Global Biogeochemical Cycles最新文献

Ocean acidification (OA) threatens coral calcification by reducing the carbonate ion concentration that corals need to build their skeletons. However, assessments of the impacts of long-term OA are scarce, limiting our understanding of the response and acclimatization of corals to high pCO₂ levels. Here we present a 42-year (1968–2010) seasonal δ¹¹B and B/Ca records from Porites corals at Dongsha Atoll, located in the northern South China Sea. Our results reveal a rapid decline in seawater pH over this period, at a rate of −0.0021 ± 0.0008 pH units per year. Of special interest is that the interannual variability in seawater pH appears to be primarily co-regulated by hydrological changes in the Pearl River and fluctuations in the strength of Kuroshio intrusion. These factors are linked to large-scale climate systems and interannual-to-decadal variability, including the Pacific Decadal Oscillation, El Nino-Southern Oscillation, and East Asian Winter Monsoon. Meanwhile, reconstructed carbonate chemistry from the coral calcifying fluid suggests that Porites corals at Dongsha Atoll are able to physiologically modulate their internal pH. This up-regulation of internal pH not only buffers seasonal fluctuations in the aragonite saturation state and sustains stable calcification rates year-round, but also aids in long-term resistance to the detrimental effects of OA.

In their 1999 paper “Widespread bacterial populations at glacier beds and their relationship to rock weathering and carbon cycling,” Sharp and co-authors initiated a paradigm shift from glaciers viewed as abiotic systems to glacier environments hosting active microbial communities and corresponding biogeochemical cycling. Since then, the field of glacier biogeochemistry has sought to elucidate how these microbes function and the consequences of their activity in glacial and proglacial environments, and for global biogeochemical cycles. Subsequent research has supported the existence of active biogeochemical cycling by the “glacial microbiome.” Paradoxically, dissolved organic matter (DOM) exported in glacier meltwater is both ancient and a labile source of organic carbon that may be readily incorporated into downstream ecosystems. Further, DOM that has been characterized in glacier systems (using both fluorescence spectroscopy and ultrahigh resolution mass spectrometry) from different locations shares specific fluorescence and molecular formulae characteristics, hinting at a potential commonality in “glacial DOM.” The recent manuscript “Gradients of Deposition and In Situ Production Drive Global Glacier Organic Matter Composition” (Holt et al., 2024, https://doi.org/10.1029/2024gb008212) addresses these two observations by employing Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to characterize DOM composition at the molecular level from glacier sites located around the globe. The use of both the powerful FT-ICR MS technique and an unparalleled global glacier data set offers a unique insight into glacier DOM variability and commonality, and the source of ancient and/or labile DOM in glacier runoff. Further, the study provides an impetus for specific future lines of investigation.

Glacial retreat due to climate warming alters the pathway through which meltwater enters Arctic fjords. In the Tyrolerfjord–Young Sound system (NE Greenland), meltwater is delivered by two contrasting rivers: the Tyroler River, which flows directly from the glacier into the fjord, and the Zackenberg River, which passes through a proglacial lake. We investigated the impact of these different glacial sources on the pelagic system and fjord sediment biogeochemistry, with a focus on carbon and iron cycling. We quantified particulate organic carbon and particulate organic nitrogen, as well as δ¹³C and δ¹⁵N of the organic matter in the suspended and sinking fractions in the water column. In sediment, we quantified total organic carbon (TOC) and total nitrogen, δ¹³C and δ¹⁵N of the organic matter, porewater concentrations of Fe, Mn, and different fractions of solid-phase Fe, O₂ microprofiles and sulfate reduction rates. We find that the passage through a proglacial lake decreases the impact of the glacier on the fjord, as the lake acts as a trap for glacial material, decreasing sediment input to the fjord system. In the fjord sediments, a stronger redox-cycling of iron was found further away from the rivers, which is mainly driven by the higher TOC content. Overall, our data suggest that, with glacial retreat, the impact of glaciers on the marine and the benthic systems in fjords will become weaker, and reduce long-term carbon sequestration in Arctic fjord sediments.

Shifts in vegetation phenology affect photosynthesis and productivity, further influencing ecosystem carbon and hydrological cycles. Over recent decades, widespread advancements in the start of the growing season (SOS) have been found to advance the peak of the growing season (POS) and enhance vegetation growth under global warming. Understanding vegetation growth dynamics from SOS to POS (i.e., start-to-peak growth) is crucial because this period represents a critical phase of carbon uptake and ecosystem productivity, directly impacting seasonal and annual climate-biosphere feedback. However, the effect of SOS on vegetation growth, especially start-to-peak growth, remains largely unknown. Using MODIS NDVI, ground FLUXNET data set, and meteorological data (2001–2022) across the Northern Hemisphere (>30°N), we found that SOS advanced by 0.11 days per year, while start-to-peak growth, indicated by the sum of daily NDVI from SOS to POS, increased by 0.13 units per year. Notably, earlier SOS significantly enhanced start-to-peak growth in 55.64% of vegetated pixels (p < 0.05). Critically, the earlier SOS was associated with a longer SOS-POS duration and lower vegetation growth rates, suggesting that the extended SOS-POS duration contributed to the observed increased start-to-peak growth. Climatic conditions, especially colder temperatures, slowed growth rates, particularly at mid-latitudes. This slowing of growth rates was observed across various vegetation types, although the magnitudes of the reduction varied among them. Overall, these findings enrich our understanding of how start-to-peak growth responded to spring phenology and climate change, offering valuable insights into future predictions of terrestrial ecosystem dynamics under global change.

Earth system models are increasingly adopting multi-layer soil frameworks to improve simulations of vertical carbon distribution. A critical parameter in these models is the e-folding depth (z_τ), which quantifies the rate at which soil organic carbon (SOC) ages with depth. Specifically, z_τ represents the soil depth at which carbon becomes e-times older (≈2.7 times older) than surface carbon. Despite its importance, most models assume constant z_τ within biomes, leaving its spatial variability largely unclear. To test this assumption, we collected multi-layer soil samples across eight forest plots spanning a subtropical montane elevational gradient (427–1,474 m) and employed radiocarbon dating to quantify vertical SOC aging patterns. Our results revealed a robust exponential increase in SOC age with depth at all elevations, alongside a 66% decline in z_τ from 78.6 cm at the base to 26.4 cm at the summit. This indicated that a 1-m increase in soil depth approximately amplified SOC age by 4-fold at the lowest elevation and 44-fold at the highest position. Despite significant changes in vegetation along the elevational gradient, vegetation type did not play an essential role in controlling z_τ variability. Instead, this elevational dependence of z_τ was primarily driven by soil water content (22.2% of variability explained), mean annual temperature (19.7%), and soil carbon-to-nitrogen ratio (19.0%). These findings suggest z_τ as an elevation-sensitive sentinel of soil carbon dynamics, urging models to incorporate its variability for projections of soil carbon persistence under climate change.

Compound extremes of temperature and acidity that extend over substantial fractions of the water column can be particularly damaging to marine organisms, as they experience not only additional stress by the potentially synergistic effects of these two stressors, but also a reduction in habitable vertical space. Here, we detect and analyze such column-compound extremes (CCX) in the Southern Ocean between 1980 and 2019, and characterize their duration, intensity, and spatial extent. To this end, we use daily output from a hindcast simulation of the Regional Ocean Modeling System (ROMS), coupled with the Biological Elemental Cycling (BEC) model. We first detect extremes in temperature and acidity ([$��H^{+}�$]) within the top 300 m using a relative threshold of 95% and then identify CCX where conditions are extreme for both stressors for at least 50 m of the water column. When analyzed on a fixed baseline, positive trends in ocean warming and acidification caused CCX to last longer, intensify, and expand throughout the Southern Ocean. In the Antarctic zone, CCX expanded between 1980 and 2019 more than ten times in volume, lasted up to 120 days longer, and doubled in anomaly. Some of the largest and longest events occurred in Antarctic Marine Protected Areas (MPAs), covering more than 200,000 km² and persisting for over 500 days. CCX in the Subantarctic and Northern zones quadrupled in volume and increased by more than 30% in anomaly. Across the Southern Ocean, the increasing occurrence of CCX exacerbates the risks to marine ecosystems from warming and acidification.

The ocean is a source of atmospheric methane (CH₄), yet the impact of mesoscale processes on CH₄ cycling remains largely unconstrained. In this study, we combined high-resolution underway observations and site-specific geochemical analyses conducted in September 2020, with methane oxidation (MOx) rates measurements and molecular analysis in September 2022, to investigate the regulation of mesoscale eddies on CH₄ production, methanotrophic activity, and emission fluxes in the South China Sea (SCS). Underway observation revealed that cyclonic eddies (CEs) increased surface CH₄ concentrations, while anticyclonic eddies (AEs) generally exhibited lower CH₄ levels. CEs observed in September 2020 after summer, enhanced CH₄ production associated with phytoplankton by transporting coastal nitrate-rich waters into the eddy core. Particulate dimethylsulfoniopropionate (DMSP_p) produced by phytoplankton was identified as a significant source of CH₄ within the mixed layer based on the significant correlations between DMSP and CH₄ (r = 0.79; p < 0.01). In contrast, elevated MOx rates and pmoA gene abundance were observed in the AEs, driven by convergence and stratification of surface seawater caused by downwelling of water masses. Compared to reference sites, the CH₄ air–sea fluxes in CEs increased by 204%, whereas the CH₄ emission flux in AEs was reduced by 25.1%. Collectively, mesoscale eddies significantly influence CH₄ cycle by altering phytoplankton composition, nutrient dynamics and microbial communities, ultimately leading to the divergent CH₄ emissions. Our results illustrated the control of mesoscale eddies on CH₄ production and oxidation and highlighted the importance of physical processes on biogeochemical cycling and greenhouse gas emissions.

Widespread increases in lake browning, which affects primary production, have been observed in northern lakes. While lake browning is attributed to increases in terrestrially derived total organic carbon (TOC) and total iron (Fe), Fe does not consistently correlate with increasing TOC over time. This temporal mismatch between TOC and Fe indicates that we still do not fully understand the causes of lake browning, especially in the context of gradually changing climatic conditions. In this study, we utilized Fennoscandian 30-year (1990–2020) time series data for 102 lakes to describe possible reasons for the temporal decoupling between TOC and Fe. Using Bayesian mixed-effects models and wavelet coherence analysis, we found evidence for differential responses of TOC and Fe concentrations to changes in precipitation, temperature, and sulfur deposition. While TOC appeared more sensitive to the effects of precipitation, temperature and sulfur deposition in individual lakes, Fe concentrations were impacted by complex interactions among these environmental variables. Although TOC and Fe increased in most lakes in response to increased temperature and precipitation, 41% of the lakes—typically with larger catchment-to-lake area ratios and shorter water residence times—exhibited a declining trend in Fe. This analysis encompasses lakes of both significant and non-significant changes over time. This decline in Fe was associated with short-timescale (2–4 years) increases in precipitation, leading to a temporal decoupling between Fe and TOC. Our findings suggest that Fe concentrations do not increase uniformly with rising temperatures and increased precipitation, especially in regions where sulfur deposition has declined due to atmospheric recovery policies.

The flux of nutrients from continents to the oceans sustains oceanic primary productivity and is a fundamental component of the carbon cycle. In most regions of the world's oceans primary productivity is limited by the supply of nutrients. In particular, iron can become limiting in the open-ocean due to its low solubility. Glaciated continents have been suggested as an underappreciated source of iron to the high-latitude oceans. Yet, uncertainty remains regarding the magnitude and spatial variability of glacially derived nutrient fluxes, and the extent to which these nutrients impact open-ocean ecosystems. To quantify lithogenic fluxes at the West Greenland margin, we measured ²³²Th and ²³⁰Th in seawater and core-top sediments across the shelf and slope. Our results highlight a negative correlation between low-salinity waters and dissolved and particulate ²³²Th, suggesting a glacial source for this lithogenic isotope. We calculated dissolved ²³²Th fluxes 5–24 μg m⁻² yr⁻¹ (100–500 m depth), and sedimentary ²³²Th fluxes 105–711 μg m⁻² yr⁻¹, higher than typical open-ocean settings and similar to margin sites influenced by large inputs from aeolian dust and rivers. A sampling transect shows that dissolved ²³²Th fluxes increase toward Greenland, confirming that lithogenic inputs are sourced laterally from the margin. Using our ²³²Th fluxes, we estimate an elevated supply of dissolved Fe which extends over the continental slope toward the open ocean. This Fe flux is large enough to support much of the local primary productivity, highlighting the importance of lithogenic fluxes in supporting the marine ecosystem in high-latitude oceans.

We present the CH₄ and N₂O budgets for anthropogenic and natural sources and sinks of Australasia (Australia and New Zealand) from 2010 to 2019 using bottom-up and top-down methods, in line with the RECCAP-2 initiative, with extensions to 2022. We show that the bottom-up CH₄ budget for Australasia (2010–2019) was a net source of 14.1 ± 5.5 Tg CH₄ yr⁻¹, with Australia and New Zealand contributing 84% and 16%, respectively. Anthropogenic sources contributed 55% of all CH₄ emissions, the rest coming from natural sources, primarily wetlands. The bottom-up N₂O budget was a net source of 0.5 ± 0.3 Tg N₂O yr⁻¹, with Australia contributing the majority (92%), mainly from natural sources (82%). Australasia top-down CH₄ (10.4 ± 0.5 Tg CH₄ yr⁻¹) and N₂O budgets (0.8 ± 0.5 Tg N₂O yr⁻¹) differ in magnitude from the bottom-up budgets but remain consistent within their uncertainties. Similar consistency is observed for Australia, while New Zealand shows significant discrepancies, particularly for N₂O, where the bottom-up estimate is 71% higher than the top-down estimate. In terms of trends, bottom-up natural wetland CH₄ emissions increased in both countries between 2010 and 2019. CH₄ emissions from enteric fermentation slightly declined in Australia but increased in New Zealand. Soil N₂O emissions from nitrogen additions increased in both countries, with a significant rise in New Zealand driving the overall positive trend in anthropogenic emissions. These findings highlight critical sectors with large mitigation potential and the significance of monitoring natural sources for possible biogeochemical-climate feedback.