Collaborative Research: The Cold Late Oligocene Arctic Ocean and its Unique Biota

这是加州科学院和佛罗里达大西洋大学的主要研究人员合作提出的一项建议。本研究是对软体动物、微化石和氧同位素的综合评估，将用于记录目前未知的晚渐新世北冰洋海洋古气候。化石将首先从阿拉斯加东北部Sagavanirktok组的Nuwok成员中收集，这是已知的唯一在北冰洋地区出现的上渐新世海洋沉积物。在实地考察之后，主要研究人员将进行分类学和氧同位素分析，以产生将构成其结论基础的信息。基于对从软体动物壳中提取的氧同位素的初步研究，第一个需要验证的假设是，北冰洋在渐新世晚期几乎和今天一样寒冷，比同时期的中低纬度海域更冷，但不像南极洲那么冷。如果这是真的，这将是地球渐新世从温室世界向冰窖世界过渡期间半球气候不对称的第一个证据。Nuwok软体动物的d18O试验值表明，与今天邻近的北冰洋相比，季节性更强。第二个假设是，努沃克晚渐新世软体动物和介形类是现代北冰洋生物群的最早表现。在渐新世晚期Nuwok生物群中，全球独一无二的似乎完全存在的属，以及在渐新世动物群中同样独特的始新世遗留软体动物的缺失，为这一观点提供了令人信服的证据。努沃克生物群提供了一个独特的机会，将北极置于全球快速气候变化时期的新生代海洋进化和多样化的全球格局中。第三种假设是，晚渐新世的努沃克软体动物和介形类动物进化得很少，这是基于它们与现存的北冰洋物种惊人的相似。这将在化石和现代北极和北大西洋动物群的比较分类分析中得到解决。这项活动的学术价值：这项研究将首次记录目前未知的晚渐新世古气候和北冰洋季节性温度波动，基于对软体动物壳的氧同位素分析。近几十年来，对渐新世全球变冷的认识急剧增加，这主要是由于对深海岩心中微化石的氧同位素研究，但对北冰洋海洋动物没有这样的研究。这项拟议的研究，使用协调的同位素和古生物学分析，将是第一个将北冰洋晚渐新世古气候置于全球背景下的研究，并允许在从温室到冰窖世界过渡的全球气候模型中考虑这种古气候。拟议的活动所产生的更广泛的影响：北冰洋的气候历史是地球历史上最后一个未解决的史诗之一。记录其渐新世晚期（2600 - 2700万年前）的古气候，包括现代冰窖世界开始时的季节性极端气候，将独特地增加对全球气候历史的整体理解。这项研究将提供北冰洋领域在从温室到冰屋世界的戏剧性转变过程中的第一个见解，并将对海洋和大陆地球科学的许多古气候相关领域产生影响。这些来自世界上最敏感但最不为人所知的环境之一的新数据将有助于考虑全球气候变化的规模、速度和潜在影响。

This is a collaborative proposal from Principal Investigators at the California Academy of Sciences and Florida Atlantic University. This study is an integrated assessment of mollusks, microfossils, and oxygen isotopes which will be used to document the presently unknown late Oligocene marine paleoclimate of the Arctic Ocean. Fossils will first be collected from the Nuwok Member of the Sagavanirktok Formation, in northeastern Alaska, the only upper Oligocene marine sediments known to crop out in the Arctic Ocean region. After fieldwork, the Principal Investigators will undertake taxonomic and oxygen isotopic analyses to generate information that will form the basis for their conclusions. Based on a pilot study of oxygen isotopes derived from mollusk shells, the first hypothesis to be tested is that the Arctic Ocean was almost as cold in the late Oligocene as it is today, that it was colder than contemporaneous mid- and low-latitude seas, but that it was not as cold as Antarctica. If true, this would be the first evidence of hemispheric climatic asymmetry during the Earth's Oligocene transition from a Greenhouse to an Icehouse world. Pilot d18O values from Nuwok mollusks imply greater seasonality than occurs in the adjacent Arctic Ocean today. A second hypothesis is that Nuwok late Oligocene mollusks and ostracodes are the earliest manifestation of the modern Arctic Ocean biota. The globally unique presence of what appear to be entirely extant genera in the late Oligocene Nuwok biota, and the equally unique absence of Eocene holdover mollusks in such an Oligocene fauna, make a compelling case for this idea. The Nuwok biota provides a unique opportunity to place the Arctic within the context of global patterns of Cenozoic marine evolution and diversification during a time of rapid global climate change. A third hypothesis is that late Oligocene Nuwok mollusks and ostracodes evolved very little, based on their uncanny resemblance to extant Arctic Ocean species. This will be addressed in comparative taxonomic analysis of fossil and modern arctic and North Atlantic faunas.The intellectual merit of the proposed activity: This study will be the first to document the presently unknown late Oligocene paleoclimate and seasonal temperature fluctuations of the Arctic Ocean, based on oxygen isotope analysis of mollusk shells. Knowledge of Oligocene global cooling has dramatically increased in recent decades, mainly due to oxygen isotope studies of microfossils in deep-sea cores, but no such work has been done on Arctic Ocean marine faunas. This proposed study, using coordinated isotopic and paleontological analyses, will be the first to place the Arctic Ocean's late Oligocene paleoclimate into a global context, and allow factoring this paleoclimate into global climate models during the transition from a Greenhouse to an Icehouse world.The broader impacts resulting from the proposed activity: The climate history of the Arctic Ocean is one of the last unsolved epics of Earth history. Documenting its late Oligocene (26-27 million years ago) paleoclimate, including seasonal extremes, during initiation of the modern Icehouse world will uniquely add to overall understanding of global climate history. This study will provide the first insights from the Arctic Ocean realm during the dramatic transition from a Greenhouse to an Ice House world, and will have implications for many paleoclimate-related fields of marine and continental geoscience. These new data from one of the world's most sensitive, but least known, environments will be useful in considering the scale, rate, and potential effects of global climate change.