Late Eocene to middle Miocene (33 to 13 million years ago) vegetation and climate development on the North American Atlantic Coastal Plain (IODP Expedition 313, Site M0027)
Late Eocene to middle Miocene (33 to 13 million years ago) vegetation and climate development on the North American Atlantic Coastal Plain (IODP Expedition 313, Site M0027)
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DOI：
10.5194/cp-10-1523-2014
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发表时间：
2014-08
影响因子：
4.3
通讯作者：
U. Kotthoff;D. Greenwood;F. McCarthy;K. Müller-Navarra;Sabine Prader;S. Hesselbo
中科院分区：
文献类型：
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作者：
U. Kotthoff;D. Greenwood;F. McCarthy;K. Müller-Navarra;Sabine Prader;S. Hesselbo
摘要。为了研究3300万~ 1300万年前北美东海岸的植被和气候动态，我们研究了美国综合海洋钻探计划（IODP）第313远征队M0027站点沉积物岩心的孢粉学，并评估了跨区域气候事件对该地区的影响。孢粉学结果与基于花粉的定量气候重建相辅相成。结果表明，早渐新世至中新世中期，纽泽西陆架腹地植被以低地橡树-山核桃林和高地针叶林为主。渐新世见证了几次针叶林的扩张，可能与降温事件有关。基于花粉的气候数据表明，渐新世的年气温从~ 11.5°C增加到16°C以上。中新世开始时的Mi-1冷却事件反映在针叶树的扩张和平均年温度下降~ 4°C，从~ 16°C到~ 12°C，大约2300万年前。在距今约2000万年的时间间隔内，几个样品也记录了相对较低的年温度，这可能反映了Mi-1a和Mi-1aa冷却事件。总体上，中新世的生态系统和气候条件与渐新世非常相似。中新世的草原，从美国其他地区在那个时期所知道的，在新泽西大陆架的腹地并不明显，可能反映了原墨西哥湾流的水分。古植被资料显示，在距今约1500万年的中新世中期气候最适宜时期条件稳定，落叶-常绿混交林类群略有增加，沼泽森林类群有所减少。基于花粉的年温度重建显示，中新世中期气候最佳时期的年平均温度为~ 14°C，比现在高~ 2°C，但比中新世前后阶段低~ 1.5°C。我们认为，由于北大西洋的调节作用，新泽西陆架腹地的植被和区域气候对渐新世和中新世气候变化的反应不如北美或欧洲其他地区敏感。对于中新世中期气候最佳时期重建的相对较低的区域温度，另一种解释可能是中新世期间阿巴拉契亚山脉的隆起，这也会影响我们花粉记录的集水区。
Abstract. We investigated the palynology of sediment cores from Site M0027 of IODP (Integrated Ocean Drilling Program) Expedition 313 on the New Jersey shallow shelf to examine vegetation and climate dynamics on the east coast of North America between 33 and 13 million years ago and to assess the impact of over-regional climate events on the region. Palynological results are complemented with pollen-based quantitative climate reconstructions. Our results indicate that the hinterland vegetation of the New Jersey shelf was characterized by oak–hickory forests in the lowlands and conifer-dominated vegetation in the highlands from the early Oligocene to the middle Miocene. The Oligocene witnessed several expansions of conifer forest, probably related to cooling events. The pollen-based climate data imply an increase in annual temperatures from ∼11.5 °C to more than 16 °C during the Oligocene. The Mi-1 cooling event at the onset of the Miocene is reflected by an expansion of conifers and mean annual temperature decrease of ∼4 °C, from ∼16 °C to ∼12 °C around 23 million years before present. Relatively low annual temperatures are also recorded for several samples during an interval around ∼20 million years before present, which may reflect the Mi-1a and the Mi-1aa cooling events. Generally, the Miocene ecosystem and climate conditions were very similar to those of the Oligocene. Miocene grasslands, as known from other areas in the USA during that time period, are not evident for the hinterland of the New Jersey shelf, possibly reflecting moisture from the proto-Gulf Stream. The palaeovegetation data reveal stable conditions during the mid-Miocene climatic optimum at ∼15 million years before present, with only a minor increase in deciduous–evergreen mixed forest taxa and a decrease in swamp forest taxa. Pollen-based annual temperature reconstructions show average annual temperatures of ∼14 °C during the mid-Miocene climatic optimum, ∼2 °C higher than today, but ∼1.5 °C lower than preceding and following phases of the Miocene. We conclude that vegetation and regional climate in the hinterland of the New Jersey shelf did not react as sensitively to Oligocene and Miocene climate changes as other regions in North America or Europe due to the moderating effects of the North Atlantic. An additional explanation for the relatively low regional temperatures reconstructed for the mid-Miocene climatic optimum could be an uplift of the Appalachian Mountains during the Miocene, which would also have influenced the catchment area of our pollen record.