ALBERT

Description: Attaching objects to bivalve shells is an increasing requirement for conservation projects, mark-recapture studies and behavioural analysis. We investigated the suitability of eight different glues to attach a metallic object to a mussel shell and confirmed the utility of the best glue in a filtration behaviour experiment using Anodonta anatina . We used removal forces up to 1.35 kg cm –2 7 d after submerging in water and found an epoxy resin and a cyanoacrylate adhesive to perform best. Not all epoxy resins or cyanoacrylate adhesives performed equally. The best performing cyanoacrylate adhesive was used to glue magnets and rubber-coated Hall sensors to 26 mussels for a filtration-behaviour experiment. Nine months after attachment, all magnets and rubber-coated Hall sensors remained attached and withstood 1.35 kg cm –2 . The epoxy resin was not chosen, because it contained Bisphenol A and required a more complex application procedure. Mussel filtration behaviours were monitored for 96 h in the presence of algae. The results showed that the presence of algae stimulated the filtration rate of A. anatina in the first 24 h. Over the experimental period, the mussels' mean filtration duration was 20 ± 12 h, while the resting duration was 16 ± 7 h. We identified a pronounced circadian rhythm, despite the long filtration duration and variation in behaviour patterns. However, at any one time some mussels were observed to be filtering. The mussels were more likely to open their shells and become active at around 20:00. Thus the majority of mussels were active at midnight and a minority at noon. We interpret the strong response to increased algal concentration and the pronounced circadian rhythm as evidence that neither the glue nor the attached sensors disturbed the mussels even in a short-term experiment. Hence, we recommend the selected cyanoacrylate adhesive for use in tagging projects and behavioural studies of freshwater mussels.

Description: In this paper, we apply patching methods to give a positive answer to the inverse differential Galois problem over function fields over Laurent series fields of characteristic zero. More precisely, we show that any linear algebraic group (that is, affine group scheme of finite type) over such a Laurent series field does occur as the differential Galois group of a linear differential equation with coefficients in any such function field (of one or several variables).

Description: We present the first study of the influence of line mixing among CO2 lines on the remote sensing retrieval of atmospheric carbon dioxide. This is done in the bands near 1.6 and 2.1 μm which will be used by the Greenhouse Gases Observatory Satellite (GOSAT) instrument and eventual successors of the Orbiting Carbon Observatory (OCO). A purely theoretical analysis is first made, based on simulations of atmospheric spectra. It shows that line mixing cannot be neglected since disregarding this process induces significant errors in the calculated absorption coefficients, leading to systematic structures in the spectral fit residuals and airmass-dependent biases in the retrieved CO2 amounts. These theoretical predictions are then confirmed by using atmospheric solar-absorption spectra measured by a ground-based Fourier transform spectrometer. It is first shown that including line mixing in the forward model used for the inversion leads to a very significant reduction of the residuals in the 2.1 μm region. Secondly, the inclusion of line mixing reduces the dependence of the retrieved CO2 on the airmass and greatly improves the consistency between values obtained independently from spectra in the 1.6 and 2.1 μm bands. These results open promising prospects for various ground-based and space-borne experiments monitoring the carbon dioxide atmospheric amounts.

Description: An analysis of SSM/I satellite data reveals that the Whaler's Bay Polynya north of Svalbard was considerably larger in the last three winters from 2012 to 2014 compared to the previous 20 years. This increased polynya size leads to strong atmospheric convection during cold air outbreaks in a region north of Svalbard that typically was ice covered in the last decades. The change in ice cover can strongly influence local temperature conditions. Dropsonde measurements from March 2013 show that the unusual ice conditions generate extreme convective boundary layer heights that are larger than the regional values reported in previous studies.

Description: An analysis of Special Sensor Microwave/Imager (SSM/I) satellite data reveals that the Whaler's Bay polynya north of Svalbard was considerably larger in the three winters from 2012 to 2014 compared to the previous 20 years. This increased polynya size leads to strong atmospheric convection during cold air outbreaks in a region north of Svalbard that was typically ice-covered in the last decades. The change in ice cover can strongly influence local temperature conditions. Dropsonde measurements from March 2013 show that the unusual ice conditions generate extreme convective boundary layer heights that are larger than the regional values reported in previous studies.

Description: Past characterizations of the land–ocean continuum were constructed either from a continental perspective through an analysis of watershed river basin properties (COSCATs: COastal Segmentation and related CATchments) or from an oceanic perspective, through a regionalization of the proximal and distal continental margins (LMEs: large marine ecosystems). Here, we present a global-scale coastal segmentation, composed of three consistent levels, that includes the whole aquatic continuum with its riverine, estuarine and shelf sea components. Our work delineates comprehensive ensembles by harmonizing previous segmentations and typologies in order to retain the most important physical characteristics of both the land and shelf areas. The proposed multi-scale segmentation results in a distribution of global exorheic watersheds, estuaries and continental shelf seas among 45 major zones (MARCATS: MARgins and CATchments Segmentation) and 149 sub-units (COSCATs). Geographic and hydrologic parameters such as the surface area, volume and freshwater residence time are calculated for each coastal unit as well as different hypsometric profiles. Our analysis provides detailed insights into the distributions of coastal and continental shelf areas and how they connect with incoming riverine fluxes. The segmentation is also used to re-evaluate the global estuarine CO2 flux at the air–water interface combining global and regional average emission rates derived from local studies.

Description: The complex coastline of the Earth is over 400 000 km long and about 40% of the world's population lives within 100 km of the sea. Past characterizations of the global coastline were constructed either from a continental perspective through an analysis of watershed river basin properties (COSCAT: Coastal Segmentation and related CATchments) or from an oceanic perspective, through a regionalization of the proximal and distal continental margins (LME: Large Marine Ecosystems). Here, we present a global-scale coastal segmentation, composed of three consistent levels, that includes the whole aquatic continuum with its riverine, estuarine and shelf sea components. Our work delineates comprehensive ensembles which retain the most important physical characteristics of both the land and shelf areas. The proposed multi-scale segmentation results in a distribution of global exorheic watersheds, estuaries and continental shelf seas among 45 major zones (MARCATS: MARgins and CATchments Segmentation) and 149 sub-units (COSCATS). Geographic and hydrologic parameters such as the surface area, volume and fresh water residence time are calculated for each coastal unit as well as different hypsometric profiles. Our analysis provides detailed insights into the distributions of coastal and continental shelf areas and how they connect with incoming riverine fluxes. These results can be used for regional analyses and combined with various typologies for upscaling and biogeochemical budgets. In addition, the three levels segmentation can be used for application in Earth System analysis.

Description: Relict dune fields that are found as far south as 14° N in the modern-day African Sahel are testament to equatorward expansions of the Sahara desert during the Late Pleistocene. However, the discontinuous nature of dune records means that abrupt millennial-timescale climate events are not always resolved. High-resolution marine core studies have identified Heinrich stadials as the dustiest periods of the last glacial in West Africa although the spatial evolution of dust export on millennial timescales has so far not been investigated. We use the major-element composition of four high-resolution marine sediment cores to reconstruct the spatial extent of Saharan-dust versus river-sediment input to the continental margin from West Africa over the last 60 ka. This allows us to map the position of the sediment composition corresponding to the Sahara–Sahel boundary. Our records indicate that the Sahara–Sahel boundary reached its most southerly position (13° N) during Heinrich stadials and hence suggest that these were the periods when the sand dunes formed at 14° N on the continent. Heinrich stadials are associated with cold North Atlantic sea surface temperatures which appear to have triggered abrupt increases of aridity and wind strength in the Sahel. Our study illustrates the influence of the Atlantic meridional overturning circulation on the position of the Sahara–Sahel boundary and on global atmospheric dust loading.

Description: Relict dune fields that are found at 14° N in the modern-day African Sahel are testament to equatorward expansions of the Sahara desert during the late Pleistocene. However, difficulties of dating dune formation mean that abrupt millennial-scale climate events are not always resolved in these records. High-resolution marine core studies have identified Heinrich Stadials as the dustiest periods of the last glacial, although no studies have mapped the spatio-temporal evolution of dust export from West Africa. We use the major-element composition of four marine sediment cores to reconstruct the spatial extent of Saharan-dust versus river-sediment input to the continental margin from West Africa over the last 60 ka. This allows us to map the position of the sediment composition corresponding to the Sahara-Sahel boundary. Our records indicate that the Sahara-Sahel boundary reached its most southerly position (13° N) during Heinrich Stadials, suggesting that these were the periods when the sand dunes formed at 14° N on the continent, rather than at the Last Glacial Maximum. We find that SSB position was closely linked to North Atlantic sea surface temperatures, which during Heinrich Stadials triggered abrupt increases of aridity and wind strength in the Sahel, exposing new dust sources. This result illustrates the influence of the Atlantic meridional overturning circulation on the southerly extent of the Sahara desert and has implications for global atmospheric dust loading.

Description: This paper, developed under the framework of the RECCAP initiative, aims at providing improved estimates of the carbon and GHG (CO2, CH4 and N2O) balance of continental Africa. The various components and processes of the African carbon and GHG budget were considered, and new and available data derived by different methodologies (based on inventories, ecosystem fluxes, models, and atmospheric inversions) were integrated. The related uncertainties were quantified and current gaps and weakness in knowledge and in the monitoring systems were also considered in order to provide indications on the future requirements. The vast majority of the results seem to agree that Africa is probably a small sink of carbon on an annual scale, with an average value of −0.61 ± 0.58 Pg C yr−1. Nevertheless the emissions of CH4 and N2O may turn Africa into a source in terms of CO2 equivalents. At sub-regional level there is a significant spatial variability in both sources and sinks, mainly due to the biome's differences and the different anthropic impacts, with southern Africa as the main source and central Africa, with its evergreen tropical forests, as the main sink. Emissions from land use change in Africa are significant (around 0.32 ± 0.05 Pg C yr−1) and even higher than the fossil fuel ones; this is a unique feature among all the continents. In addition there can be significant carbon losses from land even without changes in the land use (forest), as results from the impact of selective logging. Fires also play a significant role, with 1.03 ± 0.22 Pg C yr−1 of carbon emissions, mainly (90%) originated by savanna and woodland burning. But whether fire carbon emissions are compensated by CO2 uptake during the growing season, or are a non-reversible loss of CO2, remains unclear. Most of these figures are subjected to a significant interannual variability, on the order of ± 0.5 Pg C yr−1 in standard deviation, accounting for around 25% of the year-to-year variation in the global carbon budget. These results, even if still highly uncertain, show the important role that Africa plays in the carbon cycle at global level, both in terms of absolute values and variability.