex differences in the variance in reproductive success, which appear to be modest in the tonkean macaque; they also suggest the occurrence of hitchhiking on the Y chromosome.

Description: 〈span〉〈div〉Abstract〈/div〉Assessments of megathrust earthquake rupture patterns provide fundamental insights into the processes that control the seismic cycle along subduction zones. When large earthquakes occur in regions with sparse geodetic networks, as was the case for the magnitude (Mw) 7.6 Chiloé, Chile, earthquake of 25 December 2016, estimates of vertical coseismic deformation from fixed intertidal biotic indicators provide important evidence that help to constrain fault slip. Ten months after the Chiloé earthquake, we observed a white fringe of bleached coralline algae (Corallinaceae) along the southeastern coastline of Isla Quilán, south of Isla de Chiloé, killed by reduced tidal wetting resulting from coseismic land uplift. Our quantitative measurements of the vertical extent of algal mortality provide the first field‐based report of the effects of the 2016 earthquake. We infer Isla Quilán coseismically uplifted by 25.8±14.3  cm. The vertical extent of mortality (VEM) and the aspect (compass direction) of the bedrock surface are uncorrelated, but we find that exposure to waves and shielding from insolation may prevent or delay mortality. Focusing on sites sheltered from waves, we demonstrate that with a large number of measurements (〉100), land‐level changes as low as 25 cm may be quantitatively assessed. The absence of bleaching on Isla de Chiloé may reflect the smaller magnitude of coseismic uplift at this location or the lack of suitably sheltered bedrock surfaces. Previously published fault dislocation models are consistent with our field observations; however, the coralline algae data are on their own insufficient to discriminate between competing hypotheses over the amount of fault slip. By combining our field data with space geodetic data in a model that uses detailed fault geometry, we constrain peak slip to ∼3  m, approximately 80% of the maximum cumulative plate convergence since the last great earthquake in the region.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Assessments of megathrust earthquake rupture patterns provide fundamental insights into the processes that control the seismic cycle along subduction zones. When large earthquakes occur in regions with sparse geodetic networks, as was the case for the magnitude (Mw) 7.6 Chiloé, Chile, earthquake of 25 December 2016, estimates of vertical coseismic deformation from fixed intertidal biotic indicators provide important evidence that help to constrain fault slip. Ten months after the Chiloé earthquake, we observed a white fringe of bleached coralline algae (Corallinaceae) along the southeastern coastline of Isla Quilán, south of Isla de Chiloé, killed by reduced tidal wetting resulting from coseismic land uplift. Our quantitative measurements of the vertical extent of algal mortality provide the first field‐based report of the effects of the 2016 earthquake. We infer Isla Quilán coseismically uplifted by 25.8±14.3  cm. The vertical extent of mortality (VEM) and the aspect (compass direction) of the bedrock surface are uncorrelated, but we find that exposure to waves and shielding from insolation may prevent or delay mortality. Focusing on sites sheltered from waves, we demonstrate that with a large number of measurements (〉100), land‐level changes as low as 25 cm may be quantitatively assessed. The absence of bleaching on Isla de Chiloé may reflect the smaller magnitude of coseismic uplift at this location or the lack of suitably sheltered bedrock surfaces. Previously published fault dislocation models are consistent with our field observations; however, the coralline algae data are on their own insufficient to discriminate between competing hypotheses over the amount of fault slip. By combining our field data with space geodetic data in a model that uses detailed fault geometry, we constrain peak slip to ∼3  m, approximately 80% of the maximum cumulative plate convergence since the last great earthquake in the region.〈/span〉

Description: Newly acquired high-resolution bathymetric data (with 5 m and 2 m grid sizes) from the continental shelf off Concepción (Chile), in combination with seismic reflection profiles, reveal a distinctly different evolution for the Biobío submarine canyon compared to that of one of its tributaries. Both canyons are incised into the shelf of the active margin. Whereas the inner shelf appears to be mantled with unconsolidated sediment, the outer shelf shows the influence of strong bottom currents that form drifts of loose sediment and transport material into the Biobío submarine canyon and onto the continental slope. The main stem of the Biobío Canyon is connected to the mouth of the Biobío River and currently provides a conduit for terrestrial sediment from the continental shelf to the deep seafloor. In contrast, the head of its tributary closest to the coast is located ~24 km offshore of the present-day coastline at 120 m water depth, and it is subject to passive sedimentation. However, canyon activity within the study area is interpreted to be controlled not only by the direct input of fluvial sediments into the canyon head facilitated by the river-mouth to canyon-head connection, but also by input from southward-directed bottom currents and possibly longshore drift. In addition, about 24 km offshore of the present-day coastline, the main stem of the Biobío Canyon has steep canyon walls next to sites of active tectonic deformation that are prone to wall failure. Mass-failure events may also foster turbidity currents and contribute to canyon feeding. In contrast, the tributary has less steep canyon walls with limited evidence of canyon-wall failure and is located down-system of bottom currents from the Biobío Canyon. It consequently receives neither fluvial nor longshore sediments. Therefore, the canyon’s connectivity to fluvial or longshore sediment delivery pathways is affected by the distance of the canyon head from the coastline and the orientation of the canyon axis relative to the direction of bottom currents. The ability of a submarine canyon to act as an active conduit for large quantities of terrestrial sediment toward the deep sea during sea-level highstands may be controlled by several different conditions simultaneously. These include bottom current direction, structural deformation of the seafloor affecting canyon location and orientation as well as canyon-wall failure, shelf gradient and associated distance from the canyon head to the coast, and fluvial networks. The complex interplay between these factors may vary even within an individual canyon system, resulting in distinct levels of canyon activity on a regional scale.