ALBERT

Description: We present models of the 3-D shear velocity structure of the lithosphere and asthenosphere beneath the Hawaiian hotspot and surrounding region. The models are derived from long-period Rayleigh-wave phase velocities that were obtained from the analysis of seismic recordings collected during two year-long deployments for the Hawaiian Plume-Lithosphere Undersea Mantle Experiment. For this experiment, broad-band seismic sensors were deployed at nearly 70 seafloor sites as well as 10 sites on the Hawaiian Islands. Our seismic images result from a two-step inversion of path-averaged dispersion curves using the two-station method. The images reveal an asymmetry in shear velocity structure with respect to the island chain, most notably in the lower lithosphere at depths of 60 km and greater, and in the asthenosphere. An elongated, 100-km-wide and 300-km-long low-velocity anomaly reaches to depths of at least 140 km. At depths of 60 km and shallower, the lowest velocities are found near the northern end of the island of Hawaii. No major velocity anomalies are found to the south or southeast of Hawaii, at any depth. The low-velocity anomaly in the asthenosphere is consistent with an excess temperature of 200-250 °C and partial melt at the level of a few percent by volume, if we assume that compositional variations as a result of melt extraction play a minor role. We also image small-scale low-velocity anomalies within the lithosphere that may be associated with the volcanic fields surrounding the Hawaiian Islands.

Description: The Hawaiian Islands are the canonical example of an age-progressive island chain, formed by volcanism long thought to be fed from a hotspot source that is more or less fixed in the mantle. Geophysical data, however, have so far yielded contradictory evidence on subsurface structure. The substantial bathymetric swell is supportive of an anomalously hot upper mantle, yet seafloor heat flow in the region does not appear to be enhanced. The accumulation of magma beneath pre-existing crust (magmatic underplating) has been suggested to add chemical buoyancy to the swell, but to date the presence of underplating has been constrained only by local active-source experiments. In this study, teleseismic receiver functions derived from seismic events recorded during the PLUME project were analysed to obtain a regional map of crustal structure for the Hawaiian Swell. This method yields results that compare favourably with those from previous studies, but permits a much broader view than possible with active-source seismic experiments. Our results indicate that the crustal structure of the Hawaiian Islands is quite complicated and does not conform to the standard model of sills fed from a central source. We find that a shallow P-to-s conversion, previously hypothesized to result from the volcano-sediment interface, corresponds more closely to the boundary between subaerial and subaqueous extrusive material. Correlation between uplifted bathymetry at ocean-bottom-seismometer locations and presence of underplating suggests that much of the Hawaiian Swell is underplated, whereas a lack of underplating beneath the moat surrounding the island of Hawaii suggests that underplated crust outward of the moat has been fed from below by dykes through the lithosphere rather than by sills spreading from the island centre. Local differences in underplating may reflect focusing of magma-filled dykes in response to stress from volcanic loading. Finally, widespread underplating adds chemical buoyancy to the swell, reducing the amplitude of a mantle thermal anomaly needed to match bathymetry and supporting observations of normal heat flow.

Description: While knowledge of the energy inputs from the Sun (as it is the primary energy source) is important for understanding the solar-terrestrial system, of equal importance is the manner in which the terrestrial part of the system organizes itself in a quasi-equilibrium state to accommodate and re-emit this energy. The ROSMIC project (2014–2018 inclusive) was the component of SCOSTEP’s Variability of the Sun and Its Terrestrial Impact (VarSITI) program which supported research into the terrestrial component of this system. The four themes supported under ROSMIC are solar influence on climate, coupling by dynamics, trends in the mesosphere lower thermosphere, and trends and solar influence in the thermosphere. Over the course of the VarSITI program, scientific advances were made in all four themes. This included improvements in understanding (1) the transport of photochemically produced species from the thermosphere into the lower atmosphere; (2) the manner in which waves produced in the lower atmosphere propagate upward and influence the winds, dynamical variability, and transport of constituents in the mesosphere, ionosphere, and thermosphere; (3) the character of the long-term trends in the mesosphere and lower thermosphere; and (4) the trends and structural changes taking place in the thermosphere. This paper reviews the progress made in these four areas over the past 5 years and summarizes the anticipated research directions in these areas in the future. It also provides a physical context of the elements which maintain the structure of the terrestrial component of this system. The effects that changes to the atmosphere (such as those currently occurring as a result of anthropogenic influences) as well as plausible variations in solar activity may have on the solar terrestrial system need to be understood to support and guide future human activities on Earth.

Description: Global climate model projections suggest that 21st century climate change will bring significant drying to many regions. Runoff from glaciers is known to smooth water availability in glaciated basins, but glacier model projections show that glaciers will retreat and glacial runoff will diminish worldwide through the 21st century. So, to what extent can we expect retreating glaciers to protect downstream areas from drought as the climate continues to change? Without dynamic glacier ice in global climate models, a comprehensive picture of future drought conditions in glaciated regions has been elusive. In this talk, we present a global assessment of glacial drought buffering for all large-scale river basins. We analyse a modified drought metric computed from one global glacier model (GloGEM) forced by an ensemble of global climate models. We then extend the analysis to two additional global glacier models (PyGEM and OGGM), which allows us to discuss the robustness of runoff projections to the choice of glacier model. These results will highlight both (i) avenues for continued work on global glacier modelling as well as (ii) implications for work with water management practitioners.