DOI: 10.5061/dryad.9w0vt4bq4
title: Data from: Deep oxygen-depleted Red Sea coral reef depressions sustain resistant ecosystems

description: Persistent oxygen-depleted zones in the ocean 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
 the likelihood of their existence. 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 system. One zone maintains suboxic oxygen levels
 (~11-14 µmol kg⁻¹), while the other sustains oxygen levels below detection
 (&lt;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 warm and saline environment of
 the Red Sea interacts with the semi-enclosed depressions to restrict
 vertical mixing, limiting oxygen resupply at depth. However, 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
 (&gt;21°C). Targeted exploration of deep tropical coastal environments
 is crucial for determining if similar zones exist beyond the Red Sea and
 understanding their potential responses to climate change.
description: # Data from: Deep oxygen-depleted Red Sea coral reef depressions sustain
 resistant ecosystems (Published in PNAS Nexus) **Authors:** 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 A. Preckler, Mattie Rodrigue, Vincent A. Pieribone, Mohammad A.
 Qurban, Francesca Benzoni, and Carlos M. Duarte Correspondence: Shannon G.
 Klein; [shannon.klein@kaust.edu.sa](mailto:shannon.klein@kaust.edu.sa) The
 associated dryad repository contains ten files: ## Supplementary Data File
 1 This file contains 5 columns and is the source data file for Figure
 2(a-c) of the associated publication. Data represent the full depth
 profiles of dissolved oxygen, temperature, and salinity within two deep
 depressions of the Farasan Bank, Saudi Arabia (sites 1 and 2). Site 1 =
 Farasan Deep and Site 2 = Amq Deep. The columns are as follows: *Site is
 the site identifier (site 1 versus site 2) *Depth_m is the water depth (in
 meters) at which the data were measured *Temperature_C is temperature (in
 degrees celsius) *O2_umol_kg is dissolved oxygen (in micro mol per kg)
 *Salinity_psu is salinity (in psu) ## Supplementary Data File 2 This file
 contains 20 columns and is the source data file for Figure 2(d-l) of the
 associated publication. Columns 1 - 9 are descriptors. Columns 9 - 10 are
 data that were measured in situ, columns 11- 13 and columns 17-20 are data
 that were measured directly from discrete water samples. Columns 14 -16
 are data that were calculated based on modelling of the seawater carbonate
 system, according to the 'seacarb' package in R. Site 1 =
 Farasan Deep and Site 2 = Amq Deep. *Date (dd/mm/yyyy) when the in situ
 data were collected *Latitude (decimal form) at which the in situ data
 were collected and discrete samples were taken for further analyses
 *Longitude (decimal form) at which the in situ data were collected and
 discrete samples were taken for further analyses *Site is the site
 identifier (site 1 versus site 2) *Niskin_number is the Niskin bottle
 identifier (1, 2, 3, or 4) for discrete samples *Niskin_depth_m is the
 water depth (in meters) at which the Niskin was closed to collect the
 discrete seawater samples *Sample_ID is the replicate identifier for
 discrete samples taken from each Niskin *Asset_used refers to the
 oceanographic asset used to collect the discrete water samples
 (oceanographic rosette, manual deployment, manned submersible, or remotely
 operated vehicle) *Temperature_C is temperature in degrees celsius, which
 was measured in situ via CTD deployment *Salinity_psu is temperature in
 psu, which was measured in situ via CTD deployment *O2_winkler_umol_kg is
 dissolved oxygen (in micro mol per kg) measured via an automated Winkler
 titration method *TA_umol_kg is total alkalinity (in micro mol per kg)
 measured on discrete water samples *DIC_umol_kg is dissolved inorganic
 carbon (in micro mol per kg) measured on discrete water samples *pCO2_uatm
 is the calculated partial pressure of carbon dioxide *Omega_Ar is the
 calculated aragonite saturation state *pH_total is the calculated pH
 (total scale) *Silica_umol_l is silica (in micro mol per liter)
 *Nitrite_umol_l is nitrite (in micro mol per liter) *Nitrate_umol_l is
 nitrate (in micro mol per liter) *Phosphate_umol_l is phosphate (in micro
 mol per liter) *Cells with "n/a" indicate unavailable data. ##
 Supplementary Data File 3 This file contains 4 columns and is the source
 data file for Supplementary Fig.  9 of the associated publication. These
 data were used to compare oxygen measurements with the dual SBE 43
 polarographic oxygen sensors (sensor 1 and sensor 2), across sites 1 and 2
 and along the full depth gradients. Site 1 = Farasan Deep and Site 2 = Amq
 Deep. *Site is the site identifier (site 1 versus site 2) *Depth_m is the
 water depth (in meters) at which the data were measured *O2_SBE_sensor 1
 is dissolved oxygen measured in micro mol per kg by sensor 1
 *O2_SBE_sensor 2 is dissolved oxygen measured in micro mol per kg by
 sensor 2 *Cells with "n/a" indicate unavailable data. ##
 Supplementary Data File 4 This file contains 6 columns and is the source
 data file for Supplementary Fig. 10 of the associated publication. These
 data were used to compare in situ oxygen recordings with dissolved oxygen
 concentrations determined via the Winkler Titration of discrete water
 samples taken at sites 1 and 2. Site 1 = Farasan Deep and Site 2 = Amq
 Deep. *Site is the site identifier (site 1 versus site 2) *Depth_m is the
 water depth (in meters) at which the data were measured
 *O2_SBE_sensor1_umol_kg is dissolved oxygen measured in micro mol per kg
 by SBE sensor 1 *O2_SBE_sensor2_umol_kg is dissolved oxygen measured in
 micro mol per kg by SBE sensor 2 *O2_SBE_av_umol_kg is the average
 dissolved oxygen measured by SBE sensors 1 and 2 (in micro mol per kg) at
 the same water depth *Winkler_av_umol_kg is the average dissolved oxygen
 measured in micro mol per kg via Winkler titration of discrete water
 samples at the same water depth ## Supplementary Data File 5 This file
 contains 9 columns and is the source of data for Figure 4a of the
 associated publication, which presents the major benthic associations in
 site 1, superimposed on depth profiles of the deep-sea vehicle
 tracks. Site 1 = Farasan Deep and Site 2 = Amq Deep. *Site is the site
 identifier (site 1 versus site 2) *Dive_ID is the asset dive identifier,
 where each dive was allocated a unique code *Vehicle refers to the type of
 deep-sea vehicle used to collect video footage (remotely operated vehicle
 or manned submersible) *Latitude (decimal form) at which a video frame was
 recorded *Longitude (decimal form) at which a video frame was recorded
 *Time is the time stamp and date at which a video frame was recorded
 (yyyy/mm/dd, hh:mm:sss) *Depth_m is the water depth (in meters) at a video
 frame was recorded *Benthic_code identifies the benthic association or
 substrate type (as described in Supplementary Data File 5) *Frame_sequence
 represents the temporal sequence of video frames at each recorded
 geographic coordinate ## Supplementary Data File 6 This file contains 9
 columns and is the source of data for Figure 4b of the associated
 publication, which presents the major benthic associations in site 2,
 superimposed on depth profiles of the deep-sea vehicle tracks. Site 1 =
 Farasan Deep and Site 2 = Amq Deep. *Site is the site identifier (site 1
 versus site 2) *Dive_ID is the asset dive identifier, where each dive was
 allocated a unique code *Vehicle refers to the type of deep-sea vehicle
 used to collect video footage (remotely operated vehicle or manned
 submersible) *Latitude (decimal form) at which a video frame was recorded
 *Longitude (decimal form) at which a video frame was recorded *Time is the
 time stamp and date at which a video frame was recorded (yyyy/mm/dd,
 hh:mm:sss) *Depth_m is the water depth (in meters) at a video frame was
 recorded *Benthic_code identifies the benthic association or substrate
 type (as described in Supplementary Data File 5) *Frame_sequence
 represents the temporal sequence of video frames at each recorded
 geographic coordinate  ## Supplementary Data File 7 This file contains 7
 columns and is the source of data for Figure 5b of the associated
 publication, which presents the maximum number of lanternfish
 (*Benthosema* sp.) observed in any single video frame (Max N) of ROV
 footage between 13 open-water reference sites and the two deep depressions
 (sites 1 and 2). Site 1 = Farasan Deep and Site 2 = Amq Deep. *Dive_ID is
 the asset dive identifier, where each dive was allocated a unique code
 *Longitude (decimal form) at which a video frame was recorded *Latitude
 (decimal form) at which a video frame was recorded *Depth_m is the water
 depth (in meters) at a video frame was recorded
 *Lanternfish_presence_absence indicates the presence or absence of
 Lanternfish (*Benthosema* sp.) at each location and water depth *Site_type
 is the type of site (reference open-water site versus depression site)
 *MaxN is the maximum number of lanternfish observed in any single video
 frame (Max N) ## Supplementary Data File 8 This file contains 7 columns
 and is the source of data for Figure 5b of the associated publication.
 Comparison of estimated swimming speeds of *Benthosema* sp. individuals in
 the reference sites (*n* = 29 individuals) and site 2 (*n*= 10
 individuals), where *Benthosema* sp. aggregations were observed. Site 1 =
 Farasan Deep and Site 2 = Amq Deep. *Dive_ID is the dive identifier
 *Species of the fish measured (*Benthosema* sp.) *Pixel_mm the number of
 pixels per mm, used to measure speed of fish movement in the video
 *Speed_mm_s speed of fish movement in mm per second *Site_type is the type
 of site (reference open-water site versus depression site) ##
 Supplementary Data File 9 This file contains 6 columns with data formatted
 for analysing the relationships between environmental parameters using
 Pearson correlations. Although this data is specifically formatted for
 analysis, all raw data, including these values, are also provided in
 Supplementary Data Files 1 & 2. Site 1 = Farasan Deep and Site 2 = Amq
 Deep. *Site is the site identifier (site 1 versus site 2) *Sample_depth is
 the water depth (in meters) at which the discrete samples or data were
 collected *O2_umol_kg_seabird is dissolved oxygen (in micro mol per kg)
 measured by the SeaBird CTD *DIC_umol_kg is dissolved inorganic carbon (in
 micro mol per kg) measured on discrete water samples *pH_total is the
 calculated pH (total scale) *pH_total_log is log transformed pH (total
 scale) ## Supplementary Data File 10 This file contains 2 columns with
 data formatted for analysis with two-sample Mann-Whitney test. Although
 this data is specifically formatted for analysis, all raw data, including
 these values are also provided in Supplementary Data File 8. 
 *Swim_sp_reference_sites is the speed of fish movement in mm per second in
 the open-water reference sites. *Swim_sp_depression_sites is the speed of
 fish movement in mm per second in the depression sites. *Cells with
 "n/a" indicate unavailable data.