bluuebunny/crossref_metadata_2025 huggingface dataset:
Global direct aerosol radiative forcing, as constrained by comprehensive observations
Authors: Chung Chul E. , Chu Jung-Eun , Lee Yunha , van Noije Twan , Jeoung Hwayoung , Ha Kyung-Ja , Marks Marguerite
Published: January 2016

Abstract. Aerosols directly affect the radiative balance of the Earth through absorption and scattering of solar radiation. Although the contributions of absorption (heating) and scattering (cooling) of sunlight have proved difficult to quantify, the consensus is that anthropogenic aerosols cool the climate, partially offsetting the warming by rising greenhouse gas concentrations. Recent estimates of global direct aerosol radiative forcing are −0.35 ± 0.5 Wm−2, and these estimates depend either entirely or heavily on aerosol simulation. Here, we integrate a comprehensive suite of satellite and ground-based observations to constrain total AOD, its fine-mode fraction, the vertical distribution of aerosols and clouds, and the co-location of clouds and overlying aerosols. We find that fine-mode forcing is −0.46 Wm−2 (−0.54 ~ −0.39 Wm−2). Fine-mode aerosols include sea salt and dust aerosols, and we find that these natural aerosols pose a very large cooling (−0.44 ~ −0.26 Wm−2) when constrained by observations. When the contribution of these natural aerosols is subtracted from the fine-mode forcing, the net becomes −0.10 (−0.28 ~ +0.05) Wm−2. The net forcing arises from carbonaceous, sulfate and nitrate aerosols. Despite uncertainties in the anthropogenic fraction of these aerosols, this −0.28 ~ +0.05 Wm−2 range compels the direct aerosol forcing to be near zero.
Chemical and meteorological influences on the lifetime of NO3 at a semirural mountain site during "PARADE"
Authors: Sobanski N. , Tang M. J. , Thieser J. , Schuster G. , Pöhler D. , Fischer H. , Song W. , Sauvage C. , Williams J. , Fachinger J. , Berkes F. , Hoor P. , Platt U. , Lelieveld J. , Crowley J. N.
Published: January 2016

Abstract. Through measurements of NO2, O3, and NO3 during the PARADE campaign (PArticles and RAdicals, Diel observations of mEchanisms of oxidation) in the German Taunus mountains we derive nighttime, steady state lifetimes (τss) of NO3 and N2O5. During some nights, high NO3 (~ 200 pptv) and N2O5 (~ 1 ppbv) mixing ratios are associated with values of τss that exceeded one hour for NO3 and three hours for N2O5 near the ground. Such long boundary layer lifetimes for NO3 and N2O5 are usually only encountered in very clean/unreactive air masses whereas the PARADE measurement site is impacted by both biogenic emissions from the surrounding forest and anthropogenic emissions from the nearby urbanized/industrialised centres. Measurement of several trace gases which are reactive towards NO3 indicate that the inferred lifetimes are significantly longer than those calculated from the summed loss rate. Several potential causes for the apparently extended NO3 and N2O5 lifetimes are examined, including additional routes to formation of NO3 and the presence of a low-lying residual layer. Overall, the most likely cause of the anomalous lifetimes are related to the meteorological conditions, though additional NO3 formation due to reactions of Criegee intermediates may contribute.
A framework for accurate, long-term, global and high resolution observations of tropospheric H2O-δD pairs – a MUSICA review
Authors: Schneider M. , Wiegele A. , Barthlott S. , González Y. , Christner E. , Dyroff C. , García O. E. , Hase F. , Blumenstock T. , Sepúlveda E. , Mengistu Tsidu G. , Takele Kenea S. , Rodríguez S. , Andrey J.
Published: January 2016

Abstract. Abstract. In the lower/middle troposphere H2O-δD pairs are good proxies for moisture pathways, however their observation is challenging. The project MUSICA (MUlti-platform remote Sensing of Isotopologues for investigating the Cycle of Atmospheric water) addresses this challenge by integrating remote sensing with in-situ measurement techniques. The aim is to retrieve accurate tropospheric H2O-δD pairs from the middle infrared spectra measured from ground by the FTIR (Fourier Transform InfraRed) spectrometers of the NDACC (Network for the Detection of Atmospheric Composition Change) and the thermal nadir spectra measured by IASI (Infrared Atmospheric Sounding Interferometer) aboard the MetOp satellites. In this paper we review the MUSICA framework, present the ﬁnal MUSICA products, and outline the NDACC/FTIR’s and METOP/IASI’s potential for observing accurate and consistent H2O-δD data pairs. First, we brieﬂy resume the particularities of an H2O-δD pair retrieval. Second, we show that the remote sensing data of the ﬁnal product version are absolutely calibrated with respect to H2O and δD in-situ proﬁle references measured in the subtropics, between 0 and 7 km. Third, we empirically demonstrate that the calibrated remote sensing H2O-δD pairs can identify different lower/middle tropospheric moisture pathways and advert to the risk of misinterpretations caused by an incorrect processing of such remote sensing data. Fourth, we reveal that the different sensors (NDACC/FTIR instruments, MetOp/IASI-A, and MetOp/IASI-B) provide consistent H2O-δD pairs for very distinct atmospheric clear sky conditions. Fifth, we document the unique possibilities of the NDACC/FTIR instruments for providing long-term records (important for climatological studies) and of the MetOp/IASI sensors for observing diurnal signals on quasi global scale and with high horizontal resolution.
The performance and the characterization of Laser Ablation Aerosol Particle Time-of-Flight Mass Spectrometry (LAAP-ToF-MS)
Authors: Gemayel Rachel , Hellebust Stig , Temime-Roussel Brice , Hayeck Nathalie , Van Elteren Johannes T. , Wortham Henri , Gligorovski Sasho
Published: January 2016

Abstract. Hyphenated laser ablation-mass spectrometry instruments have been recognized as useful analytical tools for the detection and chemical characterization of aerosol particles. Here we describe the performances of a Laser Ablation Aerosol Particle-Time-of-Flight Mass Spectrometer (LAAP-ToF-MS) which was designed for aerodynamic particle sizing using two 405 nm scattering lasers and characterization of the chemical composition of single aerosol particle via ablation/ionization by a 193 nm excimer laser and detection in a bipolar time-of flight mass spectrometer with a mass resolving power of m/Δm > 600. A laboratory based optimization strategy is described for the development of an analytical methodology for characterization of atmospheric particles using the LAAP-ToF-MS instrument in combination with a particle generator, a differential mobility analyzer and an optical particle counter. We investigated the influence of a suite of variables (particle number concentration, particle size and particle composition on the detection efficiency). The detection efficiency is a product of the scattering efficiency of the laser diodes and the ionization efficiency or hit rate of the excimer laser. The scattering efficiency was found to vary between 0.6 and 1.9 % with an average of 1.1 %; the relative standard deviation (RSD) was 17.0 %. The hit rate exhibited an excellent repeatability with an average value of 63 % and an RSD of 18 %. In addition to laboratory tests, ambient air was sampled by LAAP-ToF-MS during a period of six days at the campus of Aix-Marseille University, situated in the city center of Marseille, France. The optimized LAAP-ToF-MS methodology enables high temporal resolution measurements of the chemical composition of ambient particles, provides new insights into environmental science, and a new investigative tool for atmospheric chemistry and physics, aerosol science and health impact studies.
A surface reflectance scheme for retrieving aerosol optical depth over urban surfaces in MODIS dark target retrieval algorithm
Authors: Gupta P. , Levy R. C. , Mattoo S. , Remer L. A. , Munchak L. A.
Published: January 2016

Abstract. The MODerate resolution Imaging Spectroradiometer (MODIS) instruments, aboard two Earth Observing Satellites (EOS) Terra and Aqua, provide aerosol information with nearly daily global coverage at moderate spatial resolution (10 km and 3 km). Almost 15 years of aerosol data records are now available from MODIS that can be used for various climate and air quality applications. However, the application of MODIS aerosol products for air quality concerns is limited by a reduction in retrieval accuracy over urban surfaces. Here, in this study, we address the inaccuracies produced by the MODIS dark target algorithm (MDT) Aerosol Optical Depth (AOD) retrievals over urban areas and suggest improvements by modifying the surface reflectance scheme in the algorithm. By integrating MODIS land surface reflectance and land cover type information into the aerosol surface parameterization scheme for urban areas, much of the issues associated with the standard algorithm have been mitigated for our test region, the Continental United States (CONUS). The new surface scheme takes into account the change in under lying surface type and is only applied for MODIS pixels with urban percentage (UP) larger than 20%. Over the urban areas where the new scheme has been applied (UP > 20 %), the number of AOD retrievals falling within expected error (EE %) has increased by 20 %, and the strong positive bias against ground-based sunphotometry has been eliminated. However, we note that the new retrieval introduces a small negative bias for AOD values less than 0.1, due to ultra sensitivity of the AOD retrieval to the surface parameterization under low atmospheric aerosol loadings. Global application of the new urban surface parameterization appears promising, but further research and analysis are required before global implementation.
Benchmark campaign and case study episode in Central Europe for development and assessment of advanced GNSS tropospheric models and products
Authors: Douša J. , Dick G. , Kačmařík M. , Brožková R. , Zus F. , Brenot H. , Stoycheva A. , Möller G. , Kaplon J.
Published: January 2016

Abstract. Initial objectives and design of the Benchmark campaign organized within the European COST Action ES1206 (2013-2017) are described in the paper. This campaign has aimed at supporting the development and validation of advanced GNSS tropospheric products, in particular high-resolution and ultra-fast zenith total delays (ZTD) and tropospheric gradients derived from a dense permanent network. A complex dataset was collected for the 8-week period when several extreme heavy precipitation episodes occurred in central Europe which caused severe river floods in this area. An initial processing of data sets from Global Navigation Satellite System (GNSS) and numerical weather models (NWM) provided independently estimated reference parameters – zenith tropospheric delays and tropospheric horizontal gradients. Their provision gave an overview about the product similarities and complementarities and thus a potential for improving a synergy in their optimal exploitations in future. Reference GNSS and NWM results were inter-compared and visually analysed using animated maps. ZTDs from two reference GNSS solutions compared to global ERA-Interim re-analysis resulted in the accuracy at the 10-millimeter level in terms of RMS (with a negligible overall bias), comparisons to global GFS forecast showed accuracy at the 12-millimeter level with the overall bias of -5 mm and, finally, comparisons to mesoscale ALADIN-CZ forecast resulted in the accuracy at the 8-milllimetre level with a negligible total bias. The comparison of horizontal tropospheric gradients from GNSS and NWM data demonstrated a very good agreement among independent solutions with negligible biases and the accuracy of about 0.5 mm. Visual comparisons of maps of zenith wet delays and tropospheric horizontal gradients showed very promising results for future exploitations of advanced GNSS tropospheric products in meteorological applications such as severe weather event monitoring and weather nowcasting. The GNSS products revealed a capability of providing more detailed structures in atmosphere than the state-of-the-art numerical weather models are able to capture. Initial study on contribution of hydrometeors (e.g. cloud water, ice or snow) to GNSS signal delays during severe weather reached up to 17 mm in zenith path delay and suggested to carefully account them within the functional model. The reference products will be further exploited in various specific studies using the Benchmark dataset. It is thus going to play a key role in these highly inter-disciplinary developments towards better mutual benefits from advanced GNSS and meteorological products.
Exploring the potential of the RPA system SUMO for multi-purpose boundary layer missions during the BLLAST campaign
Authors: Reuder Joachim , Båserud Line , Jonassen Marius O. , Kral Stephan , Müller Martin
Published: January 2016

Abstract. In June and July 2011 the RPA system SUMO performed a total number of 299 scientific ﬂights during the BLLAST campaign in Southern France. Three different types of missions have been performed, vertical proﬁling of the mean meteorological parameters temperature, humidity and wind, horizontal surveys of the surface temperature and horizontal transects for the estimation of turbulence. The manuscript provides an introduction to the corresponding SUMO operations, including regulatory issues, and the coordination of manned and unmanned airborne operations for boundary layer research that have been pioneered during the BLLAST campaign. The main purpose of the SUMO ﬂight strategy was atmospheric proﬁling in high temporal resolution. A total of 168 proﬁle ﬂights have been performed during the campaign with typically more than 10 ﬂights per Intensive Observational Period (IOP) day. The collected data allow for a detailed study of boundary layer structure and dynamics and will in the future also be used for further analysis, e.g. the determination of proﬁles of sensible and latent heat ﬂuxes. First tests of a corresponding method have shown very promising results and have provided surface ﬂux values in close agreement with those from ground based eddy-covariance measurements. In addition 74 horizontal surveys of the IR emission of the surface have been performed at altitudes of around 65 m. Each of those surveys covers typically an area of around 1 km and allows for an estimation of the surface temperature variability, an important information for the assessment of the heterogeneity of the surface forcing as function of soil and vegetation properties. The comparison with other surface temperature measurements shows that the raw data of the airborne and ground observations can differ considerably, but that even a very simple multiple regression method can reduce those differences to a large degree. Finally also 49 ﬂight missions for the measurement of velocity variance have been realized during the BLLAST campaign. For that SUMO has been equipped with a 5 hole probe (5HP) sensor for the determination of the ﬂow vector with 100 Hz. In particular for this application there is still need for further improvement, both with respect to the aircraft and sensor hard- and software, and the algorithms and methods for data analysis and interpretation. Nevertheless have the SUMO operations during the BLLAST campaign shown the vast potential of small and light-weight RPA systems with low infrastructural demand for atmospheric boundary layer research.
Enhancing the capabilities of a portable FTIR spectrometer for greenhouse gases measurements by addition of a second detector channel for XCO observations
Authors: Hase F. , Frey M. , Kiel M. , Blumenstock T. , Harig R. , Keens A. , Orphal J.
Published: January 2016

Abstract. The portable FTIR (Fourier-Transform InfraRed) spectrometer EM27/SUN dedicated for the precise and accurate observation of column-averaged abundances of methane and carbon dioxide has been equipped with a second detector channel which allows the detection of additional species, especially carbon monoxide. This allows an improved characterisation of observed carbon dioxide enhancements and makes the extended spectrometer especially suitable as a validat ion tool of ESA’s Sentinel 5 Precursor mission, as it now covers the same spectral region as used by the infrared channel of the TROPOMI (TROPOspheric Monitoring Instrument) sensor. The extension presented here does not rely on a dichroic, but instead a fraction of the solar beam is decoupled near the aperture stop of the spectrometer using a small plane mirror. This approach allows to maintain the camera-controlled solar tracker setup, which is referenced to the field stop in front of the primary detector. Moreover, the upgrade of existing instruments can be performed without alterating the optical setup of the primary channel and resulting changes of the instrumental characteristics of the original instrument.
HONO Measurement by Differential Photolysis
Authors: Reed C. , Brumby C. A. , Crilley L. R. , Kramer L. J. , Bloss W. J. , Seakins P. W. , Lee J. D. , Carpenter L. J.
Published: January 2016

Abstract. Nitrous acid (HONO) has been quantitatively measured in-situ by differential photolysis at 385 and 395 nm and subsequent detection as nitric oxide (NO) by the chemiluminescence reaction with ozone (O3). The technique has been evaluated by FT-IR to provide a direct HONO measurement in a simulation chamber, and compared side-by-side with a LOng Absorption Path Optical Photometer (LOPAP) in the field. The NO/O3 chemiluminescence technique is robust, well characterized and capable of sampling at low pressure whilst solid-state converter technology allows for unattended in-situ HONO measurements in combination with fast time resolution and response.
Assessment of adequate quality and collocation of reference measurements with space-borne hyperspectral infrared instruments to validate retrievals of temperature and water vapour
Authors: Calbet X.
Published: January 2016

Abstract. A method is presented to assess whether a given reference ground-based point observation, typically a radiosonde measurement, is adequately collocated and sufficiently representative of space-borne hyperspectral infrared instrument measurements. Once this assessment is made, the ground-based data can be used to validate and potentially calibrate, with a high degree of accuracy, the hyperspectral retrievals of temperature and water vapour.
Aerosol optical depth retrievals at the Izaña Atmospheric Observatory from 1941 to 2013 by using artificial neural networks
Authors: García R. D. , García O. E. , Cuevas E. , Cachorro V. E. , Barreto A. , Guirado-Fuentes C. , Kouremeti N. , Bustos J. J. , Romero-Campos P. M. , de Frutos A. M.
Published: January 2016

Abstract. This paper presents the reconstruction of a 73-year time series of the aerosol optical depth (AOD) at 500 nm at the subtropical high-mountain Izaña Atmospheric Observatory (IZO) located in Tenerife (Canary Islands, Spain). For this purpose, we have combined AOD estimates from artificial neural networks (ANNs) from 1941 to 2001 and AOD measurements directly obtained with a Precision Filter Radiometer (PFR) between 2003 and 2013. The analysis is limited to summer months (July–August–September), when the largest aerosol load is observed at IZO (Saharan mineral dust particles). The ANN AOD time series has been comprehensively validated against coincident AOD measurements performed with a solar spectrometer Mark-I (1984–2009) and AERONET (AErosol RObotic NETwork) CIMEL photometers (2004–2009) at IZO, obtaining a rather good agreement on a daily basis: Pearson coefficient, R, of 0.97 between AERONET and ANN AOD, and 0.93 between Mark-I and ANN AOD estimates. In addition, we have analysed the long-term consistency between ANN AOD time series and long-term meteorological records identifying Saharan mineral dust events at IZO (synoptical observations and local wind records). Both analyses provide consistent results, with correlations  >  85 %. Therefore, we can conclude that the reconstructed AOD time series captures well the AOD variations and dust-laden Saharan air mass outbreaks on short-term and long-term timescales and, thus, it is suitable to be used in climate analysis.
Mapping of steady-state electric fields and convective drifts in geomagnetic fields – Part 1: Elementary models
Authors: Walker A. D. M. , Sofko G. J.
Published: January 2016

Abstract. When studying magnetospheric convection, it is often necessary to map the steady-state electric field, measured at some point on a magnetic field line, to a magnetically conjugate point in the other hemisphere, or the equatorial plane, or at the position of a satellite. Such mapping is relatively easy in a dipole field although the appropriate formulae are not easily accessible. They are derived and reviewed here with some examples. It is not possible to derive such formulae in more realistic geomagnetic field models. A new method is described in this paper for accurate mapping of electric fields along field lines, which can be used for any field model in which the magnetic field and its spatial derivatives can be computed. From the spatial derivatives of the magnetic field three first order differential equations are derived for the components of the normalized element of separation of two closely spaced field lines. These can be integrated along with the magnetic field tracing equations and Faraday's law used to obtain the electric field as a function of distance measured along the magnetic field line. The method is tested in a simple model consisting of a dipole field plus a magnetotail model. The method is shown to be accurate, convenient, and suitable for use with more realistic geomagnetic field models.
Model-aided quantification of dissolved carbon and nitrogen release after windthrow disturbance in an Austrian karst system
Authors: Hartmann A. , Kobler J. , Kralik M. , Dirnböck T. , Humer F. , Weiler M.
Published: January 2016

Abstract. Karst systems are important for drinking water supply. Future climate projections indicate increasing temperature and a higher frequency of strong weather events. Both will influence the availability and quality of water provided from karst regions. Forest disturbances such as windthrow can disrupt ecosystem cycles and cause pronounced nutrient losses from the ecosystems. In this study, we consider the time period before and after the wind disturbance period (2007/08) to identify impacts on DIN (dissolved inorganic nitrogen) and DOC (dissolved organic carbon) with a process-based flow and solute transport simulation model. When calibrated and validated before the disturbance, the model disregards the forest disturbance and its consequences on DIN and DOC production and leaching. It can therefore be used as a baseline for the undisturbed system and as a tool for the quantification of additional nutrient production. Our results indicate that the forest disturbance by windthrow results in a significant increase of DIN production lasting  ∼  3.7 years and exceeding the pre-disturbance average by 2.7 kg ha−1 a−1 corresponding to an increase of 53 %. There were no significant changes in DOC concentrations. With simulated transit time distributions we show that the impact on DIN travels through the hydrological system within some months. However, a small fraction of the system outflow (< 5 %) exceeds mean transit times of > 1 year.
Vanishing coccolith vital effects with alleviated carbon limitation
Authors: Hermoso M. , Chan I. Z. X. , McClelland H. L. O. , Heureux A. M. C. , Rickaby R. E. M.
Published: January 2016

Abstract. By recreating a range of geologically relevant concentrations of dissolved inorganic carbon (DIC) in the laboratory, we demonstrate that the magnitude of the vital effects in both carbon and oxygen isotopes of coccolith calcite of multiple species relates to ambient DIC concentration. Under high DIC levels, all the examined coccoliths exhibit significantly reduced isotopic offsets from inorganic calcite compared to the substantial vital effects expressed at low (preindustrial and present-day) DIC concentrations. The supply of carbon to the cell exerts a primary control on biological fractionation in coccolith calcite via the modulation of coccolithophore growth rate, cell size and carbon utilisation by photosynthesis and calcification, altogether accounting for the observed interspecific differences between coccolith species. These laboratory observations support the recent hypothesis from field observations that the appearance of interspecific vital effect in coccolithophores coincides with the long-term Neogene decline of atmospheric CO2 concentrations and bring further valuable constraints by demonstrating a convergence of all examined species towards inorganic values at high pCO2 regimes. This study provides palaeoceanographers with a biogeochemical framework that can be utilised to further develop the use of calcareous nannofossils in palaeoceanography to derive sea surface temperature and pCO2 levels, especially during periods of relatively elevated pCO2 concentrations, as they prevailed during most of the Meso-Cenozoic.
Microbial nutrient limitation in Arctic lakes in a permafrost landscape of southwest Greenland
Authors: Burpee B. , Saros J. E. , Northington R. M. , Simon K. S.
Published: January 2016

Abstract. Permafrost is degrading across regions of the Arctic, which can lead to increases in nutrient concentrations in surface freshwaters. The oligotrophic state of many Arctic lakes suggests that enhanced nutrient inputs may have important effects on these systems, but little is known about microbial nutrient limitation patterns in these lakes. We investigated microbial extracellular enzyme activities (EEAs) to infer seasonal nutrient dynamics and limitation across 24 lakes in southwest Greenland during summer (June and July). From early to late summer, enzyme activities that indicate microbial carbon (C), nitrogen (N), and phosphorus (P) demand increased in both the epilimnia and hypolimnia by 74  % on average. Microbial investment in P acquisition was generally higher than that for N. Interactions among EEAs indicated that microbes were primarily P-limited. Dissolved organic matter (DOM, measured as dissolved organic carbon) was strongly and positively correlated with microbial P demand (R2  =  0.84 in July), while there were no relationships between DOM and microbial N demand. Microbial P limitation in June epilimnia (R2  =  0.67) and July hypolimnia (R2  =  0.57) increased with DOM concentration. The consistency of microbial P limitation from June to July was related to the amount of DOM present, with some low-DOM lakes becoming N-limited in July. Our results suggest that future changes in P or DOM inputs to these lakes are likely to alter microbial nutrient limitation patterns.
Energy balance closure on a winter wheat stand: comparing the eddy covariance technique with the soil water balance method
Authors: Imukova K. , Ingwersen J. , Hevart M. , Streck T.
Published: January 2016

Abstract. The energy balance of eddy covariance (EC) flux data is typically not closed. The nature of the gap is usually not known, which hampers using EC data to parameterize and test models. In the present study we cross-checked the evapotranspiration data obtained with the EC method (ETEC) against ET rates measured with the soil water balance method (ETWB) at winter wheat stands in southwest Germany. During the growing seasons 2012 and 2013, we continuously measured, in a half-hourly resolution, latent heat (LE) and sensible (H) heat fluxes using the EC technique. Measured fluxes were adjusted with either the Bowen-ratio (BR), H or LE post-closure method. ETWB was estimated based on rainfall, seepage and soil water storage measurements. The soil water storage term was determined at sixteen locations within the footprint of an EC station, by measuring the soil water content down to a soil depth of 1.5 m. In the second year, the volumetric soil water content was additionally continuously measured in 15 min resolution in 10 cm intervals down to 90 cm depth with sixteen capacitance soil moisture sensors. During the 2012 growing season, the H post-closed LE flux data (ETEC =  3.4 ± 0.6 mm day−1) corresponded closest with the result of the WB method (3.3 ± 0.3 mm day−1). ETEC adjusted by the BR (4.1 ± 0.6 mm day−1) or LE (4.9 ± 0.9 mm day−1) post-closure method were higher than the ETWB by 24 and 48 %, respectively. In 2013, ETWB was in best agreement with ETEC adjusted with the H post-closure method during the periods with low amount of rain and seepage. During these periods the BR and LE post-closure methods overestimated ET by about 46 and 70 %, respectively. During a period with high and frequent rainfalls, ETWB was in-between ETEC adjusted by H and BR post-closure methods. We conclude that, at most observation periods on our site, LE is not a major component of the energy balance gap. Our results indicate that the energy balance gap is made up by other energy fluxes and unconsidered or biased energy storage terms.
Parameterization of biogeochemical sediment–water fluxes using in situ measurements and a diagenetic model
Authors: Laurent A. , Fennel K. , Wilson R. , Lehrter J. , Devereux R.
Published: January 2016

Abstract. Diagenetic processes are important drivers of water column biogeochemistry in coastal areas. For example, sediment oxygen consumption can be a significant contributor to oxygen depletion in hypoxic systems, and sediment–water nutrient fluxes support primary productivity in the overlying water column. Moreover, nonlinearities develop between bottom water conditions and sediment–water fluxes due to loss of oxygen-dependent processes in the sediment as oxygen becomes depleted in bottom waters. Yet, sediment–water fluxes of chemical species are often parameterized crudely in coupled physical–biogeochemical models, using simple linear parameterizations that are only poorly constrained by observations. Diagenetic models that represent sediment biogeochemistry are available, but rarely are coupled to water column biogeochemical models because they are computationally expensive. Here, we apply a method that efficiently parameterizes sediment–water fluxes of oxygen, nitrate and ammonium by combining in situ measurements, a diagenetic model and a parameter optimization method. As a proof of concept, we apply this method to the Louisiana Shelf where high primary production, stimulated by excessive nutrient loads from the Mississippi–Atchafalaya River system, promotes the development of hypoxic bottom waters in summer. The parameterized sediment–water fluxes represent nonlinear feedbacks between water column and sediment processes at low bottom water oxygen concentrations, which may persist for long periods (weeks to months) in hypoxic systems such as the Louisiana Shelf. This method can be applied to other systems and is particularly relevant for shallow coastal and estuarine waters where the interaction between sediment and water column is strong and hypoxia is prone to occur due to land-based nutrient loads.
The OMZ and nutrients features as a signature of interannual and low frequency variability off the peruvian upwelling system
Authors: Graco M. , Purca S. , Dewitte B. , Morón O. , Ledesma J. , Flores G. , Castro C. , Gutiérrez D.
Published: January 2016

Abstract. The last years, the Humboldt Current Upwelling Ecosystem and particularly the Northern component off Peru, was a natural scenario for several studies and a "hot spot" for scientists around the world because of their unique characteristics: (1) one of the bigger catch productivity, (2) one of the shallowest, intense and acidic Oxygen Minimum Zone (OMZ), (3) one of the intense nitrogen lost areas and anammox activity, and (4) one of the strongest interannual variability associated with the Equatorial remote forcing. In this context, we examined the oceanographic and biogeochemical variability associated with the OMZ off central Peru, from a monthly time-series (1996–2009) recorded off Callao (12°02' S). Both, physical and chemical time series exhibit a significant temporal variability, with intense interannual El Niño effects in the deepening of the OMZ distribution and nutrients dynamic but also intraseasonal activity by the influence of the Equatorial Kelvin Wave (IEKW). The chemical time series indicate after 2002 year higher frequency variability in phase with the increase of the IEKW, particularly with the second mode activity. We present evidences that the IEKW appear to modulate the distribution and intensity of the OMZ in the area and in consequence an impact on the chemical structure and biogeochemical activity. The data suggest that the remote forcing could be strongest not only at interannual but also at lower temporal frequencies changing the seasonal signature of upwelling systems.
Phytoplankton community structure in the VAHINE MESOCOSM experiment
Authors: Leblanc K. , Cornet V. , Caffin M. , Rodier M. , Desnues A. , Berthelot H. , Turk-Kubo K. , Heliou J.
Published: January 2016

Abstract. The VAHINE mesocosm experiment was designed to trigger a diazotroph bloom and to follow the subsequent transfer of diazotroph derived nitrogen (DDN) in the rest of the foodweb. Three mesocosms (50 m3) located inside the Nouméa lagoon (New Caledonia, South West Pacific) were enriched with dissolved inorganic phosphate (DIP) in order to promote N2 fixation in these Low Nutrient Low Chlorophyll (LNLC) waters. Initial diazotrophic community were dominated by diatom diazotroph associations (DDAs), mainly by Rhizosolenia/Richelia intracellularis, and by Trichodesmium which fueled enough DDN to sustain the growth of other diverse diatom species and Synechococcus populations, that were well adapted to limiting DIP levels. After DIP fertilization (1 mM) on day 4, an initial lag time of 10 days was necessary for the mesocosm ecosystems to start building up biomass. Yet changes in community structure were already observed during this first period, with a significant drop of both Synechococcus and diatom populations, while Prochlorococcus benefited from DIP-addition. At the end of this first period, corresponding to when most added DIP was consumed, the diazotroph community changed drastically and became dominated by UCYN-C populations, which were accompanied by a monospecific bloom of the diatom Cylindrotheca closterium. During the second period, biomass increased sharply together with primary production and N2 fixation fluxes near tripled. Diatom populations, as well as Synechococcus and nano-phytoeukaryotes showed a re-increase towards the end of the experiment, showing efficient transfer of DDN to non diazotrophic phytoplankton.
Ocean acidification decreases plankton respiration: evidence from a mesocosm experiment
Authors: Spilling K. , Paul A. J. , Virkkala N. , Hastings T. , Lischka S. , Stuhr A. , Bermudez R. , Czerny J. , Boxhammer T. , Schulz K. G. , Ludwig A. , Riebesell U.
Published: January 2016

Abstract. Anthropogenic carbon dioxide (CO2) emissions are reducing the pH in the world's oceans. The plankton community is a key component driving biogeochemical fluxes, and the effect of increased CO2 on plankton is critical for understanding the ramifications of ocean acidification on global carbon fluxes. We determined the plankton community composition and measured primary production, respiration rates and carbon export (defined here as carbon sinking out of a shallow, coastal area) during an ocean acidification experiment. Mesocosms (~ 55 m3) were set up in the Baltic Sea with a gradient of CO2 levels initially ranging from ambient (~ 240 μatm), used as control, to high CO2 (up to ~ 1330 μatm). The phytoplankton community was dominated by dinoflagellates, diatoms, cyanobacteria and chlorophytes, and the zooplankton community by protozoans, heterotrophic dinoflagellates and cladocerans. The plankton community composition was relatively homogenous between treatments. Community respiration rates were lower at high CO2 levels. The carbon-normalized respiration was approximately 40 % lower in the high CO2 environment compared with the controls during the latter phase of the experiment. We did not, however, detect any effect of increased CO2 on primary production. This could be due to measurement uncertainty, as the measured total particular carbon (TPC) and combined results presented in this special issue suggest that the reduced respiration rate translated into higher net carbon fixation. The percent carbon derived from microscopy counts (both phyto- and zooplankton), of the measured total particular carbon (TPC) decreased from ~ 26 % at t0 to ~ 8 % at t31, probably driven by a shift towards smaller plankton (< 4 μm) not enumerated by microscopy. Our results suggest that reduced respiration lead to increased net carbon fixation at high CO2. However, the increased primary production did not translate into increased carbon export, and did consequently not work as a negative feedback mechanism for increasing atmospheric CO2 concentration.
Dynamics of transparent exopolymer particles (TEP) during the VAHINE mesocosm experiment in the New Caledonia lagoon
Authors: Berman-Frank I. , Spungin D. , Rahav E. , Van Wambeke F. , Turk-Kubo K. , Moutin T.
Published: January 2016

Abstract. In the marine environment, transparent exopolymeric particles (TEP) produced from abiotic and biotic sources link the particulate and dissolved carbon pools and are essential vectors enhancing vertical carbon flux. We characterized spatial and temporal dynamics of TEP during the VAHINE experiment that investigated the fate of diazotroph derived nitrogen and carbon in three, replicate, dissolved inorganic phosphorus (DIP)-fertilized 50 m3 enclosures in an oligotrophic New Caledonian lagoon. During the 23 days of the experiment, we did not observe any depth dependent changes in TEP concentrations in the three sampled-depths (1, 6, 12 m). TEP carbon (TEP-C) content per mesocosm averaged 28.9 ± 9.3% and 27.0 ± 7.2% of TOC in the mesocosms and surrounding lagoon respectively and was strongly and positively coupled with TOC during P2. TEP concentrations declined for the first 9 days after DIP fertilization (P1 = days 5-14) and then gradually increased during the second phase (P2 = days 15-23). Temporal changes in TEP concentrations paralleled the growth and mortality rates of the diatom-diazotroph association of Rhizosolenia and Richelia that predominated the diazotroph community during P1. By P2, increasing total primary and heterotrophic bacterial production consumed the supplemented P and reduced availability of DIP. For this period, TEP concentrations were negatively correlated with DIP availability and turnovertime of DIP (TDIP) while positively associated with enhanced alkaline phosphatase activity (APA) that occurs when the microbial populations are P-stressed. During P2, increasing bacterial production (BP) was positively correlated with higher TEP concentrations which were also coupled with the increased growth rates and aggregation of the unicellular UCYN-C diazotrophs which bloomed during this period. We conclude that the composite processes responsible for the formation and breakdown of TEP yielded a relatively stable TEP pool available as both a carbon source and facilitating aggregation and flux throughout the experiment. TEP was probably mostly influenced by abiotic physical processes during P1 while biological activity (BP, diazotrophic growth and aggregation, export production) mainly impacted TEP concentrations during P2 when DIP-availability was limited.
Greenhouse gas emissions and reactive nitrogen releases from rice production with simultaneous incorporation of wheat straw and nitrogen fertilizer
Authors: Xia Longlong , Xia Yongqiu , Ma Shutan , Wang Jinyang , Wang Shuwei , Zhou Wei , Yan Xiaoyuan
Published: January 2016

Abstract. The impacts of simultaneous inputs of crop straw and nitrogen (N) fertilizer on greenhouse gas (GHG) emissions and reactive nitrogen (Nr) releases from rice production in intensive agricultural regions are not well understood. A field experiment was established in a rice–wheat cropping system in the Taihu Lake region (TLR) of China since 2013 to evaluate the GHG intensity (GHGI), Nr intensity (NrI) and environmental costs of concurrent inputs of wheat straw and N fertilizer to rice paddies. The field experiment included five treatments of different N fertilization rates for rice production: 0 (RN0), 120 (RN120), 180 (RN180), 240 (RN240) and 300 kg N ha–1 (RN300, traditional N applied rate in the TLR). Wheat straws were fully incorporated into soil before rice transplantation in all treatments. The results showed that the response of rice yield to N application rate successfully fitted a quadratic model. Nitrous oxide (N2O) emissions were increased exponentially as N fertilization rates increased, while methane (CH4) emissions increased slightly with wheat straw rates increased. The estimated soil organic carbon sequestration rate varied from 129.58 (RN0) to 196.87 kg C ha−1 yr−1 (RN300). Seasonal average GHGI of rice production ranged from 1.20 (RN240) to 1.61 kg CO2-equivalent (CO2-eq) kg–1 (RN0), while NrI varied from 2.14 (RN0) to 10.92 g N kg−1 (RN300). CH4 emissions dominated GHGI with proportion of 70.2-88.6%, while ammonia (NH3) volatilization dominated NrI with proportion of 53.5-57.4% in all fertilization treatments. The damage costs to environment incurred by GHG and Nr releases from current rice production (RN300) accounted for 8.8% and 4.9% of farmer’s incomes, respectively. Cutting the traditional application rate of N fertilizer from 300 to 240 kg N ha−1 improved rice yield and nitrogen use efficiency by 2.14% and 10.30%, respectively, whilst simultaneously reduced GHGI by 13%, NrI by 23% and total environmental costs by 16%. Moreover, the reduction of 60 kg N ha−1 improved farmer’s income by 639 ¥ ha–1, which would provide them with an incentive to change their traditional N application rate. Our study suggests that GHG and Nr releases, especially the CH4 emission and NH3 volatilization, from rice production in the TLR could be further curbed, considering the current incorporation pattern of straw and N fertilizer.
Seasonality in Planktic Foraminifera of the Central California Coastal Upwelling Region
Authors: Davis C. V. , Russell A. D. , Gaylord B. P. , Jahncke J. , Hill T. M.
Published: January 2016

Abstract. The association between planktic foraminiferal assemblages and local hydrography make foraminifera invaluable proxies for environmental conditions. Modern foraminiferal seasonality is important for interpreting fossil distributions and shell geochemistry as paleoclimate proxies. Understanding this seasonality in an active upwelling area is also critical for anticipating which species may be vulnerable to future changes in upwelling intensity and ocean acidification. Two years (2012-2014) of plankton tows, along with Conductivity-Temperature-Density profiles and carbonate chemistry measurements taken along the North-Central California shelf offer new insights into the seasonal dynamics of planktic foraminifera in a seasonal coastal upwelling regime. This study finds an upwelling affinity for Neogloboquadrina pachyderma as well as a seasonal and upwelling associated alternation between dominance of N. pachyderma and Neogloboquadrina incompta, consistent with previous observations. Globigerina bulloides, however, shows a strong affinity for non-upwelled waters, in contrast to findings in Southern California where the species is often associated with upwelling. We also find an apparent lunar periodicity in the abundances of all species and confirm the presence of foraminifera at very low saturation state of calcite.
Accurate and precise quantification of atmospheric nitrate in streams draining land of various uses by using triple oxygen isotopes as tracers
Authors: Tsunogai Urumu , Miyauchi Takanori , Ohyama Takuya , Komatsu Daisuke D. , Nakagawa Fumiko , Obata Yusuke , Sato Keiichi , Ohizumi Tsuyoshi
Published: January 2016

Abstract. 17O anomalies were used to quantify the influence of changes in land use and population density between each catchment area on the fate of atmospheric nitrate by determining the areal distribution and seasonal variation in stable isotopic compositions including the 17O anomalies (Δ17O) of nitrate for more than 30 streams within the same watershed. Those in precipitation (wet deposition; n = 213) sampled at Sado-seki monitoring station were determined for three years as well. The deposited nitrate showed similar large 17O anomalies with those already reported for mid-latitudes: Δ17O values ranged from +18.6‰ to +32.4‰ with a three-year average of +26.3‰. However, nitrate in each inflow stream showed small annual average Δ17O values ranging from +0.5‰ to +3.1‰, which corresponds to the mixing ratios of unprocessed atmospheric nitrate to total nitrate from 1.8 ± 0.3% to 11.8 ± 1.8%, with 5.1 ± 0.5% as the average of all inflow streams. Although the annual average Δ17O values tended to be smaller in accordance with the increase in annual average nitrate concentration from 12.7 to 106.2 μmol L−1, the absolute concentrations of unprocessed atmospheric nitrate in the streams were almost stable at 2.3 ± 1.1 μmol L−1 irrespective of the changes in population density and land use in each catchment area. We conclude that changes in population density and land use between each catchment area had little impact on the concentration of atmospheric nitrate. Thus, the total nitrate concentration originated primarily from additional contribution of remineralized nitrate from both natural sources, having values of +4.4 ± 1.8‰ and −2.3 ± 0.9‰ for δ15N and δ18O, respectively, and anthropogenic sources having values of +9.2 ± 1.3‰ and −2.2 ± 1.1‰ for δ15N and δ18O, respectively. In addition, both the uniform absolute concentration of atmospheric nitrate and the low and uniform δ18O values of the remineralized portion of nitrate in the streams imply that in-stream removal of nitrate through assimilation or denitrification had small impact on the concentrations and stable isotopic compositions of nitrate in the streams, except for a few streams in summer having catchments of urban/suburban land uses. Additional measurements of the Δ17O values of nitrate together with δ15N and δ18O enabled us to exclude the contribution of unprocessed atmospheric nitrate from the determined δ15N and δ18O values of total nitrate and to use the corrected δ15N and δ18O values to evaluate the source and behaviour of the remineralized portion of nitrate in each stream.