Cold-water coral ecosystems represent a worldwide distributed carbonate factory, which is so far not considered in global carbonate budget estimations. The herein presented study evaluates the carbonate budget of a complete cold-water coral mound sequence from Challenger Mound (Belgica Mound Province, Porcupine Seabight, SW offshore Ireland; drilled during IODP Expedition 307) reaching back to the Late Pliocene (< 2.7 Ma) especially focusing on the different carbonate sources (coral-derived aragonite versus background-sediment-derived calcite-dominated carbonate). Cores from adjacent drift deposits were examined for comparison studies. Challenger Mound, which developed in a fast growth phase (unit M1; ~ 2.7 to ~ 1.6 Ma) and a slower growth phase or mound-decline (unit M2; ~ 0.8 Ma until today), separated by a so called 'mound crisis', displays increased carbonate accumulation rates for both phases (17.3 g/(cm2 × ka) for unit M1 and 5.7 g/(cm2 × ka) for unit M2) compared to adjacent drift deposits. But only about 33 to 40 wt.% of the carbonate is derived from corals. Bulk sedimentation rates of on- and off-mound deposits suggest a decline of Challenger Mound since the onset of drift deposition in the area about 1.2 Ma ago. Yet total carbonate accumulation rates as well as hemipelagic Background-Sediment-Derived Carbonate accumulation rates from Challenger Mound (unit M2) still exceed the carbonate accumulation rates of the adjacent drift deposits. The selective enrichment of Background-Sediment-Derived Carbonate (by a factor of 2.0) in a CWC Mound is herein observed for the first time. This might be caused by the different hydrodynamic behaviour and slower settlement of marine fluff rich in calcareous detritus, compared to siliciclastic sediments, and its effective baffling by the coral framework and/or the active catch of the calcareous plankton by the corals. The carbonate accumulation rates of Challenger Mound are about 4 to 12% of the carbonate accumulation rates of tropical shallow-water reefs but exceeds the carbonate accumulation rates of continental slopes by a factor of 3.9 to 11.8. The carbonate production for the entire Belgica Mound Province is estimated with 3.2 × 103 t/a for unit M1 and 1.0 × 103 t/a for unit M2.
All Science Journal Classification (ASJC) codes
- Geochemistry and Petrology