Monsoonal forcing of cold-water coral growth off southeastern Brazil during the past 160 kyr

Abstract

Abstract. Cold-water corals (CWCs) constitute important deep-water ecosystems that are under increasing environmental pressure due to ocean acidification and global warming. The sensitivity of these deep-water ecosystems to environmental change is demonstrated by abundant paleorecords drilled through CWC mounds that reveal characteristic alterations between rapid formation and dormant or erosive phases. Previous studies have identified several central parameters for driving or inhibiting CWC growth such as food supply, oxygenation, and the carbon saturation state of bottom water, yet there are still large uncertainties about the relative importance of the different environmental parameters. To advance this debate we have performed a multiproxy study on a sediment core retrieved from the 25 m high Bowie Mound, located at 866 m water depth on the continental slope off southeastern Brazil, a structure built up mainly by the CWC Solenosmilia variabilis. Our results indicate a multifactorial control on CWC growth at Bowie Mound during the past ∼ 160 kyr, which reveals distinct formation pulses during northern high-latitude glacial cold events (Heinrich stadials, HSs) largely associated with anomalously strong monsoonal rainfall over the continent. The ensuing enhanced runoff elevated the terrigenous nutrient and organic-matter supply to the continental margin and likely boosted marine productivity. The dispersal of food particles towards the CWC colonies during HSs was facilitated by the highly dynamic hydraulic conditions along the continental slope that prevailed throughout glacial periods. These conditions caused the emplacement of a pronounced nepheloid layer above Bowie Mound, thereby aiding the concentration and along-slope dispersal of organic matter. Our study thus emphasizes the impact of continental climate variability on a highly vulnerable deep-marine ecosystem.

Controlling Parameters of Benthic Deep-Sea Foraminiferal Biogeography at the Brazilian Continental Margin (11-22°S)

“…Their high abundances coincide with increased grain sizes (Figure 6), suggesting they prefer constant bottom flow velocities, as already suggested in previous studies (e.g., Schmiedl et al, 1997;de Mello e Sousa et al, 2006). Local occurrences of upper slope contourites as well as CWC mounds in the Campos Basin document an increased bottom current activity in this area as well (Viana, 2001;Viana et al, 2002;Bahr et al, 2020;Raddatz et al, 2020). On the upper slope in the subtropical part of the SACW at 430 m (sample 35) a G. subglobosa/crassa-Nuttalides umbonifer assemblage is adapted to lower nitrogen levels and reduced primary productivity, highlighted in the CCA by TN plotting contrary to it (Figure 6; Gooday, 1994;Gooday, 2003;Margreth et al, 2009;De and Gupta, 2010).…”

Coupled Oceanic and Atmospheric Controls of Deglacial Southeastern South America Precipitation and Western South Atlantic Productivity

“…Thus, it is consistent to assume that a slightly invigorated continental hydrological cycle and particularly a marked low sea level enhanced nutrient and organic matter flux into the western tropical South Atlantic during HS1, boosting oceanic productivity. This proposed link between river run-off and marine productivity further fits to the suggestion that cold-water coral mounds in the vicinity of Core M125-35-3 flourished during times of enhanced organic-matter input from the continent due to enhanced nutrient and organic-matter availability (Bahr et al, 2020). To summarize, we infer that terrestrial siliciclastic sediment and organic-matter flux to the upper slope off the Paraıba do Sul was maximal during HS1 and subsequently declined during the late deglacial and Holocene, largely owing to the rising eustatic sea level and ensuing coastline retreat.…”

Living on the edge: environmental variability of a shallow late Holocene cold-water coral mound

“…Here, ARs were calculated from the maximum and minimum core depths and the corresponding ages of those cluster based on the CT images, thus representing average ARs (Wienberg et al 2018 ; Raddatz et al 2020 ). A prominent issue in CWC mound sediments is the possible age offset between matrix sediment and coral ages (Eisele et al 2014 ; Bahr et al 2020 ). However, for Norwegian CWC mounds it has been shown, by the comparison of matrix (foraminifera) and coral ages, that these are coeval to active periods of mound growth with efficient baffling of sediment by the coral framework (López Correa et al 2012 ).…”