• European Marine Science
• Other research productsclose
• 2013-2022close
• EU close
• US close
• European Marine Science close

Long chain alkyl diols form a group of lipids occurring widely in marine environments. Recent studies have suggested several palaeoclimatological applications for proxies based on their distributions, but also revealed uncertainties about their applicability. Here we evaluate the use of long chain 1,14-alkyl diol indices for reconstruction of temperature and upwelling conditions by comparing index values, obtained from a comprehensive set of marine surface sediments, with environmental factors like sea surface temperature (SST), salinity and nutrient concentrations. Previous cultivation efforts indicated a strong effect of temperature on the degree of saturation and the chain length distribution of long chain 1,14-alkyl diols in Proboscia spp., quantified in the diol saturation index (DSI) and diol chain length index (DCI), respectively. However, values of these indices in surface sediments show no relationship with annual mean SST of the overlying water. It remains unknown what determines the DSI, although our data suggests that it may be affected by diagenesis, while the relationship between temperature and DCI may be different for different Proboscia species. In addition, contributions of algae other than Proboscia diatoms may affect both indices, although our data provide no direct evidence for additional long chain 1,14-alkyl diol sources. Two other indices using the abundance of 1,14-diols vs. 1,13-diols and C30 1,15-diols have previously been applied as indicators for upwelling intensity at different locations. The geographical distribution of their values supports the use of 1,14 diols vs. 1,13 diols [C28 + C30 1,14-diols]/[(C28 + C30 1,13-diols) + (C28 + C30 1,14-diols)] as a general indicator for high nutrient or upwelling conditions.

Atmospheric _p_CO~2~ is a critical component of the global carbon system and is considered to be the major control of Earth's past, present and future climate. Accurate and precise reconstructions of its concentration through geological time are, therefore, crucial to our understanding of the Earth system. Ice core records document _p_CO~2~ for the past 800 kyrs, but at no point during this interval were CO~2~ levels higher than today. Interpretation of older _p_CO~2~ has been hampered by discrepancies during some time intervals between two of the main ocean-based proxy methods used to reconstruct _p_CO~2~: the carbon isotope fractionation that occurs during photosynthesis as recorded by haptophyte biomarkers (alkenones) and the boron isotope composition (δ^11^B) of foraminifer shells. Here we present alkenone and δ^11^B-based _p_CO~2~ reconstructions generated from the same samples from the Plio-Pleistocene at ODP Site 999 across a glacial-interglacial cycle. We find a muted response to _p_CO~2~ in the alkenone record compared to contemporaneous ice core and δ^11^B records, suggesting caution in the interpretation of alkenone-based records at low _p_CO~2~ levels. This is possibly caused by the physiology of CO~2~ uptake in the haptophytes. Our new understanding resolves some of the inconsistencies between the proxies and highlights that caution may be required when interpreting alkenone-based reconstructions of _p_CO~2~.

Watershed management has come to be recognized as a critical issue in the Nile Basin. Upstream land use can cause degradation and soil erosion, resulting in lower agricultural yields locally and causing sedimentation downstream. The increased sediment load causes economic problems by reducing water quality, and irrigation and hydropower potential, as well as increasing flooding. This note shows how, through Basin-wide cooperation, the Nile Basin Initiative (NBI) has led efforts to address these problems, developing successful projects to deliver real results to restore the Nile.

The data relate to a paper submitted to Quaternary Science Reviews. All the data support a study of the last 94 ka recorded in core MD03-2611 and an adjacent multicore MD03-MUC 3 taken on the fringe of one of the Murray Canyons offshore Kangaroo Island. Additional data pertain to core SS0206-GC15 taken offshore Victoria south of Warrnambool, but its record only spans the last 25ka. The records are at high resolution and cover a multitude of parameters. Radiocarbon dates for these cores are presented in the supplementary section of this paper.

The reconstruction of the stable carbon isotope evolution in atmospheric CO2 (d13Catm ), as archived in Antarctic ice cores, bears the potential to disentangle the contributions of the different carbon cycle fluxes causing past CO2 variations. Here we present a new record of d13Catm before, during and after the Marine Isotope Stage 5.5 (155 000 to 105 000 years BP). The record was derived with a well established sublimation method using ice from the EPICA Dome C (EDC) and the Talos Dome ice cores in East Antarctica. We find a 0.4 permil shift to heavier values between the mean d13Catm level in the Penultimate (~ 140 000 years BP) and Last Glacial Maximum (~ 22 000 years BP), which can be explained by either (i) changes in the isotopic composition or (ii) intensity of the carbon input fluxes to the combined ocean/atmosphere carbon reservoir or (iii) by long-term peat buildup. Our isotopic data suggest that the carbon cycle evolution along Termination II and the subsequent interglacial was controlled by essentially the same processes as during the last 24 000 years, but with different phasing and magnitudes. Furthermore, a 5000 years lag in the CO2 decline relative to EDC temperatures is confirmed during the glacial inception at the end of MIS 5.5 (120 000 years BP). Based on our isotopic data this lag can be explained by terrestrial carbon release and carbonate compensation.

Despite being an abundant group of significant ecological importance the phylogenetic relationships of the Octocorallia remain poorly understood and very much understudied. We used 1132 bp of two mitochondrial protein-coding genes, nad2 and mtMutS (previously referred to as msh1), to construct a phylogeny for 161 octocoral specimens from the Atlantic, including both Isididae and non-Isididae species. We found that four clades were supported using a concatenated alignment. Two of these (A and B) were in general agreement with the of Holaxonia–Alcyoniina and Anthomastus–Corallium clades identified by previous work. The third and fourth clades represent a split of the Calcaxonia–Pennatulacea clade resulting in a clade containing the Pennatulacea and a small number of Isididae specimens and a second clade containing the remaining Calcaxonia. When individual genes were considered nad2 largely agreed with previous work with MtMutS also producing a fourth clade corresponding to a split of Isididae species from the Calcaxonia–Pennatulacea clade. It is expected these difference are a consequence of the inclusion of Isisdae species that have undergone a gene inversion in the mtMutS gene causing their separation in the MtMutS only tree. The fourth clade in the concatenated tree is also suspected to be a result of this gene inversion, as there were very few Isidiae species included in previous work tree and thus this separation would not be clearly resolved. A~larger phylogeny including both Isididae and non Isididae species is required to further resolve these clades.

This basic Agriculture Public Expenditure Review (AgPER) documents and analyzes information on the volume and structure of Liberia's past public expenditure on the agriculture sector and draws conclusions that can provide an orientation for future policies in view of the effectiveness of spending. The AgPER's focus is on the sectors of agriculture, including crops, fisheries, and forestry, in line with the New Partnership for African Development's (NEPAD) definition of the sectors of focus. This is in accordance with the Maputo Declaration and its target that governments devote ten percent of public expenditure for agricultural development with an aim towards realizing food security and poverty reduction.

Recent observations and modelling studies suggest that biogeochemical changes can mask atmospheric CO2-induced pH decreases. Data collected by the Dutch monitoring authorities in different coastal systems (North Sea, Wadden Sea, Ems-Dollard, Eastern Scheldt and Scheldt estuary) since 1975 provide an excellent opportunity to test whether this is the case in the Dutch coastal zone. The time-series were analysed using Multi-Resolution Analysis (MRA) which resulted in the identification of system-dependent patterns on both seasonal and intra-annual time scales. The observed rates of pH change greatly exceed those expected from enhanced CO2 uptake, thus suggesting that other biogeochemical processes, possibly related to changes in nutrient loading, can play a dominant role in ocean acidification.

Eurodoc Newsletter Issue #21

Coastal systems can act as filters for anthropogenic nutrient input into marine environments. Here, we assess the processes controlling the removal of phosphorus (P) and nitrogen (N) for four sites in the eutrophic Stockholm Archipelago. Bottom water concentrations of oxygen and P are inversely correlated. This is attributed to the seasonal release of P from iron (Fe)-oxide-bound P in surface sediments and from degrading organic matter. The abundant presence of sulfide in the pore water, linked to prior deposition of organic-rich sediments in a low oxygen setting (legacy of hypoxia), hinders the formation of a larger Fe-oxide-bound P pool in winter. Burial rates of P are high at all sites (0.03–0.3 mol m−2 y−1), a combined result of high sedimentation rates (0.5 to 3.5 cm yr−1) and high sedimentary P at depth (~ 30 to 50 μmol g−1). Organic P accounts for 30–50 % of reactive P burial. Apart from one site in the inner archipelago, where a vivianite-type Fe(II)-P mineral is likely present at depth, there is little evidence for sink-switching of organic or Fe-oxide bound P to authigenic P minerals. Denitrification is the major benthic nitrate-reducing process at all sites (0.09 to 1.7 mmol m−2 d−1), efficiently removing N as N2. Denitrification rates decrease seaward following the decline in bottom water nitrate and sediment organic carbon. Our results explain how sediments in this eutrophic coastal system can efficiently remove land-derived P and N, regardless of whether the bottom waters are oxic or frequently hypoxic. Hence, management strategies involving artificial reoxygenation are not expected to be successful in removing P and N, emphasizing a need for a focus on nutrient load reductions.