Development of cold-water coral mounds in the southern Alboran Sea (Western Mediterranean Sea) since the last interglacial

Cold-water coral (CWC) mounds are formed due to the sustained growth of CWCs over geological timescales (thousands to tens of thousands of years). These seabed structures are discovered along continental margins of the Atlantic Ocean and its marginal seas. They are important archives for reconstructing the long-term development of CWCs and coral mounds. However, our knowledge about the coral mound formation and associated sedimentary processes is still limited. In the Mediterranean Sea, most CWC mounds were discovered in the so-called West and East Melilla CWC mound province (WMCP and EMCP, respectively). Particularly, coral mounds in the EMCP are arranged into four sub-clusters, each marked by specific morphologies and dimensions. The coral mound formation in the northern and westernmost sub-clusters of the EMCP has been reconstructed, whereas little is known about the history of coral mounds formation in the other unexplored sub-clusters of the EMCP, as well as the entire WMCP. Therefore, this thesis focuses on the CWC mound development in the southern Alboran Sea and the dominant environmental factors favoring the coral mound formation

Cold-water coral mounds in the southern Alboran Sea (western Mediterranean Sea): Internal waves as an important driver for mound formation since the last deglaciation

Cold-water corals (CWCs) are widely distributed in the entire Alboran Sea (western Mediterranean Sea), but only along the Moroccan margin they have formed numerous coral mounds, which are constrained to the West and the East Melilla CWC mound provinces (WMCP and EMCP). While information already exists about the most recent development of the coral mounds in the EMCP, the temporal evolution of the mounds in the WMCP was unknown up to the present. In this study, we present for the first time CWC ages obtained from four sediment cores collected from different mounds of the WMCP, which allowed to decipher their development since the last deglaciation. Our results revealed two pronounced periods of coral mound formation. The average mound aggradation rates were of 75–176 cm kyr−1 during the Bølling-Allerød interstadial and the Early Holocene, only temporarily interrupted during the Younger Dryas, when aggradation rates decreased to <45 cm kyr−1. Since the Mid Holocene, mound formation significantly slowed-down and finally stagnated until today. No living CWCs thrive at present on the mounds and some mounds became even buried. The observed temporal pattern in mound formation coincides with distinct palaeoceanographic changes that significantly influenced the local environment. Within the Alboran Sea, enhanced surface ocean productivity and seabed hydrodynamics prevailed during the Bølling-Allerød and the Early Holocene. Only with the onset of the Mid Holocene, the area turned into an oligotrophic setting. The strong hydrodynamics during the mound formation periods are most likely caused by internal waves that developed along the water mass interface between the Modified Atlantic Water and the Levantine Intermediate Water. In analogue to observations from modern CWC settings, we assume that internal waves created turbulent hydrodynamic conditions that increased the lateral delivery of particulate material, promoting the availability of food for the sessile CWCs. Overall, our data point to the dominant role of the water column structure in controlling the proliferation of CWCs and hence the development of coral mounds in the southern Alboran Sea

Deglacial biogenic opal peaks revealing enhanced Southern Ocean upwelling during the last 513 ka

Strength of Southern Ocean upwelling controls the exchange of carbon dioxide (CO2) between deep ocean reservoirs and atmosphere, as well as the communication of dissolved silicon with the euphotic zone of the Southern Ocean. The silicon supply could limit diatom opal productivity in the high-latitudes of Southern Ocean and the subsequent burial of biogenic opal in underlying sediments. Here we report a record of biogenic opal export off the Prydz Bay south of the polar front of the Southern Ocean, indicating strengthened upwelling during the past five glacial terminations. In all five terminations (Isingle bondV), opal peaks occur in line with Northern Hemisphere summer insolation intensity as well as the existing IRDs, indicating that freshwater injection associated with retreat of the Northern Hemisphere ice sheets could be the cause of enhanced upwelling in the Southern Ocean during terminations. This could in turn promote CO2 outgassing, finally accelerating the completion of the terminations. In addition, the enhanced upwelling could export the Si-rich deep water to low latitudes via Antarctic Intermediate Water (AAIW) and Subantarctic Mode Water (SAMW), potentially leading to deglacial opal peaks in subtropical North Atlantic

Entwicklung von Kaltwasserkorallenhügeln in der südlichen Alboran See (westliches Mittelmeer) seit dem letzten Interglazial

Cold-water coral (CWC) mounds are formed due to the sustained growth of CWCs over geological timescales (thousands to tens of thousands of years). These seabed structures are discovered along continental margins of the Atlantic Ocean and its marginal seas. They are important archives for reconstructing the long-term development of CWCs and coral mounds. However, our knowledge about the coral mound formation and associated sedimentary processes is still limited. In the Mediterranean Sea, most CWC mounds were discovered in the so-called West and East Melilla CWC mound province (WMCP and EMCP, respectively). Particularly, coral mounds in the EMCP are arranged into four sub-clusters, each marked by specific morphologies and dimensions. The coral mound formation in the northern and westernmost sub-clusters of the EMCP has been reconstructed, whereas little is known about the history of coral mounds formation in the other unexplored sub-clusters of the EMCP, as well as the entire WMCP. Therefore, this thesis focuses on the CWC mound development in the southern Alboran Sea and the dominant environmental factors favoring the coral mound formation