Withering Snow and Ice in the Mid-latitudes: A New Archaeological and Paleobiological Record for the Rocky Mountain Region

In the mid-latitude mountains of North America, archaeological materials have been identified in association with kinetically stable “ice patches” that attracted animals and their human predators. The stable ice in these features exhibits little internal deformation or movement and can preserve otherwise perishable materials for millennia. Eight prehistoric sites have been identified in association with perennial ice patches within the Greater Yellowstone Area of Montana and Wyoming. Surveys in Colorado have produced paleobiological samples, but no definitive archaeological sites. Archaeological remains include ancient wooden dart shafts and fragments, wooden artifacts of unknown function, a wrapped leather object of unknown function, butchered animal remains, and chipped stone artifacts. Fragments of weapons ranging in age from 200 to 10 400 years suggest long-term continuity in ice patch hunting in the region. Paleobiological specimens range in age from several hundred to nearly 8000 years. Bighorn sheep (Ovis canadensis) is a presumed prey species, but the remains of bison (Bison bison) and other large ungulates also occur. Ice patches offer important insights into the use of high-elevation environments by Native Americans. Efforts are ongoing to build and maintain awareness of these resources among federal land managers and the public.Dans les montagnes de latitude moyenne de l’Amérique du Nord, du matériel archéologique a été repéré dans des « névés » cinétiquement stables où évoluaient certains animaux de même que leurs prédateurs humains. La glace stable de ces névés présente une déformation ou un mouvement interne minime, ce qui permet de préserver des matériaux périssables pendant des milliers d’années. Huit sites préhistoriques ont été répertoriés dans les névés pérennes de la grande région du Yellowstone se trouvant au Montana et au Wyoming. Au Colorado, des levés ont permis de prélever des échantillons paléo-biologiques, mais aucun site archéologique définitif. Parmi les restes archéologiques retrouvés, notons d’anciennes tiges et d’anciens fragments de propulseurs en bois, des artefacts en bois dont la fonction est inconnue, un objet enveloppé en cuir dont la fonction est inconnue, des restes d’animaux dépecés et des artefacts en pierre taillée. Des fragments d’armes âgés de 200 à 10 400 ans laissent entrevoir que la chasse a été pratiquée dans les névés de la région pendant très longtemps. L’âge des spécimens paléobiologiques varie de plusieurs centaines d’années à près de 8 000 ans. Le mouflon d’Amérique (Ovis canadensis) y est une espèce-proie présumée, et des restes de bisons (Bison bison) et d’autres grands ongulés s’y trouvent également. Les névés permettent de mieux comprendre comment les Autochtones utilisaient les milieux en haute altitude. Les responsables fédéraux de la gestion des terres et le public déploient des efforts constants pour sensibiliser les gens à ces ressources

Oceanic Boundary Conditions for Jakobshavn Glacier. Part II: Provenance and Sources of Variability of Disko Bay and Ilulissat Icefjord Waters, 1990–2011

Jakobshavn Glacier, west Greenland, has responded to temperature changes in Ilulissat Icefjord, into which it terminates. Basin waters in this fjord exchange with neighboring Disko Bay waters of a particular density at least once per year. This study determined the provenance of this isopycnic layer for 1990–2011 using hydrographic data from Cape Farewell to Baffin Bay. The warm Atlantic-origin core of the West Greenland Current never filled deep Disko Bay or entered the fjord basin because of bathymetric impediments on the west Greenland shelf. Instead, equal parts of Atlantic water and less-saline polar water filled the fjord basin and bathed Jakobshavn Glacier. The polar water fraction was often traceable to the East/West Greenland Current but sometimes to the colder Baffin Current. The huge annual temperature cycle on West Greenland Current isopycnals did not propagate into deep Disko Bay or the fjord basin because isopycnals over the west Greenland shelf were depressed during the warm autumn/winter phase of the cycle. Ilulissat Icefjord basin waters were anomalously cool in summer 2010. This was not because of the record low NAO index winter of 2009/10 or atmospheric anomalies over Baffin Bay but, possibly, because of high freshwater flux through the Canadian Arctic and a weak West Greenland Current in early 2010. Together, this caused cold Baffin Current water to flood the west Greenland shelf. Subpolar gyre warming associated with the NAO anomaly in winter 2009/10 was more likely responsible for the record warm Disko Bay and Ilulissat Icefjord basin waters of 2011/12

Internal waves in the Arctic : influence of ice concentration, ice roughness, and surface layer stratification

Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 123 (2018): 5571-5586, doi:10.1029/2018JC014096.The Arctic ice cover influences the generation, propagation, and dissipation of internal waves, which in turn may affect vertical mixing in the ocean interior. The Arctic internal wavefield and its relationship to the ice cover is investigated using observations from Ice‐Tethered Profilers with Velocity and Seaglider sampling during the 2014 Marginal Ice Zone experiment in the Canada Basin. Ice roughness, ice concentration, and wind forcing all influenced the daily to seasonal changes in the internal wavefield. Three different ice concentration thresholds appeared to determine the evolution of internal wave spectral energy levels: (1) the initial decrease from 100% ice concentration after which dissipation during the surface reflection was inferred to increase, (2) the transition to 70–80% ice concentration when the local generation of internal waves increased, and (3) the transition to open water that was associated with larger‐amplitude internal waves. Ice roughness influenced internal wave properties for ice concentrations greater than approximately 70–80%: smoother ice was associated with reduced local internal wave generation. Richardson numbers were rarely supercritical, consistent with weak vertical mixing under all ice concentrations. On decadal timescales, smoother ice may counteract the effects of lower ice concentration on the internal wavefield complicating future predictions of internal wave activity and vertical mixing.Seagliders Grant Number: N00014‐12‐10180; Deployment and subsequent analysis efforts of the ITP‐Vs Grant Numbers: N00014‐12‐10799, N00014‐12‐10140; Joint Ocean Ice Studies cruise; Beaufort Gyre Observing System2019-02-1

Introduction to special section : U.S. GLOBEC : physical processes on Georges Bank (GLOBEC)

Author Posting. © American Geophysical Union, 2003. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 108, C11 (2003): 8000, doi:10.1029/2003JC002165.Support for the guest editors was provided by NSF grant OCE 02-27679 (RB), the Bedford Institute of Oceanography (PS), and NSF grant OCE 01-07946 (CL)

Molecular Line Emission from Gravitationally Unstable Protoplanetary Disks

In the era of high resolution submillimeter interferometers, it will soon be possible to observe the neutral circumstellar medium directly involved in gas giant planet (GGP) formation at physical scales previously unattainable. In order to explore possible signatures of gas giant planet formation via disk instabilities, we have combined a 3D, non-local thermodynamic equilibrium (LTE) radiative transfer code with a 3D, finite differences hydrodynamical code to model molecular emission lines from the vicinity of a 1.4 M_J self-gravitating proto-GGP. Here, we explore the properties of rotational transitions of the commonly observed dense gas tracer, HCO+. Our main results are the following: 1. Very high lying HCO+ transitions (e.g. HCO+ J=7-6) can trace dense planet forming clumps around circumstellar disks. Depending on the molecular abundance, the proto-GGP may be directly imageable by the Atacama Large Millimeter Array (ALMA). 2. HCO+ emission lines are heavily self-absorbed through the proto-GGP's dense molecular core. This signature is nearly ubiquitous, and only weakly dependent on assumed HCO+ abundances. The self-absorption features are most pronounced at higher angular resolutions. Dense clumps that are not self-gravitating only show minor self-absorption features. 3. Line temperatures are highest through the proto-GGP at all assumed abundances and inclination angles. Conversely, due to self-absorption in the line, the velocity-integrated intensity may not be. High angular resolution interferometers such as the Submillimeter Array (SMA) and ALMA may be able to differentiate between competing theories of gas giant planet formation.Comment: 10 pages, 13 figures; Accepted by Ap

Autonomous instruments significantly expand ocean observing : an introduction to the special issue on autonomous and Lagrangian platforms and sensors (ALPS).

Author Posting. © The Oceanography Society, 2017. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 30, no. 2 (2017): 15–17, doi:10.5670/oceanog.2017.211.Oceanography relies heavily on observations to fuel new ideas and drive advances, creating a strong coupling between the science and the technological developments that enable new measurements. Novel observations, such as those that resolve new properties or scales, often lead to advances in understanding. Physical, biological, and chemical processes unfold over a broad range of scales—seconds to decades and millimeters to ocean basins—with critical interactions between scales. Observational studies work within a tradespace that balances spatial and temporal resolution, scope, and resource constraints. New platforms and sensors, along with the novel observational approaches they enable, address this challenge by providing access to an expanding range of temporal and spatial scales

Elsinore fault seismicity: The September 13, 1973, Agua Caliente Springs, California, earthquake series

A relatively small M_L = 4.8 earthquake and its aftershock series on the southern portion of the Elsinore Fault Zone in eastern San Diego County, California, provided a rare opportunity to study an area that has been subjected to variable tectonic interpretations in the past. Within 12 to 26 hours after the main shock, a network of four portable seismograph stations was established around the main event near Agua Caliente Springs to supplement the stations of the Southern California Seismographic Network. Four days after the main shock, seven additional portable seismograph stations were installed. In addition to the main event, 45 subsequent events were studied, ranging in magnitude from about 1.0 to 3.7. Of these, 36 could be termed aftershocks by their close proximity to the main event, whose proper location was determined by analysis of the aftershock series. Of the two branches of the Elsinore Fault in this region, the south branch is associated with the earthquake series. Focal mechanisms are consistent with right-lateral strike-slip along the south branch, with northeast dip at latitude 32°51′N. These conclusions are supported by hypocentral locations. Thrust activity on the two fault branches may be developing a horst between them, accounting for elevation and tilt changes observed near Agua Caliente