Pollen counts of sediment core GeoB16205-4 from Parnaiba, NE Brazil

The semi-arid northeastern (NE) Brazil vegetation is largely dominated by Caatinga, one of the largest and richest dry forests in the world. Caatinga is a strategic biome, since it has borders with Cerrado, Atlantic forests and the Amazon, acting as a potential corridor (or barrier) for biotic interchange between these regions during evolutionary times. Therefore, accurate reconstructions of past vegetation, ecological and hydrological changes in this area are critical to understanding the dynamics of biome boundaries that may play an important role in dispersal and diversi!cation mechanisms and, more specifically, the link between the long-term climate variability and tropical biodiversity. Here, we present high-resolution palynological and elemental data from marine core GeoB16205-4 retrieved off the Parnaíba River mouth (NE Brazil) mainly covering the Younger Dryas (YD). We show that the YD interval was predominantly wet in NE Brazil, yet it was not homogenous and two distinct phases could be distinguished. A marked intensi!cation of wet conditions between ~12.3 and 11.6 cal kyr BP was recorded by the expansion of tropical rainforest and tree ferns. These results are in agreement with the transient TraCE-21k coupled climate model simulation. We infer that the second pluvial phase of the YD is related to a weak AMOC due to meltwater pulses in the North Atlantic, which forces a southward shift of the Intertropical Convergence Zone and its associated rainfall. Our records provide new evidence on the establishment of an “eastern forest corridor” in the nowadays semi-arid Caatinga allowing for past biotic interchanges of plant species.

巴西东北部半干旱区的植被以卡廷加（Caatinga）为主，它是全球规模最大、物种最丰富的旱生森林之一。卡廷加属于具有战略意义的生物群系，其与塞拉多（Cerrado）、大西洋森林及亚马孙雨林接壤，在演化历程中可作为上述区域间生物交流的潜在廊道（或屏障）。因此，精准重建该区域过去的植被、生态与水文变化，对于理解生物群系边界的动态变化至关重要——这类动态在物种扩散与分化机制中发挥着重要作用，更具体而言，也有助于厘清长期气候变率与热带生物多样性之间的关联。本研究提供了采自巴西东北部帕纳伊巴河河口外的海洋岩芯GeoB16205-4的高分辨率孢粉与元素数据，该岩芯的沉积序列主要覆盖新仙女木期（Younger Dryas，YD）。研究结果显示，巴西东北部的新仙女木期整体偏湿润，但并不均一，可划分为两个显著阶段：约12.3至11.6 cal kyr BP期间，湿润条件显著增强，表现为热带雨林与树蕨类植物的扩张。这一结果与TraCE-21k瞬变耦合气候模型的模拟结果相符。我们推断，新仙女木期的第二湿润阶段与北大西洋融水脉冲引发的大西洋经向翻转环流（AMOC）减弱相关，该过程驱使热带辐合带（Intertropical Convergence Zone，ITCZ）向南移动，进而带来关联降水的变化。本研究的记录为如今半干旱的卡廷加区域曾存在“东部森林廊道”提供了新证据，该廊道曾支持植物物种的跨区域生物交流。