Formation history and material budget of holocene shelf mud depocenters in the Gulf of Cadiz

摘要

Mud depocenters (MDCs) are common elements on modern continental shelves and act as a major shallow-marine sink for fluviogenic material. These most proximal depocenters, thus, play a major role in material cycling and carbon availability on global and regional scales, though individual formation history, dependence on external forcing mechanisms, and material composition makes each of them a unique case. This study establishes a chronostratigraphic framework and deciphers the depositional dynamics for the two main MDCs on the continental shelf in the eastern Gulf of Cadiz, as a prime example, with the goal to calculate a regional sediment and carbon budget. Based on the analysis of 2040 km of subbottom profiles and 18 sediment cores, the fine-grained depocenters began to grow during maximum flooding around 6.5 cal ka BP. Sedimentation rates ranged between 2 and 35 cm/ka until 2.7 cal ka BP and increased significantly around the Roman Warm Period (30-200 cm/ka), caused by regional humidification as well as mining and agricultural activities. After 1.0 cal ka BP, sedimentation rates rose further (20-3000 cm/ka), due to land clearing in coincidence with erosion-favoring aridity during the Islamic period and the Medieval Climate Anomaly. Unprecedented sediment accumulation started with the Industrial Era. The total sediment volume of the two MDCs is 5.80 km~3 with a dry mass of 12,971 Mt. 85 Mt of organic matter and 3637 Mt of carbonate make this depocenter an important shallow-marine sink, with a total of 521 Mt carbon as a significant player in the regional terrestrial-marine carbon cycle.