 Net and anthropogenic CO 2 exchange in the Pacific represents a major contribution to the global CO 2 sink.  The Pacific is thought to have turned to a net sink of CO 2 that is growing primarily due to the increasing uptake of anthropogenic CO 2.  The equatorial region is key in determining net and anthropogenic CO 2 uptakes and their trends and variability in the Pacific.

The commercial synthetic aperture radar (SAR) market is experiencing year-over-year growth and is currently capable of imaging anywhere in the world within an hour at X-band. Surface Deformation and Change (SDC) is a mission study at NASA to investigate innovative architectures beyond the NASA-ISRO SAR (NISAR) mission in the next decade. In this article we present preliminary findings on the technical capabilities of the currently available commercial SAR data, and investigate their applicability to SDC goals, such as imaging quality and retrieval of surface motion.

Moisture transport within atmospheric rivers is driven by a complex combination of processes, including convergence of moisture from different origins which change over the atmospheric river’s life cycle. The water vapor budget within an atmospheric river enables us to understand moisture sources and sinks (horizontal flux, evaporation and precipitation). Here, we focused on the water vapor budget of the exceptional atmospheric river associated with the storm Dennis that led to record-breaking precipitation on February 15th 2020. We used the WRF model to simulate the event and applied our new water vapor budget approach to the tracked atmospheric river. We also performed two sets of sensitivity experiments: one reducing the tropical moisture, and the other modifying the ocean evaporation to assess how these two main moisture sources affect the water vapor balance within the atmospheric river. We also study changes in the atmospheric river, cyclone and associated precipitation at landfall in the sensitivity experiments. For Dennis, tropical moisture played a prominent role in the early stages of the atmospheric river, while ocean evaporation became critical later. Additionally, the reduction of evaporation and also of tropical moisture is related to a decrease in precipitation over Europe. This study offers a new approach to understanding the evolution of atmospheric rivers and highlights the importance of different moisture processes. It provides a case study that helps to unravel feedback mechanisms and the impact of different perturbations on the water vapor balance of atmospheric rivers.

A document by Mason Perry. Click on the document to view its contents.

Clarifying the relationship between regular earthquakes and slow fault slip is essential for understanding the mechanisms behind seismic activity. We hypothesize that the background seismic activity around the Guerrero seismic gap in Mexico is partially triggered by interplate slow-slip events (SSEs). Consequently, we present an extension of the spatio-temporal epidemic-type aftershock sequence (ETAS) model, which incorporates background seismicity as a piecewise constant function over time. In this study, Global Navigation Satellite System (GNSS) data is employed to identify the occurrence periods of SSEs, thereby delineating the intervals during which changes in background seismicity may occur. Due to the technical complexity of performing inference with an inhomogeneous ETAS model, this work employs a penalized maximum likelihood inference method using the Expectation-Maximization (EM) algorithm. This approach also permits the inference of the branching process for aftershocks, thus enabling the estimation of the genealogy between earthquakes. This information could be utilized to decluster earthquakes. This study elucidates how the background seismicity increases during the periods of the Guerrero SSEs, which allows for a more comprehensive understanding of seismic activity and the relationship between slow and fast earthquakes in Mexico. Our new model can be applied not only in Mexico but also at plate boundaries worldwide to quantify the impact of SSEs on seismic activity.

Dust aerosols play a crucial role in Earth’s biogeochemical processes by modulating solar radiation and affecting terrestrial ecosystem productivity. In China, extensive arid and semi-arid regions contribute to high dust aerosol emissions, yet the long-term impact of dust aerosols on gross primary productivity (GPP) remains insufficiently quantified. This study coupled the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) and the Joint UK Land Environment Simulator (JULES) to quantify the impact of dust aerosol radiative forcing on GPP in China’s terrestrial ecosystems from 2000 to 2020. Results indicated that dust aerosols significantly alter surface solar radiation components by reducing direct radiation and enhancing diffuse radiation. The mean annual decrease in direct radiation due to dust aerosols was −8.2 ± 0.2 W m⁻², while the increase in diffuse radiation was 5.3 ± 0.1 W m⁻², leading to a net reduction in total surface solar radiation of around −2.9 W m⁻². These radiative changes resulted in an average annual increase in GPP of approximately 0.11 ± 0.024 Pg C yr⁻¹, accounting for around 2% of China’s mean annual GPP of 6.44 ± 0.18 Pg C yr⁻¹ during the study period. The enhancement was particularly pronounced in regions with high dust aerosol loads, such as northwest China, and exhibited notable interannual variability. This study underscores the complex interactions between dust aerosols and terrestrial ecosystems, highlighting the importance of considering aerosol radiative effects in carbon cycle assessments and climate models.

During the Last Glacial Maximum, wetter and cooler conditions drove expanded pluvial lake systems throughout the southwestern United States. Here, we aim to understand the drivers of these hydroclimate changes using new biomarker records from Cumbres Bog, a high-elevation fen in the San Juan Mountains of southern Colorado. The leaf wax hydrogen isotope record, which we interpret as reflecting changes in the proportions of seasonal precipitation sources reaching Cumbres Bog, indicates that winter moisture delivery was reduced at the LGM, increased suddenly during the deglaciation at ca. 14.8 kyr, and then declined rapidly at ca. 11.5 kyr in association with exceptional early Holocene drought. Winter precipitation abruptly recovered at ca. 8.2 ka and remained high throughout the mid- to late-Holocene. BrGDGT-derived temperatures indicate that the southern Rockies were ca. 6.5°C colder during the LGM. Deglacial warming commenced at ca. 18.1 ka, reaching peak temperatures ~2°C greater than present in conjunction with the peak mid-Holocene drought. Deglacial warming was interrupted by small (~1-2°C) abrupt cooling events coincident with the YD and HS1. These deglacial and Holocene hydroclimate changes were accompanied by changes in terrestrial vegetation, lake evolution, and microbial community changes. Indices based on isoGDGT abundances reveal microbial community changes associated with primary succession and the expansion of methanogenic Archaea with deglacial warming. Past temperature variations significantly altered carbon cycling at the Cumbres Bog site and suggest that high alpine lacustrine ecosystems could be particularly vulnerable to future anthropogenic warming.

We explore the characteristics of EMIC waves generated in a non-dipole, compressed magnetic field at the minimum of the magnetic field. We conducted 2D full-wave simulations using the Petra-M code, focusing on a compressed dipole magnetic field line in the outer dayside magnetosphere for a range of L values ($L=8-10$). By comparing the simulation results with MMS observations, we aim to understand how the observed wave characteristics are affected by a shifting source region across different L-shells. Our findings indicate that the direction of the Poynting vector systematically changes depending on the local source location of the wave, which is consistent with the observations. EMIC waves propagate along the magnetic field line and reach both the northern and southern hemispheres; however, there is a notable difference in the power of EMIC waves between the two hemispheres, indicating seasonal asymmetries in their occurrence.

It has been widely accepted that channel geometry on alluvial fans is predominantly controlled by upstream boundary conditions and remains stable if those conditions do not change. This study challenges that notion by examining how channel width on alluvial fans varies in space and time under constant upstream conditions. Experiments using a sediment mixture (sand and crushed walnut) with constant sediment and water discharge rates reveal distinct patterns. In lower water discharge runs, total channel width decreases over time, while in higher discharge runs, it increases. Theoretical principles suggest that channel width is inversely proportional to grain size. The disproportional advancement of sand reaches relative to the fan margin, which varies across different discharge runs, drives changes in slope and channel width over time. This study highlights that surface grain-size distribution can change as the fan grows, even when external conditions remain constant, leading to variations in channel geometry.

Regime dependencies and Granger causal relationships between tropical and extratropical teleconnections are inferred using Bayesian structure learning. Using ERA5 data, an examination of the differences between the learned causal structures during particular phases of the Interdecadal Pacific Oscillation (IPO) are used to infer the role of the background state on interactions between the major climate teleconnections and in particular the dependence of the ENSO autocorrelation on the phase of the background state, and the role of the Madden Julian Oscillation as being key to link the extratropical tropospheric modes (PNA, NAO) and the equatorial surface ocean forced convective modes (IOD, ENSO). These relationships are presented as posterior distributions over possible graphical representations in terms of Dynamic Bayesian Network (DBN) models constructed from time series of empirical climate indices. General circulation model simulations are used to sample from a larger distribution of possible IPO periods and their phase dependencies.

• Earth system models (ESMs) have many tunable parameters that are difficult to estimate and weakly constrained by theory. • Kalman filter-based approaches are attractive options, but existing implementations require expensive offline hyperparameter selection. • We propose a new Kalman filter algorithm that estimates model parameters and its hyperparameter simultaneously.

We develop an earthquake simulator to study the partitioning of seismic/aseismic slip and dynamics of Earthquakes on a Heterogeneous strike-slip Fault (HFQsim) using a generalized model of a discrete fault governed by static/dynamic friction and creep in an elastic half-space. Previous versions of the simulator were shown to produce various realistic seismicity patterns (e.g., frequency-magnitude event statistics, hypocenter and slip distributions, temporal occurrence) using friction levels and creep properties that vary in space but are fixed in time. The new simulator incorporates frictional heat generation by earthquake slip leading to temperature rises, subsequent diffusion cooling into the half space, and time-dependent creep on the fault. The model assumes a power law dependence of creep velocity on the local shear stress, with temperature-dependent coefficients based on the Arrhenius equation. Temperature rises due to seismic slip produce increased aseismic slip, which can lead to further stress concentrations, aftershocks, and heat generation in a feedback loop. The partitioning of seismic/aseismic slip and space-time evolution of seismicity are strongly affected by the temperature changes on the fault. The results are also affected significantly by the difference between the static and kinetic friction levels. The model produces realistic spatio-temporal distribution of seismicity, transient aseismic slip patterns, foreshock-mainshock-aftershock sequences, and a bimodal distribution of earthquakes with background and clustered events similar to observations. The HFQsim may be used to clarify relations between fault properties and different features of seismicity and aseismic slip, and to improve the understanding of failure patterns preceding large earthquakes.

The impact of climate change on the intensity of mid-latitude cold air outbreaks is a debated topic due to uncertainty associated with internal atmospheric dynamics. Here, we employ an event-based storyline approach in which the evolution of the large-scale atmospheric circulation is nudged to reanalysis data at different global warming levels based on historical and high-emission scenario simulations. We thereby quantify the thermodynamic climate-change effects of pre-industrial, 2ºC and 4ºC warmer climates compared to present-day climate for three cold surges in East Asia during the winter 2020/21. The strongest warming occurs over northeast Asia, reaching up to +12ºC in a +4ºC warmer climate and caused by the advection of less cold air from winter ice-free regions in the Arctic, where the change of surface air temperature exceeds +20ºC. In contrast, over southern China, a moderate cooling is present from pre-industrial to present-day climates, due to the observed and expected increase in aerosol concentration, which peaks by the mid-21st century and alters the radiative balances. This cooling effect is likely to persist well into a +2ºC-warmer climate; however, it may become undetectable at the end of the 21st century (+4ºC warming). In summary, our findings underscore the important thermodynamic impact associated with Arctic amplification and cooling effect of aerosol-induced changes in the radiation budget on East Asian cold extremes.

We model the subsurface thermal field of the Apollo 17 landing site in the Taurus-Littrow valley focusing on local topographic effects and refraction of heat. Topographic effects have been accounted for in original reports, but the refraction of heat due to local thermal conductivity contrasts has not been analyzed. Refraction of heat is evident due to the extreme thermal conductivity contrast between the regolith (0.01 – 0.02 Wm-1K-1) and underlying basaltic rocks (0.5 – 1.0 Wm-1K-1). Outcrops of basalt peeking from beneath the regolith funnel the heat flow resulting in a decrease of the heat flow in low conductivity areas and an increase in high conductivity areas, respectively. The effect is enhanced by the topographic effect in craters, which become spots of very high heat flow. Two-dimensional (width 2.5 km, height 1.7 km) and three-dimensional (6 km x 5 km x 1.7 km) finite element models of conductive heat transfer indicate the commonly accepted value of 16 mWm-2 in the Taurus-Littrow site should be increased by about 3 mWm-2, i.e. by 19% to obtain an estimate representative for the valley floor at a depth where the topographic and refraction effects have attenuated (ca. 1.7 km depth). Our modeling illustrates the challenges in interpreting point-like lunar heat flow measurements and potentially contributes to planning of future thermal studies on the Moon, Mercury and Mars.

• GISS-E2.1 accurately simulates variations of precipitation 𝛿 18 O and d-excess but slightly underestimates d-excess values at low latitudes. • GISS-E2.1 overestimates 17 O-excess in polar regions, possibly due to inaccuracy in representing the supersaturation effect. • In tropical regions, the spatiotemporal distributions of d-excess and 17 O-excess are sensitive to rain evaporation.

A document by Heather L Wander. Click on the document to view its contents.

Mineral precipitation in geological formations occurs when reactive fluids of varying compositions mix, altering the porous microstructure of the rock. Basalt rocks are of particular interest for long-term CO2 storage due to their potential to rapidly mineralize CO2 into stable carbonate minerals. We investigated reactive fluid mixing and subsequent carbonate mineralization in porous basalt using time-lapse three-dimensional neutron and X-ray imaging. Two flow-through experiments with different injection rates were performed on basalt cores, where co-injected CaCl2 and Na2CO3 solutions were mixed within the porous network, leading to calcium carbonate precipitation. Time-lapse neutron imaging distinguished the two injected fluids and tracked their mixing. X-ray imaging was used to separate the solid matrix from the pore space to enable fluid analysis in the neutron images. A first experiment with a high flow rate induced a steady transverse mixing pattern, captured by a decay of the concentration variance through the sample, as measured by neutron imaging. A second experiment at a lower flow rate promoted more temporal fluctuations in the fluid distribution due to the multiphase flow of water and air in the rock. The analysis of neutron images showed a significant mixing of reactive fluids driven by these temporal fluctuations. Furthermore, a higher-resolution, synchrotron X-ray image of one of the sample rocks acquired after the experiment showed the formation of additional calcite resulting from long-term diffusive mixing. The results highlight the great potential and challenges of neutron and X-ray imaging in characterizing pore-scale mixing and precipitation in rocks.

High latitudes are predicted to continue warming at higher rates than the global average, with major implications for northern basins where concomitant deglaciation, permafrost thaw and vegetation shifts are expected. The Mackenzie River Basin, a globally significant basin, drains headwaters in the glaciated Canadian Rockies to the Arctic Ocean and is mostly underlain by permafrost. Here, we present scenarios of future change using the MESH distributed hydrological-cryospheric land surface model. MESH was forced with bias-corrected, downscaled RCM forcings and parameterized with a deep subsurface profile, organic soils, and glaciers. The model was validated against discharge, snowpack, and permafrost observations and used to simulate the hydrology and permafrost dynamics over the 21st century under the RCP8.5 climate change scenario with projected land cover change. The results show rapidly increasing rates of permafrost thaw; most of the basin will be permafrost-free by the 2080s. By late century, river discharges shift to earlier and higher peaks in response to projected increases in precipitation, temperature, snowmelt rates, despite increases in evapotranspiration from longer snow-free seasons. Baseflow discharges increase in winter, due to higher precipitation and increased basin connectivity from permafrost thaw resulting in enhanced groundwater flow. Subsurface moisture storage rises slightly but the liquid water fraction increases dramatically, increasing sub-surface runoff and river discharge. Canadian Rockies deglaciation reduces summer and annual discharge in the Athabasca and Peace headwaters. Downstream and northward of the mountain headwaters the direct impacts of climate change on river discharge dominate over those of changing land cover and glaciers.