美国布朗大学Novak, Joseph B.课题组报道了晚上新世暖期北太平洋深水形成的同位素证据。该项研究成果发表在2024年7月23日出版的《自然—地球科学》上。
据研究人员介绍，几项模拟和观测研究表明，北太平洋亚极地的深水形成可能是上新世温暖时期热盐环流的可能替代模式，上新世时期全球大气二氧化碳分压与现代大气相似(约400ppm)。
课题组研究人员通过测量从太平洋最北端Piacezian中期暖期(3.264-3.025Myr前)沉积物中收集的，底栖有孔虫Cibicidoides wuellerstorfi的δ13C来验证这一假设。数据显示，沿赤道向北极的样带，同位素负溶解无机碳逐渐增多，这与预期的上新世太平洋经向翻转环流信号相反。与较浅的ODP地点883相比，在较深的海洋钻探计划（ODP）地点887，C. wuellerstorfi的δ13C通常也更积极，这表明太平洋深处存在“自下而上”的通风。
然后，研究人员提供了ODP站点883的烯烃海面温度和出口生产力数据，这些数据表明，上新世晚期亚北极北太平洋碳酸盐岩沉积，至少在一定程度上，可能是由于较高的颗石藻出口生产，而不是像之前所认为的那样，由北太平洋深水形成。因此，研究人员认为北太平洋深水的形成不太可能发生在Piacezian暖期中期，尽管不能排除一个较浅的翻转单元。
附：英文原文
Title: Isotopic evidence against North Pacific Deep Water formation during late Pliocene warmth
Author: Novak, Joseph B., Caballero-Gill, Roco P., Rose, Rebecca M., Herbert, Timothy D., Dowsett, Harry J.
Issue&Volume: 2024-07-23
Abstract: Several modelling and observational studies suggest deep water formation in the subpolar North Pacific as a possible alternative mode of thermohaline circulation that occurred in the warm Pliocene, a time when global atmospheric partial pressure of carbon dioxide was like the modern atmosphere (~400 ppm). We test this hypothesis by measuring the δ13C of the benthic foraminifer Cibicidoides wuellerstorfi collected from northernmost Pacific mid-Piacenzian Warm Period (3.264–3.025 Myr ago) sediments. The data reveal progressively more isotopically negative dissolved inorganic carbon along a northward Equator-to-pole transect, the opposite of the expected Pliocene Pacific meridional overturning circulation signal. C.wuellerstorfi δ13C is also often more positive at the deeper Ocean Drilling Program (ODP) site 887 compared with the shallower ODP site 883, suggesting ‘bottom-up’ ventilation of the deep Pacific Ocean. We then present alkenone sea surface temperature and export-productivity data from ODP site 883, which suggest that late Pliocene subarctic North Pacific carbonate sedimentation was, at least in part, probably due to higher coccolithophore export production, rather than North Pacific Deep Water formation as previously argued. Therefore, we suggest it is unlikely that North Pacific Deep Water formation occurred in the mid-Piacenzian Warm Period, although a shallower overturning cell cannot be ruled out.
DOI: 10.1038/s41561-024-01500-7
Source: https://www.nature.com/articles/s41561-024-01500-7