Phylogenetically and functionally diverse microorganisms reside under the Ross Ice Shelf

Clara Martínez-Pérez,Federico Baltar,Rachael J Lappan,José M González,Ramiro Logares,Ramunas Stepanauskas,Daniele De Corte,Sergio E Morales,Craig Stevens,Christian Ohneiser,Sean K Bay,Gerhard J Herndl,Christina Hulbe,Chris Greening,Zihao Zhao,Blair Thomson

doi:10.1038/s41467-021-27769-5

Abstract

Throughout coastal Antarctica, ice shelves separate oceanic waters from sunlight by hundreds of meters of ice. Historical studies have detected activity of nitrifying microorganisms in oceanic cavities below permanent ice shelves. However, little is known about the microbial composition and pathways that mediate these activities. In this study, we profiled the microbial communities beneath the Ross Ice Shelf using a multi-omics approach. Overall, beneath-shelf microorganisms are of comparable abundance and diversity, though distinct composition, relative to those in the open meso- and bathypelagic ocean. Production of new organic carbon is likely driven by aerobic lithoautotrophic archaea and bacteria that can use ammonium, nitrite, and sulfur compounds as electron donors. Also enriched were aerobic organoheterotrophic bacteria capable of degrading complex organic carbon substrates, likely derived from in situ fixed carbon and potentially refractory organic matter laterally advected by the below-shelf waters. Altogether, these findings uncover a taxonomically distinct microbial community potentially adapted to a highly oligotrophic marine environment and suggest that ocean cavity waters are primarily chemosynthetically-driven systems.

Highlights

Throughout coastal Antarctica, ice shelves separate oceanic waters from sunlight by hundreds of meters of ice
Triplicate samples were collected at three depths: 30, 180, and 330 m below the bottom of the shelf. These depths correspond to three regions based on the thermohaline structure of the water column: a basal boundary layer just beneath the ice (IBL), the upper part of an intermediate layer characterized by highly variable temperature and salinity (V-IL), and the lower part of the intermediate layer characterized by linear stratification (S-IL)
Collectively, our results provide a detailed insight on the ecological strategies adopted by communities living in the world’s most extensive sub-ice shelf system

Summary

Introduction

Throughout coastal Antarctica, ice shelves separate oceanic waters from sunlight by hundreds of meters of ice. Enriched were aerobic organoheterotrophic bacteria capable of degrading complex organic carbon substrates, likely derived from in situ fixed carbon and potentially refractory organic matter laterally advected by the below-shelf waters These findings uncover a taxonomically distinct microbial community potentially adapted to a highly oligotrophic marine environment and suggest that ocean cavity waters are primarily chemosynthetically-driven systems. Waters under the permanent ice shelves are influenced by continental ice-sheet melting and are an important intermediary between subglacial outflow from the Antarctic continent and the open Ross Sea, and the Southern Ocean Despite their oceanographic significance, sub-ice shelf habitats are among the least-studied ecosystems in the world’s oceans. The environment beneath the Ross Ice Shelf was described as “similar to the abyssal ocean in being cold and aphotic” Within these waters, “sparse” populations of bacteria, microbial eukaryotes, and animals were observed[10,11]. We observed the transcription of various genes associated with lithoautotrophic and organoheterotrophic growth, uncovering the basis for previous activities reported in below-shelf waters

Methods

Results

Conclusion