Beerling David J, Harfoot Michael, Lomax Barry, Pyle John A
Department of Animal and Plant Sciences, University of Sheffield, Sheffield, UK.
Philos Trans A Math Phys Eng Sci. 2007 Jul 15;365(1856):1843-66. doi: 10.1098/rsta.2007.2046.
The discovery of mutated palynomorphs in end-Permian rocks led to the hypothesis that the eruption of the Siberian Traps through older organic-rich sediments synthesized and released massive quantities of organohalogens, which caused widespread O3 depletion and allowed increased terrestrial incidence of harmful ultraviolet-B radiation (UV-B, 280-315nm; Visscher et al. 2004 Proc. Natl Acad. Sci. USA 101, 12952-12956). Here, we use an extended version of the Cambridge two-dimensional chemistry-transport model to evaluate quantitatively this possibility along with two other potential causes of O3 loss at this time: (i) direct effects of HCl release by the Siberian Traps and (ii) the indirect release of organohalogens from dispersed organic matter. According to our simulations, CH3Cl released from the heating of coals alone caused comparatively minor O3 depletion (5-20% maximum) because this mechanism fails to deliver sufficiently large amounts of Cl into the stratosphere. The unusual explosive nature of the Siberian Traps, combined with the direct release of large quantities of HCl, depleted the model O3 layer in the high northern latitudes by 33-55%, given a main eruptive phase of less than or equal to 200kyr. Nevertheless, O3 depletion was most extensive when HCl release from the Siberian Traps was combined with massive CH3Cl release synthesized from a large reservoir of dispersed organic matter in Siberian rocks. This suite of model experiments produced column O3 depletion of 70-85% and 55-80% in the high northern and southern latitudes, respectively, given eruption durations of 100-200kyr. On longer eruption time scales of 400-600kyr, corresponding O3 depletion was 30-40% and 20-30%, respectively. Calculated year-round increases in total near-surface biologically effective (BE) UV-B radiation following these reductions in O3 layer range from 30-60 (kJm(-2)d(-1))BE up to 50-100 (kJm(-2)d(-1))BE. These ranges of daily UV-B doses appear sufficient to exert mutagenic effects on plants, especially if sustained over tens of thousands of years, unlike either rising temperatures or SO2 concentrations.
在二叠纪末期岩石中发现变异的孢粉化石，这引发了一种假说，即西伯利亚暗色岩喷发穿过较古老的富含有机质沉积物，合成并释放了大量有机卤化物，导致了广泛的臭氧损耗，并使得有害的紫外线B辐射（UV - B，280 - 315纳米；维舍尔等人，《美国国家科学院院刊》，2004年，第101卷，第12952 - 12956页）在陆地上的入射量增加。在此，我们使用剑桥二维化学传输模型的扩展版本，来定量评估这种可能性以及当时另外两种导致臭氧损耗的潜在原因：（i）西伯利亚暗色岩释放氯化氢的直接影响，以及（ii）分散有机质中有机卤化物的间接释放。根据我们的模拟，仅煤加热释放的氯甲烷导致的臭氧损耗相对较小（最大为5 - 20%），因为这种机制无法将足够大量的氯输送到平流层。西伯利亚暗色岩不同寻常的爆发性质，再加上大量氯化氢的直接释放，在主要喷发阶段小于或等于200 kyr的情况下，使模型中高北纬地区的臭氧层损耗了33 - 55%。然而，当西伯利亚暗色岩释放的氯化氢与从西伯利亚岩石中大量分散有机质合成释放的大量氯甲烷相结合时，臭氧损耗最为严重。在喷发持续时间为100 - 200 kyr的情况下，这组模型实验分别在高北纬和南纬地区产生了70 - 85%和55 - 80%的柱臭氧损耗。在400 - 600 kyr的更长喷发时间尺度上，相应的臭氧损耗分别为30 - 40%和20 - 30%。随着臭氧层的这些减少，计算得出全年近地表生物有效（BE）紫外线B辐射的增加范围为30 - 60（kJm(-2)d(-1)）BE至50 - 100（kJm(-2)d(-1)）BE。这些每日紫外线B剂量范围似乎足以对植物产生诱变作用，特别是如果持续数万年的话，这与温度升高或二氧化硫浓度升高的情况不同。
