The oxygen isotope composition of phosphate released from phytic acid by the activity of wheat and Aspergillus niger phytase
Biogeosciences Discuss., 12, 5055-5077, doi:10.5194/bgd-12-5055-2015, 2015
Hydrologic controls on DOC, As and Pb export from a polluted peatland – the importance of heavy rain events, antecedent moisture conditions and hydrological connectivity
Biogeosciences Discuss., 12, 5015-5053, doi:10.5194/bgd-12-5015-2015, 2015
Optical sampling of the flux tower footprint
Summary: Optical sampling expands our understanding of the "breathing" of terrestrial ecosystems beyond what is possible by eddy covariance alone. The light-use efficiency (LUE) model provides a useful conceptual framework for integrating optical and CO2 flux measurements. Contrasting optical and flux behaviour can reveal distinct optical types that provide key information on flux controls. Practical applications include assessment of ecosystem health, productivity and biospheric carbon sequestration.
Biogeosciences Discuss., 12, 4973-5014, doi:10.5194/bgd-12-4973-2015, 2015
Response of key stress-related genes of the seagrass Posidonia oceanica in the vicinity of submarine volcanic vents
Summary: The effects of two marine volcanic vents, utilized as proxy of ocean acidification and global changes, are studied at molecular level in P. oceanica (seagrass). Stress-related genes (antioxidants and HSP) were differently activated in the two sites, at comparable CO2 levels. Metal detoxification genes were mostly down-regulated. This suggest that plants face different types of stressors and that factors other than CO2 and acidification, can cause stress to marine organisms near volcanic vents.
Biogeosciences Discuss., 12, 4947-4971, doi:10.5194/bgd-12-4947-2015, 2015
Macroalgae contribute to nested mosaics of pH variability in a sub-Arctic fjord
Summary: The Arctic Ocean is considered the most vulnerable ecosystem to ocean acidification (OA) but very little information is available on natural variability of pH in the Arctic coastal zone. We report pH-variability at various scales in a Greenland fjord. Variability ranged up to 0.2-0.3 pH units horizontally and vertically in the fjord, between seasons and on diel basis in kelp forests and was extreme in tidal pools. Overall, primary producers played a fundamental role in producing mosaics of pH.
Biogeosciences Discuss., 12, 4907-4945, doi:10.5194/bgd-12-4907-2015, 2015
Thermokarst-lake methanogenesis along a complete talik profile
Summary: The relative magnitude of thermokarst-lake CH4 production in surface sediments vs. deeper thawed permafrost is not well understood. We assessed CH4 production potentials from a lake sediment core and adjacent permafrost tunnel in interior Alaska. CH4 production was highest in the organic-rich surface lake sediments and recently-thawed permafrost at the bottom of the talik, implying CH4 production is highly variable and that both modern and ancient OM are important to lake CH4 production.
Biogeosciences Discuss., 12, 4865-4905, doi:10.5194/bgd-12-4865-2015, 2015
Intact polar lipids of Thaumarchaeota and anammox bacteria as indicators of N-cycling in the Eastern Tropical North Pacific oxygen deficient zone
Summary: The distribution of Thaumarchaeota and anammox bacteria in the water column of the Eastern Tropical North Pacific (ETNP) oxygen deficient zone (ODZ) was investigated by collecting suspended particulate matter (SPM) and analysing it for the content of specific intact polar lipids (IPLs) produced by the two microbial groups. We found a clear niche segregation in the distribution of the two groups in the coastal waters of the ETNP, but a partial overlap of their niches in the open water setting.
Biogeosciences Discuss., 12, 4833-4864, doi:10.5194/bgd-12-4833-2015, 2015
Quantifying wind and pressure effects on trace gas fluxes across the soil–atmosphere interface
Summary: One continuing, significant source of uncertainty in global climate predictions is the combined effect of wind and pressure on trace gas fluxes. We quantified the effects of wind speed and pressure on fluxes of CO2 and CH4 within three different ecosystems. Trace gas fluxes are positively correlated with both wind speed and pressure near the soil surface but we argue that wind speed is a better proxy for general use. These results have implications for a number of global feedback mechanisms.
Biogeosciences Discuss., 12, 4801-4832, doi:10.5194/bgd-12-4801-2015, 2015
A model analysis of climate and CO2 controls on tree growth in a semi-arid woodland
Biogeosciences Discuss., 12, 4769-4800, doi:10.5194/bgd-12-4769-2015, 2015
Multi-molecular tracers of terrestrial carbon transfer across the pan-Arctic – Part 1: Comparison of hydrolysable components with plant wax lipids and lignin phenols
Summary: Currently very few studies have examined the distribution and fate of hydrolysable organic carbon (OC) in the arctic sediments, whose fate remains unclear in the context of climate change. Our study focuses on the source, distribution and fate of hydrolysable OC as compared with plant wax lipids and lignin phenols in the sediments of nine arctic and sub-arctic rivers. This multi-molecular approach allows a comprehensive investigation of terrestrial OC transfer via arctic rivers.
Biogeosciences Discuss., 12, 4721-4767, doi:10.5194/bgd-12-4721-2015, 2015
A large CO2 sink enhanced by eutrophication in a tropical coastal embayment (Guanabara Bay, Rio de Janeiro, Brazil)
Summary: Air-water fluxes of CO2 were monitored in Guanabara Bay (SE-Brazil), a tropical eutrophic coastal embayment. In contrast with other estuaries worldwilde, Guanabara Bay behaves as an annual sink of CO2 (-19.6 molC m2 yr), a property due to the concomitant effects of strong radiation intensity, thermal stratification, and high availability of nutrients which promotes massive phytoplankton development. The calculated annual CO2 sink matched the organic carbon burial reported in the literature.
Biogeosciences Discuss., 12, 4671-4720, doi:10.5194/bgd-12-4671-2015, 2015
Stable isotopes in barnacles as a tool to understand green sea turtle (Chelonia mydas) regional movement patterns
Summary: We report on the oxygen isotope signatures in green sea turtle (Chelonia mydas) barnacles (Platylepas sp.) to suggest likely regional movement patterns by mapping these onto a predictive oxygen isotope map of the Pacific. Discussing barnacle proxies potential relevance as an alternative tool with which to study green sea turtle migration, we find that these could complement traditional methods of studying connectivity between turtle populations and help inform more effective conservation policy.
Biogeosciences Discuss., 12, 4655-4669, doi:10.5194/bgd-12-4655-2015, 2015
Resilience to temperature and pH changes in a future climate change scenario in six strains of the polar diatom Fragilariopsis cylindrus
Summary: Climate change may not affect phytoplankton species as such, but may lead to changes in population structure of a species, with strains exhibiting high phenotypic plasticity dominating the population. Simulated climate scenarios showed that combined effects of increased temperature and acidification counterbalanced each other in the ecologically important model organism Fragilariopsis cylindrus. The variation among strains was larger than the variation observed due to the changes in parameters.
Biogeosciences Discuss., 12, 4627-4654, doi:10.5194/bgd-12-4627-2015, 2015
New insights of pCO2 variability in the tropical eastern Pacific Ocean using SMOS SSS
Summary: Using a temperature-salinity based extrapolation of in-situ surface pCO2, in conjunction with SMOS SSS and OSTIA SST, pCO2 is mapped within the Eastern tropical Pacific Ocean (ETPO) at high spatial (0.25°) and temporal (monthly) resolution. Strong interannual and spatial variability is identified, with net outgassing of CO2 in the gulfs of Tecuantepec and Papagayo contrasting net ingassing in the Gulf of Panama. For the period July 2010-July 2014 the ETPO was 41 uatm supersaturated.
Biogeosciences Discuss., 12, 4595-4625, doi:10.5194/bgd-12-4595-2015, 2015
Can organic matter flux profiles be diagnosed using remineralisation rates derived from observed tracers and modelled ocean transport rates?
Summary: We explore whether ocean model transport rates, in the form of a transport matrix, can be used to estimate remineralisation rates from dissolved nutrient concentrations and infer spatial variability in vertical fluxes of particulate organic carbon. Estimated remineralisation rates are significantly sensitive to uncertainty in the observations and the modelled circulation. The remineralisation of dissolved organic matter is an additional source of uncertainty when inferring vertical fluxes.
Biogeosciences Discuss., 12, 4557-4593, doi:10.5194/bgd-12-4557-2015, 2015
Water column biogeochemistry of oxygen minimum zones in the eastern tropical North Atlantic and eastern tropical South Pacific Oceans
Biogeosciences Discuss., 12, 4495-4556, doi:10.5194/bgd-12-4495-2015, 2015
Simultaneous high C fixation and high C emissions in Sphagnum mires
Summary: While pristine, growing peatlands are often considered to be net sinks of carbon dioxide (CO2), fluxes vary considerably and these systems can be net sinks or sources of CO2. To explain part of this huge variation, we here present a phenomenon of peat moss (Sphagnum) driven CO2 production. Due to the acid excreted by Sphagnum, bicarbonate in the surface water is transformed into CO2. Thus, while these systems have high CO2 fixation rates due to growing Sphagnum, they show a net emission of CO2.
Biogeosciences Discuss., 12, 4465-4494, doi:10.5194/bgd-12-4465-2015, 2015
Interdependencies between temperature and moisture sensitivities of CO2 emissions in European land ecosystems
Summary: Our experiments showed that in cold areas (e.g. northern latitudes or mountain areas) warming as well as rain events will have a larger impact on CO2 emissions. Increased moisture in dry areas or drying of wet areas will largely promote CO2 emissions. Irrigation of arable lands might have a higher impact on CO2 emissions in warmer regions in the South of Europe than in the North.
Biogeosciences Discuss., 12, 4433-4464, doi:10.5194/bgd-12-4433-2015, 2015
Response of CO2 and H2O fluxes of a mountainous tropical rain forest in equatorial Indonesia to El Niño events
Summary: The time series analysis of the main meteorological parameters and CO2 and H2O fluxes in the tropical rain forest in Central Sulawesi showed a high sensitivity of Evapotranspiration (ET) and Gross Primary Production (GPP) to meteorological variations caused by El Niño-Southern Oscillation events. Incoming solar radiation is the main governing factor that is responsible for ET and GPP variability. Changes of precipitation due to moderate ENSO events did not cause any notable effect on ET and GPP.
Biogeosciences Discuss., 12, 4405-4431, doi:10.5194/bgd-12-4405-2015, 2015
Major constrains of the pelagic food web efficiency in the Mediterranean Sea
Summary: The paper deals with the possible constrains that can control carbon fluxes in the Mediterranean Sea and affect the microbial part of the pelagic marine food webs. It is a synthesis and elaboration of more than 80 experiments of predations carried out in the whole Mediterranean Sea and that cover a wide range of trophic conditions. One of the main result is that always microzooplankton feed on prokaryotic components also in eutrophic conditions when of course herbivory prevails.
Biogeosciences Discuss., 12, 4365-4403, doi:10.5194/bgd-12-4365-2015, 2015
Global spatiotemporal distribution of soil respiration modeled using a global database
Biogeosciences Discuss., 12, 4331-4364, doi:10.5194/bgd-12-4331-2015, 2015
Chemical footprints of anthropogenic nitrogen deposition on recent soil C : N ratios in Europe
Summary: Spatial clustering of anthropogenic nitrogen deposition reveals that European C:N ratio varies more across soils of natural ecosystems with low pollution. It turns out that surprisingly only such soils are the most affected by nitrogen accumulation and therefore most responsive to short-term N supply. While an inverse correlation between atmospheric nitrogen and soil C:N seems intuitive, we provide novel insights into the real magnitude and spatial distribution of this relationship since 1880.
Biogeosciences Discuss., 12, 4315-4330, doi:10.5194/bgd-12-4315-2015, 2015
Dinitrogen fixation and dissolved organic nitrogen fueled primary production and particulate export during the VAHINE mesocosms experiment (New Caledonia lagoon)
Biogeosciences Discuss., 12, 4273-4313, doi:10.5194/bgd-12-4273-2015, 2015
Convergent modeling of past soil organic carbon stocks but divergent projections
Summary: Soil carbon models are primary tool to project soil carbon balance under changing environment and management. This study shows that carbon model produces divergent projections although accurate reproduction of measured soil carbon. This projection uncertainty is mainly due to insufficient understanding on microbial processes and soil carbon composition. Climate conditions and land management in terms of carbon input also have significant effects.
Biogeosciences Discuss., 12, 4245-4272, doi:10.5194/bgd-12-4245-2015, 2015
Geographic and seasonal variation of dissolved methane and aerobic methane oxidation in Alaskan lakes
Summary: We assessed the importance of aerobic CH4 oxidation in Alaskan lakes. We conducted field measurement of dissolved CH4 and O2 together with determination of the CH4 oxidation rate. We found that during winter, CH4 oxidation was limited by O2 concentration and during summer, by CH4 concentration. In addition to seasonal variations, the type of permafrost on which the lakes were located was identified as a key factor, indicating that landscape processes play an important role in lake CH4 cycling.
Biogeosciences Discuss., 12, 4213-4243, doi:10.5194/bgd-12-4213-2015, 2015
The 3He flux gauge in the Sargasso Sea: a determination of physical nutrient fluxes to the euphotic zone at the Bermuda Atlantic time series site
Summary: A long-standing enigma in oceanography is the process in which nutrients are supplied to the sunlit zone of the low nutrient regions of the ocean. In this work, we present one approach for quantifying the physical supply of nitrate to the euphotic zone in the Sargasso Sea through the use of gas tracers. We find that the nitrate supplied is more than enough to support the rates of net community production (balance of photosynthesis respiration) observed.
Biogeosciences Discuss., 12, 4183-4211, doi:10.5194/bgd-12-4183-2015, 2015
On the vertical distribution of the chlorophyll a concentration in the Mediterranean Sea: a basin scale and seasonal approach
Summary: The spatio-temporal variability of the vertical distribution of the chlorophyll concentration in the Mediterranean Sea is investigated. Results are based on a large database of fluorescence profiles inter-calibrated from ocean color satellite data. They indicate that two types of chlorophyll seasonality coexist in the Mediterannean Sea. The shape of the chlorophyll profile is very dynamic during winter and the deep chlorophyll maximum is a dominant feature of Mediterranean chlorophyll profile.
Biogeosciences Discuss., 12, 4139-4181, doi:10.5194/bgd-12-4139-2015, 2015
Seagrass meadows as a globally significant carbonate reservoir
Summary: There has been a growing interest in quantifying the capacity of seagrass ecosystems to act as carbon sinks as a natural way of offsetting anthropogenic carbon emissions to the atmosphere. However, most of the efforts have focused on the organic fraction and ignored the inorganic carbon pool. This study offers the first global assessment of the PIC stocks and accumulation rates in seagrass sediments, identifying these ecosystems as important contributors to carbonate dynamics in coastal areas.
Biogeosciences Discuss., 12, 4107-4138, doi:10.5194/bgd-12-4107-2015, 2015
Multiple soil nutrient competition between plants, microbes, and mineral surfaces: model development, parameterization, and example applications in several tropical forests
Biogeosciences Discuss., 12, 4057-4106, doi:10.5194/bgd-12-4057-2015, 2015
The role of watershed characteristics, permafrost thaw, and wildfire on dissolved organic carbon biodegradability and water chemistry in Arctic headwater streams
Biogeosciences Discuss., 12, 4021-4056, doi:10.5194/bgd-12-4021-2015, 2015
Positive trends in organic carbon storage in Swedish agricultural soils due to unexpected socio-economic drivers
Summary: Soil carbon dynamics of the past two decades in Swedish agricultural soils were assessed using three consecutive soil inventories. We found a significant increase in country-wide soil carbon concentrations, which is in contrast to trends reported in neighboring countries. We explained that by a significant rise of the proportion of leys in Swedish agriculture, which was found to be strongly related to the increase in horse population. Human lifestyle can affect soil carbon.
Biogeosciences Discuss., 12, 3991-4019, doi:10.5194/bgd-12-3991-2015, 2015
Changes in dissolved iron deposition to the oceans driven by human activity: a 3-D global modelling study
Summary: The global atmospheric cycle of Fe is simulated accounting for natural and anthropogenic sources, proton and ligand promoted Fe mobilisation from dust aerosol and changes in anthropogenic emissions and thus in atmospheric acidity. Simulations show that Fe-dissolution may have doubled in the last 150 years and is expected to decrease in the future due to air pollution regulations. Projected reductions in dissolved Fe deposition can further limit the primary productivity over HNLC waters.
Biogeosciences Discuss., 12, 3943-3990, doi:10.5194/bgd-12-3943-2015, 2015
A new parameterization for surface ocean light attenuation in Earth System Models: assessing the impact of light absorption by colored detrital material
Summary: Light absorption by colored detrital material (CDM) was included in a fully coupled Earth System Model. Greater light limitation associated with CDM caused biological productivity to move higher up the water column, which increased surface chlorophyll and biomass. Concurrently, total biomass decreased leaving more nutrients in the water. Regional changes were analyzed by comparing the competing factors of diminished light availability and increased nutrient availability on phytoplankton growth.
Biogeosciences Discuss., 12, 3905-3942, doi:10.5194/bgd-12-3905-2015, 2015
Short-term changes of the mesozooplankton community and copepod gut pigment in the Chukchi Sea in autumn
Summary: Zooplankton community showed no clear changes with a strong wind event (SWE) and dominant copepods prepared for diapause. However, the feeding intensity of the copepods increased with the reflection of the temporal phytoplankton bloom, which was enhanced by the SWE. On the other hand, because of the relatively long generation length of copepods, a smaller effect was detected for their abundance, population structure, lipid accumulation and gonad maturation within the short-term period.
Biogeosciences Discuss., 12, 3879-3904, doi:10.5194/bgd-12-3879-2015, 2015
Potential and limitations of finite element modelling in assessing structural integrity of coralline algae under future global change
Summary: Using Finite element modelling (FEM) we show that a simplified geometric FE-model can predict the structural strength of the coralline algal skeleton. We compared a series of 3D geometric FE-models with increasing complexity to a biologically accurate model derived from computed tomography (CT) scan data. Using geometric models provides the basis for a better understanding of the potential effect of climate change on the structural integrity of these organisms.
Biogeosciences Discuss., 12, 3855-3877, doi:10.5194/bgd-12-3855-2015, 2015
Transmissivity of solar radiation within a Picea sitchensis stand under various sky conditions
Summary: We tested the hypothesis that diffuse radiation from cloudy and overcast skies penetrates the canopy more effectively than direct radiation from clear skies. We compared the flux density and spectral properties of direct and diffuse radiation above, within and below a forest stand under sunny, cloudy and overcast conditions in a thinned Sitka spruce forest. We recorded vertical (1m resolution) and horizontal (2.5m resolution) profiles of radiation penetration at 1nm resolution.
Biogeosciences Discuss., 12, 3825-3853, doi:10.5194/bgd-12-3825-2015, 2015
Drivers and uncertainties of future global marine primary production in marine ecosystem models
Summary: We analyze changes of marine net primary production (NPP) and its drivers for the 21st century in 9 marine ecosystem models under the RCP8.5 scenario. NPP decreases in 5 models, increases in 1 model and 3 models show no significant trend. The main drivers include stronger nutrient limitation, but in many models warming-induced increases in phytoplankton growth outbalance the nutrient effect. Temperature-driven increases in grazing and other loss processes cause a net decrease in biomass and NPP.
Biogeosciences Discuss., 12, 3731-3824, doi:10.5194/bgd-12-3731-2015, 2015
Modeling photosynthesis of discontinuous plant canopies by linking Geometric Optical Radiative Transfer model with biochemical processes
Summary: We advance the Geometric Optical Radiative Transfer model and derive analytical solutions to radiation absorption by sunlit/shaded leaves. We link the radiative transfer process with biochemical diffusion process to model canopy photosynthesis. Modeled Gross Primary Production could explain more than 80% variance of flux tower measurements at both hourly and daily scales. Ambient CO2 concentration influences daytime photosynthesis, which needs to be considered in terrestrial ecosystem models.
Biogeosciences Discuss., 12, 3675-3729, doi:10.5194/bgd-12-3675-2015, 2015
Ground cover rice production system facilitates soil carbon and nitrogen stocks at regional scale
Biogeosciences Discuss., 12, 3647-3674, doi:10.5194/bgd-12-3647-2015, 2015
Spatio-temporal analysis of nitrogen cycling in a mixed coniferous forest of the northern United States
Summary: We used stable nitrogen isotopes from red pine trees to determine the history of nitrogen cycling within the Deming Lake watershed at Itasca State Park. With nearly 250 years of data, results suggest a major decline in nitrogen availability in red pine beginning in the early 20th century. We believe this synchronous decline is the result of the fire suppression in the state park, which has allowed the emergence of competing understory species.
Biogeosciences Discuss., 12, 3617-3646, doi:10.5194/bgd-12-3617-2015, 2015
Anthropogenic point and non-point nitrogen inputs into Huai River Basin and their impacts on riverine ammonia-nitrogen flux
Biogeosciences Discuss., 12, 3577-3615, doi:10.5194/bgd-12-3577-2015, 2015
Sediment CO2 efflux from cleared and intact temperate mangroves and tidal flats
Summary: We investigated the impact of temperate mangrove clearance on CO2 efflux from the sediment to the atmosphere. Our results suggest that carbon stored within temperate mangrove sediment is released over a period of years to decades after mangrove clearance. Disturbance of the surface biofilm resulted in elevated CO2 efflux across all habitats, suggesting the important role of surface biofilm communities in mediating CO2 efflux.
Biogeosciences Discuss., 12, 3547-3576, doi:10.5194/bgd-12-3547-2015, 2015
The contribution of tephra constituents during biogenic silica determination: implications for soil and paleoecological studies
Summary: Biogenic silica (BSi) is used as a proxy by soil scientists to identify biological effects on the Si cycle and by paleoecologists to study environmental changes. We show the presence of tephra constituents can make measurements erroneous at low BSi concentrations, with repercussions for soil and paleoecological studies. However, we also show that glass shards do not produce an identical dissolution signal to that of BSi, meaning they can be distinguished with appropriate experimental setups.
Biogeosciences Discuss., 12, 3505-3545, doi:10.5194/bgd-12-3505-2015, 2015
Factors influencing CO2 and CH4 emissions from coastal wetlands in the Liaohe Delta, Northeast China
Biogeosciences Discuss., 12, 3469-3503, doi:10.5194/bgd-12-3469-2015, 2015
Eddy covariance methane flux measurements over a grazed pasture: effect of cows as moving point sources
Biogeosciences Discuss., 12, 3419-3468, doi:10.5194/bgd-12-3419-2015, 2015
Representing northern peatland microtopography and hydrology within the Community Land Model
Biogeosciences Discuss., 12, 3381-3418, doi:10.5194/bgd-12-3381-2015, 2015
Sources and transfer mechanisms of dissolved organic matter during storm and inter-storm conditions in a lowland headwater catchment: constraints from high-frequency molecular data
Summary: The origin of stream dissolved organic matter (DOM) in a lowland headwater catchment was investigated using high frequency sampling combined with chemical biomarkers analysis. Inter-storm stream DOM corresponds to the flushing of soil DOM reservoirs, while storm stream DOM would also result from three additional mechanisms: biofilm destabilization, surface and sub-surface erosion.
Biogeosciences Discuss., 12, 3349-3379, doi:10.5194/bgd-12-3349-2015, 2015
Deriving seasonal dynamics in ecosystem properties of semi-arid savannas using in situ based hyperspectral reflectance
Summary: Relationships between ecosystem properties of semi-arid savanna and reflected solar radiance between 350-1800 nm were investigated. Normalised combinations of reflectance for the near infrared, shortwave infrared, and 600 to 700 nm were strongly affected by solar and viewing angular effects. Ecosystem properties of savannas were strongly correlated to reflectance 350-1800nm, and normalised combinations of reflectance were strong predictors of the savanna ecosystem properties.
Biogeosciences Discuss., 12, 3315-3347, doi:10.5194/bgd-12-3315-2015, 2015
Redox regime shifts in microbially-mediated biogeochemical cycles
Summary: Despite their global importance redox reactions mediated by micro-organisms are often crudely represented in biogeochemical models. We show that including the dynamics of microbial growth in such a model can cause sudden shifts between redox states in response to an environmental change. We identify the conditions required for these redox regime shifts, and predict that they are likely in the modern day sulfur and nitrogen cycles, and potentially the iron cycle in the ancient ocean.
Biogeosciences Discuss., 12, 3283-3314, doi:10.5194/bgd-12-3283-2015, 2015
Living (Rose Bengal stained) benthic foraminiferal faunas along a strong bottom-water oxygen gradient on the Indian margin (Arabian Sea)
Biogeosciences Discuss., 12, 3245-3282, doi:10.5194/bgd-12-3245-2015, 2015
Ideas and Perspectives: On the emission of amines from terrestrial vegetation in the context of atmospheric new particle formation
Summary: In this article we summarise recent science, which shows how airborne amines, specifically methylamines (MAs), play a key role in atmospheric new particle formation (NPF) by stabilising small molecule clusters. Agricultural emissions are assumed to constitute the most important MA source, but given the short atmospheric residence time of MAs, they can hardly have a direct impact on NFP events observed in remote regions. This leads us to the presentation of existing knowledge focussing on natural
Biogeosciences Discuss., 12, 3211-3243, doi:10.5194/bgd-12-3211-2015, 2015
Spatiotemporal patterns of tundra fires: late-Quaternary charcoal records from Alaska
Summary: Tundra fires may have increased as a result of anthropogenic climate change. To evaluate this hypothesis in the context of natural variability, we reconstructed fire history of the late Quaternary in the Alaskan tundra. Fire-return intervals are spatially variable, ranging from 1648 to 6045 years at our sites. The rarity of historical fires implies that increased fire frequency may greatly alter the structure and function of tundra ecosystems.
Biogeosciences Discuss., 12, 3177-3209, doi:10.5194/bgd-12-3177-2015, 2015
Identifying climatic drivers of tropical forest dynamics
Summary: We used a forest dynamic model, calibrated with data from the 20-year study site of Paracou, French Guiana, to test a set of climatic variables on tree growth and mortality probabilities. Severe droughts decreased annual growth and mortality rates, high precipitation increased mortality rates and high temperature decreased tree growth. Best resistance to drought was found for trees with high wood density and for trees with small current diameters.
Biogeosciences Discuss., 12, 3145-3176, doi:10.5194/bgd-12-3145-2015, 2015
Global soil nitrous oxide emissions in a dynamic carbon–nitrogen model
Summary: The response of terrestrial nitrous oxide production to global change is strongly controlled by the response of tropical soils. We show - by applying a new model – that global N2O production is strongly sensitive to temperature, but the sensitivity is dampened if CO2 increase co-occurs.
Biogeosciences Discuss., 12, 3101-3143, doi:10.5194/bgd-12-3101-2015, 2015
Growth and production of the copepod community in the southern area of the Humboldt Current System
Summary: Increasing coastal upwelling in the Humboldt Current is negatively affecting zooplankton biomass and secondary production, as reflected in a gradual decrease in copepod biomass in recent years. A more extended upwelling period causes substantial loss of copepod biomass from the coastal zone due to offshore advection. Excess of upwelling, induced by climate change, may thus negatively impact biological production at lower trophic levels in this highly productive large marine ecosystem.
Biogeosciences Discuss., 12, 3057-3099, doi:10.5194/bgd-12-3057-2015, 2015
Growth response of temperate mountain grasslands to inter-annual variations of snow cover duration
Summary: It is shwon that inter-annual variations in the primary productivity of mountain grasslands are primarily governed by variations in the length of the snow-free period and to a much lesser extent by temperature and precipitation during the growing season. Meteorological variables controlling snow cover dynamics are thus of paramount importance to understand and model the amount and timing of biomass production in mountain pastures.
Biogeosciences Discuss., 12, 3025-3055, doi:10.5194/bgd-12-3025-2015, 2015
Environmental controls on the boron and strontium isotopic composition of aragonite shell material of cultured Arctica islandica
Summary: We report the first high-resolution strontium (87Sr/86Sr and δ88/86Sr) and boron (δ11B) isotopic values in the aragonite shell of cultured Arctica islandica. These results suggest that well-preserved sub-fossil specimens may be use to determine the past Sr isotopic composition of seawater. The δ11B in this experiment suggests that the boron uptake of the shell changes at a temperature threshold of 13 °C and a species-specific fractionation factor may be required for seawater pH reconstructions.
Biogeosciences Discuss., 12, 2979-3023, doi:10.5194/bgd-12-2979-2015, 2015
Monitoring seasonal and diurnal changes in photosynthetic pigments with automated PRI and NDVI sensors
Summary: NDVI and PRI sensors (SRS, Decagon Inc.) exhibited complementary responses during spring photosynthetic activation in evergreen and deciduous stands. In evergreens, PRI was most strongly influenced by changing chlorophyll:carotenoid pool sizes over the several weeks of the study, while it was most affected by xanthophyll cycle pigment activity at the diurnal time scale. These automated PRI and NDVI sensors offer new ways to explore environmental and physiological constraints on photosynthesis.
Biogeosciences Discuss., 12, 2947-2978, doi:10.5194/bgd-12-2947-2015, 2015
Photosynthetic production in the Central Arctic during the record sea-ice minimum in 2012
Biogeosciences Discuss., 12, 2897-2945, doi:10.5194/bgd-12-2897-2015, 2015
Carbon export and transfer to depth across the Southern Ocean Great Calcite Belt
Summary: The transfer of particulate organic carbon (POC) into the deep ocean is an important atmospheric carbon dioxide sink. Concentration and flux measurements from the Southern Ocean Great Calcite Belt region show that the relationship between POC and biogenic mineral fluxes varies with depth, from the surface to 1000 meters below. The results suggest that the transfer of POC into the deep ocean is more closely related to phytoplankton community structure than to mineral composition alone.
Biogeosciences Discuss., 12, 2843-2896, doi:10.5194/bgd-12-2843-2015, 2015
High methane emissions dominate annual greenhouse gas balances 30 years after bog rewetting
Biogeosciences Discuss., 12, 2809-2842, doi:10.5194/bgd-12-2809-2015, 2015
Temperature-dependence of the relationship between pCO2 and dissolved organic carbon in lakes
Summary: The relationship between the pCO2 and DOC concentration was tested in a Tropical area. Unlike the positive relationship reported for lake waters before, we found no significant relationship in our lakes, despite very broad ranges in both pCO2 and DOC. The strength of pCO2 vs. DOC relationships declines with increasing water temperature, suggesting substantial differences in carbon cycling in warm lakes, which must be considered when upscaling limnetic carbon cycling to global scales.
Biogeosciences Discuss., 12, 2787-2808, doi:10.5194/bgd-12-2787-2015, 2015
Modelling the climatic drivers determining photosynthesis and carbon allocation in evergreen Mediterranean forests using multiproxy long time series
Summary: We developed a process-based model for evergreen Mediterranean forests. We used multiproxy data including eddy covariance CO2 flux and annual growth dendrochronological time series. The model explicitly takes into account the influence of climatic variability to calculate photosynthesis and carbon allocation. We analyzed long-time acclimation processes and climatic trade-offs between the C-source and the C-sink. There is much potentiality to apply the model at a larger scale.
Biogeosciences Discuss., 12, 2745-2786, doi:10.5194/bgd-12-2745-2015, 2015
Storage and transformation of organic matter fractions in cryoturbated permafrost soils across the Siberian Arctic
Biogeosciences Discuss., 12, 2697-2743, doi:10.5194/bgd-12-2697-2015, 2015
Capturing optically important constituents and properties in a marine biogeochemical and ecosystem model
Summary: Results are presented from a numerical model that explicitly includes spectral irradiance and optically important water constituents. The model captures 3D biogeochemical, ecosystem and optical observations, including surface reflectance analogous to ocean colour satellite observations. Sensitivity experiments demonstrate the relative importance of each of the water constituents, and the feedbacks between the light field, fitness of phytoplankton types and the biogeochemistry of the ocean.
Biogeosciences Discuss., 12, 2607-2695, doi:10.5194/bgd-12-2607-2015, 2015
Experimental assessment of environmental influences on the stable isotopic composition of Daphnia pulicaria and their ephippia
Summary: We show that the stable (C, N, O) isotopic composition of the water flea Daphnia pulicaria is strongly related to that of the diet (C, N) and the water they live in (O). We also show that the stable isotopic composition of the sheaths of Daphnia resting eggs (ephippia) is indicative of the isotopic composition of Daphnia that produced them. This implies that stable isotope ratios of fossil Daphnia ephippia can provide information on past ecological and climatic developments in and around lakes.
Biogeosciences Discuss., 12, 2573-2606, doi:10.5194/bgd-12-2573-2015, 2015
Changes in soil carbon, nitrogen and phosphorus due to land-use changes in Brazil
Biogeosciences Discuss., 12, 2533-2571, doi:10.5194/bgd-12-2533-2015, 2015
Soil carbon and nitrogen erosion in forested catchments: implications for erosion-induced terrestrial carbon sequestration
Summary: In the southern parts of the Sierra Nevada Mountains in California, we investigated erosion of carbon and nitrogen from low-order catchments. We found that eroded sediments were OM rich, with a potential for significant gaseous and dissolved loss of OM during transport or after depositional in downslope or downstream depositional landform positions.
Biogeosciences Discuss., 12, 2491-2532, doi:10.5194/bgd-12-2491-2015, 2015
Coupled isotopes of plant wax and hemicellulose markers record information on relative humidity and isotopic composition of precipitation
Summary: Stable water isotopes (18O/16O and 2H/1H) are invaluable proxies for paleoclimate research. Here we use a coupled 18O/16O and 2H/1H biomarker approach based on plant-derived sugars and n-alkanes. Applying this innovative approach to a topsoil transect allows (i) calculating the deuterium-excess of leaf water as proxy for relative humidity and (ii) calculating the plant source water isotopic composition (~precipitation). The approach is validated by the presented climate transect results.
Biogeosciences Discuss., 12, 2459-2489, doi:10.5194/bgd-12-2459-2015, 2015
The role of photo- and thermal degradation for CO2 and CO fluxes in an arid ecosystem
Summary: Recent studies have suggested the potential importance of abiotic decomposition (photodegradation) in arid ecosystems. This study focuses on the measurement and understanding of abiotic fluxes. Photodegradation fluxes have not been observed. Thermal degradation fluxes were observed in the field (for CO) and in the laboratory (for CO2). Previous studies have potentially overestimated the role of photodegradation or misinterpreted thermal degradation fluxes as photodegradation fluxes.
Biogeosciences Discuss., 12, 2429-2457, doi:10.5194/bgd-12-2429-2015, 2015
Mesozooplankton structure and functioning during the onset of the Kerguelen phytoplankton bloom during the Keops2 survey
Biogeosciences Discuss., 12, 2381-2427, doi:10.5194/bgd-12-2381-2015, 2015
Technical Note: Cost-efficient approaches to measure carbon dioxide (CO2) fluxes and concentrations in terrestrial and aquatic environments using mini loggers
Summary: Measurements of concentrations and fluxes of carbon dioxide (CO2) are fundamental for our understanding of carbon cycling and greenhouse gas balances. We are presently limited by the high cost of such measurements making it difficult to properly investigate variability in space and time. This study presents measurement approaches that are very resource efficient in terms of equipment cost and measurement labour time, opening new opportunities to advance our knowledge on CO2 across landscapes.
Biogeosciences Discuss., 12, 2357-2380, doi:10.5194/bgd-12-2357-2015, 2015
Relationship between N : P : Si ratio and phytoplankton community composition in a tropical estuarine mangrove ecosystem
Summary: The present work aims at understanding importance of Brzezinski-Redfield ratio as a determinant of natural phytoplankton community composition in a mangrove ecosystem. Results show that nutrient concentrations were intricately balanced that never became limited and complemented well with concept of modified Redfield ratio in study area. Based on microscopy and rbcL sequencing, we show recent concepts of phytoplankton functional traits and elemental stoichiometry also occur in mangrove habitat.
Biogeosciences Discuss., 12, 2307-2355, doi:10.5194/bgd-12-2307-2015, 2015
Assessment of model estimates of land–atmosphere CO2 exchange across Northern Eurasia
Summary: Each year the forests and tundra of Northern Eurasia sequester carbon dioxide (CO2), helping to offset sources to the atmosphere such as fossil fuel emissions. We used results from climate models to better understand the region's land-atmosphere CO2 exchange from 1960-1990. Model estimates were assessed in comparisons to independent ground and satellite measurements. The model suggest the region is storing less carbon over time, and the stored carbon is cycling through soils more quickly.
Biogeosciences Discuss., 12, 2257-2305, doi:10.5194/bgd-12-2257-2015, 2015
The dynamic of annual carbon allocation to wood in European forests is consistent with a combined source-sink limitation of growth: implications for modelling
Summary: We provide an evaluation of the spatio-temporal dynamics of annual carbon allocation to wood in European forests. Our study supports the premise that European forest growth is under a complex control including both source and sink limitations. The relative influences of the different growth drivers strongly vary across years and spatial ecological gradients. We suggest a straightforward modelling framework to implement these combined forest growth limitations into terrestrial biosphere models.
Biogeosciences Discuss., 12, 2213-2255, doi:10.5194/bgd-12-2213-2015, 2015
Seasonal and inter-annual variability in wetland methane emissions simulated by CLM4Me' and CAM-chem and comparisons to observations of concentrations
Biogeosciences Discuss., 12, 2161-2212, doi:10.5194/bgd-12-2161-2015, 2015
Fundamental molecules of life are pigments which arose and evolved to dissipate the solar spectrum
Summary: We show that the fundamental molecules of life (those common to all three domains of life; archea, bacteria, and eukaryote) including nucleotides, amino acids, enzyme cofactors, and porphyrin agglomerates, absorb light strongly from 230 to 280nm (in the UV-C) and have chemical affinity to RNA and DNA. This supports the "thermodynamic dissipation theory for the origin of life" which suggests that life and evolution got its start by dissipating the prevailing Archean UV-C sunlight into heat.
Biogeosciences Discuss., 12, 2101-2160, doi:10.5194/bgd-12-2101-2015, 2015
Patterns and persistence of hydrologic carbon and nutrient export from collapsing upland permafrost
Summary: As high latitudes warm, carbon and nitrogen stored in permafrost soil will be vulnerable to erosion and transport to Arctic streams and rivers. We sampled outflow from 83 permafrost collapse features in Alaska. Permafrost collapse caused substantial increases in dissolved organic carbon and inorganic nitrogen but decreased methane concentration by 90%. Upland thermokarst may be a dominant linkage transferring carbon and nutrients from terrestrial to aquatic ecosystems as the Arctic warms.
Biogeosciences Discuss., 12, 2063-2100, doi:10.5194/bgd-12-2063-2015, 2015
WETCHIMP-WSL: intercomparison of wetland methane emissions models over West Siberia
Summary: We evaluated 21 forward models and 5 inversions over West Siberia, in terms of CH4 emissions and simulated wetland areas and compared these results to an intensive in situ CH4 flux dataset, several wetland maps, and two satellite inundation products. In addition to assembling a definitive collection of methane emissions estimates for the region, we were able to identify the types of wetland maps and model features necessary for accurate simulations of high-latitude wetlands.
Biogeosciences Discuss., 12, 1907-1973, doi:10.5194/bgd-12-1907-2015, 2015
Phosphorus release capacity of soluble P fertilizers and insoluble rock phosphate in response to phosphate solubilizing bacteria and poultry manure and their effect on plant growth promotion and P utilization efficiency of chilli (Capsicum annuum L.)
Summary: P release capacity of soil amended with RP varied between 6.0–11.5mg kg-1 while the soluble P fertilizers i.e. SSP and DAP displayed a maximum of 73 and 68mg P kg-1 at the start of the experiment (day 0). However, the P released tendency from SSP and DAP declined during incubation and at the end 82 and 79% of P initially present had been lost from the mineral pool. Integrated use of PSB and PM with RP in ½RP+½PM+PSB treatment stimulated P mineralization by releasing a maximum of 25mg P kg-1.
Biogeosciences Discuss., 12, 1839-1873, doi:10.5194/bgd-12-1839-2015, 2015
Scaling impacts on environmental controls and spatial heterogeneity of soil organic carbon stocks
Biogeosciences Discuss., 12, 1721-1751, doi:10.5194/bgd-12-1721-2015, 2015
Disruption of metal ion homeostasis in soils is associated with nitrogen deposition-induced species loss in an Inner Mongolia steppe
Summary: We demonstrate that N addition reduced species richness, acidified soil and disturbed nutrient homeostasis in soil in an Inner Mongolia steppe. We further reveal that an increase in inorganic-N concentration, depletion of base cations (Ca2+ and Mg2+) and mobilization of Mn2+ and Cu2+ in soils were involved in reduction in species richness in the temperate steppe of northern China, highlighting the involvment of nutrient mobilization in decline in species richness of alkaline grasslands.
Biogeosciences Discuss., 12, 1689-1719, doi:10.5194/bgd-12-1689-2015, 2015
Seasonality of sea ice controls interannual variability of summertime ΩA at the ice shelf in the Eastern Weddell Sea – an ocean acidification sensitivity study
Summary: As anthropogenic CO2 increases and sea ice dynamics change with climate, understanding the trend in these characteristics of variability in the seasonal drivers of ΩA will become increasingly important. We investigate the major drivers of interannual to seasonal scale variability of ΩA. We show that the critical climate (physical-biogeochemical) sensitivities for ΩA at the Antarctic ice self are the timing and rate of sea ice thaw and the resulting onset and persistence of phytoplankton blooms.
Biogeosciences Discuss., 12, 1653-1687, doi:10.5194/bgd-12-1653-2015, 2015
Assessing the potential of amino acid δ13C patterns as a carbon source tracer in marine sediments: effects of algal growth conditions and sedimentary diagenesis
Summary: A tiny fraction of marine algae escapes decomposition and is buried in sediments, but tools are needed to track the fate of algal organic carbon. We tested whether naturally occurring isotope variability among amino acids from algae and bacteria can be used as source fingerprints. We found that isotope fingerprints track algal amino acid sources with high fidelity across different growth conditions, and that the fingerprints can be used to quantify bacterial amino acids in sediments.
Biogeosciences Discuss., 12, 1613-1651, doi:10.5194/bgd-12-1613-2015, 2015
Impact of seawater carbonate chemistry on the calcification of marine bivalves
Biogeosciences Discuss., 12, 1543-1571, doi:10.5194/bgd-12-1543-2015, 2015
Microbial assemblages on a cold-water coral mound at the SE Rockall Bank (NE Atlantic): interactions with hydrography and topography
Biogeosciences Discuss., 12, 1509-1542, doi:10.5194/bgd-12-1509-2015, 2015
Reconstruction of super-resolution fields of ocean pCO2 and air–sea fluxes of CO2 from satellite imagery in the Southeastern Atlantic
Summary: We have reconstructed maps of air-sea CO2 fluxes at high resolution (4 km) offshore of the Benguela region using Sea Surface Temperature and ocean colour data at this resolution, and CarbonTracker CO2 fluxes data at low resolution (110 km). The inferred representation of pCO2 improves the description provided by CarbonTracker, enhancing the small scale variability. We obtain that not only the resolution, but the inferred pCO2 data itself is closer to in-situ measurements of pCO2.
Biogeosciences Discuss., 12, 1405-1452, doi:10.5194/bgd-12-1405-2015, 2015
Modelling the effect of soil moisture and organic matter degradation on biogenic NO emissions from soils in Sahel rangeland (Mali)
Summary: This study provides seasonal and inter annual variation of biogenic NO emission fluxes in a Sahelian rangeland in Mali, a region where intense NO emissions occur during the wet season. Emissions are related to their biogeochemical origin, to the quantity of biomass, to the quantity of livestock, which drive the N pool and N turnover in the soil. This study gives an insight in the different N inputs to the soil and in N production processes in the soil at the origin of the emission.
Biogeosciences Discuss., 12, 1155-1203, doi:10.5194/bgd-12-1155-2015, 2015
Constraints on the applicability of the organic temperature proxies UK'37, TEX86 and LDI in the subpolar region around Iceland
Summary: This research reports a test the applicability of three organic-derived temperature proxies (UK'37, TEX86 and LDI) at high latitudes around Iceland. A range of samples including suspended particular material (SPM), trapped descending particles and surface sediments were collected for testing the different proxies in the water column and the sediment.The combination of three independent SST organic proxies provided important information about seasonality or differences in habitat depth.
Biogeosciences Discuss., 12, 1113-1153, doi:10.5194/bgd-12-1113-2015, 2015
Carbon stocks and soil sequestration rates of riverine mangroves and freshwater wetlands
Summary: Riverine wetlands of the Pacific coast of Mexico had large ecosystem C stocks (784.5 MgC ha-1 for mangroves, 722.2 MgC ha-1 for peat swamps, and 336.5 MgC ha-1 for marshes). Long-term soil C sequestration values in mangroves were 1.3 ± 0.2 MgC ha-1yr-1. C stocks and soil nitrogen stocks were in general larger for upland compared to lowland mangroves
Biogeosciences Discuss., 12, 1015-1045, doi:10.5194/bgd-12-1015-2015, 2015
GDGT distributions in the East Siberian Sea: implications for organic carbon export, burial and degradation
Summary: Siberian permafrost contains large amounts of organic carbon that may be released by climate warming. We collected and analysed samples from the East Siberian Sea, using GDGT biomarkers to trace the sourcing and deposition of organic carbon across the shelf. We show that branched GDGTs may be used to trace river erosion. Results from modelling show that organic carbon on the shelf is a complex process involving river-derived and coastal-derived material as well as marine carbon production.
Biogeosciences Discuss., 12, 637-674, doi:10.5194/bgd-12-637-2015, 2015
Nutrient and mercury deposition and storage in an alpine snowpack of the Sierra Nevada, USA
Summary: Snowpack and precipitation samples were collected along two elevation gradients in the Tahoe Basin during winter and spring from 2011-2014 to evaluate spatial and temporal deposition patterns of nitrogen, phosphorus, and mercury. Study results reflect the highly dynamic nature of snowpack chemical storage, while basin-wide estimates identify snowpack chemical loading from atmospheric deposition as a substantial source of nutrient and pollutant input to the Lake Tahoe watershed each year.
Biogeosciences Discuss., 12, 593-636, doi:10.5194/bgd-12-593-2015, 2015
Ba, B, and U element partitioning in magnesian calcite skeletons of Octocorallia corals
Summary: The variations of element profiles in biogenic CaCO3 are widely used for identifying differences in biological and physicochemical processes associated with element partitioning. Octocorallia coral skeletons can provide long-term records of environmental conditions in intermediate and deep waters. The change in skeletal Ba/Ca with depth parallels that in the dissolved Ba concentration being linked to ocean nutrient cycling. We did not observe pronounced environmental controls in B/Ca and U/Ca.
Biogeosciences Discuss., 12, 413-444, doi:10.5194/bgd-12-413-2015, 2015
Modeling the global emission, transport and deposition of trace elements associated with mineral dust
Summary: A new technique to determine a size-fractionated global soil elemental emission inventory based on a global soil and a mineralogical datasets is introduced. Spatial variability of mineral dust elemental fractions (8 elements such as Ca,Fe,Al ) is identified on a global scale, particularly for Ca. The ratio of Ca/Al, ranged between 0.1-5.0, and is confirmed as an indicator of dust source regions by global dust model. Total and soluble dust element fluxes into different ocean basins are estimated.
Biogeosciences Discuss., 11, 17491-17541, doi:10.5194/bgd-11-17491-2014, 2014
Lunar periodicity in the shell flux of some planktonic foraminifera in the Gulf of Mexico
Biogeosciences Discuss., 11, 17187-17205, doi:10.5194/bgd-11-17187-2014, 2014
Stable isotope paleoclimatology of the earliest Eocene using kimberlite-hosted mummified wood from the Canadian Subarctic
Summary: The recent discovery of mummified wood (non-petrified) within kimberlite diamond mines in Northwest Territories, Canada, has prompted a paleoclimatic investigation of the time in which the trees grew - the earliest Eocene (ca. 53.3 Ma). Multiple proxy records derived from these samples suggest that during greenhouse climates of the Eocene, subarctic Canada was characterized by high temperatures (+16 C above modern), and multidecadal variability in cloudiness and temperature on 20-30 year cycles.
Biogeosciences Discuss., 11, 16269-16308, doi:10.5194/bgd-11-16269-2014, 2014
Peru upwelling plankton respiration: calculations of carbon flux, nutrient retention efficiency and heterotrophic energy production
Biogeosciences Discuss., 11, 16177-16206, doi:10.5194/bgd-11-16177-2014, 2014
Environmental factors controlling lake diatom communities: a meta-analysis of published data
Summary: I re-analyze information published during the last decades concerning the effect of different environmental predictors on the structure of benthic diatom communities in world lakes, providing a scientific basis for the implementation of new paleoenvironmental inference models. I consider highly relevant the publication of this article in a widely known journal, provided the noticeable demand on paleolimnological meta-studies supporting the use of such biological proxies at a pancontinental scale
Biogeosciences Discuss., 11, 15889-15909, doi:10.5194/bgd-11-15889-2014, 2014
Modelling forest lines and forest distribution patterns with remote sensing data in a mountainous region of semi-arid Central Asia
Biogeosciences Discuss., 11, 14667-14698, doi:10.5194/bgd-11-14667-2014, 2014