Variations in Earth's 1D viscosity structure in different tectonic regimes

Earth’s long-wavelength geoid provides insights into the thermal, structural, and compositional evolution of the mantle. Historically, most estimates of mantle viscosity using the long-wavelength geoid have considered radial variations with depth in a symmetric Earth. Global estimates of this kind suggest an increase in viscosity from the upper mantle to lower mantle of roughly 2 -- 3 orders of magnitude. Using a spatio-spectral localization technique with the geoid, here we estimate a series of locally constrained viscosity-depth profiles covering two unique regions, the Pacific and Atlantic hemispheres, which show distinct rheological properties. The Pacific region exhibits the conventional Earth's 1D rheology with a factor of roughly 80-100 increase in viscosity occurring at transition zone depths (400 - 800 km). The Atlantic region in contrast does not show significant viscosity jumps with depth, and instead has a near uniform viscosity in the top 1000~km. The inferred viscosity variations between our two regions could be due to the prevalence of present-day subduction in the Pacific and the infrequence of slabs in the Atlantic, combined with a possible hydrated transition zone and mid-mantle of the Atlantic region by ancient subduction during recent supercontinent cycles. Rigid slab material within the top 800 km, with about 90\% Majoritic garnet in the form of subducted oceanic crust, coupled with unique regional mantle structures, may be generating a strong transition zone viscosity interface for the Pacific region. These effective lateral variations in mantle viscosity could play a role in the observed deformation differences between the Pacific and Atlantic hemispheres.

Wintertime Rossby Wave Breaking Persistence in Extended-range Seasonal Forecasts of Atlantic Tropical Cyclone Activity

In this study, we examine the wintertime environmental precursors of summer anticyclonic wave breaking (AWB) over the North Atlantic region and assess the applicability of these precursors in predicting AWB impacts on seasonal tropical cyclone (TC) activity. We show that predictors representing the environmental impacts of subtropical AWB on seasonal TC activity improve the skill of extended-range seasonal forecasts of TC activity. There is a significant correlation between boreal winter and boreal summer AWB activity via AWB-forced phases of the quasi-stationary North Atlantic Oscillation (NAO). Years with above-normal boreal summer AWB activity over the North Atlantic region also show above-normal AWB activity in the preceding boreal winter that tends to force a positive phase of the NAO that persists through the spring. These conditions are sustained by continued AWB throughout the year, particularly when El Niño-Southern Oscillation plays less of a role at forcing the large-scale circulation. While individual AWB events are synoptic and nonlinear with little predictability beyond 8-10 days, the strong dynamical connection between winter and summer wave breaking lends enough persistence to AWB activity to enable predictability of its potential impacts on TC activity. We find that the winter-summer relationship improves the skill of extended-range seasonal forecasts from as early as an April lead time, particularly for years when wave breaking has played a crucial role in suppressing TC development.

The 852/3 CE Mount Churchill eruption: examining the potential climatic and societal impacts and the timing of the Medieval Climate Anomaly in the North Atlantic Region

The 852/3 CE eruption of Mount Churchill, Alaska, was one of the largest first millennium volcanic events, with a magnitude of 6.7 (VEI 6) and a tephra volume of 39.4–61.9 km3 (95 % confidence). The spatial extent of the ash fallout from this event is considerable and the cryptotephra (White River Ash east; WRAe) extends as far as Finland and Poland. Proximal ecosystem and societal disturbances have been linked with this eruption; however, wider eruption impacts on climate and society are unknown. Greenland ice-core records show that the eruption occurred in winter 852/3 ± 1 CE and that the eruption is associated with a relatively moderate sulfate aerosol loading, but large abundances of volcanic ash and chlorine. Here we assess the potential broader impact of this eruption using palaeoenvironmental reconstructions, historical records and climate model simulations. We also use the fortuitous timing of the 852/3 CE Churchill eruption and its extensively widespread tephra deposition of the White River Ash (east) (WRAe) to examine the climatic expression of the warm Medieval Climate Anomaly period (MCA; ca. 950–1250 CE) from precisely linked peatlands in the North Atlantic region. The reconstructed climate forcing potential of 852/3 CE Churchill eruption is moderate compared with the eruption magnitude, but tree-ring-inferred temperatures report a significant atmospheric cooling of 0.8 °C in summer 853 CE. Modelled climate scenarios also show a cooling in 853 CE, although the average magnitude of cooling is smaller (0.3 °C). The simulated spatial patterns of cooling are generally similar to those generated using the tree-ring-inferred temperature reconstructions. Tree-ring inferred cooling begins prior to the date of the eruption suggesting that natural internal climate variability may have increased the climate system’s susceptibility to further cooling. The magnitude of the reconstructed cooling could also suggest that the climate forcing potential of this eruption may be underestimated, thereby highlighting the need for greater insight into, and consideration of, the role of halogens and volcanic ash when estimating eruption climate forcing potential. Precise comparisons of palaeoenvironmental records from peatlands across North America and Europe, facilitated by the presence of the WRAe isochron, reveal no consistent MCA signal. These findings contribute to the growing body of evidence that characterizes the MCA hydroclimate as time-transgressive and heterogeneous, rather than a well-defined climatic period. The presence of the WRAe isochron also demonstrates that no long-term (multidecadal) climatic or societal impacts from the 852/3 CE Churchill eruption were identified beyond areas proximal to the eruption. Historical evidence in Europe for subsistence crises demonstrate a degree of temporal correspondence on interannual timescales, but similar events were reported outside of the eruption period and were common in the 9th century. The 852/3 CE Churchill eruption exemplifies the difficulties of identifying and confirming volcanic impacts for a single eruption, even when it is precisely dated.

Addressing Pediatric Developmental and Mental Health in Primary Care Using Tele-Education

This study evaluates the effectiveness of an early childhood tele-education program in preparing community pediatric clinicians to manage developmental and mental health disorders in young children. Community pediatric clinicians from rural, underserved, or school-based health center practices in the mid-Atlantic region participated in a weekly tele-education videoconference. There was a significant knowledge gain evidenced by the percentage of questions answered correctly from pre- to post- didactic exposure ( P < .001). Participants reported an increase in knowledge from pre- ( P < .001) and in confidence from pre- to post- participation ( P < .001). Practice management changes demonstrated an encouraging trend toward managing patients in the Medical Home, as compared with immediately deferring to specialists following participation. This early childhood tele-education videoconferencing program is a promising response to the urgent need to confidently increase the role of pediatricians in the provision of care for childhood developmental and mental health disorders.

The U.S. South Atlantic Region

This chapter describes the South Atlantic region and the major issues facing this marine fisheries ecosystem, and presents some summary statistics related to the 90 indicators of ecosystem-based fisheries management (EBFM) criteria. The South Atlantic contains the third-highest number of managed taxa of the eight regional U.S. marine ecosystems, including commercially and recreationally important reef fishes (snappers and groupers), penaeid shrimps, coastal migratory pelagic fishes (cobia, mackerels, dolphin/wahoo), and coral reef resources. The South Atlantic is a species-rich environment subject to several major stressors that include habitat loss, sea-level rise, ocean acidification, and intermittent high category hurricanes with increasing frequency over the past decades, along with the consequences of overfishing that continue to affect LMRs in this region. Overall, EBFM progress has been made in terms of implementing ecosystem-level planning, advancing knowledge of ecosystem principles, and in assessing risks and vulnerabilities to ecosystems through ongoing investigations into climate vulnerability and species prioritizations for stock and habitat assessments. Although the South Atlantic is progressing toward EBFM, little overall progress has been observed toward applying ecosystem-level emergent properties into management frameworks. While the South Atlantic is advancing in terms of its LMR management priorities and ecosystem efforts, some challenges remain to effectively implement formalized EBFM planning. Limited information regarding the status and biomass of fishery stocks and protected species in this region, and data gaps for many environmental factors have constrained EBFM implementation and prevented the application of ecosystem-level properties into management actions.

The U.S. Mid-Atlantic Region

This chapter describes the Mid-Atlantic region and the major issues facing this marine fisheries ecosystem, and presents some summary statistics related to the 90 indicators of ecosystem-based fisheries management (EBFM) criteria. While containing lower numbers of managed taxa among the eight regional U.S. marine ecosystems, this region has relatively well-managed state and federal fisheries that are important both nationally and along the U.S. Atlantic coast, including Atlantic menhaden, blue crab, eastern oyster, black sea bass, summer flounder, and striped bass. The Mid-Atlantic is an environment that is subject to stressors that include habitat loss, coastal development, nutrient loading, climate-related species range shifts, hurricanes, other ocean uses, and proliferation of invasive species. Overall, EBFM progress has been made at the regional and subregional level in terms of implementing ecosystem-level planning, advancing knowledge of ecosystem principles, and in assessing risks and vulnerabilities to ecosystems through ongoing investigations into climate vulnerability and species prioritizations for stock and habitat assessments. While information has been obtained and models developed, only partial progress has been observed toward applying ecosystem-level emergent properties or reference points into management frameworks. While the Mid-Atlantic is leading in many aspects of its LMR and ecosystem-centric efforts, challenges remain toward effectively implementing additional facets of EBFM, and particularly enacting ecosystem-level control rules. This ecosystem is excelling in the areas of LMR and socioeconomic status, the quality of its governance system, and is relatively productive, as related to the determinants of successful LMR management.