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Open ocean dead zones in the tropical North Atlantic Ocean

This study is the first report of the formation of dead zones in the open ocean. A combination of multiple ocean observing system elements (mooring, floats, satellites, ships) allowed us to reconstruct the generation of the dead zones and to connect the formation to enhanced respiration within mesoscale ocean eddies. The dead zones present specific threats to the ecosystem, such as the interruption of the diurnal migration of zooplankters.

Continuous and discontinuous variation in ecosystem carbon stocks with elevation across a treeline ecotone

Here we investigate how ecosystem carbon stocks vary with elevation shifting from the closed forest to open alpine tundra, in the mountains of southern Norway. Above-ground carbon stocks decreased with elevation, with a clear breakpoint at the forest line, while the organic horizon soil carbon stocks increased linearly with elevation. Overall, ecosystem carbon stocks increased with elevation above the treeline and decreased with elevation below, demonstrating the importance of the treeline.

Use of Ra isotopes to deduce rapid transfer of sediment-derived inputs off Kerguelen

We investigated the origin and mechanisms of the natural iron fertilization that sustains a phytoplankton bloom downstream of the Kerguelen Islands. We used radium isotopes to trace the fate of shelf waters that may transport iron and other micronutrients towards offshore waters. We show that shelf waters are rapidly transferred offshore and may be transported across the polar front (PF). The PF may thus not be a strong physical barrier for chemical elements released by the shelf sediments.

Evaluation of coral reef carbonate production models at a global scale

Production of calcium carbonate by coral reefs is important in the global carbon cycle. Using a global framework we evaluate four models of reef calcification against observed values. The temperature-only model showed significant skill in reproducing coral calcification rates. The absence of any predictive power for whole reef systems highlights the importance of coral cover and the need for an ecosystem modelling approach accounting for population dynamics in terms of mortality and recruitment.

Drought in forest understory ecosystems – a novel rainfall reduction experiment

Biogeosciences
DOI 10.5194/bg-12-961-2015
17 February 2015

This paper introduces a novel rainfall reduction experiment to investigate drought effects on soil-forest-understory-ecosystems. An annual drought with a return period of 40 years was imposed, while other ecosystem variables (humidity, air & soil temperature) remained unaffected. The first year of drought showed considerable changes in soil moisture dynamics, which affected leaf stomatal conductance of understory species as well as evapotranspiration rates of the forest understory ecosystem.

Simulated anthropogenic CO₂ storage and acidification of the Mediterranean Sea

Biogeosciences
DOI 10.5194/bg-12-781-2015
10 February 2015

Different observational-based estimates of CO₂ uptake and resulting acidification of the Mediterranean Sea vary widely. A new study finds that even the smallest of those is an upper limit because the approach used assumes air-sea CO₂ equilibrium. Then along with a lower limit from new fine-scale numerical model simulations, the authors bracket Mediterranean Sea CO₂ uptake and acidification rates. They conclude that its rate of surface acidifcation is much like that for typical ocean waters.

Technical Note: Maximising accuracy and minimising cost of a potentiometrically regulated ocean acidification simulation system

This article describes a low-cost, easy set-up, ocean acidification simulation system that reliably mimics the effects of elevated atmospheric carbon dioxide on seawater chemistry. The accessible design of this system, along with our suggestions for the validation of pH control and characterisation of seawater chemistry, will enable researchers on a limited budget to generate high quality, repeatable data documenting the response of marine organisms to ocean acidification.

Processes determining the marine alkalinity and calcium carbonate saturation state distributions

We examine and discuss the portion of ocean alkalinity that varies in response to carbonate cycling and riverine alkalinity inputs using a new tracer, Alk*. We use this tracer to quantify the controls on marine carbonate saturation: At depth, we find carbonate cycling to be a minor control relative to organic matter cycling and pressure changes. In well-equilibrated surface water, we find carbonate cycling to be less important than temperature changes and freshwater cycling.

Estimated stocks of circumpolar permafrost carbon with quantified uncertainty ranges and identified data gaps

This study provides an updated estimate of organic carbon stored in the northern permafrost region. The study includes estimates for carbon in soils (0 to 3 m depth) and deeper sediments in river deltas and the Yedoma region. We find that field-data is still scarce from many regions. Total estimated carbon storage is ~1300 Pg with an uncertainty range of between 1100 to 1500 Pg. Around 800 Pg carbon is perennially frozen, equivalent to all carbon dioxide currently in the Earths atmosphere.

Long-term trends at the Boknis Eck time series station (Baltic Sea), 1957–2013: does climate change counteract the decline in eutrophication?

A time series of 9 oceanic parameters from the coastal time series station Boknis Eck (BE, South Western Baltic Sea) in the period of 1957-2013 is analysed with respect to seasonal cycles and longterm trends. Most striking was a paradoxical decreasing trend in oxygen with a simultaneous decline in eutrophication. Possible reasons for this paradox, e.g. processes related to warming temperatures such as increased decomposition of organic matter or altered ventilation, are discussed.

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