COLLABORATIVE RESEARCH: A combined phytolith-isotope geochemistry approach to paleo-vegetation reconstruction in Montana

合作研究：蒙大拿州新生代古植被重建的植硅体-同位素地球化学组合方法密歇根大学Carolyn Stroemberg、华盛顿大学Carolyn Stroemberg的Nathan Shelton和Selena Smith草地约占地球陆地植被的40%，为人类提供主食(如玉米、水稻、小麦)。正在进行的人为气候变化究竟将如何影响草原生态系统和农作物生产力是一个至关重要的问题，要解决这个问题，首先需要了解这些重要的生物群是如何组装的。根据植物大型化石、共同进化的哺乳动物、稳定同位素数据、化石土壤和植硅体(植物硅)数据，科学界知道，在中新生代的某个时候，草原生态系统在洲际地理尺度上分散。然而，由于不同的指标对草原的出现提出了不同的空间和时间模式(例如，北美与非洲)，这一深刻的生态转变的细节不太确定。在大多数地区，只应用了一种古植被替代物，因此对可能影响植被解释的不同记录中的潜在采样和攻丝偏差了解很少。此外，潜在的重要环境异质性仍然没有记录在案。为了解决这些问题，PI将使用跨学科、多代理的方法来重建过去40 Ma蒙大拿州草原的演变，这可以直接与基于古土壤的古气候重建进行比较。具体地说，PI将使用植硅体、成壤碳酸盐和从古土壤中收集的有机质(即评估光合作用途径的碳同位素)来构建长期、高分辨率的古植被记录。它们将集中于三个关键的气候转变，它们被广泛认为对北美牧草的存在和丰度产生了重大影响，即始新世-渐新世转变(EOT)、渐新世-中新世转变(OMT)和中新世中晚期转变(MLMT)。

Collaborative Research: A combined phytolith-isotope geochemistry approach to Cenozoic paleo-vegetation reconstruction in MontanaNathan Shelton and Selena Smith, University of MichiganCarolyn Stroemberg, University of WashingtonGrasslands make up ~40% of Earth's terrestrial vegetation and provide humans with our staple foods (e.g., corn, rice, wheat). Exactly how ongoing anthropogenic climate change will impact grassland ecosystems and agricultural crop productivity is a crucial question, and addressing it requires knowledge of how these important biomes were assembled in the first place. Based on plant macrofossils, co-evolved mammals, stable isotopic data, fossil soils, and phytolith (plant silica) data, the scientific community knows that grassland ecosystems dispersed at an intercontinental geographic scale sometime during the mid-Cenozoic. However, because different proxies suggest different scenarios for the emergence of grasslands both in terms of gross spatial and temporal patterns (e.g., North America vs. Africa), the details of this profound ecological transition are less certain. In most areas, only one paleo-vegetation proxy has been applied, so very little is understood about potential sampling and taphonomic biases in different records that could affect vegetation interpretation. In addition, potentially important environmental heterogeneity remains undocumented. To resolve these issues, the PIs will use an interdisciplinary, multi-proxy approach to reconstructing the evolution of grasslands in Montana over the past ~40 Ma that can be compared directly with a paleoclimatic reconstruction based on paleosols. Specifically, the PIs will construct a long-term, high-resolution record of paleovegetation using phytoliths, pedogenic carbonates, and organic matter collected from paleosols (i.e., C isotopes to assess photosynthetic pathways). They will focus on three critical climatic transitions that are broadly believed to have significantly impacted the presence and abundance of grasses in North America, namely the Eocene-Oligocene transition (EOT), the Oligocene-Miocene transition (OMT), and the Middle-Late Miocene transition (MLMT).