Late Quaternary Development of a deep-water Carbonate Mound in the northeast Atlantic

Abstract

Numerous carbonate mounds have been discovered along the NW European Continental Margin. Many of them are covered by thickets of the ahermatypic corals. To unravel the processes active on the mound, in a case study on Propeller Mound its carbonate budget has been assessed and the mound development has been modelled. In addition benthic foraminiera assemblages have been analysed. Propeller Mound is a ~150m elevated mound in the Porcupine Seabight ca. 90 nautical miles west off South-Ireland. The carbonate budget shows that on Propeller Mound the sediments contain on average >50 wt.-% CaCO3 for the last 175kyrs. In contrast, the sediments from the reference sites off Propeller Mound contain <37 wt.-% CaCO3 for Holocene and <23 wt.-% CaCO3 for glacial sediments. The approximately 30 wt.-% difference between on- and off-mound locations represents the carbonate input due to aragonite added by the corals but extended hiatuses reduce the net long-term CaCO3 accumulation rates on Propeller Mound to ~5% of the off-mound signal. Stable oxygen isotope data, AMS 14C and U/Th ages show that glacial and interglacial sediments were either not deposited or were later eroded on the mound. Instead, almost exclusively interstadial sequences stabilised by loose coral frameworks have been preserved. These sedimentary patterns may be linked to the changing influence of Mediterranean Outflow Water at the mound location. Distinct similarities between benthic foraminiferal assemblages found on-mound with assemblages found in the Mediterranean Sea also point towards a link between MOW and the mound. This interactions result in a spatially and temporally complex sedimentary record on Propeller Mound, impossible to correlate.In contrast to on mound sediments, those deposited in the areas adjacent to Propeller Mound contain more or less continuous records. The discrepancy between on and off-mound sediments imply that at least for the last ~300kyrs Propeller Mound has been shrinking.