The Final Stages of Slip and Volcanism on an Oceanic Detachment Fault at 13°48′N, Mid-Atlantic Ridge

While processes associated with initiation and maintenance of oceanic detachment faults are becoming better constrained, much less is known about the tectonic and magmatic conditions that lead to fault abandonment. Here we present results from near‐bottom investigations using the submersible Alvin and autonomous underwater vehicle Sentry at a recently extinct detachment fault near 13°48′N, Mid‐Atlantic Ridge, that allow documentation of the final stages of fault activity and magmatism. Seafloor imagery, sampling, and near‐bottom magnetic data show that the detachment footwall is intersected by an ~850 m‐wide volcanic outcrop including pillow lavas. Saturation pressures in these vesicular basalts, based on dissolved H2O and CO2, are less than their collection pressures, which could be explained by eruption at a shallower level than their present depth. Sub‐bottom profiles reveal that sediment thickness, a loose proxy for seafloor age, is ~2 m greater on top of the volcanic terrain than on the footwall adjacent to the hanging‐wall cutoff. This difference could be explained by current‐driven erosion in the axial valley or by continued slip after volcanic emplacement, on either a newly formed or pre‐existing fault. Since current speeds near the footwall are unlikely to be sufficient to cause significant erosion, we favor the hypothesis that detachment slip continued after the episode of magmatism, consistent with growing evidence that oceanic detachments can continue to slip despite hosting magmatic intrusions

Formation of Lava Samples Collected by Three Alvin Submersible Dives at 14°N on the Mid-Atlantic Ridge

In 2018, a research cruise investigated the Mid-Atlantic Ridge at 14°N. During this expedition the seafloor was mapped using the AUV Sentry and basaltic lavas were collected using the HOV Alvin. To better understand the origin of these lavas, major element compositions of 40 basaltic glasses from three Alvin dives were measured using the BSU SXFive Electron Microprobe and trace element contents were measured on 33 samples using solution ICP-MS. Trace element ratios and patterns are important tools for investigating magmatic processes because they can be used to evaluate different magmatic processes; such as the amount of melting of the Earth\u27s mantle that produces the magma and the extents of crystallization prior to eruption. Lavas collected on dives AL4953 and AL4954 have similar Rare Earth Element patterns, but variable elemental abundances, suggesting fractional crystallization was an important process in their formation. By contrast, lavas collected on dive AL4955 have variable trace element patterns and ratios, indicating a change in the extents of mantle melting. To further investigate the differences in these compositions, we will use numerical models to quantify the percent of mantle melting and extents of crystallization that led to the formation of lavas erupted in this region

The relative importance of physiological and behavioral adaptation in diving endotherms: a case study with great cormorants

Extensive morphological and physiological adjustments are assumed to underpin the adaptations of diving birds to high thermoregulatory costs. However, the role of behavioural adaptations has received little consideration. We have assessed the relative importance of physiological and behavioural adjustments in aquatic endotherms by studying the case of the poorly insulated great cormorant (Phalacrocorax carbo) in two contrasting thermal environments: Normandy (water temperature 12°C) and Greenland (water temperature 5°C). Major differences were found in the feeding behaviour of birds breeding in the two regions. Greenland birds showed a 70% reduction in time spent swimming relative to those in Normandy. Reduction in Greenland was achieved first by reducing time spent on the surface between dives and secondly by returning to land in between intensive bouts of diving. Total daily energy intake of cormorants was similar in both areas but prey capture rates in Greenland were 150% higher than those in Normandy. Our study shows that in a cold foraging environment, poorly insulated great cormorants significantly increase their foraging efficiency. To do this they rely on ecological adaptive patterns (minimization of time spent swimming in cold water and increased prey capture rates) far more than physiological adaptations (minimizing instantaneous costs). This finding supports predictions by Grémillet and Wilson (1999) that great cormorants can cope with a wide range of abiotic parameters despite their morphological handicaps, provided they can adjust their distribution to exploit dense prey patches

Age-related effects on breeding phenology and success of common guillemots Uria aalge at a North Sea colony

Capsule: Common Guillemots Uria aalge show delayed breeding and marked age-related changes in reproductive success consistent with improved performance with experience. Aims: To determine age of first breeding and age-related effects on breeding phenology and success of Common Guillemots. Methods: Resighting data from a long-term colour-ringing study of Common Guillemot chicks were combined with observations of breeding phenology and success to follow the recruitment process, breeding phenology and success of 62 birds at a major North Sea colony over a 30-year period. Results: The median age of first breeding of Common Guillemots was 6.6 years. There were no detectable costs of first breeding on return rates or the likelihood of breeding the next season but first time breeders bred later and less successfully. Age of first breeding and lifetime breeding success both varied among individuals but there was no clear optimal age of first breeding and early first breeding was not associated with higher lifetime breeding success. Conclusions: Common Guillemots in the Isle of May population delayed breeding for 3–4 years beyond physiological maturity. The marked increase in breeding success with age was consistent with improved performance with experience rather than selection for higher quality individuals. Findings from this study will inform population models by providing improved estimates of age of first breeding and age-related changes in reproductive performance

Density-dependent foraging and colony growth in a pelagic seabird species under varying environmental conditions

Intra-specific competition for food resources affects both foraging behaviour and population growth rates in many species, highlighting a need to better understand how changing environmental conditions affect individuals in populations of different sizes. Using chick-rearing northern gannets as a model, we examined the influence of colony size on per capita population growth rates over 2 time periods (1994-2000 and 2000-2009) and on foraging trip durations in each of 2 years (2000 and 2009) at 10 colonies in 2 separate regions of the UK and Ireland (the North Sea and the Celtic/Irish Sea). The slope of the relationship between population size and foraging trip duration in 2009 was less than one quarter of that in 2000, suggesting a much weaker influence of population size in 2009, presumably due to less intense intra-specific competition for prey resources at sea. There was also regional variation, with colonies in the Celtic/Irish Sea growing substantially slower for their size over the period between 2000 and 2009 than did colonies bordering the North Sea, whilst observed trip durations in 2009 were on average 13% shorter than predicted from population size at colonies bordering the North Sea, but 32% longer than predicted at colonies in the Celtic and Irish Seas. These data suggest less favourable conditions for gannets in the latter region in recent years, and that annual variation in trip durations will be particularly marked at large colonies, making them especially vulnerable to adverse effects of low prey availability at sea

The Cocos and Carnegie Aseismic Ridges: a Trace Element Record of Long-term Plume-Spreading Center Interaction

The aseismic Cocos and Carnegie Ridges, two prominent bathymetric features in the eastern Pacific, record ∼20 Myr of interaction between the Galápagos hotspot and the adjacent Galápagos Spreading Center. Trace element data determined by inductively coupled plasma-mass spectrometry in >90 dredged seamount lavas are used to estimate melt generation conditions and mantle source compositions along the ridges. Lavas from seamount provinces on the Cocos Ridge are alkalic and more enriched in incompatible trace elements than any in the Galápagos archipelago today. The seamount lavas are effectively modeled as small degree melts of a Galápagos plume source. Their eruption immediately follows the failure of a rift zone at each seamount province's location. Thus the anomalously young alkalic lavas of the Cocos Ridge, including Cocos Island, are probably caused by post-abandonment volcanism following either a ridge jump or rift failure, and not the direct activity of the Galápagos plume. The seamounts have plume-like signatures because they tap underlying mantle previously infused with Galápagos plume material. Whereas plume heterogeneities appear to be long-lived, tectonic rearrangements of the ridge plate boundary may be the dominant factor in controlling regional eruptive behavior and compositional variations

Monogenetic near-island seamounts in the Galapagos Archipelago

Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 21(12), (2020): e2020GC008914, https://doi.org/10.1029/2020GC008914.Rarely have small seamounts on the flanks of hotspot derived ocean‐island volcanoes been the targets of sampling, due to sparse high‐resolution mapping near ocean islands. In the Galápagos Archipelago, for instance, sampling has primarily targeted the subaerial volcanic edifices, with only a few studies focusing on large‐volume submarine features. Sampling restricted to these large volcanic features may present a selection bias, potentially resulting in a skewed view of magmatic and source processes because mature magmatic systems support mixing and volcanic accretion that overprints early magmatic stages. We demonstrate how finer‐scale sampling of satellite seamounts surrounding the volcanic islands in the Galápagos can be used to lessen this bias and thus, better constrain the evolution of these volcanoes. Seamounts were targeted in the vicinity of Floreana and Fernandina Islands, and between Santiago and Santa Cruz. In all regions, individual seamounts are typically monogenetic, but each seamount field requires multigenerational magmatic episodes to account for their geochemical variability. This study demonstrates that in the southern and eastern regions the seamounts are characterized by greater geochemical variability than the islands they surround but all three regions have (Sr‐Nd‐He) isotopic signatures that resemble neighboring islands. Variations in seamount chemistry from alkalic to tholeiitic near Fernandina support the concept that islands along the center of the hotspot track undergo greater mean depths of melting, as predicted by plume theory. Patterns of geochemical and isotopic enrichment of seamounts within each region support fine‐scale mantle heterogeneities in the mantle plume sourcing the Galápagos hotspot.This work was carried out with funding from National Science Foundation Division of Ocean Sciences (OCE‐1634952 to V. D. Wanless, OCE‐1634685 to S. A. Soule). The authors have no competing interests to declare. We thank Sally Gibson and three anonymous reviewers for providing detailed and critical feedback on this manuscript.2021-05-0

A roadmap for China to peak carbon dioxide emissions and achieve a 20% share of non-fossil fuels in primary energy by 2030

As part of its Paris Agreement commitment, China pledged to peak carbon dioxide (CO2) emissions around 2030, striving to peak earlier, and to increase the non-fossil share of primary energy to 20% by 2030. Yet by the end of 2017, China emitted 28% of the world's energy-related CO2 emissions, 76% of which were from coal use. How China can reinvent its energy economy cost-effectively while still achieving its commitments was the focus of a three-year joint research project completed in September 2016. Overall, this analysis found that if China follows a pathway in which it aggressively adopts all cost-effective energy efficiency and CO2 emission reduction technologies while also aggressively moving away from fossil fuels to renewable and other non-fossil resources, it is possible to not only meet its Paris Agreement Nationally Determined Contribution (NDC) commitments, but also to reduce its 2050 CO2 emissions to a level that is 42% below the country's 2010 CO2 emissions. While numerous barriers exist that will need to be addressed through effective policies and programs in order to realize these potential energy use and emissions reductions, there are also significant local environmental (e.g., air quality), national and global environmental (e.g., mitigation of climate change), human health, and other unquantified benefits that will be realized if this pathway is pursued in China