Habitat heterogeneity of hadal trenches: Considerations and implications for future studies

Heather A Stewart,Alan J Jamieson

doi:10.1016/j.pocean.2018.01.007

Heather A Stewart, Alan J Jamieson

Open Access

https://doi.org/10.1016/j.pocean.2018.01.007

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Abstract

The hadal zone largely comprises a series of subduction trenches that do not form part of the continental shelf-slope rise to abyssal plain continuum. Instead they form geographically isolated clusters of deep-sea (6000–11,000 m water depth) environments. There is a growing realization in hadal science that ecological patterns and processes are not driven solely by responses to hydrostatic pressure, with comparable levels of habitat heterogeneity as observed in other marine biozones. Furthermore, this heterogeneity can be expressed at multiple scales from inter-trench levels (degrees of geographical isolation, and biochemical province), to intra-trench levels (variation between trench flanks and axis), topographical features within the trench interior (sedimentary basins, ridges, escarpments, ‘deeps’, seamounts) to the substrate of the trench floor (seabed-sediment composition, mass movement deposits, bedrock outcrop). Using best available bathymetry data combined with the largest lander-derived imaging dataset that spans the full depth range of three hadal trenches (including adjacent slopes); the Mariana, Kermadec and New Hebrides trenches, the topographic variability, fine-scale habitat heterogeneity and distribution of seabed sediments of these three trenches have been assessed for the first time. As well as serving as the first descriptive study of habitat heterogeneity at hadal depths, this study also provides guidance for future hadal sampling campaigns taking into account geographic isolation, total trench particulate organic matter flux, maximum water depth and area.

Highlights

The hadal zone differs somewhat from shallower marine environments because it is not a direct continuation of the preceding biozones per se, but rather the descending continuum from the coasts over the continental slopes and rises onto the abyssal plains eventually fragment into clusters of often vastly isolated hadal areas of varying size, depth, length, latitude and seismicity
Of the 34 subduction trenches and trench faults, 26 are located in the Pacific Ocean (76%), with three of the 13 hadal troughs (23%) located in the Pacific Ocean
The geographic distance matrix calculated in kilometres, for each point, for all combinations, from a database of deepest points of the 27 subduction trenches (Table 2), 13 troughs and seven trench faults between 6000 m water depth and full ocean depth

Summary

Introduction

The hadal zone (water depths exceeding 6000 m) differs somewhat from shallower marine environments (littoral; < 200 m, bathyal; 200–2000 m and abyssal; 2000–6000 m; Gage and Tyler, 1991) because it is not a direct continuation of the preceding biozones per se, but rather the descending continuum from the coasts over the continental slopes and rises onto the abyssal plains eventually fragment into clusters of often vastly isolated hadal areas of varying size, depth, length, latitude and seismicity These areas combined total over 800,000 km−2 and represents the deepest 45% of the global ocean (Jamieson et al, 2010). Despite a range of diverse deep-sea technological capabilities that are possible (Danovaro et al, 2014), full ocean depth rated instruments and vehicles are

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