Hadal trenches are dynamic hotspots for early diagenesis in the deep sea

Ronnie N Glud,Morten Larsen,Frank Wenzhöfer,Heather A Stewart,Anni Glud,Alan J Jamieson,Bo Thamdrup,Peter Berg,Ashley A Rowden,Kazumasa Oguri,Hamed Sanei

doi:10.1038/s43247-020-00087-2

Abstract

The deepest part of the global ocean, hadal trenches, are considered to act as depocenters for organic material. Relatively high microbial activity has been demonstrated in the deepest sections of some hadal trenches, but the deposition dynamics are thought to be spatially and temporally variable. Here, we explore sediment characteristics and in-situ benthic oxygen uptake along two trenches with contrasting surface primary productivity: the Kermadec and Atacama trenches. We find that benthic oxygen consumption varies by a factor of about 10 between hadal sites but is in all cases intensified relative to adjacent abyssal plains. The benthic oxygen uptake of the two trench regions reflects the difference in surface production, whereas variations within each trench are modulated by local deposition dynamics. Respiratory activity correlates with the sedimentary inventories of organic carbon and phytodetrital material. We argue that hadal trenches represent deep sea hotspots for early diagenesis and are more diverse and dynamic environments than previously recognized.

Highlights

The deepest part of the global ocean, hadal trenches, are considered to act as depocenters for organic material
Reliable sample recovery from great depth can be confounded by severe artefacts related to shifts in hydrostatic pressure and transient heating, which may compromise the assessment of biological activity and early diagenesis in recovered sediment[15,16,17]
While the diffusion mediated O2 uptake (DOU) only represent about 50% of the total O2 uptake in fauna-rich coastal sediments, parallel measurements down to 4000 m depth have shown that the total and the diffusive mediated O2 consumption rates converge with increasing water depth as macrofauna biomass attenuates, and rates of these two measures become statistically indifferent at deep sea settings[18]

Summary

Introduction

The deepest part of the global ocean, hadal trenches, are considered to act as depocenters for organic material. Recent in situ measurements in the deepest sedimentary basins of trenches suggest that this pattern might be reversed in the hadal realm, and that intensified deposition of organic matter could enhance biological activity and benthic carbon mineralization at these sites[13,19,20].

Results

Conclusion