Marine ecosystems provide essential services to the Earth System and society. These ecosystems are threatened by anthropogenic activities and climate change. Climate change increases the risk of passing tipping points; for example, the Atlantic Meridional Overturning Circulation (AMOC) might tip under future global warming leading to additional changes in the climate system. Here, we look at the effect of an AMOC weakening on marine ecosystems by forcing the Community Earth System Model v2 (CESM2) with low (SSP1-2.6) and high (SSP5-8.5) emission scenarios from 2015 to 2100. An additional freshwater flux is added in the North Atlantic to induce extra weakening of the AMOC. In CESM2, the AMOC weakening has a large impact on phytoplankton biomass and temperature fields through various mechanisms that change the supply of nutrients to the surface ocean. We drive a marine ecosystem model, EcoOcean, with phytoplankton biomass and temperature fields from CESM2. In EcoOcean, we see negative impacts in Total System Biomass (TSB), which are larger for high trophic level organisms. The strongest net effect is seen in the high emission scenario, but the effect of the extra AMOC weakening on TSB is larger in the low emission scenario. On top of anthropogenic climate change, TSB decreases by -3.78% and -2.03% in SSP1-2.6 and SSP5-8.5, respectively due to the AMOC weakening. These results show that marine ecosystems will be under increased threat if the AMOC weakens which might put additional stresses on socio-economic systems that are dependent on marine biodiversity as a food and income source.

The terrestrial planet Venus is classified by astronomers as an inferior planet because it is located closer to the Sun than the Earth. Venus orbits the Sun at a mean distance of 108.21 Million Km and receives an average annual solar irradiance of 2601.3 W/m 2 , which is 1.911 times that of the Earth. A set of linked forward and inverse climate modelling studies were undertaken to determine whether a process of atmospheric energy retention and recycling could be established by a mechanism of energy partition between the solid illuminated surface and an overlying fully transparent, non-greenhouse gas atmosphere. Further, that this atmospheric process could then be used to account for the observed discrepancy between the average annual solar insolation flux and the surface tropospheric average annual temperature for Venus. Using a geometric climate model with a globular shape that preserves the key fundamental property of an illuminated globe, namely the presence on its surface of the dual environments of both a lit and an unlit hemisphere; we established that the internal energy flux within our climate model is constrained by a process of energy partition at the surface interface between the illuminated ground and the overlying air. The dual environment model we have designed permits the exploration and verification of the fundamental role that the atmospheric processes of thermal conduction and convection have in establishing and maintaining surface thermal enhancement within the troposphere of this terrestrial planet. We believe that the duality of energy partition ratio between the lit and unlit hemispheres applied to the model, fully accounts for the extreme atmospheric "greenhouse effect" of the planet Venus. We show that it is the meteorological process of air mass movement and energy recycling through the mechanism of convection and atmospheric advection, associated with the latitudinal hemisphere encompassing Hadley Cell that accounts for the planet's observed enhanced atmospheric surface warming. Using our model, we explore the form, nature and geological timing of the climatic transition that turned Venus from a paleo water world into a high-temperature, high-pressure carbon dioxide world.

In May 2024, a series of coronal mass ejections (CMEs) resulted in the first ’severe’ (G4-level) geomagnetic storm watch in nearly 20 years. This event evolved into a significant space weather event, including an ’extreme’ (G5) geomagnetic storm, moderate (S2) solar radiation storm, and strong (R3) radio blackout. The widespread visibility of auroras at unusually low latitudes attracted global media attention. Using extreme value theory (EVT), this study estimates the return periods for the May 2024 storm based on several geomagnetic indices. The results indicate that while the storm’s magnitude was a 1-in-12.5-year event, its duration was a 1-in-41-year event. This discrepancy highlights the storm’s unusual longevity compared to its intensity. Updated EVT analyses incorporating recent data refine these return period estimates, providing critical insights into the frequency of such extreme space weather events.

The Mekong river is one of the most complex river systems in the world that is shared by six nations in Southeast Asia. The river still remains relatively undammed (most existing dams are in the tributaries and are small), and its hydrology today is dominated by large natural flow variations that support the highly productive agricultural and riverine ecological systems; however, this is changing due to the alterations in land use and construction of new dams both in the tributaries the mainstream. Understanding the changes in surface water dynamics is therefore crucial to provide realistic future predictions of changes in downstream floodplain and riverine ecology due to the construction of dams in the upstream. While the existing dams have caused little impact on mainstream flows, those under construction and planned are likely to cause severe and potentially permanent damage to downstream hydro-agro-ecological systems, and adversely impact the livelihood of millions. Here, using hydrodynamic model simulations (CaMa-Flood), we show that the effects of flow regulation on downstream river-floodplain dynamics are relatively predictable along the mainstream Mekong, but flow regulations could potentially disrupt the flood dynamics in the Tonle Sap River (TSR) and small distributaries in the Mekong Delta. Results suggest that TSR flow reversal could cease if the Mekong flood pulse is dampened by 50% and delayed by one-month. While flood occurrence in the vicinity of the Tonle Sap Lake and middle reach of the delta could increase due to enhanced low flow, it could decrease by up to five months in other areas due to dampened high flow, particularly during dry years. Further, areas flooded for less than five months and over six months are likely to be impacted significantly by flow regulations, but those flooded for 5-6 months could be impacted the least.

Taupo Volcano, located in the central part of the TVZ (Taupo volcanic Zone), North Island of New Zealand, is one of the most productive Rhyolitic centres in the world. Although its last eruption occurred about 1800 years ago, 16 periods of unrest have been identified including surface deformation, hydrothermal eruptions, and seismic swarms since 1870. The town of Taupo lies on the north-eastern shore of the lake filling the caldera of the volcano and is located close to recent seismic swarms and local surface deformation episodes highlighted in this report. The aim of this work is to study the different periods of episodic deformation, contrasting with the long-term deformation of the Taupo region, in order to constrain the sources generating local deformation. For this, an analysis of GPS (continuous and campaign stations) and InSAR data (from two satellites, EnviSAT and ALOS) was conducted. After correcting the data for several external factors such as subsidence generated by water pumping in the Wairakei-Tauhara geothermal station and displacements associated with slow slip events along the Hikurangi subduction interface, periods of local deformation have been identified. We highlight two periods of uplift with rates of 10 mm/yr in 2004-2008 and in 2011-2013 accompanied by more or less rapid horizontal deformation punctuated by seismic swarms. The geodetic data were inverted to characterize the deformation sources using the GBIS software, allowing the use of different analytical models. In order to explain the different periods of deformation over time, at least three sources at different locations are needed, revealing the presence of different processes at depths ranging from ∼ 10 km to ∼ 0.5 km and whose causes can vary given the complexity of the tectonic context characterizing the region.

Surface crevasses on the Greenland Ice Sheet capture nearly half of the seasonal runoff, yet their role in transferring meltwater to the bed has received little attention compared to that of supraglacial lakes and moulins. Here, we present observations of crevasse ponding and investigate controls on their hydrological behaviour at a fast-moving, marine-terminating sector of the Greenland Ice Sheet. We map surface meltwater, crevasses, and surface-parallel stress across a ~2,700 km² region using satellite data and contemporaneous uncrewed aerial vehicle (UAV) surveys. From 2017-2019 an average of 26% of the crevassed area exhibited ponding at locations that remained persistent between years despite rapid advection rates. We find that the spatial distribution of ponded crevasses does not relate to previously proposed methods for predicting the distribution of supraglacial lakes (elevation and topography) or crevasses (von Mises stress thresholds), suggesting the operation of some other physical control(s). Ponded crevasse fields were preferentially located in regions of compressive surface-parallel mean stress, which we interpret to result from the hydraulic isolation of these systems, in contrast to unponded crevasse fields, which we suggest are able to drain into the wider supraglacial and englacial network. UAV observations show that ponded crevasses can drain episodically and rapidly, likely through hydrofracture. We therefore propose that the surface stress regime informs a spatially heterogeneous transfer of meltwater through crevasses to the bed of ice sheets, with potential consequences for processes such as subglacial drainage and the heating of ice via latent heat release by refreezing meltwater.

A document by David Shean. Click on the document to view its contents.

In the present study, using sixty-three and fifty-six years of continuous observations, we investigate the long-term oscillations and residual trends, respectively, in the E- and F-region ionosonde measured parameters over Juliusruh, Europe. Using the Lomb-Scargle periodogram (LSP) long-term variations are estimated before the trend estimation. We found that the amplitude of the annual oscillation is higher than the 11-year solar cycle variation in the critical frequencies of the daytime E (foE) and Es (foEs) layers. A weak semi-annual oscillation is also identified in the foE. In the F-region, except for daytime hmF2, and nighttime foF2, the amplitude of the 11-year solar cycle variation is higher than the annual oscillation. The LSP estimated periods and their corresponding amplitudes are used to construct a model E- and F-region ionospheric parameters that are in good agreement with the observation. The linear trend estimation is derived by applying a least-squares fit analysis to the residuals, subtracting the model from the observation. Except for the daytime foF2, all the other parameters like nighttime foF2, day and nighttime h’F, and hmF2 show a negative trend. Present results suggest that the greenhouse effect is a prime driver for the observed long-term trend in the F-region. Interestingly, weak negative trends in the foE and foEs are found which contradicts an earlier investigation. The present study suggests that the changes in the upper stratospheric ozone and mesosphere wind shear variability could be the main driver for the observed weak negative trends in the foE, and foEs, respectively.

The origin of Kiruna-type magnetite-apatite deposits, which are thought to form by magmatic and/or hydrothermal processes, has recently come under renewed scrutiny. Geological and geochemical studies of volcanic-hosted magnetite deposits that include magnetite lava flows and ash layers at El Laco, a volcano in the Central Volcanic Zone, northern Chile, suggest a formation by eruptive emplacement of an iron oxide-rich melt. The generation of such exotic high density, low viscosity melts by dissociation from an andesitic host magma contaminated by shallow crustal sediments has only recently been shown experimentally. The dynamics of volcanic emplacement have remained enigmatic because the high density of iron-rich melts seems to negate their eruption potential. Yet, observations of ubiquitous vesiculation, degassing structures, and steam-heated alteration provide important clues that volatiles had a pivotal role in the volcanic emplacement. Here, we posit a scenario in which an iron-rich immiscible liquid gravitationally separates from its andesitic parent magma in a shallow magma reservoir and subsequently rises as a bubbly suspension along volcano-tectonic faults extending to the flanks of the edifice. We test this hypothesis through numerical models that capture both the deformation of the volcanic edifice as well as the melt transport within. Preliminary results indicate that separation of a low-viscosity, iron- and volatile-rich melt from a silicic magma within a reasonable time is possible only if an interconnected melt drainage networks forms at the granular scale. Results further suggest that magma reservoir deflation and/or minor local extension combined with the topographic load of the edifice may explain normal faults connecting the magma reservoir with magnetite flow locations on the volcano flanks. Finally, our models show that hydrostatically driven flow of iron-rich melts into these faults at depth may trigger volatile exsolution and bubble expansion to provide sufficient driving force for an eruptive emplacement. Although the case for such magmatic ore formation is perhaps strongest at El Laco, evidence from other localities suggests that similar processes have been at work. The new insights derived from our models may, therefore, apply more generally to Kiruna-type deposits elsewhere.

Aqueous S[IV] species (HSO3−, SO32−) derived from volcanogenic atmospheric SO2 are  important to planetary habitability through their roles in proposed origins-of-life chemistry and influence on atmospheric sulfur haze formation, but the early cycling of S[IV] is poorly understood. Here, we combine new laboratory constraints on S[IV] disproportionation kinetics with a novel aqueous photochemistry model to estimate the concentrations of S[IV] in natural waters on prebiotic Earth. We show that S[IV] disproportionation is slow in pH≥ 7 waters, with timescale T≥ 1 year at room temperature, meaning that S[IV] was present in prebiotic natural waters. However, we also show that photolysis of S[IV] by UV light on prebiotic Earth limited [S[IV]]< 100μM in global-mean steady-state. Because of photolysis, [S[IV]] was much lower in natural waters compared to the concentrations generally invoked in laboratory simulations of origins-of-life chemistry (≥ 10 mM), meaning further work is needed to confirm whether laboratory S[IV]- dependent prebiotic chemistries could have functioned in nature. [S[IV]]≥ 1μM in terrestrial waters for: (1) SO2 outgassing ≥ 20× modern, (2) pond depths < 10 cm, or UV-attenuating agents present in early waters or the prebiotic atmosphere. Marine S[IV] was sub-saturated with respect to atmospheric SO2, meaning that atmospheric SO2  deposition was efficient and that, within the constraints of present knowledge, UV-attenuating sulfur hazes could only have persisted on prebiotic Earth if sulfur emission rates were very high (≳ 100× modern). Our work illustrates the synergy between planetary science, geochemistry and synthetic organic chemistry towards understanding the emergence and maintenance of life on early Earth.

Iron is the fourth most common element found in the earth crust. Although it may not be as important for soil fertility as, e.g., phosphorus, nitrogen and organic matter, its absence would be detrimental to plant growth. At the same time, iron oxides are highly correlated with phosphorus availability. Iron is thus an indicator for soil fertility and the usability of an area for cultivation of crop. A relatively high spectral resolution is needed for mapping iron oxide contents with spectral reflectance data, and remote sensing is the only suitable tool for surveying large areas at a high temporal and spatial interval. Sentinel-2 MSI (MultiSpectral Instrument) is the Landsat-like spatial resolution (10–60 m) super-spectral instrument of the European Space Agency (ESA), aimed at additional data continuity for global land surface monitoring with Landsat and Satellite Pour l’Observation de la Terre (SPOT) missions. Several studies with simulated and real data have been conducted in the last several years to show the potential of Sentinel-2 MSI, including its use for geological remote sensing, mineral mapping in particular. Sentinel-2 has several bands that cover the 0.9 μm iron absorption feature, while space-borne sensors traditionally used for geologic remote sensing, like ASTER and Landsat, had only one band in this feature. In this paper, we show a comparison of Sentinel-2 and AVIRIS to demonstrate the usability of the VNIR bands for mapping the near-infrared iron absorption feature. Next, we present spectral indices for mapping iron minerals that are important in soil fertility and mineral exploration.

Mixed bedrock-alluvial rivers can exhibit partial alluvial cover, which may play an important role in controlling bedrock erosion rates and landscape evolution. However, numerical morphodynamic models generally are unable to predict the pattern of alluviation in these channels. Hence we present a new two-dimensional depth-averaged morphodynamic model that can be applied to both fully alluvial and mixed bedrock-alluvial channels, and we use the model to gain insight into the mechanisms responsible for the development of sediment patches and patterns of bedrock alluviation. The model computes hydrodynamics, sediment transport, and bed evolution, using a roughness partitioning that accounts for differential roughness of sediment and bedrock, roughness due to sediment transport, and form drag. The model successfully replicates observations of bar development and migration from a fully alluvial flume experiment, and it models persistent sediment patches observed in a mixed bedrock-alluvial flume experiment. Numerical experiments in which the form drag, sediment transport roughness, and ripple factor correction were neglected did not successfully reproduce the observed persistent sediment cover in the mixed bedrock-alluvial case, suggesting that accounting for these different roughness components is critical to successfully model sediment dynamics in bedrock channels.

Terrestrial wetlands are a highly significant carbon reservoir in North America. Forested wetlands, or swamps, are an important category of North American wetland and include boreal forested peatlands, swamps dominated by needle-leaved trees including Thuja (cedar), Picea (Spruce), Larix (Tamarack) or Taxodium (bald cypress), swamps dominated by broad-leaved trees or shrubs including Fraxinus (Ash), Ulmus (Elm), or Acer (Maple), as well as mangroves. The Second State of the Carbon Cycle Report estimates that forested wetlands may make up ~55% of the total terrestrial wetland area for North America, although estimates vary considerably due to different mapping conventions and classification systems across national and provincial borders, and also due to the ongoing impacts of land use change. Additionally, that report suggests that forested wetlands contain larger total carbon pools than non-forested wetlands, and that forested wetlands effect 53% of the estimated 123 Tg total wetland annual carbon sink for North America. Uncertainties in the sizes of the forested wetland soil carbon pools continue to be significant due in part to insufficient data on variabilities in carbon densities across diverse swamp types. Further, there are limited data on the rates of vertical accretion of swamp soils and the associated long-term rates of carbon accumulation, needed for better predicting impacts of climate warming on carbon sequestration in swamp soils. We present here a comparative synthesis of swamp soil carbon properties including bulk densities, organic carbon contents, soil thicknesses, rates of vertical accretion and rates of long-term carbon accumulation, from >200 swamp sites. We compare these properties for broad-leaf swamps (including mangroves), needle-leaf swamps, mixed swamps, and shrub-dominated swamps, and also compare across North American Ecoregions. The results show significant variability across peat-forming and mineral swamps, and indicate rates of carbon accumulation in some swamp types similar to those of northern bogs and fens.

Anthropogenic carbon emissions and associated climate change are driving rapid warming, acidification, and deoxygenation in the ocean, which increasingly stress marine ecosystems. On top of long-term trends, short term variability of marine stressors can have major implications for marine ecosystems and their management. As such, there is a growing need for predictions of marine ecosystems on monthly, seasonal, and multi-month timescales. Previous studies have demonstrated the ability to make reliable predictions of the surface ocean physical and biogeochemical state months to years in advance, but few studies have investigated forecasts of multiple stressors simultaneously or assessed the forecast skill below the surface. Here, we use the Community Earth System Model (CESM) Seasonal to Multiyear Large Ensemble (SMYLE) along with novel observation-based biogeochemical and physical products to quantify the predictive skill of dissolved inorganic carbon, dissolved oxygen, and temperature in the surface and subsurface ocean. CESM SMYLE demonstrates high physical and biogeochemical predictive skill multiple months in advance in key oceanic regions and frequently outperforms persistence forecasts. We find up to 10 months of skillful forecasts, with particularly high skill in the Northeast Pacific (Gulf of Alaska and California Current Large Marine Ecosystems) for temperature, surface DIC, and subsurface oxygen. Our findings suggest that dynamical marine ecosystem prediction could support actionable advice for decision making.

The rapidly melting Totten Glacier of East Antarctica drains a basin containing ~3.5 m sea-level rise equivalent of ice, but the Totten Glacier dynamics and interaction with the Southern Ocean since the Last Glacial Maximum is not well understood. To better understand the response of the glacier to present and future climate changes, an accurate reconstruction of the retreat history of the Totten Glacier is needed. Hence, this study uses a multiproxy approach in analyzing beryllium isotopes, the first such record from this location, and grain size of a sediment core collected from the continental slope adjacent to Totten Glacier. The results, when evaluated together with nearby proxy records, reveal that the initial deglaciation of the Totten Glacier sector of the East Antarctic Ice Sheet began at ~18 ka BP. The rapid deglaciation from ~9 ka BP that followed is assumed to be caused by the intrusion of modified Circumpolar Deep Water to the grounding zone of the Totten Glacier. This intrusion may also be coupled with a weaker Antarctic Slope Current and southward shift of Antarctic easterlies. This result contributes to the body of knowledge regarding the dynamical response of marine-terminating glaciers to climate variability during the last deglaciation.

Salt marshes are ecosystems with significant economic and environmental value. They provide numerous ecosystem services and act as natural coastal defences by buffering storm waves and stabilising sediments (Leonardi et al., 2016). However, with accelerating rate in sea-level rise, possible increases in storm intensity and increasing land reclamation, it is not clear whether salt marshes will be able to retain their resilience. The current paradigm is that a positive sediment budget supports the survival and accretion of salt marshes while a negative sediment budget causes marsh degradation (Ganju et al. 2015). Here we present the results of a series of studies that used a sediment budget approach and an integration of modelling and paleoenvironmental analysis to investigate the resilience of estuaries and salt marshes to rise in sea-level, change in storm activity and anthropogenic interventions. The Ribble Estuary, North-West England, was used as a test case, as it is one of the largest salt marsh systems in Europe, it was subject to several anthropogenic interventions (e. g. embankment construction) and it was anthropogenically restored through managed realignment to provide coastal protection against flooding (Pontee et al., 2014). The various processes were investigated using the hydrodynamic model Delft3D to simulate the estuary morpho-dynamics under selected scenarios, and optically stimulated luminescence (OSL), geochemistry and particle size analysis to reconstruct the past evolution and adaptation of the estuary morphology. Results showed that sea-level rise threatens estuary and marsh stability by promoting ebb dominance and triggering a net export of sediment. Conversely, storm surges promote flood dominance and trigger a net import of sediment, therefore aiding the resilience of the system. Storms with the highest intensities also have the potential to counteract the negative impact of sea-level rise by masking its effects on the sediment budget. The addition of embankments, on the other hand, can further promote ebb dominance in the system and intensify sediment export, further threatening marsh stability. ReferencesLeonardi, N. et al. (2016). PNAS, 113(1), 64-68.Ganju, N.K. et al. (2015). Geoph. Res. Lett., 42(19), 7992-8000.Pontee, N.I. et al. (2009). Eng. Sust., 162(4), 223-228.

Enhanced water management systems depend on accurate estimation of hydraulic properties of subsurface formations. This is while hydraulic conductivity of geologic formations could vary significantly. Herein, we studied an intensively managed area located in the Upper Sangamon Watershed in Central Illinois, U.S.A., and generated 2D maps of hydraulic conductivity over a large-scale region with quantified uncertainties in different depth layers. In doing so, we made use of low cost, small-scale measurements obtained from the Electrical Earth Resistivity together with more accurate, more expensive pumping tests in a calibration framework based on Kriging. We offered a cost-effective approach to reliably characterize the hydraulic conductivity properties in under-sampled sites and can be particularly used in obtaining large-scale parameter maps for a region using small-scale measurements in an efficient way. This work also includes optimal sensor placement, where the best locations for future data collection are selected by considering the current confidence levels estimated by the Kriging model, which is related to the expected value of information from future sensor data. Our approach is based on the Bayesian experimental design, which selects the best locations, out of a set of candidate locations, based on the value of information that each location is expected to offer.

Cold temperatures limit nitrate-N load reductions of woodchip bioreactors in higher-latitude climates. This two-year, on-farm (Willmar, Minnesota, USA) study was conducted to determine whether field-scale nitrate-N removal of woodchip bioreactors can be improved by the addition of cold-adapted, locally isolated bacterial denitrifying strains (bioaugmentation) or dosing with a carbon (C) source (biostimulation). In Spring 2017, biostimulation removed 66% of the nitrate-N load, compared to 21% and 18% for bioaugmentation and control, respectively. The biostimulation nitrate-N removal rate (NRR) was also significantly greater, 15.0 g N m-1 d-1, versus 5.8 and 4.4 g N m-1 d-1, for bioaugmentation and control, respectively. Bioclogging of the biostimulation beds limited dosing for the remainder of the experiment; NRR was greater for biostimulation in Fall 2017, but in Spring 2018 there were no differences among treatments. Carbon dosing did not increase outflow dissolved organic C concentration. The abundance of one of the inoculated strains, Cellulomonas sp. strain WB94, increased over time, while another, Microvirgula aerodenitrificans strain BE2.4, increased briefly, returning to background levels after 42 days. Eleven days after inoculation in Spring 2017, outflow nitrate-N concentrations of bioaugmentation were sporadically reduced compared to the control for two weeks but were insignificant over the study period. The study suggests that biostimulation and bioaugmentation are promising technologies to enhance nitrate removal during cold conditions. A means of controlling bioclogging is needed for biostimulation, and improved means of inoculation and maintaining abundance of introduced strains is needed for bioaugmentation. In conclusion, biostimulation showed greater potential than bioaugmentation for increasing nitrate removal in a woodchip bioreactor, whereas both methods need improvement before implementation at the field scale.