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Ice shelves influence the mass balance of the Antarctic Ice Sheet by restricting the flow of ice across the grounding zone. Their ability to restrict ice flow is sensitive to changes in their extent or thickness. Full thickness fractures, known as rifts, create tabular icebergs which reduce ice shelf extent. We present a method for measuring rift width using ICESat-2 laser altimetry, as part of a larger effort to detect, catalog and measure various characteristics of Antarctic rifts. We validate the results using optical satellite imagery and data from Global Navigation Satellite System (GNSS) receivers around "Halloween Crack" on Brunt Ice Shelf, East Antarctica. During the study period a further rift, "North Rift" formed and rapidly calved a ~1270 km2 iceberg. In response to this second rift, the opening of Halloween Crack approached stagnation before returning to opening at a reduced rate. We suggest the opening rate is controlled by the ice shelf geometry and degree of contact with a pinning point at McDonald Ice Rumples, and its influence on the large-scale ice flow field. We replicate the general pattern of opening using an inverse finite element model, and discuss the response of the ice shelf to the calving. We use historical satellite imagery and previously published ice-front positions to demonstrate the importance of McDonald Ice Rumples to the long-term calving and advance cycle of Brunt Ice Shelf.

Compositional heterogeneities within Europa’s ice shell likely impact the dynamics and habitability of the ice and subsurface ocean, but the total inventory and distribution of impurities within th...

Maladaptation to modern diets has been implicated in several chronic disorders. Given the higher prevalence of disease such as dental caries and chronic gum diseases in industrialized societies, we sought to investigate the impact of different subsistence strategies on oral health and physiology, as documented by the oral microbiome. To control for confounding variables such as environment and host genetics, we sampled saliva from three pairs of populations of hunter-gatherers and traditional farmers living in close proximity in the Philippines. Deep shotgun sequencing of salivary DNA generated high-coverage microbiomes along with human genomes. Comparing these microbiomes with publicly available data from individuals living on a Western diet revealed that abundance ratios of core species were significantly correlated with subsistence strategy, with hunter-gatherers and Westerners occupying either end of a gradient of Neisseria against Haemophilus, and traditional farmers falling in between. Species found preferentially in hunter-gatherers included microbes often considered as oral pathogens, despite their hosts' apparent good oral health. Discriminant analysis of gene functions revealed vitamin B5 autotrophy and urease-mediated pH regulation as candidate adaptations of the microbiome to the hunter-gatherer and Western diets, respectively. These results suggest that major transitions in diet selected for different communities of commensals and likely played a role in the emergence of modern oral pathogens.

The presence of smooth, young surfaces indicates that regions of Enceladus and Europa have been resurfaced through recent or ongoing activity related to the eruption of liquid water from subsurface reservoirs. For interior material to erupt or flow out onto the surfaces of these satellites, fractures would have to vertically penetrate the ice shell to the depth of a subsurface reservoir or ocean. Here we use linear elastic fracture mechanics to show that accounting for fracture interactions makes it much more difficult for fractures to penetrate the entire ice shell than previous estimates. We found that fractures that originate from the surface are unlikely to penetrate the entire shell thickness, even for the upper range of tectonic stresses estimated for each moon. Tensile fractures that initiate from the bottom of the icy shell—as observed in terrestrial ice shelves—propagate further into the icy shell than surface crevasses but still do not penetrate the entire ice thickness. However, full ice shell thickness fracture is possible if shear failure connects the surface with deep-penetrating basal fractures in thinner ice shell thicknesses and under certain stress conditions. This suggests that the combination of tensile and shear failure may be important and necessary for the formation of a connection from the surface to the ocean below.

Here we investigate the largest acceleration in ice flow across all of Antarctica between ∼2008 InSAR and 2014 Landsat velocity mappings. This occurred in glaciers that used to feed into the Wordie Ice Shelf on the west Antarctic Peninsula, which rapidly disintegrated in ∼1989. Between 2008 and 2014, these glaciers experienced at least a threefold increase in surface elevation drawdown relative to the 2002–2008 time period. After ∼20 yrs of relative stability, it is unlikely that the ice shelf collapse played a role in the large response. Instead, we find that the rapid acceleration and surface drawdown is linked to enhanced melting at the ice-ocean boundary, attributable to changes in winds driven by global atmospheric circulation patterns, namely the El Nino–Southern Oscillation (ENSO) and Southern Annular Mode (SAM), linking changes in grounded ice to atmospheric-driven ocean warming.

A conceptual design is presented for a low complexity, heritage-based flyby mission to Io, Jupiter’s innermost Galilean satellite and the most volcanically active body in the Solar System. The design addresses the 2011 Decadal Surveys recommendation for a New Frontiers class mission to Io and is based upon the result of the June 2012 NASA-JPL Planetary Science Summer School. A science payload is proposed to investigate the link between the structure of Io’s interior, it’s volcanic activity, it’s surface composition, and it’s tectonics. A study of Io’s atmospheric processes and Io’s role in the Jovian magnetosphere is also planned. The instrument suite includes a visible/near IR imager, a magnetic field and plasma suite, a dust analyzer and a gimbaled high gain antenna to perform radio science investigations. Payload activity and spacecraft operations would be powered by three Advanced Stirling Radioisotope Generators (ASRG). The primary mission includes 10 flybys with close-encounter altitudes as low as 100 km. The mission risks are mitigated by ensuring that relevant components are radiation tolerant and by using redundancy and flight-proven parts in the design. The spacecraft would be launched on an Atlas V rocket with a delta-v of 1.3 km/s. Three gravity assists (Venus, Earth, Earth) would be used to reach the Jupiter system in a 6-year cruise. The resulting concept demonstrates the rich scientific return of a flyby mission to Io.

Exploration of the furthest reaches of our planet, as well as other planetary bodies, typically requires the use of robotic platforms due to the extreme environments encountered. Some of the harshest conditions on earth are found in Antarctica and require the use of autonomous underwater vehicles (AUVs) to explore remote and hazardous areas beneath the ice. The custom-built Icefin under-ice unmanned underwater vehicle (UUV) has been developed for deployment in permanently ice-covered oceans, such as those found in Antarctica, with the intent of furthering relevant technology for future missions to Europa, a moon of Jupiter with an icecovered ocean. The design of the vehicle flows from program requirements that provide a road map for maximizing scientific data collection with the low-risk and low-logistical impact needed for polar science. Lessons learned from Antarctic deployment of the Icefin vehicle can be extrapolated for future polar AUV design.

Recent advances in the capabilities of autonomous underwater vehicles suggest their growing utility in support of oceanographic inquiry. Towards developing autonomous systems to aid in monitoring and exploration of the polar, under-ice environment, this paper examines multi-vehicle teams consisting of autonomous profilers, a class of low-cost autonomous underwater vehicles that can only actuate their depth. Existing research on the under-ice environment documents the existence of depth-dependent ocean currents, which can be opportunistically leveraged to coordinate the motion of a team of autonomous profilers. As such, this paper proposes a backstepping control strategy that enables teams of autonomous profilers to execute established networked control algorithms; the backstepping controllers are examined through simulation and deployment on a team of differential-drive robots.

On the evolutionary timescale, milk and milk products are relatively recent additions to adult human diets that have had profound impacts on our culture, biology, genetics, and behavior. All mammals produce milk to feed their offspring, with lactose as the principal carbohydrate. Humans, however, are one of the few species to incorporate milk and dairy products from other animals into their diet. This change in diet was followed by the genetic adaptation of lactase persistence (LP) in some human populations. LP—the continued expression of the gut enzyme lactase into adulthood—is the most strongly selected single-gene trait to have evolved in Europeans and some African groups over the last 10,000 years, and is the strongest and most often cited example of recent natural selection, gene–culture coevolution, and convergent evolution in humans. This chapter examines the deep evolutionary origins of lactose as the principal carbohydrate in milk, the archeological evidence for milk and dairy product production and consumption by adult humans, and the genetics and evolutionary history of LP. Lastly it explores some possible factors that have shaped the uneven global distribution of LP today.

Milk and dairy food consumption can lead to a range of adverse clinical symptoms, the best known of which is lactose intolerance (LI). LI is defined as experiencing gastrointestinal symptoms following the ingestion of lactose. While LI is often caused by a genetically determined reduction of lactase production in adulthood, it is important to note that other causes exist. In addition, adverse gastrointestinal and other symptoms following milk and dairy food consumption may not necessarily be the result of LI. Despite our deeper understanding of food sensitivities and their overlap with irritable bowel syndrome, misattribution of gastrointestinal symptoms to lactose ingestion in self-reporting lactose-intolerant individuals remains common. In this chapter we discuss the complexities of lactose-related and lactose-independent adverse gastrointestinal and other symptoms associated with milk and dairy food consumption as well as the nutritional consequences of dairy food avoidance.

Icy satellite surfaces are riddled with geological indicators that can inform what lies beneath. Here we investigate effects of trapped or perched subsurface liquid water on the surface above. We use two models to investigate these effects: first, an analytical model to determine the flexural response of an ice shell to the existence of trapped water, and second, a discrete element model that simulates collapse of ice through granular interactions to determine possible topography that would result from this stress being placed on the ice. We find that for Europa's likely trapped water pockets below chaos terrains and a localized sea below Enceladus' South Polar Terrain, these models can reproduce observed geology of both features. Thus, we postulate that it is likely that Europa's chaos terrains and Enceladus' South Polar Terrain formed due to a similar mechanism: ice collapse above trapped water.

Iceberg calving and basal melting are the two primary mass loss processes from the Antarctic ice sheet, accounting for approximately equal amounts of mass loss. Basal melting under ice shelves has been increasingly well constrained in recent work, but changes in iceberg calving rates remain poorly quantified. Here we examine the processes that precede iceberg calving, and focus on initiation and propagation of ice-shelf rifts. Using satellite imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Multi-angle Imaging Spectroradiometer (MISR), we monitored five active rifts on the Amery Ice Shelf, Antarctica, from 2002 to 2014. We found a strong seasonal component: propagation rates were highest during (austral) summer and nearly zero during winter. We found substantial variability in summer propagation rates, but found no evidence that the variability was correlated with large-scale environmental drivers, such as atmospheric temperature, winds or sea-ice concentration. We did find a positive correlation between large propagation events and the arrival of tsunamis in the region. The variability appears to be related to visible structural boundaries within the ice shelf, e.g. suture zones or crevasse fields. This suggests that a complete understanding of rift propagation and iceberg calving needs to consider local heterogeneities within an ice shelf.

Among the biocultural innovations associated with the Neolithic, dairying and the evolution of lactose tolerance is the most studied. Expression of the enzyme lactase, which digests the milk sugar lactose, decreases after weaning in mammals, including most humans. However, some humans express lactase throughout adulthood—a trait known as lactase persistence (LP). Striking observations about LP evolution include: (i) a strong correlation between LP frequency and a history of herding and dairying; (ii) genetic patterns indicating LP-associated variants have increased in frequency through natural selection; (iii) two of these variants have been experimentally shown to affect lactase expression in adults; and (iv) archaeological and ancient DNA data indicate dairying pre-dated the rise of LP-associated variants. This chapter reviews the biology and archaeology of LP, examines some of the hypotheses formulated to explain its distribution, and outlines how simulation modelling has contributed to our understanding of its evolution.

Ice shelf rifts are predecessors to iceberg calving events. Observations of their morphology over time and interaction with their surroundings are presented. Newly-available Landsat-derived annual velocity data and laser altimetry from NASA's ICESat, ICESat-2 and Operation IceBridge missions were used to characterize several ice shelf rift systems. Actively propagating ice shelf rifts exhibit uplift on both sides, with an offset in height between the two rift walls, suggesting an asymmetric buoyancy force resulting from the rifting process itself. It is observed that the direction of the asymmetry is the same for rifts within a single ice shelf, but not between ice shelves. This finding suggests a rheological or basal properties influence on rift formation and buoyancy asymmetry. It is shown that this asymmetry can be accounted for by modeling ice shelf rifts as subvertical faults. With time and inactivity, rift walls eventually relax and become rounded off. Measurements of widening suggest that rift infilling is active on many active rifts. Active rifts experience higher spreading rates than do dormant rifts. Lastly, two candidate processes are identified for rift nucleation (subvertical basal crevassing and localized melt). It is found that more than any other ice shelf in this study, rifting in Pine Island Glacier is driven by ocean heat variations and is showing signs of increasing destabilization.

[1] Iceberg calving from ice shelves accounts for nearly half of the mass loss from the Antarctic Ice Sheet, yet our understanding of this process is limited. The precursor to iceberg calving is large through-cutting fractures, called “rifts,” that can propagate for decades after they have initiated until they become iceberg detachment boundaries. To improve our knowledge of rift propagation, we monitored the lengths of 78 rifts in 13 Antarctic ice shelves using satellite imagery from the Moderate Resolution Imaging Spectroradiometer and Multiangle Imaging Spectroradiometer between 2002 and 2012. This data set allowed us to monitor trends in rift propagation over the past decade and test if variation in trends is controlled by variable environmental forcings. We found that 43 of the 78 rifts were dormant, i.e., propagated less than 500 m over the observational interval. We found only seven rifts propagated continuously throughout the decade. An additional eight rifts propagated for at least 2 years prior to arresting and remaining dormant for the rest of the decade, and 13 rifts exhibited isolated sudden bursts of propagation after 2 or more years of dormancy. Twelve of the fifteen active rifts were initiated at the ice shelf fronts, suggesting that front-initiated rifts are more active than across-flow rifts. Although we did not find a link between the observed variability in rift propagation rate and changes in atmospheric temperature or sea ice concentration correlated with, we did find a statistically significant correlation between the arrival of tsunamis and propagation of front-initiated rifts in eight ice shelves. This suggests a connection between ice shelf rift propagation and mechanical ocean interaction that needs to be better understood.

Observations indicate that substantial changes in the dynamics of marine-terminating ice sheets and glaciers are tightly coupled to calving-induced changes in the terminus position. However, the calving process itself remains poorly understood and is not well parametrized in current numerical ice sheet models. In this study, we address this uncertainty by deriving plausible upper and lower limits for the maximum stable ice thickness at the calving face of marine-terminating glaciers, using two complementary models. The first model assumes that a combination of tensile and shear failure can render the ice cliff near the terminus unstable and/or enable pre-existing crevasses to intersect. A direct consequence of this model is that thick glaciers must terminate in deep water to stabilize the calving front, yielding a predicted maximum ice cliff height that increases with increasing water depth, consistent with observations culled from glaciers in West Greenland, Antarctica, Svalbard and Alaska. The second model considers an analogous lower limit derived by assuming that the ice is already fractured and fractures are lubricated by pore pressure. In this model, a floating ice tongue can only form when the ice entering the terminus region is relatively intact with few pre-existing, deeply penetrating crevasses.

The Icefin vehicle is a novel, custom under-ice unmanned underwater vehicle. This vehicle was designed for polar sub-ice deployment and was deployed to McMurdo, Antarctica in November of 2014. An overview of the unique vehicle design is presented here, along with a summary of the deployment testing in Antarctica. Lessons learned from this deployment provided an opportunity for design improvements to the vehicle. An updated vehicle design is presented including the changes resulting from polar sub-ice field testing.

[1] The south polar terrain (SPT) of Saturn’s moon Enceladus is a mysteriously active region that exhibits intriguing tectonic signatures and widespread fracturing. The central region of the nearly-circular SPT is depressed into the surface by a few hundred meters and bounded by a ring of cliffs roughly 1 km high. In this study, we investigate whether this depression and surrounding mountainous uplift is consistent with the morphology of terrestrial rift basins and the possibility that the SPT could have formed during a tectonic event analogous to those of such rift basins on Earth. Using three mechanical models of basin formation, we compare our predicted topography of the SPT with observed topography of the region. The first of three models we consider assumes crustal stretching by factor b, and predicts a basin depth of roughly 600 m, closely matching previously published estimates of the depth at the SPT. Models of extension and compression, assuming an elastic response in the ice crust, predict best-fit mountain uplift of roughly 1820 m and 1130 m, respectively. Our preferred model suggests that the icy shell in the SPT has been stretched, but the extension is (partially) balanced by compression along the edges of the basin leading to the uplift of the mountains along the boundary, thereby implying that the SPT may have a tectonic origin analogous to that of a terrestrial basin.

Genetic testing for obesity risk is increasingly available to the public but few studies have examined motivational or affective reactions. Here we report findings from a “vignette” study investigating reactions to “higher-risk” and “average-risk” results for the obesity-related FTO gene in two groups: a panel sample of individuals with weight concerns, for whom testing may have treatment implications (n = 306, mean age = 45 years, mean BMI = 35) and a student sample (n = 395, mean age = 25 years, mean BMI = 23), for whom testing would have implications for obesity prevention. Participants were given FTO gene information that described higher-risk alleles as linked with modest weight gain and slightly higher risk of obesity. They responded to both higher- and average-risk vignettes, with order randomized. Interest in genetic testing was high overall, and higher in panel respondents than students (93% vs. 78% would “probably” or “definitely” have the test; P < 0.001). In students, a higher-risk result generated higher motivation to change (d = 0.15; P < 0.001), but also slightly higher negative affect (d = 0.03, P < 0.001) and fatalism (d = 0.05, P < 0.001) than an average-risk result. Panel respondents also had higher motivation to change (d = 0.17, P < 0.001) as well as relief about having an explanation for their body weight (d = 0.02, P = 0.013) in the higher-risk condition, but no increase in fatalism or depression. These results suggest that at the level of anticipated responses to FTO gene feedback, higher-risk results had positive motivational effects with minimal changes in negative affect or fatalism. Genetic testing has the potential to be a useful clinical or preventive tool when combined with appropriate information.