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
The millennium-old hydrogeology textbook The Extraction of Hidden Waters by the Persian mathematician and engineer Abubakr Mohammad Karaji (953 CE–1029 CE) Hydrology and Earth System Sciences DOI 10.5194/hess-24-761-2020 27 February 2020 We revisit and shed light on the textbook The Extraction of Hidden Waters by the Persian mathematician and engineer Abubakr Mohammad Karaji. Ground-breaking ideas and descriptions of hydrological and hydrogeological perceptions such as components of the hydrological cycle, groundwater quality and driving factors for groundwater flow were presented in the book. We speculate that Karaji’s book is the first of its kind to provide a construction and maintenance manual for an engineering project. Read more
Cryoconite: an efficient accumulator of radioactive fallout in glacialenvironments The Cryosphere DOI 10.5194/tc-14-657-2020 25 February 2020 Cryoconite is the sediment found on the surface of glaciers. The paper presents cryoconite as an environmental matrix able to accumulate natural and artificial radioactivity with unprecedented efficiency. Only samples from sites where nuclear accidents and explosions occurred present a stronger radioactive contamination. The peculiarities of glacial environments are responsible for this extreme feature, making cryoconite a useful tool tool for the monitoring of environmental radioactivity. Read more
Quantifying hail size distributions from the sky – application of drone aerial photogrammetry Atmospheric Measurement Techniques DOI 10.5194/amt-13-747-2020 25 February 2020 Collecting measurements of hail size and shape is difficult due to the infrequent and dangerous nature of hailstorms. To improve upon this, a new technique called HailPixel is introduced for measuring hail using aerial imagery collected by a drone. A combination of machine learning and computer vision methods is used to extract the shape of thousands of hailstones from the aerial imagery. The improved statistics from the much larger HailPixel dataset show significant benefits. Read more
Surface water as a cause of land degradation from dryland salinity Hydrology and Earth System Sciences DOI 10.5194/hess-24-717-2020 25 February 2020 Secondary dryland salinity is a global land degradation issue. Our understanding of causal processes is adapted from wet and hydrologically connected landscapes and concludes that low end-of-catchment runoff indicates land clearing alters water balance in favour of increased infiltration and rising groundwater that bring salts to the surface causing salinity. This study shows surface flows play an important role in causing valley floor recharge and dryland salinity in low-gradient landscapes. Read more
Variations in soil chemical and physical properties explain basin-wideAmazon forest soil carbon concentrations SOIL DOI 10.5194/soil-6-53-2020 20 February 2020 Amazon soils hold as much carbon © as is contained in the vegetation. In this work we sampled soils across 8 different Amazonian countries to try to understand which soil properties control current Amazonian soil C concentrations. We confirm previous knowledge that highly developed soils hold C through clay content interactions but also show a previously unreported mechanism of soil C stabilization in the younger Amazonian soil types which hold C through aluminium organic matter interactions. Read more
A multi-model analysis of teleconnected crop yield variability in a range of cropping systems Earth System Dynamics DOI 10.5194/esd-11-113-2020 20 February 2020 In this study, we analyse the impacts of three major climate oscillations on global crop production. Our results show that maize, rice, soybean, and wheat yields are influenced by climate oscillations to a wide extent and in several important crop-producing regions. We observe larger impacts if crops are rainfed or fully fertilized, while irrigation tends to mitigate the impacts. These results can potentially help to increase the resilience of the global food system to climate-related shocks. Read more
Modal shift in North Atlantic seasonality during the last deglaciation Climate of the Past DOI 10.5194/cp-16-265-2020 18 February 2020 Here, mid-ocean seasonality is resolved through time, using differences in the oxygen isotope composition between individual shells of the commonly used (sub)polar planktonic foraminifera species in ocean-climate reconstruction, N. pachyderma and G. bulloides . Single-specimen isotope measurements during the deglacial period revealed a surprising bimodality, the cause of which was investigated. 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
A new look at the environmental conditions favorable to secondary ice production Atmospheric Chemistry and Physics DOI 10.5194/acp-20-1391-2020 13 February 2020 This study attempts identification of mechanisms of secondary ice production (SIP) based on the observation of small faceted ice crystals. It was found that in both mesoscale convective systems and frontal clouds, SIP was observed right above the melting layer and extended to the higher altitudes with colder temperatures. A principal conclusion of this work is that the freezing drop shattering mechanism is plausibly accounting for the measured ice concentrations in the observed condition. Read more
