Evolution of Oceanography of the Central Northwest Pacific Over the Past 10 Million Years With Focus on Late Miocene Global Cooling

IF 3.2 2区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Paleoceanography and Paleoclimatology Pub Date : 2023-12-01 DOI:10.1029/2023pa004789

Kenji M. Matsuzaki

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Abstract

Since the middle Miocene climatic transition, the Earth's climate has steadily cooled. The late Miocene global cooling (LMGC) and the Northern Hemisphere Glaciation (NHG) were two key cooling events occurring during this time. To better understand the mechanisms underlying these cooling events, changes in radiolarian microfossil assemblages were examined in this study, aiming at the reconstructing of oceanographic changes that have occurred at Ocean Drilling Program site 1208 during the last 10 million years. Sea surface temperatures (SSTs) were reconstructed based on radiolarian species that were extant 0–10 million years ago. Reconstructed SSTs were then compared with previously published alkenone‐based SSTs at site 1208, and it was found that overall, using SSTs based only on extant radiolarian species yielded a correct record for the last 10 million years. However, large discrepancies were observed between radiolarian‐ and alkenone‐based SSTs during LMGC and the NHG. These discrepancies were attributed to the sustained influence of subsurface water (at depths from ∼50 to 100 m) on assemblages of radiolarians during extreme cooling events. Relative abundances of other radiolarian groups indicated that during LMGC, there was a reorganization of the regional oceanography that probably weakened the Pacific meridional overturning circulation, increased the meridional temperature gradient, and caused a southward migration of the subtropical front. Probably, the North Pacific intermediate water expanded southeastward during NHG.

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过去 1000 万年西北太平洋中部海洋学的演变，聚焦中新世晚期全球变冷

自中新世中期气候转变以来，地球气候持续变冷。中新世晚期的全球变冷（LMGC）和北半球冰川（NHG）是这一时期发生的两个关键变冷事件。为了更好地了解这些降温事件的发生机制，本研究考察了放射虫微化石组合的变化，旨在重建大洋钻探计划1208站点在过去1000万年间发生的海洋变化。根据 0-10 万年前现存的放射虫物种重建了海面温度（SST）。然后将重建的海表温度与之前公布的基于烯酮的 1208 号站点的海表温度进行比较，结果发现，总体而言，仅根据现存的放射虫物种重建的海表温度能够正确记录过去 1000 万年的海表温度。然而，在 LMGC 和 NHG 期间，观察到基于放射虫的海温与基于烯酮的海温之间存在巨大差异。这些差异是由于在极端降温事件期间，地下水（深度为 50 至 100 米）对放射虫群的持续影响造成的。其他放射虫类群的相对丰度表明，在 LMGC 期间，区域海洋学发生了重组，可能削弱了太平洋经向翻转环流，增加了经向温度梯度，并导致副热带锋面南移。在 NHG 期间，北太平洋中间水可能向东南方向扩展。

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来源期刊

Paleoceanography and Paleoclimatology Earth and Planetary Sciences-Atmospheric Science

CiteScore

6.20

自引率

11.40%

发文量

107

期刊介绍： Paleoceanography and Paleoclimatology (PALO) publishes papers dealing with records of past environments, biota and climate. Understanding of the Earth system as it was in the past requires the employment of a wide range of approaches including marine and lacustrine sedimentology and speleothems; ice sheet formation and flow; stable isotope, trace element, and organic geochemistry; paleontology and molecular paleontology; evolutionary processes; mineralization in organisms; understanding tree-ring formation; seismic stratigraphy; physical, chemical, and biological oceanography; geochemical, climate and earth system modeling, and many others. The scope of this journal is regional to global, rather than local, and includes studies of any geologic age (Precambrian to Quaternary, including modern analogs). Within this framework, papers on the following topics are to be included: chronology, stratigraphy (where relevant to correlation of paleoceanographic events), paleoreconstructions, paleoceanographic modeling, paleocirculation (deep, intermediate, and shallow), paleoclimatology (e.g., paleowinds and cryosphere history), global sediment and geochemical cycles, anoxia, sea level changes and effects, relations between biotic evolution and paleoceanography, biotic crises, paleobiology (e.g., ecology of “microfossils” used in paleoceanography), techniques and approaches in paleoceanographic inferences, and modern paleoceanographic analogs, and quantitative and integrative analysis of coupled ocean-atmosphere-biosphere processes. Paleoceanographic and Paleoclimate studies enable us to use the past in order to gain information on possible future climatic and biotic developments: the past is the key to the future, just as much and maybe more than the present is the key to the past.