Georges Lemaître Centre for Earth and Climate Research, Earth and Life Institute, Université Catholique de Louvain, Chemin du Cyclotron 2, 1348 Louvain-la-Neuve, Belgium.
Nature. 2013 Feb 14;494(7436):222-5. doi: 10.1038/nature11790.
Glacial-interglacial cycles characterized by long cold periods interrupted by short periods of warmth are the dominant feature of Pleistocene climate, with the relative intensity and duration of past and future interglacials being of particular interest for civilization. The interglacials after 430,000 years ago were characterized by warmer climates and higher atmospheric concentrations of carbon dioxide than the interglacials before, but the cause of this climatic transition (the so-called mid-Brunhes event (MBE)) is unknown. Here I show, on the basis of model simulations, that in response to insolation changes only, feedbacks between sea ice, temperature, evaporation and salinity caused vigorous pre-MBE Antarctic bottom water formation and Southern Ocean ventilation. My results also show that strong westerlies increased the pre-MBE overturning in the Southern Ocean via an increased latitudinal insolation gradient created by changes in eccentricity during austral winter and by changes in obliquity during austral summer. The stronger bottom water formation led to a cooler deep ocean during the older interglacials. These insolation-induced differences in the deep-sea temperature and in the Southern Ocean ventilation between the more recent interglacials and the older ones were not expected, because there is no straightforward systematic difference in the astronomical parameters between the interglacials before and after 430,000 years ago. Rather than being a real 'event', the apparent MBE seems to have resulted from a series of individual interglacial responses--including notable exceptions to the general pattern--to various combinations of insolation conditions. Consequently, assuming no anthropogenic interference, future interglacials may have pre- or post-MBE characteristics without there being a systematic change in forcings. These findings are a first step towards understanding the magnitude change of the interglacial carbon dioxide concentration around 430,000 years ago.
冰期-间冰期旋回的特点是长冷期被短温暖期打断，这是更新世气候的主要特征，过去和未来间冰期的相对强度和持续时间对文明尤其重要。43 万年前以后的间冰期气候比以前的间冰期更温暖，大气中二氧化碳浓度也更高，但这种气候转变的原因（所谓的中布容事件（MBE））尚不清楚。在这里，我根据模型模拟表明，仅在太阳辐射变化的情况下，海冰、温度、蒸发和盐度之间的反馈就会导致强烈的间冰期前南极底层水形成和南大洋通风。我的结果还表明，强西风通过在南大洋中增加纬度太阳辐射梯度，以及在夏季和冬季通过变化偏心率来增加夏季的纬度太阳辐射梯度，从而增加了间冰期前的南大洋西风。更强的底层水形成导致较老的间冰期深海更冷。这些由于太阳辐射变化而导致的深海温度和南大洋通风的差异在较新的间冰期和较老的间冰期之间是出乎意料的，因为在 43 万年前之前和之后的间冰期之间，天文参数没有明显的系统差异。与其说是一个真正的“事件”，不如说明显的 MBE 似乎是由于一系列个别间冰期对各种太阳辐射条件组合的响应而导致的，包括对一般模式的显著例外。因此，在没有人为干扰的情况下，未来的间冰期可能具有间冰期前或间冰期后的特征，而没有太阳辐射强迫的系统变化。这些发现是理解 43 万年前左右间冰期二氧化碳浓度幅度变化的第一步。
