Formation History and Material Budget of Holocene Shelf Mud Depocenters in the Gulf of Cadiz

Hanebuth, T., King, M.L., Lobo, F.J. & Mendes, I.

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 km3 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.

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