ALBERT

Description: 〈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.

Description: 〈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.

Description: 〈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., doi: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.

Description: 〈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., doi: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.

Description: 〈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.

Description: 〈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.

Description: 〈b〉Reviews and syntheses: Dams, water quality and tropical reservoir stratification〈/b〉〈br〉 R. Scott Winton, Elisa Calamita, and Bernhard Wehrli〈br〉 Biogeosciences Discuss., doi: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.

Description: 〈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.

Description: 〈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.

Description: 〈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., doi: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.

Description: 〈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., doi: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.

Description: 〈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.

Description: 〈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.

Description: 〈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.

Description: 〈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.

Description: 〈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〉

Description: 〈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〉

Description: 〈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.

Description: 〈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.

Description: 〈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.org10.5194/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.

Description: 〈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.

Description: 〈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.

Description: 〈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.org10.5194/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.

Description: 〈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.org10.5194/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.

Description: 〈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.org10.5194/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.

Description: 〈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.org10.5194/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.

Description: 〈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.org10.5194/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.

Description: 〈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.

Description: 〈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.

Description: 〈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.

Description: 〈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.

Description: 〈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.

Description: 〈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., doi: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.

Description: 〈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.

Description: 〈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.

Description: 〈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.org10.5194/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.

Description: 〈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.org10.5194/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.

Description: 〈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.

Description: 〈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.org10.5194/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.

Description: 〈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.org10.5194/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.

Description: 〈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.

Description: 〈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.

Description: 〈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.

Description: 〈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.org10.5194/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.

Description: 〈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.

Description: 〈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.org10.5194/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.

Description: 〈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., doi: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.

Description: 〈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.

Description: 〈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.

Description: 〈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., doi: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.

Description: 〈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., doi: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.

Description: 〈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.

Description: 〈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.

Description: 〈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.

Description: 〈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.org10.5194/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.

Description: 〈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.org10.5194/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.

Description: 〈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.

Description: 〈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., doi: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.

Description: 〈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.

Description: 〈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〉

Description: 〈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〉

Description: 〈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.

Description: 〈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., doi: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.

Description: 〈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.org10.5194/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.

Description: 〈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.org10.5194/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〉.

Description: 〈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.

Description: 〈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〉

Description: 〈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〉.

Description: 〈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., doi: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.

Description: 〈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.org10.5194/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.

Description: 〈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.

Description: 〈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., doi: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.

Description: 〈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.org10.5194/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.

Description: 〈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.

Description: 〈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.

Description: 〈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.

Description: 〈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., doi: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.

Description: 〈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., doi: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.

Description: 〈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., doi: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.

Description: 〈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., doi: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.

Description: 〈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.

Description: 〈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.org10.5194/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.

Description: 〈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.org10.5194/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.

Description: 〈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., doi: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.

Description: 〈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.

Description: 〈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〉

Description: 〈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.org10.5194/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.

Description: 〈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., doi: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.

Description: 〈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.

Description: 〈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.org10.5194/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.

Description: 〈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.

Description: 〈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.

Description: 〈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.org10.5194/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.

Description: 〈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〉