IODP Expedition 307 Drills Cold-Water Coral Mound Along the Irish Continental Margin

Abstract

Introduction Over the past decade, oceanographic and geophysical surveys along the slope of the Porcupine Seabight off the southwestern continental margin of Ireland have identified upwards of a thousand enigmatic mound-like structures (Figs. 1 and 2). The mounds of the Porcupine Seabight rise from the seafl oor in water depths of 600–900 m and formimpressive conical bodies several kilometers wide and up to 200 m high. Although a few mounds such as Thérèse Mound and Galway Mound are covered by a thriving thicket of coldwater corals, most mound tops and fl anks are covered by dead coral rubble or are entirely buried by sediment (De Mol et al., 2002; Fig. 2, Beyer et al., 2003). Lophelia pertusa (Fig.3) and Madrepora oculata are the most prominent cold-water corals growing without photosynthetic symbionts. The widespread discovery of large and numerous coral-bearing banks and the association of these corals with the mounds have generated signifi cant interest as to the composition, origin and development of these mound structures.Challenger Mound, in the Belgica mound province, has an elongated shape oriented along a north-northeast to south-southwest axis and ispartially buried under Pleistocene drift sediments. In high-resolution seismic profiles the mounds appear to root on an erosion surface (van Rooij et al., 2003). During IODP Expedition307 the Challenger Mound in the Porcupine Seabight was drilled with the goal of unveiling the origin and depositional processes withinthese intriguing sedimentary structures. Challenger Mound, unlike its near neighbors the Thérèse and Galway mounds, has little to no livecoral coverage and, therefore, was chosen as the main target for drilling activities, so that no living ecosystem would be disturbed

Carbonate mounds in shallow and deep time

“…In general, the biomarker data show lower abundance of past microbial communities in the mound section compared to the sediments below the mound base and from the reference site. Biomarkers for living microbial populations were not detected in the mound sequence, which is in coherence with relatively low cell count data (Ferdelman et al, 2006). Methane, ethane and propane were detected below the mound.…”

“…Meanwhile, IODP Expedition 307 on Challenger Mound in Porcupine Seabight off Ireland had drilled and sampled in detail a full mound section (Ferdelman et al, 2006;Kano et al, 2007;Foubert and Henriet, 2009), IOC-UNESCO had launched the Geosphere-Biosphere Coupling processes (GBCP) programme with a focus on capacity building around mound research, mound scientists had teamed up in projects like CARBONATE (ESF EuroMARC -Carbonate mound drilling at mid-latitudes) and with microbiologists in MiCROSYSTEMS (ESF EuroDIVERSITY -Microbial Diversity and Functionality in Cold-water Coral Ecosystems) and microbialites were found to form a substantial component… of sub-recent tropical reefs (IODP Tahiti Exp. 310, ESF EuroMARC project CHECREEF)!…”

Subsurface microbiology and biogeochemistry of a deep, cold‐water carbonate mound from the Porcupine Seabight (IODP Expedition 307)

“…The Challenger Mound (781–815 m water depth) is a prominent mound structure, 155 m in height and partially buried with sediment and dead cold-water coral ( Lophelia pertusa ) rubble (Ferdelman et al ., 2006). It is one of 66 mounds which make up the Belgica Mound Province in the Porcupine Seabight on the south-west Irish continental margin (Ferdelman et al ., 2006; Fig.…”

“…Seismic profiles have shown that some mounds are covered by tens of metres of sediment or dead coral rubble (De Mol et al ., 2002; Huvenne et al ., 2007) and others are slowly being buried (e.g. Challenger Mound, Ferdelman et al ., 2006). There are also living mounds with a thriving community of cold-water corals ( Lophelia pertusa and Madrepora oculata ) in close association with other organisms as part of a diverse cold-water coral reef ecosystem (De Mol et al ., 2007).…”

“…During the Integrated Ocean Drilling Program (IODP) Expedition 307 (Ferdelman et al ., 2006) the first complete section through a modern cold-water coral mound, and to beneath its base, was recovered from the Challenger Mound in the Belgica Mound Province of the Porcupine Seabight. The objectives of Expedition 307 were to test whether: (i) gas seeps acted as a prime trigger for mound genesis, (ii) prominent erosional surfaces reflected global oceanographic events, (iii) the mound is a high-resolution palaeoenvironmental recorder, and (iv) these mounds are present-day analogues for Phanerozoic reef and mud mounds.…”