Steady decline in mean annual air temperatures in the first 30 k.y. after the Cretaceous-Paleogene boundary
Steady decline in mean annual air temperatures in the first 30 k.y. after the Cretaceous-Paleogene boundary
复制标题
前30年年平均气温稳步下降
作者：
O'Connor L
白垩纪-古近纪（K-Pg）界线标志着白垩纪的五个主要地块之一。在不同的时间尺度上，气候系统对火流星撞击和大规模火山活动的反应方式备受争议。我们利用加拿大萨斯喀彻温省（古纬度~55°N）两个地点化石泥炭中分支四醚脂质（brGDGT）的分布，生成了过去~4 k. y的年平均气温（MAAT）的高分辨率（千年）记录。白垩纪和前30 k.y.古近纪我们的研究表明，MAAT的范围从16到29 °C，最高值出现在古近纪的前一千年。早第三纪平均温度约为25 ° C，维持或加强了最近一次暖化，随后在随后的约30 k.y.内普遍冷却至约20 °C。没有突然的边界后冷却（例如，“撞击冬天”）或突然变暖在我们的数据中是明显的，这意味着如果发生了这样的现象，它们的持续时间相对较短（即，次千年尺度）。此外，没有明显的长期冲击火山驱动的变暖。观测到的温度变化范围远大于相同时间间隔内海洋代用记录的温度变化范围。因此，我们的研究结果更恰当地界定了这一关键时期陆地温度变化的幅度和持续时间这是非鸟类恐龙灭绝和哺乳动物兴起的主要背景。
The Cretaceous-Paleogene (K-Pg) boundary marks one of the five major mass extinctions of the Phanerozoic. The ways in which the climate system responded to a bolide impact and extensive volcanism at this time over different time scales are highly debated. We used the distribution of branched tetraether lipids (brGDGT) from fossil peats at two sites in Saskatchewan, Canada (paleolatitude ~55°N), to generate a high-resolution (millennial) record of mean annual air temperature (MAAT) spanning the last ~4 k.y. of the Cretaceous and the first ~30 k.y. of the Paleogene. Our study shows that MAATs ranged from 16 to 29 °C, with the highest value in the first millennia of the Paleogene. The earliest Paleogene averaged ~25 °C—maintaining or enhancing warmth from the latest Cretaceous—followed by a general cooling to ~20 °C over the following ~30 k.y. No abrupt postboundary cooling (e.g., an “impact winter”) or abrupt warming is evident in our data, implying that if such phenomena occurred, their duration was relatively short-lived (i.e., sub-millennial-scale). Further, no long-term impactor volcanism-driven warming is evident. The range of temperature change observed is considerably greater than that derived from marine proxy records over the same time interval. Our findings therefore more properly place bounds on the magnitude and duration of temperature change on land during this critical interval—the main setting for the demise of nonavian dinosaurs and the rise of mammals.