Shijun Jiang

In this study, we investigate calcareous nannofossils from deep-sea sediments spanning the Eocene–Oligocene Transition (EOT) at seven ODP/IODP Sites distributed from the Southern Ocean (SO) to tropical regions. We aimed to update and improve the biochronological framework through high-resolution analysis and expand nannofossil biostratigraphic data for this crucial interval. Mid- to low-paleolatitude sections include ODP Holes 1265A (Walvis Ridge), 757B (Ninetyeast Ridge), 711A (Madingley Rise), and IODP Hole U1333A (Equatorial Pacific), whereas SO mid- to high-paleolatitude sections comprise ODP Holes 1090B (Agulhas Ridge), 689D (Maud Rise), and 738B (Kerguelen Plateau). We identified known primary bioevents, confirming their reliability, and additional bioevents that improve EOT biostratigraphic resolution. At high paleolatitudes, the Highest Occurrences (HOs) of Reticulofenestra oamaruensis gr., represented by the simultaneous extinction of three R. oamaruensis morphotypes, and R. clatrata (~34.08 Ma) approximate the Eocene–Oligocene Boundary (EOB). The HO of Discoaster saipanensis is confirmed as a distinctive marker of EOT onset at mid- to low paleolatitudes. Additional events close to the EOB include the HO of Cribrocentrum helianthus at high paleolatitudes (34.03–33.94 Ma) and the Increase Beginning (IB) of Reticulofenestra daviesii, remarkably isochronous between high and mid- to low paleolatitudes (34.04–33.84 Ma). Finally, the Lowest Occurrence (LO) of Furcatolithus akropodus (33.97–33.91 Ma) is confirmed as a useful bioevent characterizing the lowermost Oligocene at mid- to low paleolatitudes.

The Paleocene-Eocene Thermal Maximum is a key analog for future climate change. However, how terrestrial ecosystems responded to this extreme warming remains uncertain. We integrate a dynamic global vegetation model with a carbon-isotope mass-balance framework to quantify terrestrial carbon-cycle feedbacks. Our simulations reveal that ancient high-latitude carbon stocks were vast but highly sensitive to extreme warming. We identify a fundamental non-linearity in the terrestrial response: while moderate warming triggers ecosystem shifts, extreme warming drives an abrupt collapse of land carbon, releasing up to ~900 petagrams. This decline stems from a bipolar ecological shift where massive tropical forest loss and accelerated soil heterotrophic respiration overwhelm high-latitude greening and carbon dioxide fertilization. Furthermore, hybrid scenarios combining terrestrial release of sedimentary methane and volcanic carbon dioxide provide the best fit to the geological record. We identify critical thermal thresholds, warning that future terrestrial carbon-climate feedbacks could be more severe than currently projected.

Estuarine and intertidal ecosystems play a crucial role in the Earth's carbon cycle, influencing carbon storage and transformation processes. This study investigates the distribution and composition of organic carbon (OC) pools in the intertidal sediments of the Pearl River Estuary, China, focusing on water-soluble organic carbon (WSOC), hot-water extractable organic carbon (HWOC), acid-extractable organic carbon (HCl-OC), and alkali-extractable organic carbon (NaOH-OC). We analyzed 21 sampling sites across the estuary to assess spatial variations and correlations with total organic carbon (TOC). Results show significant variability in TOC content, ranging from 0.99 g/kg to 66.16 g/kg, with higher values near the main river channels and human activity zones. WSOC levels were relatively uniform but higher in areas influenced by river mouths and pollution sources. HWOC and HCl-OC were more concentrated in sites with substantial organic matter inputs, indicating areas of significant carbon accumulation and long-term stability. NaOH-OC showed higher concentrations in urban and industrial areas, reflecting complex and resistant organic matter inputs. The linear regression analysis showed a strong positive correlation between TOC and HWOC (Adj. R² = 0.83), suggesting that a significant portion of the TOC in these sediments consisted of hot-water extractable organic matter. Additionally, a moderately strong correlation was observed between TOC and HCl-OC (Adj. R² = 0.74), indicating that acid-extractable organic carbon also contributed substantially to the TOC composition. These findings enhance our understanding of organic carbon dynamics in estuarine sediments and provide valuable insights for regional carbon storage assessments and ecological management.

Current studies on ecological risk primarily focus on single pollutants or persistent organic pollutants in aquatic ecosystems. However, methods for assessing the joint probabilistic ecological risk of multiple pollutant types—such as inorganic contaminants, organic compounds, and microplastics—remain scarce. Here, we introduce the SPI model, a novel framework for assessing the combined ecological risk of diverse pollutants to aquatic biota. The SPI model integrates Species Sensitivity Distribution (SSD), Probabilistic Risk Assessment (PRA), and the Inclusion-Exclusion Principle (IEP) to provide a comprehensive risk evaluation. The model computes individual and joint ecological risks, offering a holistic assessment of the impacts of pollutants on aquatic ecosystems. The SPI model has been successfully applied to various water bodies in China, including the Songhua River Basin, Yellow River, Bohai Sea, and Pearl River Estuary, and has been recognized for its significant contribution to the field. Our case studies reveal that joint ecological risks often exceed 10% in major aquatic ecosystems, prompting the establishment of ecological risk alert thresholds at 25% and 50%. This model represents a significant advancement in ecological risk assessment and offers a valuable tool for proactive environmental management.

The moderate impact of rapid global warming on oceanic redox and biodiversity during the Paleocene-Eocene thermal maximum (PETM; ~55.9 Ma) contrasts with other hyperthermal events in Earth’s history, and remains mostly unexplained. Here, we use lithium isotope (δ⁷Li) proxy and Earth system model simulations to reconstruct continental weathering regimes during the PETM. Negative δ⁷Li excursions of 3–4‰ in shallow-marine carbonates suggests globally increased erosion rates and decreased weathering intensities. Further, large negative δ⁷Li excursions of 4–5‰ in siliciclastic successions reflect enhanced accumulation of detrital clays exhumed from previous clay-rich sedimentary rocks, rather than those from weathering of igneous rocks. Changes in continental weathering regimes and associated flux of nutrients to oceans provide an explanation to the muted increase in oceanic anoxia and overall biodiversity loss during the PETM. The concomitant increases in physical erosion and clay delivery also enhanced organic carbon burial efficiency, permitting rapid return of global climate to pre-perturbation state.

Geologic records support a short-lived carbon release, known as the pre-onset excursion (POE), shortly before the Paleocene-Eocene Thermal Maximum (PETM; ~ 56 Ma). However, the source and pace of the POE carbon release and its relationship to the PETM remain unresolved. Here we show a high-temporal-resolution stratigraphic record spanning the POE and PETM from the eastern Tethys Ocean that documents the evolution of surface ocean carbon cycle, redox and eutrophication, confirming the global nature of the POE. Biomarkers extracted from the sedimentary record indicate a smaller environmental perturbation during the POE than that during the PETM in the eastern Tethys Ocean. Earth system modeling constrained by observed δ¹³C and pH data indicates that the POE was driven by a largely thermogenic CO₂ source, likely associated with sill intrusions prior to the main eruption phase of the North Atlantic Igneous Province and possibly biogeochemical feedbacks involving the release of biogenic methane.

海洋沉积物的元素含量及其比值记录了物源特征、化学风化过程与气候演变等信息, 是古环境重建的重要工具。以西藏日喀则弧前盆地吉定剖面白垩系昂仁组的连续海相沉积序列为研究对象, 利用X射线荧光光谱技术(XRF)获取高时间分辨率的主量与微量元素含量数据, 综合分析Fe/Mn、Al/Mg、Rb/Sr、Ti/Ca等多种气候-环境敏感元素比值的垂向变化与协同演化特征, 重建了研究区的古气候、化学风化强度、陆源物质通量、物源以及初级生产力的长期变化特征。结果表明: (1)白垩纪期间, 研究区整体处于暖湿气候背景, 其演化过程可划分为三个阶段: 下段(约104~99Ma)暖湿程度波动增强; 中段(约99~88Ma)在塞诺曼期达极热峰值后转降入波动性降温; 上段(约88~83Ma)呈“双峰式”变冷特征。(2)冈底斯岩浆弧持续构造隆升, 为盆地提供了稳定且丰富的新鲜物源, 研究区风化作用强度主要受控于降水变化, 属典型的动力限制型风化体系。(3)通过陆源碎屑输入的营养物质对海洋初级生产力具有关键调控作用。

This special issue of Mesozoic is dedicated to the memory of a great specialist in carbonate sedimentology, Dr Juan Li, who passed away on July 19th, 2023. Juan Li sadly left us while logging the Paleocene-Eocene thermal maximum (PETM) interval in the Tibetan Himalaya. This special issue has collected contributions to Mesozoic–Cenozoic geological studies from the Qinghai-Tibet Plateau from colleagues, friends, and fellow scientists to express our remembrance and regret.

终结恐龙时代的白垩纪–古近纪（K-Pg）界线事件发生在6600万年前，由于小行星撞击，地球生态环境发生剧变，导致海洋和陆地生物的大规模灭绝，当时海洋里占据绝对优势地位的初级生产者—颗石藻的灭绝尤为严重。初级生产者是食物链的基础，了解海洋初级生产在极端环境下的破坏与灾后恢复过程，对于研究当今全球变化下海洋生物碳泵变化及其控制机制具有重要的借鉴意义。比较了前人提出的劫难海洋（Strangelove Ocean）、活跃海洋（Living Ocean）、弹性海洋（Resilient Ocean）以及异质海洋（Heterogeneous Ocean）等四个假说，评述每个假说在解释K-Pg事件后海洋生物泵如何运行方面的合理性与不足。综合分析全球海盆多点同时具有高精度旋回控制和表层–深海δ13C垂向梯度的数据，以探索K-Pg界线事件后全球海洋生物碳泵效率的变化，指出：（1）K-Pg事件前所有洋盆δ13C垂向梯度与现代海洋一致，这个梯度从陆架到深海有逐渐增加的趋势；（2）K-Pg事件后全球海洋δ13C垂向梯度消失；（3）K-Pg事件后δ13C垂向梯度消失主要是由于海洋表层δ13C突然负偏，其负偏幅度随着从陆架到深海逐渐减小。K-Pg事件后主要初级生产者从较大的颗石藻转变为较小的微型浮游生物，由于真光层中微生物碳泵的作用，更多难降解的惰性溶解有机碳能够下沉到海底，生物碳泵的效率得以提高。微型生物主导的生物碳泵效率不如颗石藻主导的高，但其长期运行能从海洋表层中去除足够的营养盐和有害物质，不仅为更高营养级生物提供食物来源，而且改善K-Pg事件后恶化的海洋物理化学环境，为整个海洋生态系统的恢复和发展铺平道路。关键海洋初级生产者的变换及其控制因素是深时碳循环领域未来需要重点研究的科学问题，而K-Pg事件后生物碳泵表现出的区域或全球变化模式，有助于了解不同海洋生态系统在极端环境压力下如何运作，为人类更好地理解和预测当前快速全球变化对不同海洋生态系统的影响提供借鉴。