May 2025
Davies, T.W. and Smyth, T. (2025), Darkening of the Global Ocean. Glob Change Biol, 31: e70227. https://doi.org/10.1111/gcb.70227
This study used 20 years of Aqua MODIS data of the diffuse attenuation coefficient of light over the global oceans and found that it had increased across 75,341,181 km2 (21%) of the global ocean between 2003 and 2022, resulting in photic zone (areas with high productivity) depths reducing by more than 50 m across 32,449,129 km2 (9%) by area. Their results demonstrated that this darkening is not limiited to the coastal zones. This darkening of the ocean could have profound affects on the global ocean ecosystem.
Figure: Darkening of the Global Ocean. (A) The rate change (units per year) in the diffuse attenuation coefficient for downwelling irradiance at 490 nm [ΔKd(490)] measured from MODIS Aqua between 2003 and 2022 in 9 km resolution. Reds indicate regions where Kd(490) is increasing (oceans are getting darker), while blues indicate regions where Kd(490) is decreasing (oceans are getting lighter). White indicates regions where there was no statistically significant change in Kd(490) over the period 2003–2022. Values of ΔKd(490) were derived for each 9 km resolution pixel using quantile regression to the median performed on the fitted values of an Autoregressive Integrated Moving Average (ARIMA) model of annual averaged Kd(490) data. (B) International Hydrographic Office sea regions ranked according to the percentage of their area over which Kd(490) is increasing. Numbers inset above bars give the absolute area where Kd(490) is increasing in 10,000 km2.
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