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Low-latitude northern hemisphere oceanographic and climatic responses to early shoaling of the Central American Seaway

机译：低纬度北半球对早期中美洲海道浅滩的海洋学和气候响应

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The opening and closing of ocean gateways has played a major role in shaping global climate by altering oceanic and at-mospheric circulation. This study uses planktonic foraminifer assemblage-based sea surface temperature (SST) estimates (Modem Ana-log Technique) to examine the eastern tropical Pacific (ETP) and subtropical Northwest Atlantic (NWA) during the early stages of shoaling of the Central American Seaway (CAS). In the subtropical NWA (DSDP 103 and ODP 1006), the 5.2 to 5.1 Ma interval is char-acterized by an increase in SST and sea surface salinity, indicating a strengthening of the Florida Current (FC) and Gulf Stream (GS). Sea surface temperature in the ETP Warm Pool (DSDP Site 84) remained relatively stable between 6.9 and 5.1 Ma, during which El Nino-like conditions persisted. A slight cooling is observed after this interval (with synchronous warming in the NWA), followed by the onset of major cooling at ～3.2 Ma, both of which are preceded by a shall owing of the thermocline. Stepwise cooling is attributed to enhanced At-lantic meridional overturn cicrulation (AMOC), which caused a shoaling of the main tropical thermocline, thereby strengthening the Walker Circulation and weakening the Pacific North Equatorial Counter Current. Antithetical changes in surface current strength in the NWA and ETP suggest a southward migration of the Intertropical Convergence Zone ～4.3 Ma. During the mid-Pliocene, SST in the Pan-ama Basin was ～0.8℃ cooler than today, while the subtropical NWA was only ～1.1℃ warmer. This corroborates evidence for reduced meridional SST gradients during the mid-Pliocene as well as the hypothesis that more vigorous ocean circulation—particularly in the NWA—was critical during this period. The timing of SST changes in the ETP and NWA (～5.1 Ma) suggest that the termination of permanent El Nino and enhanced AMOC did not contribute significantly to the onset of major Northern Hemisphere glaciation (NHG), as both of these events occur well before the beginning of the glacial cycles. However, these processes may have contributed to the development of the small ice sheets of the late Miocene and early Pliocene, but were most likely only preconditioning factors for the onset of major NHG. However, changes in SST and relative thermocline position suggest that high-latitude processes and global cooling may have influenced thermal structure in the ETP. The SST estimates provided indicate that even in its early stages, the shoaling of the CAS had significant implications for low-latitude ocean circulation and thermal structure, as well as for some of the most significant global climate events of the late Neogene.
机译：通过改变海洋和大气环流，打开和关闭海洋通道在塑造全球气候中发挥了重要作用。这项研究使用基于浮游有孔虫组合的海面温度（SST）估算值（调制解调器模拟技术）来研究中美洲海道（SHO）的浅滩化早期的东部热带太平洋（ETP）和亚热带西北大西洋（NWA）（ CAS）。在亚热带NWA（DSDP 103和ODP 1006）中，SST和海面盐度的增加表征了5.2Ma到5.1Ma的间隔，表明佛罗里达洋流（FC）和墨西哥湾流（GS）的增强。 ETP暖池（DSDP站点84）中的海面温度在6.9至5.1 Ma之间保持相对稳定，在此期间类似厄尔尼诺现象的状况持续存在。在此时间间隔后观察到略微冷却（在NWA中同步升温），随后在〜3.2 Ma处开始大冷却，这两者之前都应有温跃层。逐步降温归因于增强的大西洋经向翻转环流（AMOC），这引起了主要热带热带跃层的淡入，从而加强了沃克环流并减弱了太平洋北赤道逆流。 NWA和ETP中表面电流强度的相反变化表明，热带辐合带〜4.3 Ma向南迁移。在上新世中期，巴拿马盆地的海表温度比今天低约0.8℃，而亚热带的西北水温仅比现在低约1.1℃。这证实了上新世中期期间子午海温梯度减小的证据，以及这一时期至关重要的假说是，更剧烈的海洋环流（尤其是在西北水域）至关重要。 ETP和NWA（〜5.1 Ma）的SST变化的时间表明，永久性厄尔尼诺现象的终止和AMOC的增强对北半球主要冰期作用（NHG）的发生没有明显贡献，因为这两个事件都早于发生冰川周期的开始。但是，这些过程可能有助于中新世晚期和上新世早期小冰盖的发展，但很可能只是主要NHG发生的前提条件。但是，SST和相对温跃层位置的变化表明，高纬度过程和整体冷却可能影响了ETP中的热结构。提供的SST估计值表明，即使在早期阶段，CAS的消隐对低纬度海洋环流和热力结构，也对新近纪晚期的一些最重要的全球气候事件都具有重大影响。

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