Role of Southern Ocean stratification in glacial atmospheric CO2 reduction evaluated by a three‐dimensional ocean general circulation model.
Role of Southern Ocean stratification in glacial atmospheric CO2 reduction evaluated by a three‐dimensional ocean general circulation model.
复制标题
通过三维海洋环流模型评估南大洋分层在冰川大气二氧化碳减排中的作用。
作者：
Kobayashi;H.;Abe‐Ouchi;A.;& Oka;A.
众所周知，冰期大气中的二氧化碳浓度比间冰期低得多。然而，以前的研究使用海洋环流模式（OGCM）未能再现这一点。末次冰盛期的古气候代用资料显示南大洋盐度高（>37.0实用盐度单位），水团停留时间长（>3000年），表明南大洋盐度分层增强，储存了更多的碳。以往的OGCM对盐度和水团年龄的再现性不够，可能影响大气CO2浓度的再现性。这项研究调查的作用，增加分层的南大洋在冰川CO2变化使用OGCM。我们发现，在东南极洲的深水形成是需要解释在南大西洋的高盐度。与先前的估计相比，更咸的南大洋深海导致大气CO2浓度增加。这部分是由于南极底层水的运输量增加，以及太平洋深处水团年龄的相关减少。另一方面，垂直混合作用的减弱有助于溶解无机碳垂直梯度的增大和大气CO2浓度的降低。然而，我们表明，它是无法解释所有的冰川CO2变化的贡献南大洋。我们的研究结果表明，详细了解南大洋分层增强对太平洋的影响，对于了解冰川-间冰期海洋碳循环变化背后的机制至关重要。
Atmospheric carbon dioxide (CO2) concentration during glacial periods is known to be considerably lower than during interglacial periods. However, previous studies using an ocean general circulation model (OGCM) fail to reproduce this. Paleoclimate proxy data of the Last Glacial Maximum indicate high salinity (>37.0 practical salinity unit) and long water mass residence time (>3000 years) in the Southern Ocean, suggesting that salinity stratification was enhanced and more carbon was stored there. Reproducibility of salinity and water mass age is considered insufficient in previous OGCMs, which might affect the reproducibility of atmospheric CO2concentration. This study investigated the role of increased stratification of the Southern Ocean in the glacial CO2variation using an OGCM. We found that deep water formation in East Antarctica is required to explain high salinity in South Atlantic. Saltier deep Southern Ocean resulted in increased atmospheric CO2concentration against previous estimates. This is partly due to increased volume transport of Antarctic Bottom Water and associated decrease in the water mass age of the deep Pacific Ocean. On the other hand, weakening of vertical mixing contributed to increase of the vertical gradient of dissolved inorganic carbon and decrease of atmospheric CO2concentration. However, we show that it is unable to explain all of the glacial CO2variations by the contribution of the Southern Ocean. Our findings indicate that detailed understanding of the impact of enhanced stratification in the Southern Ocean on the Pacific Ocean might be crucial to understanding the mechanisms behind the glacial‐interglacial ocean carbon cycle variations.