Enhanced but highly variable bioturbation around seamounts in the northwest Pacific

Abstract

Seamounts are a unique ecosystem in marine environment, but the relevant understanding is limited. In this study, sedimentation and bioturbation around the Pako Guyot of Magellan, and the Lamont, Scripps, Arnold, and Pot Guyots of Marcus-Wake seamounts in the northwest Pacific were evaluated using 230Thex and 210Pbex as tracers. Our results showed that the linear sedimentation rate and the mass accumulation rate ranged from 0.12 to 2.50 mm/ka and from 0.06 to 1.14 kg/m2/ka with averages of 1.27 ± 0.80 mm/ka and 0.49 ± 0.30 kg/m2/ka respectively. The accumulation flux of organic carbon in surface sediments was estimated to be 0.10–4.52 g C/m2/ka. The bioturbation coefficients ranged from 1.01 to 27.1 cm2/a with an average of 10.8 ± 9.2 cm2/a, which is higher than those in abyssal sediments or predicted by traditional empirical equations. The enhanced bioturbation supports the view that seamounts are hotspots for pelagic and benthic organisms. The bioturbation intensity showed a great variability with the maximum around 40 km away from the edge of seamount summit. The bioturbation coefficient correlated positively with sedimentation rate and accumulation flux of organic carbon in surface sediments, indicating that the supply of organic matter is a main driving force for enhanced bioturbation around the seamounts. The increase in sedimentary organic matter promotes the activities of benthic organisms. More research is needed to gain a deep understanding of bioturbation in seamounts in the context of future climate change.