Recent  

Permafrost thaw releases methane. This greenhouse gas can be emitted into the atmosphere or transported by Arctic rivers. Methane measurements are lacking in large Arctic River regions. In the Kolyma River (Northeast Siberia), we measured dissolved methane to map its distribution with great spatial detail. The river’s edge and river junctions had the highest methane concentrations compared to other river areas. Microbial communities showed that the river’s methane comes from the adjacent land.

Coral reefs face increasing pressures from environmental change at present. The coral reef physical framework is formed through the production of calcium carbonate by corals, crustose coralline algae (CCA), and other calcifying algae. The Kimberley bioregion, located in the northern part of Western Australia, has largely escaped land-based anthropogenic impacts and this study provides important data on reef building processes we are lacking from an undisturbed set of marine habitats.

Greenhouse gases released by human activity cause a global rise in mean temperatures. While scientists can predict how much of these gases accumulate in the atmosphere based on human derived sources but also oceanic sinks, it is rather difficult to predict the major influence of coastal ecosystems. We provide a detailed study on the occurrence, composition and controls of substances, which suppress gas exchange. We thus help to determine what controls coastal greenhouse gas fluxes.

With this study, we want to highlight the importance of studying both land and ocean together, and water and sediment together, as these systems function as a continuum and determine how organic carbon derived from permafrost is broken down, and its effect on global warming. While on one hand it appears that organic carbon is removed from sediments along the pathway of transport from river to ocean, it also appears to remain relatively ‘fresh’, despite this removal and its very old age.

We used earth observation and datasets of environmental drivers (floods, river channel migration, precipitation and forest fires) to study the space-time dynamics of natural and cultural subtropical grasslands at the foot of the Himalayas. The changes in surface area and heterogeneity of grassland patches, which serve as habitat for the prey of the Royal Bengal Tiger, are attributed to a decrease of anthropogenic disturbances and a relocation of the dominant river channel of the Karnali River.

The primary nitrite maximum is a ubiquitous upper ocean feature where nitrite accumulates, but we still do not understand its formation and the co-occurring microbial processes involved. Using correlative methods and rates measurements, we found strong spatial patterns between environmental conditions and depth of the nitrite maxima, but not the concentration of the maxima. Nitrification was a major producer of nitrite, with occasional high nitrite production from phytoplankton near the coast.

Recent forest decline requires understanding forest response to multi-seasonal meteorology. We investigate meteorology over 3 years preceding events of low forest greenness in Europe in 2000–2020 in a highly systematic and quantitative way. We identify time periods when meteorological variables and weather systems are significantly anomalous or persistent. Our interdisciplinary results present progress in understanding how changing meteorology will impact forest performance in this century.

Boreal forests, historically a global sink for atmospheric CO₂, store carbon in vast soil reservoirs. To predict how such stores will respond to climate warming we need to understand climate-ecosystem feedbacks. We find boreal forest soil carbon stores are maintained through enhanced nitrogen cycling with climate warming providing direct evidence for a key feedback. Further application of the approach demonstrated here will improve our understanding of the limits of climate-ecosystem feedbacks.

We present a first species specific evaluation of marine core-top dinoflagellate cyst carbon isotope fractionation (ε_p) in order to establish natural pCO₂ dependency and explore its geological deep-time paleo-pCO₂ proxy potential. We build a first version of the paleo-CO₂ proxy based on Operculodinium centrocarpum. ε_p differs between species and is controlled by pCO₂ and nutrients. Our results illustrate the value of δ¹³C analyses on single micrometer-scale sedimentary organic carbon particles.

Better estimates of atmospheric nitrogen (N) deposition are needed to accurately assess ecosystem risk and impacts from deposition of nutrients and acidity. Using measurements and modeling, we estimate total N deposition is 6.6 kg N ha^-1 yr^-1 at a forest site in the southern Appalachian Mountains, a region sensitive to atmospheric deposition. Reductions in deposition of reduced forms of N (ammonia and ammonium) will be needed to meet the lowest estimates of N critical loads for the region.

Why do plants distributional range size vary enormously? This study provides evidence that seed mass, intraspecific seed mass variation, seed dispersal mode and phylogeny contribute to explaining species distribution variation on the geographic scale. Our study clearly shows the importance of including seed life-history traits in modeling and predicting the impact of climate change on species distribution of seed plants.

In the frame of my PhD research, I studied the pollution of West Saronikos Gulf from heavy metals throughout the study of marine sediment cores. It is a deep gulf (max depth 440 m) near Athens affected by industries and volcanic activity. Eight cores were received from various stations and depths and analyzed for their content in heavy metals and their geochemical characteristics. The results were evaluated by using statistical methods, environmental indicators and comparison with old data.

Estimates of the ocean sink of anthropogenic carbon vary across various approaches. We show that the global ocean carbon sink can be estimated by three parameters, two of which approximate the ocean ventilation in the Southern Ocean and the North Atlantic, and one approximates the chemical capacity of the ocean to take up carbon. With observations of these parameters, we estimate that the global ocean carbon sink is 10 % larger than previously assumed and cut uncertainties in half.

Compound events threaten marine ecosystems. Here, we investigate the potentially harmful combination of marine heatwaves with low phytoplankton productivity. Using satellite-based observations, we show that these compound events are frequent in the low latitudes. We then investigate the drivers of these compound events using Earth System models. The models share similar drivers in the low latitudes, but disagree in the high latitudes due to divergent factors limiting phytoplankton production.

In order to quantify C transport and emission and main environmental factors controlling the C cycle on Siberian rivers, we investigated the largest tributary of the Ob River, the Ket River basin, via measuring spatial and seasonal variations in CO₂ and CH₄ concentrations and emissions, together with hydrochemical analyses. The obtained results are useful for large scale modelling of C emission and export fluxes from permafrost-free boreal rivers of under-represented region of the world.

We evaluated the performance of a land surface model (ELMv1-CNP) that includes both nitrogen (N) and phosphorus (P) limitation on carbon cycle processes. We show that ELMv1-CNP produces realistic estimates of present-day carbon pools and fluxes. We show that global C sources and sinks are significantly affected by P limitation. Our study suggests that introduction of P limitation in land surface models likely have substantial consequences for projections of future carbon uptake.

For the first time, our study highlights the synergistic and additive effects a 9-month warming and acidification combined stress on the early life stages of a Mediterranean azooxanthellate coral, Astroides calycularis. Our results predict a decrease of dispersion, settlement, post-settlement growth and survival under future global change and that larvae and recruits of A. calycularis are stages of interest for this Mediterranean coral resistance, resilience and conservation.

Different land types emit a different quantity of methane, with wetlands being one of the largest sources of methane emissions, contributing to climate change. This study finds variations in land types using the methane total column data from Sentinel 5-precursor satellite with a machine learning algorithm. The variations in land types were identified with high confidence, demonstrating that the methane emissions from the wetland and other land types substantially affect the total column.

Spruce and larch trees are effective archiving species for historical atmospheric mercury using growth rings of bole wood. Mercury stable isotope analysis proved an effective tool in helping to characterise industrial mercury signals and assess mercury uptake pathways (leaf uptake for both wood and bark) and mercury cycling within the trees.

We carry out a two-year continuous observation in the northern Jiangsu Coast. Our results show that: The distribution of crab burrows was unimodal across the shore in cold seasons, and bimodal in warm seasons. The density of crab burrows was lower in sites with stronger hydrodynamics and lower suspended sediment concentration. The governing factors of crab burrow distribution in cold seasons were organic matter content and soil salinity, while in warm seasons water content also played a role.

Forests play important role in global carbon cycle. Hemiboreal forests are located in a transitional zone between boreal and temperate zones and are characterised by higher variability in dominating tree species. We analysed carbon exchange of a hemiboreal forest using two measurement systems located on the same tower. The lower system could detect the influence of clearcuts and tower guywire tunnels, while the higher system allowed to assess the carbon balance of the full landscape.

Increased spruce bark beetle outbreaks was seen recently in Sweden. When Norway spruce trees are attacked, they increase their production of volatile compounds, attempting to kill the beetles. We provide new insights to how the Norway spruce act when infested, and found the emitted volatiles to increase up to 700 times and saw a change in compound blend. We estimate that the 2020 bark beetle outbreak in Sweden could have increased the total monoterpene emissions from the forest by more than 10 %.

Given the sparsity of observational constraints on micronutrients such as zinc (Zn), we assess the sensitivities of a framework for objective parameter optimisation in an oceanic Zn cycling model. Our ensemble of optimisations towards synthetic data with varying kinds of uncertainty shows that deficiencies related to model complexity and the choice of misfit function generally have a greater impact on the retrieval of model Zn-uptake behaviour than does the limitation of data coverage.

The intensity of the oceanic trap of CO₂ released by anthropogenic activities depends on the alkalinity brought by the continental weathering. Between ocean and continent, coastal water and estuaries can limit or favour the alkalinity transfer. This study investigate new interactions between dissolved metals and alkalinity in the oxygen depleted zone of estuaries.