Seasonal hydrology drives rapid shifts in the flux and composition of dissolved and particulate organic carbon and major and trace ions in the Fraser River, Canada
Summary: This study presents seasonal cycles of organic matter concentration and composition in the Fraser River. Dissolved organic matter patterns are linked to flushing of shallow soil layers during spring snowmelt and fall rain events. The preliminary Hg data set indicates significant changes in concentrations during the spring freshet. Organic carbon export, as both area-normalized yield and the proportion of basin primary productivity, in the Fraser River is typical of large rivers globally.
Biogeosciences, 12, 5597-5618, doi:10.5194/bg-12-5597-2015, 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, 12, 5583-5596, doi:10.5194/bg-12-5583-2015, 2015
The biogeochemical structuring role of horizontal stirring: Lagrangian perspectives on iron delivery downstream of the Kerguelen Plateau
Summary: Field campaigns are instrumental in providing ground truth for understanding and modeling global ocean biogeochemical budgets. A survey however can only inspect a fraction of the global oceans, typically a region hundreds of kilometers wide for a temporal window of the order of (at most) several weeks. In this spatiotemporal domain, mesoscale variability can mask climatological contrasts. Here we propose the use of multisatellite-based Lagrangian diagnostics to solve this issue.
Biogeosciences, 12, 5567-5581, doi:10.5194/bg-12-5567-2015, 2015
Sharp ecotones spark sharp ideas: comment on "Structural, physiognomic and above-ground biomass variation in savanna–forest transition zones on three continents – how different are co-occurring savanna and forest formations?" by Veenendaal et al. (2015)
Summary: Remote sensing studies indicate that tropical forest and savanna can be alternative stable states maintained by a feedback between tree cover and fire. Veenendaal et al. (2015) attempted to refute this hypothesis with an extensive field study of the vegetation structure and soil conditions at forest–savanna transition zones. With a re-analysis of their data and a conceptual model, we show that in fact the results agree with the idea of forest–savanna bistability.
Biogeosciences, 12, 5563-5566, doi:10.5194/bg-12-5563-2015, 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 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 from remineralisation rates.
Biogeosciences, 12, 5547-5562, doi:10.5194/bg-12-5547-2015, 2015
Responses of soil microbial communities and enzyme activities to nitrogen and phosphorus additions in Chinese fir plantations of subtropical China
Summary: We examined how N and P addition influenced soil microbial community composition and enzyme activities in subtropical China. The results showed that C and N cycling enzymes were more sensitive to nutrient additions than P cycling enzymes and Gram-positive bacteria were most closely related to soil nutrient cycling enzymes. Combined additions of N and P fertilizer are recommended to promote soil fertility and microbial activity in this kind of plantation.
Biogeosciences, 12, 5537-5546, doi:10.5194/bg-12-5537-2015, 2015
Seasonal variation in grass water content estimated from proximal sensing and MODIS time series in a Mediterranean Fluxnet site
Biogeosciences, 12, 5523-5535, doi:10.5194/bg-12-5523-2015, 2015
Technical Note: Towards resolving in situ, centimeter-scale location and timing of biomineralization in calcareous meiobenthos – the calcein–osmotic pump method
Summary: We present an innovative method using osmotic pumps and the fluorescent marker calcein to help identify where and when calcareous bottom-dwelling organisms mineralize in sediments. These organisms, and their geochemical signatures in their carbonate, are the ocean’s storytellers helping us understand past marine conditions. For many species, the timing and location of their calcite growth is not known. Knowing this will enable us to reconstruct past marine environments with greater accuracy.
Biogeosciences, 12, 5515-5522, doi:10.5194/bg-12-5515-2015, 2015
Air–sea CO2 fluxes in the East China Sea based on multiple-year underway observations
Summary: We report the most comprehensive data set of surface seawater pCO2 and air-sea CO2 fluxes in the East China Sea (ECS) based on 24 surveys conducted in 2006-2011. We categorized the ECS into five different domains characterized by different physics and biogeochemistry to better characterize the seasonality of the pCO2 dynamics and to better constrain the CO2 flux. The annual average CO2 influx into the entire ECS shelf was 6.9+/-4.0 mmol m-2 d-1, about twice the global average in an ocean margin.
Biogeosciences, 12, 5495-5514, doi:10.5194/bg-12-5495-2015, 2015
Impact of earthworm Lumbricus terrestris living sites on the greenhouse gas balance of no-till arable soil
Summary: The impact of earthworms on the greenhouse gas emissions has received much attention recently. We studied the importance of the earthworm Lumbricus terrestris on the emissions in no-till arable soil, both in the field and in the laboratory. The results suggest that L. terrestris can markedly regulate the effects of cultivation practises on the global warming potential of arable soil and that high N2O emissions observed in no-till soils can partly be explained by its abundance.
Biogeosciences, 12, 5481-5493, doi:10.5194/bg-12-5481-2015, 2015
Comparative study of vent and seep macrofaunal communities in the Guaymas Basin
Summary: The absence of biogeographic barrier between seep and vent ecosystems in the Guaymas Basin offers the opportunity to assess the role of environmental conditions in the distribution of macrofaunal communities. Our results showed that community structure was primarily shaped by common abiotic factors. In addition, a high number of common species were shared, suggesting frequent connections between the two ecosystems. Overall, this study supports the hypothesis of a continuum among vents and seeps.
Biogeosciences, 12, 5455-5479, doi:10.5194/bg-12-5455-2015, 2015
Oxygen minimum zones in the tropical Pacific across CMIP5 models: mean state differences and climate change trends
Summary: We analyze simulations of the Pacific Ocean oxygen minimum zones (OMZs) from 11 Earth system model contributions to the Coupled Model Intercomparison Project Phase 5, focusing on the mean state, climate change projections, and interannual variability. We analyse biases with respect to observations and consistency of results across simulations.
Biogeosciences, 12, 5429-5454, doi:10.5194/bg-12-5429-2015, 2015
A comparison of benthic foraminiferal Mn / Ca and sedimentary Mn / Al as proxies of relative bottom-water oxygenation in the low-latitude NE Atlantic upwelling system
Summary: We highlight the proxy potential of foraminiferal Mn/Ca determined by secondary ion mass spectrometry and flow-through inductively coupled plasma optical emission spectroscopy for recording changes in bottom-water oxygen conditions. Comparisons with Mn sediment bulk measurements from the same sediment core largely agree with the results. High foraminiferal Mn/Ca occurs in samples from times of high productivity export and corresponds with the benthic foraminiferal faunal composition.
Biogeosciences, 12, 5415-5428, doi:10.5194/bg-12-5415-2015, 2015
Natural and anthropogenic methane fluxes in Eurasia: a mesoscale quantification by generalized atmospheric inversion
Biogeosciences, 12, 5393-5414, doi:10.5194/bg-12-5393-2015, 2015
Dynamics of air–sea CO2 fluxes in the northwestern European shelf based on voluntary observing ship and satellite observations
Biogeosciences, 12, 5371-5391, doi:10.5194/bg-12-5371-2015, 2015
Comment on "Solute-specific scaling of inorganic nitrogen and phosphorus uptake in streams" by Hall et al. (2013)
Summary: Hall et al. (2013) presented a synthesis of 969 nutrient tracer experiments and used a scaling method to test the hypothesis that nutrient demand is constant with increasing stream size. In this comment we present a reanalysis of a subset of the data used by Hall et al. (2013) and propose that their correlations between nutrient uptake lengths and specific discharge are inadvertently spurious. Therefore, the conclusions derived from such correlations are debatable.
Biogeosciences, 12, 5365-5369, doi:10.5194/bg-12-5365-2015, 2015
Tree water relations can trigger monoterpene emissions from Scots pine stems during spring recovery
Summary: Boreal coniferous trees emit plenty of volatile monoterpenes into the atmosphere. At our measurement site in Finland, we found a springtime relation between the high monoterpene emission from Scots pine stem and tree water relations. Hence, we suggest that the transient monoterpene burst may be a consequence of the spring recovery of the stem and that the dominant processes and environmental drivers triggering the monoterpene emissions are different between pine stems and foliage.
Biogeosciences, 12, 5353-5363, doi:10.5194/bg-12-5353-2015, 2015
Responses of leaf traits to climatic gradients: adaptive variation versus compositional shifts
Summary: By analysing the quantitative leaf-traits along extensive temperature and moisture gradients with generalized linear models, we found that metabolism-related traits are universally acclimated to environmental conditions, rather than being fixed within plant functional types. The results strongly support a move towards Dynamic Global Vegetation Models in which continuous, adaptive trait variation provides the fundamental mechanism for changes in ecosystem properties along environmental gradients.
Biogeosciences, 12, 5339-5352, doi:10.5194/bg-12-5339-2015, 2015
Latitudinal and temporal distributions of diatom populations in the pelagic waters of the Subantarctic and Polar Frontal zones of the Southern Ocean and their role in the biological pump
Summary: Diatom and major components of the flux collected by two sediment traps in subantarctic and polar frontal zones were studied. Despite significant differences in the composition and magnitude of the flux, POC flux was similar between sites. The development of a group of bloom-forming diatoms during summer led to the formation of aggregates and enhanced POC export. Our results suggest that high biogenic silica accumulation rates should be interpreted as a proxy for iron-limited diatom assemblages.
Biogeosciences, 12, 5309-5337, doi:10.5194/bg-12-5309-2015, 2015
Derivation of greenhouse gas emission factors for peatlands managed for extraction in the Republic of Ireland and the United Kingdom
Summary: We quantified carbon dioxide emissions from drained peat extraction sites in the Republic of Ireland and the United Kingdom and also measured a range of greenhouse gases that are released to the atmosphere with the burning of peat. Our derived carbon dioxide emission factors were considerably lower than those derived by the IPCC, which has major implications for National Inventory reporting under the United Nations Framework Convention on Climate Change (UNFCCC) and the Kyoto Protocol.
Biogeosciences, 12, 5291-5308, doi:10.5194/bg-12-5291-2015, 2015
Iron encrustations on filamentous algae colonized by Gallionella-related bacteria in a metal-polluted freshwater stream
Summary: We studied filamentous macroscopic algae growing in metal-rich stream water that leaked from a former uranium-mining district. These algae were encrusted with Fe-deposits that were associated with microbes, mainly Gallionella-related Fe-oxidizing bacteria, and extracellular polymeric substances. Algae with a lower number of chloroplasts often exhibited discontinuous series of precipitates, likely due to the intercalary growth of algae which allowed them to avoid detrimental encrustation.
Biogeosciences, 12, 5277-5289, doi:10.5194/bg-12-5277-2015, 2015
Seasonal methane accumulation and release from a gas emission site in the central North Sea
Biogeosciences, 12, 5261-5276, doi:10.5194/bg-12-5261-2015, 2015
Ocean acidification does not affect magnesium composition or dolomite formation in living crustose coralline algae, Porolithon onkodes in an experimental system
Biogeosciences, 12, 5247-5260, doi:10.5194/bg-12-5247-2015, 2015
Reconstruction of super-resolution 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) in the offshore Benguela region using sea surface temperature and ocean colour data and CarbonTracker CO2 fluxes data at low resolution (110 km). The inferred representation of pCO2 improves the description provided by CarbonTracker, enhancing small-scale variability. We find that the resolution, as well as the inferred pCO2 data itself, is closer to in situ measurements of pCO2.
Biogeosciences, 12, 5229-5245, doi:10.5194/bg-12-5229-2015, 2015
Controls on terrestrial carbon feedbacks by productivity versus 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, 12, 5211-5228, doi:10.5194/bg-12-5211-2015, 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, 12, 5199-5210, doi:10.5194/bg-12-5199-2015, 2015
Assessing net community production in a glaciated Alaskan fjord
Biogeosciences, 12, 5185-5198, doi:10.5194/bg-12-5185-2015, 2015
The greenhouse gas balance of a drained fen peatland is mainly controlled by land-use rather than soil organic carbon content
Biogeosciences, 12, 5161-5184, doi:10.5194/bg-12-5161-2015, 2015
Environmental forcing does not induce diel or synoptic variation in the carbon isotope content of forest soil respiration
Summary: Soil respiration and its stable isotopes were studied in a subalpine forest. There was strong diel variability in soil efflux but not in the isotope content of soil efflux or CO2 from biological activity in the soil. Following rain, soil efflux increased, but the isotope content of these fluxes did not change. Temporal variation in the isotope content of soil efflux was unrelated to environmental variables. Results confirmed established theory regarding diffusive soil gas transport.
Biogeosciences, 12, 5143-5160, doi:10.5194/bg-12-5143-2015, 2015
The Measuring Ammonia in Nature (MAN) network in the Netherlands
Biogeosciences, 12, 5133-5142, doi:10.5194/bg-12-5133-2015, 2015
Quantifying the biological impact of surface ocean light attenuation by colored detrital matter in an ESM using a new optical parameterization
Summary: Light absorption by colored detrital material (CDM) was included in a fully coupled Earth system model. Chlorophyll and biomass increased near the surface but decreased at greater depths when CDM was included. 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, 12, 5119-5132, doi:10.5194/bg-12-5119-2015, 2015
Downward particle flux and carbon export in the Beaufort Sea, Arctic Ocean; the role of zooplankton
Summary: POC fluxes obtained in the Eastern Beaufort Sea in August 2009 from drifting sediment traps were low (1-15 mg C m-2d-1), compared to long-term data which show higher but variable fluxes (10-40 mg C m-2d-1). Composition of sinking particles, especially faecal pellets, highlighted the role of the zooplankton community and its trophic structure in the transition of carbon from the productive surface zone to the deep ocean. Carbon flux at this season results from a heterotrophic driven ecosystem.
Biogeosciences, 12, 5103-5117, doi:10.5194/bg-12-5103-2015, 2015
Response of respiration and nutrient availability to drying and rewetting in soil from a semi-arid woodland depends on vegetation patch and a recent wildfire
Biogeosciences, 12, 5093-5101, doi:10.5194/bg-12-5093-2015, 2015
Effects of fluctuating hypoxia on benthic oxygen consumption in the Black Sea (Crimean shelf)
Biogeosciences, 12, 5075-5092, doi:10.5194/bg-12-5075-2015, 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, 12, 5061-5074, doi:10.5194/bg-12-5061-2015, 2015
The influence of C3 and C4 vegetation on soil organic matter dynamics in contrasting semi-natural tropical ecosystems
Summary: We demonstrate and explain differential patterns in SOM dynamics in C3/C4 mixed ecosystems at various spatial scales across contrasting climate and soils. This study shows that the interdependence between biotic and abiotic factors ultimately determines whether SOM dynamics of C3- and C4-derived vegetation are at variance in ecosystems where both vegetation types coexist. The results also highlight the far-reaching implications that vegetation thickening may have for the stability of deep SOM.
Biogeosciences, 12, 5041-5059, doi:10.5194/bg-12-5041-2015, 2015
On the vertical distribution of the chlorophyll a concentration in the Mediterranean Sea: a basin-scale and seasonal approach
Summary: The spatiotemporal variability in the vertical distribution of the chlorophyll concentration in the Mediterranean Sea is investigated. Results are based on a large database of fluorescence profiles intercalibrated from ocean color satellite data. They indicate that two types of chlorophyll seasonality coexist in the Mediterranean 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, 12, 5021-5039, doi:10.5194/bg-12-5021-2015, 2015
Living (Rose-Bengal-stained) benthic foraminiferal faunas along a strong bottom-water oxygen gradient on the Indian margin (Arabian Sea)
Biogeosciences, 12, 5005-5019, doi:10.5194/bg-12-5005-2015, 2015
Seagrass meadows as a globally significant carbonate reservoir
Summary: There has been 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 PIC stocks and accumulation rates in seagrass sediments, identifying these ecosystems as important contributors to carbonate dynamics in coastal areas.
Biogeosciences, 12, 4993-5003, doi:10.5194/bg-12-4993-2015, 2015
Assessing the potential of amino acid 13C 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. Since 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 diagnostic 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 sediment.
Biogeosciences, 12, 4979-4992, doi:10.5194/bg-12-4979-2015, 2015
Factors influencing CO2 and CH4 emissions from coastal wetlands in the Liaohe Delta, Northeast China
Summary: Coastal wetlands vegetated by common reed and rice paddies emit significant amounts of methane to the atmosphere whereas sea-blite marshes are net sinks for atmospheric methane. The main controlling factors for the methane emissions are water table, temperature, soil organic carbon and salinity. The methane emissions from coastal wetlands can be reduced by creating fluctuating water tables, including water tables below the soil surface, as well as by occasional flooding by high-salinity water.
Biogeosciences, 12, 4965-4977, doi:10.5194/bg-12-4965-2015, 2015
Biogeochemistry of a large and deep tropical lake (Lake Kivu, East Africa: insights from a stable isotope study covering an annual cycle
Biogeosciences, 12, 4953-4963, doi:10.5194/bg-12-4953-2015, 2015
Reconsidering the role of carbonate ion concentration in calcification by marine organisms
Summary: Calcification by marine organisms reacts to changing seawater carbonate chemistry, but it is unclear which components of the carbonate system drive the observed response. This study uncovers proportionalities between different carbonate chemistry parameters. These enable us to understand why calcification often correlates well with carbonate ion concentration, and they imply that net CaCO3 formation in high latitudes is not more vulnerable to ocean acidification than formation in low latitudes.
Biogeosciences, 12, 4939-4951, doi:10.5194/bg-12-4939-2015, 2015
Fundamental molecules of life are pigments which arose and co-evolved as a response to the thermodynamic imperative of dissipating the prevailing solar spectrum
Summary: We show that the fundamental molecules of life (those common to all three domains of life: Archaea, Bacteria, Eukaryota), 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 arose and evolved as a response to dissipating the prevailing Archaean UV-C sunlight into heat.
Biogeosciences, 12, 4913-4937, doi:10.5194/bg-12-4913-2015, 2015
Macroalgae contribute to nested mosaics of pH variability in a subarctic 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, 12, 4895-4911, doi:10.5194/bg-12-4895-2015, 2015
Are recent changes in sediment manganese sequestration in the euxinic basins of the Baltic Sea linked to the expansion of hypoxia?
Biogeosciences, 12, 4875-4894, doi:10.5194/bg-12-4875-2015, 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 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, 12, 4861-4874, doi:10.5194/bg-12-4861-2015, 2015
Multi-molecular tracers of terrestrial carbon transfer across the pan-Arctic: comparison of hydrolyzable components with plant wax lipids and lignin phenols
Summary: Currently very few studies have examined the distribution and fate of hydrolyzable organic carbon (OC) in Arctic sediments, whose fate remains unclear in the context of climate change. Our study focuses on the source, distribution and fate of hydrolyzable OC as compared with plant wax lipids and lignin phenols in the sedimentary particles of nine Arctic and sub-Arctic rivers. This multi-molecular approach allows for a comprehensive investigation of terrestrial OC transfer via Arctic rivers.
Biogeosciences, 12, 4841-4860, doi:10.5194/bg-12-4841-2015, 2015
Ground cover rice production systems increase soil carbon and nitrogen stocks at regional scale
Summary: We demonstrate for the first time that a ground cover rice production system (GCRPS) significantly increased soil organic C and total N stocks at spatially representative paired sites under varying edaphic conditions. Our results suggest that GCRPS is a stable and sustainable technique that maintains key soil functions, while increasing rice yield and expanding the cultivation into regions where it has been hampered by low seasonal temperatures and/or a lack of irrigation water.
Biogeosciences, 12, 4831-4840, doi:10.5194/bg-12-4831-2015, 2015
Preface: Climate extremes and biogeochemical cycles in the terrestrial biosphere: impacts and feedbacks across scales
Biogeosciences, 12, 4827-4830, doi:10.5194/bg-12-4827-2015, 2015