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The productivity of aquatic ecosystems depends on the supply of limiting nutrients. The invasion of the Laurentian Great Lakes, the world’s largest freshwater ecosystem, by dreissenid (zebra and quagga) mussels has dramatically altered the ecology of these lakes. A key open question is how dreissenids affect the cycling of phosphorus (P), the nutrient that limits productivity in the Great Lakes. We show that a single species, the quagga mussel, is now the primary regulator of P cycling in the lower four Great Lakes. By virtue of their enormous biomass, quagga mussels sequester large quantities of P in their tissues and dramatically intensify benthic P exchanges. Mass balance analysis reveals a previously unrecognized sensitivity of the Great Lakes ecosystem, where P availability is now regulated by the dynamics of mussel populations while the role of the external inputs of phosphorus is suppressed. Our results show that a single invasive species can have dramatic consequences for geochemical cycles even in the world’s largest aquatic ecosystems. The ongoing spread of dreissenids across a multitude of lakes in North America and Europe is likely to affect carbon and nutrient cycling in these systems for many decades, with important implications for water quality management.

Connections between glaciation, chemical weathering, and the global carbon cycle could steer the evolution of global climate over geologic time, but even the directionality of feedbacks in this system remain to be resolved. Here, we assemble a compilation of hydrochemical data from glacierized catchments, use this data to evaluate the dominant chemical reactions associated with glacial weathering, and explore the implications for long-term geochemical cycles. Weathering yields from catchments in our compilation are higher than the global average, which results, in part, from higher runoff in glaciated catchments. Our analysis supports the theory that glacial weathering is characterized predominantly by weathering of trace sulfide and carbonate minerals. To evaluate the effects of glacial weathering on atmospheric pCO₂, we use a solute mixing model to predict the ratio of alkalinity to dissolved inorganic carbon (DIC) generated by weathering reactions. Compared with nonglacial weathering, glacial weathering is more likely to yield alkalinity/DIC ratios less than 1, suggesting that enhanced sulfide oxidation as a result of glaciation may act as a source of CO₂ to the atmosphere. Back-of-the-envelope calculations indicate that oxidative fluxes could change ocean–atmosphere CO₂ equilibrium by 25 ppm or more over 10 ky. Over longer timescales, CO₂ release could act as a negative feedback, limiting progress of glaciation, dependent on lithology and the concentration of atmospheric O₂. Future work on glaciation–weathering–carbon cycle feedbacks should consider weathering of trace sulfide minerals in addition to silicate minerals.

Seasonal snow cover is the largest single component of the cryosphere in areal extent, covering an average of 46 × 106 km2 of Earth's surface (31 % of the land area) each year, and is thus an important expression and driver of the Earth's climate. In recent years, Northern Hemisphere spring snow cover has been declining at about the same rate (∼ −13 % per decade) as Arctic summer sea ice. More than one-sixth of the world's population relies on seasonal snowpack and glaciers for a water supply that is likely to decrease this century. Snow is also a critical component of Earth's cold regions' ecosystems, in which wildlife, vegetation, and snow are strongly interconnected. Snow water equivalent (SWE) describes the quantity of water stored as snow on the land surface and is of fundamental importance to water, energy, and geochemical cycles. Quality global SWE estimates are lacking. Given the vast seasonal extent combined with the spatially variable nature of snow distribution at regional and local scales, surface observations are not able to provide sufficient SWE information. Satellite observations presently cannot provide SWE information at the spatial and temporal resolutions required to address science and high-socio-economic-value applications such as water resource management and streamflow forecasting. In this paper, we review the potential contribution of X- and Ku-band synthetic aperture radar (SAR) for global monitoring of SWE. SAR can image the surface during both day and night regardless of cloud cover, allowing high-frequency revisit at high spatial resolution as demonstrated by missions such as Sentinel-1. The physical basis for estimating SWE from X- and Ku-band radar measurements at local scales is volume scattering by millimeter-scale snow grains. Inference of global snow properties from SAR requires an interdisciplinary approach based on field observations of snow microstructure, physical snow modeling, electromagnetic theory, and retrieval strategies over a range of scales. New field measurement capabilities have enabled significant advances in understanding snow microstructure such as grain size, density, and layering. We describe radar interactions with snow-covered landscapes, the small but rapidly growing number of field datasets used to evaluate retrieval algorithms, the characterization of snowpack properties using radar measurements, and the refinement of retrieval algorithms via synergy with other microwave remote sensing approaches. This review serves to inform the broader snow research, monitoring, and application communities on progress made in recent decades and sets the stage for a new era in SWE remote sensing from SAR measurements.

The oxygenation of Earth’s surface environment dramatically altered key biological and geochemical cycles and ultimately ushered in the rise of an ecologically diverse biosphere. However, atmospheric oxygen partial pressures (pO₂) estimates for large swaths of the Precambrian remain intensely debated. Here we evaluate and explore the use of carbonate cerium(Ce) anomalies (Ce/Ce*) as a quantitative atmospheric pO₂ proxy and provide estimates of Proterozoic pO₂ using marine carbonates from a unique Precambrian carbonate succession—the Paleoproterozoic Pethei Group. In contrast to most previous work, wemeasure Ce/Ce* on marine carbonate precipitates that formed in situ across a depth gradient, building on previous detailed sedimentology and stratigraphy to constrain the paleo-depth of each sample. Measuring Ce/Ce* across a full platform to basin depth gradient, we found only minor depleted Ce anomalies restricted to the platform and upper slope facies. We combine these results with a Ce oxidation model to provide a quantitative constraint on atmospheric pO₂ 1.87 billion years ago (Ga). Our results suggest Paleoproterozoic atmospheric oxygen concentrations were low, near 0.1% of the present atmospheric level. This work provides another crucial line of empirical evidence that atmospheric oxygen levels returned to low concentrations following the Lomagundi Event, and remained low enough for large portions of the Proterozoic to have impacted the ecology of the earliest complex organisms.

Twenty-five years ago this month, Thomas Gold published a seminal manuscript suggesting the presence of a “deep, hot biosphere” in the Earth’s crust. Since this publication, a considerable amount of attention has been given to the study of deep biospheres, their role in geochemical cycles, and their potential to inform on the origin of life and its potential outside of Earth. Overwhelming evidence now supports the presence of a deep biosphere ubiquitously distributed on Earth in both terrestrial and marine settings. Furthermore, it has become apparent that much of this life is dependent on lithogenically sourced high-energy compounds to sustain productivity. A vast diversity of uncultivated microorganisms has been detected in subsurface environments, and we show that H₂, CH₄, and CO feature prominently in many of their predicted metabolisms. Despite 25 years of intense study, key questions remain on life in the deep subsurface, including whether it is endemic and the extent of its involvement in the anaerobic formation and degradation of hydrocarbons. Emergent data from cultivation and next-generation sequencing approaches continue to provide promising new hints to answer these questions. As Gold suggested, and as has become increasingly evident, to better understand the subsurface is critical to further understanding the Earth, life, the evolution of life, and the potential for life elsewhere. To this end, we suggest the need to develop a robust network of interdisciplinary scientists and accessible field sites for long-term monitoring of the Earth’s subsurface in the form of a deep subsurface microbiome initiative.

Although initially viewed as oases within a barren deep ocean, hydrothermal vent and methane seep communities are now recognized to interact with surrounding ecosystems on the sea floor and in the water column, and to affect global geochemical cycles. The importance of understanding these interactions is growing as the potential rises for disturbance from oil and gas extraction, seabed mining and bottom trawling. Here we synthesize current knowledge of the nature, extent and time and space scales of vent and seep interactions with background systems. We document an expanded footprint beyond the site of local venting or seepage with respect to elemental cycling and energy flux, habitat use, trophic interactions, and connectivity. Heat and energy are released, global biogeochemical and elemental cycles are modified, and particulates are transported widely in plumes. Hard and biotic substrates produced at vents and seeps are used by “benthic background” fauna for attachment substrata, shelter, and access to food via grazing or through position in the current, while particulates and fluid fluxes modify planktonic microbial communities. Chemosynthetic production provides nutrition to a host of benthic and planktonic heterotrophic background species through multiple horizontal and vertical transfer pathways assisted by flow, gamete release, animal movements, and succession, but these pathways remain poorly known. Shared species, genera and families indicate that ecological and evolutionary connectivity exists among vents, seeps, organic falls and background communities in the deep sea; the genetic linkages with inactive vents and seeps and background assemblages however, are practically unstudied. The waning of venting or seepage activity generates major transitions in space and time that create links to surrounding ecosystems, often with identifiable ecotones or successional stages. The nature of all these interactions is dependent on water depth, as well as regional oceanography and biodiversity. Many ecosystem services are associated with the interactions and transitions between chemosynthetic and background ecosystems, for example carbon cycling and sequestration, fisheries production, and a host of non-market and cultural services. The quantification of the sphere of influence of vents and seeps could be beneficial to better management of deep-sea environments in the face of growing industrialization.

Submarine hydrothermal systems are critical for global geochemical cycles. However, hydrothermal fluid chemistry is influenced by multiple overlapping processes, making it difficult to isolate the effects of individual factors. In this study, we applied independent component analysis (ICA) to a global database of hydrothermal fluids to extract the key factors controlling fluid chemistry. The ICA results identified magma differentiation and phase separation as the key controls for major elements, gases, and rare earth elements (REEs). With increasing magmatic differentiation, the CO2 and F concentrations increase, whereas the La/Yb values and Eu anomalies decrease. Associated mineral compositional changes reduce Ca and H2 while increasing Mn/Fe and the K, Li, Pb, Sb, Au, and Ag concentrations. During phase separation, volatiles partition into the vapor phase, whereas metals exhibit element‐specific partitioning. This leads to the vapor‐rich fluids being enriched in trivalent middle REEs and reduced Eu anomalies. pH exerts a strong control on Fe, Mn, Co, Cu, Zn, and REE mobility but has a limited influence on REE patterns. Sediment‐hosted systems show elevated CH4 and NH3 levels although the sediment interaction appears to minimally affect the major elements and REEs. Acid sulfate fluids, formed by reactions between mixed magmatic fluids and seawater with highly altered rocks at high water–rock ratios, exhibit distinct chemical compositions, such as flat REE patterns. These findings demonstrate the utility of ICA for resolving overlapping geochemical processes in hydrothermal systems. Expanding the hydrothermal fluid database will enhance future efforts to model the hydrothermal contributions to oceanic geochemical budgets.

Eolian dust transport and deposition are important geophysical processes which influence global bio-geochemical cycles. Currently, reliable deposition data are scarce in central and east Asia. Located at the boundary of central and east Asia, Xinjiang Province of northwestern China has long played a strategic role in cultural and economic trade between Asia and Europe. In this paper, we investigated the spatial distribution and temporal variation in dust deposition and ambient PM10 (particulate matter in aerodynamic diameter ≤ 10µm) concentration from 2000 to 2013 in Xinjiang Province. This variation was assessed using environmental monitoring records from 14 stations in the province. Over the 14 years, annual average dust deposition across stations in the province ranged from 255.7 to 421.4tkm-2. Annual dust deposition was greater in southern Xinjiang (663.6tkm-2) than northern (147.8tkm-2) and eastern Xinjiang (194.9tkm-2). Annual average PM10 concentration across stations in the province varied from 100 to 196µgm-3 and was 70, 115 and 239µgm-3 in northern, eastern and southern Xinjiang, respectively. The highest annual dust deposition (1394.1tkm-2) and ambient PM10 concentration (352µgm-3) were observed in Hotan, which is located in southern Xinjiang and at the southern boundary of the Taklamakan Desert. Dust deposition was more intense during the spring and summer than other seasons. PM10 was the main air pollutant that significantly influenced regional air quality. Annual average dust deposition increased logarithmically with ambient PM10 concentration (R2 ≥ 0.81). While the annual average dust storm frequency remained unchanged from 2000 to 2013, there was a positive relationship between dust storm days and dust deposition and PM10 concentration across stations. This study suggests that sand storms are a major factor affecting the temporal variability and spatial distribution of dust deposition in northwest China.

As important metal sulfides in the geochemical cycle of sulfur, the characteristics and formation processes of pyrites can provide useful clues regarding their environment. Based on previous findings, shale pyrites were divided into three major classes (euhedral pyrites, framboidal pyrites (framboids) and metasomatic pyrites) and six sub-classes in this study. At the microscopic scale, each type of pyrite is associated with a different formation process. Framboids are formed by burst nucleation in environments with a homogeneous distribution of nutrients while euhedral pyrites are usually formed on pre-existing sites (such as =FeS on the minerals surface) in the heterogeneous system. Metasomatic pyrites formed by the replacement of other ions in accountable material by iron ions and hydrogen sulfide ions in hydrothermal events. The morphology and isotope value of pyrite provide information to track the origins of their nutrient and characteristics of sulfur and iron pools. In addition, the trace element content of pyrite can serve as a proxy for paleo-ocean trace element abundance, indicating changes in atmospheric oxygen content. Additionally, pyrite can also serves as an indicator of shale gas reservoirs.

Actinium‐227 (227Ac) has been used as a powerful tracer of diapycnal mixing in the ocean, assuming that it is conservative and originates mainly from deep‐sea sediments. However, here we show an unexpectedly large source (continental margin) and sink (scavenging) of 227Ac in the ocean, based on high‐resolution 227Ac distributions obtained for the first time by mooring Mn‐fibers in the East Sea (Japan Sea). Although we expected a decrease in radium‐228 (228Ra) to 227Ac ratios with depth owing to their different half‐lives, the ratios increased with depth in the upper layer, indicating efficient removal of 227Ac by particle scavenging. In addition, unusually high 227Ac activities (∼15 dpm m−3) were observed in the surface layer, likely due to the horizontal transport of 227Ac‐enriched shelf water. Thus, our results suggest refining our understanding of the geochemical cycle and application of 227Ac in the ocean. Plain Language Summary Distributions of 227Ac provide crucial information for the vertical mixing of the deep ocean on timescales of up to 100 years. However, behaviors of 227Ac in the ocean have not been well understood to date because of its extremely low concentration. In this study, we for the first time determined high‐resolution 227Ac profiles by mooring Mn‐fibers in a marginal sea of the northwestern Pacific Ocean. Our results display that the shelf source inputs as well as efficient removal by particle scavenging have been overlooked so far. In particular, we emphasize that the removal of 227Ac by particle scavenging revealed in this study should be considered when using 227Ac as a tracer of mixing rates in the ocean. Key Points The high‐resolution measurement of 227Ac with our Mn‐fiber mooring method agrees very well with the onboard Mn‐fiber filtration method Significantly high 227Ac activities, which might originate from the 227Ac‐enriched shelf water, are observed in the surface layer (0–100 m) High 227Ac scavenging rates are calculated based on the increasing trend of 228Ra to 227Ac ratio with depth in the upper layer (0–1,000 m)