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Mercury distribution and transport in the North Atlantic Ocean along the Geotraces-GA01 transect

We first report the mercury distribution in the water section across the subpolar and subtropical gyres of the North Atlantic Ocean (GEOTRACES-GA01 transect). It allows the characterisation of various seawater types in terms of mercury content and the quantification of mercury transport associated with the Atlantic Meridional Overturning Circulation. It shows the nutrient-like biogeochemical behaviour of mercury in this ocean.

Interannual drivers of the seasonal cycle of CO₂ in the Southern Ocean

The Southern Ocean accounts for a large portion of the variability in oceanic CO₂ uptake. However, the drivers of these changes are not understood due to a lack of observations. In this study, we used an ensemble of gap-filling methods to estimate surface CO₂. We found that winter was a more important driver of longer-term variability driven by changes in wind stress. Summer variability of CO₂ was driven primarily by increases in primary production.

Ideas and perspectives: hydrothermally driven redistribution and sequestration of early Archaean biomass – the “hydrothermal pump hypothesis”

The origin of organic matter in the oldest rocks on Earth is commonly ambiguous (biotic vs. abiotic). This problem culminates in the case of hydrothermal chert veins that contain abundant organic matter. Here we demonstrate a microbial origin of kerogen embedded in a 3.5 Gyr old hydrothermal chert vein. We explain this finding with the large-scale redistribution of biomass by hydrothermal fluids, emphasizing the interplay between biological and abiological processes on the early Earth.

Satellite remote sensing reveals a positive impact of living oyster reefs on microalgal biofilm development

Biogeosciences
DOI 10.5194/bg-15-905-2018
13 February 2018

Using satellite technology and a life-size experiment, we analysed the impact of oyster reefs on mats of microscopic algae that develop within coastal mudflats. We showed that the relationship between microalgae and oysters is not limited to a one-way process where microalgae are a food source to oysters, but that oysters also promote microalgae mats development, presumably by providing nutrients to them. This might yield new insights into coastal ecosystem management.

Modelling ocean-colour-derived chlorophyll a

This study provides a demonstration that a biogeochemical/ecosystem/optical computer model which explicitly captures how light is radiated at the surface of the ocean and can be used as a laboratory to explore products (such as Chla) that are derived from satellite measurements of ocean colour. It explores uncertainties that arise from data input used to derive the algorithms for the products, and issues arising from the interplay between optically important constituents in the ocean.

Reviews and syntheses: to the bottom of carbon processing at the seafloor

Organic carbon processing at the seafloor is studied by geologists to better understand the sedimentary record, by biogeochemists to quantify burial and respiration, by organic geochemists to elucidate compositional changes, and by ecologists to follow carbon transfers within food webs. These disciplinary approaches have their strengths and weaknesses. This award talk provides a synthesis, highlights the role of animals in sediment carbon processing and presents some new concepts.

Continuous measurement of air–water gas exchange by underwater eddy covariance

We use the aquatic eddy covariance technique – developed first for benthic O₂flux measurements – right below the air–water interface (~ 4 cm) to determine gas exchange rates and coefficients. This use of the technique is particularly useful in studies of gas exchange and its dynamics and controls. The approach can thus help reduce the recognized problem of large uncertainties linked to gas exchange estimates in traditional aquatic ecosystem studies.

Reviews and syntheses: on the roles trees play in building and plumbing the critical zone

This review represents the outcome from an invigorating workshop discussion that involved tree physiologists, geomorphologists, ecologists, geochemists, and hydrologists and developed nine hypotheses that could be tested. We argue these hypotheses point to the essence of issues we must explore if we are to understand how the natural system of the earth surface evolves, and how humans will affect its evolution. This paper will create discussion and interest both before and after publication.

Global consequences of afforestation and bioenergy cultivation on ecosystem service indicators

Many climate change mitigation scenarios require negative emissions from land management. However, environmental side effects are often not considered. Here, we use projections of future land use from two land-use models as input to a vegetation model. We show that carbon removal via bioenergy production or forest maintenance and expansion affect a range of ecosystem functions. Largest impacts are found for crop production, nitrogen losses, and emissions of biogenic volatile organic compounds.

Vertical segregation among pathways mediating nitrogen loss (N2 and N2O production) across the oxygen gradient in a coastal upwelling ecosystem

This investigation characterizes the variability of pathways involved in N loss in the water column over the continental shelf off central Chile during the development of the upwelling season. Our results highlight the links between several pathways involved in N removal, and considering the extreme variation in oxygen observed could help to understand the ecological and biogeochemical implications due to global warming when intensification and/or expansion of the oceanic OMZs are projected.

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