Co-variation of metabolic rates and cell-size in coccolithophores
Summary: Metabolic rates and cell-size in coccolithophore algae co-vary consistently in a large number of separate culture experiments as temperature, irradiance, nutrient and pCO2 conditions change. These changes are comparable to the changes in cell size observed in the natural environment, both in the modern ocean and in marine sediments. Changes in coccolithophore cell size in the field will help understand how this key phytoplancton species reacts to climate change.
Biogeosciences Discuss., 12, 6215-6284, doi:10.5194/bgd-12-6215-2015, 2015
New insights into the organic carbon export in the Mediterranean Sea from 3-D modeling
Summary: The dissolved fraction of organic carbon has already been identified as a major source of carbon at depth in the Mediterranean Sea, however export estimation from observations are scarce. We developped a coupling between an hydrodynamical simulation (NEMO-MED12) and a biogeochemical model (Eco3M-MED) to provide at Basin scale an evaluation of organic carbon export, its variability and its form. Dissolved organic carbon appears to be dominant in most regions, especially in the Eastern Basin.
Biogeosciences Discuss., 12, 6147-6213, doi:10.5194/bgd-12-6147-2015, 2015
The Measuring Ammonia in Nature (MAN) network in the Netherlands
Biogeosciences Discuss., 12, 6115-6146, doi:10.5194/bgd-12-6115-2015, 2015
Dam tailwaters compound the effects of reservoirs on the longitudinal transport of organic carbon in an arid river
Summary: Dams impact river reaches. Upstream of dams, reservoirs transform terrestrial organic carbon and produce authochthonous – derived organic carbon. In addition, tailwater reaches below dams may produce and export similar amounts of organic carbon as stored behind dams. Our work demonstrates that not only do reservoirs need to be considered for their capacity to store and transform organic carbon, but also the combined impact of their tailwater ecosystems should to be considered as well.
Biogeosciences Discuss., 12, 6081-6114, doi:10.5194/bgd-12-6081-2015, 2015
Probing the past 30 year phenology trend of US deciduous forests
Summary: We performed model inter-comparison and selected best model capturing the spatial and temporal variations of observations to predict trend of forest phenology over the past 3 decades. Our results show that phenological trends, which are dominantly driven by temperature changes, are not uniform over the contiguous U.S., with a significant spring advance in the East, an autumn delay in the Northeast and West, but no evidence of change elsewhere.
Biogeosciences Discuss., 12, 6037-6080, doi:10.5194/bgd-12-6037-2015, 2015
Inter-decadal changes in the intensity of the Oxygen Minimum Zone off Concepción, Chile (~ 36° S) over the last century
Biogeosciences Discuss., 12, 6003-6035, doi:10.5194/bgd-12-6003-2015, 2015
Comment on "Solute specific scaling of inorganic nitrogen and phosphorus uptake in streams" by Hall et al. (2013)
Biogeosciences Discuss., 12, 5991-6001, doi:10.5194/bgd-12-5991-2015, 2015
Model estimates of climate controls on pan-Arctic wetland methane emissions
Summary: We used a process-based model to investigate the sensitivities of pan-Arctic wetland methane emissions to climate factors, as a function of climate. Over the period 1960-2006, temperature was the dominant driver of trends in emissions. Wetlands north of 60N were temperature-limited, and wetlands south of 60N latitude were water-limited. Projected future warming will cause water-limited wetlands to expand northward over the next century, lessening the role of temperature in the future.
Biogeosciences Discuss., 12, 5941-5989, doi:10.5194/bgd-12-5941-2015, 2015
Quantifying the influence of CO2 seasonality on future ocean acidification
Summary: Our results show that accounting for oceanic CO2 seasonality is crucial to projecting the future onset of critical ocean acidification levels (i.e. aragonite under-saturation). In particular, seasonality will bring forward the initial onset of month-long under-saturation by a global average of 17 years. Importantly, wide-spread under-saturation is projected to occur once atmospheric CO2 reaches 486ppm in the North Pacific and 511ppm in the Southern Ocean, independent of emissions scenario.
Biogeosciences Discuss., 12, 5907-5940, doi:10.5194/bgd-12-5907-2015, 2015
Influence of wood density in tree-ring based annual productivity assessments and its errors in Norway spruce
Summary: Annual variations in wood density partially compensated ring width variations in Picea abies. If neglected, annual biomass increment was underestimated by up to 15%. The relative prediction interval of plot-level annual biomass increment ranged from 20 to 40%. The uncertainty related to the allometric models parameters were about 10% only. The errors related to variations in wood density were much larger, the biggest component being the variability between trees.
Biogeosciences Discuss., 12, 5871-5905, doi:10.5194/bgd-12-5871-2015, 2015
Optimising methodology for determining the effect of ocean acidification on bacterial extracellular enzymes
Summary: pH has a significant effect on the artificial fluorophore for glucosidase and protease activity, while artificial aminopeptidase substrate alters the pH of seawater. Reduction of coastal seawater pH to 7.8 was shown to increase β-glucosidase activity rapidly (0.5h), while no significant response was detected for leucine aminopeptidase. Seawater acidified by bubbling CO2 gas resulted in elevated β-glucosidase activity and bacterial cell numbers, although seasonal effects were observed.
Biogeosciences Discuss., 12, 5841-5870, doi:10.5194/bgd-12-5841-2015, 2015
Environmental drivers of drought deciduous phenology in the Community Land Model
Summary: We compared monthly leaf area index (LAI) estimates from the Community Land Model (CLM) in stress/drought deciduous regions of the world to a satellite derived estimate of LAI. This comparison revealed an issue in the CLM in which leaves begin to grow during the dry season due to unrealistic soil water movement. We introduced a rainfall trigger to the stress deciduous algorithm to address this issue, then showed the impacts of this change on the fire cycle and stored carbon.
Biogeosciences Discuss., 12, 5803-5839, doi:10.5194/bgd-12-5803-2015, 2015
Controls on terrestrial carbon feedbacks by productivity vs. turnover in the CMIP5 Earth System Models
Summary: Terrestrial carbon feedbacks are a large uncertainty in climate change. We separate modeled feedback responses into those governed by changed carbon inputs (productivity) and changed outputs (turnover). The disaggregated responses show that both are important in controlling inter-model uncertainty. Interactions between productivity and turnover are also important, and research must focus on these interactions for more accurate projections of carbon cycle feedbacks.
Biogeosciences Discuss., 12, 5757-5801, doi:10.5194/bgd-12-5757-2015, 2015
Seasonal characterization of CDOM for lakes in semi-arid regions of Northeast China using excitation-emission matrices fluorescence and parallel factor analysis (EEM-PARAFAC)
Summary: Our results of this study show that 1) Two humic-like peaks C and two protein-like B and T peaks were identified using PARAFAC in CDOM for lakes in Northeast China; 2)The average fluorescence intensity of the four components differed with seasonal variation; 3) Components 1 and 2 exhibited strong linear correlation (R2=0.633); 4)There were significantly positive linear relationships between CDOM absorption coefficients and Fmax; 5)A significant relationship (R2=0.931) was found between salinity
Biogeosciences Discuss., 12, 5725-5756, doi:10.5194/bgd-12-5725-2015, 2015
Linking dissolved organic matter composition to metal bioavailability in agricultural soils: effect of anionic surfactants
Summary: Irrigation with greywater can increase the risk of metal toxicity to plants and soil organisms due to the presence of anionic surfactants derived from household products. Three agricultural soils were treated with anionic surfactants and the total concentration of soluble metal increased. However, that was accompanied by the solubilisation of soil organic compounds that bind metals and yield complexes of low bioavailability, which substantially reduces the potential risk of metal toxicity.
Biogeosciences Discuss., 12, 5697-5723, doi:10.5194/bgd-12-5697-2015, 2015
Dynamics of air–sea CO2 fluxes in the North-West European Shelf based on Voluntary Observing Ship (VOS) and satellite observations
Biogeosciences Discuss., 12, 5641-5695, doi:10.5194/bgd-12-5641-2015, 2015
Effects of flooding on organic carbon consumption in the East China Sea
Biogeosciences Discuss., 12, 5609-5639, doi:10.5194/bgd-12-5609-2015, 2015
Halocarbon emissions and sources in the equatorial Atlantic Cold Tongue
Summary: This manuscript covers the first measurements of CHBr3, CH2Br2 and CH3I from the equatorial Atlantic during the Cold Tongue season, identifying this region and season as a source for these compounds. For the first time, we calculated diapycnal fluxes, and showed that the fluxes from below the mixed layer to the surface are not sufficient to balance the mixed layer budget. Hence, we conclude that mixed layer production has to take place despite a pronounced sub-mixed-layer-maximum.
Biogeosciences Discuss., 12, 5559-5608, doi:10.5194/bgd-12-5559-2015, 2015
Estimation of nutrient contributions from the ocean across a river basin using stable isotope analysis
Summary: Recycling of total nitrogen (TN) from the ocean to river basin ecosystems has been actively investigated. Previous studies demonstrated that marine-derived nutrients (MDN) play a large role in river ecosystems. However, little research has been devoted to understanding the contribution of runs of salmon to MDN across the entire river basin. Therefore we conducted field experiments to understand the recycling of TN from the ocean across an entire river basin using stable isotope analysis.
Biogeosciences Discuss., 12, 5535-5557, doi:10.5194/bgd-12-5535-2015, 2015
Seasonal variation in vegetation water content estimated from proximal sensing and MODIS time series in a Mediterranean Fluxnet site
Biogeosciences Discuss., 12, 5503-5533, doi:10.5194/bgd-12-5503-2015, 2015
Is average chain length of plant lipids a potential proxy for vegetation, environment and climate changes?
Biogeosciences Discuss., 12, 5477-5501, doi:10.5194/bgd-12-5477-2015, 2015
Mitigation of agriculture emissions in the tropics: comparing forest land-sparing options at the national level
Summary: Emission from agriculture-driven deforestation can be mitigated by reducing the expansion of agriculture into forests through intensification and utilizing non-forested land for agriculture. Climate smart agriculture can reduce emissions from existing agricultural land. Tropical countries which are priorities for action, can be identified by assessing the mitigation potential of these interventions, by assessing capacity for implementation and the risks associated with these approaches.
Biogeosciences Discuss., 12, 5435-5475, doi:10.5194/bgd-12-5435-2015, 2015
Reconstructing European forest management from 1600 to 2010
Summary: Studying century-scale ecological processes and their legacy effects requires accounting for forest management. In this study we produce spatially and temporally explicit maps of European forest management from 1600 to 2010. The most important changes between 1600 and 2010 are: an increase of 593 000km2 in conifers at the expense of deciduous forest, a 612 000km2 decrease in unmanaged forest, a 152 000km2 decrease in coppice management, and a 818 000km increase in high stand management.
Biogeosciences Discuss., 12, 5365-5433, doi:10.5194/bgd-12-5365-2015, 2015
Responses of N2O flux to water level fluctuation and other environmental factors at littoral zone of Miyun Reservoir: a comparison with CH4 fluxes
Biogeosciences Discuss., 12, 5333-5363, doi:10.5194/bgd-12-5333-2015, 2015
Evidence for biological shaping of hair ice
Summary: We investigated an unusual ice type, called hair ice. It grows on the surface of dead wood of broad-leaf trees at temperatures slightly below 0°C.We describe this phenomenon and present our biological, physical and chemical investigations to gain insight in the properties and processes related to hair ice: we found, that a winter-acive fungus in the wood is required. Ice segregation is the common mechanism. Chemical analyses show a complex mixture of several thousand lignin/ tannin compounds.
Biogeosciences Discuss., 12, 5293-5332, doi:10.5194/bgd-12-5293-2015, 2015
Detection and attribution of global change effects on river nutrient dynamics in a large Mediterranean basin
Summary: Nitrate and dissolved phosphate concentration time-series (1980-2011) from 50 sampling stations across a large Mediterranean river basin were analyzed using Dynamic Factor Analysis and complementary methods in order to disentangle the role of hydrology, land-use practices, and global climatic phenomena on nutrient patterns, with the overall aim of understanding how the different aspects of global change affected nutrient dynamics in the basin.
Biogeosciences Discuss., 12, 5259-5291, doi:10.5194/bgd-12-5259-2015, 2015
The greenhouse gas balance of a drained fen peatland is mainly controlled by land-use rather than soil organic carbon content
Biogeosciences Discuss., 12, 5201-5258, doi:10.5194/bgd-12-5201-2015, 2015
Links between surface productivity and deep ocean particle flux at the Porcupine Abyssal Plain (PAP) sustained observatory
Summary: This study uses observations from both a mooring at the surface and a sediment trap at around 3000m in the northeast Atlantic. Observations of nitrogen and carbon are used to calculate the seasonal net community production (NCP) and new production, and we find that there is a larger uptake of carbon than would traditionally be expected. Only a small fraction of the surface production reaches the sediment trap, and using a particle-tracking approach we find that the source regions vary widely.
Biogeosciences Discuss., 12, 5169-5199, doi:10.5194/bgd-12-5169-2015, 2015
Air–sea CO2 fluxes in the East China Sea based on multiple-year underway observations
Biogeosciences Discuss., 12, 5123-5167, doi:10.5194/bgd-12-5123-2015, 2015
Predicting landscape-scale CO2 flux at a pasture and rice paddy with long-term hyperspectral canopy reflectance measurements
Summary: This research used a long-term dataset of near-surface canopy hyperspectral reflectance collected over five years to test the ability of these measurements to predict ecosystem carbon flux at a pasture and rice paddy in the California Delta, USA. We determined that each reflectance sampling event best captured the integrated prior week of carbon dioxide uptake, providing an important benchmark for understanding the lagged correlation between ecosystem carbon uptake and biochemical reflectance.
Biogeosciences Discuss., 12, 5079-5122, doi:10.5194/bgd-12-5079-2015, 2015
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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