Global Biogeochemical Cycles最新文献

The Southern Ocean south of 35°S represents a small source of natural inorganic carbon for the atmosphere but a major sink of anthropogenic carbon. The magnitude of the inorganic carbon sink, and the sequestration of inorganic and organic carbon strongly depend on the rate at which they are subducted below the mixed layer. We use a global ocean model at 0.25° resolution to quantify the drivers of the pathways of total and anthropogenic dissolved inorganic carbon (DIC) and organic carbon (OC) across and within the time-varying mixed layer of five physically consistent regions of the Southern Ocean over the period 1995–2014. Total DIC is brought into the mixed layer through obduction south of the Antarctic Circumpolar Current (ACC) and subducted north of the ACC, resulting in a net obduction of 11.2 PgC/year, with advective processes being responsible for about two-thirds of the total transfer. Anthropogenic carbon is brought to the mixed layer through the ocean surface in all regions but mainly subducted north of the ACC, with the subduction (1.05 PgC/year) being achieved through both advection and diffusion, each dominating respectively north and south of the Subantarctic Front. Two thirds of the organic carbon are subducted through the gravitational pump (1.9 PgC/year) and one-third through physical transfer (0.9 PgC/year), with an equivalent contribution from advection and diffusion. At the local scale, advective fluxes largely dominate other physical processes in transferring carbon across the base of the mixed layer, and are found to be increased near topographic features and boundary currents.

Anthropogenic nitrogen (N) deposition is increasing globally and has been documented to enhance soil carbon (C) storage; however, its concurrent effects on ecosystem phosphorus (P) limitation remain unclear. By conducting a meta-analysis of 360 observations from 63 field N addition experiments in forest, grassland, and cropland ecosystems, we systematically assessed the consequence of terrestrial ecosystem P limitation under increasing N deposition. Our results demonstrate that N deposition significantly increased soil N:P, plant C:P and N:P ratios by 12%–29%, suggesting intensified P limitation across terrestrial ecosystems. Critically, N deposition induced differential responses between plants and soil microorganisms, with plants experiencing more severe P limitation. Notably, ectomycorrhizal (ECM) symbiosis is useful for alleviating P limitation in plants, whereas arbuscular mycorrhizal (AM) symbiosis is more useful for microorganisms in this context than for plants. Furthermore, the magnitude of N-induced P limitation varied substantially across ecosystems, with particularly strong effects observed in croplands compared with forests and grasslands. This discrepancy may be attributed to the higher dependence of cultivated crops on P for achieving rapid growth under intensive breeding conditions. The response of C:P and N:P ratios in soils and plants negatively correlated with soil pH changes but was significant only in AM-dominated ecosystems. This suggests that the former is more sensitive to N-induced pH shifts than ECM-associated ecosystems. Our findings demonstrate that mycorrhizal types mediate the ecosystem trajectory of N-induced P limitation, highlighting the critical role of plant-microbial interactions in mitigating the impacts of increasing N deposition and climate change.

The stability of dissolved organic matter (DOM) significantly influences the regional and global carbon budget balances. However, current studies on DOM have largely overlooked the winter–spring season in temperate inland waters of the Northern Hemisphere, a critical transitional period characterized by low biological productivity, low temperatures. Here, we selected three representative inland aquatic ecosystems in China, rivers, lakes and ponds, to elucidate the driving mechanisms of environmental and intrinsic properties on the biodegradability (BDOC) of DOM. Results indicated that dissolved organic carbon (DOC) concentrations in rivers, lakes and ponds did not differ significantly with means of 7.52, 8.21 and 10.71 mg L⁻¹, respectively. BDOC was highest in rivers (44.53%), followed by lakes (37.58%), and lowest in ponds (33.71%). We first observed that the physicochemical and DOM properties of rivers, lakes and ponds exhibited homogeneity during winter–spring season. Humic-like substances were identified as the primary components of DOM in these aquatic ecosystems during this period. DOC and BDOC were strongly influenced by oxidation reduction potential, electrical conductivity, total nitrogen, total phosphorus, ammonium nitrogen, chlorophyll a, spectral slope, specific ultraviolet absorbance at 254 nm, and humification index. Although geographical (longitude and latitude), climatic (temperature and precipitation), and anthropogenic factors (population and gross domestic product) also exerted effects on DOC and BDOC, their influence was relatively weak. Environmental and intrinsic properties jointly determined the homogenization of DOM in inland waters during winter–spring season. These findings have important implications for understanding the effects of both environmental and intrinsic properties on DOM at a geoclimatic scale.

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.