Numerous Sublinear Sets of Holes in Sediment on the Northern Mid-Atlantic Ridge Point to Knowledge Gaps in Understanding Mid-Ocean Ridge Ecosystems

Michael Vecchione,Odd Aksel Bergstad

doi:10.3389/fmars.2022.812915

Abstract

On 13 July 2004, during an expedition exploring biodiversity along the northern Mid-Atlantic Ridge, an ROV dive recorded videos of numerous sublinear sets of holes in sediment at ca. 2,082 m depth. The location was north of the Azores. Each set appeared track-like. Lengths of individual series ranged from &lt; 1 m to many meters. Each was straight or gently curved. Some series intersected or crossed. Close examination of the holes showed them to be elongate, with the long axis parallel to the axis of the series. The holes were ca. 6 × 1.5 cm, with distance between holes similar to hole length. The holes that appeared to be most recently formed were each surrounded by raised sediment. Holes that appeared older were partly filled with sediment and the raised surrounding sediment was less obvious. Overall, these lebensspuren created small-scale heterogeneity in the local soft-bottom benthic ecosystem. The source of the holes or how they were constructed is unknown, but the raised sediment may indicate excavation by an infaunal organism or digging and removal by e.g., a feeding appendage of a large epifaunal animal. None of our closeups showed any sign of living organisms inhabiting the holes. Whether the holes were connected beneath the sediment surface was not visible. The traces observed are reminiscent of ichnofossils reported from deep marine facies. We hope that future studies of the lebensspuren we report here will resolve the mystery of what created them.

Highlights

The accumulation of pelagic detritus at the sediment-water interface
At one of the sediment-covered MAR-ECO locations, we encountered numerous widespread lebensspuren in a pattern that seemed reminiscent of tracks from an unknown animal
On 13 July 2004, remotely operated vehicles (ROVs) Bathysaurus was used to explore benthic habitats centered around 2,082 m depth in the vicinity of 42◦ 56 N 028◦ 36 W (Figure 1)

Summary

Introduction

The accumulation of pelagic detritus at the sediment-water interface. lebensspuren are often the only indication in visual surveys of the presence of infaunal or mobile animals capable of avoiding camera platforms. One field project within CoML, entitled Patterns and Processes of the Ecosystem of the Northern mid-Atlantic (MARECO), focused on the Mid-Atlantic Ridge between Iceland and the Azores (Bergstad et al, 2008; Vecchione et al, 2010) using a broad suite of methods (Wenneck et al, 2008). Often thought of as primarily hard substrate, the Mid-Atlantic Ridge is largely covered with sediment (Niedzielski et al, 2013; Priede et al, 2013a). At one of the sediment-covered MAR-ECO locations, we encountered numerous widespread lebensspuren in a pattern that seemed reminiscent of tracks from an unknown animal. We describe here those traces in the sediment and consider their similarity to ichnofossils

Methods

Results

Conclusion