The coastal upwelling zones, occupying only ~0.5% of the global ocean, account for ~10% of the global primary productivity. The CO₂ fixation by primary producers amplifies in the upwelling zones during global warming due to the higher nutrient supply. Based on the presumption that the nutrient-deficient coastal ocean is less productive, the state of the oligotrophic coastal ocean is often neglected in the productivity-climate change studies. The present study investigated the changes in the primary productivity, redox condition, and nutrient content, using algal abundance, total organic carbon, and various major, trace, and rare earth elements and yttrium (REY) proxies, of the oligotrophic equatorial eastern Tethyan coastal ocean across the Paleocene-Eocene Thermal Maximum (PETM), a prominent paleo-global warming event. Despite the lower nutrient (lower Ni_EF, Cu_EF, and Zn_EF) contents, and invariable salinity, pH, and light conditions, the PETM interval shows extensive growth of coralline red algae in the hypoxic-oxic water column. Based on these observations, and inferences drawn from the previous laboratory experiments, conducted on the algal growth in varying pCO₂ by others, we postulate that the increased atmospheric CO₂ concentrations during the PETM probably enhanced the primary productivity of the oligotrophic Tethyan coastal ocean. If so, then the oligotrophic coastal ocean may be considered as an effective CO₂ sink and likely to play a pivotal role in carbon cycle-climate connection studies.

沿海上升流区仅占全球海洋面积的约 0.5%，占全球初级生产力的约 10%。CO ₂由于更高的养分供应，初级生产者的固定作用在全球变暖期间在上升流区放大。基于营养缺乏的沿海海洋生产力较低的假设，贫营养沿海海洋的状态在生产力-气候变化研究中经常被忽视。本研究使用贫营养的赤道东部特提斯海岸沿岸的藻类丰度、总有机碳以及各种主要、微量和稀土元素和钇 (REY) 替代物，调查了初级生产力、氧化还原条件和养分含量的变化横跨古新世-始新世最高温度（PETM）的海洋，这是一个突出的古全球变暖事件。尽管养分较低（较低的 Ni _EF、Cu _EF和 Zn _EF) 含量，以及不变的盐度、p H 和光照条件，PETM 间隔显示珊瑚红藻在缺氧-缺氧水柱中广泛生长。基于这些观察结果以及从先前实验室实验中得出的推论，其他人对不同p CO ₂中藻类的生长进行了推测，我们假设在 PETM 期间增加的大气 CO ₂浓度可能提高了贫营养的特提斯沿海海洋的初级生产力. 如果是这样，那么贫营养沿海海洋可能被认为是一种有效的CO ₂汇，并可能在碳循环-气候联系研究中发挥关键作用。