Benthic carbon mineralization in hadal trenches: Assessment by in situ O2 microprofile measurements

• Published in: Deep-sea research. Part I, Oceanographic research papers Oceanographic research papers, 2016-10, Vol.116, p.276-286
• Main Authors: Wenzhöfer, F., Oguri, K., Middelboe, M., Turnewitsch, R., Toyofuku, T., Kitazato, H., Glud, R.N.
• Format: Article
• Language: English
• Subjects: Abyssal zones; Benthic carbon mineralization; Benthic O2 uptake; Carbon; Consumption; Deep sea; Deep sea environments; Hadal trenches; in situ; Lander technology; Marine; O2 microrpofiles; Sediments; Surface water; Trenches
• ISSN: 0967-0637; 1879-0119
• DOI: 10.1016/j.dsr.2016.08.013

Hadal trenches are considered to act as depo-centers for organic material at the trench axis and host unique and elevated biomasses of living organisms as compared to adjacent abyssal plains. To explore the diagenetic activity in hadal trench environments we quantified in situ benthic O2 consumption rates and sediment characteristics from the trench axis of two contrasting trench systems in the Pacific Ocean; the Izu-Bonin Trench underlying mesotrophic waters and the Tonga Trench underlying oligotrophic waters. In situ oxygen consumption at the Izu-Bonin Trench axis site (9200m; 746±103µmolm−2d−1; n=27) was 3-times higher than at the Tonga Trench axis site (10800 m; 225±50µmolm−2d−1; n=7) presumably reflecting the higher surface water productivity in the Northern Pacific. Comparing benthic O2 consumption rates measured in the central hadal Tonga Trench to that of nearby (60km distance) abyssal settings (6250m; 92±44µmolm−2d−1; n=16) revealed a 2.5 higher activity at the trench bottom. Onboard investigations on recovered sediment furthermore revealed that the prokaryotic abundance and concentrations of phytopigments followed this overall trend (i.e minimum values at the abyssal site followed by higher values from the Tonga and Izu-Bonin Trenches axis, respectively). Excess 210Pb profiles suggested that mass-wasting events contributed to the deposition of material enhancing the concentration of organic matter in the central trench as compared to the abyssal settings. Our results complement recent findings from the Challenger deep in the Mariana Trench area, which also revealed elevated diagenetic activity in the central trench underpinning the importance of hadal ecosystems for the deep sea carbon cycling. •Trench axis sediments host elevated benthic oxygen consumption rates.•Down-slope material transport fuel benthic communities with labile matter.•Benthic hadal diagenetic activity is linked to regional pelagic primary production.•Trench bottom sediments show elevated prokaryotic abundances.