Major research initiatives have been undertaken within the Arctic Ocean, highlighting this area's global importance and vulnerability to climate change. In 2015, the international GEOTRACES program addressed this importance by devoting intense research activities to the Arctic Ocean. Among various tracers, we used radium and carbonate system data to elucidate the functioning and vulnerability of the hydrographic regime of the Canadian Arctic Archipelago, bridging the Pacific and Atlantic oceans.

Soil aggregation is crucial for soil functioning. While the role of bacteria and fungi in soil aggregation is well established, how predators feeding on microbes modify soil aggregation has hardly been investigated. We showed for the first time that protists modify soil aggregation, presumably through changes in the production of bacterial mucilage, and that collembolans reduce soil aggregation, presumably by reducing the abundance of saprotrophic fungi.

Changes on plant traits associated with climate warming might alter vegetation–climate interactions. We investigated experimentally the effects of enhanced permafrost thaw and soil nutrients on a wide set of tundra shrub traits. We found a coordinated trait response to some treatments, which suggests a shift in shrub resource, growth and defence strategies. This shift might feed back into permafrost thaw – through mechanisms associated with water demand – and into carbon and energy fluxes.

The Functionally Assembled Terrestrial Ecosystem Simulator (FATES) is enhanced to mimic the ecological, biophysical, and biogeochemical processes following a logging event. The model can specify the timing and aerial extent of logging events; determine the survivorship of cohorts in the disturbed forest; and modifying the biomass, coarse woody debris, and litter pools. This study lays the foundation to simulate land use change and forest degradation in FATES as part of an Earth system model.

We present a simple model that describes, for the first time, the dynamic two-way interactions between soil organic matter and soil physical properties (porosity, pore size distribution, bulk density and layer thickness). The model was able to accurately reproduce the changes in soil organic carbon, soil bulk density and surface elevation observed during 63 years in a field trial, as well as soil water retention curves measured at the end of the experimental period.

Small lakes are important but variable sources of greenhouse gas emissions. We performed lab experiments to determine spatial patterns and drivers of CO₂ and CH₄ emission and sediment gas production within a lake. The observed high spatial variability of emissions and production could be explained by the degradability of the sediment organic matter. We did not see correlations between production and emissions and suggest on-site flux measurements as the most accurate way for determing emissions.

Inositol phosphates (IPs) are a major pool of organic P in soil. However, information on their diversity and abundance in soil is limited. We isolated IPs from soil and characterised them using solution nuclear magnetic resonance (NMR) spectroscopy. For the first time, we provide direct spectroscopic evidence for the existence of a multitude of lower-order IPs in soil extracts previously not detected with NMR. Our findings will help provide new insight into the cycling of IPs in ecosystems.

In this study, using extensive field observations and a numerical model, we analyzed the physical and biogeochemical structure of a coastal system following an extreme flood event. Our results suggest that a number of anomalous observations were driven by a co-occurrence of peculiar meteorological conditions and increased riverine discharges. Our results call for attention to the combined effects of hydrological and meteorological extremes that are anticipated to increase in frequency.

Nitrate pollution of freshwaters and methane emissions into the atmosphere are crucial factors in deteriorating the quality of drinking water and in contributing to global climate change. Here, we report vertical concentration and stable isotope profiles of CH₄, NO₃^-, NO₂^-, and NH₄⁺ in the water column of Fohnsee (southern Bavaria, Germany) that may indicate linkages between nitrate-dependent anaerobic methane oxidation and the anaerobic oxidation of ammonium.

High-latitude warming thaws permafrost, exposing minerals to weathering and fluvial transport. We studied the effects of abrupt thaw and associated weathering on carbon cycling in western Canada. Permafrost collapse affected < 1 % of the landscape yet enabled carbonate weathering associated with CO₂ degassing in headwaters and increased bicarbonate export across watershed scales. Weathering may become a driver of carbon cycling in ice- and mineral-rich permafrost terrain across the Arctic.

Agroforestry has been shown to alter the microclimate and to lead to higher carbon sequestration above ground and in the soil. In this study, we investigated the impact of agroforestry systems on system-scale evapotranspiration (ET) due to concerns about increased water losses to the atmosphere. Results showed small differences in annual sums of ET over agroforestry relative to monoculture systems, indicating that agroforestry in Germany can be a land use alternative to monoculture agriculture.

A growing body of studies challenges the paradigm that methane (CH₄) production occurs only under anaerobic conditions. Our field experiments revealed that oxic CH₄ production is closely related to phytoplankton metabolism and is indeed a common feature in five contrasting African lakes. Nevertheless, we found that methanotrophic activity in surface waters and CH₄ emissions to the atmosphere were predominantly fuelled by CH₄ generated in sediments and physically transported to the surface.