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From seismic models to mantle temperatures: Uncertainties related to mineralogical complexities and limited tomographic resolution

Geophysical Journal International - Fri, 04/18/2025 - 00:00

SummaryMany geophysical studies require knowledge on the present-day temperature distribution in Earth’s mantle. One example are geodynamic inverse models, which utilize data assimilation techniques to reconstruct mantle flow back in time. The thermal state of the mantle can be estimated from seismic velocity perturbations imaged by tomography with the help of thermodynamic models of mantle mineralogy. Unique interpretations of the tomographically imaged seismic heterogeneity can either be obtained by incorporating additional data sets or requires assumptions on the chemical composition of the mantle. However, even in the case of (assumed) known chemical composition, both the seismic and the mineralogical information are significantly affected by inherent limitations and different sources of uncertainty. Here, we investigate the theoretical ability to estimate the thermal state of the mantle from tomographic models in a synthetic closed-loop experiment. The ‘true’ temperature distribution of the mantle is taken from a 3-D mantle circulation model with Earth-like convective vigour. We aim to recover this reference model after: 1) mineralogical mapping from the ‘true’ temperatures to seismic velocities, 2) application of a tomographic filter to mimic the effect of limited seismic resolution, and 3) mapping of the ‘imaged’ seismic velocities back to temperatures. We test and quantify the interplay of tomographically damped and blurred seismic heterogeneity in combination with different approximations for the mineralogical ‘inverse’ conversion from seismic velocities to temperature. Owing to imperfect knowledge of the parameters governing mineral anelasticity, we additionally investigate the effects of over- or underestimating the corresponding correction to the underlying mineralogical model. Our results highlight that, given the current limitations of seismic tomography and the incomplete knowledge of mantle mineralogy, magnitudes and spatial scales of a temperature field obtained from global seismic models deviate significantly from the true state, even in the idealized case of known bulk chemical composition. The average deviations from the reference model are on the order of 50–100 K in the upper mantle and – depending on the resolving capabilities of the respective tomography – can increase with depth throughout the lower mantle to values of up to 200 K close to the core-mantle boundary. Furthermore, large systematic errors exist in the vicinity of phase transitions due to the associated mineralogical complexities. When used to constrain buoyancy forces in time-dependent geodynamic simulations, errors in the temperature field might grow non-linearly due to the chaotic nature of mantle flow. This could be particularly problematic in combination with advanced implementations of compressibility, in which densities are extracted from thermodynamic mineralogical models with temperature-dependent phase assemblages. Erroneous temperatures in this case might activate ‘wrong’ phase transitions and potentially flip the sign of the associated Clapeyron slopes, thereby considerably altering the model evolution. Additional testing is required to evaluate the behaviour of different compressibility formulations in geodynamic inverse problems. Overall, the strategy to estimate the present-day thermodynamic state of the mantle must be selected carefully to minimize the influence of the collective set of uncertainties.

Coastal management model plays the long game against the rising tides

Phys.org: Earth science - Thu, 04/17/2025 - 20:22

To protect against rising sea levels in a warming world, coastal cities typically follow a standard playbook with various protective infrastructure options. For example, a seawall could be designed based on the latest climate projections, with the city officials then computing its cost-benefit ratio and proceeding to build, accordingly.

Upwelling Near Fronts Initiate Offshore Phytoplankton Blooms

EOS - Thu, 04/17/2025 - 20:11

Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: Journal of Geophysical Research: Oceans

Warm western boundary currents play a role in lateral transport of heat, salt, and biogeochemical tracers, including nutrients. When these poleward western boundary currents separate from the coast to the east, they seem to drag biologically productive water from near shore regions to offshore. Cross-shelf lateral flows have, therefore, been considered a cause of offshore phytoplankton blooms. However, these currents generate and interact with mesoscale eddies after they separate from the coast.

Chapman et al. [2025] conduct a series of high-resolution observations to investigate the importance of vertical water motions induced by meso- and sub-mesoscale flows associated with these mesoscale eddies. The results suggest that secondary circulation caused by eddy flows near fronts along the East Australian Current induces the offshore phytoplankton bloom over 100 kilometers.

Citation: Chapman, C. C., Sloyan, B. M., Schaeffer, A., Suthers, I. M., & Pitt, K. A. (2024). Offshore plankton blooms via mesoscale and sub-mesoscale interactions with a western boundary current. Journal of Geophysical Research: Oceans, 129, e2023JC020547. https://doi.org/10.1029/2023JC020547

—Takeyoshi Nagai, Editor, JGR: Oceans

Text © 2024. The authors. CC BY-NC-ND 3.0
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Mechanisms for early spring peak of extratropical cyclone activity in East Asia explained

Phys.org: Earth science - Thu, 04/17/2025 - 20:10

Extratropical cyclones (or low-pressure systems) traveling along the Kuroshio in East Asia most frequently occur in spring, bringing heavy rain and snowfall in the region. Researchers at the University of Tsukuba unveiled the mechanism underlying the peak observed in the activity of Kuroshio cyclones during spring using four-dimensional atmospheric data spanning several decades. Their findings revealed that air over Eurasia warmed from winter to spring intensified the low-level jet stream around the East China Sea, increasing the occurrence probability of low-pressure systems during spring.

Scientists crack ocean's code for predicting China's persistent summer rains

Phys.org: Earth science - Thu, 04/17/2025 - 19:26

Extreme rainfall events can cause devastating floods, landslides, and widespread damage, yet predicting them remains a major challenge. While scientists often study how often and how intensely it rains, the duration of rainfall is just as critical in assessing its impact. However, research on long-lasting extreme rainfall has been limited—until now.

Editorial Board

Earth and Planetary Science Letters - Thu, 04/17/2025 - 19:10

Publication date: 1 June 2025

Source: Earth and Planetary Science Letters, Volume 659

Author(s):

Porphyritic olivine chondrules with enstatite chondrite isotopic composition as a main building block of Earth

Earth and Planetary Science Letters - Thu, 04/17/2025 - 19:10

Publication date: 1 June 2025

Source: Earth and Planetary Science Letters, Volume 659

Author(s): Yves Marrocchi, Tahar Hammouda, Maud Boyet, Guillaume Avice, Alessandro Morbidelli

Modeling the stratigraphic record of glacioeustatic sea-level rise and sediment starvation following Snowball Earth

Earth and Planetary Science Letters - Thu, 04/17/2025 - 19:10

Publication date: 1 June 2025

Source: Earth and Planetary Science Letters, Volume 659

Author(s): A.R. Nordsvan, K.W. Bauer, C.L. Colleps, R.N. Mitchell, N.R. McKenzie

Petrogenesis of Chang'E-6 basalts and implication for multi-episode volcanism in the lunar farside basin

Earth and Planetary Science Letters - Thu, 04/17/2025 - 19:10

Publication date: 1 June 2025

Source: Earth and Planetary Science Letters, Volume 659

Author(s): Dehan Shen, Shijie Li, Shaolin Li, Yingkui Xu, Yang Li, Mingbao Li, Deliang Wang, Ronghua Pang, Yuwei Zhang, Zhipeng Han

Thermodynamics of light elements stratification in the earth's outer core and implications

Earth and Planetary Science Letters - Thu, 04/17/2025 - 19:10

Publication date: 1 June 2025

Source: Earth and Planetary Science Letters, Volume 659

Author(s): Jibamitra Ganguly

Thermodynamic constraints on devolatilization of variably altered oceanic ultramafic rocks during subduction: Implications for subarc mantle oxidation

Earth and Planetary Science Letters - Thu, 04/17/2025 - 19:10

Publication date: 1 June 2025

Source: Earth and Planetary Science Letters, Volume 659

Author(s): Weigang Peng, Katy A. Evans, James A.D. Connolly, Yi-Bing Li, Han Hu, Lifei Zhang

Topographic signature of magmatic emplacement at depth: The case of the Larderello-Travale Geothermal area (Northern Apennines, Italy)

Earth and Planetary Science Letters - Thu, 04/17/2025 - 19:10

Publication date: 1 June 2025

Source: Earth and Planetary Science Letters, Volume 659

Author(s): Riccardo Lanari, Marco Bonini, Andrea Sembroni, Samuele Papeschi, Chiara Del Ventisette, Adam G.G. Smith, Matteo Lupi, Domenico Montanari