We used stable nitrogen isotopes from red pine trees to determine the history of nitrogen (N) cycling within the Deming Lake watershed at Itasca State Park. With nearly 250 years of data, results suggest a major decline in N availability in red pine beginning in the early 20th century based on detection of significant breakpoints. We believe this synchronous decline is the result of the fire suppression in the state park, though alternative biological and physical mechanisms cannot be ruled out.

The transfer of particulate organic carbon (POC) into the deep ocean is an important atmospheric carbon dioxide sink. Observations from the Southern Ocean Great Calcite Belt region show that the relationship between POC and biogenic mineral fluxes varies with depth, between the surface and 1000m below. The results suggest that the transfer of POC into the deep ocean is more closely related to phytoplankton community structure than to mineral composition alone.

The global atmospheric cycle of Fe is simulated accounting for natural and combustion sources, proton- and organic ligand-promoted Fe dissolution from dust aerosol and changes in anthropogenic emissions, and thus in atmospheric acidity. Simulations show that Fe dissolution may have increased in the last 150 years and is expected to decrease due to air pollution regulations. Reductions in dissolved-Fe deposition can further limit the primary productivity over high-nutrient-low-chlorophyll water.

We performed high-frequency samplings of zooplankton community and gut pigment of copepods in the Chukchi Sea. Zooplankton showed no changes with a strong wind event and dominant copepods prepared for diapause. Yet, feeding activity of the copepods increased as a result of temporal phytoplankton bloom, enhanced by the wind event. Because of the long generation length of copepods, a smaller effect was detected for their abundance, population, lipid accumulation and gonad maturation.

Tundra fires may have increased as a result of anthropogenic climate change. To evaluate this hypothesis in the context of natural variability, we reconstructed fire history of the late Quaternary in the Alaskan tundra. Fire-return intervals are spatially variable, ranging from 1648 to 6045 years at our sites. The rarity of historical fires implies that increased fire frequency may greatly alter the structure and function of tundra ecosystems.

Phytoplankton community structure at a high spatial resolution (<3km) was studied in the North Sea during a cruise in May 2011. A first comparison with PHYSAT reflectance anomalies enables the extrapolation of the community structure rather than a dominant type at the North Sea scale and was interpreted with its hydrological characteristics. This will seriously improve our understanding of the influence of community structure on biogeochemical processes at the daily and basin scales.

We investigate the utility of satellite measurements of solar-induced chlorophyll fluorescence (SIF) in constraining gross primary productivity (GPP). We simulate SIF with the biosphere model BETHY coupled with the fluorescence model SCOPE. The model simulates well the patterns of SIF. SIF is sensitive to leaf chlorophyll and incoming radiation but not to the key physiological parameter Vcmax controlling GPP. Thus, further model development is necessary before SIF can be used to constrain GPP.

Nitrate and dissolved phosphate concentration time series (1980--2011) from 50 sampling stations across a large Mediterranean river basin were analyzed using dynamic factor analysis and complementary methods in order to disentangle the role of hydrology, land-use practices, and global climatic phenomena on nitrate and phosphate patterns, with the aim of understanding how the different aspects of global change affected nutrient dynamics in the basin.

Spatial clustering of anthropogenic nitrogen deposition reveals that European C:N ratio varies more across soils of natural ecosystems with low pollution. It turns out surprisingly that such soils are the most affected by nitrogen accumulation and therefore most responsive to short-term N supply. While an inverse correlation between atmospheric nitrogen and soil C:N seems intuitive, we provide novel insights into the real magnitude and spatial distribution of this relationship since 1880.

NDVI and PRI sensors (SRS, Decagon Inc.) exhibited complementary responses during spring photosynthetic activation in evergreen and deciduous stands. In evergreens, PRI was most strongly influenced by changing chlorophyll:carotenoid pool sizes over the several weeks of the study, while it was most affected by xanthophyll cycle pigment activity at the diurnal timescale. These automated PRI and NDVI sensors offer new ways to explore environmental and physiological constraints on photosynthesis.

Recent studies have suggested the potential importance of abiotic decomposition (photodegradation) in arid ecosystems. This study focuses on the measurement and understanding of abiotic fluxes. Photodegradation fluxes have not been observed. Thermal degradation fluxes were observed in the field (for CO) and in the laboratory (for CO2 and CO). Previous studies have potentially overestimated the role of photodegradation or misinterpreted thermal degradation fluxes as photodegradation fluxes.

The effects of two marine volcanic vents, utilized as proxy of ocean acidification and global changes, are studied at molecular level in P. oceanica (seagrass). Stress-related genes (antioxidants and HSP) were differently activated in the two sites, at comparable CO2 levels. Metal detoxification genes were mostly down-regulated. This suggests that plants face different types of stressors and that factors other than CO2 and acidification can cause stress to marine organisms near volcanic vents.