Extended Data Fig. 5: Large chlorophyll-a ([Chla]) anomaly in numerous small box regions during 2019–2020 Australian wildfires.

a, [Chla] time-series was calculated in 4,681 of 10° by 10° boxes from 1997 to 2020 in the broad South Pacific and Southern Ocean (20° S–60° S; 120° E–80° W). Yellow circles and yellow dashed boxes are examples to show the center and coverage of each box region. Box moves by 1° eastward and southward sequentially illustrated by the black arrows. Box position 1, 151, 4,531 and 4,681 denoting the edge of the study region are shown as examples on the map of annual [Chla] climatology. The ratio of monthly [Chla] to its monthly climatology is calculated for each 10° by 10° box starting from October 1997 to May 2020. Black circles: centre locations of 10° by 10° boxes where \(\frac{{\rm{m}}{\rm{o}}{\rm{n}}{\rm{t}}{\rm{h}}{\rm{l}}{\rm{y}}[{\rm{C}}{\rm{h}}{\rm{l}}{\rm{a}}]}{[{\rm{C}}{\rm{h}}{\rm{l}}{\rm{a}}]{\rm{c}}{\rm{l}}{\rm{i}}{\rm{m}}{\rm{a}}{\rm{t}}{\rm{o}}{\rm{l}}{\rm{o}}{\rm{g}}{\rm{y}}} > 2.5\) before the 2019–2020 wildfires (from October 1997 to August 2019); red circles: centre locations of 10° by 10° boxes where \(\frac{{\rm{monthly}}[{\rm{Chla}}]}{[{\rm{Chla}}]{\rm{climatology}}} > 2.5\) during or after the 2019–2020 wildfires (from September 2019 to May 2020). Historically, regions with a large anomaly (black circles) are mostly located in coastal waters (for example, east coast of Australia). In contrast, during the 2019–2020 Australian wildfires (red circles), large areas of the open ocean show a high [Chla] anomaly (for example, south of Australia and Pacific sector of the Southern Ocean). Oceanic [Chla] anomalies of this magnitude are unprecedented in the historical record. Some of the black and red circles are on land because a fraction of the 10° by 10° box around these circles covers the ocean. b, Ratio of monthly [Chla] to its corresponding monthly climatologies for each box region from 1997 to 2020. c, Frequency distributions of the monthly [Chla] to monthly climatology ratios over the historical and 2019–2020 austral summers.