Surface melting is widespread around the periphery of Antarctica and predicted to increase significantly. This could impact sea-level rise by allowing surface-derived meltwater to reach the ice-sheet bed and modify glacier flow into the ocean. This mechanism has received little attention in Antarctica, partly because evidence for it happening today has only recently been published, by members of our team. This mechanism is likely to become increasingly important as Antarctica warms and we will take the first steps towards understanding and predicting these changes. We will test three hypotheses: (1) short-term changes in ice velocity indicated by satellite data result from surface meltwater reaching the bed of outlet glaciers in the Antarctic Peninsula, (2) this is widespread in Antarctica today, and (3) this results in a measurable increase in mean annual ice discharge. We propose a targeted field campaign supported by the British Antarctic Survey (BAS) on an Antarctic Peninsula outlet glacier, to test hypothesis 1 using a combination of well-established and more experimental techniques. BAS will support the fieldwork because of our field site's proximity to Rothera Research Station. Immediate outcomes will include a direct comparison of in situ melt rates (from energy-budget weather stations) and ice dynamic changes (from GPS and uncrewed aerial vehicles) and subglacial water flow (from passive seismometers and ice-penetrating radar). We will also conduct a continent-wide remote sensing survey, using synthetic aperture radar and multi-spectral imagery to comprehensively map meltwater on grounded ice (most similar efforts have focused on floating ice shelves) and short-term velocity variations. Comprehensive new datasets from the field and remote-sensing surveys will be used to test our three hypotheses. There is rapid growth in the glaciology community's interest in surface melting and hydrology on Antarctic ice shelves. This project will take the discipline in a new, but related direction and make important progress in understanding the different processes involved in the response of grounded ice to increasing melt rates. As one of the first projects to focus on this aspect of atmosphere/ice-dynamics coupling, we will produce early insights into both the drivers and implications of short-term changes in ice flow velocity caused by surface melting. For example, showing conclusively that meltwater directly impacts Antarctic ice dynamics would have significant implications for our understanding of the response of Antarctica to atmospheric warming, as it did in Greenland when the phenomenon was first detected there nearly 20 years ago. This work will also have implications for other fields, as surface-to-bed meltwater flow may have implications for ice rheology, subglacial hydrology, submarine melting and calving, ocean circulation, and ocean biogeochemistry.

In many low and middle income countries, the full enjoyment of the right to health is inhibited by deficiencies in the health system, including inadequate infrastructure, human resources, and medicines and equipment. Citizen-led accountability initiatives have the potential to foster bottom up responses. They can contribute to strengthening health systems by mobilizing marginalized communities with limited access to quality health care and supporting their engagement with state authorities to demand accountability. Over the last decade, numerous examples have shown that these initiatives have been effective in making the health sector, and other public sectors, more responsive and accountable. However, understanding of the complex pathways through which citizen-led accountability initiatives lead to positive change remains limited. Their function depends on building networks of relationships that connect citizens in collective action, and engage them in dynamic interactions with state authorities. Adaptation to political and social context is also critical. Innovative methodological approaches are needed to understand how these network-generating processes function and how they can be enhanced to improve health system responsiveness to marginalized communities. The proposed research will address this challenge by applying a systems thinking approach. The science of systems thinking offers valuable tools for understanding and strengthening complex change processes. This project will employ the systems thinking tool called Social Network Analysis to study how networks of marginalized citizens work together and interact with authorities to demand health system accountability. The research will be carried out in two phases with indigenous communities participating in a well-established citizen-led accountability initiative in rural Guatemala. Citizen networks in these communities are actively working to monitor health system deficiencies, participate in local health decision-making spaces, communicate their needs to state authorities, and form alliances to advocate for structural improvements. In the first phase, social network analysis will be applied in these communities to provide insight into: 1. patterns of communication and support within the citizen networks that carry out these activities, and 2. patterns of interaction between citizens and state authorities at different levels and the responses they receive. Following in the systems thinking approach, this knowledge will be applied to strengthen the citizen networks in the second phase. In this phase, participants from the first phase will interpret: 1. how the patterns identified influence their capacity to meet their goals, and 2. how their network is influenced by local political and social context. Participants will draw on these insights to identify strategic actions to strengthen their networks' effectiveness in mobilizing their communities and communicating with authorities. The knowledge produced by this project will be directly relevant for strengthening citizen-led action for health system accountability to marginalized communities in Guatemala. Understanding of the influence of network qualities on citizen-led initiatives' capacity to meet their goals will be more broadly relevant to development agencies and practitioners working to support the mobilization of bottom up pressure for accountability. The development of an applied Social Network Analysis tool through this project will also offer a valuable resource for researchers to gain insights into the function of citizen networks in other settings, and identify broader patterns in their interactions that contribute to strengthen health system responsiveness.

This NSF Materials World Network Program allows research into a new class of artificial nanophotonic materials, which make use of our ability to use nanofabrication in conjunction with intrinsic materials properties to tailor the linear and nonlinear optical response of those metamaterials. The main challenges towards a comprehensive understanding and experimental realization of nonlinear optical properties of metamaterials are that a theory of surface and bulk nonlinear optics of metamaterials is yet to be developed, and a practical means to fabricate and test such a theory are missing as well. The main goal of this research program is to achieve these milestones. The program synergistically matches three collaborators, two in the UK and one in the US, with an established record of collaboration to investigate the properties and materials strategies for fabricating these materials. The central rationale for the group is that the UK group provides strong theoretical and fabrication capabilities while the US group provides fabrication, optical testing, and materials capabilities. In addition, we will make use of local instrumentation capabilities in both the UK and the US to fabricate and test these materials. The program is constructed to enable travel to and from each country by students and to a more limited extent the professors. The research to be undertaken here has several areas of broad impact. First, it is a project, which will foster an interdisciplinary examination of the fundamental materials science of artificial metamaterials, which includes fabrication, materials physics, optical physics, and theory. Second it will enable two groups in the US and the UK, with a strong history of interactions and complementary expertise and capabilities to collaborate. This work will involve the opportunity for both graduate and undergraduate students to collaborate and travel in an international setting. Third, the program has concrete plans and procedures to seek out recruitment of diverse student collaborators. Our immediate record in this area is strong including one woman PhD student in theory and two undergraduates. Recruitment for this program will be done via four outreach talks to undergrads at Columbia in Electrical Engineering and Applied Physics and Applied Mathematics Departments every year via active participation in research opportunities for undergraduates and undergraduate research opportunities program at Columbia. Fourth, the project will enable students to collaborate via extended visits and shorter trips with a major National Laboratory, i.e. Brookhaven, in their new Nanocenter, which one of the PIs was the founding director, as well as the London Centre for Nanotechnology, a facility shared by the University College London and Imperial College London.

Subduction zones are a key valve mediating global S processing and the climatic effects of arc volcanism, the economic potential of arc magmas, and the oxidation state of solid Earth reservoirs. Yet, the inputs, processing and recycling of S throughout the subduction system are still inaccurately known. This international project targets major unknowns in the sulfur cycle at subduction zones. The US-NSF focus of this project (PI Plank, LDEO) will fill a key knowledge gap in terms of S inputs to the mantle at subduction zones. It will involve extensive analysis of sedimentary sections at the Tonga, Marianas, Aleutians, Alaska and Central America trenches, chosen to represent end-member oceanic environments for sulfur deposition and diagenesis and extreme isotopic variations. Ocean Drilling Programs cores will be analyzed by XRF core scanning, a strategic approach to quantify heterogeneously disseminated pyrite and barite, major hosts of sulfur in sediment. Core scanning results will guide discrete sampling for bulk sulfur and sulfur isotope analyses at the University of Palermo, in collaboration with Prof. Aiuppa and Vizzini. Pilot data collected in Palermo demonstrate the quality of the coupled Elemental Analyzer-Mass Spectrometry technique and the clear sulfide- vs. sulfate-dominated regimes that may occur in a single sedimentary section. The outcome will be the first comprehensive estimates (with uncertainties) for the fluxes and isotopic compositions of S into end-member trenches and improved global estimates. The UK-NERC part of this project (PI Mather, Oxford) will take a novel approach to understanding volcanic arc S outputs. It will measure for the first time the sulfur isotopic composition in undegassed olivine-hosted arc melt inclusions. Pilot data collected at NERC Ion Microprobe Facility at Edinburgh demonstrate the viability of the technique, and yield positive delta(34)S in melt inclusions from Fuego volcano. Planned work will include well-studied melt inclusions suites from the same subducting systems as the sediment targets (above). This will ensure close collaboration between the US and UK parts of this project, and allow for the first-time direct tracing of sulfur isotopes from sediment input to arc output.

The Hawaiian-Emperor Seamount Chain is arguably the world's best known example of hotspot magmatism, where volcanic activity and earthquakes occur far from plate boundaries. Nevertheless, questions remain about the fundamental processes that control such magmatism and seismicity along the 5800-km-long, 0-80 Ma, chain, in part because the volume and compositions of frozen magma that has been added to the surface and base of Pacific oceanic crust is too poorly known. The aim of this study is to use 'state of the art' marine seismic imaging techniques to constrain the thickness and composition of the magmatic material created by the Hawaiian hotspot, how it varies along the seamount chain, and how the Pacific oceanic plate has deformed in response to volcano loading. This study, which is a collaborative one with US scientists at Lamont-Doherty Earth Observatory, will utilize reprocessed seismic reflection and refraction data acquired on previous research cruises (e.g. R/V Robert D. Conrad C2308, R/V Thomas Washington Roundabout 2, and R/V Maurice Ewing EW9801), together with a new data set that will be acquired onboard R/V Marcus G. Langseth during late summer, 2018 and early summer, 2019. The Langseth cruises, which have been funded by the National Science Foundation (Marine Geology and Geophysics Division), will acquire deep penetration seismic reflection data using a 15 km long streamer and a large tuned airgun array and wide-angle reflection/refraction data using 70 Ocean Bottom Seismometers spaced at 15 km intervals along four 500-km-long transects of the chain. The transect locations have been carefully chosen to represent variations in the timing of magma emplacement and volume flux, the age of oceanic lithosphere at the time of loading and the presence/absence of a mid-plate topographic swell, and are sufficiently long to capture the response of the lithosphere to volcano loading out to the flexural bulge. The reprocessed and processed seismic reflection profiles and velocity models created from wide-angle seismic data will constrain the volume and distribution of magmatic addition to the surface and base of the crust, the nature of the stratigraphic fill in the flanking flexural moats and the relative role of faulting within the flexed volcanic edifice and underlying oceanic plate. The seismic constraints will be integrated with swath bathymetry and potential field data, compared to other marine geophysical studies of hotspot magmatism and used as the basis for thermal and mechanical modeling in order to gain fundamental insights into crust and lithosphere rheology and stress state and to inform potential geohazards along the chain such as large-scale slope failures, fault slip and tsunamigenic earthquakes. The study proposed here is central to NERC's strategy especially as it involves discovery science that impacts on how planet Earth works, how it deforms in response to surface and sub-surface loads and how it might deform in the future.