Morphometric characteristics and paleogeographic implication of glacial cirques in Eastern Black Sea Mountains (Türkiye)

Abstract

The Eastern Black Sea Mountains, located in the northeastern region of Anatolia and running parallel to the Black Sea coast, underwent glaciation during the Quaternary. The mountain range contains 811 cirque sites. Although the majority of the cirques are simple, 309 are complex, according to their developmental features. In Anatolia, intensive cirque development is observed only on north-facing slopes in several mountains, while in the Black Sea Mountains, 66.5 % of the cirques are located on north-facing slopes and 14.5 % on south-facing slopes. Differences in cirque morphometry between the north- and south-facing slopes were primarily influenced by aspect, which had a significant influence on Quaternary glaciation. While the northwest-facing cirques are the largest, the east- and southeast-facing cirques are the smallest. This situation is related to that air masses that bring rain to the mountains generally come from the northwest. The mean cirque floor elevation is 2815 m, while 90 % of the cirques have floor elevations between 2479 and 3130 m. In light of these measurements, the former Equilibrium Line Altitude (ELA), initially positioned above 2480 m, underwent a complete stabilization at elevations exceeding 2800 m within the Black Sea Mountains. However, these averages are not sufficient to represent the former ELA across the mountain. According to the cirque floor elevations, the cirques in the N-sector have a mean elevation of 2760 m, while the cirques in the S-sector have a mean elevation of 3004 m, and there is a 244 m difference between the two sectors. In the NW basin, the cirques start at 2434 m and reach a permanent former ELA level at 2743 m. In the SE basin, on the other hand, the cirques start at 2635 m and become permanent at 2920 m. Aspect had a significant effect on the distribution of other morphological elements associated with the cirques. The N-sector cirques harbor 73.5 % of the cirque lakes and 81.8 % of the rock glaciers. The average depth of the cirques in the northern sector stands at 388 m, whereas it diminishes to 341 m in the southern sector. Negative correlations emerge between former ELA levels and both latitude and distance from the watershed, while positive correlations align with distance from the coast. Based on these correlations and the associated distribution maps, a clear trend emerges: the former ELA diminishes as one travels north, approaches the coast, and encounters decreasing topographic elevations.