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.
Highlights
We argue that the most dominant environmental factor for triggering Cold-water corals (CWCs) growth was elevated river runoff during periods of strong monsoonal rainfall in the coastal hinterland, which provided nutrients and organic matter that enhanced the food supply of CWC colonies
Bowie Mound lies within the Antarctic Intermediate Water (AAIW), which probably boosted CWC growth at the eastern Brazilian slope
In the case of Bowie Mound, it is possible that enhanced production (Pahnke and Zahn, 2005; Pahnke et al, 2008) and/or nutrientenrichment of the AAIW (Poggemann et al, 2017) during phases of weak Atlantic Meridional Overturning Circulation (AMOC) could have triggered its episodic formation phases
Summary
Cold-water corals (CWCs) are hotspots of biodiversity in the deep-sea (Roberts and Cairns, 2014), important constituents of the deep-water carbon cycle (Lindberg and Mienert, 2005; Titschack et al, 2009, 2015, 2016; White et al, 2012; Cathalot et al, 2015), and potent bioengineers due to their sediment-baffling capacity that allows for enormous sediment accumulation rates of up to 1500 cm kyr−1 during maximum CWC mound formation phases (Titschack et al, 2015; Wienberg and Titschack, 2017, Wienberg et al, 2018). Changes in the properties and spatial configuration of ambient intermediate- or deep-water masses may strongly impact CWCs through changes in the dissolved oxygen concentration and the seawater parameters pH, alkalinity, and carbonate-ion concentration. All these parameters affect the capacity of CWCs to build their aragonitic framework (e.g., Form and Riebesell, 2012; Maier et al, 2012; Lunden et al, 2014; Hennige et al, 2015; Büscher et al, 2017; Auscavitch et al 2020). Despite the proximity of CWC mounds situated on the continental slope to adjacent continents, the role of terrestrial nutrient and POC input is still a matter of debate (Wienberg et al, 2010; Hanz et al, 2019; Fentimen et al, 2020)
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