Nature2014-06-17 3:22 PM

源于主星金属性的三类太阳系外行星半径 Three regimes of extrasolar planet radius inferred from host star metallicities

论文摘要 

在第一批太阳系外行星发现后不久,曾有人提出,主星金属性(氢和氦以外的元素的丰度)在行星系统的形成中起一定作用。在这篇论文中,Buchhave等人报告了超过400个恒星(它们拥有600个可能是太阳系外行星的天体)的金属性和其他恒星参数,发现太阳系外行星能被归入由在统计上不同的金属性区域和行星半径确定的三个类别。这三个类别分别是与地球相似的太阳系外行星、具有石质核心和氢/氦外层的气体矮太阳系外行星、和冰质/气体巨型太阳系外行星。

Abstract 

The land and ocean act as a sink for fossil-fuel emissions, thereby slowing the rise of atmospheric carbon dioxide concentrations1. Although the uptake of carbon by oceanic and terrestrial processes has kept pace with accelerating carbon dioxide emissions until now, atmospheric carbon dioxide concentrations exhibit a large variability on interannual timescales2, considered to be driven primarily by terrestrial ecosystem processes dominated by tropical rainforests3. We use a terrestrial biogeochemical model, atmospheric carbon dioxide inversion and global carbon budget accounting methods to investigate the evolution of the terrestrial carbon sink over the past 30 years, with a focus on the underlying mechanisms responsible for the exceptionally large land carbon sink reported in 2011 (ref. 2). Here we show that our three terrestrial carbon sink estimates are in good agreement and support the finding of a 2011 record land carbon sink. Surprisingly, we find that the global carbon sink anomaly was driven by growth of semi-arid vegetation in the Southern Hemisphere, with almost 60 per cent of carbon uptake attributed to Australian ecosystems, where prevalent La Niña conditions caused up to six consecutive seasons of increased precipitation. In addition, since 1981, a six per cent expansion of vegetation cover over Australia was associated with a fourfold increase in the sensitivity of continental net carbon uptake to precipitation. Our findings suggest that the higher turnover rates of carbon pools in semi-arid biomes are an increasingly important driver of global carbon cycle inter-annual variability and that tropical rainforests may become less relevant drivers in the future. More research is needed to identify to what extent the carbon stocks accumulated during wet years are vulnerable to rapid decomposition or loss through fire in subsequent years.

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