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

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.

Spatial variability of prokaryotic and viral abundances in the Kermadec and Atacama Trench regions

“…For the Kermadec Trench, we restricted this abundance assessment to sediment cores with intact surfaces (K4, K6). These two sites represented the higher and lower bounds of the observed range in in situ benthic O 2 uptake along the trench axis (Glud et al 2021) and we thus assume that they represent the full range of prokaryotic and viral abundance at our Kermadec Trench sites. Viral abundances were in a similar range of 1.1 × 10 8 to 5.7 × 10 8 viruses mL −1 and 1.1 × 10 7 to 7.9 × 10 8 viruses mL −1 for Kermadec Trench and Atacama Trench surface sediment, respectively (Fig.…”

Respiration by “marine snow” at high hydrostatic pressure: Insights from continuous oxygen measurements in a rotating pressure tank

“…However, also the newly attached microorganisms will encounter higher pressure levels to which they are not adapted (Tholosan et al 1999 ; Grossart and Gust 2009 ; Marietou and Bartlett 2014 ), especially if the sinking speed of mineral‐ballasted aggregates increases in the bathypelagic zone (Berelson 2002 ; Fischer and Karakas 2009 ). Irrespective of the ultimate extent of inhibition of organic carbon degradation in sinking aggregates, the pressure‐adapted microbial communities in hadal sediments possess the proven potential to degrade the settling aggregates at high rate (Glud et al 2013 ; Glud et al 2021 ).…”

“…Two common observations question the general validity of the “Martin curve.” First, the vertical POC flux determined with sediment traps is often lower than the deep‐sea carbon demand (Martin et al 1987 ; Aristegui et al 2009 ; Herndl and Reinthaler 2013 ). Second, there are surprising records of relatively fresh organic matter and viable phytoplankton very deep in the ocean (Lochte and Turley 1988 ; Smith et al 1996 ; Danovaro et al 2003 ; Boetius et al 2013 ; Glud et al 2013 ; Agusti et al 2015 ; Thomsen et al 2017 ; Glud et al 2021 ). Several mechanisms have been proposed as to why the attenuation of the vertical POC flux is weaker than predicted by the “Martin curve,” such as (1) the occurrence of nonsinking particles that are not readily collected by sediment traps (Martin et al 1987 ; Herndl and Reinthaler 2013 ; Belcher et al 2016 ), (2) the existence of “particle injection pumps” that supplement the gravitational sinking of particles (Boyd et al 2019 ), (3) the significance of primary production through chemosynthesis in the aphotic zone (Aristegui et al 2009 ; Tamburini et al 2009 ; Herndl and Reinthaler 2013 ), and (4) the inhibitory effect of hydrostatic pressure on organic carbon degradation in sinking particles (Turley 1993 ; Tamburini et al 2006 ; de Jesus Mendes et al 2007 ).…”

Hadal Mud Dragons: First Insight Into the Diversity of Kinorhyncha From the Atacama Trench

“…Nonetheless, studies conducted in hadal trenches have revealed relatively abundant benthic communities, particularly meiofauna (Danovaro et al, 2002;Schmidt and Martínez Arbizu, 2015;Leduc et al, 2016). Many hadal trenches are close to land and receive organic inputs from terrestrial and coastal sources, increasing microbial activity (Wenzhöfer et al, 2016;Glud et al, 2021) and supporting higher benthic densities than expected for greater depths (Danovaro et al, 2002;Jamieson et al, 2010). In addition, the persistent rain of particulate organic matter (POM) from the surface layers is deposited along the trench axis (von Huene and Scholl, 1991;Turnewitsch et al, 2014).…”

“…In addition, the persistent rain of particulate organic matter (POM) from the surface layers is deposited along the trench axis (von Huene and Scholl, 1991;Turnewitsch et al, 2014). Among others, the Atacama Trench underlies one of the most productive surface waters, which results in high total trench POC flux (Steward and Jamieson, 2018;Glud et al, 2021), reduced sediment grain size and exceptionally high meiofaunal abundance at hadal depths (7800 m) (Danovaro et al, 2002). As reported by Danovaro et al (2002), abundance of all meiofauna taxa were notably higher at hadal station in comparison with bathyal depths, and this trend also includes the kinorhynchs (0.2 ± 0.3 and 46 ± 40 ind./10 cm 2 , at 1050 and 7800 m, respectively).…”