Mineral formation induced by cable bacteria performing long-distance electron transport in marine sediments Biogeosciences DOI 10.5194/bg-16-811-2019 13 February 2019 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. Read more
Evidence for a major missing source in the global chloromethane budget from stable carbon isotopes Atmospheric Chemistry and Physics DOI 10.5194/acp-19-1703-2019 8 February 2019 Chloromethane is the most important natural carrier of chlorine to the stratosphere. From a newly determined carbon isotope effect of −11.2 ‰ for the tropospheric loss of CH3Cl we derive a tropical rainforest CH3Cl source of 670 ± 200 Gg a−1, 60 % smaller than previous estimates. A revision of previous bottom-up estimates using above-ground biomass instead of rainforest area strongly supports this lower estimate. Our results suggest a large unknown tropical value of 1530 ± 200 Gg a−1. Read more
Four decades of Antarctic surface elevation changes from multi-mission satellite altimetry The Cryosphere DOI 10.5194/tc-13-427-2019 5 February 2019 We developed an approach to combine measurements of seven satellite altimetry missions over the Antarctic Ice Sheet. Our resulting monthly grids of elevation changes between 1978 and 2017 provide unprecedented details of the long-term and interannual variation. Derived mass changes agree well with contemporaneous data of surface mass balance and satellite gravimetry and show which regions were responsible for the significant accelerations of mass loss in recent years. Read more
Power spectra of random heterogeneities in the solid earth Solid Earth DOI 10.5194/se-10-275-2019 5 February 2019 Recent seismological observations clarified that the velocity structure of the crust and upper mantle is randomly heterogeneous. I compile reported power spectral density functions of random velocity fluctuations based on various types of measurements. Their spectral envelope is approximated by the third power of wavenumber. It is interesting to study what kinds of geophysical processes created such a power-law spectral envelope at different scales and in different geological environments. Read more
Emergent stationarity in Yellow River sediment transport and the underlying shift of dominance: from streamflow to vegetation Hydrology and Earth System Sciences DOI 10.5194/hess-23-549-2019 30 January 2019 Our study shows that there is declining coupling between sediment concentration and discharge from daily to annual scales for gauges across the Yellow River basin (YRB). Not only the coupling, but also the magnitude of sediment response to discharge variation decreases with long-term mean discharge. This emergent stationarity can be related to sediment retardation by vegetation, suggesting the shift of dominance from water to vegetation as mean annual discharge increases. Read more
Long-term erosion of the Nepal Himalayas by bedrock landsliding: the role of monsoons, earthquakes and giant landslides Earth Surface Dynamics DOI 10.5194/esurf-7-107-2019 25 January 2019 We mapped eight monsoon-related (> 100 m2) and large (> 0.1 km2) landslides in the Nepal Himalayas since 1970. Adding inventories of Holocene landslides, giant landslides (> 1 km3), and landslides from the 2015 Gorkha earthquake, we constrain the size–frequency distribution of monsoon- and earthquake-induced landslides. Both contribute ~50 % to a long-term (> 10 kyr) total erosion of ~2 mm yr-1, matching the long-term exhumation rate. Large landslides rarer than10Be sampling time drive erosion. Read more
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 Biogeosciences DOI 10.5194/bg-16-409-2019 25 January 2019 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. Read more
Positive matrix factorization of organic aerosol: insights from a chemical transport model Atmospheric Chemistry and Physics DOI 10.5194/acp-19-973-2019 24 January 2019 The ability of positive matrix factorization (PMF) factor analysis to identify and quantify the organic aerosol (OA) sources accurately is tested in this modeling study. The estimated uncertainty of the contribution of fresh biomass burning is less than 30 % and of the other primary sources is less than 40 %, when these sources contribute more than 20 % to the OA. Τhe first oxygenated OA factor includes mainly highly aged OA, while the second oxygenated OA factor contains fresher secondary OA. Read more
Heinrich events show two-stage climate response in transient glacial simulations Climate of the Past DOI 10.5194/cp-15-153-2019 24 January 2019 Heinrich events are among the dominant modes of glacial climate variability. They are caused by massive ice discharges from the Laurentide Ice Sheet into the North Atlantic. In previous studies, the climate changes were either seen as resulting from freshwater released from the melt of the discharged icebergs or by ice sheet elevation changes. With a coupled ice sheet–climate model, we show that both effects are relevant with the freshwater effects preceding the ice sheet elevation effects. Read more
Quantifying new water fractions and transit time distributions using ensemble hydrograph separation: theory and benchmark tests Hydrology and Earth System Sciences DOI 10.5194/hess-23-303-2019 18 January 2019 How long does it take for raindrops to become streamflow? Here I propose a new approach to this old problem. I show how we can use time series of isotope data to measure the average fraction of same-day rainfall appearing in streamflow, even if this fraction varies greatly from rainstorm to rainstorm. I show that we can quantify how this fraction changes from small rainstorms to big ones, and from high flows to low flows, and how it changes with the lag time between rainfall and streamflow. Read more
