Open ocean dead zones in the tropical North Atlantic Ocean
Summary: This study is the first report of the formation of dead zones in the open ocean. A combination of multiple ocean observing system elements (mooring, floats, satellites, ships) allowed us to reconstruct the generation of the dead zones and to connect the formation to enhanced respiration within mesoscale ocean eddies. The dead zones present specific threats to the ecosystem, such as the interruption of the diurnal migration of zooplankters.
Biogeosciences, 12, 2597-2605, doi:10.5194/bg-12-2597-2015, 2015
Soil moisture and land use are major determinants of soil microbial community composition and biomass at a regional scale in northeastern China
Biogeosciences, 12, 2585-2596, doi:10.5194/bg-12-2585-2015, 2015
Audit of the global carbon budget: estimate errors and their impact on uptake uncertainty
Biogeosciences, 12, 2565-2584, doi:10.5194/bg-12-2565-2015, 2015
Eutrophication mitigation in rivers: 30 years of trends in spatial and seasonal patterns of biogeochemistry of the Loire River (1980–2012)
Summary: Based on large, long-term and high-quality data sets, this study describes the mitigation of eutrophication in the Loire River basin since 1980. Reducing direct phosphate inputs in the early 1990s has led to a significant decrease in algal biomass although Corbicula spp. clams invaded the river during this period and have probably played a significant role in phytoplankton decline. A powerful trend and seasonality analysis showed that these changes considerably affected river biogeochemistry.
Biogeosciences, 12, 2549-2563, doi:10.5194/bg-12-2549-2015, 2015
Large-eddy simulations of surface roughness parameter sensitivity to canopy-structure characteristics
Summary: We used large-eddy simulations to test the sensitivity of roughness parameters to characteristics of canopy structure. We found that displacement height scaled with maximum canopy height, aerodynamic canopy height with maximum canopy height and leaf area index, and eddy-penetration depth with gap fraction. Using a decade of observations, we found that fixed parameterizations of roughness performed well but that empirical approaches that incorporated canopy structure preformed even better.
Biogeosciences, 12, 2533-2548, doi:10.5194/bg-12-2533-2015, 2015
First on-line isotopic characterization of N2O above intensively managed grassland
Biogeosciences, 12, 2517-2531, doi:10.5194/bg-12-2517-2015, 2015
Modelling the response of yields and tissue C : N to changes in atmospheric CO2 and N management in the main wheat regions of western Europe
Biogeosciences, 12, 2489-2515, doi:10.5194/bg-12-2489-2015, 2015
Large fluxes and rapid turnover of mineral-associated carbon across topographic gradients in a humid tropical forest: insights from paired 14C analysis
Summary: We used measurements of radiocarbon to model the decomposition of organic matter associated with minerals in tropical rainforest soils, using contemporary and archived samples. Most organic matter decomposed over 11 to 26 years, while a smaller portion decomposed over centuries. Rates were similar among soils with strongly differing physical and chemical properties, but declined with a proxy for oxygen limitation. Previous models based on one time point may underestimate decomposition rates.
Biogeosciences, 12, 2471-2487, doi:10.5194/bg-12-2471-2015, 2015
Corrigendum to "Boron incorporation in the foraminifer Amphistegina lessonii under a decoupled carbonate chemistry" published in Biogeosciences, 12, 1753–1763, 2015
Biogeosciences, 12, 2469-2469, doi:10.5194/bg-12-2469-2015, 2015
Changes of the CO2 and CH4 production potential of rewetted fens in the perspective of temporal vegetation shifts
Summary: In this paper, the CO2 and CH4 production due to the subaqueous decomposition of the five most abundant plant species, which are considered to be representative of different rewetting stages, will be presented. Beside continuous gas flux measurements, bulk chemical analyses of plant tissue were performed to gain insights into changing litter characteristics. With respect to temporal vegetation shifts in rewetted fens, the results provide new insights into the climate effect of these ecosystems.
Biogeosciences, 12, 2455-2468, doi:10.5194/bg-12-2455-2015, 2015
Dynamics of greenhouse gases (CO2, CH4, N2O) along the Zambezi River and major tributaries, and their importance in the riverine carbon budget
Summary: CO2 and CH4 concentrations and fluxes in the Zambezi River basin are well below the median/average values reported previously for tropical rivers, streams and reservoirs, and mainly controlled by the connectivity with floodplains and the presence of waterfalls and man-made reservoirs. The mass balance suggests that carbon transport to the ocean represents the major component (~60%) of the budget, while emissions to the atmosphere account for less than 40% of the total carbon yield.
Biogeosciences, 12, 2431-2453, doi:10.5194/bg-12-2431-2015, 2015
Reconciling single-chamber Mg / Ca with whole-shell δ18O in surface to deep-dwelling planktonic foraminifera from the Mozambique Channel
Summary: In this paper we present, for the first time, results from single-chamber Mg/Ca analyses combined with single-shell δ18O and δ13C for four planktonic foraminiferal species from a sediment trap in the Mozambique Channel. Eddy-induced hydrographic variability is reflected in test carbonate chemistry of these different species. A species-specific depth-resolved mass balance model confirms distinctive migration and calcification patterns for each species as a function of hydrography.
Biogeosciences, 12, 2411-2429, doi:10.5194/bg-12-2411-2015, 2015
Phytoplankton dynamics in contrasting early stage North Atlantic spring blooms: composition, succession, and potential drivers
Biogeosciences, 12, 2395-2409, doi:10.5194/bg-12-2395-2015, 2015
Nitrate limitation and ocean acidification interact with UV-B to reduce photosynthetic performance in the diatom Phaeodactylum tricornutum
Biogeosciences, 12, 2383-2393, doi:10.5194/bg-12-2383-2015, 2015
Biogeochemical variability in the central equatorial Indian Ocean during the monsoon transition
Summary: In 2010, a first-of-its-kind deployment of biological sensors on a mooring in the central Indian Ocean revealed interesting variability in chlorophyll (a proxy for ocean productivity) at timescales of about 2 weeks. Using the mooring data with satellite observations and a biogeochemical model, it was determined that local wind mixing and entrainment, rather than mixed Rossby gravity waves, were likely responsible for much of the observed variability.
Biogeosciences, 12, 2367-2382, doi:10.5194/bg-12-2367-2015, 2015
Corrigendum to "Global cropland monthly gross primary production in the year 2000" published in Biogeosciences, 11, 3871–3880, 2014
Biogeosciences, 12, 2365-2366, doi:10.5194/bg-12-2365-2015, 2015
Glacial meltwater and primary production are drivers of strong CO2 uptake in fjord and coastal waters adjacent to the Greenland Ice Sheet
Summary: The Greenland Ice Sheet releases large amounts of freshwater, which strongly influences the biogeochemistry of the adjacent fjord systems and continental shelves. Here we present seasonal observations of the carbonate system in the surface waters of a west Greenland tidewater outlet glacier fjord. Our data reveal a permanent undersaturation of CO2 in the surface layer of the entire fjord and adjacent shelf, creating a high annual uptake of 65gCm-2yr-1.
Biogeosciences, 12, 2347-2363, doi:10.5194/bg-12-2347-2015, 2015
Predicting the denitrification capacity of sandy aquifers from in situ measurements using push–pull 15N tracer tests
Biogeosciences, 12, 2327-2346, doi:10.5194/bg-12-2327-2015, 2015
On the use of the post-closure methods uncertainty band to evaluate the performance of land surface models against eddy covariance flux data
Summary: The energy balance of eddy covariance (EC) flux data is normally not closed. Therefore, EC flux data are usually post-closed, i.e. the measured turbulent fluxes are adjusted so as to close the energy balance. We propose to use in model evaluation the post-closure method uncertainty band (PUB) to account for the uncertainty in EC data originating from lacking energy balance closure. Working with only a single post-closing method might result in severe misinterpretations in model-data comparison.
Biogeosciences, 12, 2311-2326, doi:10.5194/bg-12-2311-2015, 2015
Fossilized bioelectric wire – the trace fossil Trichichnus
Biogeosciences, 12, 2301-2309, doi:10.5194/bg-12-2301-2015, 2015
Carbon exchange between the atmosphere and subtropical forested cypress and pine wetlands
Summary: Carbon dioxide exchange (NEE) between the atmosphere and forested subtropical wetlands is quantified at three locations for 2 years. Each forested wetland showed net carbon uptake (retained in the soil and biomass or transported laterally via overland flow) from the atmosphere both monthly and annually. Changes in NEE were clearly a function of seasonality in solar insolation, air temperature and flooding, which suppressed heterotrophic soil respiration.
Biogeosciences, 12, 2285-2300, doi:10.5194/bg-12-2285-2015, 2015
Characterization of particulate organic matter in the Lena River delta and adjacent nearshore zone, NE Siberia – Part 2: Lignin-derived phenol compositions
Biogeosciences, 12, 2261-2283, doi:10.5194/bg-12-2261-2015, 2015
Effects of CO2 and iron availability on rbcL gene expression in Bering Sea diatoms
Biogeosciences, 12, 2247-2259, doi:10.5194/bg-12-2247-2015, 2015
Organic-matter quality of deep permafrost carbon – a study from Arctic Siberia
Summary: Climatic warming is affecting permafrost, including decomposition of organic matter (OM). However, quantitative data for the quality of OM and its availability for decomposition is limited. We analyzed the quality of OM in late Pleistocene (Yedoma) and Holocene (thermokarst) deposits. A lack of depth trends reveals a constant quality of OM showing that permafrost acts like a freezer, preserving OM quality. This OM will be susceptible to decomposition under climatic warming.
Biogeosciences, 12, 2227-2245, doi:10.5194/bg-12-2227-2015, 2015
Global analysis of seasonality in the shell flux of extant planktonic Foraminifera
Biogeosciences, 12, 2207-2226, doi:10.5194/bg-12-2207-2015, 2015
Radiative forcing bias of simulated surface albedo modifications linked to forest cover changes at northern latitudes
Biogeosciences, 12, 2195-2205, doi:10.5194/bg-12-2195-2015, 2015
A simple optical index shows spatial and temporal heterogeneity in phytoplankton community composition during the 2008 North Atlantic Bloom Experiment
Summary: The ratio of simple optical properties measured from underwater autonomous platforms, such as floats and gliders, is used as a new tool for studying phytoplankton distribution in the North Atlantic Ocean. The resolution that optical instruments carried by autonomous platforms provide allows us to study phytoplankton patchiness and its drivers in the oceanic systems.
Biogeosciences, 12, 2179-2194, doi:10.5194/bg-12-2179-2015, 2015
Distribution of PAHs and the PAH-degrading bacteria in the deep-sea sediments of the high-latitude Arctic Ocean
Biogeosciences, 12, 2163-2177, doi:10.5194/bg-12-2163-2015, 2015
Impact of seawater [Ca2+] on the calcification and calciteMg / Ca of Amphistegina lessonii
Summary: A culture study with the benthic foraminifer Amphistegina lessonii was conducted at varying seawater [Ca2+] and constant [Mg2+]. Results showed optimum growth rates and test thickness at ambient seawater Mg/Ca and a calcite Mg/Ca which is controlled by the relative seawater ratio. Results support the conceptual biomineralization model by Nehrke et al. (2013); however, our refined flux-based model suggests transmembrane transport fractionation that is slightly weaker than expected.
Biogeosciences, 12, 2153-2162, doi:10.5194/bg-12-2153-2015, 2015
Reconstruction of secular variation in seawater sulfate concentrations
Summary: Seawater sulfate concentrations are closely related to the oxygenation history of Earth's surface environment. We develop two approaches for quantification of ancient seawater sulfate concentrations based on the sulfur isotopic composition of pyrite and carbonate-associated sulfur (CAS). Our analysis indicates low seawater sulfate (<5mM) at 635 million years ago, rising in a stepwise manner to near-modern levels (~20-30mM) by about 250 million years ago.
Biogeosciences, 12, 2131-2151, doi:10.5194/bg-12-2131-2015, 2015
Modeling the impact of agricultural land use and management on US carbon budgets
Biogeosciences, 12, 2119-2129, doi:10.5194/bg-12-2119-2015, 2015
Greenhouse gas exchange of rewetted bog peat extraction sites and a Sphagnum cultivation site in northwest Germany
Biogeosciences, 12, 2101-2117, doi:10.5194/bg-12-2101-2015, 2015
Using O2 to study the relationships between soil CO2 efflux and soil respiration
Biogeosciences, 12, 2089-2099, doi:10.5194/bg-12-2089-2015, 2015
Methanotrophy within the water column of a large meromictic tropical lake (Lake Kivu, East Africa)
Biogeosciences, 12, 2077-2088, doi:10.5194/bg-12-2077-2015, 2015
Numerical analysis of the primary processes controlling oxygen dynamics on the Louisiana shelf
Summary: Our study suggests that a combination of physical processes and sediment oxygen consumption determine the spatial extent and temporal dynamics of hypoxia on the Louisiana shelf. In summer, stratification isolates oxygen-rich surface waters from hypoxic bottom waters; oxygen outgasses to the atmosphere at this time. A large fraction of primary production occurs below the pycnocline in summer, but this primary production does not strongly affect the spatial extent of hypoxic bottom waters.
Biogeosciences, 12, 2063-2076, doi:10.5194/bg-12-2063-2015, 2015
Inorganic carbon dynamics of melt-pond-covered first-year sea ice in the Canadian Arctic
Summary: We investigated the evolution of inorganic carbon within landfast sea ice in Resolute Passage during the spring and summer melt period. Low TA and TCO2 concentrations observed in sea ice and brine were associated with the percolation of meltwater from melt ponds. Meltwater was continuously supplied to the ponds which prevented melt ponds from fully equilibrating with the atmospheric CO2 concentration, promoting a continuous uptake of CO2 from the atmosphere.
Biogeosciences, 12, 2047-2061, doi:10.5194/bg-12-2047-2015, 2015
Flux variations and vertical distributions of siliceous Rhizaria (Radiolaria and Phaeodaria) in the western Arctic Ocean: indices of environmental changes
Biogeosciences, 12, 2019-2046, doi:10.5194/bg-12-2019-2015, 2015
The combined effects of nitrification inhibitor and biochar incorporation on yield-scaled N2O emissions from an intensively managed vegetable field in southeastern China
Summary: New nitrification inhibitor CP (chlorinated pyridine) application caused a significant decrease in yield-scaled N2O emissions in an intensively managed vegetable field, while biochar amendment had no significant influence on cumulative N2O emissions but significantly decreased soil pH and yield-scaled N2O emissions. Overall, taking environmental and economic benefits into consideration, CP application in the vegetable field was the best procedure for reducing the yield-scaled N2O emissions.
Biogeosciences, 12, 2003-2017, doi:10.5194/bg-12-2003-2015, 2015
Biostratigraphic evidence for dramatic Holocene uplift of Robinson Crusoe Island, Juan Fernández Ridge, SE Pacific Ocean
Biogeosciences, 12, 1993-2001, doi:10.5194/bg-12-1993-2015, 2015
Fe and C co-limitation of heterotrophic bacteria in the naturally fertilized region off the Kerguelen Islands
Biogeosciences, 12, 1983-1992, doi:10.5194/bg-12-1983-2015, 2015
Marine sources of bromoform in the global open ocean – global patterns and emissions
Biogeosciences, 12, 1967-1981, doi:10.5194/bg-12-1967-2015, 2015
The contribution of zooplankton faecal pellets to deep-carbon transport in the Scotia Sea (Southern Ocean)
Summary: In the Scotia Sea, the zooplankton community shifting from a herbivorous to omnivorous diet strongly influences the chance of faecal pellets to reach the bottom. Faecal pellet flux was mainly a product of the vertically migrating and deeper-dwelling zooplankton in the iron-fertilized and iron-limited region respectively. The results demonstrate that the behaviour of the zooplankton community plays a critical role in controlling the quantity and quality of carbon exported in this area.
Biogeosciences, 12, 1955-1965, doi:10.5194/bg-12-1955-2015, 2015
Riparian and in-stream controls on nutrient concentrations and fluxes in a headwater forested stream
Summary: Terrestrial inputs are considered the major driver of longitudinal patterns of nutrient concentration. Yet we show that longitudinal trends result from hydrological mixing with terrestrial inputs and in-stream processes. We challenge the idea that nutrient concentrations decrease downstream when in-stream net uptake is high. Conversely, in-stream processes can strongly affect stream nutrient chemistry and fluxes even in the absence of consistent longitudinal trends in nutrient concentration.
Biogeosciences, 12, 1941-1954, doi:10.5194/bg-12-1941-2015, 2015
Dissolved greenhouse gases (nitrous oxide and methane) associated with the naturally iron-fertilized Kerguelen region (KEOPS 2 cruise) in the Southern Ocean
Biogeosciences, 12, 1925-1940, doi:10.5194/bg-12-1925-2015, 2015
Poor correlation between phytoplankton community growth rates and nutrient concentration in the sea
Summary: We question here is whether phytoplankton community growth rates respond to nutrient concentration in a similar manner to phytoplankton species composing the community, that is, following Monod's model. In situ marine community growth rates in relation to nutrient concentration and the behaviour of a simple multi-species community model show that community growth rate does not follow Monod's model. We observed here that this can be explained as a consequence of change in size structure.
Biogeosciences, 12, 1915-1923, doi:10.5194/bg-12-1915-2015, 2015
Technical Note: Methionine, a precursor of methane in living plants
Summary: Plants are known as a source of methane (CH4), but the biochemical mechanisms involved in CH4 formation are still unknown. Employing 13C-labelled methionine clearly identified the sulfur-bound methyl group of methionine as a carbon precursor of CH4 released from lavender plants. When relating CH4 emission rates to dark respiration of intact plants, we found a molar CH4:CO2 emission ratio of 2.0 ±1.1 (pmol:µmol). After physical stress CH4 release rates greatly increased.
Biogeosciences, 12, 1907-1914, doi:10.5194/bg-12-1907-2015, 2015
Microbial iron uptake in the naturally fertilized waters in the vicinity of the Kerguelen Islands: phytoplankton–bacteria interactions
Summary: In this manuscript, we present the results of iron uptake measured in the naturally iron-fertilized area during the Kerguelen Ocean and Plateau compared Study 2 cruise (KEOPS2). Iron uptake by bulk community and several size fractions (microplankton, pico-nanoplankton and bacteria) are presented, compared and discussed in the present paper. This work also presents first investigations on the potential competition between bacteria and phytoplankton for access to iron.
Biogeosciences, 12, 1893-1906, doi:10.5194/bg-12-1893-2015, 2015
Carbon dioxide transport across the hillslope–riparian–stream continuum in a boreal headwater catchment
Summary: Carbon dioxide transport between the terrestrial and aquatic systems was dominated by export from the near-stream riparian zone. Over the year, riparian export was highest during autumn storms and the spring snowmelt event. This resulted in high downstream export during these periods with vertical evasion from the stream surface accounting for 60% of the total stream water export, highlighting the importance of evasion to carbon export via the aquatic conduit.
Biogeosciences, 12, 1881-1892, doi:10.5194/bg-12-1881-2015, 2015
Multi-isotope labelling of organic matter by diffusion of 2H/18O-H2O vapour and 13C-CO2 into the leaves and its distribution within the plant
Summary: We present a new technique to label organic matter (OM) at its place of formation by the application of 13C, 18O and 2H through the gaseous phase. The label diffused into leaves was incorporated into assimilates and was detected in plant tissues. This technique can be applied in soil sciences, e.g. to trace the decomposition pathways of soil OM inputs, or in plant physiology and palaeoclimatic reconstruction, e.g. to further investigate the origin of the 18O and 2H signal in tree ring cellulose.
Biogeosciences, 12, 1865-1879, doi:10.5194/bg-12-1865-2015, 2015
Pyrogenic carbon from tropical savanna burning: production and stable isotope composition
Summary: Around half of all pyrogenic carbon (charcoal+soot) derived from wildfires comes from semi-annual burning of tropical savannas. This pyrogenic carbon is significant because it is a component of global aerosols capable of modulating the greenhouse effect and is resistant to degradation. We use controlled field burns in northern Australian savannas to determine how much pyrogenic carbon is formed, how much of this is recalcitrant and how it is partitioned between ground residues and airborne soot.
Biogeosciences, 12, 1849-1863, doi:10.5194/bg-12-1849-2015, 2015