Benthic Carbon Mineralization in Hadal Trenches: Insights From In Situ Determination of Benthic Oxygen Consumption

• Published in: Geophysical research letters 2018-03, Vol.45 (6), p.2752-2760
• Main Authors: Luo, Min, Glud, Ronnie N., Pan, Binbin, Wenzhöfer, Frank, Xu, Yunping, Lin, Gang, Chen, Duofu
• Format: Article
• Language: English
• Subjects: Axes (reference lines); Benthic communities; Carbon; carbon mineralization; Diagenesis; Distance; hadal zone; Hot spots; Incubation period; Mineralization; Ocean floor; Oceanic trenches; Organic carbon; Organic matter; Oxygen; Oxygen consumption; Oxygen uptake; Primary production; Sediment; Sediments; terrestrial organic matter; Total organic carbon; total oxygen uptake; Trenches; Tropical climate; Turnover rate; Uptake; Water column; Water depth
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2017GL076232

Hadal trenches have been proposed as depocenters of organic material and hot spots for organic matter mineralization. In this study, we for the first time quantified the total benthic O2 uptake in hadal trenches using in situ chamber incubations. Three trenches in the tropical Pacific were targeted and exhibited relatively high diagenetic activity given the great water depths, that is, the Mariana Trench (2.0 × 102 μmol O2 m−2 d−1, 10,853 m), the Mussau Trench (2.7 ± 0.1 × 102 μmol O2 m−2 d−1, 7,011 m), and the New Britain Trench (6.0 ± 0.1 × 102 μmol O2 m−2 d−1, 8,225 m). Combined with the analyses of total organic carbon and δ13C of total organic carbon in the sediments and previously published in situ O2 microprofiles from hadal settings, we suggest that hadal benthic carbon mineralization partly is governed by the surface production and also is linked to the distance from land. Therefore, we highlight that terrestrial organic matter can be of importance in sustaining benthic communities in some hadal settings. Plain Language Summary Hadal trenches that refer to seafloor areas covered by a water column with depths >6,000 m have been proposed as depocenters of organic material and hot spots for organic matter mineralization. We applied in situ benthic chamber incubation techniques within three trenches in the tropical Pacific Ocean (the Mariana Trench, the Mussau Trench, and the New Britain Trench) and thereby reported the first benthic total O2 uptake rates measured in hadal settings. The benthic carbon mineralization rates generally show a positive correlation with the net primary production in respective provinces and the sedimentary total organic carbon (TOC) level. Analyses of TOC contents and δ13C of TOC indicated a downslope transport of sediment containing a large amount of terrestrial organic matter, possibly via mass‐wasting events to the axis of New Britain Trench off the New Britain Island. Therefore, we speculate that both surface production regimes and the distance from land are closely connected with the benthic carbon mineralization rate at the trench axes. The elevated organic carbon turnover rate may in part result from preferential concentration of relatively labile organic matter in the surface sediments of trench axes or efficient utilization of refractory terrestrial material under extreme pressure. Key Points Total oxygen uptakes were measured for the first time in hadal trenches using in situ benthic chamber incubations Data compi