Persistent oxygen-depleted zones are known primarily from enclosed basins in temperate regions or the open-ocean (including oxygen minimum and limiting zones). However, little is known about the potential for such zones in tropical coastal domains, despite warmer temperatures and complex geomorphological structures in some tropical areas increasing their likelihood. Here, we report two subsurface oxygen-depleted zones within deep depressions of the Red Sea’s Difaht Farasan—a carbonate platform hosting the world’s third-largest contiguous tropical coral reef system3. One zone maintains suboxic oxygen levels (~11-14 µmol kg⁻¹), while the other sustains oxygen levels below detection (<2 µmol kg⁻¹). The suboxic zone shows no fixed nitrogen loss, while the near-anoxic zone hosts anaerobic microbial populations and shows signs of nitrogen loss. We propose that the Red Sea’s warm and saline environment interacts with the semi-enclosed depressions to restrict vertical mixing, limiting oxygen resupply at depth. Yet, unlike most other oxygen-depleted zones, our deep-sea vehicle surveys demonstrate that these zones support resistant aerobically respiring taxa, indicating an unusual capacity to reduce aerobic oxygen demands at high temperatures (>21°C). Targeted exploration of deep tropical coastal environments is crucial to determine if similar zones exist beyond the Red Sea and their potential responses to climate change.
Shannon G. Klein, Larissa Frühe, Anieka J. Parry, Fabio Marchese, Megan K. B. Nolan, Elisa Laiolo, Kah Kheng Lim, Alexandra Steckbauer, Jessica Breavington, Christopher A. Hempel, Kate von Krusenstiern, Froukje M. van der Zwan, Eleonora Re, Taiba Alamoudi, Jacqueline V. Alva Garcia, Silvia Arossa, Carlos Angulo-Preckler, Mattie Rodrigue, Vincent A. Pieribone, Mohammad A. Qurban, Francesca Benzoni, and Carlos M. Duarte.
- Data storage and availability
- Sampling Overview
- Water chemistry data processing
- Sequence data processing
- Data analysis
- Contact
Raw sequencing data can be accessed in the Sequence Read Archive (SRA) of NCBI under PRJNA899789. Bacterial sequences can be downloaded using accession numbers SRR22244354 - SRR22244374 Protist sequences can be downloaded using accession numbers SRR22244609 - SRR22244629 Included in the uploaded bioproject are also metabarcoding reads targeting the COI amplicon, which have not been used in the published paper due to bad quality.
Supplementary files and non-sequencing data can be found the below linked DRYAD repository. https://datadryad.org/stash/share/ndIWIGf28mmJ-nUc5HqPEuqPQggpeTYRjIDaMt5imEQ
All code used to analyse and visualise data is stored in this GitHub repository.
- Code for Pearson correlations analysing the relationship between environmental parameters, Mann-Whitney test analysing fish swimming speeds between site 2 and the open-water reference sites can be found here Statistics_EnvParam&Visuals
- Code for CTD data processing can be found here
- Code for amplicon sequence variant (ASV) inference using DADA2 available in DADA2_Inference
- Code for cleaning and removal of contaminant sequences available in Decontam&Cleaning
Clean data tables as input for data analysis can be accessed via dryad or here https://github.com/lexscience/Klein-2024/blob/main/clean_V3V4.csv for V3V4 SSU rRNA gene bacterial matrix or here https://github.com/lexscience/Klein-2024/blob/main/clean_V4.csv for V4 SSU rRNA gene protists matrix
- Code to produce Figure 3 - Non-metrical multidimensional scaling (NMDS) NMDS_Species and relative abundance taxonomy charts Taxonomy for eDNA metabarcoding datasets is deposited. The accompanying environmental data used for eDNA data anlysis is available here https://github.com/lexscience/Klein-2024/blob/main/samdf.csv
Project lead by Shannon Klein [@DrShannonKlein] - shannon.klein@kaust.edu.sa . Repository created and curated by [@lexscience] - larissa.fruehe@oceanx.org . Feel free to contact us.