ALBERT

Beschreibung: 〈b〉Estimating the soil N〈sub〉2〈/sub〉O emission intensity of croplands in northwest Europe〈/b〉〈br〉 Vasileios Myrgiotis, Mathew Williams, Robert M. Rees, and Cairistiona F. E. Topp〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-490,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 This study focuses on a northwest European cropland region and shows that the type of crop growing on a soil has notable effects on the emission of nitrous oxide (N〈sub〉2〈/sub〉O – a greenhouse gas) from that soil. It was found that N〈sub〉2〈/sub〉O emissions from soils under oilseed cultivation are significantly higher than soils under cereal cultivation. This variation is mostly explained by the fact that oilseeds require more nitrogen (fertiliser) than cereals especially at early crop growth stages.

Beschreibung: 〈b〉Nutrient distribution and nitrogen and oxygen isotopic composition of nitrate in water masses of the subtropical South Indian Ocean〈/b〉〈br〉 Natalie C. Harms, Niko Lahajnar, Birgit Gaye, Tim Rixen, Kirstin Dähnke, Markus Ankele, Ulrich Schwarz-Schampera, and Kay-Christian Emeis〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-511,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 The Indian Ocean subtropical gyre is a large oligotrophic area that is likely to adjust to continued warming by increasing stratification, reduced nutrient supply, and decreasing biological production. In this study, we investigated concentrations of nutrients and stable isotopes of nitrate. We determine the lateral influence of water masses entering the gyre from the northern Indian Ocean and from the Southern Ocean and quantify the input of nitrogen by N〈sub〉2〈/sub〉-fixation into the surface layer.

Beschreibung: 〈b〉Organic signatures in Pleistocene cherts from Lake Magadi (Kenya), analogs for early Earth hydrothermal deposits〈/b〉〈br〉 Manuel Reinhardt, Walter Goetz, Jan-Peter Duda, Christine Heim, Joachim Reitner, and Volker Thiel〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-513,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Organic matter in Archean hydrothermal cherts may contain molecular traces of early life. Alteration processes during and after deposition, however, may have obliterated potential biosignatures. Our results from modern analog samples (Pleistocene cherts from Lake Magadi, Kenya) show that biomolecules can survive early hydrothermal destruction in the macromolecular fraction of the organic matter. A conservation of molecular biosignatures in Archean hydrothermal cherts therefore seems possible.

Beschreibung: 〈b〉Reviews and syntheses: Dams, water quality and tropical reservoir stratification〈/b〉〈br〉 R. Scott Winton, Elisa Calamita, and Bernhard Wehrli〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-510,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 A global boom in dam construction throughout the world’s tropics motivated us to review and synthesize information on the water quality impacts of dams with a focus on low latitude contexts and scope for mitigation. Sediment trapping and reservoir stratification are key process driving chemical and ecological impacts to tropical rivers. We analyze the 54 most-voluminous low latitude reservoirs and find that stratification seems to be a ubiquitous phenomenon.

Beschreibung: 〈b〉Floodwater Impact on Galveston Bay Phytoplankton Taxonomy, Pigment Composition and Photo-Physiological State following Hurricane Harvey from Field and Ocean Color (Sentinel-3A OLCI) Observations〈/b〉〈br〉 Bingqing Liu, Eurico J. D'Sa, and Ishan D. Joshi〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-504,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 An approach using bio-optical field and ocean color (Sentinel-3A OLCI) data combined with inversion models allowed for the first time, an assessment of phytoplankton response (changes in taxonomy, pigment composition and physiological state) to a large hurricane-related floodwater perturbation in a turbid estuary. The study revealed the transition in phytoplankton community species as well as the spatiotemporal distributions of phytoplankton diagnostic pigments in the floodwater impacted bay.

Beschreibung: 〈b〉Stand age and species composition effects on surface albedo in a mixedwood boreal forest〈/b〉〈br〉 Mohammad Abdul Halim, Han Y. H. Chen, and Sean C. Thomas〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-501,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Using field data collected over 4 years across a range of stand ages, we investigated how seasonal surface albedo in boreal forest varies with stand age, stand structure, and composition. Our results indicate that successional change in species composition is a key driver of age-related patterns in albedo, with hardwood species associated with higher albedo. The patterns described have important implications for both climate modelling and 〈q〉climate-smart〈/q〉 boreal forest management.

Beschreibung: 〈b〉Three decades of simulated global terrestrial carbon fluxes from a data assimilation system confronted to different periods of observations〈/b〉〈br〉 Karel Castro-Morales, Gregor Schürmann, Christoph Köstler, Christian Rödenbeck, Martin Heimann, and Sönke Zaehle〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-517,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 To obtain nearly thirty years of global terrestrial carbon fluxes, we simultaneously incorporated in a land surface model three different time periods of two observational data sets: absorbed photosynthetic active radiation and atmospheric CO〈sub〉2〈/sub〉 concentrations. One decade of data is enough to improve the modeled long-term trends and seasonal amplitudes of the assimilated variables, particularly in boreal regions. This model has the potential to provide short-term predictions of land carbon fluxes.

Beschreibung: 〈b〉The influence of reservoir traits on carbon dioxide emissions in the Belo Monte hydropower complex, Xingu River, Amazon – Brazil〈/b〉〈br〉 Kleiton R. Araújo, Henrique O. Sawakuchi, Dailson J. Bertassoli Júnior, André O. Sawakuchi, Karina D. Silva, Thiago V. Bernardi, Nicholas D. Ward, and Tatiana S. Pereira〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-53,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Little information is available about run-of-the-river carbon dioxide (CO〈sub〉2〈/sub〉) emission and how reservoir type influence CO〈sub〉2〈/sub〉 production. With this regard we evaluated the CO〈sub〉2〈/sub〉 fluxes of Belo Monte hydropower complex and observed variability in CO〈sub〉2〈/sub〉 emission related to the type of environment, among reservoirs and the land use of flooded areas after impoundment. Our results emphasize that reservoir type could contribute on CO〈sub〉2〈/sub〉 emissions.

Beschreibung: 〈b〉Role of Microbial Communities in the Weathering and Stalactite Formation in Karst Topography〈/b〉〈br〉 Tung-Yi Huang, Bing-Mu Hsu, Cheng-Wei Fan, Hsin-Chi Tsai, Chien-Yi Tung, and Jung-Sheng Chen〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-12,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 This study surveyed the bacterial genetic material from environment around a limestone gulch, namely scrapes on speleothem surface, dripping water through speleothem, earth under a plan limestone wall, and scrapes from the plan wall. By the estimation of bioinformatics prediction, the relative abundance of bacteria inducing calcium precipitation in scrapes of speleothems and the water were about 100 times higher than the plan wall, while weathering related bacteria were plenty on the plan wall.

Beschreibung: 〈b〉Hyposalinity tolerance inthecoccolithophorid 〈i〉Emiliania huxleyi〈/i〉 under the influence of ocean acidification involves enhanced photosynthetic performance〈/b〉〈br〉 Jiekai Xu, John Beardall, and Kunshan Gao〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-4,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 A lot of papers studying Ocean acidification (OA) have been published while no related reports can be found on the combined effects of OA with decreased salinity on coccolithophores yet.Thus, we investigated the physiological responses of an Emiliania huxleyi strain grown at 2CO〈sub〉2〈/sub〉 concentrations and 3 levels of salinity and found cells could tolerate reduced salinity under OA as its increased light capturing capability, which suggests a potential niche extension of coccolithophores in the future.

Beschreibung: 〈b〉Mapping trends in woody cover throughout Namibian savanna with MODIS seasonal phenological metrics and field inventory data〈/b〉〈br〉 Vladimir R. Wingate, Nikolaus J. Kuhn, Stuart R. Phinn, and Cornelis van der Waal〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-28,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉Woody vegetation is an integral component of savannas. Here, two main change processes alter woody vegetation, namely shrub encroachment and deforestation. Both impact a range of ecosystem services and functions across scales. Accurate estimates of change, including spatial extent, rate and drivers are lacking. This is primarily due to savanna vegetation comprising woody and herbaceous vegetation, each of which exhibit divergent phenological characteristics, and vary importantly in their response to climatic and environmental factors. This study uses phenological metrics derived from the MODIS MOD13Q1 NDVI time-series to model woody cover as a function of field measurements, and to map trends across Namibia. These metrics enhance the contrasting phenological characteristics of woody and herbaceous vegetation, and standardizes their annual response to climatic and environmental factors by integrating short term variation. Trends in woody cover are excellent indicators of shrub encroachment and deforestation. Trend significance was computed using the Mann-Kendall test, while change statistics, including the rate and spatial extent of change were derived using the Theil-Sen slope. Change was evaluated in relation to drivers including land-use, population, biomes and precipitation. An overall decrease in woody cover was identified, with the most pronounced decreases found in urban and densely populated areas. Decreases in woody cover were not homogenously distributed; losses predominated in tropical desert and dry forests, but gains were found across shrub lands.〈/p〉

Beschreibung: 〈b〉Regulation of N〈sub〉2〈/sub〉O emissions from acid organic soil drained for agriculture: Effects of land use and season〈/b〉〈br〉 Arezoo Taghizadeh-Toosi, Lars Elsgaard, Tim J. Clough, Rodrigo Labouriau, Vibeke Ernstsen, and Søren O. Petersen〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-14,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉Drained organic soils are extensively used for cereal and high-value cash crop production or as grazing land, but emissions of nitrous oxide (N〈sub〉2〈/sub〉O) are enhanced by the drainage and cultivation. A study was conducted to investigate the regulation of N〈sub〉2〈/sub〉O emissions in a raised bog area drained for agriculture. The area has been classified as potentially acid sulfate soil, and we hypothesised that pyrite oxidation was a potential driver of N〈sub〉2〈/sub〉O emissions. Two sites with rotational grass, and two sites with a potato crop, were equipped for monitoring of N〈sub〉2〈/sub〉O emissions, as well as sub-soil N〈sub〉2〈/sub〉O concentrations at 5, 10, 20, 50 and 100 cm depth, during spring and autumn 2015. Precipitation, air and soil temperature, soil moisture, water table (WT) depth, and soil mineral N were recorded during weekly field campaigns. In late April and early September, intact cores were collected to 1 m depth at adjacent grassland and potato sites for analysis of soil properties, which included acid volatile sulfide (AVS) and chromium-reducible sulfur (CRS) to quantify, respectively, iron monosulfide (FeS) and pyrite (FeS〈sub〉2〈/sub〉), as well as total reactive iron (TRFe) and nitrite (NO〈sub〉2〈/sub〉〈sup〉−〈/sup〉). Soil organic matter composition and total reduction capacity was also determined. The soil pH varied between 4.7 and 5.4. Equivalent soil gas phase concentrations of N〈sub〉2〈/sub〉O ranged from around 10 µL L〈sup〉−1〈/sup〉 at grassland sites to several hundred µL L〈sup〉−1〈/sup〉 at potato sites, in accordance with lower soil mineral N concentrations at grassland sites. Total N〈sub〉2〈/sub〉O emissions during 152–174 days were 3–6 kg N〈sub〉2〈/sub〉O-N ha〈sup〉−1〈/sup〉 for rotational grass, and 19–21 kg N〈sub〉2〈/sub〉O-N ha〈sup〉−1〈/sup〉 for potato sites. Statistical analyses by graphical models showed that soil N〈sub〉2〈/sub〉O concentration in the capillary fringe was the strongest predictor for N〈sub〉2〈/sub〉O emissions in spring, and for grassland sites also in the autumn. For potato sites in the autumn, nitrate (NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉) availability in the top soil, together with temperature, were the main controls on N〈sub〉2〈/sub〉O emissions. Pyrite oxidation coupled with NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 reduction could not be dismissed as a source of N〈sub〉2〈/sub〉O, but the total reduction capacity of the peat soil was much higher than explained by the FeS〈sub〉2〈/sub〉 concentration. The concentrations of TRFe were also much higher than pyrite concentrations, and potentially chemodenitrification could have been a source of N〈sub〉2〈/sub〉O during WT drawdown in spring. The N〈sub〉2〈/sub〉O emissions associated with rapid soil wetting and WT rise in autumn were consistent with biological denitrification. Soil N availability and seasonal WT changes were important controls of N〈sub〉2〈/sub〉O emissions.〈/p〉

Beschreibung: 〈b〉Temporal variability in foraminiferal morphology and geochemistry at the West Antarctic Peninsula: a sediment trap study〈/b〉〈br〉 Anna Mikis, Katharine R. Hendry, Jennifer Pike, Daniela N. Schmidt, Kirsty M. Edgar, Victoria Peck, Frank J. C. Peeters, Melanie J. Leng, Michael P. Meredith, Chloe L. Todd, Sharon Stammerjohn, and Hugh Ducklow〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-19,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Antarctic marine calcifying organisms are threatened by regional climate change and ocean acidification. Future projections of regional carbonate production are challenging due to the lack of historical data combined with complex climate variability. We present a six-year record of flux, morphology, and geochemistry of an Antarctic planktonic foraminifera, which shows that their growth is most sensitive to sea-ice dynamics, and is linked with the El Niño Southern Oscillation.

Beschreibung: 〈b〉Variations in the summer oceanic 〈i〉p〈/i〉CO〈sub〉2〈/sub〉 and carbon sink in Prydz Bay using the self-organizing map analysis approach〈/b〉〈br〉 Suqing Xu, Keyhong Park, Yanmin Wang, Liqi Chen, Di Qi, and Bingrui Li〈br〉 Biogeosciences, 16, 797-810, https://doi.org/10.5194/bg-16-797-2019, 2019〈br〉 In this study we applied the self-organizing map (SOM) method to estimate the oceanic 〈i〉p〈/i〉CO〈sub〉2〈/sub〉 in Prydz Bay derived from its main controlling factors. The RMSE of the SOM-derived 〈i〉p〈/i〉CO〈sub〉2〈/sub〉 was 22.14 µatm compared to SOCAT datasets. Our results showed that the monthly averaged uptake of atmospheric CO〈sub〉2〈/sub〉 for February 2015 was 23.57±6.36 TgC. Strong potential anthropogenic CO〈sub〉2〈/sub〉 uptake in the 〈q〉shelf region〈/q〉 will enhance ocean acidification (OA) in the deep water of Prydz Bay and subsequently affect deep OA.

Beschreibung: 〈b〉Automatic high-frequency measurements of full soil greenhouse gas fluxes in a tropical forest〈/b〉〈br〉 Elodie Alice Courtois, Clément Stahl, Benoit Burban, Joke Van den Berge, Daniel Berveiller, Laëtitia Bréchet, Jennifer Larned Soong, Nicola Arriga, Josep Peñuelas, and Ivan August Janssens〈br〉 Biogeosciences, 16, 785-796, https://doi.org/10.5194/bg-16-785-2019, 2019〈br〉 Measuring greenhouse gases (GHGs) from a natural ecosystem remains a contemporary challenge. We tested the use of appropriate technology for the estimation of soil fluxes of the three main GHGs in a tropical rainforest for 4 months. We showed that our design allowed the continuous high-frequency measurement of the three gases in a tropical biome and provide recommendations for its implementation. This study is a major step in the estimation of the global GHG budget of tropical forests.

Beschreibung: 〈b〉El Niño–Southern Oscillation (〈i〉ENSO〈/i〉) event reduces CO〈sub〉2〈/sub〉 uptake of an Indonesian oil palm plantation〈/b〉〈br〉 Christian Stiegler, Ana Meijide, Yuanchao Fan, Ashehad Ashween Ali, Tania June, and Alexander Knohl〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-49,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 We show the response of a commercial oil palm plantation in Indonesia to the extreme El Niño–Southern Oscillation (ENSO) event in 2015. Our measurements and model suggest that without human-induced forest fires and related smoke emission, the observed negative impact on oil palm carbon dioxide greenhouse gas fluxes, carbon accumulation and yield due to ENSO-related drought would have been less pronounced. With respect to climate change we highlight the importance of fire prevention in the area.

Beschreibung: 〈b〉High-frequency variability of CO〈sub〉2〈/sub〉 in Grand Passage, Bay of Fundy, Nova Scotia〈/b〉〈br〉 Rachel M. Horwitz, Alex E. Hay, William J. Burt, Richard A. Cheel, Joseph Salisbury, and Helmuth Thomas〈br〉 Biogeosciences, 16, 605-616, https://doi.org/10.5194/bg-16-605-2019, 2019〈br〉 High-frequency CO〈sub〉2〈/sub〉 measurements are used to quantify the daily and tidal cycles of dissolved carbon in the Bay of Fundy – home to the world's largest tides. The oscillating tidal flows drive a net carbon transport, and these results suggest that previously unaccounted for tidal variation could substantially modulate the coastal ocean's response to global ocean acidification. Evaluating the impact of rising atmospheric CO〈sub〉2〈/sub〉 on coastal systems requires understanding this short-term variability.

Beschreibung: 〈b〉Pyrite oxidization accelerates bacterial carbon sequestration in copper mine tailings〈/b〉〈br〉 Yang Li, Zhaojun Wu, Xingchen Dong, Zifu Xu, Qixin Zhang, Haiyan Su, Zhongjun Jia, and Qingye Sun〈br〉 Biogeosciences, 16, 573-583, https://doi.org/10.5194/bg-16-573-2019, 2019〈br〉 This paper contributes to the study of bacterial carbon sequestration in mine tailings. Previous studies focused on carbonate mineral precipitation, while the role of autotrophs in carbon sequestration has been neglected. Carbon sequestration in two mine tailings treated with FeS〈sub〉2〈/sub〉 was analyzed using 〈sup〉13〈/sup〉C isotope labeling, pyrosequencing, and DNA SIP to identify carbon fixers. This paper is the first to investigate carbon sequestration by autotrophic groups in mine tailings.

Beschreibung: 〈b〉Oxygen isotope composition of the final chamber of planktic foraminifera provides evidence of vertical migration and depth-integrated growth〈/b〉〈br〉 Hilde Pracht, Brett Metcalfe, and Frank J. C. Peeters〈br〉 Biogeosciences, 16, 643-661, https://doi.org/10.5194/bg-16-643-2019, 2019〈br〉 In palaeoceanography the shells of single-celled foraminifera are routinely used as proxies to reconstruct the temperature, salinity and circulation of the ocean in the past. Traditionally a number of specimens were pooled for a single stable isotope measurement; however, technical advances now mean that a single shell or chamber of a shell can be measured individually. Three different hypotheses regarding foraminiferal biology and ecology were tested using this approach.

Beschreibung: 〈b〉Long chain diols in settling particles in tropical oceans: insights into sources, seasonality and proxies〈/b〉〈br〉 Marijke W. de Bar, Jenny Ullgren, Robert C. Thunnell, Stuart G. Wakeham, Geert-Jan A. Brummer, Jan-Berend W. Stuut, Jaap S. Sinninghe Damsté, and Stefan Schouten〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-15,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 We have analyzed sediment traps from the Cariaco Basin, tropical Atlantic and Mozambique Channel to evaluate seasonal imprints in the concentrations and fluxes of long-chain diols, and the LDI proxy (sea surface temperature proxy) and Diol Index (upwelling indicator). Despite significant degradation, LDI-derived temperatures are very similar for the sediment traps and seafloor sediments, and correspond with annual mean SST.

Beschreibung: 〈b〉Evidence for microbial iron reduction in the methanogenic sediments of the oligotrophic SE Mediterranean continental shelf〈/b〉〈br〉 Hanni Vigderovich, Lewen Liang, Barak Herut, Fengping Wang, Eyal Wurgaft, Maxim Rubin-Blum, and Orit Sivan〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-21,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 Microbial iron reduction participates in important biogeochemical cycles. In the last decade iron reduction has been observed in many aquatic sediments below its classical zone, in the methane production zone, suggesting a link between the two cycles. Here we present evidence for microbial iron reduction in the methanogenic depth of the oligotrophic SE Mediterranean continental shelf using mainly geochemical and microbial sedimentary profiles and suggest possible mechanisms for this process.

Beschreibung: 〈b〉Seasonality of archaeal lipid flux and GDGT-based thermometry in sinking articles of high latitude oceans: Fram Strait (79° N) and Antarctic Polar Front (50° S)〈/b〉〈br〉 Eunmi Park, Jens Hefter, Gehard Fischer, Morten H. Iversen, Simon Ramondenc, Eva-Maria Nöthig, and Gesine Mollenhauer〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-34,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 We analyzed GDGT based proxy temperatures in the polar oceans. In the eastern Fram Strait (79° N), the nutrient distribution may determine the depth habit of Thaumarchaeota and thus the proxy temperature. In the Antarctic Polar Front (50° S), the contribution of Euryarchaeota or the nonlinear correlation between the proxy values and temperatures may cause the warm biases of the proxy temperatures relative to SSTs.

Beschreibung: 〈b〉Export fluxes of dissolved inorganic carbon to the northern Indian Ocean from the Indian monsoonal rivers〈/b〉〈br〉 Moturi S. Krishna, Rongali Viswanadham, Mamidala H. K. Prasad, Vuravakonda R. Kumari, and Vedula V. S. S. Sarma〈br〉 Biogeosciences, 16, 505-519, https://doi.org/10.5194/bg-16-505-2019, 2019〈br〉 An order-of-magnitude variability in DIC was found within the Indian estuaries due to significant variability in size of rivers, precipitation pattern and lithology in the catchments. Indian monsoonal estuaries annually export ∼ 10.3 Tg of DIC to the northern Indian Ocean, of which 75 % enters into the Bay of Bengal. Our results indicated that chemical weathering of carbonate and silicate minerals by soil CO〈sub〉2〈/sub〉 is the major source of DIC in the Indian monsoonal rivers.

Beschreibung: 〈b〉Stable carbon and nitrogen isotopic composition of leaves, litter, and soils of various ecosystems along an elevational and land-use gradient at Mount Kilimanjaro, Tanzania〈/b〉〈br〉 Friederike Gerschlauer, Gustavo Saiz, David Schellenberger Costa, Michael Kleyer, Michael Dannenmann, and Ralf Kiese〈br〉 Biogeosciences, 16, 409-424, https://doi.org/10.5194/bg-16-409-2019, 2019〈br〉 Mount Kilimanjaro is an iconic environmental asset under serious threat due to increasing human pressures and climate change constraints. We studied variations in the stable isotopic composition of carbon and nitrogen in plant, litter, and soil material sampled along a strong land-use and altitudinal gradient. Our results show that, besides management, increasing temperatures in a changing climate may promote carbon and nitrogen losses, thus altering the stability of Kilimanjaro ecosystems.

Beschreibung: 〈b〉Neglecting plant–microbe symbioses leads to underestimation of modeled climate impacts〈/b〉〈br〉 Mingjie Shi, Joshua B. Fisher, Richard P. Phillips, and Edward R. Brzostek〈br〉 Biogeosciences, 16, 457-465, https://doi.org/10.5194/bg-16-457-2019, 2019〈br〉 The ability of plants to slow climate change by taking up carbon hinges in part on there being ample soil nitrogen. We used a model that accounts for the carbon cost to plants of supporting nitrogen-acquiring microbes to explore how nitrogen limitation affects climate. Our model predicted that nitrogen limitation will enhance temperature and decrease precipitation; thus, our results suggest that carbon spent to support nitrogen-acquiring microbes is a critical component of the Earth's climate.

Beschreibung: 〈b〉A simple time-stepping scheme to simulate leaf area index, phenology, and gross primary production across deciduous broadleaf forests in the eastern United States〈/b〉〈br〉 Qinchuan Xin, Yongjiu Dai, and Xiaoping Liu〈br〉 Biogeosciences, 16, 467-484, https://doi.org/10.5194/bg-16-467-2019, 2019〈br〉 Terrestrial biosphere models that simulate both leaf dynamics and canopy photosynthesis are required to understand vegetation–climate interactions. A time-stepping scheme is proposed to simulate leaf area index, phenology, and gross primary production via climate variables. The method performs well on simulating deciduous broadleaf forests across the eastern United States; it provides a simplified and improved version of the growing production day model for use in land surface modeling.

Beschreibung: 〈b〉Sedimentary alkalinity generation and long-term alkalinity development in the Baltic Sea〈/b〉〈br〉 Erik Gustafsson, Mathilde Hagens, Xiaole Sun, Daniel C. Reed, Christoph Humborg, Caroline P. Slomp, and Bo G. Gustafsson〈br〉 Biogeosciences, 16, 437-456, https://doi.org/10.5194/bg-16-437-2019, 2019〈br〉 This work highlights that iron (Fe) dynamics plays a key role in the release of alkalinity from sediments, as exemplified for the Baltic Sea. It furthermore demonstrates that burial of Fe sulfides should be included in alkalinity budgets of low-oxygen basins. The sedimentary alkalinity generation may undergo large changes depending on both organic matter loads and oxygen conditions. Enhanced release of alkalinity from the seafloor can increase the CO〈sub〉2〈/sub〉 storage capacity of seawater.

Beschreibung: 〈b〉Large-scale predictions of salt-marsh carbon stock based on simple observations of plant community and soil type〈/b〉〈br〉 Hilary Ford, Angus Garbutt, Mollie Duggan-Edwards, Jordi F. Pagès, Rachel Harvey, Cai Ladd, and Martin W. Skov〈br〉 Biogeosciences, 16, 425-436, https://doi.org/10.5194/bg-16-425-2019, 2019〈br〉 Carbon stored in coastal wetlands is of global relevance to climate regulation, but broadscale inventories of this "blue carbon" are lacking. Sampling salt marshes in the UK, we developed a predictive tool with the capacity to predict up to 44 % of spatial variation in soil carbon from simple observations of plant community and soil type. Marsh-specific maps of soil carbon were also produced, demonstrating the application of this easy-to-use tool for landscape-scale predictions of blue carbon.

Beschreibung: 〈b〉Global variability of carbon use efficiency in terrestrial ecosystems〈/b〉〈br〉 Xiaolu Tang, Nuno Carvalhais, Catarina Moura, Bernhard Ahrens, Sujan Koirala, Shaohui Fan, Fengying Guan, Wenjie Zhang, Sicong Gao, Vincenzo Magliulo, Pauline Buysse, Shibin Liu, Guo Chen, Wunian Yang, Zhen Yu, Jingjing Liang, Leilei Shi, Shenyan Pu, and Markus Reichstein〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-37,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Vegetation CUE is a key measure of carbon transfer from the atmosphere to terrestrial biomass. This study modelled global CUE with published observations using random forest. CUE varied with ecosystem types and spatially decreased with latitude, challenging the previous conclusion that CUE was independent of environmental controls. Our results emphasize a better understanding of environmental controls on CUE to reduce uncertainties in prognostic land-process model simulations.

Beschreibung: 〈b〉Mineral formation induced by cable bacteria performing long-distance electron transport in marine sediments〈/b〉〈br〉 Nicole M. J. Geerlings, Eva-Maria Zetsche, Silvia Hidalgo-Martinez, Jack J. Middelburg, and Filip J. R. Meysman〈br〉 Biogeosciences, 16, 811-829, https://doi.org/10.5194/bg-16-811-2019, 2019〈br〉 Multicellular cable bacteria form long filaments that can reach lengths of several centimeters. They affect the chemistry and mineralogy of their surroundings and vice versa. How the surroundings affect the cable bacteria is investigated. They show three different types of biomineral formation: (1) a polymer containing phosphorus in their cells, (2) a sheath of clay surrounding the surface of the filament and (3) the encrustation of a filament via a solid phase containing iron and phosphorus.

Beschreibung: 〈b〉Dissolved inorganic nitrogen in a tropical estuary at Malaysia: transport and transformation〈/b〉〈br〉 Shan Jiang, Moritz Müller, Jie Jin, Ying Wu, Kun Zhu, Guosen Zhang, Aazani Mujahid, Tim Rixen, Mohd Fakharuddin Muhamad, Edwin Sien Aun Sia, Faddrine Holt Ajon Jang, and Jing Zhang〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-7,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Three cruises were conducted in the Rajang river estuary, Malaysia. The results revealed that the decomposition of terrestrial organic matter and the subsequent soil leaching was the main source for dissolved inorganic nitrogen (DIN) in the fresh river water. Pore water exchange and ammonification enhanced DIN concentration in the estuary water, while intensities of DIN addition varied between seasons. The riverine DIN flux could reach 101.5 ton(N)/d, supporting the coastal primary productivity.

Beschreibung: 〈b〉Carbon balance of a restored and cutover raised bog: implications for restoration and comparison to global trends〈/b〉〈br〉 Michael M. Swenson, Shane Regan, Dirk T. H. Bremmers, Jenna Lawless, Matthew Saunders, and Laurence W. Gill〈br〉 Biogeosciences, 16, 713-731, https://doi.org/10.5194/bg-16-713-2019, 2019〈br〉 Abbeyleix Bog in the Irish Midlands contains areas that were historically harvested for peat and then abandoned as well as areas that were never harvested. This study measured the carbon balance for both harvested locations and unharvested locations at Abbeyleix Bog. Measurements were conducted in the field over 2 years. This was carried out to understand how the historic harvesting and later abandonment of peat affect greenhouse gas emissions.

Beschreibung: 〈b〉Main drivers of transparent exopolymer particle distribution across the surface Atlantic Ocean〈/b〉〈br〉 Marina Zamanillo, Eva Ortega-Retuerta, Sdena Nunes, Pablo Rodríguez-Ros, Manuel Dall'Osto, Marta Estrada, Maria Montserrat Sala, and Rafel Simó〈br〉 Biogeosciences, 16, 733-749, https://doi.org/10.5194/bg-16-733-2019, 2019〈br〉 Many marine microorganisms produce polysaccharide-rich transparent exopolymer particles (TEPs) for rather unknown reasons but with important consequences for the ocean carbon cycle, sea–air gas exchange and formation of organic aerosols. Here we compare surface–ocean distributions of TEPs and physical, chemical and biological variables along a N–S transect in the Atlantic Ocean. Our data suggest that phytoplankton and not bacteria are the main TEP producers, and solar radiation acts as a sink.

Beschreibung: 〈b〉Gas transfer velocities of CO〈sub〉2〈/sub〉 in subtropical monsoonal climate streams and small rivers〈/b〉〈br〉 Siyue Li, Rong Mao, Yongmei Ma, and Vedula V. S. S. Sarma〈br〉 Biogeosciences, 16, 681-693, https://doi.org/10.5194/bg-16-681-2019, 2019〈br〉 We provide a first determination of 〈i〉k〈/i〉 in human-impacted subtropical streams and small rivers. High and highly variable 〈i〉k〈/i〉 values reflect different controls on water turbulence. New models of 〈i〉k〈/i〉 are developed using water depth and flow velocity. We show that previous estimates of riverine CO〈sub〉2〈/sub〉 evasion from subtropical streams and small rivers are conservative and highlight the importance of incorporating scale-appropriate 〈i〉k〈/i〉 measurements into extensive 〈i〉p〈/i〉CO〈sub〉2〈/sub〉 investigations for accurate C budgets.

Beschreibung: 〈b〉Current, steady-state and historical weathering rates of base cations at two forest sites in northern and southern Sweden: A comparison of three methods〈/b〉〈br〉 Sophie Casetou-Gustafson, Harald Grip, Stephen Hillier, Sune Linder, Bengt A. Olsson, Magnus Simonsson, and Johan Stendahl〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-47,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 More reliable mineral weathering estimates are required to ensure sustainable forest growth. Thus, weathering estimates obtained by the three different methods were compared against other major base cation fluxes at ecosystem scale in N and S Sweden. The large discrepancy in weathering rates for Ca, Mg and K between mass balance and the other methods suggest that there were additional sources for tree uptake in the soil besides weathering and measured depletion in exchangeable base cations.

Beschreibung: 〈b〉Frequency and intensity of nitrogen addition alter soil inorganic sulfur fractions but the effects vary with mowing management in a temperate steppe〈/b〉〈br〉 Tianpeng Li, Heyong Liu, Ruzhen Wang, Xiao-Tao Lü, Junjie Yang, Yunhai Zhang, Peng He, Zhirui Wang, Xingguo Han, and Yong Jiang〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-526,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉Sulfur (S) availability plays a vital role in driving functions of terrestrial ecosystems, which can be largely affected by soil inorganic S fractions and pool size. Enhanced ecosystem nitrogen (N) input can significantly affect soil S availability, but it still remains largely unknown if the N effect varies with frequency of N addition and mowing management in grasslands. To investigate changes in soil S pool and inorganic S fractions (water-soluble S, adsorbed S, available S, and insoluble S), we conducted a field experiment with different frequencies (twice vs. monthly additions per year) and intensities (i.e. 0, 1, 2, 3, 5, 10, 15, 20, and 50 g N m〈sup〉−2〈/sup〉 year〈sup〉−1〈/sup〉) of NH〈sub〉4〈/sub〉NO〈sub〉3〈/sub〉 addition and mowing (unmowing vs. mowing) over six years in a temperate grassland of northern China. Soil water-soluble and adsorbed S concentrations significantly increased, while insoluble S decreased with increasing intensity of N input. Such changes were correlated with soil pH and total inorganic nitrogen (TIN) concentration. High frequency of N addition increased the concentrations of water-soluble S, adsorbed S and available S as compared to low frequency of N addition in mown plots. Mowing significantly decreased all soil inorganic S fractions by reducing S replenishment via plant residue return. Mowing significantly interacted with both N addition intensity and frequency to affect inorganic S fractions, in that adsorbed S and available S showed no response to N addition intensity in unmown plots but significantly increased in mown plots under high N frequency. Mowing interacted with N addition intensity to decrease soil S pool size, suggesting that biomass removal under N input would cause soil S depletion in this temperate grassland. Nitrogen addition could replenish soil available S by promoting dissolution of soil insoluble S with decreasing soil pH and mineralization of organic S due to increasing plant S uptake. Our results further indicated that using large and infrequent N addition to simulate N deposition can overestimate the main effects of N deposition and mowing on soil S availability in semi-arid grasslands.〈/p〉

Beschreibung: 〈b〉Variation in brachiopod microstructure and isotope geochemistry under low-pH–ocean acidification conditions〈/b〉〈br〉 Facheng Ye, Hana Jurikova, Lucia Angiolini, Uwe Brand, Gaia Crippa, Daniela Henkel, Jürgen Laudien, Claas Hiebenthal, and Danijela Šmajgl〈br〉 Biogeosciences, 16, 617-642, https://doi.org/10.5194/bg-16-617-2019, 2019〈br〉 〈p〉In the last few decades and in the near future 〈span〉CO〈sub〉2〈/sub〉〈/span〉-induced ocean acidification is potentially a big threat to marine calcite-shelled animals (e.g. brachiopods, bivalves, corals and gastropods). Despite the great number of studies focusing on the effects of acidification on shell growth, metabolism, shell dissolution and shell repair, the consequences for biomineral formation remain poorly understood. Only a few studies have addressed the impact of ocean acidification on shell microstructure and geochemistry. In this study, a detailed microstructure and stable isotope geochemistry investigation was performed on nine adult brachiopod specimens of 〈i〉Magellania venosa〈/i〉 (Dixon, 1789). These were grown in the natural environment as well as in controlled culturing experiments under different pH conditions (ranging from 7.35 to 〈span〉8.15±0.05〈/span〉) over different time intervals (214 to 335 days). Details of shell microstructural features, such as thickness of the primary layer, density and size of endopunctae and morphology of the basic structural unit of the secondary layer were analysed using scanning electron microscopy. Stable isotope compositions (〈span〉〈i〉δ〈/i〉〈sup〉13〈/sup〉C〈/span〉 and 〈span〉〈i〉δ〈/i〉〈sup〉18〈/sup〉O〈/span〉) were tested from the secondary shell layer along shell ontogenetic increments in both dorsal and ventral valves. Based on our comprehensive dataset, we observed that, under low-pH conditions, 〈i〉M. venosa〈/i〉 produced a more organic-rich shell with higher density of and larger endopunctae, and smaller secondary layer fibres. Also, increasingly negative 〈span〉〈i〉δ〈/i〉〈sup〉13〈/sup〉C〈/span〉 and 〈span〉〈i〉δ〈/i〉〈sup〉18〈/sup〉O〈/span〉 values are recorded by the shell produced during culturing and are related to the 〈span〉CO〈sub〉2〈/sub〉〈/span〉 source in the culture set-up. Both the microstructural changes and the stable isotope results are similar to observations on brachiopods from the fossil record and strongly support the value of brachiopods as robust archives of proxies for studying ocean acidification events in the geologic past.〈/p〉

Beschreibung: 〈b〉Baseline for ostracod-based northwestern Pacific and Indo-Pacific shallow-marine paleoenvironmental reconstructions: ecological modeling of species distributions〈/b〉〈br〉 Yuanyuan Hong, Moriaki Yasuhara, Hokuto Iwatani, and Briony Mamo〈br〉 Biogeosciences, 16, 585-604, https://doi.org/10.5194/bg-16-585-2019, 2019〈br〉 This study analyzed microfaunal assemblages in surface sediments from 52 sites in Hong Kong marine waters. We selected 18 species for linear regression modeling to statistically reveal the relationship between species distribution and environmental factors. These results show environmental preferences of commonly distributed species on Asian coasts, providing a robust baseline for past environmental reconstruction of the broad Asian region using microfossils in sediment cores.

Beschreibung: 〈b〉Zero to moderate methane emissions in a densely rooted, pristine Patagonian bog – biogeochemical controls as revealed from isotopic evidence〈/b〉〈br〉 Wiebke Münchberger, Klaus-Holger Knorr, Christian Blodau, Verónica A. Pancotto, and Till Kleinebecker〈br〉 Biogeosciences, 16, 541-559, https://doi.org/10.5194/bg-16-541-2019, 2019〈br〉 Processes governing CH〈sub〉4〈/sub〉 dynamics have been scarcely studied in southern hemispheric bogs. These can be dominated by cushion-forming plants with deep and dense roots suppressing emissions. Here we demonstrate how the spatial distribution of root activity drives a pronounced pattern of CH〈sub〉4〈/sub〉 emissions, likewise also possible in densely rooted northern bogs. We conclude that presence of cushion vegetation as a proxy for negligible CH〈sub〉4〈/sub〉 emissions from cushion bogs needs to be interpreted with caution.

Beschreibung: 〈b〉A conservation palaeobiological approach to assess faunal response of threatened biota under natural and anthropogenic environmental change〈/b〉〈br〉 Sabrina van de Velde, Elisabeth L. Jorissen, Thomas A. Neubauer, Silviu Radan, Ana Bianca Pavel, Marius Stoica, Christiaan G. C. Van Baak, Alberto Martínez Gándara, Luis Popa, Henko de Stigter, Hemmo A. Abels, Wout Krijgsman, and Frank P. Wesselingh〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-6,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉Palaeoecological records are required to test ecological hypotheses necessary for conservation strategies as short-term observations can be insufficiently to capture natural variability and identify drivers of biotic change. Here, we demonstrate the importance of an integrated conservation palaeobiology approach to make validated decisions for conservation and mitigating action. Our model system is the Razim-Sinoie Lake complex (RSL) in the Danube Delta (Black Sea coast, Romania), a dynamic coastal lake system hosting unique Pontocaspian mollusc species that are now severely under threat. The Pontocaspians refer to an endemic species group that evolved in the Black Sea and Caspian Sea basins under reduced salinity settings over the past few million years. The natural, pre-industrial RSL contained a salinity gradient from fresh to mesohaline (18 ppm), until human interventions reduced the inflow of mesohaline Black Sea water into the lake system. We reconstruct the evolution of the RSL over the past 2000 years from integrated sedimentary facies and faunal analyses based on 11 age-dated sediment cores and investigate the response of mollusc species and communities to those past environmental changes. Three species associations (〈q〉marine〈/q〉, 〈q〉Pontocaspian〈/q〉, 〈q〉freshwater〈/q〉) exist and their spatiotemporal shifts through the system are documented. Variable salinity gradients developed, with marine settings (and faunas) dominating in the southern part of the system and freshwater conditions (and faunas) in the northern and western parts. Pontocaspian species have mostly occurred in the centre of the RSL within the marine–freshwater salinity gradient. Today, freshwater species dominate the entire system, and only a single Pontocaspian species (〈i〉Monodacna colorata〈/i〉) is found alive. We show that the human-induced reduced marine influence in the system has been a major driver of the decline of the endemic Pontocaspian biota. It urges for improved conservation actions by re-establishing a salinity gradient in the lake system to preserve these unique species.〈/p〉

Beschreibung: 〈b〉Physiological and biochemical responses of 〈i〉Emiliania huxleyi〈/i〉 to ocean acidification and warming are modulated by UV radiation〈/b〉〈br〉 Shanying Tong, David A. Hutchins, and Kunshan Gao〈br〉 Biogeosciences, 16, 561-572, https://doi.org/10.5194/bg-16-561-2019, 2019〈br〉 Most previous studies concerning the effects of environmental changes on marine organisms have been carried out under 〈q〉photosynthetically active radiation only〈/q〉 conditions, with solar ultraviolet radiation (UVR) not being considered. In this study, we found that UVR can counteract the negative effects of the 〈q〉greenhouse〈/q〉 treatment on the calcification rate to photosynthesis rate ratio, and may be a key stressor when considering the impacts of future greenhouse conditions on 〈i〉E. huxleyi〈/i〉.

Beschreibung: 〈b〉Evaluating multi-year, multi-site data on the energy balance closure of eddy-covariance flux measurements at cropland sites in southwestern Germany〈/b〉〈br〉 Ravshan Eshonkulov, Arne Poyda, Joachim Ingwersen, Hans-Dieter Wizemann, Tobias K. D. Weber, Pascal Kremer, Petra Högy, Alim Pulatov, and Thilo Streck〈br〉 Biogeosciences, 16, 521-540, https://doi.org/10.5194/bg-16-521-2019, 2019〈br〉 We compared the energy balance closure (EBC) under varying environmental conditions and investigated a wide range of possible reasons for the energy imbalance. As measures for the imbalance, we used ordinary linear regression, the energy balance ratio (EBR), and the energy residual. The EBR was also investigated as a function of buoyancy, friction velocity, and atmospheric stability. Moreover, the relationship between the EBC and flux source area or footprint was also investigated.

Beschreibung: 〈b〉Global soil-climate-biome diagram: linking surface soil properties to climate and biota〈/b〉〈br〉 Xia Zhao, Yuanhe Yang, Haihua Shen, Xiaoqing Geng, and Jingyun Fang〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-449,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Despite significant progress in digital soil mapping techniques and the rapid increase in observed soil information, quantitative linkages between soil, climate and biota remain unclear at global scale. By compiling a large global soil database, we mapped eight major soil properties based on machine learning algorithms and developed a global soil-climate-biome diagram. Our results suggest a co-evolution of soil, climate and biota under global environmental change.

Beschreibung: 〈b〉The ballast effect of lithogenic matter and its influences on the carbon fluxes in the Indian Ocean〈/b〉〈br〉 Tim Rixen, Birgit Gaye, Kay-Christian Emeis, and Venkitasubramani Ramaswamy〈br〉 Biogeosciences, 16, 485-503, https://doi.org/10.5194/bg-16-485-2019, 2019〈br〉 Data obtained from sediment trap experiments in the Indian Ocean indicate that lithogenic matter ballast increases organic carbon flux rates on average by 45 % and by up to 62 % at trap locations in the river-influenced regions of the Indian Ocean. Such a strong lithogenic matter ballast effect implies that land use changes and the associated enhanced transport of lithogenic matter may significantly affect the CO〈sub〉2〈/sub〉 uptake of the organic carbon pump in the receiving ocean areas.

Beschreibung: 〈b〉Environment Gradient related Dissimilatory Nitrate Reduction to Ammonium in Huangmao Sea Estuary: Rates and Community Diversity〈/b〉〈br〉 Ran Jiang, Shu-Xin Zhang, Gou Wei, Rui He, Li-Ling Yang, and Xin-Sheng Chai〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-31,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Since the nitrogen related eutrophication has become a severe problem in the Pearl River Delta complex area(PRE) in South China, it is important to have further understanding of nitrogen cycles in this area. The significant geographic and climatic differences in PRE and other estuaries, up to date there is lack of studies about the microbial mediated the dissimilatory nitrate reduction to ammonium(DNRA) pathways. This study provide a better understanding of DNRA in South China estuaries.

Beschreibung: 〈b〉Towards a more complete quantification of the global carbon cycle〈/b〉〈br〉 Miko U. F. Kirschbaum, Guang Zeng, Fabiano Ximenes, Donna L. Giltrap, and John R. Zeldis〈br〉 Biogeosciences, 16, 831-846, https://doi.org/10.5194/bg-16-831-2019, 2019〈br〉 Globally, C is added to the atmosphere from fossil fuels and deforestation, balanced by ocean uptake and atmospheric increase. The difference (residual sink) is equated to plant uptake. But this omits cement carbonation; transport to oceans by dust; riverine organic C and volatile organics; and increased C in plastic, bitumen, wood, landfills, and lakes. Their inclusion reduces the residual sink from 3.6 to 2.1 GtC yr〈sup〉-1〈/sup〉 and thus the inferred ability of the biosphere to alter human C emissions.

Beschreibung: 〈b〉Multi-year effect of wetting on CH〈sub〉4〈/sub〉 flux at taiga–tundra boundary in northeastern Siberia deduced from stable isotope ratios of CH〈sub〉4〈/sub〉〈/b〉〈br〉 Ryo Shingubara, Atsuko Sugimoto, Jun Murase, Go Iwahana, Shunsuke Tei, Maochang Liang, Shinya Takano, Tomoki Morozumi, and Trofim C. Maximov〈br〉 Biogeosciences, 16, 755-768, https://doi.org/10.5194/bg-16-755-2019, 2019〈br〉 (1) Wetting event with extreme precipitation increased methane emission from wetland, especially two summers later, despite the decline in water level after the wetting. (2) Isotopic compositions of methane in soil pore water suggested enhancement of production and less significance of oxidation in the following two summers after the wetting event. (3) Duration of water saturation in the active layer may be important for predicting methane emission after a wetting event in permafrost ecosystems.

Beschreibung: 〈b〉Preface: Ernst Maier-Reimer and his way of modelling the ocean〈/b〉〈br〉 Christoph Heinze and Klaus Hasselmann〈br〉 Biogeosciences, 16, 751-753, https://doi.org/10.5194/bg-16-751-2019, 2019〈br〉

Beschreibung: 〈b〉Biomarker evidence for the occurrence of anaerobic ammonium oxidation in the eastern Mediterranean Sea during Quaternary and Pliocene sapropel formation〈/b〉〈br〉 Darci Rush, Helen M. Talbot, Marcel T. J. van der Meer, Ellen C. Hopmans, Ben Douglas, and Jaap S. Sinninghe Damsté〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-27,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Sapropels are layers of sediment that regularly occur in the Mediterranean. They indicate periods when the Mediterranean Sea water that contained no oxygen, a gas vital for most large organisms. This research investigated a key process in the nitrogen cycle (anerobic ammonium oxidation; anammox), which removes nitrogen – an important nutrient to algae – from the water, during sapropel events. Using lipids to trace this process, we found that anammox was active during the no oxygen times.

Beschreibung: 〈b〉Multi-trace-element sea surface temperature coral reconstruction for the southern Mozambique Channel reveals teleconnections with the tropical Atlantic〈/b〉〈br〉 Jens Zinke, Juan P. D'Olivo, Christoph J. Gey, Malcolm T. McCulloch, J. Henrich Bruggemann, Janice M. Lough, and Mireille M. M. Guillaume〈br〉 Biogeosciences, 16, 695-712, https://doi.org/10.5194/bg-16-695-2019, 2019〈br〉 Here we report seasonally resolved sea surface temperature (SST) reconstructions for the southern Mozambique Channel in the SW Indian Ocean, a region located along the thermohaline ocean surface circulation route, based on multi-trace-element temperature proxy records preserved in two 〈i〉Porites〈/i〉 sp. coral cores for the past 42 years. Particularly, we show the suitability of both separate and combined Sr / Ca and Li / Mg proxies for improved multielement SST reconstructions.

Beschreibung: 〈b〉Modeling anaerobic soil organic carbon decomposition in Arctic polygon tundra: insights into soil geochemical influences on carbon mineralization〈/b〉〈br〉 Jianqiu Zheng, Peter E. Thornton, Scott L. Painter, Baohua Gu, Stan D. Wullschleger, and David E. Graham〈br〉 Biogeosciences, 16, 663-680, https://doi.org/10.5194/bg-16-663-2019, 2019〈br〉 Arctic warming exposes soil carbon to increased degradation, increasing CO〈sub〉2〈/sub〉 and CH〈sub〉4〈/sub〉 emissions. Models underrepresent anaerobic decomposition that predominates wet soils. We simulated microbial growth, pH regulation, and anaerobic carbon decomposition in a new model, parameterized and validated with prior soil incubation data. The model accurately simulated CO〈sub〉2〈/sub〉 production and strong influences of water content, pH, methanogen biomass, and competing electron acceptors on CH〈sub〉4〈/sub〉 production.

Beschreibung: 〈b〉Benthic alkalinity and DIC fluxes in the Rhône River prodelta generated by decoupled aerobic and anaerobic processes〈/b〉〈br〉 Jens Rassmann, Eryn M. Eitel, Cécile Cathalot, Christophe Brandily, Bruno Lansard, Martial Taillefert, and Chrsitophe Rabouille〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-32,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉Estuarine regions are generally considered a net source of atmospheric CO〈sub〉2〈/sub〉 as a result of the high organic carbon (OC) mineralization rates in the water column and their sediments. Yet, the intensity of anaerobic respiration processes in the sediments tempered by the reoxidation of reduced metabolites controls the net production of alkalinity from sediments that may partially buffer the metabolic CO〈sub〉2〈/sub〉 generated by OC respiration. In this study, a benthic chamber was deployed in the Rhône River prodelta and the adjacent continental shelf (Gulf of Lions, NW Mediterranean) to assess the fluxes of total alkalinity (TA) and dissolved inorganic carbon (DIC) from the sediment. Concurrently, 〈i〉in situ〈/i〉 O〈sub〉2〈/sub〉 and pH microprofiles, electrochemical profiles, pore water and solid composition were measured in surface sediments to identify the main biogeochemical processes controlling the net production of alkalinity in these sediments. The benthic fluxes of TA and DIC, ranging between 14 and 74 mmol m〈sup〉−2〈/sup〉 d〈sup〉−1〈/sup〉 and 18 and 78 mmol m〈sup〉−2〈/sup〉 d〈sup〉−1〈/sup〉, respectively, were up to 8 times higher than the DOU fluxes (10.4 ± 0.9 mmol m〈sup〉−2〈/sup〉 d〈sup〉−1〈/sup〉) close to the river mouth, but their intensity decreased offshore, as a result of the decline in OC inputs. Low nitrate concentrations and strong pore water sulfate gradients indicated that the majority of the TA and DIC was produced by sulfate and iron reduction. Despite the complete removal of sulfate from the pore waters, dissolved sulfide concentrations were low due to the precipitation and burial of iron sulfide minerals (12.5 mmol m〈sup〉−2〈/sup〉 d〈sup〉−1〈/sup〉 near the river mouth), while soluble organic-Fe(III) complexes were concurrently found throughout the sediment column. The presence of organic-Fe(III) complexes together with low sulfide concentrations and high sulfate consumption suggests a dynamic system driven by the variability of the organic and inorganic particulate input originating from the river. By preventing reduced substances from being reoxidized, the precipitation and burial of iron sulfide decouples the iron and sulfur cycles from oxygen, therefore allowing a flux of alkalinity out of the sediments. In these conditions, the sediment provides a source of alkalinity to the bottom waters which mitigates the effect of the benthic DIC flux on the carbonate chemistry of coastal waters.〈/p〉

Beschreibung: 〈b〉Ideas and perspectives: Carbon leaks from flooded land: do we need to replumb the inland water active pipe?〈/b〉〈br〉 Gwenaël Abril and Alberto V. Borges〈br〉 Biogeosciences, 16, 769-784, https://doi.org/10.5194/bg-16-769-2019, 2019〈br〉 Based on classical concepts in ecology, and a literature survey, we highlight the importance of flooded land as a preferential source of atmospheric carbon to aquatic systems at the global scale. Studies in terrestrial and aquatic ecosystems could be reconciled by considering the occurrence of an efficient wetland CO〈sub〉2〈/sub〉 pump to river systems. New methodological approaches coupling hydrology and ecology are also necessary to improve scientific knowledge on carbon fluxes at the land–water interface.

Beschreibung: 〈b〉Diversity, distribution and nitrogen use strategies of bacteria in the South China Sea basin〈/b〉〈br〉 Yuan-Yuan Li, Xiao-Huang Chen, Peng-Fei Wu, Dong-Xu Li, Lin Lin, and Da-Zhi Wang〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-529,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Systematic studies on diversities and nitrogen use strategies of bacterial communities in the South China Sea basin are still scarce. Here, we applied high-throughput sequencing, bioinformatic analysis and qPCR assays, and found that the depth was a significant explanatory variable for the bacterial populations from different water masses. Amino acids and ammonium were the major nitrogen sources for bacteria while urea, ammonia and nitrite played vital roles in different regions of the basin.

Beschreibung: 〈b〉Ostracods as ecological and isotopic indicators of lake water salinity changes: The Lake Van example〈/b〉〈br〉 Jeremy McCormack, Finn Viehberg, Derya Akdemir, Adrian Immenhauser, and Ola Kwiecien〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-476,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 We juxtapose changes in ostracod taxonomy, morphology (noding) and oxygen (δ〈sup〉18〈/sup〉O) and carbon (δ〈sup〉13〈/sup〉C) isotopic composition for the last 150 kyr with independent low-resolution salinity proxies. We demonstrate that for Lake Van, salinity is the most important factor influencing the composition of the ostracod assemblage and the formation of nodes on the valves of limnocytherinae species. Ostracod δ〈sup〉18〈/sup〉O shows a higher sensibility towards climatic and hydrological variations than the bulk isotopy.

Beschreibung: 〈b〉Spatial changes in soil stable isotopic composition in response to carrion decomposition〈/b〉〈br〉 Sarah W. Keenan, Sean M. Schaeffer, and Jennifer M. DeBruyn〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-498,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Decaying animals perturb soil biogeochemical cycles. Stable δ〈sup〉15〈/sup〉N composition, which reflects the sum of all biogeochemical processes, increases during decay and persists for years. Enrichment following beaver decay persisted after one year, and was evident up to 10 cm depth and 60 cm from the decaying animals, beyond where soils were visibly impacted by decomposition. Nutrients sourced from decaying animals represent an integral and long-lived component of nitrogen cycling in soils.

Beschreibung: 〈b〉Assessment of time of emergence of anthropogenic deoxygenation and warming: insights from a CESM simulation from 850 to 2100 CE〈/b〉〈br〉 Angélique Hameau, Juliette Mignot, and Fortunat Joos〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-523,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 The observed decrease of oxygen and warming in the ocean may adversely affect marine ecosystems and their services. We analyse results from an Earth System Model for the last millennium and the 21st century. We find changes in temperature and oxygen due to fossil fuel burning and other human activities to exceed natural variations in many ocean regions already today. Natural variability is biased low in earlier studies neglecting forcing from past volcanic eruptions and solar change.

Beschreibung: 〈b〉Dissolved organic carbon mobilized from organic horizons of mature and harvested black spruce plots in a mesic boreal region〈/b〉〈br〉 Keri Bowering, Kate A. Edwards, Xinbiao Zhu, and Susan E. Ziegler〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-516,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 We examined the effects of season and tree harvesting on the flow of water and the organic carbon (OC) it carries from boreal forest soils. We found that more OC was lost from the harvested forest because more precipitation reached the soil surface, but that during periods of flushing in autumn and snowmelt a limit on the amount of water-extractable OC is reached. These results have implications for how we predict the effect of changing precipitation regimes on the loss of carbon in forests.

Beschreibung: 〈b〉Impact of peatlands on carbon dioxide (CO〈sub〉2〈/sub〉) emissions from the Rajang River and Estuary, Malaysia〈/b〉〈br〉 Denise Müller-Dum, Thorsten Warneke, Tim Rixen, Moritz Müller, Antje Baum, Aliki Christodoulou, Joanne Oakes, Bradley D. Eyre, and Justus Notholt〈br〉 Biogeosciences, 16, 17-32, https://doi.org/10.5194/bg-16-17-2019, 2019〈br〉 Southeast Asian peat-draining rivers are potentially strong sources of carbon to the atmosphere due to the large amounts of organic carbon stored in those ecosystems. We present the first assessment of CO〈sub〉2〈/sub〉 emissions from the Rajang River, the largest peat-draining river in Malaysia. The peatlands’ influence on the CO〈sub〉2〈/sub〉 emissions from the Rajang River was smaller than expected, probably due to their proximity to the coast. Therefore, the Rajang was only a moderate source of CO〈sub〉2〈/sub〉 to the atmosphere.

Beschreibung: 〈b〉Neogene Caribbean elasmobranchs: diversity, paleoecology and paleoenvironmental significance of the Cocinetas Basin assemblage (Guajira Peninsula, Colombia)〈/b〉〈br〉 Jorge Domingo Carrillo-Briceño, Zoneibe Luz, Austin Hendy, László Kocsis, Orangel Aguilera, and Torsten Vennemann〈br〉 Biogeosciences, 16, 33-56, https://doi.org/10.5194/bg-16-33-2019, 2019〈br〉 By combining taxonomy and geochemistry, we corroborated the described paleoenvironments from a Neogene fossiliferous deposit of South America. Shark teeth specimens were used for taxonomic identification and as proxies for geochemical analyses. With a multidisciplinary approach we refined the understanding about the paleoenvironmental setting and the paleoecological characteristics of the studied groups, in our case, for the bull shark and its incursions into brackish waters.

Beschreibung: 〈b〉Controls on zooplankton methane production in the central Baltic Sea〈/b〉〈br〉 Beate Stawiarski, Stefan Otto, Volker Thiel, Ulf Gräwe, Natalie Loick-Wilde, Anna K. Wittenborn, Stefan Schloemer, Janine Wäge, Gregor Rehder, Matthias Labrenz, Norbert Wasmund, and Oliver Schmale〈br〉 Biogeosciences, 16, 1-16, https://doi.org/10.5194/bg-16-1-2019, 2019〈br〉 The understanding of surface water methane production in the world oceans is still poor. By combining field studies and incubation experiments, our investigations suggest that zooplankton contributes to subthermocline methane enrichments in the central Baltic Sea by methane production within the digestive tract of copepods and/or by methane production through release of methane precursor substances into the surrounding water, followed by microbial degradation to methane.

Beschreibung: 〈b〉Early season N〈sub〉2〈/sub〉O emissions under variable water management in rice systems: source-partitioning emissions using isotope ratios along a depth profile〈/b〉〈br〉 Elizabeth Verhoeven, Matti Barthel, Longfei Yu, Luisella Celi, Daniel Said-Pullicino, Steven Sleutel, Dominika Lewicka-Szczebak, Johan Six, and Charlotte Decock〈br〉 Biogeosciences, 16, 383-408, https://doi.org/10.5194/bg-16-383-2019, 2019〈br〉 This study utilized state-of-the-art measurements of nitrogen isotopes to evaluate nitrogen cycling and to assess the biological sources of the potent greenhouse gas, N〈sub〉2〈/sub〉O, in response to water-saving practices in rice systems. Water-saving practices did emit more N〈sub〉2〈/sub〉O, and high N〈sub〉2〈/sub〉O production had a lower 〈sup〉15〈/sup〉N isotope signature. Modeling and visual interpretation indicate that these emissions mostly came from denitrification or nitrifier denitrification, controlled upstream by nitrification rates.

Beschreibung: 〈b〉Rhizosphere to the atmosphere: contrasting methane pathways, fluxes and geochemical drivers across the terrestrial-aquatic wetland boundary〈/b〉〈br〉 Luke C. Jeffrey, Damien T. Maher, Scott Johnston, Kylie Maguire, Andrew D. L. Steven, and Douglas R. Tait〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-11,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Wetlands represent the largest natural source of methane (CH〈sub〉4〈/sub〉), so understanding CH〈sub〉4〈/sub〉 drivers are important for climate models and management. We compared several CH〈sub〉4〈/sub〉 pathways of a remediated subtropical Australian wetland. We found permanently innundated sites emitted more CH〈sub〉4〈/sub〉 than seasonally innundated sites and that the soil properties within each site strongly correlated to CH〈sub〉4〈/sub〉 emissions. This suggests that selective remediation of suitable soil types may help mitigate unwanted CH〈sub〉4〈/sub〉 emissions.

Beschreibung: 〈b〉Monitoring changes in forestry and seasonal snow using surface albedo during 1982–2016 as an indicator〈/b〉〈br〉 Terhikki Manninen, Tuula Aalto, Tiina Markkanen, Mikko Peltoniemi, Kristin Böttcher, Sari Metsämäki, Kati Anttila, Pentti Pirinen, Antti Leppänen, and Ali Nadir Arslan〈br〉 Biogeosciences, 16, 223-240, https://doi.org/10.5194/bg-16-223-2019, 2019〈br〉 The surface albedo time series CLARA-A2 SAL was used to study trends in the timing of the melting season of snow and preceding albedo value in Finland during 1982–2016 to assess climate change. The results were in line with operational snow depth data, JSBACH land ecosystem model, SYKE fractional snow cover and greening-up data. In the north a clear trend to earlier snowmelt onset, increasing melting season length, and decrease in pre-melt albedo (related to increased stem volume) was observed.

Beschreibung: 〈b〉Global atmospheric CO〈sub〉2〈/sub〉 inverse models converging on neutral tropical land exchange, but disagreeing on fossil fuel and atmospheric growth rate〈/b〉〈br〉 Benjamin Gaubert, Britton B. Stephens, Sourish Basu, Frédéric Chevallier, Feng Deng, Eric A. Kort, Prabir K. Patra, Wouter Peters, Christian Rödenbeck, Tazu Saeki, David Schimel, Ingrid Van der Laan-Luijkx, Steven Wofsy, and Yi Yin〈br〉 Biogeosciences, 16, 117-134, https://doi.org/10.5194/bg-16-117-2019, 2019〈br〉 We have compared global carbon budgets calculated from numerical inverse models and CO〈sub〉2〈/sub〉 observations, and evaluated how these systems reproduce vertical gradients in atmospheric CO〈sub〉2〈/sub〉 from aircraft measurements. We found that available models have converged on near-neutral tropical total fluxes for several decades, implying consistent sinks in intact tropical forests, and that assumed fossil fuel emissions and predicted atmospheric growth rates are now the dominant axes of disagreement.

Beschreibung: 〈b〉Biogeochemical response of the Mediterranean Sea to the transient SRES-A2 climate change scenario〈/b〉〈br〉 Camille Richon, Jean-Claude Dutay, Laurent Bopp, Briac Le Vu, James C. Orr, Samuel Somot, and François Dulac〈br〉 Biogeosciences, 16, 135-165, https://doi.org/10.5194/bg-16-135-2019, 2019〈br〉 We evaluate the effects of climate change and biogeochemical forcing evolution on the nutrient and plankton cycles of the Mediterranean Sea for the first time. We use a high-resolution coupled physical and biogeochemical model and perform 120-year transient simulations. The results indicate that changes in external nutrient fluxes and climate change may have synergistic or antagonistic effects on nutrient concentrations, depending on the region and the scenario.

Beschreibung: 〈b〉Weathering rates in Swedish forest soils〈/b〉〈br〉 Cecilia Akselsson, Salim Belyazid, Johan Stendahl, Roger Finlay, Bengt Olsson, Martin Erlandsson Lampa, Håkan Wallander, Jon Petter Gustafsson, and Kevin Bishop〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-1,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 The release of elements from soil through weathering is an important process, controlling nutrient availability for plants and recovery from acidification. However, direct measurements cannot be done, and present estimates are burdened with high uncertainties. In this paper we use different approaches to quantify weathering rates in different scales in Sweden, and discuss the pros and cons. The study contributes to more robust assessments of sustainable harvesting of forest biomass.

Beschreibung: 〈b〉Humic surface waters of frozen peat bogs (permafrost zone) are highly resistant to bio- and photodegradation〈/b〉〈br〉 Liudmila S. Shirokova, Artem V. Chupakov, Svetlana A. Zabelina, Natalia V. Neverova, Dahedrey Payandi-Rolland, Carole Causseraund, Jan Karlsson, and Oleg S. Pokrovsky〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-528,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Regardless of size and landscape context of surface water in frozen peatland region on NE Europe, the bio- and photo-degradability of dissolved organic matter (DOM) over a month of incubation across a range of temperatures was below 10 %. We challenged the paradigm of dominance of photolysis and biodegradation in DOM processing in surface waters from frozen peatlands and we hypothesize the peat porewater DOM degradation and respiration of sediments as main drivers of CO〈sub〉2〈/sub〉 emission in this region.

Beschreibung: 〈b〉Emergent relationships with respect to burned area in global satellite observations and fire-enabled vegetation models〈/b〉〈br〉 Matthias Forkel, Niels Andela, Sandy P. Harrison, Gitta Lasslop, Margreet van Marle, Emilio Chuvieco, Wouter Dorigo, Matthew Forrest, Stijn Hantson, Angelika Heil, Fang Li, Joe Melton, Stephen Sitch, Chao Yue, and Almut Arneth〈br〉 Biogeosciences, 16, 57-76, https://doi.org/10.5194/bg-16-57-2019, 2019〈br〉 Weather, humans, and vegetation control the occurrence of fires. In this study we find that global fire–vegetation models underestimate the strong increase of burned area with higher previous-season plant productivity in comparison to satellite-derived relationships.

Beschreibung: 〈b〉Optimal inverse estimation of ecosystem parameters from observations of carbon and energy fluxes〈/b〉〈br〉 Debsunder Dutta, David S. Schimel, Ying Sun, Christiaan van der Tol, and Christian Frankenberg〈br〉 Biogeosciences, 16, 77-103, https://doi.org/10.5194/bg-16-77-2019, 2019〈br〉 Canopy structural and leaf photosynthesis parameterizations are often fixed over time in Earth system models and represent large sources of uncertainty in predictions of carbon and water fluxes. We develop a moving window nonlinear optimal parameter inversion framework using constraining flux and satellite reflectance observations. The results demonstrate the applicability of the approach for error reduction and capturing the seasonal variability of key ecosystem parameters.

Beschreibung: 〈b〉The export flux of particulate organic carbon derived from 〈sup〉210〈/sup〉Po∕〈sup〉210〈/sup〉Pb disequilibria along the North Atlantic GEOTRACES GA01 transect: GEOVIDE cruise〈/b〉〈br〉 Yi Tang, Nolwenn Lemaitre, Maxi Castrillejo, Montserrat Roca-Martí, Pere Masqué, and Gillian Stewart〈br〉 Biogeosciences, 16, 309-327, https://doi.org/10.5194/bg-16-309-2019, 2019〈br〉 Oceanographers try to understand the ocean’s role in the global carbon cycle. Trace levels of natural radionuclides can inform this connection and their half-lives provide an estimate of the timing of processes. We used the 210Po and 210Pb pair to examine the export of carbon from the surface ocean to depth along the GEOVIDE GEOTRACES cruise track. We found that the flux was regionally variable, that upwelling was an important regional factor, and that both large and small particles drove flux.

Beschreibung: 〈b〉Soil nitrogen response to shrub encroachment in a degrading semi-arid grassland〈/b〉〈br〉 Thomas Turpin-Jelfs, Katerina Michaelides, Joel A. Biederman, and Alexandre M. Anesio〈br〉 Biogeosciences, 16, 369-381, https://doi.org/10.5194/bg-16-369-2019, 2019〈br〉 Increasing shrub cover promotes land degradation in semi-arid grasslands and has the potential to impact the soil nitrogen pool, which is essential to primary production. Our study showed that increasing shrub cover concentrates soil nitrogen into localised patches beneath shrub canopies. Further, we determined that increasing shrub cover inhibits inputs of nitrogen by the soil microbial community. Thus, we conclude this phenomenon can perturb nitrogen cycling in these ecosystems.

Beschreibung: 〈b〉Subaqueous speleothems (Hells Bells) formed by the interplay of pelagic redoxcline biogeochemistry and specific hydraulic conditions in the El Zapote sinkhole, Yucatán Peninsula, Mexico〈/b〉〈br〉 Simon Michael Ritter, Margot Isenbeck-Schröter, Christian Scholz, Frank Keppler, Johannes Gescher, Lukas Klose, Nils Schorndorf, Jerónimo Avilés Olguín, Arturo González-González, and Wolfgang Stinnesbeck〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-520,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Unique and spectacular under water speleothems termed as Hells Bells where recently reported from sinkholes (cenotes) of the Yucatán Peninsula, Mexico. However, the mystery of their formation remained unresolved. Here, we present detailed geochemical analyses and delineate that the growth of Hells Bells results from a combination of biogeochemical processes and variable hydraulic conditions within the cenote.

Beschreibung: 〈b〉Drivers of 21〈sup〉st〈/sup〉 Century carbon cycle variability in the North Atlantic Ocean〈/b〉〈br〉 Matthew P. Couldrey, Kevin I. C. Oliver, Andrew Yool, Paul R. Halloran, and Eric P. Achterberg〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-16,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Determining how much carbon dioxide (CO〈sub〉2〈/sub〉) the oceans absorb is key to predicting human-caused climate change. A computer model of the ocean shows how the North Atlantic will change up to the end of the century. Year-to-year variations are mostly caused by changes in ocean temperature and seawater chemistry, altering CO〈sub〉2〈/sub〉 solubility. By 2100, human emissions cause the biggest changes. The near term changes are physically driven, which may be more predictable than biological changes.

Beschreibung: 〈b〉Characterizing organic matter composition in small Low and High Arctic catchments using terrestrial colored dissolved organic matter (cDOM)〈/b〉〈br〉 Caroline Coch, Bennet Juhls, Scott F. Lamoureux, Melissa Lafrenière, Michael Fritz, Birgit Heim, and Hugues Lantuit〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2019-9,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Climate change affects Arctic ecosystems. This includes the thawing of permafrost (ground below 0°C) and an increase in rainfall. Both have substantial impacts on the chemical composition of river water. We compared the composition of small rivers in the Low and High Arctic with the large Arctic rivers. The constituents in our smaller rivers are more susceptible to degradation, thus, they could potentially increase carbon dioxide emissions. Rainfall events led to a similar effect.

Beschreibung: 〈b〉Diurnal regulation of photosynthetic light absorption, electron transport and carbon fixation in two contrasting oceanic environments〈/b〉〈br〉 Nina Schuback and Phillipe D. Tortell〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-524,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Understanding the dynamics of primary productivity requires mechanistic insight into the coupling of light absorption, electron transport and carbon fixation in response to environmental variability. Measuring such rates and over diurnal timescales in contrasting regions allowed us to gain information on the regulation of photosynthetic efficiencies, with implications for the interpretation of bio-optical data, and the parameterization of models needed to monitor productivity over large scales.

Beschreibung: 〈b〉Comparison of CO〈sub〉2〈/sub〉 and O〈sub〉2〈/sub〉 fluxes demonstrate retention of respired CO〈sub〉2〈/sub〉 in tree stems from a range of tree species〈/b〉〈br〉 Boaz Hilman, Jan Muhr, Susan E. Trumbore, Norbert Kunert, Mariah S. Carbone, Päivi Yuval, S. Joseph Wright, Gerardo Moreno, Oscar Pérez-Priego, Mirco Migliavacca, Arnaud Carrara, José M. Grünzweig, Yagil Osem, Tal Weiner, and Alon Angert〈br〉 Biogeosciences, 16, 177-191, https://doi.org/10.5194/bg-16-177-2019, 2019〈br〉 Combined measurement of CO〈sub〉2〈/sub〉 / O〈sub〉2〈/sub〉 fluxes in tree stems suggested that on average 41 % of the respired CO〈sub〉2〈/sub〉 was not emitted locally to the atmosphere. This finding strengthens the recognition that CO〈sub〉2〈/sub〉 efflux from tree stems is not an accurate measure of respiration. The CO〈sub〉2〈/sub〉 / O〈sub〉2〈/sub〉 fluxes did not vary as expected if CO〈sub〉2〈/sub〉 dissolution in the xylem sap was the main driver for the CO〈sub〉2〈/sub〉 retention. We suggest the examination of refixation of respired CO〈sub〉2〈/sub〉 as a possible mechanism for CO〈sub〉2〈/sub〉 retention.

Beschreibung: 〈b〉Warming effect on nitrogen fixation in Mediterranean macrophyte sediments〈/b〉〈br〉 Neus Garcias-Bonet, Raquel Vaquer-Sunyer, Carlos M. Duarte, and Núria Marbà〈br〉 Biogeosciences, 16, 167-175, https://doi.org/10.5194/bg-16-167-2019, 2019〈br〉 We assess the impact of warming on nitrogen fixation in three key Mediterranean macrophytes by experimentally measuring sediment nitrogen fixation rates at current and projected seawater temperature by 2100 under a scenario of moderate greenhouse gas emissions. The temperature dependence of nitrogen fixation could potentially increase rates by 37 % by the end of the century, with important consequences for primary production in coastal ecosystems.

Beschreibung: 〈b〉Response of soil respiration and soil microbial biomass carbon and nitrogen to grazing management in the Loess Plateau, China〈/b〉〈br〉 Zhen Wang, Xiuli Wan, Mei Tian, Xiaoyan Wang, Junbo Chen, Xianjiang Chen, Shenghua Chang, and Fujiang Hou〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-531,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 A two-year soil respiration were measured in a long-term rotational grazing experiment plots with precise grazing intensity in warm and cold season grazing grassland on the Loess Plateau, China. We found grazing season and grazing patterns significantly affected the rate of soil respiration. Grazing intensities tended to increase soil microbial biomass carbon and soil microbial biomass nitrogen, while grazing season had little effect on soil microbial biomass nitrogen.

Beschreibung: 〈b〉Plant functional traits determined the latitudinal variations in soil microbial functions: evidence from a forest transect in China〈/b〉〈br〉 Zhiwei Xu, Guirui Yu, Xinyu Zhang, Ruili Wang, Ning Zhao, Nianpeng He, and Qiufeng Wang〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-499,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Plant functional traits have increasingly been studied as determinants of ecosystem propertie. While the relationships between biological community structures and ecological functions remain poorly understood at the large scale. We found that there was considerable variation in the profiles of different substrate use along the NSTEC. The soil silt content and plant functional traits together shaped the biogeographical pattern of the soil microbial substrate use.

Beschreibung: 〈b〉Modeling oceanic nitrate and nitrite concentrations and isotopes using a 3-D inverse N cycle model〈/b〉〈br〉 Taylor S. Martin, François Primeau, and Karen L. Casciotti〈br〉 Biogeosciences, 16, 347-367, https://doi.org/10.5194/bg-16-347-2019, 2019〈br〉 Nitrite is a key intermediate in many nitrogen (N) cycling processes in the ocean, particularly in areas with low oxygen that are hotspots for N loss. We have created a 3-D global N cycle model with nitrite as a tracer. Stable isotopes of N are also included in the model and we are able to model the isotope fractionation associated with each N cycling process. Our model accurately represents N concentrations and isotope distributions in the ocean.

Beschreibung: 〈b〉On the role of climate modes in modulating the air–sea CO〈sub〉2〈/sub〉 fluxes in eastern boundary upwelling systems〈/b〉〈br〉 Riley X. Brady, Nicole S. Lovenduski, Michael A. Alexander, Michael Jacox, and Nicolas Gruber〈br〉 Biogeosciences, 16, 329-346, https://doi.org/10.5194/bg-16-329-2019, 2019〈br〉 〈p〉The air–sea 〈span〉CO〈sub〉2〈/sub〉〈/span〉 fluxes in eastern boundary upwelling systems (EBUSs) vary strongly in time and space, with some of the highest flux densities globally. The processes controlling this variability have not yet been investigated consistently across all four major EBUSs, i.e., the California (CalCS), Humboldt (HumCS), Canary (CanCS), and Benguela (BenCS) Current systems. In this study, we diagnose the climatic modes of the air–sea 〈span〉CO〈sub〉2〈/sub〉〈/span〉 flux variability in these regions between 1920 and 2015, using simulation results from the Community Earth System Model Large Ensemble (CESM-LENS), a global coupled climate model ensemble that is forced by historical and RCP8.5 radiative forcing. Differences between simulations can be attributed entirely to internal (unforced) climate variability, whose contribution can be diagnosed by subtracting the ensemble mean from each simulation. We find that in the CalCS and CanCS, the resulting anomalous 〈span〉CO〈sub〉2〈/sub〉〈/span〉 fluxes are strongly affected by large-scale extratropical modes of variability, i.e., the North Pacific Gyre Oscillation (NPGO) and the North Atlantic Oscillation (NAO), respectively. The CalCS has anomalous uptake of 〈span〉CO〈sub〉2〈/sub〉〈/span〉 during the positive phase of the NPGO, while the CanCS has anomalous outgassing of 〈span〉CO〈sub〉2〈/sub〉〈/span〉 during the positive phase of the NAO. In contrast, the HumCS is mainly affected by El Niño–Southern Oscillation (ENSO), with anomalous uptake of 〈span〉CO〈sub〉2〈/sub〉〈/span〉 during an El Niño event. Variations in dissolved inorganic carbon (DIC) and sea surface temperature (SST) are the major contributors to these anomalous 〈span〉CO〈sub〉2〈/sub〉〈/span〉 fluxes and are generally driven by changes to large-scale gyre circulation, upwelling, the mixed layer depth, and biological processes. A better understanding of the sensitivity of EBUS 〈span〉CO〈sub〉2〈/sub〉〈/span〉 fluxes to modes of climate variability is key in improving our ability to predict the future evolution of the atmospheric 〈span〉CO〈sub〉2〈/sub〉〈/span〉 source and sink characteristics of the four EBUSs.〈/p〉

Beschreibung: 〈b〉Highly branched isoprenoids for Southern Ocean semi-quantitative sea ice reconstructions: a pilot study from the Western Antarctic Peninsula〈/b〉〈br〉 Maria-Elena Vorrath, Juliane Müller, Oliver Esper, Gesine Mollenhauer, Christian Haas, Enno Schefuß, and Kirsten Fahl〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-518,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 The study highlights new approaches in the investigation of past sea ice in Antarctica to reconstruct the climate conditions in earth's history and reveal its future development under global warming. We examined the distribution of organic remains from different algae at the Western Antarctic Peninsula and compared it to fossil and satellite records. We evaluated IPSO〈sub〉25〈/sub〉 – the sea ice proxy for the Southern Ocean with 25 carbon atoms – as a useful tool for sea ice reconstructions in this region.

Beschreibung: 〈b〉Simulating growth-based harvest adaptive to future climate change〈/b〉〈br〉 Rasoul Yousefpour, Julia E. M. S. Nabel, and Julia Pongratz〈br〉 Biogeosciences, 16, 241-254, https://doi.org/10.5194/bg-16-241-2019, 2019〈br〉 Global forest resources are accounted for to establish their potential to sink carbon in woody biomass. Climate prediction models realize the effects of future global forest utilization rates, defined by population demand and its evolution over time. However, forest management approaches consider the supply side to realize a sustainable forest carbon stock and adapt the harvest rates to novel climate conditions. This study simulates such an adaptive sustained yield approach.

Beschreibung: 〈b〉Varying relationships between fire radiative power and fire size at a global scale〈/b〉〈br〉 Pierre Laurent, Florent Mouillot, Maria Vanesa Moreno, Chao Yue, and Philippe Ciais〈br〉 Biogeosciences, 16, 275-288, https://doi.org/10.5194/bg-16-275-2019, 2019〈br〉 Fire propagation and fire size are usually considered to be proportional to fire intensity. We used a global database of fire patch size and fire radiative power, used as a proxy of fire intensity, to test this relationship at a global scale. We showed that in some regions fire size tends to saturate when a regional fire intensity threshold is reached. We concluded that increasing landscape fragmentation limits fire propagation and this effect should be accounted for in global fire modules.

Beschreibung: 〈b〉Interpreting eddy covariance data from heterogeneous Siberian tundra: land-cover-specific methane fluxes and spatial representativeness〈/b〉〈br〉 Juha-Pekka Tuovinen, Mika Aurela, Juha Hatakka, Aleksi Räsänen, Tarmo Virtanen, Juha Mikola, Viktor Ivakhov, Vladimir Kondratyev, and Tuomas Laurila〈br〉 Biogeosciences, 16, 255-274, https://doi.org/10.5194/bg-16-255-2019, 2019〈br〉 We analysed ecosystem-scale measurements of methane exchange between Arctic tundra and the atmosphere, taking into account the large variations in vegetation and soil properties. The measurements are spatial averages, but using meteorological and statistical modelling techniques we could estimate methane emissions for different land cover types and quantify how well the measurements correspond to the spatial variability. This provides a more accurate estimate of the regional methane emission.

Beschreibung: 〈b〉The post-monsoon carbon biogeochemistry of the Hooghly–Sundarbans estuarine system under different levels of anthropogenic impacts〈/b〉〈br〉 Manab Kumar Dutta, Sanjeev Kumar, Rupa Mukherjee, Prasun Sanyal, and Sandip Kumar Mukhopadhyay〈br〉 Biogeosciences, 16, 289-307, https://doi.org/10.5194/bg-16-289-2019, 2019〈br〉 The study focused on understanding C biogeochemistry of two adjacently located estuaries undergoing different levels of anthropogenic stresses. Different parameters related to C cycling were measured in an anthropogenically influenced and a mangrove-dominated estuary. Although the entire estuarine system acted as a source of carbon dioxide to the regional atmosphere, emission approximately 17 times higher was noticed from the anthropogenically affected estuary compared to mangrove-dominated one.

Beschreibung: 〈b〉Microclimatic and ecophysiological conditions experienced by epiphytic bryophytes in an Amazonian rain forest〈/b〉〈br〉 Nina Löbs, David Walter, Cybelli G. G. Barbosa, Sebastian Brill, Gabriela R. Cerqueira, Marta de Oliveira Sá, Alessandro C. de Araújo, Leonardo R. de Oliveira, Florian Ditas, Daniel Moran-Zuloaga, Ana Paula Pires Florentino, Stefan Wolff, Ricardo H. M. Godoi, Jürgen Kesselmeier, Sylvia Mota de Oliveira, Meinrat O. Andreae, Christopher Pöhlker, and Bettina Weber〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-521,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 Cryptogamic organisms, as i.e. bryophytes, lichens, and algae, cover major parts of vegetation in the Amazonian rain forest, but their relevance in biosphere-atmosphere exchange, climate processes, and nutrient cycling is largely unknown. Over the duration of two years we measured their water content, temperature, and light conditions to get better insights into their physiological activity pattern and thus, their potential impact on local, regional, and even global biogeochemical processes.

Beschreibung: 〈b〉Quantifying global N〈sub〉2〈/sub〉O emissions from natural ecosystem soils using trait-based biogeochemistry models〈/b〉〈br〉 Tong Yu and Qianlai Zhuang〈br〉 Biogeosciences, 16, 207-222, https://doi.org/10.5194/bg-16-207-2019, 2019〈br〉 〈p〉A group of soil microbes plays an important role in nitrogen cycling and 〈span〉N〈sub〉2〈/sub〉O〈/span〉 emissions from natural ecosystem soils. We developed a trait-based biogeochemical model based on an extant process-based biogeochemistry model, the Terrestrial Ecosystem Model (TEM), by incorporating the detailed microbial physiological processes of nitrification. The effect of ammonia-oxidizing Archaea (AOA), ammonia-oxidizing bacteria (AOB), and nitrite-oxidizing bacteria (NOB) was considered in modeling nitrification. Microbial traits, including microbial biomass and density, were explicitly considered. In addition, nitrogen cycling was coupled with carbon dynamics based on stoichiometry theory between carbon and nitrogen. The model was parameterized using observational data and then applied to quantifying global 〈span〉N〈sub〉2〈/sub〉O〈/span〉 emissions from global terrestrial ecosystem soils from 1990 to 2000. Our estimates of 〈span〉8.7±1.6〈/span〉 Tg N yr〈span〉〈sup〉−1〈/sup〉〈/span〉 generally agreed with previous estimates during the study period. Tropical forests are a major emitter, accounting for 42 % of the global emissions. The model was more sensitive to temperature and precipitation and less sensitive to soil organic carbon and nitrogen contents. Compared to the model without considering the detailed microbial activities, the new model shows more variations in response to seasonal changes in climate. Our study suggests that further information on microbial diversity and ecophysiology features is needed. The more specific guilds and their traits shall be considered in future soil 〈span〉N〈sub〉2〈/sub〉O〈/span〉 emission quantifications.〈/p〉

Beschreibung: 〈b〉The importance of mineral determinations to PROFILE base cation weathering release rates: A case study〈/b〉〈br〉 Sophie Casetou-Gustafson, Cecilia Akselsson, Stephen Hillier, and Bengt A. Olsson〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-522,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 PROFILE base cation weathering estimates using the directly measured XRPD mineralogy compared to different indirectly determined A2M mineralogies (regional versus site-specific) were overall similar, however, the underlying contribution from different minerals to the overall rates differed. Descriptions of the dissolution rate kinetics of the plagioclase mineral group as well as major K-bearing minerals (K-feldspars and micas) should be improved for future soil and forest management studies.

Beschreibung: 〈b〉Enhanced microbial nitrogen transformations in association with macrobiota from the rocky intertidal〈/b〉〈br〉 Catherine A. Pfister and Mark A. Altabet〈br〉 Biogeosciences, 16, 193-206, https://doi.org/10.5194/bg-16-193-2019, 2019〈br〉 Microbial assemblages on host plants and animals are an increasingly recognized biological phenomenon. We present evidence that microbes in association with mussels and seaweeds are contributing greatly to nitrogen cycling in coastal marine areas, often many times that of the microbes that are simply free-living in seawater. The addition of dissolved organic carbon increased nutrient uptake by microbes, suggesting that coastal species enhance microbial metabolism through resource provisioning.

Beschreibung: 〈b〉A novel isotope pool dilution approach to quantify gross rates of key abiotic and biological processes in the soil phosphorus cycle〈/b〉〈br〉 Wolfgang Wanek, David Zezula, Daniel Wasner, Maria Mooshammer, and Judith Prommer〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-519,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Efforts to understand the global phosphorus (P) cycle are limited by the scarcity of global data on rates of soil P processes, as well as of its environmental controls. We here present a novel approach using radiophosphorus labelling of soils, which allows to measure fluxes of abiotic and biotic soil P processes. This approach is also suitable for strongly weathered and P depleted soils. Biotic processes are corrected for abiotic ones by comparing life and sterile soils.

Beschreibung: 〈b〉The composition and distribution of semi-labile dissolved organic matter across the southwest Pacific〈/b〉〈br〉 Christos Panagiotopoulos, Mireille Pujo-Pay, Mar Benavides, France Van Wambeke, and Richard Sempéré〈br〉 Biogeosciences, 16, 105-116, https://doi.org/10.5194/bg-16-105-2019, 2019〈br〉 〈p〉The distribution and dynamics of dissolved organic carbon (DOC) and dissolved combined neutral sugars (DCNS) were studied across an increasing oligotrophic gradient (18 to 22〈span〉〈sup〉∘〈/sup〉〈/span〉 S latitude) in the tropical South Pacific Ocean, spanning from the Melanesian Archipelago (MA) area to the western part of the South Pacific gyre (WGY), in austral summer as a part of the OUTPACE project. Our results show that DOC and DCNS concentrations exhibited no statistical differences between the MA and WGY areas (0–200 m: 47–81 〈span〉µ〈/span〉M C for DOC and 0.2-4.2 〈span〉µ〈/span〉M C for DCNS). However, due to a deepening of the euphotic zone, a deeper penetration of DOC was noticeable at 150 m of depth at the WGY area. Excess DOC (DOC〈span〉〈sub〉EX〈/sub〉〈/span〉) was determined as the difference between surface and deep-sea DOC values, and euphotic zone integrated stocks of both DOC and DOC〈span〉〈sub〉EX〈/sub〉〈/span〉 were higher in the WGY than the MA area. Considering DOC〈span〉〈sub〉EX〈/sub〉〈/span〉 as representative of semi-labile DOC (DOC〈span〉〈sub〉SL〈/sub〉〈/span〉), its residence time was calculated as the ratio of DOC〈span〉〈sub〉SL〈/sub〉〈/span〉 to bacterial carbon demand (BCD). This residence time was 〈span〉176±43〈/span〉 days (〈span〉〈i〉n〈/i〉=3〈/span〉) in the WGY area, about 3 times longer than in the MA area (〈span〉〈math xmlns="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" dspmath="mathml"〉〈mrow〉〈msub〉〈mi〉T〈/mi〉〈mi mathvariant="normal"〉r〈/mi〉〈/msub〉〈mo〉=〈/mo〉〈mn mathvariant="normal"〉51〈/mn〉〈mo〉±〈/mo〉〈mn mathvariant="normal"〉13〈/mn〉〈/mrow〉〈/math〉〈span〉〈svg xmlns:svg="http://www.w3.org/2000/svg" width="59pt" height="12pt" dspmath="mathimg" md5hash="1f1229457353a2de9b9b4ab9265d8598"〉〈image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-105-2019-ie00001.svg" width="59pt" height="12pt" src="bg-16-105-2019-ie00001.png"〉〈/image〉〈/svg〉〈/span〉〈/span〉 days, 〈span〉〈i〉n〈/i〉=8〈/span〉), suggesting an accumulation of semi-labile dissolved organic matter (DOM) in the surface waters of WGY. Average epipelagic (0–200 m) DCNS yields (DCNS 〈span〉×〈/span〉 DOC〈span〉〈sup〉−1〈/sup〉〈/span〉) based on volumetric data were roughly similar in both areas, accounting for 〈span〉∼2.8〈/span〉 % of DOC. DCNS exhibited a longer residence time in WGY (〈span〉〈math xmlns="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" dspmath="mathml"〉〈mrow〉〈msub〉〈mi〉T〈/mi〉〈mi mathvariant="normal"〉r〈/mi〉〈/msub〉〈mo〉=〈/mo〉〈mn mathvariant="normal"〉91〈/mn〉〈mo〉±〈/mo〉〈mn mathvariant="normal"〉41〈/mn〉〈/mrow〉〈/math〉〈span〉〈svg xmlns:svg="http://www.w3.org/2000/svg" width="59pt" height="12pt" dspmath="mathimg" md5hash="f17dc1a9c613f69ead3c360780a5771c"〉〈image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-105-2019-ie00002.svg" width="59pt" height="12pt" src="bg-16-105-2019-ie00002.png"〉〈/image〉〈/svg〉〈/span〉〈/span〉 days, 〈span〉〈i〉n〈/i〉=3〈/span〉) than in MA (〈span〉〈math xmlns="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" dspmath="mathml"〉〈mrow〉〈msub〉〈mi〉T〈/mi〉〈mi mathvariant="normal"〉r〈/mi〉〈/msub〉〈mo〉=〈/mo〉〈mn mathvariant="normal"〉31〈/mn〉〈mo〉±〈/mo〉〈mn mathvariant="normal"〉10〈/mn〉〈/mrow〉〈/math〉〈span〉〈svg xmlns:svg="http://www.w3.org/2000/svg" width="59pt" height="12pt" dspmath="mathimg" md5hash="027f5be64f6d4c7ff36441bfd093e774"〉〈image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-105-2019-ie00003.svg" width="59pt" height="12pt" src="bg-16-105-2019-ie00003.png"〉〈/image〉〈/svg〉〈/span〉〈/span〉 days, 〈span〉〈i〉n〈/i〉=8〈/span〉), further suggesting that this DCNS pool persists longer in the surface waters of the WGY. The accumulation of DOC〈span〉〈sub〉EX〈/sub〉〈/span〉 in the surface waters of WGY is probably due to very slow bacterial degradation due to nutrient and/or energy limitation of heterotrophic prokaryotes, indicating that biologically produced DOC can be stored in the euphotic layer of the South Pacific gyre for a long period.〈/p〉

Beschreibung: 〈b〉Multiyear methane ebullition measurements from water and bare peat surfaces of a patterned boreal bog〈/b〉〈br〉 Elisa Männistö, Aino Korrensalo, Pavel Alekseychik, Ivan Mammarella, Olli Peltola, Timo Vesala, and Eeva-Stiina Tuittila〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-532,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 We studied methane emitted as episodic bubble release (ebullition) from water and bare peat surfaces of a boreal bog in three subsequent years. There was more ebullition from water than from bare peat surfaces, and it was controlled by peat temperature, water level, atmospheric pressure and weekly temperature sum. However, the contribution of methane bubbles to the total ecosystem methane emission was small. This new information can be used to improve process models of peatland methane dynamics.

Beschreibung: 〈b〉Comprehensive characterization of an Aspen (〈i〉Populus tremuloides〈/i〉) leaf litter sample that maintained ice nucleation activity for 48 years〈/b〉〈br〉 Yalda Vasebi, Marco E. Mechan Llontop, Regina Hanlon, David G. Schmale III, Russell Schnell, and Boris A. Vinatzer〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-496,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Ice nucleation particles (INPs) help ice form at temperatures as high as −4 °C and contribute to the formation of precipitation. Leaf litter contains a high concentration of INPs but the organisms that produce them are unknown. Here, we cultured two bacteria and one fungus from leaf litter that produce INPs similar to those found in leaf litter. This suggests that leaf litter may be an important habitat of these organisms and supports a role of these organisms as producers of atmospheric INPs.

Beschreibung: 〈b〉Global trends in marine nitrate N isotopes from observations and a neural network-based climatology〈/b〉〈br〉 Patrick A. Rafter, Aaron Bagnell, Dario Marconi, and Timothy DeVries〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-525,2019〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 The N isotopic composition of nitrate (〈q〉nitrate 〈i〉δ〈/i〉〈sup〉15〈/sup〉N〈/q〉) is a useful tracer of ocean N cycling and many other ocean processes. Here, we use a global compilation of marine nitrate 〈i〉δ〈/i〉〈sup〉15〈/sup〉N as an input, training, and validating dataset for an artificial neural network (a.k.a., 〈q〉machine learning〈/q〉) and examine basin-scale trends in marine nitrate 〈i〉δ〈/i〉〈sup〉15〈/sup〉N from the surface to the seafloor.

Beschreibung: The tundra plays a pivotal role in the Arctic mercury (Hg) cycling by storing atmospheric Hg deposition and shuttling it to the Arctic Ocean. A recent study revealed that 70 % of the atmospheric Hg deposition to the tundra occurs by gaseous elemental mercury (GEM or Hg(0)) uptake by vegetation and soils. Processes controlling land – atmosphere exchange of Hg(0) in the Arctic tundra are therefore central, but remain understudied. Here, we combine Hg stable isotope analysis of Hg(0) in the atmosphere, interstitial snow and soil pore air, with Hg(0) flux measurements in a tundra ecosystem at Toolik field station in northern Alaska (USA). In dark winter months, planetary boundary layer (PBL) conditions and Hg(0) concentrations were generally stable throughout the day and small Hg(0) net deposition occurred. In spring, halogen-induced atmospheric mercury depletion events (AMDE's) occurred, with fast re-emission of Hg(0) after AMDE's resulting in net emission fluxes of Hg(0). During the short snow-free growing season in summer, vegetation uptake of atmospheric Hg(0) enhanced atmospheric Hg(0) net deposition to the Arctic tundra. At night, when PBL conditions were stable, ecosystem uptake of atmospheric Hg(0) led to a depletion of atmospheric Hg(0). The night time decline of atmospheric Hg(0) was concomitant with a depletion of lighter Hg(0) isotopes in the atmospheric Hg pool. The enrichment factor, ε202Hg = −4.2 ‰ ± 1.0 ‰ was consistent with the preferential uptake of light Hg(0) isotopes by vegetation. Hg(0) flux measurements indicated a partial re-emission of Hg(0) during daytime, when solar radiation was strongest. Hg(0) concentrations in soil pore air were depleted relative to atmospheric Hg(0) concentrations, concomitant with an enrichment of lighter Hg(0) isotopes in the soil pore air (ε202Hgsoilair-atmosphere = −1.00 ‰ (±0.25 ‰) and E199Hgsoilair-atmosphere = 0.07 ‰ (±0.04 ‰)). These first Hg stable isotope measurements of Hg(0) in soil pore air are consistent with the fractionation previously observed during Hg(0) oxidation by natural humic acids suggesting abiotic oxidation as a cause for observed soil Hg(0) uptake.

Beschreibung: Marine calcification is an important component of the global carbon cycle. The mechanism by which some organisms take up inorganic carbon for the production of their shells or skeletons, however, remains only partly known. Although foraminifera are responsible for a large part of the global calcium carbonate production, the process by which they concentrate inorganic carbon is debated. Some evidence suggests that seawater is taken up and participates relatively unaltered in the process of calcification, whereas other results suggest the involvement of transmembrane transport and the activity of enzymes like carbonic anhydrase. Here, we tested whether inorganic carbon uptake relies on the activity of carbonic anhydrase using incubation experiments with the large benthic, symbiont-bearing foraminifer Amphistegina lessonii. Calcification rates, determined by the alkalinity anomaly method, showed that inhibition of carbonic anhydrase by acetazolamide (AZ) stopped most of the calcification process. Inhibition of photosynthesis by either 3-(3,4-Dichlorophenyl)-1,1-dimethylurea (DCMU) or by incubating the foraminifera in the dark, also decreased calcification rates, but to a lesser degree than with AZ. Results from this study show that carbonic anhydrase plays a key role in biomineralization of Amphistegina lessonii and indicates that calcification of those large benthic foraminifera might, to a certain extent, benefit from ocean acidification.

Beschreibung: In this study, the concentrations of 12 metals: Ca, Na, Sr, Mg, Ba, Mn, Cu, Pb, V, Y, U and Cd in shells of bivalve molluscs (aragonitic: Cerastoderma glaucum, Mya arenaria and Limecola balthica and bimineralic: Mytilus trossulus) and arthropods (calcitic: Amphibalanus improvisus) were obtained. The main goal was to determine the incorporation patterns of shells built with different calcium carbonate polymorphs. The role of potential biological control on the shell chemistry was assessed by comparing the concentrations of trace elements between younger and older individuals (different size classes). The potential impact of environmental factors on the observed elemental concentrations in the studied shells is discussed. Specimens were collected from brackish waters of the Baltic Sea (the Gulf of Gdansk). For every species, 40 individuals (ten in each size class) were selected. Pre-cleaned shells were analysed by ICP-OES and ICP-MS to determine the concentrations of metals. The distributions of elements both differ between species and exhibit high intraspecific variability. Calcitic shells preferentially incorporated Mg 〉 Sr 〉 Na, aragonitic shells incorporated Na 〉 Sr 〉 Mg, and bimineralic shells accumulated Na approximately two times more intensively, than Mg and Sr which remained at similar levels. Among all species, the calcitic shells of A. improvisus most effectively concentrated the majority of the studied elements, especially Mg 〉 Mn 〉 Ba, which was contrary to the shells of aragonitic molluscs that contained the lowest levels of trace elements. The size-dependent distributions of elements in shells did not exhibit a consistent pattern. The highest significant differences were found for the bimineralic shells of M. trossulus, while the smallest were found for aragonitic shells; if any variability occurred, it was observed in heavy metals (Pb, Cd). Our results indicate that elemental variability, especially that of Mg and Sr, is dominated by the properties of the crystal lattice. The inconsistent variability of trace element concentrations between species and within single populations supports the important role of species-specific biological control of the biomineralization process and indicates that environmental factors have a significant influence on the incorporation of trace elements into the shells.

Beschreibung: With projected increasing intensity of hurricanes and large uncertainty in the path of forest recovery from hurricanes, studies are needed to understand the fundamental response of forests to canopy opening and debris deposition: the response of the abiotic factors underneath the canopy. Through manipulative experiments and instrumenting hurricane María in the Luquillo Experimental Forest of Puerto Rico, this study found a long recovery time of the primary abiotic factors (light, throughfall, and temperature) influenced by the disturbance of canopy opening, and complex responses by the secondary abiotic factors (humidity, soil moisture, and leaf saturation) influenced by the disturbance of the primary factors. Recovery took up to 9 years for beneath canopy light, while throughfall recovery took 6 years. Air and soil temperature seemingly recovered fairly quickly from each disturbance, however temperature was the most important modulator of secondary factors, which followed the long-term patterns of the throughfall. While the soil remained wetter and humidity stayed lower until recovery, leaves in the litter and canopy were wetter and drier, with evidence that leaves dry out faster in low rainfall and saturate faster in high rainfall after disturbance. Comparison of satellite and field data before and after the 2017 hurricane showed the utility of satellites in expanding the data coverage, but the muted response of the satellite data suggest they measure dense forest as well as thin forest that is not as disturbed by hurricanes. Thus, quick recovery times recorded by satellites should not be assumed representative of all of the forest.