bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms of Trichodesmium bloom demise within the New Caledonia Lagoon during the VAHINE mesocosm experiment
Authors: Spungin D. , Pfreundt U. , Berthelot H. , Bonnet S. , AlRoumi D. , Natale F. , Hess W. R. , Bidle K. D. , Berman-Frank I.
Published: January 2016

Abstract. The globally important marine diazotrophic cyanobacterium Trichodesmium blooms regularly in the New Caledonian lagoons (Sowthwestern Pacific). We exploited the development of a Trichodesmium bloom in the lagoon waters outside the enclosed VAHINE mesocosms to specifically investigate the cellular processes mediating its decline. Trichodesmium cells (and associated microbiota) were sampled from the time of surface accumulation to biomass demise using a series of enclosed incubations to elucidate the stressors and subcellular underpinning of rapid (~ 24 h) biomass demise and disappearance. The development and decline of Trichodesmium populations was rapid with extensive surface accumulations (blooms) appearing within 24 h on the surface waters of the lagoon. Rapid decline of > 90 % biomass after 24 h of peak accumulation was observed in p opulations that were collected and incubated under ambient conditions. Metatranscriptomic profiling of Trichodesmium biomass 8 h and 22 h after bottle incubation of surface accumulations revealed evidence for phosphorus (P) and iron (Fe) stress, with upreg ulation of genes required to increase their availability and transport. In contrast, genes responsible for nutrient storage were downregulated. Total viral abundance, assessed by SYBR-green staining and analytical flow cytometry, oscillated throughout the experiment and showed no significant relationship with Trichodesmium bloom development or demise. Enhanced caspase-specific activity and upregulation of a suite of metacaspase genes during bloom demise implicated autocatalytic programmed cell death (PCD) as the mechanistic cause. At the same time, genes associated with buoyancy and gas-vesicle production were strongly downregulated concomitant with high concentrations of transparent exopolymeric particles (TEP), greatly aiding aggregation and expediting vertical flux to depth. Our results demonstrate that the rapid demise of this high-density, Trichodesmium surface bloom over 24 h was not caused by specific lytic infection but was rather induced by PCD in response to combined nutrient and oxidative stressors.
Community change of microorganisms in the Muztagata and Dunde glacier and climatic and environmental implications
Authors: Chen Yong , Li Xiang-Kai , Si Jing , WU Guang-Jian , Tian Li-De , Xiang Shu-Rong
Published: January 2016

Abstract. Microorganisms are continuously blown onto the glacier snow, and thus the glacial depth profiles provide excellent geographic archives of the microbial communities. However, it is uncertain about how the microbial communities respond to the climatic and environmental changes over the glacier ice. In the present study, the live microbial density, stable isotopic ratios, 18O/16O in the precipitation, and mineral particle concentrations along the glacial depth profiles were collected from ice cores from the Muztagata glacier and the Dunde ice cap. Six bacterial 16S rRNA gene clone libraries were established from the Dunde ice core. The Muztagata ice core presented seasonal response patterns for both live and total cell density with high cell density occurring in the warming spring and summer. Both ice core data showed a frequent association of dust and microorganisms in the ice. Genera Polaromas sp., Pedobacter sp, Flavobacterium sp., Cryobacteriium sp., and Propionibacterium/Blastococcus sp. frequently appeared at the six tested ice layers, and constituted the dominant species endemic to the Dunde ice cap, whereas some genera such as Rhodoferax sp., Variovorax sp., Sphingobacterium sp., Cyanobacterium sp., Knoellia sp., and Luteolibacter sp. rarely presented in the ice. In conclusion, data present a discrete increase of microbial cell density in the warming seasons and biogeography of the microbial communities associated with the predominance of a few endemic groups in the local glacial regions. This reinforces our hypothesis of dust-borne and post-deposition being the main agents interactively controlling microbial load in the glacier ice.
Effects of in situ CO2 enrichment on structural characteristics, photosynthesis, and growth of the Mediterranean seagrass Posidonia oceanica
Authors: Cox T. E. , Gazeau F. , Alliouane S. , Hendriks I. E. , Mahacek P. , Le Fur A. , Gattuso J.-P.
Published: January 2016

Abstract. Seagrass are expected to benefit from increased carbon availability under future ocean acidification. This hypothesis has been little tested by in situ manipulation. To test for ocean acidification effects on seagrass meadows under controlled CO2/pH conditions, we used a Free Ocean Carbon Dioxide Enrichment (FOCE) system which allows for the precise manipulation of pH as an offset from the ambient. This system was deployed in a Posidonia oceanica meadow at 11 m depth in the Northwestern Mediterranean Sea. It consisted of two benthic enclosures, an experimental and a control unit both 1.7 m3, and an additional reference plot in the ambient (2 m2) to account for structural artifacts. The meadow was monitored from April to November 2014. The pH of the experimental enclosure was lowered by 0.26 pH units for the second half of the eight-month study. Changes in P. oceanica leaf biometrics, photosynthesis, and leaf growth accompanied seasonal changes recorded in the environment and values were similar between the two enclosures. Leaf thickness may change in response to lower pH but this requires further testing. Results suggest any benefit from ocean acidification, over the next century, on Posidonia physiology and growth may be minimal. The limited stimulation casts doubts on speculations that elevated CO2 would confer resistance to thermal stress and increase buffering capacity of meadows.
Carbon and nitrogen stocks in particle-size fractions of topsoil along a 3000 km aridity gradient in northern China
Authors: Wang X. G. , Sistla S. A. , Wang X. B. , Lü X. T. , Han X. G.
Published: January 2016

Abstract. Climate factors such as aridity significantly influence soil carbon (C) and nitrogen (N) stocks in terrestrial ecosystems. Further, soil composition plays an important role in driving changes of soil C and N stocks at regional scale. However, it remains uncertain whether such changes result from the variation of different soil particle-size factions or the C and N concentrations in those fractions. We examined the distribution of total C and N in both bulk soil and different soil particle-size fractions, including sand (53-2000 μm), silt (2-53 μm) and clay (<2 μm), along a 3000 km transect in arid and semi-arid grasslands of northern China. Across the whole transect, sand content was positively and silt content was negatively correlated with increasing aridity. Carbon stock in bulk soils (0-10 cm) ranged from 4.36 to 46.16 Mg C ha-1, while N stock ranged from 0.22 to 4.28 Mg N ha-1 across different sampling sites on the transect. The total C and N concentrations and stocks in bulk soils as well as in the three particle-size fractions tended to be negatively correlated with aridity. The concentrations and stocks of total C and N in bulk soils were positively correlated with silt and clay contents and negatively correlated with sand content. There were positive correlations between the concentrations and stocks of C or N in bulk soils and the C or N concentrations in the three soil particle-size fractions. By characterizing such a large scale aridity gradient, our results highlight that aridity would decrease soil C and N stocks both by favoring increased sand content and by decreasing C and N concentrations in all the three soil fractions. These patterns thus have significant implications for understanding soil C and N sequestration under scenarios of increasing aridity in global drylands that are predicted to occur this century.
Underestimation of boreal soil carbon stocks by mathematical soil carbon models linked to soil nutrient status
Authors: Ťupek B. , Ortiz C. , Hashimoto S. , Stendahl J. , Dahlgren J. , Karltun E. , Lehtonen A.
Published: January 2016

Abstract. Inaccurate estimate of the largest terrestrial carbon pool, soil organic carbon (SOC) stock, is the major source of uncertainty in simulating feedback of climate warming on ecosystematmosphere carbon exchange by process based ecosystem and soil carbon models. Although the models need to simplify complex environmental processes of soil carbon sequestration, in a large mosaic of environments a missing key driver could lead into a modelling bias in predictions of SOC stock change. We aimed to evaluate SOC stock estimates of process based models (Yasso07, Q, and CENTURY) against the Swedish forest soil inventory data (3230 samples) organized by recursive partitioning method into distinct soil groups with underlying SOC stock development linked to physicochemical conditions. The Yasso07 and Q models that used only climate and litterfall input data and ignored soil properties generally agreed with two third of measurements. However, in fertile sites with high nitrogen deposition, high cation exchange capacity, or moderately increased soil water content, Yasso07 and Q underestimated SOC stocks. Accounting for soil texture (clay, silt, and sand content) and structure (bulk density) in CENTURY model showed no improvement on carbon stock estimates, as CENTURY deviated in similar manner. Our analysis suggested that the soils with poorly predicted SOC stocks, as characterized by the high nutrient status and well sorted parent material, indeed have had other predominat drivers of SOC stabilization lacking in the models presumably the mycorrhizal organic uptake and organo-mineral stabilization processes. Our results imply that the role of soil nutrient status as regulator of organic matter mineralization has to be re-evaluated, since correct steady state SOC stocks are decisive for predicting future SOC change.
Effect of ocean acidification on the structure and fatty acid composition of a natural plankton community in the Baltic Sea
Authors: Bermúdez J. R , Winder M. , Stuhr A. , Almén A. K. , Engström-Öst J. , Riebesell U.
Published: January 2016

Abstract. Increasing atmospheric carbon dioxide (CO2) is changing seawater chemistry towards reduced pH, which consequently affects various properties of marine organisms. Coastal and brackish water communities are expected to be less affected by ocean acidification (OA) as these communities are typically adapted to high fluctuations in CO2 and pH. Here we investigate the response of a coastal brackish water plankton community to increasing CO2 levels as projected for the coming decades and the end of this century in terms of community and biochemical fatty acid (FA) composition. A Baltic Sea plankton community was enclosed in a set of off-shore mesocosms and subjected to a CO2 gradient ranging from natural concentrations (~347 μatm pCO2) up to values projected for the year 2100 (~1333 μatm pCO2). We show that the phytoplankton community composition was resilient to CO2 and did not diverge between the treatments. Seston FA composition was influenced by community composition, which in turn was driven by silicate and phosphate limitation in the mesocosms, and showed no difference between the CO2 treatments. These results suggest that CO2 effects are dampened in coastal communities that already experience high natural fluctuations in pCO2. Although this coastal plankton community was tolerant to high pCO2 levels, hypoxia and CO2 uptake by the sea can aggravate acidification and may lead to pH changes outside the currently experienced range for coastal organisms.
Technical Note: Rapid Normal-phase Separation of Phytoplankton Lipids by Ultra-High Performance Supercritical Fluid Chromatography (UHPSFC)
Authors: Brandsma J. , Sutton T. R. , Herniman J. M. , Hunter J. E. , Biggs T. E. G. , Evans C. , Brussaard C. P. D. , Postle A. D. , Jenkins T. J. , Langley G. J.
Published: January 2016

Abstract. Lipid metabolism is one of the cornerstones of biochemistry, and these chemically diverse biomolecules play key roles in molecular physiology and mediate interactions between microbes and their environment that play out on cell ular to ecosystem scales. Marine phytoplankton fix in the range of 1 billion tonnes of carbon as lipid biomass each year, which goes on to fuel higher trophic levels or ends up in the marine dissolved organic matter pool. Yet despite the importance of the vast marine lipidome for global biogeochemistry, surprisingly little is known about its diverse inventory of molecular structures, or the influence that dynamic environmental conditions exert on microbial lipid synthesis, remodelling and turnover. To aid in this research, a high-throughput platform for comprehensive analysis of phytoplankton lipids was developed using Ultra-High Performance Supercritical Fluid Chromatography (UHPSFC). This recently developed technology combines a primary supercritical fluid (CO2) mobile phase with an organic co-solvent of choice. Using a simple 10 minute gradient and a sub-2 μm particle column, UHPSFC efficiently separates all of the major neutral and polar lipid classes encountered in phytoplankton in a single analysis. These can then be measured by tandem mass spectrometry using established precursor and neutral mass loss scans. To demonstrate the analytical power of this novel platform the lipid compositions of a diverse range of phytoplankton species grown in culture, as well as phytoplankton community samples from the Western Antarctic Peninsula, were analysed. With higher chromatographic resolution and a much shorter analysis time than current liquid chromatography methods, the application of U HPSFC has considerable potential to benefit large-scale lipidomic studies, including in the field of environmental microbiology.
Oxygen Utilization and Downward Carbon Flux in an Oxygen-Depleted Eddy in the Eastern Tropical North Atlantic
Authors: Fiedler B. , Grundle D. , Schütte F. , Karstensen J. , Löscher C. R. , Hauss H. , Wagner H. , Loginova A. , Kiko R. , Silva P. , Körtzinger A.
Published: January 2016

Abstract. The occurrence of mesoscale eddies that develop an extreme low oxygen environment at shallow depth (about 40 to 100 m) has recently been reported for the eastern tropical North Atlantic (ETNA). Their hydrographic structure suggests that the water mass inside the eddy is well isolated from ambient waters supporting the development of severe near-surface oxygen deficits. So far, hydrographic and biogeochemical characterization of these eddies was limited to a few autonomous surveys, using moorings, underwater gliders and profiling floats. In this study we present results from the first dedicated biogeochemical survey of one of these eddies conducted in March 2014 near the Cape Verde Ocean Observatory (CVOO). At the time of the survey the eddy core showed lowest oxygen concentrations of less than 5 μmol kg−1 and a pH of approx. 7.6 at the lower boundary of the euphotic zone. Correspondingly, the aragonite saturation level dropped to 1 thereby creating unfavorable conditions for calcifying organisms at this shallow depth. To our knowledge, such enhanced acidity within near-surface waters has never been reported before for the open Atlantic Ocean. Vertical distributions of particulate and dissolved organic matter (POM, DOM) generally show elevated concentrations in the surface mixed layer, but particularly DOM also accumulates beneath the oxygen minimum. Considering reference data from the upwelling region where these eddies are formed, we determined the oxygen consumption through remineralization of organic matter and found an enhancement of apparent oxygen utilization rates (aOUR, 0.26 μmol kg−1 d−1) by almost one order of magnitude when compared with typical values for the open North Atlantic. Computed downward fluxes for particulate organic carbon (POC) at 100 m were about 0.19 to 0.23 g C m−2 d−1 which clearly exceed fluxes typical for an oligotrophic open ocean setting. The observations support the view that the oxygen depleted eddies can be viewed as isolated, westwards propagating upwelling systems as their own.
Laurentide Ice Sheet basal temperatures during the last glacial cycle as inferred from borehole data
Authors: Pickler C. , Beltrami H. , Mareschal J.-C.
Published: January 2016

Abstract. Thirteen temperature–depth profiles ( ≥  1500 m) measured in boreholes in eastern and central Canada were inverted to determine the ground surface temperature histories during and after the last glacial cycle. The sites are located in the southern part of the region that was covered by the Laurentide Ice Sheet. The inversions yield ground surface temperatures ranging from −1.4 to 3.0 °C throughout the last glacial cycle. These temperatures, near the pressure melting point of ice, allowed basal flow and fast flowing ice streams at the base of the Laurentide Ice Sheet. Despite such conditions, which have been inferred from geomorphological data, the ice sheet persisted throughout the last glacial cycle. Our results suggest some regional trends in basal temperatures with possible control by internal heat flow.
Quantification of southwest China rainfall during the 8.2 ka BP event with response to North Atlantic cooling
Authors: Liu Y. , Hu C.
Published: January 2016

Abstract. The 8.2 ka BP event could provide important information for predicting abrupt climate change in the future. Although published records show that the East Asian monsoon area responded to the 8.2 ka BP event, there is no high resolution quantitative reconstructed climate record in this area. In this study, a reconstructed 10-yr moving average annual rainfall record in south west China during the 8.2 ka BP event is presented by comparing two high-resolution stalagmite δ18O records from the same moisture transport pathway. Trends between the reconstructed rainfall sequence and stalagmite Mg/Ca record, another proxy of rainfall, are compared. The reconstructed record shows that the mean annual rainfall in southwest China during the central 8.2 ka BP event is less than that of present (1950 ~ 1990) by ~200 mm, and decreased by ~ 350 mm in ~70 years experiencing an extreme drying period lasting ~50 years. Further analysis suggests that the rainfall decrease in southwest China coupled with the Greenland cooling, the correlation between the annual rainfall and the Greenland ice core δ18O, an indicator of temperature, during the 8.2 ka BP event is significantly higher than today, and may provide insights into abrupt climate prediction under warming conditions.
Bering Sea surface water conditions during Marine Isotope Stages 12 to 10 at Navarin Canyon (IODP Site U1345)
Authors: Caissie Beth E. , Brigham-Grette Julie , Cook Mea S. , Colmenero-Hidalgo Elena
Published: January 2016

Abstract. Records of past warm periods are essential for understanding interglacial climate system dynamics. Marine Isotope Stage 11, occurred ~410 ka when global ice volume was the lowest, sea level was the highest and terrestrial temperatures were the warmest of the last 500 kyrs. This interval with its extreme character has been considered an analog for the near future. The Bering Sea is ideally situated to record how opening or closing the Pacific-Arctic Ocean gateway (Bering Strait) impacted primary productivity, sea ice, and sediment transport in the past; however, little is known about this region prior to 125 ka. IODP Expedition 323 to the Bering Sea offered the unparalleled opportunity to look in detail at time periods older than had been previously retrieved using gravity and piston cores. Here we present a multi-proxy record for Marine Isotope Stages 12-10 from Site U1345 located near the shelf-slope break. MIS 11 is bracketed by highly productive laminated intervals that may have been triggered by flooding of the Beringian shelf. Low insolation is associated with higher productivity, which was likely driven by increased upwelling. During the majority of MIS 11 however, high stratification appears to have led to lowered productivity in both the northern Atlantic and the northern Pacific. U1345, located near the marginal ice zone, experienced seasonal sea ice throughout both the glacial and interglacial stages. When global eustatic sea level was at its peak, Beringian tidewater glaciers advanced, driven by decreasing insolation, reduced seasonality, and high humidity due to high sea level and ice-free summers. Multiple examples of Pacific-Atlantic teleconnections are presented including laminations deposited at the end of MIS 11 in sync with millennial scale stadial events seen in the North Atlantic.
Detecting the onset and effects of major northern hemisphere glaciation in the abyssal tropical Atlantic Ocean
Authors: Wilson Brent , Hayek Lee-Ann C.
Published: January 2016

Abstract. The cooling trend of the Neogene resulted in the diachronous development of glacial conditions, southern high latitudes glaciating before northern. This cooling culminated in the early Pleistocene (2.54 Ma) onset of major glaciation, during which large areas of high latitude land and sea in both hemispheres were periodically blanketed with ice. However, this onset and its impact at low latitude abyssal depths are elusive. This paper examines the abyssal benthic foraminiferal commun ity in the Atlantic Ocean near the Northern Equatorial Countercurrent, in ODP Hole 926A (Ceara Rise), off the River Amazon. Using an assemblage turnover index (ATI), a related conditioned-on-boundary index (CoBI) and SHE analysis, we show how a change in mean assemblage turnover coincides with the early Pleistocene onset of northern hemisphere major glaciation. The community comprises primarily phytodetritivores (Alabaminenella weddellensis, Epistominella exigua and Globocassidulina subglobosa), the proportional abundances of which differ before and after 2.54 Ma. Coupled with changes in the abundances of Nuttallides umbonifera, Bulimina spp. and Uvigerina spp., alterations in the abundances of the phytodetritivores after 2.54 Ma show that the adjustment in biotic turnover at depth resulted from enhanced organic carbon flux from sea surface water. This was probably related to forced southward repositioning of the inter-tropical convergence zone (ITCZ) by the growth of the northern hemisphere ice caps. This was coupled with an increase in bottom current velocity, as shown by a change in the abundance of Cibicidoides wuellerstorfi.
A nondimensional framework for exploring the relief structure of landscapes
Authors: Grieve S. W. D. , Mudd S. M. , Hurst M. D. , Milodowski D. T.
Published: January 2016

Abstract. Considering the relationship between erosion rate and the relief structure of a landscape within a non-dimensional framework facilitates the comparison of landscapes undergoing forcing at a range of scales, and allows broad scale patterns of landscape evolution to be observed. We present software which automates the extraction and processing of relevant topographic parameters to rapidly generate non-dimensional erosion rate and relief data for any landscape where high resolution topographic data is available. Individual hillslopes are identified using a connected components technique which allows spatial averaging to be performed over geomorphologically meaningful spatial units, without the need for manual identification of hillslopes. The software is evaluated on four landscapes across the continental United States, three of which have been studied previously using this technique. We show that it is possible to identify whether landscapes are in topographic steady state. In locations such as Cascade Ridge, CA a clear signal of an erosional gradient can be observed. In the Southern Appalachians, non-dimensional erosion rate and relief data is interpreted as evidence for a landscape decaying following uplift during the Miocene. An analysis of the sensitivity of this method to free parameters used in the data smoothing routines is presented which allows users to make an informed choice of parameters when interrogating new topographic data using this method. A method to constrain the critical graident of the nonlinear sediment flux law is also presented which provides an independent constraint on this parameter for three of the four study landscapes.
Experimental migration of knickpoints: influence of style of base-level fall and bed lithology
Authors: Grimaud J.-L. , Paola C. , Voller V.
Published: January 2016

Abstract. Knickpoints are fascinating and common geomorphic features whose dynamics influence the development of landscapes and source-to-sink systems – in particular the upstream propagation of erosion. Here, we study river profiles and associated knickpoints experimentally in a microflume filled with a cohesive substrate made of silica, water and kaolinite. We focus on the effect on knickpoint dynamics of varying the distribution of base-level fall (rate, increment, and period) and substrate strength, i.e., kaolinite content. Such simple cases are directly comparable to both bedrock and alluvial river systems. Under a constant rate of base-level fall, knickpoints of similar shape are periodically generated, highlighting self-organized dynamics in which steady forcing leads to multiple knickpoint events. Temporary shielding of the bed by alluvium controls the spacing between these unit knickpoints. Shielding is, however, not effective when base-level drops exceed alluvium thickness. While the base-level fall rate controls the overall slope of experiments, it is not instrumental in dictating the major characteristics of unit knickpoints. Instead the velocity, face slope and associated plunge pool depth of these knickpoints are all strongly influenced by lithology. The period between knickpoints is set by both alluvium thickness and base-level fall rate, allowing use of knickpoint spacing along rivers as an indicator of base-level fall rate.
Rhetorics of possibility and inevitability in commercial drone tradescapes
Authors: Jackman A. H.
Published: January 2016

Abstract. Drones have been posited as the "signature device of the present moment" (Noys, 2014). Whilst research into the proliferation of drones in military and defence spheres is gaining notable momentum, drones in commercial and "civilian" contexts "have remained widely unnoticed in academic research" (Klauser and Pedrozo, 2015:285). Complementing emergent scholarship in this area, this paper seeks to both explore and assert the trade show as a valuable site of (industry and advocacy) community "copresence" (McCann, 2011). Drawing upon empirical data, this paper unpacks the rhetorical framing of the commercial drone in the trade-show environment. In so doing, it explores two dominant rhetorical framings, or "techniques of imagination" (Kinsley, 2012:1559), of the commercial drone: those of possibility and inevitability. Such an analysis seeks to respond to calls advocating further attention to the "making of the drone", prior to its "functioning" (Klauser and Pedrozo, 2015) and end-point applications.
Der Kieler Geographentag 1969 – Modernisierungsschub, Mythos, Paradigmenwandel oder vergessene Geschichte?
Authors: Weichhart P.
Published: January 2016

Abstract. Geschichte kann man als die wertende Interpretation und Deutung der Vergangenheit aus der Sicht der jeweiligen Gegenwart ansehen. So kann ein bestimmtes Ereignis der Vergangenheit aus der Perspektive der Gegenwart als besonders bedeutsam, wirkmächtig und konsequenzenreich beurteilt werden oder aber zumindest für eine Zeit in Vergessenheit geraten. Auch in der Geschichte wissenschaftlicher Disziplinen gibt es immer wieder Geschehnisse und Konstellationen, die später als Schlüsselereignisse oder Tipping Points gedeutet werden – unabhängig davon, ob das auch die Zeitgenossen so gesehen haben. Im Falle des Kieler Geographentages war die Einstufung als Schlüsselereignis sowohl zur damaligen Zeit als auch für die Jahre danach durchaus gegeben. Dieser Geographentag – beziehungsweise die dort abgehaltene Diskussionsveranstaltung, die von den geographischen Fachschaften durchgeführt wurde, sowie die ausführlichen Erörterungen und Stellungnahmen im Gefolge dieses „Events" – wurde immer wieder als „Wende", „Umbruch", „Revolution" oder Symbol eines Paradigmenwandels interpretiert. Heute, 46 Jahre danach, lässt sich natürlich die Frage stellen, ob dieses lange Zeit als höchst bedeutsam eingestufte Ereignis für die aktuelle Entwicklung der Geographie immer noch relevant ist und den gegenwärtigen Status des Faches tatsächlich nachhaltig beeinflusst hat.
Spatial and Temporal Variation of Bulk Snow Properties in North Boreal and Tundra Environments Based on Extensive Field Measurements
Authors: Hannula H.-R. , Lemmetyinen J. , Kontu A. , Derksen C. , Pulliainen J.
Published: January 2016

Abstract. In this paper, an extensive dataset of snow in situ measurements, collected in support of airborne SAR-acquisitions in Sodankylä and Saariselkä test sites in northern Finland, is used to analyse the heterogeneity of bulk snow properties (snow depth, density and water equivalent) over different land cover types in northern taiga and tundra areas. In addition, the applicability of different spatial frequencies of snow sampling to estimate the true snow conditions is investigated. Overall, the highest variability in bulk snow properties was found over sparsely vegetated land cover groups, but the scale of variation was smaller in forested areas, as these areas exhibited a low correlation length in snow depth. This implies that more frequent measurements should be executed in forested (~ every < 5 m) than in open areas (~ every 7.5–12.5 m) to catch the true variability in snow depth. The results also indicated that the current spatial resolutions of space borne microwave radiometers and radars used for the remote retrieval of bulk snow properties are all well above the limit to fully describe the spatial variation of e.g. snow depth even in open areas. This conclusion supports the demand of research investigating high-resolution parameter retrieval in remote sensing of snow, e.g. using advanced SAR techniques.
European UV DataBase (EUVDB) as a repository and quality analyzer for solar spectral UV irradiance monitored in Sodankylä
Authors: Heikkilä A. , Kaurola J. , Lakkala K. , Karhu J. M. , Kyrö E. , Koskela T. , Engelsen O. , Slaper H. , Seckmeyer G.
Published: January 2016

Abstract. Databases gathering atmospheric data have great potential not only as data storages but also in serving as platforms for coherent quality assurance (QA). We report on the flagging system and QA tools designed for and implemented in the European UV DataBase EUVDB (http://uv.fmi.fi/uvdb/) for measured data on solar spectral UV irradiance. Spectra scanned by the Brewer#037 MkII spectroradiometer in Sodankylä (67.37 °N, 26.63 °E) over the years 1990–2014 and uploaded into the database are examined using the inherent QA tools of the database. The study demonstrates the performance of the QA tools of the EUVDB. In addition, it yields an overall view of the availability and quality of the solar UV spectra recorded in Sodankylä over a quarter of a century. Over 90 % of the four main quality indicators are flagged as GREEN, indicating the highest achievable quality. For the BLACK flags, denoting data not meeting the pre-defined requirements, the percentages for all the indicators remain below 0.12 %.
In search of traceability: two decades of calibrated Brewer UV measurements in Sodankylä and Jokioinen
Authors: Mäkelä J. S. , Lakkala K. , Meinander O. , Kaurola J. , Koskela T. , Karhu J. M. , Karppinen T. , Kyrö E. , de Leeuw G. , Heikkilä A.
Published: January 2016

Abstract. The two Brewer spectrometers of the Finnish Meteorological Institute at Jokioinen and Sodänkylä have been maintained and calibrated according to the highest levels of the WMO/GAW recommendations, with rigorous quality control and quality assurance. However, the WMO/GAW recommendations are ambiguous on a number of decisions which need to be made when the response of the Brewer is calculated. The decisions have been left to the individual operators. Even within FMI, the two stations have used slightly different procedures, both completely consistent with the GAW recommendations. We suggest that the Brewer community should in the future address this ambiguity.
PMCAMx-2015 evaluation over Europe against AERONET and MODIS aerosol optical depth measurements
Authors: Panagiotopoulou Antigoni , Charalambidis Panagiotis , Fountoukis Christos , Pilinis Christodoulos , Pandis Spyros N.
Published: January 2016

Abstract. The ability of the chemical transport model (CTM) PMCAMx to reproduce aerosol optical depth (AOD) measurements by the Aerosol Robotic Network (AERONET) and the Moderate Resolution Imaging Spectroradiometer (MODIS) over Europe during a photochemically active period is evaluated. Periods with high dust levels are excluded so the analysis focuses on the ability of the model to simulate the mostly secondary aerosol and its interactions with water. PMCAMx reproduces the monthly mean MODIS and AERONET AOD values over the Iberian Peninsula, the British Isles, central Europe, and Russia with fractional bias less than 15 % and fractional error less than 30 %. However, the model overestimates the AOD over northern Europe probably due to an overestimation of organic aerosol and sulfates. On the other end, PMCAMx underestimates the monthly mean MODIS AOD over the Balkans, the Mediterranean, and the South Atlantic. These errors are probably due to an underestimation of sulfates. Sensitivity tests indicate that the evaluation results of the monthly mean AODs are quite sensitive to the relative humidity (RH) fields used by PMCAMx, but are not sensitive to the simulated size distribution and the black carbon mixing state.
Development of aroCACM/MPMPO 1.0: a model to simulate secondary organic aerosol from aromatic precursors in regional models
Authors: Dawson M. L. , Xu J. , Griffin R. J. , Dabdub D.
Published: January 2016

Abstract. The atmospheric oxidation of aromatic compounds is an important source of secondary organic aerosol (SOA) in urban areas. The oxidation of aromatics depends strongly on the levels of nitrogen oxides NOx). However, details of the mechanisms by which oxidation occurs are only recently being elucidated. Xu et al. (2015) developed an updated version of the gas-phase Caltech Atmospheric Chemistry Mechanism (CACM) designed to simulate toluene and m-xylene oxidation in chamber experiments over a range of NOx conditions. The output from such a mechanism can be used in thermodynamic predictions of gas-particle partitioning leading to SOA. The current work reports the development of a model for SOA formation that combines the gas-phase mechanism of Xu et al. (2015) with an updated lumped SOA partitioning scheme (MPMPO) that allows partitioning to multiple aerosol phases and that is designed for use in larger scale three-dimensional models. The resulting model is termed aroCACM/MPMPO 1.0. The model is integrated into the University of California, Irvine – California Institute of Technology (UCI-CIT) airshed model, which simulates the South Coast Air Basin (SoCAB) of California. Simulations using 2012 emissions indicate that “low- NOx” pathways to SOA formation from aromatic oxidation play an important role, even in regions that typically exhibit high NOx concentrations.
A new metric for climate models that includes field and spatial dependencies using Gaussian Markov Random Fields
Authors: Nosedal-Sanchez A. , Jackson C. S. , Huerta G.
Published: January 2016

Abstract. A new metric for climate model evaluation has been developed that potentially mitigates some of the limitations that exist for observing and representing field and space dependencies of climate phenomena. Traditionally such dependencies have been ignored when climate models have been evaluated against observational data, which makes it difficult to assess whether any given model is simulating observed climate for the right reasons. The new metric uses Gaussian Markov Random Fields for estimating field and space dependencies within a first order grid point neighborhood structure. We illustrate the ability of Gaussian Markov Random Fields to represent empirical estimates of field and space covariances using "witch hat" graphs. We further use the new metric to evaluate the tropical response of a climate model (CAM3.1) to changes in two parameters important to its representation of cloud and precipitation physics. Overall, the inclusion of dependency information did not alter significantly the recognition of those regions of parameter space that best approximated observations. However there were some qualitative differences in the shape of the response surface that suggest how such a measure could affect estimates of model uncertainty.
Evaluation of NorESM-OC (versions 1 and 1.2), the ocean carbon-cycle stand-alone configuration of the Norwegian Earth System Model (NorESM1)
Authors: Schwinger J. , Goris N. , Tjiputra J. , Kriest I. , Bentsen M. , Bethke I. , Ilicak M. , Assmann K. , Heinze C.
Published: January 2016

Abstract. Idealised and hindcast simulations performed with the stand-alone ocean carbon-cycle configuration of the Norwegian Earth System Model (NorESM-OC) are described and evaluated. We present simulation results of two different model versions at different grid resolutions and using two different atmospheric forcing data sets. Model version NorESM-OC1 corresponds to the version that is included in the fully coupled model NorESM-ME1, which participated in CMIP5. The main update between NorESM-OC1 and NorESM-OC1.2 is the addition of two new options for the treatment of sinking particles. We find that using a constant sinking speed, which has been the standard in NorESM's ocean carbon cycle module HAMOCC (HAMburg Ocean Carbon Cycle model) does not transport enough particulate organic carbon (POC) into the deep ocean below approximately 2000 m depth. The two newly implemented parameterisations, a particle aggregation scheme with prognostic sinking speed, and a simpler scheme prescribing a linear increase of sinking speed with depth, provide better agreement with observed POC fluxes. Additionally, reduced deep ocean biases of oxygen and remineralised phosphate indicate a better performance of the new parameterisations. For model version 1.2, a re-tuning of the ecosystem parameterisation has been performed, which (i) reduces previously too high primary production in high latitudes, (ii) consequently improves model results for surface nutrients, and (iii) reduces alkalinity and dissolved inorganic carbon biases at low latitudes. We use hindcast simulations with prescribed observed and constant (pre-industrial) atmospheric CO2 concentrations to derive the past and contemporary ocean carbon sink. For the period 1990–1999 we find an average ocean carbon uptake ranging from 2.01 to 2.58 Pg C yr-1 depending on model version, grid resolution and atmospheric forcing data set.
A High-order Staggered Finite-Element Vertical Discretization for Non-Hydrostatic Atmospheric Models
Authors: Guerra J. E. , Ullrich P. A.
Published: January 2016

Abstract. Atmospheric modeling systems require economical methods to solve the non-hydrostatic Euler equations. Two major differences between hydrostatic models and a full non-hydrostatic description lies in the vertical velocity tendency and numerical stiffness associated with sound waves. In this work we introduce a new arbitrary-order vertical discretization entitled the Staggered Nodal Finite Element Method (SNFEM). Our method uses a generalized discrete derivative that consistently combines the Discontinuous Galerkin and Spectral Element methods on a staggered grid. Our combined method leverages the accurate wave propagation and conservation properties of spectral elements with staggered methods that eliminate stationary (2Δx) modes. Furthermore, high-order accuracy also eliminates the need for a reference state to maintain hydrostatic balance. In this work we demonstrate the use of high vertical order as a means of improving simulation quality at relatively coarse resolution. We choose a test case suite that spans the range of atmospheric ﬂows from predominantly hydrostatic to nonlinear in the Large Eddy regime. Our results show that there is a distinct benefit in using the high-order vertical coordinate at low resolutions with the same robust properties of the low-order alternative.
On computation of Hough functions
Authors: Wang H. , Boyd J. P. , Akmaev R. A.
Published: January 2016

Abstract. Hough functions are the eigenfunctions of Laplace’s tidal equation governing ﬂuid motion on a rotating sphere with a resting basic state. Several numerical methods have been used in the past. In this paper, we compare two of those methods: normalized associated Legendre polynomial expansion and Chebyshev collocation. Both methods are not widely used, but both have some advantages over the commonly-used unnormalized associated Legendre polynomial expansion method. Comparable results are obtained using both methods. For the ﬁrst method we note some details on numerical implementation. The Chebyshev collocation method was ﬁrst used for Laplace tidal problem by Boyd (1976) and is relatively easy to use. A compact Matlab code is provided for this method. We also illustrate the importance and effect of including a parity factor in Chebyshev polynomial expansions for modes with odd zonal wavenumbers.
Modeling global water use for the 21st century: the Water Futures and Solutions (WFaS) initiative and its approaches
Authors: Wada Y. , Flörke M. , Hanasaki N. , Eisner S. , Fischer G. , Tramberend S. , Satoh Y. , van Vliet M. T. H. , Yillia P. , Ringler C. , Burek P. , Wiberg D.
Published: January 2016

Abstract. To sustain growing food demand and increasing standard of living, global water use increased by nearly 6 times during the last 100 years, and continues to grow. As water demands get closer and closer to the water availability in many regions, each drop of water becomes increasingly valuable and water must be managed more efficiently and intensively. However, soaring water use worsens water scarcity conditions already prevalent in semi-arid and arid regions, increasing uncertainty for sustainable food production and economic development. Planning for future development and investments requires that we prepare water projections for the future. However, estimations are complicated because the future of the world's waters will be influenced by a combination of environmental, social, economic, and political factors, and there is only limited knowledge and data available about freshwater resources and how they are being used. The Water Futures and Solutions (WFaS) initiative coordinates its work with other ongoing scenario efforts for the sake of establishing a consistent set of new global water scenarios based on the shared socio-economic pathways (SSPs) and the representative concentration pathways (RCPs). The WFaS "fast-track" assessment uses three global water models, namely H08, PCR-GLOBWB, and WaterGAP. This study assesses the state of the art for estimating and projecting water use regionally and globally in a consistent manner. It provides an overview of different approaches, the uncertainty, strengths and weaknesses of the various estimation methods, types of management and policy decisions for which the current estimation methods are useful. We also discuss additional information most needed to be able to improve water use estimates and be able to assess a greater range of management options across the water–energy–climate nexus.
High-frequency monitoring of water fluxes and nutrient loads to assess the effects of controlled drainage on water storage and nutrient transport
Authors: Rozemeijer J. C. , Visser A. , Borren W. , Winegram M. , van der Velde Y. , Klein J. , Broers H. P.
Published: January 2016

Abstract. High nitrogen (N) and phosphorus (P) fluxes from upstream agriculture threaten aquatic ecosystems in surface waters and estuaries, especially in areas characterized by high agricultural N and P inputs and densely drained catchments like the Netherlands. Controlled drainage has been recognized as an effective option to optimize soil moisture conditions for agriculture and to reduce unnecessary losses of fresh water and nutrients. This is achieved by introducing control structures with adjustable overflow levels into subsurface tube drain systems. A small-scale (1 ha) field experiment was designed to investigate the hydrological and chemical changes after introducing controlled drainage. Precipitation rates and the response of water tables and drain fluxes were measured in the periods before the introduction of controlled drainage (2007–2008) and after (2009–2011). For the N and P concentration measurements, auto-analyzers for continuous records were combined with passive samplers for time-averaged concentrations at individual drain outlets. The experimental setup enabled the quantification of changes in the water and solute balance after introducing controlled drainage. The results showed that introducing controlled drainage reduced the drain discharge and increased the groundwater storage in the field. To achieve this, the overflow levels have to be elevated in early spring, before the drain discharge stops due to dryer conditions and falling groundwater levels. The groundwater storage in the field would have been larger if the water levels in the adjacent ditch were controlled as well by an adjustable weir. The N concentrations and loads increased, which was largely related to elevated concentrations in one of the three monitored tube drains. The P loads via the tube drains reduced due to the reduction in discharge after introducing controlled drainage. However, this may be counteracted by the higher groundwater levels and the larger contribution of N- and P-rich shallow groundwater and overland flow to the surface water.
Spatio-temporal variability of snow water equivalent in the extra-tropical Andes Cordillera from distributed energy balance modeling and remotely sensed snow cover
Authors: Cornwell E. , Molotch N. P. , McPhee J.
Published: January 2016

Abstract. Seasonal snow cover is the primary water source for human use and ecosystems along the extratropical Andes Cordillera. Despite its importance, relatively little research has been devoted to understanding the properties, distribution and variability of this natural resource. This research provides high-resolution (500 m), daily distributed estimates of end-of-winter and spring snow water equivalent over a 152 000 km2 domain that includes the mountainous reaches of central Chile and Argentina. Remotely sensed fractional snow-covered area and other relevant forcings are combined with extrapolated data from meteorological stations and a simplified physically based energy balance model in order to obtain melt-season melt fluxes that are then aggregated to estimate the end-of-winter (or peak) snow water equivalent (SWE). Peak SWE estimates show an overall coefficient of determination R2 of 0.68 and RMSE of 274 mm compared to observations at 12 automatic snow water equivalent sensors distributed across the model domain, with R2 values between 0.32 and 0.88. Regional estimates of peak SWE accumulation show differential patterns strongly modulated by elevation, latitude and position relative to the continental divide. The spatial distribution of peak SWE shows that the 4000–5000 m a.s.l. elevation band is significant for snow accumulation, despite having a smaller surface area than the 3000–4000 m a.s.l. band. On average, maximum snow accumulation is observed in early September in the western Andes, and in early October on the eastern side of the continental divide. The results presented here have the potential of informing applications such as seasonal forecast model assessment and improvement, regional climate model validation, as well as evaluation of observational networks and water resource infrastructure development.