Global Biogeochemical Cycles最新文献

Predicting dissolved organic carbon (DOC) mineralization and removal rates across the aquatic continuum is vital for addressing questions relating to carbon cycling, ecosystem functioning, contaminant transport and drinking water safety. Previous research has shown a decline in DOC reactivity with increasing water retention time (WRT), implying reduced processing rates from headwaters to the coast. However, these findings were largely based on bioassays and lake data, which may not reflect real-world conditions across the full aquatic continuum. Using an expanded field-based data set and a statistical model comparison exercise, we found evidence for a more rapid decline in DOC reactivity with WRT than previously reported. Headwaters may therefore act as even stronger DOC processing hotspots than previously recognized. We present updated equations for predicting DOC removal as a function of WRT, which should replace existing formulations in modeling studies to avoid underestimating removal, particularly in headwaters. In a boreal case study, for example, updated equations predict nearly 40% higher DOC mineralization across the aquatic continuum than previous formulations. In addition, we recommend a steady-state Vollenweider approach for simulating DOC transmission in open systems such as lakes, rather than the commonly used exponential decay model, which assumes closed-system dynamics. Nonetheless, large residual variance highlights the limitations of these simple models. Future efforts should focus on developing more nuanced approaches that better capture the complexity of DOC dynamics across diverse aquatic environments.

Marine cold seeps, where subsurface methane-rich fluids discharge at seafloors, are “oases of life” that sustain highly active organic carbon (OC) and iron (Fe) cycling along the global continental margins. However, the interactions between Fe and OC and their impacts on the development and long-term carbon preservation of cold seep ecosystems remain largely unknown. Here, we analyzed the reactive Fe-bound organic carbon (Fe-OC) contents, carbon isotopic compositions, and potential sources in the upper 30 cm sediments across different development stages of cold seeps in the South China Sea. We show that Fe-OC contents in surface sediments of the early-stage seep ecosystem, formed during recent hydrate exploration activities, are ∼45% higher than those in the adjacent non-seep sediments, while transiting to the mature seep stage, Fe-OC contents decline by 31% alongside a 48% reduction in reactive iron oxides (FeR) contents. Over this transition, the contribution of methane-derived OC to Fe-OC decreased from 24 ± 10% to 17 ± 7%. Compared with other marine non-seep sedimentary environments, cold seep sediments maintain relatively high levels of Fe-OC with significantly elevated Fe-OC:FeR molar ratios, suggesting the distinct formation and preservation mechanisms of Fe and OC associations at cold seeps. These findings highlight the key role of Fe-OC associations in retaining methane-derived OC in the early-stage seeps, while a certain fraction of Fe and marine OC associations can persist through the changing redox and geochemical conditions during cold seep development. These insights are necessary to comprehend the dynamics and inner workings of carbon cycling in marine cold seeps.

Marine heatwaves (MHWs) are receiving fast-growing attention due to their devastating ecological and socioeconomic impacts under global warming. Despite studies on the response of phytoplankton abundance to MHWs, their effects on phytoplankton size structure (PSS), a crucial property of phytoplankton community, are poorly understood. Here, we present a global assessment of PSS changes during MHWs based on multi-satellite observations. We find that MHWs tend to increase the dominance of smaller-size phytoplankton in mid-low latitudes, while shifting PSS toward larger-size species in high latitudes. Compared with the high-latitude oceans, PSS are more susceptible to MHWs in mid-low latitudes (ML). Hotspots of PSS shifting to smaller species are observed in the tropical oceans, the eastern boundary upwelling systems, and the mid-latitude transition zones, mainly due to reduced nutrient availability associated with changes in oceanic processes. In contrast, the shift of PSS to larger size classes in the high-latitude oceans is likely attributed to increased light exposure during MHWs. The potential recovery time of these PSS disturbance exhibits marked spatial heterogeneities and suggests a more elastic phytoplankton community during MHWs in ML. These results extend our understanding of the phytoplankton responses to MHWs and have important implications for global fisheries and carbon cycling.

Fe(III) (oxyhydr)oxides are well-known for their role in organic carbon (OC) stabilization in terrestrial soils. Coastal and estuarine soils typically act as iron sinks and receive a high input of OC. However, tidal submersion induces anoxic and reducing conditions that favor the microbial reductive dissolution of Fe(III) (oxyhydr)oxides, followed by the partial formation of Fe(II) minerals. However, the potential of these minerals—such as siderite, vivianite and iron sulfides—to stabilize C has only recently received attention. In this review, we (a) elucidate methodological constraints in Fe(II) mineral analysis, (b) highlight formation mechanisms of Fe(II) minerals and (c) their interactions with organic matter (OM) and inorganic C and (d) explore their role in C stabilization. Fe(II) minerals interact with OM through surface complexation, coprecipitation or physical entrapment, despite their typically low surface charge. These interactions are facilitated by surface-reactive chemical species such as potential-determining ions, divalent cations and functional surface groups, enabling Fe(II) minerals to bind or occlude OC in anoxic settings. During Fe(II) mineral formation, dissolved inorganic C can be exported as total alkalinity or precipitated as stable carbonates, both contributing to long-term inorganic C sequestration. Emerging research indicates that Fe(II) mineral interactions with organic and inorganic C likely binds 5.8–16.6 Tg C yr⁻¹, a potential overlooked global C sink with yet unexplored long-term stability. This review thus emphasizes the geochemical relevance of Fe(II) minerals beyond transient redox products as they may constitute a persistent and quantifiable carbon sink in anoxic sediments, warranting further exploration.

Atmospheric phosphorus (P) deposition has become a significant external P source for terrestrial and aquatic ecosystems, influencing functions such as productivity by altering P bioavailability. However, systematic quantification of atmospheric P deposition in China is still lacking. Based on data from the China Wet Deposition Observation Network (ChinaWD) from 2014 to 2022, we explored the wet deposition fluxes, spatiotemporal patterns, and influencing factors of various atmospheric P components. The annual average wet deposition fluxes of total P (TP), dissolved total P (DTP), and total particulate P (TPP) in China were 0.63 ± 0.44, 0.34 ± 0.19 and 0.29 ± 0.26 kg P ha⁻¹ yr⁻¹, respectively, with total deposition amounts of 0.60, 0.33 and 0.28 Tg P yr⁻¹. Over 9 years, TP deposition flux declined at a rate of approximately 0.085 ± 0.022 kg P ha⁻¹ yr⁻¹ per year, potentially reflecting the sustained efforts of China in forest fire prevention and air quality management. This is the first network-based, long-term quantification of wet P deposition patterns across China, laying a foundation for assessing its ecological impacts.

The biological carbon pump (BCP) plays a critical role in sequestering atmospheric CO₂ into the deep ocean; however, the influence of fine-scale oceanic processes, encompassing mesoscale and submesoscale features, on basin-scale carbon export remains poorly understood. Using a high-resolution physical-biogeochemical model and Biogeochemical-Argo (BGC-Argo) observations in the Subtropical Countercurrent (STCC) region of the Northwest Pacific, we demonstrate that fine-scale processes significantly modulate carbon export through seasonally varying impacts on nutrient supply and phytoplankton growth. BGC-Argo observations reveal that cyclonic eddies enhance and anticyclonic eddies suppress particulate organic carbon (POC) concentrations and inventories through isopycnal displacement, providing critical evidence for the localized role of eddy dynamics and an observational foundation for exploring the basin-scale impacts of fine-scale processes. Compared to lower-resolution simulations, high-resolution models reveal that baroclinic instabilities enhance nutrient supply and phytoplankton growth in summer and autumn, increasing POC export by 42.4%. In contrast, frontogenesis-induced downwelling reduces nutrients and phytoplankton growth in winter and spring, reducing export by up to 35.8%. Over a full annual cycle, these opposing effects result in a modest net basin-scale enhancement of 2.6%–5.0% from fine-scale resolution. These results reveal a seasonally opposing role of fine-scale processes in regulating carbon export through biological pathways, demonstrating that resolving mesoscale-to-submesoscale dynamics across complete seasonal cycles is essential for accurately quantifying the ocean's biological carbon pump.

Understanding the oceanic Copper (Cu) budget is essential for tracing nutrient pathways, interpreting ancient sediment records, and assessing global environmental changes. However, the global oceanic Cu cycle remains imbalanced, largely due to insufficient studies on the flux and isotopic composition of authigenic Cu in oxic pelagic sediments. Here, we present the Cu isotopic compositions of pelagic sediments collected from the western (non-hydrothermal area) and eastern South (hydrothermal area) Pacific Ocean. These results indicate that authigenic Cu in pelagic sediments is primarily hosted by iron-manganese (oxyhydr)oxides. The isotopic composition of authigenic Cu in pelagic sediments (0.01‰ ± 0.13‰, 2SD) is considerably lighter than the previously assumed value of ∼0.3‰, which was based on the Cu isotopic compositions of iron-manganese crusts and nodules. Using these new isotopic constraints, together with a newly calculated Cu flux to pelagic sediments of 15.2 × 10⁸ mol yr⁻¹, we propose a new, balanced oceanic budget for Cu isotopes. This study precisely defines the flux and isotopic composition of the largest oceanic Cu sink, placing new constraints on the marine Cu cycle.

Dissolved organic nitrogen (DON) is the dominant form of bioavailable nitrogen in the euphotic zone of subtropical gyres, where nitrate (NO₃⁻) concentrations are low. However, identifying regions where DON consumption may support surface ocean productivity remains challenging due to the relatively narrow range in euphotic zone DON concentrations. The stable isotopic composition (δ¹⁵N) of DON has recently emerged as a sensitive tool for identifying regions of DON production and consumption in the surface ocean. Here, we report DON concentration and δ¹⁵N measurements in the upper ∼300 m from a >10, 000 km zonal GO-SHIP transect along ∼30°S in the South Pacific (P06-2017 transect) from the Chilean to the Australian coasts. We observed higher upper 50 m DON concentrations in the east associated with DON production in regions with elevated primary productivity. Upper 50 m DON δ¹⁵N decreases from east to the west, coincident with a gradient in the δ¹⁵N of subsurface (i.e., 100–200 m) NO₃⁻, consistent with subsurface NO₃⁻ fueling DON production. Further, both the partial and complete assimilation of surface NO₃⁻ observed along the transect are imprinted on the δ¹⁵N of surface DON. An inverse relationship between the concentration and δ¹⁵N of surface DON was found in the western portion of the transect, consistent with DON consumption by phytoplankton. Combining concentrations and δ¹⁵N of DON, we identified regions of DON production and consumption across the largest subtropical ocean gyre.

The ocean plays a major role in controlling atmospheric carbon at decadal to millennial timescales, with benthic carbon representing the only geologic-scale storage of oceanic carbon. Despite its importance, detailed benthic ocean observations are limited and representation of the benthic carbon cycle in ocean and Earth system models (ESMs) is mostly empirical with little prognostic capacity, which hinders our ability to properly understand the long-term evolution of the carbon cycle and climate change-related feedbacks. The Benthic Ecosystem and Carbon Synthesis (BECS) working group, with the support of the US Ocean Carbon & Biogeochemistry Program (OCB), identified key challenges limiting our understanding of benthic systems, opportunities to act on these challenges, and pathways to increase the representation of these systems in global modeling and observational efforts. We propose a set of priorities to advance mechanistic understanding and better quantify the importance of the benthos: (a) implementing a model intercomparison exercise with existing benthic models to support future model development, (b) data synthesis to inform both model parameterizations and future observations, (c) increased deployment of platforms and technologies in support of in situ benthic monitoring (e.g., from benchtop to field mesocosm), and (d) global coordination of a benthic observing program (“GEOSed”) to fill large regional data gaps and evaluate the mechanistic understanding of benthic processes acquired throughout the previous steps. Addressing these priorities will help inform solutions to both global and regional resource management and climate adaptation strategies.

Fjord sediments are global sinks of organic carbon (OC), contributing to the long-term storage of atmospheric CO₂. Despite this recognition, the transfer and burial of OC in fjord sediments are still poorly quantified and suffer from a sampling bias toward distal environments where marine OC is dominant. Here we present organic geochemical data obtained on sediment samples (suspended river sediments, fjord sediment trap, surface fjord sediments, sediment core) collected in the Baker river-fjord system, with a particular focus on the Baker River submarine delta, which is fed by Chile's largest river. We measured total OC contents and OC stable isotope composition to quantify the amount and type of OC (marine or terrestrial) stored in the fjord submarine delta. We find that OC fluxes are twice higher in summer (106 ± 6 g OC/m²/yr) than in winter (53 ± 3 g OC/m²/yr) due to higher sediment discharge from meltwater. Sediment trap OC fluxes are on the same order of magnitude than those in the nearby sediment core (103 ± 15 g OC/m²/yr) during the last 35 years, suggesting rapid OC burial in sediments. Carbon isotopes suggest that the OC stored in the fjord submarine delta is predominantly of terrestrial origin. We calculate that the Baker submarine delta buries 3.8 ± 0.6 kt OC/yr, which corresponds to 26 ± 11% of the estimated OC annual flux delivered by the Baker River (14.4 ± 5.5 kt OC/yr). Fjord deltas should thus be considered in fjord OC budgets as they could significantly raise global estimates of terrestrial OC burial in marine sediments.