A short-term sink for atmospheric CO2 in subtropical mode water of the North Atlantic Ocean

Large-scale features of ocean circulation, such as deep water formation in the northern North Atlantic Ocean, are known to regulate the long-term physical uptake of CO2 from the atmosphere by moving CO2-laden surface waters into the deep ocean. But the importance of CO2 uptake into water masses that ventilate shallower ocean depths, such as subtropical mode waters of the subtropical gyres, are poorly quantified. Here we report that, between 1988 and 2001, dissolved CO2 concentrations in subtropical mode waters of the North Atlantic have increased at a rate twice that expected from these waters keeping in equilibrium with increasing atmospheric CO2. This accounts for an extra 0.4-2.8 Pg C (1 Pg = 10(15) g) over this period (that is, about 0.03-0.24 Pg C yr(-1)), equivalent to 3-10% of the current net annual ocean uptake of CO2 (ref. 3). We suggest that the lack of strong winter mixing events, to greater than 300 m in depth, in recent decades is responsible for this accumulation, which would otherwise disturb the mode water layer and liberate accumulated CO2 back to the atmosphere. However, future climate variability (which influences subtropical mode water formation) and changes in the North Atlantic Oscillation (leading to a return of deep winter mixing events) may reduce CO2 accumulation in subtropical mode waters. We therefore conclude that, although CO2 uptake by subtropical mode waters in the North Atlantic--and possibly elsewhere--does not always represent a long-term CO2 sink, the phenomenon is likely to contribute substantially to interannual variability in oceanic CO2 uptake.     

钢包预热过程热应力影响因子及预报模型

运用有限元软件ABAQUS建立钢包包衬的线性弹性模型,模拟钢包预热过程包衬的热应力,分析包衬厚度及其材料物理性能对包衬内最大热应力和钢壳表面温度的影响;采用偏最小二乘法建立包衬厚度及材料物理性能与包衬内最大热应力、钢壳表面温度间的预报模型。结果表明,工作衬材料物理性能对包衬最大应力和钢壳表面温度起主要影响作用;较之于无绝热衬,有绝热衬钢包永久衬材料物理性能对钢包热应力和钢壳表面温度的影响作用显著降低。     

Axoplasmic organelles: Quantitative differences between ventral and dorsal root fibres of the rat

Zusammenfassung Motorische und sensible Nervenfasern lassen sich im Bereich der Rückenmarkswurzeln (Ratte, L₅) aufgrund der Mengenverteilung der Axonorganellen unterscheiden. Bei vergleichbarem Faserkaliber haben Vorderwurzelfasern signifikant mehr Neurotubuli und axoplasmatisches Retikulum als Hinterwurzelfasern.

---

---

This investigation was supported by the Fonds zur Förderung der wissenschaftlichen Forschung in Österreich.

---

The authors gratefully acknowledge the excellent technical assistance of MissL. Henning and MissB. Fritsche.     

The Phaeodactylum genome reveals the evolutionary history of diatom genomes

Diatoms are photosynthetic secondary endosymbionts found throughout marine and freshwater environments, and are believed to be responsible for around one-fifth of the primary productivity on Earth. The genome sequence of the marine centric diatom Thalassiosira pseudonana was recently reported, revealing a wealth of information about diatom biology. Here we report the complete genome sequence of the pennate diatom Phaeodactylum tricornutum and compare it with that of T. pseudonana to clarify evolutionary origins, functional significance and ubiquity of these features throughout diatoms. In spite of the fact that the pennate and centric lineages have only been diverging for 90 million years, their genome structures are dramatically different and a substantial fraction of genes ( approximately 40%) are not shared by these representatives of the two lineages. Analysis of molecular divergence compared with yeasts and metazoans reveals rapid rates of gene diversification in diatoms. Contributing factors include selective gene family expansions, differential losses and gains of genes and introns, and differential mobilization of transposable elements. Most significantly, we document the presence of hundreds of genes from bacteria. More than 300 of these gene transfers are found in both diatoms, attesting to their ancient origins, and many are likely to provide novel possibilities for metabolite management and for perception of environmental signals. These findings go a long way towards explaining the incredible diversity and success of the diatoms in contemporary oceans.     

Small changes in expression affect predisposition to tumorigenesis.

We have used quantitative measures of gene expression to show that constitutional 50% decreases in expression of one adenomatous polyposis coli tumor suppressor gene (APC) allele can lead to the development of familial adenomatous polyposis.     

Comparison of the genomes of two Xanthomonas pathogens with differing host specificities

The genus Xanthomonas is a diverse and economically important group of bacterial phytopathogens, belonging to the gamma-subdivision of the Proteobacteria. Xanthomonas axonopodis pv. citri (Xac) causes citrus canker, which affects most commercial citrus cultivars, resulting in significant losses worldwide. Symptoms include canker lesions, leading to abscission of fruit and leaves and general tree decline. Xanthomonas campestris pv. campestris (Xcc) causes black rot, which affects crucifers such as Brassica and Arabidopsis. Symptoms include marginal leaf chlorosis and darkening of vascular tissue, accompanied by extensive wilting and necrosis. Xanthomonas campestris pv. campestris is grown commercially to produce the exopolysaccharide xanthan gum, which is used as a viscosifying and stabilizing agent in many industries. Here we report and compare the complete genome sequences of Xac and Xcc. Their distinct disease phenotypes and host ranges belie a high degree of similarity at the genomic level. More than 80% of genes are shared, and gene order is conserved along most of their respective chromosomes. We identified several groups of strain-specific genes, and on the basis of these groups we propose mechanisms that may explain the differing host specificities and pathogenic processes.