Scaling carbon fluxes from eddy covariance sites to globe: synthesis andevaluation of the FLUXCOM approach Biogeosciences DOI 10.5194/bg-17-1343-2020 26 March 2020 We test the approach of producing global gridded carbon fluxes based on combining machine learning with local measurements, remote sensing and climate data. We show that we can reproduce seasonal variations in carbon assimilated by plants via photosynthesis and in ecosystem net carbon balance. The ecosystem’s mean carbon balance and carbon flux trends require cautious interpretation. The analysis paves the way for future improvements of the data-driven assessment of carbon fluxes. FLUXCOM approach">Read more
No nitrogen fixation in the Bay of Bengal? Biogeosciences DOI 10.5194/bg-17-851-2020 27 February 2020 Oxygen minimum zones (OMZs) are ocean areas severely depleted in oxygen as a result of physical, chemical, and biological processes. Biologically, organic material is produced in the sea surface and exported to deeper waters, where it respires. In the Bay of Bengal (BoB), an OMZ is present, but there are traces of oxygen left. Our study now suggests that this is because one key process, nitrogen fixation, is absent in the BoB, thus preventing primary production and consecutive respiration. Read more
Dimensions of marine phytoplankton diversity Biogeosciences DOI 10.5194/bg-17-609-2020 18 February 2020 Phytoplankton are an essential component of the marine food web and earth’s carbon cycle. We use observations, ecological theory and a unique trait-based ecosystem model to explain controls on patterns of marine phytoplankton biodiversity. We find that different dimensions of diversity (size classes, biogeochemical functional groups, thermal norms) are controlled by a disparate combination of mechanisms. This may explain why previous studies of phytoplankton diversity had conflicting results. Read more
Microbial community composition and abundance after millennia of submarine permafrost warming Biogeosciences DOI 10.5194/bg-16-3941-2019 8 November 2019 Permafrost temperatures increased substantially at a global scale, potentially altering microbial assemblages involved in carbon mobilization before permafrost thaws. We used Arctic Shelf submarine permafrost as a natural laboratory to investigate the microbial response to long-term permafrost warming. Our work shows that millennia after permafrost warming by > 10 °C, microbial community composition and population size reflect the paleoenvironment rather than a direct effect through warming. Read more
Physical constraints for respiration in microbial hotspots in soil and their importance for denitrification Biogeosciences DOI 10.5194/bg-16-3665-2019 27 September 2019 A combination of gas chromatography and X-ray CT reveals the microscale processes that govern soil respiration. Aerobic and anaerobic respiration in microbial hotspots depends not only on the quality and quantity of soil organic matter, but also on the spatial distribution of hotspots. Denitrification kinetics are mainly governed by hotspot architecture due to local competition for oxygen during growth. Cumulative behavior is mainly governed by water saturation due to the overall supply with O2. Read more
Ideas and perspectives: is shale gas a major driver of recent increase in global atmospheric methane? Biogeosciences DOI 10.5194/bg-16-3033-2019 14 August 2019 Atmospheric methane has risen rapidly since 2008 and has become more depleted in 13C, in contrast to the trend towards more 13C enrichment in the late 20th century. Many have used this isotopic evidence to infer an increased biogenic source. Here I analyze the 13C trend with the consideration that methane from shale gas is somewhat depleted in 13C compared to other fossil fuels. I conclude that shale gas may be responsible for a third of the global increase from all sources. Read more
Global soil–climate–biome diagram: linking surface soil properties to climate and biota Biogeosciences DOI 10.5194/bg-16-2857-2019 25 July 2019 Surface soils interact strongly with both climate and biota and provide fundamental ecosystem services. However, the quantitative linkages between soil, climate, and biota remain unclear at a 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 shifts in soil properties under global climate and land cover change. Read more
Dissolved organic matter at the fluvial–marine transition in the Laptev Sea using in situ data and ocean colour remote sensing Biogeosciences DOI 10.5194/bg-16-2693-2019 11 July 2019 In this article, we present the variability and characteristics of dissolved organic matter at the fluvial–marine transition in the Laptev Sea from a unique dataset collected during 11 Arctic expeditions. We develop a new relationship between dissolved organic carbon (DOC) and coloured dissolved organic matter absorption, which is used to estimate surface water DOC concentration from space. We believe that our findings help current efforts to monitor ongoing changes in the Arctic carbon cycle. Read more
Responses of an abyssal meiobenthic community to short-term burial with crushed nodule particles in the south-east Pacific Biogeosciences DOI 10.5194/bg-16-2329-2019 6 June 2019 To elucidate the potential effects of crushed nodule particle deposition on abyssal meiobenthos, we covered abyssal soft sediment in the Peru Basin (4200 m depth) with approximately 2 cm of this nodule material for 11 d. About half of the meiobenthos migrated from the sediment into the added material, and nematode feeding type proportions in that added layer were altered. These results considerably contribute to our understanding of the short-term responses of deep-sea meiobenthos to burial. Read more
Reciprocal bias compensation and ensuing uncertainties in model-based climate projections: pelagic biogeochemistry versus ocean mixing Biogeosciences DOI 10.5194/bg-16-1865-2019 6 May 2019 Anthropogenic greenhouse gas emissions trigger complex climate feedbacks. Output form Earth system models provides a basis for related political decision-making. One challenge is to arrive at reliable model parameter estimates for the ocean biogeochemistry module. We illustrate pitfalls through which flaws in the ocean module are masked by wrongly tuning the biogeochemistry and discuss ensuing uncertainties in climate projections. Read more
