Vegetation and climate changes during the Early–Late Pliocene Transition (∼ 3.6 Ma) in the Burdur Basin (Southwestern Anatolia): a comparison with the Mediterranean

Abstract

The Early-Late Pliocene transition (∼ 3.6 Ma) is a key period for understanding future climate change linked to increases in greenhouse gases. Around the Western Mediterranean Basin, the Early-Late Pliocene transition was marked by the establishment of a Mediterranean climate with summer droughts, cool/wet winters and latitudinal gradients. However, environmental changes in the eastern part of the Mediterranean area during the Early-Late Pliocene transition have rarely been documented. Here, we propose to reconstruct the environmental and climate changes during the Early-Late Pliocene transition from the Burdur Basin sequence, located in Southwestern Türkiye. This study aims to (1) characterize vegetation patterns, lake dynamics, and water level fluctuations using pollen and Non-Pollen Palynomorph (NPP) proxies, and (2) examine the morphological features of large Poaceae pollen grains (Cerealia-type). We also aim to quantitatively reconstruct climate changes through a multi-method approach, including the Modern Analogue Technique, Weighted Averaging Partial Least Squares regression, Random Forest, and Boosted Regression Trees and the Climatic Amplitude Method.

The results indicate that, during the Early-Late Pliocene transition at Burdur, the vegetation was dominated by steppes with Poaceae, Artemisia, and Amaranthaceae. Subsequently, arboreal taxa decreased and an alternation between steppe grasslands with deciduous Quercus and steppes dominated by Amaranthaceae became evident. The lacustrine ecosystem was characterized by semi-aquatic vegetation and freshwater algae, exhibiting alternating oligotrophic and eutrophic conditions. Large Poaceae pollen grains (Cerealia-type) are recorded in the Burdur Basin sequence, but their percentages are lower than those at Acıgöl to the west, a nearby record dated to the Pleistocene. The morphological characteristics of these large Poaceae pollen grains from Burdur are similar to those of domesticated cereals from recent periods, preventing a clear distinction between wild and domesticated Poaceae pollen. Pollen-inferred climate reconstructions show similar trends across the five methods, with reconstructed values during the Early-Late transition being close to present-day values at Burdur region. Following a climatic optimum in precipitation and temperature during the Early Pliocene, our results indicate an alternation between cool/wet conditions and warmer/drier conditions during the Late Pliocene in Southwestern Anatolia. Around the Mediterranean Basin, records show that the Early Pliocene had warmer conditions compared to modern values and wetter conditions, with a north (wetter)-south (drier) gradient in terms of precipitation. The Late Pliocene is characterized by colder and more humid conditions in the Western Mediterranean, while the Eastern Mediterranean (Southwestern Türkiye) and Central Asia experienced more arid conditions. A weak Atlantic Meridional Overturning Circulation (AMOC) is identified in Europe during the Late Pliocene, leading to cooler and wetter conditions primarily in the Northwestern Mediterranean. While model simulations of PlioMIP2 show warmer conditions and a latitudinally contrasted precipitation pattern, with wetter conditions in Northern Europe and drier conditions in the south during the mid-Pliocene Warm Period (3.264–3.025 Ma).