Global Biogeochemical Cycles最新文献

Salt marshes are crucial for blue carbon sequestration and the mitigation of climate change. While submarine groundwater discharge (SGD) is increasingly recognized as an important pathway for carbon export in salt marsh tidal creek systems, current research predominantly relies on point-scale, time-series observations of creek water. Investigations employing extensive spatial coverage and depth-resolved sampling within creek networks remain limited. This study implemented a sampling campaign across spring-neap tidal cycles encompassing a wide area of a tidal creek and collecting groundwater samples from multiple depths at the creek bottom within the North Inlet-Winyah Bay National Estuarine Research Reserve System in South Carolina, United States. By employing radium isotopes (²²⁶Ra and ²²⁸Ra) as tracers, we quantified SGD and associated carbon fluxes and elucidated the biogeochemical transformation processes occurring within the marsh-creek basin. The results reveal substantial blue carbon exports via creek bottom SGD: a dissolved inorganic carbon (DIC) flux of 241 ± 61 mmol/m²/d and net negative fluxes of dissolved organic carbon (−22 ± 5 mmol/m²/d) and total nitrogen (−0.98 ± 0.27 mmol/m²/d). DIC as the predominant form of carbon export via SGD is comparable to the carbon sequestration capacity of primary productivity and surpasses the net carbon burial of the marsh. A comparative analysis across the globe indicates that tidal creeks are a significant component influencing the coastal carbon budget balance process. These findings further highlight the critical role of groundwater-transported carbon fluxes in the coastal carbon cycle, particularly within tidal creek basins, and emphasize the necessity of integrating groundwater processes into blue carbon assessments to effectively address climate change.

The Arctic is undergoing rapid climate change, with thawing permafrost and shifts in vegetation altering nitrogen (N) delivery into streams. These changes can significantly affect microbial biofilm diversity and functional roles, yet knowledge of streambed microbial biofilms remains scarce across the Arctic. This study examines the biogeographic and temporal patterns of prokaryotic sediment diversity and N functional genes across a biogeographical gradient in Arctic regions. We sampled sediment from 27 streams across four Arctic regions, including 14 streams in Greenland that were sampled at three timepoints throughout the open-water; all other streams were sampled once in midsummer. We analyzed 16S rRNA gene sequencing and quantified six genes involved in the N-fixation (nifH), nitrification (amoA, nxrB), and denitrification (nirS, norB and nosZ). Our results showed that prokaryotic and N functional gene abundances varied among regions, with higher abundance in areas with more catchment vegetation and higher organic matter availability. However, the composition of prokaryote communities and N functional genes showed no regional differences. Prokaryotic abundance and diversity tended to increase toward late summer. This study highlights how catchment properties, particularly organic matter and vegetation, influence stream prokaryotic communities and their role in N cycling, providing key insights into ecosystem responses to climate change in the Arctic.

Southern South America (SSA) is an important source of dust, and its associated micronutrient trace elements, to the waters of the Southern Ocean. As part of the UK contribution to the International GEOTRACES program, an aerosol sampling site (Carcass Island) was established in the western Falkland (Malvinas) Islands, downwind of dust sources in Patagonia. Samples were collected over two 7-month long periods and analyzed for soluble and total trace elements. Results indicated that dust was the dominant source of aerosol iron and manganese, elements with limiting or co-limiting roles for Southern Ocean primary productivity. Other micronutrient trace elements (e.g., copper and zinc) appeared to be more strongly affected by anthropogenic inputs, even in this sparsely populated region. Trace element fractional solubility at Carcass Island appears consistent with previous observations over the wider Atlantic Ocean. In the case of iron, a hyperbolic increase in solubility with decreasing atmospheric iron concentration was observed. This relationship has been suggested to indicate enhancement of solubility during atmospheric transport, but the very little available information on iron solubility in the region makes this difficult to verify. Soluble manganese to iron ratios in aerosols at Carcass Island suggest that deposition of SSA dust is unable to alleviate Mn deficiency in the waters of the Atlantic sector of the Southern Ocean.

Permafrost degradation under a warming climate has altered hydrological and biogeochemical processes across the Arctic. Although increasing fluxes of weathering-derived ions (e.g., Ca²⁺, Mg²⁺, and SO₄²⁻) have been reported in Arctic rivers, the underlying mechanisms and hotspots within basins remain poorly understood due to limited analysis of environmental drivers such as climate and permafrost dynamics. We investigated long-term trends (1980–2022) in Ca²⁺, Mg²⁺, and SO₄²⁻ concentrations in the Kolyma River in northeastern Siberia, and examined basin-wide changes in air temperature, precipitation, soil temperature, and active layer thickness. We found significant increases in ion concentrations, which were strongly correlated with rising subsurface soil temperatures (r = 0.61) and active layer deepening (r = 0.78) in the Yedoma-rich Kolyma Lowland. These findings, along with the concentration ratios, suggest that sulfuric-acid-driven carbonate weathering has intensified in the deeper part of the active layer—where previously frozen minerals become newly exposed—thereby enhancing ion discharges to rivers. Record-high concentrations were observed in 2020, when an extreme heatwave occurred, and produced exceptionally high subsurface soil temperatures (5.6°C; average 3.8 ± 0.6°C) during the thawed period (May–October) and active layer thicknesses (116.5 cm; average 100.3 ± 10.8 cm). These results underscore the sensitivity of Arctic river systems to heatwave-induced permafrost degradation, which rapidly intensifies subsurface weathering and solute mobilization. Given the widespread distribution of Yedoma across the Arctic, similar responses may occur in other watersheds. Continued monitoring of water chemistry and permafrost dynamics is essential to understand changes in Arctic river biogeochemistry.

Permafrost degradation under a warming climate has altered hydrological and biogeochemical processes across the Arctic. Although increasing fluxes of weathering-derived ions (e.g., Ca²⁺, Mg²⁺, and SO₄²⁻) have been reported in Arctic rivers, the underlying mechanisms and hotspots within basins remain poorly understood due to limited analysis of environmental drivers such as climate and permafrost dynamics. We investigated long-term trends (1980–2022) in Ca²⁺, Mg²⁺, and SO₄²⁻ concentrations in the Kolyma River in northeastern Siberia, and examined basin-wide changes in air temperature, precipitation, soil temperature, and active layer thickness. We found significant increases in ion concentrations, which were strongly correlated with rising subsurface soil temperatures (r = 0.61) and active layer deepening (r = 0.78) in the Yedoma-rich Kolyma Lowland. These findings, along with the concentration ratios, suggest that sulfuric-acid-driven carbonate weathering has intensified in the deeper part of the active layer—where previously frozen minerals become newly exposed—thereby enhancing ion discharges to rivers. Record-high concentrations were observed in 2020, when an extreme heatwave occurred, and produced exceptionally high subsurface soil temperatures (5.6°C; average 3.8 ± 0.6°C) during the thawed period (May–October) and active layer thicknesses (116.5 cm; average 100.3 ± 10.8 cm). These results underscore the sensitivity of Arctic river systems to heatwave-induced permafrost degradation, which rapidly intensifies subsurface weathering and solute mobilization. Given the widespread distribution of Yedoma across the Arctic, similar responses may occur in other watersheds. Continued monitoring of water chemistry and permafrost dynamics is essential to understand changes in Arctic river biogeochemistry.

The Hawaii Aerosol Time-Series (HATS) was a coordinated effort to simultaneously monitor atmospheric and water column dust dynamics in the North Pacific Subtropical Gyre. Throughout 2022 and 2023, HATS measured the composition of water column particles and made complementary measurements of aerosol chemistry and deposition fluxes. Here we report the inventories, elemental composition, dust-relative residence times, and internal dynamics of size-fractionated marine particles at Station ALOHA from four expeditions between September 2022 and August 2023. Mixed layer inventories of lithogenic particulate elements (Al, Fe, and Ti) varied by factors of 9 and 5 in small (0.2–51 μm) and large (>51 μm) particles, respectively, and by factors of 3 and 2 through 300 m depth; much less than the factor of 25–42 variations of these elements observed in aerosols. Mixed layer residence times of small lithogenic particles, relative to dust fluxes, ranged from <1 day to 12 days and from 1 week to 6 months through 300 m, demonstrating persistent rapid packaging into large particles near the surface. Fractional lability of Fe and Al in marine particles ranged from 6% to 89% and 22%–80%, respectively, in the upper 200 m, with Fe showing greater variability across size fractions. Scavenged Fe was more abundant below 200 m than at the surface, coincident with longer particulate residence times and larger lithogenic inventories in the upper mesopelagic. Ti-normalized lithogenic ratios of marine particles were mostly lower than the aerosol time-series, suggesting loss of Fe and Al from minerals post-deposition and/or unquantified lateral inputs of Ti-rich material.

The Hawaii Aerosol Time-Series (HATS) was a coordinated effort to simultaneously monitor atmospheric and water column dust dynamics in the North Pacific Subtropical Gyre. Throughout 2022 and 2023, HATS measured the composition of water column particles and made complementary measurements of aerosol chemistry and deposition fluxes. Here we report the inventories, elemental composition, dust-relative residence times, and internal dynamics of size-fractionated marine particles at Station ALOHA from four expeditions between September 2022 and August 2023. Mixed layer inventories of lithogenic particulate elements (Al, Fe, and Ti) varied by factors of 9 and 5 in small (0.2–51 μm) and large (>51 μm) particles, respectively, and by factors of 3 and 2 through 300 m depth; much less than the factor of 25–42 variations of these elements observed in aerosols. Mixed layer residence times of small lithogenic particles, relative to dust fluxes, ranged from <1 day to 12 days and from 1 week to 6 months through 300 m, demonstrating persistent rapid packaging into large particles near the surface. Fractional lability of Fe and Al in marine particles ranged from 6% to 89% and 22%–80%, respectively, in the upper 200 m, with Fe showing greater variability across size fractions. Scavenged Fe was more abundant below 200 m than at the surface, coincident with longer particulate residence times and larger lithogenic inventories in the upper mesopelagic. Ti-normalized lithogenic ratios of marine particles were mostly lower than the aerosol time-series, suggesting loss of Fe and Al from minerals post-deposition and/or unquantified lateral inputs of Ti-rich material.

Marine particulate organic matter (POM) is a complex geochemical mixture comprising both living and detrital particles with a variety of sources, ages, and cycling rates. In the Arctic, the main source of POM is marine plankton biomass with variable contributions from resuspended sediments, sea-ice algae, glaciers, and rivers. Stable (δ¹³C, δ¹⁵N) and radiocarbon (as Δ¹⁴C) isotopic measurements, together with elemental stoichiometry (C:N ratios), provide insight into POM sources, cycling, diagenetic state, and ecophysiological processes. Climate change alters water column stratification, nutrient delivery, primary production, and terrestrial C fluxes that directly impact Arctic POM biogeochemistry. Here we report POM δ¹³C, δ¹⁵N, Δ¹⁴C values and C:N ratios from samples collected from the subsurface chlorophyll-a maximum throughout the Canadian Arctic Archipelago (CAA), together with previous data from Baffin Bay, and quantify relative contributions of organic matter (OM) from allochthonous sources such as rivers and sediment resuspension in the CAA. Terrestrial and sedimentary OM contributions ranged from 1%–79% and 1%–24%, respectively, with high terrestrial contributions nearest the Mackenzie River, as well as smaller CAA rivers. Low POM Δ¹⁴C values and higher sedimentary OM contribution estimates reveal where tidal currents across shallow CAA straits resuspend aged sedimentary OM to the upper water column. We find below-Redfield C:N ratios across the CAA, likely indicative of a nutrient-limited community dominated by picophytoplankton. POM isotopic and stoichiometric data reveal a biogeochemical mosaic within the Canadian Arctic POM—from highly productive autotrophic regions with high C:N ratios to oligotrophic picoplankton-dominated ecosystems with low C:N ratios.

Marine particulate organic matter (POM) is a complex geochemical mixture comprising both living and detrital particles with a variety of sources, ages, and cycling rates. In the Arctic, the main source of POM is marine plankton biomass with variable contributions from resuspended sediments, sea-ice algae, glaciers, and rivers. Stable (δ¹³C, δ¹⁵N) and radiocarbon (as Δ¹⁴C) isotopic measurements, together with elemental stoichiometry (C:N ratios), provide insight into POM sources, cycling, diagenetic state, and ecophysiological processes. Climate change alters water column stratification, nutrient delivery, primary production, and terrestrial C fluxes that directly impact Arctic POM biogeochemistry. Here we report POM δ¹³C, δ¹⁵N, Δ¹⁴C values and C:N ratios from samples collected from the subsurface chlorophyll-a maximum throughout the Canadian Arctic Archipelago (CAA), together with previous data from Baffin Bay, and quantify relative contributions of organic matter (OM) from allochthonous sources such as rivers and sediment resuspension in the CAA. Terrestrial and sedimentary OM contributions ranged from 1%–79% and 1%–24%, respectively, with high terrestrial contributions nearest the Mackenzie River, as well as smaller CAA rivers. Low POM Δ¹⁴C values and higher sedimentary OM contribution estimates reveal where tidal currents across shallow CAA straits resuspend aged sedimentary OM to the upper water column. We find below-Redfield C:N ratios across the CAA, likely indicative of a nutrient-limited community dominated by picophytoplankton. POM isotopic and stoichiometric data reveal a biogeochemical mosaic within the Canadian Arctic POM—from highly productive autotrophic regions with high C:N ratios to oligotrophic picoplankton-dominated ecosystems with low C:N ratios.

Tropical forests play a vital role in the global carbon cycle and land–atmosphere interactions. Estimating tropical forest carbon–water dynamics is challenging due to observational and modeling uncertainties. This study leverages the “Trends and drivers of the regional scale terrestrial sources and sinks of carbon dioxide” (TRENDY) project models and satellite observations to assess changes (2003–2021) in vegetation carbon, gross primary production (GPP), evapotranspiration (ET), and net biosphere production (NBP) in the Amazon and Congo. Atmospheric CO₂, climate variability, and land use and land cover changes constrain these variables between 1700 and 2021 with the overall increasing trends of carbon stock and fluxes. The models overestimate vegetation carbon and GPP, while ET and NBP are consistent with observations. Fire-activated models predict lower values for vegetation carbon and GPP, ET, and NBP, aligning more closely with observations. The higher ET from fire-activated models may result from enhanced soil evaporation due to increased canopy openings. Fire-inactivated models could well estimate the magnitudes of NBP. The high vegetation carbon in nitrogen-enabled models points to simulation uncertainties and imbalance in model numbers regarding the nitrogen cycle. Although the nitrogen cycle enhances water use efficiency in both the Amazon and Congo, the models show a higher sensitivity to the nitrogen cycle in the Congo. This study highlights the challenges in accurately representing tropical biogeochemical cycles and the values of satellite products in model evaluations, underscoring the need for standard modeling protocols that address biogeochemical components (e.g., nutrient cycles) to better resolve process-based representations.