Collaborative Research: Was There a Shift Toward Small, Non-Fossilizing Plankton after the End of the Cretaceous Mass Extinction?

生活在海洋表层的浮游植物，从阳光和二氧化碳中产生有机物。这种初级产品构成了大多数海洋食物网的基础，是全球碳循环的关键部分。在现代海洋中，浮游生物正受到变暖和海洋酸化的影响。过去地质时期海洋温度和化学的自然变化可以帮助我们理解变暖和酸化等压力源的长期影响。6600万年前的白垩纪-古近纪（K-Pg）大灭绝事件就是这样一个全球性的变化时期。钙质（化石形成）纳米浮游生物是白垩纪海洋中主要的初级生产者之一。然而，这一类群93%的物种在K-Pg边界灭绝，它们再也没有占据优势地位。以前对浮游生物对K-Pg事件反应的研究通常局限于对留下物理化石记录的物种的研究。因此，这些研究只提供了古代浮游生物生态系统的部分观点。这项工作将通过使用被称为生物标志物的化学化石来克服这一限制。这些新数据将与传统的物理化石一起用于重建K-Pg事件后海洋浮游生物群落的变化。人们通常认为，非石化浮游植物填补了石灰质纳米浮游生物减少留下的空白。这项研究将有助于验证这一假设。记录非石化和石化浮游生物的变化将提高我们对浮游生物生态长期变化的理解，以及这些变化如何改变海洋碳循环。该项目将培训早期职业研究人员和本科生，并将与德克萨斯州奥斯汀和科罗拉多州博尔德的组织和项目合作，通过外展和教育活动将结果传播给更广泛的受众。该项目将从突尼斯、西班牙和美国墨西哥湾沿岸的5个地点开发脂质生物标志物、钙质纳米浮游生物和浮游有孔虫的数据集。突尼斯的三个地点（El Kef， Elles和El Melah）代表了大陆架的深度样带（古深度为200-500米），Caravaca代表了更深的水域（~600-1000米），而Brazos代表了一个浅层大陆架，这将使我们能够测试北非和美国墨西哥湾沿岸平原之间的区域差异。这些数据将允许检验以下假设：在K-Pg灭绝之后，低多样性的非石化浮游植物群落在低多样性的钙质纳米浮游生物“灾难”群落期间大量繁殖。钙质纳米浮游生物多样性的随后恢复与非石化浮游植物的减少有关。异养浮游有孔虫组合的变化与整个自养浮游生物组合的周转有关。灭绝后的初级生产者群落主要由较小的浮游植物，如藻类和蓝藻，增加了浅水的碳循环，减少了向深海的碳出口。该研究将提高我们对白垩纪大灭绝结束后的恢复的认识，并提高我们对浮游生物生态学在海洋生态系统变化中的作用的全面认识。此外，重建整个浮游生物生态系统，而不仅仅是化石的部分，将代表着我们研究古代海洋的工具包的重大改进。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Phytoplankton, which live in the surface ocean, produce organic matter from sunlight and carbon dioxide. This primary production forms the base of most marine food webs and is a critical part of the global carbon cycle. In the modern ocean plankton are being impacted by warming and ocean acidification. Natural changes in ocean temperature and chemistry in the geologic past can help us understand the long-term effects of stressors such as warming and acidification. The Cretaceous-Paleogene (K-Pg) mass extinction event ~66 million years ago was one such time of global change. Calcareous (fossil-forming) nanoplankton were one of the dominant primary producers in the Cretaceous ocean. However, 93% of species of this group went extinct at the K-Pg boundary, and they were never again as dominant. Previous studies of the plankton response to the K-Pg event have generally been limited to studies of species which leave a physical fossil record. Thus, these studies provided only a partial view of ancient plankton ecosystems. The proposed work will overcome this limitation by using chemical fossils called biomarkers. These new data will be used together with traditional physical fossils to reconstruct changes in the marine plankton community following the K-Pg event. It has often been assumed that non-fossilizing phytoplankton filled the gap left by the decline in calcareous nannoplankton. This study will help test that hypothesis. Documenting the changes in both non-fossilizing and fossilizing plankton will improve our understanding of long-term changes in plankton ecology, and of how those changes could alter the ocean carbon cycle. This project will train early career researchers and undergraduate students, and will disseminate results to broader audiences through outreach and educational activities in partnership with organizations and programs in Austin, TX and Boulder, CO.The project will develop datasets of lipid biomarkers, calcareous nannoplankton, and planktic foraminifera from 5 sites in Tunisia, Spain, and the US Gulf Coast. Three sites in Tunisia (El Kef, Elles, and El Melah) represent a depth transect on a continental shelf (paleodepths of 200-500 m), Caravaca represents deeper water (~600-1000 m), while Brazos represent a shallow shelf which will allow us to test regional variability between north Africa and the US Gulf Coastal Plain. These data will allow tests of the following hypotheses:1. A low-diversity assemblage of non-fossilizing phytoplankton bloomed in the aftermath of the K-Pg extinction, during the time of low diversity calcareous nannoplankton “disaster” assemblages.2. Subsequent recovery of calcareous nannoplankton diversity is associated with a decline in non-fossilizing phytoplankton.3. Shifts in the heterotrophic planktic foraminifera assemblages are tied to turnover in the whole autotrophic plankton assemblage.4. The post-extinction community of primary producers was dominated by smaller phytoplankton like algae and cyanobacteria, and would have increased carbon recycling in shallow waters and reduced carbon export to the deep sea.The study will improve our understanding of the recovery after the end Cretaceous mass extinction and in our overall understanding of the role of plankton ecology in marine ecosystem change. Additionally, reconstructing the whole plankton ecosystem, and not just the part that fossilizes, would represent a significant improvement of our toolkit to investigate ancient oceans.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.