Uptake Of Atmospheric Carbon Dioxide Research Articles

Methane emissions offset atmospheric carbon dioxide uptake in coastal macroalgae, mixed vegetation and sediment ecosystems

Coastal ecosystems can efficiently remove carbon dioxide (CO2) from the atmosphere and are thus promoted for nature-based climate change mitigation. Natural methane (CH4) emissions from these ecosystems may counterbalance atmospheric CO2 uptake. Still, knowledge of mechanisms sustaining such CH4 emissions and their contribution to net radiative forcing remains scarce for globally prevalent macroalgae, mixed vegetation, and surrounding depositional sediment habitats. Here we show that these habitats emit CH4 in the range of 0.1 – 2.9 mg CH4 m−2 d−1 to the atmosphere, revealing in situ CH4 emissions from macroalgae that were sustained by divergent methanogenic archaea in anoxic microsites. Over an annual cycle, CO2-equivalent CH4 emissions offset 28 and 35% of the carbon sink capacity attributed to atmospheric CO2 uptake in the macroalgae and mixed vegetation habitats, respectively, and augment net CO2 release of unvegetated sediments by 57%. Accounting for CH4 alongside CO2 sea-air fluxes and identifying the mechanisms controlling these emissions is crucial to constrain the potential of coastal ecosystems as net atmospheric carbon sinks and develop informed climate mitigation strategies.

Climate change drives rapid decadal acidification in the Arctic Ocean from 1994 to 2020.

The Arctic Ocean has experienced rapid warming and sea ice loss in recent decades, becoming the first open-ocean basin to experience widespread aragonite undersaturation [saturation state of aragonite (Ωarag) < 1]. However, its trend toward long-term ocean acidification and the underlying mechanisms remain undocumented. Here, we report rapid acidification there, with rates three to four times higher than in other ocean basins, and attribute it to changing sea ice coverage on a decadal time scale. Sea ice melt exposes seawater to the atmosphere and promotes rapid uptake of atmospheric carbon dioxide, lowering its alkalinity and buffer capacity and thus leading to sharp declines in pH and Ωarag. We predict a further decrease in pH, particularly at higher latitudes where sea ice retreat is active, whereas Arctic warming may counteract decreases in Ωarag in the future.

The land-to-ocean loops of the global carbon cycle

Carbon storage by the ocean and by the land is usually quantified separately, and does not fully take into account the land-to-ocean transport of carbon through inland waters, estuaries, tidal wetlands and continental shelf waters-the 'land-to-ocean aquatic continuum' (LOAC). Here we assess LOAC carbon cycling before the industrial period and perturbed by direct human interventions, including climate change. In our view of the global carbon cycle, the traditional 'long-range loop', which carries carbon from terrestrial ecosystems to the open ocean through rivers, is reinforced by two 'short-range loops' that carry carbon from terrestrial ecosystems to inland waters and from tidal wetlands to the open ocean. Using a mass-balance approach, we find that the pre-industrial uptake of atmospheric carbon dioxide by terrestrial ecosystems transferred to the ocean and outgassed back to the atmosphere amounts to 0.65 ± 0.30 petagrams of carbon per year (±2 sigma). Humans have accelerated the cycling of carbon between terrestrial ecosystems, inland waters and the atmosphere, and decreased the uptake of atmospheric carbon dioxide from tidal wetlands and submerged vegetation. Ignoring these changing LOAC carbon fluxes results in an overestimation of carbon storage in terrestrial ecosystems by 0.6 ± 0.4 petagrams of carbon per year, and an underestimation of sedimentary and oceanic carbon storage. We identify knowledge gaps that are key to reduce uncertainties in future assessments of LOAC fluxes.

Definitions and methods to estimate regional land carbon fluxes for the second phase of the REgional Carbon Cycle Assessment and Processes Project (RECCAP-2)

Abstract. Regional land carbon budgets provide insights into the spatial distribution of the land uptake of atmospheric carbon dioxide and can be used to evaluate carbon cycle models and to define baselines for land-based additional mitigation efforts. The scientific community has been involved in providing observation-based estimates of regional carbon budgets either by downscaling atmospheric CO2 observations into surface fluxes with atmospheric inversions, by using inventories of carbon stock changes in terrestrial ecosystems, by upscaling local field observations such as flux towers with gridded climate and remote sensing fields, or by integrating data-driven or process-oriented terrestrial carbon cycle models. The first coordinated attempt to collect regional carbon budgets for nine regions covering the entire globe in the RECCAP-1 project has delivered estimates for the decade 2000–2009, but these budgets were not comparable between regions due to different definitions and component fluxes being reported or omitted. The recent recognition of lateral fluxes of carbon by human activities and rivers that connect CO2 uptake in one area with its release in another also requires better definitions and protocols to reach harmonized regional budgets that can be summed up to a globe scale and compared with the atmospheric CO2 growth rate and inversion results. In this study, using the international initiative RECCAP-2 coordinated by the Global Carbon Project, which aims to be an update to regional carbon budgets over the last 2 decades based on observations for 10 regions covering the globe with a better harmonization than the precursor project, we provide recommendations for using atmospheric inversion results to match bottom-up carbon accounting and models, and we define the different component fluxes of the net land atmosphere carbon exchange that should be reported by each research group in charge of each region. Special attention is given to lateral fluxes, inland water fluxes, and land use fluxes.

Forest production efficiency increases with growth temperature

Forest production efficiency (FPE) metric describes how efficiently the assimilated carbon is partitioned into plants organs (biomass production, BP) or—more generally—for the production of organic matter (net primary production, NPP). We present a global analysis of the relationship of FPE to stand-age and climate, based on a large compilation of data on gross primary production and either BP or NPP. FPE is important for both forest production and atmospheric carbon dioxide uptake. We find that FPE increases with absolute latitude, precipitation and (all else equal) with temperature. Earlier findings—FPE declining with age—are also supported by this analysis. However, the temperature effect is opposite to what would be expected based on the short-term physiological response of respiration rates to temperature, implying a top-down regulation of carbon loss, perhaps reflecting the higher carbon costs of nutrient acquisition in colder climates. Current ecosystem models do not reproduce this phenomenon. They consistently predict lower FPE in warmer climates, and are therefore likely to overestimate carbon losses in a warming climate.

The Northeast Atlantic is running out of excess carbonate in the horizon of cold-water corals communities

The oceanic uptake of atmospheric carbon dioxide (CO2) emitted by human activities alters the seawater carbonate system. Here, the chemical status of the Northeast Atlantic is examined by means of a high-quality database of carbon variables based on the GO-SHIP A25 section (1997–2018). The increase of atmospheric CO2 leads to an increase in ocean anthropogenic carbon (Cant) and a decrease in carbonate that is unequivocal in the upper and mid-layers (0–2,500 m depth). In the mid-layer, the carbonate content in the Northeast Atlantic is maintained by the interplay between the northward spreading of recently conveyed Mediterranean Water with excess of carbonate and the arrival of subpolar-origin waters close to carbonate undersaturation. In this study we show a progression to undersaturation with respect to aragonite that could compromise the conservation of the habitats and ecosystem services developed by benthic marine calcifiers inhabiting that depth-range, such as the cold-water corals (CWC) communities. For each additional ppm in atmospheric pCO2 the waters surrounding CWC communities lose carbonate at a rate of − 0.17 ± 0.02 μmol kg−1 ppm−1. The accomplishment of global climate policies to limit global warming below 1.5–2 ℃ will avoid the exhaustion of excess carbonate in the Northeast Atlantic.

Processes and Microorganisms Involved in the Marine Nitrogen Cycle: Knowledge and Gaps

Nitrogen (N) is a key element for life in the oceans. It controls primary productivity in many parts of the global ocean, consequently playing a crucial role in the uptake of atmospheric carbon dioxide. The marine N cycle is driven by multiple biogeochemical transformations mediated by microorganisms, including processes contributing to the marine fixed N pool (N2 fixation) and retained N pool (nitrification, assimilation, and dissimilatory nitrate reduction to ammonia), as well as processes contributing to the fixed N loss (denitrification, anaerobic ammonium oxidation and nitrite-dependent anaerobic methane oxidation). The N cycle maintains the functioning of marine ecosystems and will be a crucial component in how the ocean responds to global environmental change. In this review, we summarize the current understanding of the marine microbial N cycle, the functional N genes involved, the ecology and distribution of the participating microorganisms, and the main impacts of anthropogenic activities on the marine N cycle.

A carbon sink-driven approach to estimate gross primary production from microwave satellite observations

Global estimation of Gross Primary Production (GPP) - the uptake of atmospheric carbon dioxide by plants through photosynthesis - is commonly based on optical satellite remote sensing data. This presents a source-driven approach since it uses the amount of absorbed light, the main driver of photosynthesis, as a proxy for GPP. Vegetation Optical Depth (VOD) estimates obtained from microwave sensors provide an alternative and independent data source to estimate GPP on a global scale, which may complement existing GPP products. Recent studies have shown that VOD is related to aboveground biomass, and that both VOD and temporal changes in VOD relate to GPP. In this study, we build upon this concept and propose a model for estimating GPP from VOD. Since the model is driven by vegetation biomass, as observed through VOD, it presents a carbon sink-driven approach to quantify GPP and, therefore, is conceptually different from common source-driven approaches. The model developed in this study uses single frequencies from active or passive microwave VOD retrievals from C-, X- and Ku-band (Advanced Scatterometer (ASCAT) and Advanced Microwave Scanning Radiometer for Earth Observation (AMSR-E)) to estimate GPP at the global scale. We assessed the ability for temporal and spatial extrapolation of the model using global GPP from FLUXCOM and in situ GPP from FLUXNET. We further performed upscaling of in situ GPP based on different VOD data sets and compared these estimates with the FLUXCOM and MODerate-resolution Imaging Spectroradiometer (MODIS) GPP products. Our results show that the model developed for individual grid cells using VOD and change in VOD as input performs well in predicting temporal patterns in GPP for all VOD data sets. For spatial extrapolation of the model, however, additional input variables are needed to represent the spatial variability of the VOD-GPP relationship due to differences in vegetation type. As additional input variable, we included the grid cell median VOD (as a proxy for vegetation cover), which increased the model performance during cross validation. Mean annual GPP obtained for AMSR-E X-band data tends to overestimate mean annual GPP for FLUXCOM and MODIS but shows comparable latitudinal patterns. Overall, our findings demonstrate the potential of VOD for estimating GPP. The sink-driven approach provides additional information about GPP independent of optical data, which may contribute to our knowledge about the carbon source-sink balance in different ecosystems.

Convergence in Maximum Stomatal Conductance of C3 Woody Angiosperms in Natural Ecosystems Across Bioclimatic Zones.

Stomatal conductance (gs) in terrestrial vegetation regulates the uptake of atmospheric carbon dioxide for photosynthesis and water loss through transpiration, closely linking the biosphere and atmosphere and influencing climate. Yet, the range and pattern of gs in plants from natural ecosystems across broad geographic, climatic, and taxonomic ranges remains poorly quantified. Furthermore, attempts to characterize gs on such scales have predominantly relied upon meta-analyses compiling data from many different studies. This approach may be inherently problematic as it combines data collected using unstandardized protocols, sometimes over decadal time spans, and from different habitat groups. Using a standardized protocol, we measured leaf-level gs using porometry in 218 C3 woody angiosperm species in natural ecosystems representing seven bioclimatic zones. The resulting dataset of 4273 gs measurements, which we call STraits (Stomatal Traits), was used to determine patterns in maximum gs (gsmax) across bioclimatic zones and whether there was similarity in the mean gsmax of C3 woody angiosperms across ecosystem types. We also tested for differential gsmax in two broadly defined habitat groups – open-canopy and understory-subcanopy – within and across bioclimatic zones. We found strong convergence in mean gsmax of C3 woody angiosperms in the understory-subcanopy habitats across six bioclimatic zones, but not in open-canopy habitats. Mean gsmax in open-canopy habitats (266 ± 100 mmol m-2 s-1) was significantly higher than in understory-subcanopy habitats (233 ± 86 mmol m-2 s-1). There was also a central tendency in the overall dataset to operate toward a gsmax of ∼250 mmol m-2 s-1. We suggest that the observed convergence in mean gsmax of C3 woody angiosperms in the understory-subcanopy is due to a buffering of gsmax against macroclimate effects which will lead to differential response of C3 woody angiosperm vegetation in these two habitats to future global change. Therefore, it will be important for future studies of gsmax to categorize vegetation according to habitat group.

Productivity Evolution in the South Brazilian Bight During the Last 40,000 Years

AbstractMarine productivity largely controls the oceanic uptake of atmospheric carbon dioxide and contributed to the global climate changes that led to the termination of the last glacial cycle. Past changes in marine productivity were presumably associated with disturbances in the Atlantic meridional overturning circulation (AMOC). In the South Atlantic, however, the evolution of marine productivity throughout the last glacial–interglacial cycle is still poorly constrained mainly due to the scarcity of records with high temporal resolution. Here we present high‐resolution records of paleoproductivity and upper‐water‐column properties from the western subtropical South Atlantic covering the last 40,000 years. Our records are based on faunal and stable oxygen isotopic analyses of planktonic foraminifera from a marine sediment core collected from an upwelling region off southeastern South America (27°S). We used the relative abundance of eutrophic planktonic foraminifera (i.e., Globigerinita glutinata and Globigerina bulloides) as proxies of primary productivity. Our findings reveal, for the first time, enhanced primary productivity during Heinrich Stadials along the last glacial, when the AMOC showed reduced strength. Additionally, our results reveal decreased primary productivity over the Last Glacial Maximum, a period of markedly lower sea level; and the Younger Dryas, when the AMOC showed only moderate reductions. The most outstanding productivity decline, however, is depicted at the onset of the Holocene, when the AMOC recovers its strength. We hypothesize that the observed changes were triggered by the dynamics of the Brazil Current primarily driven by disturbances in the AMOC.

Assessing the relationship between microwave vegetation optical depth and gross primary production

At the global scale, the uptake of atmospheric carbon dioxide by terrestrial ecosystems through photosynthesis is commonly estimated through vegetation indices or biophysical properties derived from optical remote sensing data. Microwave observations of vegetated areas are sensitive to different components of the vegetation layer than observations in the optical domain and may therefore provide complementary information on the vegetation state, which may be used in the estimation of Gross Primary Production (GPP). However, the relation between GPP and Vegetation Optical Depth (VOD), a biophysical quantity derived from microwave observations, is not yet known. This study aims to explore the relationship between VOD and GPP. VOD data were taken from different frequencies (L-, C-, and X-band) and from both active and passive microwave sensors, including the Advanced Scatterometer (ASCAT), the Soil Moisture Ocean Salinity (SMOS) mission, the Advanced Microwave Scanning Radiometer for Earth Observation System (AMSR-E) and a merged VOD data set from various passive microwave sensors. VOD data were compared against FLUXCOM GPP and Solar-Induced chlorophyll Fluorescence (SIF) from the Global Ozone Monitoring Experiment-2 (GOME-2). FLUXCOM GPP estimates are based on the upscaling of flux tower GPP observations using optical satellite data, while SIF observations present a measure of photosynthetic activity and are often used as a proxy for GPP. For relating VOD to GPP, three variables were analyzed: original VOD time series, temporal changes in VOD (ΔVOD), and positive changes in VOD (ΔVOD≥0). Results show widespread positive correlations between VOD and GPP with some negative correlations mainly occurring in dry and wet regions for active and passive VOD, respectively. Correlations between VOD and GPP were similar or higher than between VOD and SIF. When comparing the three variables for relating VOD to GPP, correlations with GPP were higher for the original VOD time series than for ΔVOD or ΔVOD≥0 in case of sparsely to moderately vegetated areas and evergreen forests, while the opposite was true for deciduous forests. Results suggest that original VOD time series should be used jointly with changes in VOD for the estimation of GPP across biomes, which may further benefit from combining active and passive VOD data.

Ocean acidification and calcium carbonate saturation states in the coastal zone of the West Antarctic Peninsula

The polar oceans are particularly vulnerable to ocean acidification; the lowering of seawater pH and carbonate mineral saturation states due to uptake of atmospheric carbon dioxide (CO2). High spatial variability in surface water pH and saturation states (Ω) for two biologically-important calcium carbonate minerals calcite and aragonite was observed in Ryder Bay, in the coastal sea-ice zone of the West Antarctic Peninsula. Glacial meltwater and melting sea ice stratified the water column and facilitated the development of large phytoplankton blooms and subsequent strong uptake of atmospheric CO2 of up to 55 mmol m-2 day-1 during austral summer. Concurrent high pH (8.48) and calcium carbonate mineral supersaturation (Ωaragonite ~3.1) occurred in the meltwater-influenced surface ocean. Biologically-induced increases in calcium carbonate mineral saturation states counteracted any effects of carbonate ion dilution. Accumulation of CO2 through remineralisation of additional organic matter from productive coastal waters lowered the pH (7.84) and caused deep-water corrosivity (Ωaragonite ~0.9) in regions impacted by Circumpolar Deep Water. Episodic mixing events enabled CO2-rich subsurface water to become entrained into the surface and eroded seasonal stratification to lower surface water pH (8.21) and saturation states (Ωaragonite ~1.8) relative to all surface waters across Ryder Bay. Uptake of atmospheric CO2 of 28 mmol m-2 day-1 in regions of vertical mixing may enhance the susceptibility of the surface layer to future ocean acidification in dynamic coastal environments. Spatially-resolved studies are essential to elucidate the natural variability in carbonate chemistry in order to better understand and predict carbon cycling and the response of marine organisms to future ocean acidification in the Antarctic coastal zone.

МОДЕЛЬНЫЕ ОЦЕНКИ ВКЛАДА ЭКОСИСТЕМЫ В ОБМЕН УГЛЕКИСЛЫМ ГАЗОМ МЕЖДУ ОКЕАНОМ И АТМОСФЕРОЙ В БАРЕНЦЕВОМ МОРЕ, "Фундаментальная и прикладная гидрофизика"

A three-dimensional mathematical ecosystem model has been combined with a circulation and a sea-ice models of the Barents Sea. The ecosystem model describes the interaction of phytoplankton, zooplankton, dissolved inorganic nitrogen, total inorganic carbon, alkalinity, organic and inorganic parts of detritus. The paper presents the results of calculations of the chlorophyll-a concentration in the period of maximum spring phytoplankton bloom in the Barents Sea, as well as the results of calculations of CO2 flux between the atmosphere and the sea under various conditions. The correspondence between the zones of the intensive growth of phytoplankton during the bloom period and the position of the Polar Front has been demonstrated. The estimation of the ocean-atmosphere CO2 exchange intensity in the presence and absence of the biological CO2 pump has been carried out. For the case without taking into account the oceanic biological uptake of atmospheric carbon dioxide it was found that the maximum values of CO2 flux can be observed in the areas of the ice edge. Taking into account the oceanic biological uptake of atmospheric CO2 leads to the spatial correspondence of the zones of maximal CO2 flux from the atmosphere and the zones of high primary production in the ocean surface layer. The results of the present study show that the spatial variability of the carbon dioxide flux from the atmosphere to the ocean is determined by the spatial variability of the primary production to a much greater extent than by the variations in the sea surface temperature.

In this issue ofWeather

We focus on aspects of the weather in India in two of our articles, beginning on p. 83 with Ancy Thomas and her co-authors’ paper, which asks ‘How accurate are the weather forecasts available to the public in India?’ As in much of the world, services are now available from a range of providers, in particular through mobile phones and personal computers. As in Britain, there is much interest in the weather in India, where heat, drought, pollution, chill and torrential rainfall are common visitors, but on an irregular basis. As elsewhere in the world, orography plays an important part in the variability of the Indian climate and day-to-day weather. Compared with a range of weather parameters, observed at both manned and automatic weather stations of the India Meteorological Department, forecasts from the Real Time Weather System, AccuWeather and Weather Underground all verify relatively poorly, although performance varies in space and time, as well as by parameter. Sporadic rainfall is a characteristic of the weather of India, in the months preceding the arrival of the monsoon in June and July. Priya Narayanan and her co-authors look at changes in this precipitation in ‘Trend analysis and forecast of pre-monsoon rainfall over India’ on p. 94. They conclude that although changes in this rainfall can be seen in data, the variation is different by month and location. In addition, it seems likely that the trend towards change will persist in future years. On p. 88 James and Samuel Curran look at the record of atmospheric carbon dioxide from Mauna Loa observatory in Hawaii in order to examine the rate at which this atmospheric carbon is sequestered. ‘Indications of positive feedback in climate change due to a reduction in Northern Hemisphere biomass uptake of atmospheric carbon dioxide’ explains that, although there is not only an increase in year-on-year atmospheric carbon dioxide, the evidence of significant carbon sequestration in this record is changing. The intra-annual fall in concentrations between May and September shows that this may be reaching a limit, the oceans and biomass less able to absorb the CO2 we produce. Finally a viewpoint article ‘Shakespeare's Tempest, witchcraft and the Little Ice Age’ looks at the rather gruesome effects of the relatively cold climate between 1350 and 1850. Gerald Stanhill shows how crop failures, shipwrecks and more generally tough living conditions in Europe led to witchcraft trials and their portrayal in the works of William Shakespeare, starting on p. 100.

Indications of positive feedback in climate change due to a reduction in Northern Hemisphere biomass uptake of atmospheric carbon dioxide

Mauna Loa Observatory data for atmospheric carbon dioxide (CO2) reveal, within each calendar year, a regular seasonal fluctuation: in summer, a drop in concentration occurs as the Northern Hemisphere drives uptake of CO2 into biomass, whereas in autumn/winter an increase in CO2 occurs as the Northern Hemisphere releases it through biodegradation. Analysis of the magnitude of this drop allows an estimate to be made of the biomass activity each year in the Northern Hemisphere. There are indications of a small decline in such activity since around 2006. This has potentially serious climate change implications as it may be evidence of positive feedback.

Annual cycles of phytoplankton biomass in the subarctic Atlantic and Pacific Ocean

AbstractHigh‐latitude phytoplankton blooms support productive fisheries and play an important role in oceanic uptake of atmospheric carbon dioxide. In the subarctic North Atlantic Ocean, blooms are a recurrent feature each year, while in the eastern subarctic Pacific only small changes in chlorophyll (Chl) are seen over the annual cycle. Here we show that when evaluated using phytoplankton carbon biomass (Cphyto) rather than Chl, an annual bloom in the North Pacific is evident and can even rival blooms observed in the North Atlantic. The annual increase in subarctic Pacific phytoplankton biomass is not readily observed in the Chl record because it is paralleled by light‐ and nutrient‐driven decreases in cellular pigment levels (Cphyto:Chl). Specifically, photoacclimation and iron stress effects on Cphyto:Chl oppose the biomass increase, leading to only modest changes in bulk Chl. The magnitude of the photoacclimation effect is quantified using descriptors of the near‐surface light environment and a photophysiological model. Iron stress effects are diagnosed from satellite chlorophyll fluorescence data. Lastly, we show that biomass accumulation in the Pacific is slower than that in the Atlantic but is closely tied to similar levels of seasonal nutrient uptake in both basins. Annual cycles of satellite‐derived Chl and Cphyto are reproduced by in situ autonomous profiling floats. These results contradict the long‐standing paradigm that environmental conditions prevent phytoplankton accumulation in the subarctic Northeast Pacific and suggest a greater seasonal decoupling between phytoplankton growth and losses than traditionally implied. Further, our results highlight the role of physiological processes in shaping bulk properties, such as Chl, and their interpretation in studies of ocean ecosystem dynamics and climate change.

Foraging behaviour of the epaulette shark Hemiscyllium ocellatum is not affected by elevated CO2

Abstract Increased oceanic uptake of atmospheric carbon dioxide (CO2) is a threat to marine organisms and ecosystems. Among the most dramatic consequences predicted to date are behavioural impairments in marine fish which appear to be caused by the interference of elevated CO2 with a key neurotransmitter receptor in the brain. In this study, we tested the effects of elevated CO2 on the foraging and shelter-seeking behaviours of the reef-dwelling epaulette shark, Hemiscyllium ocellatum. Juvenile sharks were exposed for 30 d to control CO2 (400 µatm) and two elevated CO2 treatments (615 and 910 µatm), consistent with medium- and high-end projections for ocean pCO2 by 2100. Contrary to the effects observed in teleosts and in some other sharks, behaviour of the epaulette shark was unaffected by elevated CO2. A potential explanation is the remarkable adaptation of H. ocellatum to low environmental oxygen conditions (hypoxia) and diel fluctuations in CO2 encountered in their shallow reef habitat. This ability translates into behavioural tolerance of near-future ocean acidification, suggesting that behavioural tolerance and subsequent adaptation to projected future CO2 levels might be possible in some other fish, if adaptation can keep pace with the rate of rising CO2 levels.

The contribution of zooplankton faecal pellets to deep-carbon transport in the Scotia Sea (Southern Ocean)

Abstract. The northern Scotia Sea contains the largest seasonal uptake of atmospheric carbon dioxide yet measured in the Southern Ocean. This study examines one of the main routes by which this carbon fluxes to the deep ocean: through the production of faecal pellets (FPs) by the zooplankton community. Deep sediment traps were deployed at two sites with contrasting ocean productivity regimes (P3, naturally iron-fertilized, and P2, iron-limited) within the same water mass. The magnitude and seasonal pattern of particulate organic carbon (POC) and FPs in the traps was markedly different between the two sites. Maximum fluxes at P3 (22.91 mg C m−2 d−1; 2534 FP m−2 d1) were 1 order of magnitude higher than at P2 (4.01 mg C m−2 d−1; 915 FP m−2 d1, with flux at P3 exhibiting a double seasonal peak, compared to a single flatter peak at P2. The maximum contribution of FP carbon to the total amount of POC was twice as high at P3 (91%) compared to P2 (40%). The dominant FP category at P3 varied between round, ovoidal, cylindrical and tabular over the course of the year, while, at P2, ovoidal FPs were consistently dominant, always making up more than 60% of the FP assemblage. There was also a difference in the FP state between the two sites, with FPs being relatively intact at P3, while FPs were often fragmented with broken peritrophic membranes at P2. The exception was ovoidal FPs, which were relatively intact at both sites. Our observations suggest that there was a community shift from a herbivorous to an omnivorous diet from spring through to autumn at P3, while detritivores had a higher relative importance over the year at P2. Furthermore, the flux was mainly a product of the vertically migrating zooplankton community at P3, while the FP flux was more likely to be generated by deeper-dwelling zooplankton feeding on recycled material at P2. The results demonstrate that the feeding behaviour and vertical distribution of the zooplankton community plays a critical role in controlling the magnitude of carbon export to the deep ocean in this region.

Endolithic microbial communities in carbonate precipitates from serpentinite-hosted hyperalkaline springs of the Voltri Massif (Ligurian Alps, Northern Italy).

The Voltri Massif is an ophiolitic complex located in the Ligurian Alps close to the city of Genova (Northern Italy) where several springs discharge high pH (up to 11.7), low salinity waters produced by the active serpentinization of the ultramafic basement. Mixing of these hyperalkaline waters with the river waters along with the uptake of atmospheric carbon dioxide forms brownish carbonate precipitates covering the bedrock at the springs. Diverse archaeal and bacterial communities were detected in these carbonate precipitates using 454 pyrosequencing analyses of 16S ribosomal RNA (rRNA) genes. Archaeal communities were dominated by members of potential methane-producing and/or methane-oxidizing Methanobacteriales and Methanosarcinales (Euryarchaeota) together with ammonia-oxidizing Nitrososphaerales (Thaumarchaeota) similar to those found in other serpentinization-driven submarine and terrestrial ecosystems. Bacterial communities consisted of members of the Proteobacteria, Actinobacteria, Planctomycetes, Bacteroidetes, Chloroflexi, and Verrucomicrobia phyla, altogether accounting for 92.2% of total retrieved bacterial 16S rRNA gene sequences. Amongst Bacteria, potential chemolithotrophy was mainly associated with Alpha- and Betaproteobacteria classes, including nitrogen-fixing, methane-oxidizing or hydrogen-oxidizing representatives of the genera Azospirillum, Methylosinus, and Hydrogenophaga/'Serpentinomonas', respectively. Besides, potential chemoorganotrophy was attributed mainly to representatives of Actinobacteria and Planctomycetales phyla. The reported 16S rRNA gene data strongly suggested that hydrogen, methane, and nitrogen-based chemolithotrophy can sustain growth of the microbial communities inhabiting the carbonate precipitates in the hyperalkaline springs of the Voltri Massif, similarly to what was previously observed in other serpentinite-hosted ecosystems.

絹の研究（3） カイコやクモが大気中の二酸化炭素を絹繊維に固定

絹の研究（3） カイコやクモが大気中の二酸化炭素を絹繊維に固定