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Article
| Open AccessHighly variable iron content modulates iceberg-ocean fertilisation and potential carbon export
Iron is critical for fueling marine primary productivity, but its concentration is often vanishingly low in the ocean. Here, the authors show that though icebergs serve as vehicles delivering the largest supply of iron to polar oceans, the amount of iron they carry varies widely.
- Mark J. Hopwood
- , Dustin Carroll
- & Humberto E. González
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Article
| Open AccessAbiotic synthesis of graphite in hydrothermal vents
Deciphering the origin, age, and composition of deep marine organic carbon remains a challenge for understanding the dynamics of the marine carbon cycle. Here, the authors identify (sub)micron-sized graphite emanating from both high and low temperature hydrothermal vents along the East Pacific Rise, and suggest graphite is a source of old carbon in the deep ocean.
- Emily R. Estes
- , Debora Berti
- & George W. Luther III
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Article
| Open AccessRegulation of priming effect by soil organic matter stability over a broad geographic scale
Global soil carbon dynamics are regulated by the modification of soil organic matter (SOM) decomposition by plant carbon input (priming effect). Here, the authors collect soil data along a 2200 km grassland transect on the Tibetan Plateau and find that SOM stability is the major control on priming effect.
- Leiyi Chen
- , Li Liu
- & Yuanhe Yang
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Article
| Open AccessGlobal mycorrhizal plant distribution linked to terrestrial carbon stocks
Mycorrhizas—mutualistic relationships formed between fungi and most plant species—are functionally linked to soil carbon stocks. Here the authors map the global distribution of mycorrhizal plants and quantify links between mycorrhizal vegetation patterns and terrestrial carbon stocks.
- Nadejda A. Soudzilovskaia
- , Peter M. van Bodegom
- & Leho Tedersoo
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Article
| Open AccessIsotopic composition of oceanic dissolved black carbon reveals non-riverine source
Rivers are thought to be the largest source of the recalcitrant and abundant black carbon in the ocean. Here, Wagner and colleagues find distinct pools of black carbon between rivers and the open ocean, challenging the long-held assumption that marine black carbon is of terrestrial origin.
- Sasha Wagner
- , Jay Brandes
- & Aron Stubbins
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Article
| Open AccessMinimal biomass deposition in banded iron formations inferred from organic matter and clay relationships
Banded iron formations could have formed in the early oceans due to microbial metabolism. Here Dodd and colleagues find little organic carbon in these formations, indicating microbial iron cycling was minimal and could have limited the recycling of important nutrients to overlying waters.
- Matthew S. Dodd
- , Dominic Papineau
- & Juha A. Karhu
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Article
| Open AccessSeasonal dynamics of stem N2O exchange follow the physiological activity of boreal trees
Forest soil is known to be a source of the greenhouse gas N2O, but the impact of what is planted in that soil has long been overlooked. Here Machacova and colleagues quantify seasonal N2O fluxes from common boreal tree species in Finland, finding that all trees are net sources of this gas.
- Katerina Machacova
- , Elisa Vainio
- & Mari Pihlatie
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Article
| Open AccessRice production threatened by coupled stresses of climate and soil arsenic
Current projections on rice production do not consider the coupled stresses of impending climate change and the toxin arsenic in paddy soils. Here, the authors examined potential compounding impacts of soil arsenic and a changing climate on rice production and show that climate-induced changes in soil arsenic behaviour and plant response will lead to currently unforeseen losses in paddy rice grain productivity and quality.
- E. Marie Muehe
- , Tianmei Wang
- & Scott Fendorf
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Article
| Open AccessSoil net nitrogen mineralisation across global grasslands
Nitrogen mineralisation (Nmin), an important index of soil fertility, is often determined in the laboratory, with an uncertain relationship to Nmin under field conditions. Here the authors show that combining laboratory measurements with environmental data greatly improves predictions of field Nmin at a global scale.
- A. C. Risch
- , S. Zimmermann
- & B. Moser
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Article
| Open AccessThe interplay between regeneration and scavenging fluxes drives ocean iron cycling
Iron is crucial for marine photosynthesis, but observational constraints on the magnitude of key iron cycle processes are lacking. Here the authors use a range of observational data sets to demonstrate that the balance between iron re-supply and removal in the subsurface controls upper ocean iron limitation.
- Alessandro Tagliabue
- , Andrew R. Bowie
- & Philip W. Boyd
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Article
| Open AccessConstraining the rise of oxygen with oxygen isotopes
The loss of anomalous sulfur isotope compositions from sedimentary rocks has been considered a symptom of permanent atmospheric oxygenation. Here the authors show sulfur and oxygen isotope evidence from < 2.31 Ga sedimentary barium sulphates (barites) from the Turee Creek Basin, W. Australia, demonstrating the influence of local non-atmospheric processes on anomalous sulfur isotope signals.
- B. A. Killingsworth
- , P. Sansjofre
- & S. V. Lalonde
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Article
| Open AccessUnexpected large evasion fluxes of carbon dioxide from turbulent streams draining the world’s mountains
Freshwater systems are important components of the carbon cycle, but the extent of their role in CO2 fluxes is poorly understood. Here Horgby and colleagues show that mountain streams are a surprisingly large source of CO2 to the atmosphere, with annual emissions that belie their spatial extent.
- Åsa Horgby
- , Pier Luigi Segatto
- & Tom J. Battin
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Article
| Open AccessLake sedimentary biogenic silica from diatoms constitutes a significant global sink for aluminium
Diatoms drive biogeochemical cycling of aluminum by incorporating this element into their shells, but this process has not been quantified in freshwater systems. Here the authors quantify diatom-mediated aluminum fluxes in lakes and determine that they rival the aluminum sink in the global ocean.
- Dong Liu
- , Peng Yuan
- & Wenxiao Fan
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Review Article
| Open AccessThe importance of Antarctic krill in biogeochemical cycles
Swarms of crustaceans called krill dominate Antarctic ecosystems, yet their influence on biogeochemical cycles remains a mystery. Here Cavan and colleagues review the role of krill in the Southern Ocean, and the impact of the krill fishery on ocean fertilisation and the carbon sink.
- E. L. Cavan
- , A. Belcher
- & P. W. Boyd
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Article
| Open AccessTiming and origin of natural gas accumulation in the Siljan impact structure, Sweden
Fractured rocks of impact craters have been suggested to be suitable hosts for deep microbial communities on Earth, and potentially other terrestrial planets, yet direct evidence remains elusive. Here, the authors show that the Siljan impact structure is host to long-term deep methane-cycling microbial activity.
- Henrik Drake
- , Nick M. W. Roberts
- & Mats E. Åström
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Matters Arising
| Open AccessReply to ‘Wiggle-match radiocarbon dating of the Taupo eruption’
- Richard N. Holdaway
- , Brendan Duffy
- & Ben Kennedy
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Article
| Open AccessMarine nitrogen fixers mediate a low latitude pathway for atmospheric CO2 drawdown
Iron fertilisation of the high latitude oceans is a well-established biological mechanism to explain the ice age drawdown of atmospheric CO2, yet modelling has so far struggled to account for a sufficient drawdown via this mechanism. Here, the authors propose that N2 fixers, which inhabit the lower latitude ocean, made a significant contribution to CO2 drawdown and so amplified the global response to iron fertilisation during ice ages.
- Pearse J. Buchanan
- , Zanna Chase
- & Nathaniel L. Bindoff
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Article
| Open AccessGlobal ocean methane emissions dominated by shallow coastal waters
The ocean emits the greenhouse gas methane, but its vastness renders estimations challenging. Here the authors use machine learning to map global ocean methane fluxes, finding a disproportionate contribution from shallow coastal waters, and a link between primary production and methane cycling.
- Thomas Weber
- , Nicola A. Wiseman
- & Annette Kock
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Article
| Open AccessOrganic sulfur was integral to the Archean sulfur cycle
Marine chemistry during the Early Earth (over 2.7 billion years ago) is commonly inferred to have been inorganically sulfate-reducing. Here, the authors argue that organic sulfur cycling may have played a previously unrecognized, yet important, role in the formation of ancient Archean marine sulfides.
- Mojtaba Fakhraee
- & Sergei Katsev
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Article
| Open AccessArchaeal lipid biomarker constraints on the Paleocene-Eocene carbon isotope excursion
The Paleocene-Eocene Thermal Maximum (c. 55 million years ago) was a period associated with massive carbon injection into the atmosphere, yet discrepancies in carbon isotope proxy records have led to substantial uncertainties in the source, scale, and timing of carbon emissions. Here, the authors propose that membrane lipids of marine planktonic archaea can reliably record the carbon isotope excursion and surface ocean warming, giving a new constraint for the source and size of the PETM carbon emissions.
- Felix J. Elling
- , Julia Gottschalk
- & Ann Pearson
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Article
| Open AccessThe role of marine sediment diagenesis in the modern oceanic magnesium cycle
The oceanic magnesium cycle is closely linked to Earth’s carbon cycle and long-term climate change, due to processes such as continental weathering and authigenic mineral formation. Here, the authors update the global oceanic magnesium budget by quantifying the flux of magnesium from oceans to marine sediments and the associated isotopic fractionation.
- Richard D. Berg
- , Evan A. Solomon
- & Fang-Zhen Teng
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Article
| Open AccessMesophilic microorganisms build terrestrial mats analogous to Precambrian microbial jungles
Microbes venturing onto land could have impacted biogeochemical cycles billions of years before terrestrial plants, but insight into this process on ancient Earth has remained elusive. With the discovery and analysis of microbial mats analogous to those of the Precambrian, Finke and colleagues infer how these microbial jungles likely shaped ecology and climate.
- N. Finke
- , R. L. Simister
- & S. A. Crowe
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Article
| Open AccessReducing greenhouse gas emissions of Amazon hydropower with strategic dam planning
Some dams produce large amounts of GHGs and it is important to see whether future dams will satisfy sustainable energy goals. Here the authors estimate the range of GHG emission intensities expected for 351 proposed and 158 existing Amazon dams and find that existing Amazon hydropower reservoirs collectively emit 14 Tg CO2eq per year, and that if all proposed Amazon dams are built, annual emissions would increase 5-fold.
- Rafael M. Almeida
- , Qinru Shi
- & Alexander S. Flecker
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Article
| Open AccessVegetation structural change since 1981 significantly enhanced the terrestrial carbon sink
There lacks systematic analysis on the importance of vegetation structural change in the global terrestrial carbon cycle. Here the authors conducted a multi-model comparison analysis and find that the increase in leaf area index has been responsible for 12.4% of the accumulated terrestrial carbon sink from 1981 to 2016.
- Jing M. Chen
- , Weimin Ju
- & Xuehe Lu
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Article
| Open AccessThe paleoclimatic footprint in the soil carbon stock of the Tibetan permafrost region
There was extensive degradation during the warm middle Holocene and permafrost area was reduced substantially. Here the authors synthesize data across the Tibetan permafrost region and find that paleoclimate is more important than modern climate in shaping current permafrost carbon distribution, and its importance increases with soil depth.
- Jinzhi Ding
- , Tao Wang
- & Lin Zhao
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Article
| Open AccessIn vivo epigenetic editing of Sema6a promoter reverses transcallosal dysconnectivity caused by C11orf46/Arl14ep risk gene
Although many neuropsychiatric risk genes are known to contribute to epigenetic regulation of gene expression, very little is known about specific chromatin-associated mechanisms that govern the formation and maintenance of neuronal connectivity. Here, the authors report that transcallosal connectivity is critically dependent on C11orf46/ARL14EP, a nuclear protein encoded in the chromosome 11p13 WAGR risk locus, and that RNA-guided epigenetic editing of hyperexpressed Sema6a gene promoters in C11orf46-knockdown neurons resulted in normalization of expression and rescue of transcallosal dysconnectivity via repressive chromatin remodeling.
- Cyril J. Peter
- , Atsushi Saito
- & Atsushi Kamiya
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Article
| Open AccessMarked isotopic variability within and between the Amazon River and marine dissolved black carbon pools
Black carbon produced by the burning of biomass and fuels is the most stable carbon compound in nature, yet its path from land to the deep ocean where it persists for thousands of years remains mysterious. Here Coppola and colleagues characterize the black carbon exported by the Amazon River, the largest river in the world.
- Alysha I. Coppola
- , Michael Seidel
- & Michael W. I. Schmidt
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Perspective
| Open AccessThe future of Blue Carbon science
The role of Blue Carbon in climate change mitigation and adaptation has now reached international prominence. Here the authors identified the top-ten unresolved questions in the field and find that most questions relate to the precise role blue carbon can play in mitigating climate change and the most effective management actions in maximising this.
- Peter I. Macreadie
- , Andrea Anton
- & Carlos M. Duarte
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Article
| Open AccessPlant roots increase both decomposition and stable organic matter formation in boreal forest soil
Understanding mechanisms of soil organic matter (SOM) decomposition and stabilisation improves soil-climate feedback predictions. Here the authors show that roots in boreal forest promote organic nitrogen economy and provide a framework on how roots affect decomposition and stabilisation of SOM.
- Bartosz Adamczyk
- , Outi-Maaria Sietiö
- & Jussi Heinonsalo
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Article
| Open AccessMicroscale pH variations during drying of soils and desert biocrusts affect HONO and NH3 emissions
The mechanisms that determine the composition of nitrogen gas emissions from soil remain unclear. A biocrust mechanistic model was developed to resolve puzzling dynamics of nitrous acid and ammonia emissions from drying soil pointing to previously unknown microscale pH zonation in thinning water films that affect soil biogeochemical fluxes.
- Minsu Kim
- & Dani Or
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Article
| Open AccessSignificant contribution of metastable particulate organic matter to natural formation of silver nanoparticles in soils
Silver nanoparticles are known environmental contaminants, however it is unclear whether they arise in soils through natural processes, anthropogenic processes, or both. Here Huang and colleagues offer fresh insight into the natural formation of these contaminants by soil particulate organic matter exposed to solar irradiation.
- Ying-Nan Huang
- , Ting-Ting Qian
- & Dong-Mei Zhou
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Review Article
| Open AccessIce sheets matter for the global carbon cycle
Ice sheets have long been overlooked as regulators of the global carbon cycle. In this Review, Wadham and colleagues show how the growth and retreat of ice sheets support the productivity of the oceans and variably store or release organic carbon–in effect, these frozen landscapes must be considered in future assessments of climate impacts on biogeochemical cycling.
- J. L. Wadham
- , J. R. Hawkings
- & K. E. Kohfeld
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Article
| Open AccessGlobal subsoil organic carbon turnover times dominantly controlled by soil properties rather than climate
The sensitivity of soil organic carbon (SOC) in subsoil (below 0.3 m) to climate change is poorly constrained. Here, the authors map global subsoil (0.3–1 m soil layer) SOC turnover times and find that temperature and in general climate effects are secondary to effects due to soil properties at both local and global scales—this now needs to be regarded for diagnosing subsoil SOC dynamics.
- Zhongkui Luo
- , Guocheng Wang
- & Enli Wang
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Article
| Open AccessRainfall drives variation in rates of change in intrinsic water use efficiency of tropical forests
How the water use efficiency of trees changes with atmospheric CO2 variations has mostly been studied on short time scales. Here, a newly compiled data set covering 1915 to 1995 shows how rates of change in water use efficiency vary with location and rainfall over the global tropics on a decadal scale.
- Mark A. Adams
- , Thomas N. Buckley
- & Tarryn L. Turnbull
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Article
| Open AccessNet carbon emissions from African biosphere dominate pan-tropical atmospheric CO2 signal
Tropical land ecosystems contain vast carbon reservoirs, but their influence on atmospheric CO2 is poorly understood. Here the authors use new carbon-observing satellites to reveal a large emission source over northern tropical Africa, where there are large soil carbon stores and substantial land use changes.
- Paul I. Palmer
- , Liang Feng
- & Peter Somkuti
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Article
| Open AccessMicrobial carbon use efficiency predicted from genome-scale metabolic models
Microbial respiration releases carbon from the soil. Here, the authors estimate bacterial carbon use efficiency in soils for over 200 species using constraint-based modeling, incorporate the values into an ecosystem model, and find that shifts in community composition may impact carbon storage.
- Mustafa Saifuddin
- , Jennifer M. Bhatnagar
- & Adrien C. Finzi
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Article
| Open AccessUsing B isotopes and B/Ca in corals from low saturation springs to constrain calcification mechanisms
Ocean acidification is expected to have a negative impact on calcifying organisms, however, our understanding of the acclimation potential of corals in their natural habit is currently limited. Here, the authors find that scleractinian corals living in high pCO2 conditions cannot fully adapt the chemistry of their internal calcifying fluid compared to corals growing in ambient conditions.
- M. Wall
- , J. Fietzke
- & A. Paytan
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Article
| Open AccessManganese and iron deficiency in Southern Ocean Phaeocystis antarctica populations revealed through taxon-specific protein indicators
Low manganese availability could be a major control of phytoplankton growth in the Southern Ocean. Here the authors identify proteomic signatures of low manganese and iron availability in phytoplankton cultures and detect those signatures in Antarctic field samples.
- Miao Wu
- , J. Scott P. McCain
- & Erin M. Bertrand
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Review Article
| Open AccessSubseafloor life and its biogeochemical impacts
Subseafloor microbial activities are central to global biogeochemical cycles, affecting Earth’s surface oxidation, ocean chemistry, and climate. Here the authors review present understanding of subseafloor microbes and their activities, identify research gaps, and recommend approaches to fill those gaps.
- Steven D’Hondt
- , Robert Pockalny
- & Arthur J. Spivack
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Article
| Open AccessGlobal ecological predictors of the soil priming effect
The global ecological predictors of soil priming remain unclear. Here the authors conducted a global survey of soils from 86 global locations using an isotopic approach and find that in more mesic sites with high SOC concentrations, soil priming effects are more likely to be negative.
- Felipe Bastida
- , Carlos García
- & Manuel Delgado-Baquerizo
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Article
| Open AccessWeathering in a world without terrestrial life recorded in the Mesoproterozoic Velkerri Formation
Prior to the expansion of life on to land, abiotic weathering may have resulted in different boundary conditions affecting the composition of the biosphere. Here the authors studied clay minerals from a Precambrian rock record to reveal the weathering processes and find difference in weathering produced minerals preserved in the Mesoproterozoic Velkerri Formation.
- Mehrnoush Rafiei
- & Martin Kennedy
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Article
| Open AccessRevisiting enteric methane emissions from domestic ruminants and their δ13CCH4 source signature
Global average, geographical distribution and temporal variations of the 13C isotopic signature of enteric fermentation emissions are not well understood. Here the authors established a global dataset and show a larger emission increase between the two periods (2002–2006 and 2008–2012) than previous studies.
- Jinfeng Chang
- , Shushi Peng
- & Philippe Bousquet
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Article
| Open AccessControls of soil organic matter on soil thermal dynamics in the northern high latitudes
Soils in the northern permafrost region contain large quantities of organic carbon, formed over long time scales under cold climates. Here the authors test a number of soil properties and show that soil organic carbon is the dominant factor controlling thermal diffusivity among 200 sites in high latitude regions.
- Dan Zhu
- , Philippe Ciais
- & Gustaf Hugelius
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Article
| Open AccessMicrobial spatial footprint as a driver of soil carbon stabilization
The processes driving soil carbon accretion remain to be poorly understood. Here the authors combined X-ray micro-tomography and zymography to demonstrate that plant-stimulated soil pore formation is a major, hitherto unrecognized, determinant of whether new C inputs are stored or lost to the atmosphere.
- A. N. Kravchenko
- , A. K. Guber
- & Y. Kuzyakov
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Article
| Open AccessAnoxygenic photosynthesis and the delayed oxygenation of Earth’s atmosphere
Competition dynamics between early Earth photosynthetic microorganisms are unclear. Here, the authors demonstrate that competition for light and nutrients between oxygenic phototrophs and Fe-based photosynthesizers in surface oceans provides a novel ecophysiological mechanism for the protracted oxygenation of Earth’s atmosphere.
- Kazumi Ozaki
- , Katharine J. Thompson
- & Christopher T. Reinhard
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Article
| Open AccessFuture nitrogen availability and its effect on carbon sequestration in Northern Eurasia
The impact of nitrogen availability on carbon sequestration in terrestrial ecosystems under climate change is understudied. Here the authors project that increases in N availability over the 21st century associated with warmer soils and the legacy of past N fertiliser use on abandoned croplands will be the primary drivers of a 21st century net carbon sink in Northern Eurasia.
- David W. Kicklighter
- , Jerry M. Melillo
- & Qianlai Zhuang
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Article
| Open AccessThe influence of geostrophic strain on oceanic ageostrophic motion and surface chlorophyll
The ocean’s swirling eddies are known to influence primary productivity, yet understanding of these processes has been hampered by a lack of resolution. Here the authors combine in-situ drifter, altimeter-based feature tracking, and satellite chlorophyll data to quantify how phytoplankton respond to surface mesoscale phenomena across the globe.
- Zhengguang Zhang
- , Bo Qiu
- & Seth Travis
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Article
| Open AccessLoss of fixed nitrogen causes net oxygen gain in a warmer future ocean
Ocean anoxic events threaten marine ecosystems, and they are predicted to increase as the climate warms. Using model simulations, Oschlies and colleagues show that in spite of rising temperatures, after transitory deoxygenation, microbial denitrification could lead to oxygen increases that exceed preindustrial levels.
- Andreas Oschlies
- , Wolfgang Koeve
- & Paul Kähler
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Article
| Open AccessPetroleum exploration increases methane emissions from northern peatlands
Human disturbance of peatland environments due to geological exploration activities can significantly alter peatland greenhouse gas exchange. Here, the authors study peatland disturbance in Alberta, Canada, and estimate that induced methane emissions are approximately 4.4–5.1 kt higher per year than in undisturbed conditions.
- Maria Strack
- , Shari Hayne
- & Bin Xu