.2024 Oct 12;14(1):23867.

doi: 10.1038/s41598-024-74181-2.

The meteorological drivers of mass coral bleaching on the central Great Barrier Reef during the 2022 La Niña

Lara Shania Richards^{1 2 3}, Steven Thomas Siems^{4 5 6}, Yi Huang^{5 6 7}, Wenhui Zhao^{5 7}, Daniel Patrick Harrison^{5 8}, Michael John Manton⁴, Michael John Reeder^{4 6}

Affiliations

¹ School of Earth, Atmosphere and Environment, Monash University, Clayton, 3800, Australia. Lara.Richards@monash.edu.
² Reef Restoration and Adaptation Program, Coffs Harbour, Australia. Lara.Richards@monash.edu.
³ The ARC Centre of Excellence for Climate Extremes, Melbourne, Australia. Lara.Richards@monash.edu.
⁴ School of Earth, Atmosphere and Environment, Monash University, Clayton, 3800, Australia.
⁵ Reef Restoration and Adaptation Program, Coffs Harbour, Australia.
⁶ The ARC Centre of Excellence for Climate Extremes, Melbourne, Australia.
⁷ School of Geography, Earth and Atmospheric Science, The University of Melbourne, Melbourne, 3010, Australia.
⁸ National Marine Science Centre, Southern Cross University, Coffs Harbour, 2450, Australia.

PMID:39394244
PMCID: PMC11470093
DOI: 10.1038/s41598-024-74181-2

The meteorological drivers of mass coral bleaching on the central Great Barrier Reef during the 2022 La Niña

Lara Shania Richards et al. Sci Rep.2024.

.2024 Oct 12;14(1):23867.

doi: 10.1038/s41598-024-74181-2.

Authors

Lara Shania Richards^{1 2 3}, Steven Thomas Siems^{4 5 6}, Yi Huang^{5 6 7}, Wenhui Zhao^{5 7}, Daniel Patrick Harrison^{5 8}, Michael John Manton⁴, Michael John Reeder^{4 6}

Affiliations

¹ School of Earth, Atmosphere and Environment, Monash University, Clayton, 3800, Australia. Lara.Richards@monash.edu.
² Reef Restoration and Adaptation Program, Coffs Harbour, Australia. Lara.Richards@monash.edu.
³ The ARC Centre of Excellence for Climate Extremes, Melbourne, Australia. Lara.Richards@monash.edu.
⁴ School of Earth, Atmosphere and Environment, Monash University, Clayton, 3800, Australia.
⁵ Reef Restoration and Adaptation Program, Coffs Harbour, Australia.
⁶ The ARC Centre of Excellence for Climate Extremes, Melbourne, Australia.
⁷ School of Geography, Earth and Atmospheric Science, The University of Melbourne, Melbourne, 3010, Australia.
⁸ National Marine Science Centre, Southern Cross University, Coffs Harbour, 2450, Australia.

PMID:39394244
PMCID: PMC11470093
DOI: 10.1038/s41598-024-74181-2

Abstract

The frequencies of marine heatwaves and thermal coral bleaching events (CBEs) over the Great Barrier Reef (GBR) continue to increase with five mass CBEs reported since 2016. While changes in the local meteorology, such as reduced wind speeds and decreased cloud cover, are known to heat the shallow reef waters, little consideration has been given to the overriding synoptic meteorology. The 2022 CBE, occurring under La Niña conditions, saw ocean temperatures at Davies Reef increase 1.9 $^{\circ} C$ over 19-days and subsequently cool 2.1 $^{\circ} C$ back to seasonal norms over eight days. This event was found to be triggered by repeated Rossby wave breaking disrupting the local trade winds, thus inhibiting the latent heat flux. Latent heat fluxes, the primary driver of the event, tripled as the trade winds returned via rapid coastal ridging. These same synoptic features are concurrent with the historic Lismore flooding located hundreds of kilometres south of the GBR.

Keywords: Coral bleaching; Great Barrier Reef; Marine heatwave; Trade winds.

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Conflict of interest statement

The authors declare no competing interests.

Figures

**Figure 1**
Reference maps of key areas mentioned in this study. Panel (a) shows the ERA5 bathymetric map of the GBR region, while panel (b) shows the Australian domain. Davies Reef is denoted by the pale yellow star and Lismore by the pink star. The GBR extent is indicated by the red outline in both panels. Both panels were generated using Python 3.9.6 (http://www.python.org) including matplotlib 3.7.1 and Cartopy 0.21.1.

**Figure 2**
AIMS 2022 4 m ocean temperature at Davies Reef (black) compared to the 1996–2024 7-day moving mean (grey) and ±1SD for the December–April period (blue dashed) with the 29.4 $^{\circ}$ C threshold (red dashed). Red dots indicate the 2022 CBE start and end dates, while purple dots show the MHW start and end dates.

**Figure 3**
Event comparison during the 1996–2024 December–April periods. Coral bleaching years are indicated in red. The area between the Davies Reef $T_{4 m}$ daily average ocean temperature and the +1SD curve (a) and above 29.4 $^{\circ}$ C (b) are shown by the squares (degree heating days), while the number of days represented by the horizontal line. It is important to note that the event comparison used in this study is location specific to Davies Reef. Thus, as 2006 (southern GBR localised bleaching) is the only reported bleaching year not to influence the central GBR (or Davies Reef), its true intensity will not be present in this analysis. Data was not available for $T_{4 m}$ during April 23 $rd$ –30 $th$ 2024, which may have a small impact on the +1SD value but not the 29.4 $^{\circ}$ C threshold. Panel (c) shows the Bureau of Meteorology seasonally averaged Southern Oscillation Index (SOI) for 1996–2024. Red markers indicate the eight GBR CBEs. SOI values >7 indicate La Niña periods and SOI values < − 7 indicate El Niño periods.

**Figure 4**
Panel (a) shows the AIMS Davies Reef AWS observational ocean temperatures between February 15 $th$ -March 23 $rd$ 2022. The 4 m (blue), 8.5 m (purple) and 18.5 m (green) ocean temperatures are shown with their daily average (thicker line) and 10-min observations (thinner line) to represent the diurnal cycle. Panel (b) shows the daily tidal range observed at the Townsville tide gauge roughly 100 km south-west of Davies Reef.

**Figure 5**
Davies Reef daily averages between February 15 $th$ -March 23 $rd$ , 2022. Panel (a) shows the 1 $^{\circ}$ daytime cloud fraction for Davies Reef using Himawari-8/AHI satellite data and AIMS daily accumulated precipitation. Panel (b) shows the ERA5 net surface energy budget. The stacked bar chart shows the individual flux components; short-wave ( $Q_{SW}$ , pink), long-wave ( $Q_{LW}$ , green), sensible heat ( $Q_{H}$ , brown) and latent heat ( $Q_{E}$ , blue), where positive (negative) values represent incoming (outgoing) flux. Panel (c) shows AIMS observational ocean temperature at 4 m (blue) vs AIMS surface wind speed (black) and wind barbs (ms $^{- 1}$ ) with the 29.8 $^{\circ}$ C local bleaching threshold (red dashed). Panel (d) shows AIMS surface air temperature (maroon) vs surface relative humidity (blue dashed).

**Figure 6**
ERA5 atmospheric soundings taken at 0000 UTC (1000 LST) using the closest grid point to Davies Reef. Red lines show air temperature ( $^{\circ}$ C), while the blue lines show dew point temperature ( $^{\circ}$ C). The black line represents the parcel trajectory when lifted from the surface indicating convective available potential energy (red shaded) and convective inhibition (blue shaded) values for the profile.

**Figure 7**
Himawari-8/AHI true colour satellite imagery at 0000 UTC (1000 LST) supplied by the P-Tree System, Japan Aerospace Exploration Agency (JAXA) (https://www.eorc.jaxa.jp/ptree/). The GBR region is outlined in red, while Davies Reef is represented by the pale yellow star and Lismore by the pink star.

**Figure 8**
Heating period showing February 13 $th$ –March 4 $th$ 2022, at the surface, 500 hPa and 250 hPa. All panels are derived from ERA5 data showing wind speed and wind streamlines at each level with pressure (4 hPa intervals) contours at the surface and height contours at 500 hPa (50 m intervals) and 250 hPa (120 m intervals). Pale yellow star represents Davies Reef and pink star represents the location of the 2022 severe floods (Lismore, New South Wales).

**Figure 9**
Same as Fig. 8, but showing the cooling period from March 10 $th$ –18 $th$ 2022.

See this image and copyright information in PMC

References

1. Australian Institute of Marine Science (AIMS). Coral Bleaching Events (2024).https://www.aims.gov.au/research-topics/environmental-issues/coral-bleac..., last accessed: 13/05/2024.
1. Great Barrier Reef Marine Park Authority (GBRMPA), Australian Institute of Marine Science (AIMS), and Commonwealth Scientific and Industrial Research Organisation (CSIRO). Reef snapshot: Summer 2021-22 (Great Barrier Reef Marine Park Authority, 2022).
1. McGowan, H. & Theobald, A. Atypical weather patterns cause coral bleaching on the Great Barrier Reef, Australia during the 2021–2022 La Nina.Sci. Rep.13, 6397–6397. 10.1038/s41598-023-33613-1 (2023). - DOI - PMC - PubMed
1. Spady, B. L. et al. Unprecedented early-summer heat stress and forecast of coral bleaching on the Great Barrier Reef, 2021–2022.F1000Res11, 127. 10.12688/f1000research.108724.4 (2022). - PMC - PubMed
1. Glynn, P. W. Widespread coral mortality and the 1982–83 El Niño Warming Event.Environ. Conserv.11, 133–146. 10.1017/S0376892900013825 (1984). - DOI

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The meteorological drivers of mass coral bleaching on the central Great Barrier Reef during the 2022 La Niña

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The meteorological drivers of mass coral bleaching on the central Great Barrier Reef during the 2022 La Niña

Authors

Affiliations

Abstract

Conflict of interest statement

Figures

References

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