Cold-water coral mound development underneath an eastern boundary upwelling system - the great wall of(f) Mauritania
Final Report Abstract
The DFG-project focused on the reconstruction of the long-term spatio-temporal coral mound development within the 240-km-long Mauritanian coral mound province and the environmental and oceanographic conditions controlling their formation. The obtained results provide the following new insights into the development of this coral mound province and coral mound formation in general: Coral mound formation within the Mauritanian coral mound province shows a highly diachronous pattern between the two mound chains as well as along its latitudinal expansion. Even neighbouring coral mounds exhibit temporally significant differences in their time of formation.- Mean mound aggradation rates are lower and show less variability for the northern coral mounds compared to the south. High aggradation rates are restricted to coral mounds from the Tamxat mound complex in the south. - Independent from their spatial position or their time of formation, almost all coral mounds exhibited comparable very well confined temperature, salinity, dissolved oxygen and food conditions during their formation phases, which suggest a specific oceanographic situation during their formation. Only the youngest mound formation phase within the southern deeper mound chain exhibited colder and fresher conditions with a reduced bottom water oxygenation. This mound formation phase points clearly to a second oceanographic configuration that was favourable for coral mound formation and highlights that the interplay of several environmental parameters is responsible for coral mound formation and that various configurations might be favourable to foster their formation. - The comparison of both sediment cores adjacent to the coral mounds suggest an increased salinitydriven density differentiation of the South and North Atlantic Central Water (SACW,NACW) during the last glacial (21 – 60 ka). - Comparing all proxy records from coral-mounds and the adjacent seafloor clearly suggest (i) the presence of the SACW/NACW water mass boundary during phases of coral mound formation; (ii) improved oxygen and food supply conditions at the coral mound core sites compared to the adjacent seafloor core sites, and (iii) an enrichment of fine siliciclastic sediment within the coral mounds highlighting the baffling efficiency of the coral framework during mound formation. - According to the TraCE-21k simulation, phases of a strengthened Atlantic Meridional Overturning Circulation (AMOC; e.g., Bølling-Allerød, Last Glacial Maximum) are characterised by high Glacial North Atlantic Intermediate Water production linked to southward strengthened NACW transport that resulted, combined with the enhance NACW-SACW density differentiation, in the underriding of the NACW below the SACW – an oceanographic configuration that was favourable for coral mound formation off Mauritania. In contrast, phases of weakened AMOC resulted in a regional predominance of SACW that hindered mound formation – a scenario that could clearly be confirmed for the Heinrich Stadial 1. - The refined methodological approach introduced in this project (the use of coupled proxy records obtained from coral mound and sediment cores retrieved from the adjacent seafloor) proved extremely successful to constrain environmental conditions favourable for coral mound formation in the past and for the reconstruction of the regional palaeoceanography, especially the detection of intermediate-depth water-mass boundaries.
Publications
- (2018) The giant Mauritanian cold-water coral mound province: oxygen control on coral mound formation. Quaternary Science Reviews 185:135-152
Wienberg C, Titschack J, Freiwald A, Frank N, Lundälv T, Taviani M, Beuck L, Schröder-Ritzrau A, Krengel T, Hebbeln D
(See online at https://doi.org/10.1016/j.quascirev.2018.02.012)
