South Australian algal bloom investigation with VIIRS SST and Chlr-A data

Ocean temperature analysis

• Water depth measured: 10.0 m
• Sampling area per cell: 0.5625 km²
• Reference temperature: 15.0°C

GAB

• Average temperature: 17.5°C (range 13.2–24.1°C)
• Cooling trend: -0.121°C per year (±0.038°C) — statistically reliable
• Days warmer than normal per year: 564   Cooler than normal: 6

9 heat waves detected (88 days total) — unusually warm threshold: above 20.0°C

• Jan 17 2018 – Jan 28 2018: 7 days · avg 21.6°C (+1.6°C above threshold) · peak 24.1°C (+4.1°C)
• Feb 5 2018 – Feb 27 2018: 12 days · avg 20.7°C (+0.6°C above threshold) · peak 21.5°C (+1.4°C)
• Apr 16 2018 – Apr 21 2018: 5 days · avg 20.4°C (+0.4°C above threshold) · peak 20.7°C (+0.7°C)
• Feb 7 2019 – Mar 13 2019: 21 days · avg 20.9°C (+0.8°C above threshold) · peak 21.8°C (+1.8°C)
• Mar 16 2019 – Mar 21 2019: 5 days · avg 20.4°C (+0.4°C above threshold) · peak 21.2°C (+1.2°C)
• Jan 26 2020 – Feb 10 2020: 10 days · avg 20.8°C (+0.8°C above threshold) · peak 21.5°C (+1.4°C)
• Feb 18 2023 – Feb 25 2023: 7 days · avg 20.7°C (+0.6°C above threshold) · peak 21.3°C (+1.3°C)
• Jan 9 2025 – Jan 14 2025: 5 days · avg 20.7°C (+0.7°C above threshold) · peak 21.3°C (+1.3°C)
• Jan 16 2025 – Feb 7 2025: 16 days · avg 20.8°C (+0.8°C above threshold) · peak 21.9°C (+1.8°C)

Ceduna W

• Average temperature: 17.1°C (range 12.9–23.6°C)
• Cooling trend: -0.086°C per year (±0.042°C) — statistically reliable
• Days warmer than normal per year: 403   Cooler than normal: 14

9 heat waves detected (61 days total) — unusually warm threshold: above 19.5°C

• Jan 18 2018 – Jan 25 2018: 5 days · avg 20.5°C (+1.0°C above threshold) · peak 21.5°C (+2.0°C)
• Feb 6 2018 – Feb 17 2018: 6 days · avg 20.4°C (+0.9°C above threshold) · peak 21.6°C (+2.1°C)
• Jan 27 2019 – Feb 3 2019: 6 days · avg 20.1°C (+0.6°C above threshold) · peak 20.8°C (+1.3°C)
• Feb 23 2019 – Mar 1 2019: 6 days · avg 20.6°C (+1.1°C above threshold) · peak 21.2°C (+1.7°C)
• Dec 28 2019 – Jan 3 2020: 5 days · avg 20.5°C (+1.0°C above threshold) · peak 21.0°C (+1.5°C)
• Jan 27 2020 – Feb 12 2020: 9 days · avg 20.5°C (+1.0°C above threshold) · peak 21.8°C (+2.3°C)
• Feb 19 2023 – Feb 25 2023: 6 days · avg 20.4°C (+0.9°C above threshold) · peak 21.0°C (+1.5°C)
• Jan 9 2025 – Jan 14 2025: 5 days · avg 19.9°C (+0.4°C above threshold) · peak 20.6°C (+1.1°C)
• Jan 16 2025 – Feb 8 2025: 13 days · avg 20.3°C (+0.8°C above threshold) · peak 22.4°C (+2.9°C)

Ceduna E

• Average temperature: 16.6°C (range 12.0–22.2°C)
• Cooling trend: -0.097°C per year (±0.036°C) — statistically reliable
• Days warmer than normal per year: 362   Cooler than normal: 27

10 heat waves detected (71 days total) — unusually warm threshold: above 18.8°C

• Jan 18 2018 – Jan 25 2018: 6 days · avg 19.8°C (+0.9°C above threshold) · peak 20.8°C (+1.9°C)
• Feb 6 2018 – Feb 15 2018: 5 days · avg 19.5°C (+0.7°C above threshold) · peak 21.3°C (+2.5°C)
• Apr 19 2018 – Apr 24 2018: 5 days · avg 19.1°C (+0.3°C above threshold) · peak 19.4°C (+0.6°C)
• Jan 22 2019 – Feb 4 2019: 11 days · avg 19.9°C (+1.0°C above threshold) · peak 21.5°C (+2.7°C)
• Feb 23 2019 – Mar 5 2019: 8 days · avg 19.9°C (+1.0°C above threshold) · peak 20.8°C (+1.9°C)
• Feb 7 2020 – Feb 15 2020: 6 days · avg 19.8°C (+1.0°C above threshold) · peak 21.1°C (+2.3°C)
• Feb 20 2023 – Feb 25 2023: 5 days · avg 20.4°C (+1.6°C above threshold) · peak 21.8°C (+2.9°C)
• Jan 7 2025 – Jan 27 2025: 13 days · avg 19.7°C (+0.9°C above threshold) · peak 20.8°C (+2.0°C)
• Feb 1 2025 – Feb 8 2025: 6 days · avg 19.1°C (+0.3°C above threshold) · peak 19.6°C (+0.7°C)
• Feb 24 2025 – Mar 24 2025: 6 days · avg 19.2°C (+0.4°C above threshold) · peak 19.7°C (+0.9°C)

Pt Lincoln W

• Average temperature: 16.3°C (range 11.5–20.8°C)
• Cooling trend: -0.097°C per year (±0.033°C) — statistically reliable
• Days warmer than normal per year: 285   Cooler than normal: 25

8 heat waves detected (58 days total) — unusually warm threshold: above 18.4°C

• Jan 16 2018 – Jan 21 2018: 5 days · avg 19.6°C (+1.2°C above threshold) · peak 20.8°C (+2.4°C)
• Apr 8 2018 – Apr 14 2018: 5 days · avg 18.8°C (+0.4°C above threshold) · peak 19.1°C (+0.6°C)
• Apr 17 2018 – Apr 24 2018: 7 days · avg 18.8°C (+0.4°C above threshold) · peak 19.2°C (+0.8°C)
• Jan 19 2019 – Jan 29 2019: 7 days · avg 19.2°C (+0.8°C above threshold) · peak 20.4°C (+2.0°C)
• Feb 23 2019 – Mar 2 2019: 6 days · avg 19.4°C (+1.0°C above threshold) · peak 20.3°C (+1.9°C)
• Apr 1 2021 – Apr 8 2021: 6 days · avg 18.8°C (+0.3°C above threshold) · peak 19.1°C (+0.7°C)
• Feb 15 2023 – Feb 26 2023: 9 days · avg 19.2°C (+0.7°C above threshold) · peak 20.3°C (+1.9°C)
• Jan 12 2025 – Feb 2 2025: 13 days · avg 19.2°C (+0.7°C above threshold) · peak 20.4°C (+1.9°C)

Pt Lincoln E

• Average temperature: 16.8°C (range 12.0–23.4°C)
• Cooling trend: -0.085°C per year (±0.050°C) — statistically reliable
• Days warmer than normal per year: 386   Cooler than normal: 46

7 heat waves detected (56 days total) — unusually warm threshold: above 20.0°C

• Feb 5 2018 – Mar 10 2018: 16 days · avg 20.8°C (+0.9°C above threshold) · peak 22.5°C (+2.6°C)
• Apr 7 2018 – Apr 12 2018: 5 days · avg 20.3°C (+0.4°C above threshold) · peak 20.7°C (+0.7°C)
• Jan 22 2019 – Feb 4 2019: 11 days · avg 20.9°C (+0.9°C above threshold) · peak 22.1°C (+2.1°C)
• Feb 20 2019 – Mar 3 2019: 8 days · avg 21.3°C (+1.4°C above threshold) · peak 23.4°C (+3.5°C)
• Feb 7 2020 – Feb 18 2020: 5 days · avg 20.4°C (+0.4°C above threshold) · peak 21.0°C (+1.0°C)
• Feb 11 2025 – Feb 18 2025: 5 days · avg 21.6°C (+1.6°C above threshold) · peak 22.9°C (+2.9°C)
• Feb 22 2025 – Mar 23 2025: 6 days · avg 21.0°C (+1.0°C above threshold) · peak 22.9°C (+2.9°C)

Spencer Gulf N

• Average temperature: 17.7°C (range 10.3–25.6°C)
• Cooling trend: -0.012°C per year (±0.078°C) — not statistically reliable
• Days warmer than normal per year: 699   Cooler than normal: 114

12 heat waves detected (90 days total) — unusually warm threshold: above 22.6°C

• Jan 19 2018 – Jan 26 2018: 5 days · avg 24.0°C (+1.4°C above threshold) · peak 24.6°C (+2.0°C)
• Feb 5 2018 – Feb 28 2018: 11 days · avg 23.3°C (+0.7°C above threshold) · peak 25.6°C (+3.0°C)
• Jan 14 2019 – Jan 30 2019: 7 days · avg 23.6°C (+1.0°C above threshold) · peak 24.5°C (+1.9°C)
• Feb 2 2019 – Feb 9 2019: 6 days · avg 23.6°C (+1.0°C above threshold) · peak 24.3°C (+1.7°C)
• Feb 24 2019 – Mar 3 2019: 7 days · avg 23.9°C (+1.2°C above threshold) · peak 24.8°C (+2.2°C)
• Jan 26 2022 – Feb 2 2022: 6 days · avg 23.7°C (+1.1°C above threshold) · peak 24.3°C (+1.7°C)
• Jan 12 2023 – Jan 20 2023: 6 days · avg 23.1°C (+0.5°C above threshold) · peak 24.1°C (+1.4°C)
• Feb 20 2023 – Feb 26 2023: 5 days · avg 23.8°C (+1.2°C above threshold) · peak 24.7°C (+2.1°C)
• Jan 12 2024 – Jan 25 2024: 6 days · avg 23.3°C (+0.7°C above threshold) · peak 25.2°C (+2.6°C)
• Feb 18 2024 – Mar 3 2024: 10 days · avg 23.4°C (+0.8°C above threshold) · peak 24.0°C (+1.3°C)
• Jan 10 2025 – Jan 29 2025: 13 days · avg 23.6°C (+1.0°C above threshold) · peak 24.2°C (+1.6°C)
• Feb 6 2025 – Feb 19 2025: 8 days · avg 23.7°C (+1.1°C above threshold) · peak 24.8°C (+2.1°C)

Spencer Gulf C

• Average temperature: 17.3°C (range 11.3–23.8°C)
• Cooling trend: -0.049°C per year (±0.067°C) — not statistically reliable
• Days warmer than normal per year: 519   Cooler than normal: 83

9 heat waves detected (86 days total) — unusually warm threshold: above 21.4°C

• Jan 19 2018 – Jan 25 2018: 5 days · avg 22.2°C (+0.9°C above threshold) · peak 23.2°C (+1.8°C)
• Feb 5 2018 – Feb 28 2018: 10 days · avg 22.0°C (+0.6°C above threshold) · peak 22.3°C (+1.0°C)
• Mar 4 2018 – Mar 10 2018: 5 days · avg 21.7°C (+0.3°C above threshold) · peak 22.0°C (+0.7°C)
• Jan 22 2019 – Feb 12 2019: 15 days · avg 22.1°C (+0.7°C above threshold) · peak 23.1°C (+1.7°C)
• Feb 20 2019 – Mar 13 2019: 13 days · avg 22.2°C (+0.8°C above threshold) · peak 23.3°C (+1.9°C)
• Feb 20 2023 – Feb 26 2023: 5 days · avg 22.2°C (+0.9°C above threshold) · peak 22.9°C (+1.6°C)
• Feb 8 2024 – Feb 13 2024: 5 days · avg 21.9°C (+0.5°C above threshold) · peak 22.3°C (+1.0°C)
• Jan 16 2025 – Feb 3 2025: 12 days · avg 22.4°C (+1.0°C above threshold) · peak 23.1°C (+1.8°C)
• Feb 6 2025 – Mar 2 2025: 16 days · avg 22.3°C (+1.0°C above threshold) · peak 23.8°C (+2.5°C)

Spencer Gulf S

• Average temperature: 16.9°C (range 11.3–23.2°C)
• Cooling trend: -0.075°C per year (±0.055°C) — statistically reliable
• Days warmer than normal per year: 420   Cooler than normal: 63

7 heat waves detected (74 days total) — unusually warm threshold: above 20.3°C

• Jan 19 2018 – Jan 25 2018: 5 days · avg 21.3°C (+0.9°C above threshold) · peak 22.3°C (+1.9°C)
• Feb 5 2018 – Feb 15 2018: 6 days · avg 21.1°C (+0.7°C above threshold) · peak 21.8°C (+1.5°C)
• Feb 17 2018 – Mar 6 2018: 10 days · avg 20.8°C (+0.5°C above threshold) · peak 21.5°C (+1.2°C)
• Jan 22 2019 – Feb 10 2019: 13 days · avg 21.2°C (+0.9°C above threshold) · peak 22.2°C (+1.9°C)
• Feb 21 2019 – Mar 7 2019: 11 days · avg 21.4°C (+1.1°C above threshold) · peak 22.4°C (+2.1°C)
• Jan 18 2025 – Feb 19 2025: 23 days · avg 21.5°C (+1.2°C above threshold) · peak 22.7°C (+2.4°C)
• Feb 24 2025 – Mar 24 2025: 6 days · avg 20.9°C (+0.6°C above threshold) · peak 21.5°C (+1.2°C)

SVG - NW

• Average temperature: 17.4°C (range 10.8–26.6°C)
• Cooling trend: -0.057°C per year (±0.094°C) — not statistically reliable
• Days warmer than normal per year: 418   Cooler than normal: 91

8 heat waves detected (62 days total) — unusually warm threshold: above 22.1°C

• Feb 5 2018 – Mar 6 2018: 7 days · avg 22.7°C (+0.6°C above threshold) · peak 24.5°C (+2.4°C)
• Jan 12 2019 – Feb 10 2019: 16 days · avg 23.4°C (+1.3°C above threshold) · peak 26.6°C (+4.5°C)
• Feb 24 2019 – Mar 3 2019: 7 days · avg 23.5°C (+1.4°C above threshold) · peak 24.3°C (+2.2°C)
• Dec 29 2019 – Jan 14 2020: 6 days · avg 22.8°C (+0.7°C above threshold) · peak 23.9°C (+1.8°C)
• Jan 9 2023 – Jan 17 2023: 5 days · avg 22.6°C (+0.5°C above threshold) · peak 23.0°C (+0.9°C)
• Feb 18 2024 – Feb 27 2024: 5 days · avg 22.7°C (+0.6°C above threshold) · peak 23.5°C (+1.4°C)
• Jan 10 2025 – Jan 27 2025: 9 days · avg 23.3°C (+1.2°C above threshold) · peak 24.0°C (+2.0°C)
• Feb 2 2025 – Feb 12 2025: 7 days · avg 23.3°C (+1.2°C above threshold) · peak 24.0°C (+1.9°C)

SVG - NE

• Average temperature: 17.5°C (range 11.1–24.9°C)
• Cooling trend: -0.008°C per year (±0.100°C) — not statistically reliable
• Days warmer than normal per year: 421   Cooler than normal: 86

5 heat waves detected (40 days total) — unusually warm threshold: above 22.3°C

• Jan 14 2019 – Feb 7 2019: 12 days · avg 23.6°C (+1.3°C above threshold) · peak 24.6°C (+2.3°C)
• Feb 25 2019 – Mar 3 2019: 5 days · avg 24.1°C (+1.8°C above threshold) · peak 24.9°C (+2.5°C)
• Jan 9 2023 – Jan 17 2023: 5 days · avg 23.1°C (+0.7°C above threshold) · peak 23.6°C (+1.2°C)
• Jan 10 2025 – Jan 29 2025: 9 days · avg 23.4°C (+1.0°C above threshold) · peak 24.1°C (+1.8°C)
• Feb 2 2025 – Feb 18 2025: 9 days · avg 23.3°C (+0.9°C above threshold) · peak 24.4°C (+2.0°C)

SVG - SW

• Average temperature: 16.9°C (range 10.6–23.2°C)
• Cooling trend: -0.083°C per year (±0.072°C) — statistically reliable
• Days warmer than normal per year: 392   Cooler than normal: 85

4 heat waves detected (71 days total) — unusually warm threshold: above 20.9°C

• Feb 5 2018 – Mar 16 2018: 19 days · avg 21.4°C (+0.5°C above threshold) · peak 22.4°C (+1.5°C)
• Jan 22 2019 – Feb 12 2019: 13 days · avg 21.6°C (+0.7°C above threshold) · peak 22.1°C (+1.2°C)
• Feb 23 2019 – Mar 3 2019: 8 days · avg 22.2°C (+1.3°C above threshold) · peak 22.8°C (+1.8°C)
• Jan 10 2025 – Mar 26 2025: 31 days · avg 21.8°C (+0.9°C above threshold) · peak 23.2°C (+2.3°C)

SVG - SE

• Average temperature: 17.3°C (range 11.2–24.0°C)
• Cooling trend: -0.075°C per year (±0.081°C) — not statistically reliable
• Days warmer than normal per year: 430   Cooler than normal: 79

5 heat waves detected (62 days total) — unusually warm threshold: above 21.5°C

• Jan 17 2018 – Jan 25 2018: 5 days · avg 22.4°C (+0.9°C above threshold) · peak 23.8°C (+2.2°C)
• Feb 5 2018 – Mar 6 2018: 15 days · avg 22.1°C (+0.6°C above threshold) · peak 23.7°C (+2.1°C)
• Jan 22 2019 – Feb 12 2019: 12 days · avg 22.3°C (+0.8°C above threshold) · peak 22.8°C (+1.2°C)
• Feb 23 2019 – Mar 9 2019: 10 days · avg 22.6°C (+1.0°C above threshold) · peak 24.0°C (+2.5°C)
• Jan 18 2025 – Feb 22 2025: 20 days · avg 22.5°C (+1.0°C above threshold) · peak 23.6°C (+2.1°C)

KI - W

• Average temperature: 16.6°C (range 13.0–21.5°C)
• Cooling trend: -0.089°C per year (±0.040°C) — statistically reliable
• Days warmer than normal per year: 318   Cooler than normal: 20

8 heat waves detected (78 days total) — unusually warm threshold: above 19.2°C

• Jan 16 2018 – Jan 25 2018: 5 days · avg 20.1°C (+0.9°C above threshold) · peak 21.2°C (+2.0°C)
• Feb 6 2018 – Feb 15 2018: 5 days · avg 20.1°C (+0.9°C above threshold) · peak 21.1°C (+2.0°C)
• Feb 17 2018 – Mar 3 2018: 7 days · avg 19.7°C (+0.5°C above threshold) · peak 20.2°C (+1.0°C)
• Jan 14 2019 – Feb 10 2019: 16 days · avg 20.0°C (+0.8°C above threshold) · peak 21.2°C (+2.0°C)
• Feb 19 2019 – Mar 2 2019: 9 days · avg 20.1°C (+0.9°C above threshold) · peak 21.3°C (+2.1°C)
• Jan 26 2022 – Feb 2 2022: 6 days · avg 19.6°C (+0.4°C above threshold) · peak 20.0°C (+0.9°C)
• Jan 7 2025 – Feb 17 2025: 24 days · avg 20.1°C (+1.0°C above threshold) · peak 21.2°C (+2.0°C)
• Mar 24 2025 – Mar 29 2025: 6 days · avg 19.7°C (+0.5°C above threshold) · peak 20.2°C (+1.0°C)

KI - E

• Average temperature: 16.5°C (range 11.4–22.0°C)
• Cooling trend: -0.089°C per year (±0.050°C) — statistically reliable
• Days warmer than normal per year: 330   Cooler than normal: 54

8 heat waves detected (96 days total) — unusually warm threshold: above 19.7°C

• Jan 16 2018 – Jan 25 2018: 6 days · avg 20.8°C (+1.1°C above threshold) · peak 21.9°C (+2.2°C)
• Feb 6 2018 – Feb 15 2018: 5 days · avg 20.3°C (+0.6°C above threshold) · peak 20.6°C (+0.9°C)
• Feb 26 2018 – Mar 6 2018: 7 days · avg 20.1°C (+0.5°C above threshold) · peak 20.6°C (+0.9°C)
• Jan 14 2019 – Feb 13 2019: 19 days · avg 20.5°C (+0.9°C above threshold) · peak 22.0°C (+2.3°C)
• Feb 15 2019 – Mar 7 2019: 12 days · avg 20.4°C (+0.8°C above threshold) · peak 21.3°C (+1.6°C)
• Mar 17 2019 – Mar 23 2019: 5 days · avg 20.1°C (+0.4°C above threshold) · peak 20.4°C (+0.7°C)
• Feb 20 2023 – Feb 26 2023: 5 days · avg 20.3°C (+0.6°C above threshold) · peak 20.9°C (+1.2°C)
• Jan 5 2025 – Mar 25 2025: 37 days · avg 20.6°C (+0.9°C above threshold) · peak 21.8°C (+2.2°C)

Victor - W

• Average temperature: 16.2°C (range 11.4–21.8°C)
• Cooling trend: -0.104°C per year (±0.052°C) — statistically reliable
• Days warmer than normal per year: 273   Cooler than normal: 70

6 heat waves detected (63 days total) — unusually warm threshold: above 19.3°C

• Jan 16 2018 – Jan 25 2018: 5 days · avg 20.2°C (+1.0°C above threshold) · peak 21.8°C (+2.6°C)
• Jan 12 2019 – Feb 13 2019: 16 days · avg 20.0°C (+0.7°C above threshold) · peak 20.9°C (+1.7°C)
• Feb 24 2019 – Mar 2 2019: 6 days · avg 20.4°C (+1.2°C above threshold) · peak 21.0°C (+1.8°C)
• Feb 19 2023 – Feb 26 2023: 6 days · avg 20.1°C (+0.9°C above threshold) · peak 21.0°C (+1.7°C)
• Dec 10 2024 – Dec 25 2024: 7 days · avg 19.9°C (+0.6°C above threshold) · peak 20.8°C (+1.6°C)
• Jan 8 2025 – Feb 22 2025: 23 days · avg 20.3°C (+1.1°C above threshold) · peak 21.4°C (+2.1°C)

Victor - E

• Average temperature: 15.7°C (range 11.1–21.5°C)
• Cooling trend: -0.078°C per year (±0.050°C) — statistically reliable
• Days warmer than normal per year: 220   Cooler than normal: 101

8 heat waves detected (77 days total) — unusually warm threshold: above 18.6°C

• Jan 17 2018 – Jan 25 2018: 6 days · avg 19.8°C (+1.2°C above threshold) · peak 21.5°C (+2.9°C)
• Feb 6 2018 – Feb 15 2018: 7 days · avg 19.3°C (+0.7°C above threshold) · peak 20.1°C (+1.5°C)
• Jan 22 2019 – Feb 11 2019: 12 days · avg 19.2°C (+0.6°C above threshold) · peak 20.4°C (+1.8°C)
• Feb 24 2019 – Mar 9 2019: 9 days · avg 19.5°C (+0.9°C above threshold) · peak 20.5°C (+1.9°C)
• Dec 5 2024 – Dec 20 2024: 5 days · avg 19.5°C (+0.9°C above threshold) · peak 20.9°C (+2.3°C)
• Dec 28 2024 – Feb 8 2025: 24 days · avg 19.7°C (+1.1°C above threshold) · peak 21.1°C (+2.5°C)
• Feb 11 2025 – Feb 22 2025: 9 days · avg 19.5°C (+0.9°C above threshold) · peak 20.4°C (+1.8°C)
• Feb 24 2025 – Mar 23 2025: 5 days · avg 19.0°C (+0.4°C above threshold) · peak 19.5°C (+0.9°C)

Lk Alex

• Average temperature: 16.5°C (range 9.9–24.7°C)
• Cooling trend: -0.006°C per year (±0.123°C) — not statistically reliable
• Days warmer than normal per year: 205   Cooler than normal: 78

4 heat waves detected (23 days total) — unusually warm threshold: above 21.2°C

• Jan 14 2019 – Feb 5 2019: 8 days · avg 22.5°C (+1.3°C above threshold) · peak 23.8°C (+2.6°C)
• Feb 25 2019 – Mar 3 2019: 5 days · avg 23.4°C (+2.2°C above threshold) · peak 24.2°C (+3.0°C)
• Dec 24 2019 – Jan 1 2020: 5 days · avg 21.5°C (+0.4°C above threshold) · peak 22.2°C (+1.0°C)
• Dec 5 2024 – Dec 20 2024: 5 days · avg 22.1°C (+0.9°C above threshold) · peak 22.8°C (+1.7°C)

Victor Harbour-Mt Gambier

• Average temperature: 15.3°C (range 10.7–20.2°C)
• Cooling trend: -0.061°C per year (±0.033°C) — statistically reliable
• Days warmer than normal per year: 176   Cooler than normal: 110

7 heat waves detected (71 days total) — unusually warm threshold: above 17.5°C

• Jan 5 2018 – Jan 25 2018: 15 days · avg 18.4°C (+0.9°C above threshold) · peak 19.5°C (+2.0°C)
• Jan 29 2019 – Feb 4 2019: 6 days · avg 18.2°C (+0.8°C above threshold) · peak 19.1°C (+1.6°C)
• Feb 24 2019 – Mar 6 2019: 8 days · avg 18.4°C (+0.9°C above threshold) · peak 18.9°C (+1.4°C)
• Mar 31 2021 – Apr 8 2021: 7 days · avg 17.8°C (+0.4°C above threshold) · peak 18.1°C (+0.6°C)
• Jan 25 2022 – Jan 29 2022: 5 days · avg 19.1°C (+1.7°C above threshold) · peak 19.9°C (+2.4°C)
• Feb 19 2023 – Feb 24 2023: 5 days · avg 17.8°C (+0.3°C above threshold) · peak 18.5°C (+1.0°C)
• Jan 1 2025 – Feb 14 2025: 25 days · avg 18.4°C (+0.9°C above threshold) · peak 20.2°C (+2.8°C)

Mt Gambier

• Average temperature: 15.3°C (range 11.6–20.2°C)
• Cooling trend: -0.039°C per year (±0.037°C) — statistically reliable
• Days warmer than normal per year: 169   Cooler than normal: 106

8 heat waves detected (93 days total) — unusually warm threshold: above 17.6°C

• Jan 5 2018 – Feb 17 2018: 20 days · avg 18.5°C (+0.9°C above threshold) · peak 20.2°C (+2.5°C)
• Mar 6 2018 – Mar 15 2018: 6 days · avg 18.1°C (+0.5°C above threshold) · peak 18.8°C (+1.1°C)
• Jan 10 2019 – Feb 19 2019: 21 days · avg 18.4°C (+0.7°C above threshold) · peak 19.1°C (+1.4°C)
• Feb 24 2019 – Mar 7 2019: 8 days · avg 18.6°C (+1.0°C above threshold) · peak 19.7°C (+2.1°C)
• Feb 1 2024 – Feb 14 2024: 12 days · avg 18.1°C (+0.5°C above threshold) · peak 18.9°C (+1.3°C)
• Mar 1 2024 – Mar 11 2024: 6 days · avg 18.1°C (+0.4°C above threshold) · peak 18.3°C (+0.7°C)
• Jan 11 2025 – Feb 12 2025: 13 days · avg 18.6°C (+0.9°C above threshold) · peak 19.8°C (+2.2°C)
• Mar 1 2025 – Mar 29 2025: 7 days · avg 17.9°C (+0.2°C above threshold) · peak 18.1°C (+0.4°C)

Pt Fairy

• Average temperature: 15.5°C (range 9.4–25.1°C)
• Cooling trend: -0.044°C per year (±0.052°C) — not statistically reliable
• Days warmer than normal per year: 254   Cooler than normal: 162

8 heat waves detected (71 days total) — unusually warm threshold: above 18.8°C

• Jan 6 2018 – Jan 11 2018: 5 days · avg 19.1°C (+0.3°C above threshold) · peak 19.3°C (+0.5°C)
• Jan 26 2018 – Mar 2 2018: 20 days · avg 20.2°C (+1.4°C above threshold) · peak 25.1°C (+6.2°C)
• Jan 10 2019 – Jan 16 2019: 5 days · avg 19.6°C (+0.8°C above threshold) · peak 20.7°C (+1.9°C)
• Jan 20 2019 – Feb 14 2019: 15 days · avg 19.9°C (+1.1°C above threshold) · peak 20.8°C (+2.0°C)
• Jan 23 2022 – Jan 29 2022: 5 days · avg 19.7°C (+0.9°C above threshold) · peak 21.3°C (+2.5°C)
• Feb 8 2024 – Feb 25 2024: 10 days · avg 19.5°C (+0.7°C above threshold) · peak 20.9°C (+2.1°C)
• Jan 31 2025 – Feb 7 2025: 5 days · avg 19.8°C (+0.9°C above threshold) · peak 20.6°C (+1.8°C)
• Feb 11 2025 – Feb 16 2025: 6 days · avg 19.9°C (+1.1°C above threshold) · peak 22.2°C (+3.4°C)

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Yearly mean values (chlr-a)

| Group      |      GAB |   Ceduna W |   Ceduna E |   Pt Lincoln W |   Pt Lincoln E |   Spencer Gulf N |   Spencer Gulf C |   Spencer Gulf S |   SVG - NW |   SVG - NE |   SVG - SW |   SVG - SE |   KI - W |   KI - E |   Victor - W |   Victor - E |   Lk Alex |   Victor Harbour-Mt Gambier |   Mt Gambier |   Pt Fairy |
|:-----------|---------:|-----------:|-----------:|---------------:|---------------:|-----------------:|-----------------:|-----------------:|-----------:|-----------:|-----------:|-----------:|---------:|---------:|-------------:|-------------:|----------:|----------------------------:|-------------:|-----------:|
| 2012       | 0.395075 |   0.704127 |   0.62447  |       0.424389 |       0.479383 |          2.09308 |         0.526196 |         0.512825 |    2.37877 |    4.18012 |   0.711444 |   0.742047 | 0.282815 | 0.540881 |     0.585828 |     0.682859 |  nan      |                    0.467531 |     0.332491 |   0.784586 |
| 2013       | 0.47089  |   0.775856 |   0.706796 |       0.437607 |       0.490458 |          2.33492 |         0.611009 |         0.608825 |    2.75805 |    4.55311 |   0.792129 |   0.87921  | 0.289305 | 0.555602 |     0.444416 |     0.51717  |   10.7002 |                    0.447544 |     0.315183 |   0.730188 |
| 2014       | 0.359467 |   0.786139 |   0.809266 |       0.555249 |       0.529739 |          2.25154 |         0.528562 |         0.583451 |    2.58515 |    4.72018 |   0.785615 |   0.730013 | 0.333831 | 0.606861 |     0.470669 |     0.617708 |  nan      |                    0.520572 |     0.301768 |   0.653584 |
| 2017       | 0.420358 |   0.719711 |   0.750979 |       0.472473 |       0.477375 |          2.16509 |         0.55729  |         0.553885 |    2.55451 |    3.80648 |   0.758223 |   0.804488 | 0.294448 | 0.562252 |     0.505473 |     0.511924 |   24.6263 |                    0.440204 |     0.317932 |   0.765035 |
| 2018       | 0.374212 |   0.676656 |   0.616501 |       0.393879 |       0.416414 |          1.93521 |         0.548518 |         0.505213 |    2.14749 |    3.28013 |   0.712456 |   0.764651 | 0.269927 | 0.522626 |     0.394739 |     0.463087 |   23.5477 |                    0.387717 |     0.288127 |   0.581171 |
| 2019       | 0.375582 |   0.691767 |   0.633042 |       0.451581 |       0.484225 |          2.00372 |         0.560138 |         0.499253 |    2.25286 |    3.86962 |   0.683958 |   0.703383 | 0.279634 | 0.477494 |     0.358079 |     0.428672 |   23.8018 |                    0.391544 |     0.277845 |   0.612534 |
| 2020       | 0.427576 |   0.775579 |   0.724257 |       0.493186 |       0.476527 |          2.04482 |         0.530192 |         0.50209  |    2.48055 |    4.08964 |   0.664259 |   0.693749 | 0.297335 | 0.495834 |     0.384684 |     0.497005 |   19.7804 |                    0.52211  |     0.395027 |   0.695104 |
| 2021       | 0.334956 |   0.597513 |   0.581799 |       0.446657 |       0.433315 |          1.74886 |         0.5243   |         0.488959 |    2.19237 |    3.42195 |   0.614813 |   0.610256 | 0.275859 | 0.483064 |     0.385646 |     0.50852  |   16.2773 |                    0.43047  |     0.300323 |   0.702936 |
| 2022       | 0.357808 |   0.671229 |   0.603623 |       0.389092 |       0.450971 |          1.96852 |         0.531655 |         0.529475 |    2.24708 |    3.66757 |   0.60951  |   0.656991 | 0.279882 | 0.484602 |     0.581118 |     0.678748 |  nan      |                    0.461897 |     0.340982 |   0.791325 |
| 2023       | 0.366831 |   0.693477 |   0.628672 |       0.459894 |       0.509031 |          1.94362 |         0.547301 |         0.597199 |    2.38479 |    3.63854 |   0.831204 |   0.755583 | 0.333343 | 0.678843 |     0.82325  |     0.795522 |  nan      |                    0.513577 |     0.286142 |   0.680048 |
| 2024Q1     | 0.454326 |   1.15619  |   1.81511  |       2.28553  |       0.770145 |          2.1871  |         0.581775 |         0.794668 |    2.63438 |    3.39618 |   0.724994 |   0.694829 | 0.716583 | 0.786435 |     0.532364 |     1.09447  |   30.723  |                    1.55208  |     0.463185 |   0.816965 |
| 2024Q2     | 1.3662   |   1.82643  |   1.88289  |       1.34329  |       0.859269 |          2.07278 |         0.751773 |         0.864611 |    2.3182  |    3.31705 |   0.878533 |   0.797009 | 0.476847 | 0.960647 |     1.13285  |     1.28257  |   32.9429 |                    0.706783 |     0.391611 |   0.837316 |
| 2024Q3     | 0.483385 |   1.15536  |   1.35677  |       0.842483 |       0.683304 |          1.80349 |         0.655805 |         0.902387 |    1.69659 |    3.89979 |   0.74611  |   0.717173 | 0.410024 | 0.763577 |     0.837046 |     1.14057  |   27.4474 |                    0.674633 |     0.379422 |   1.05563  |
| 2024Q4     | 0.311394 |   0.696075 |   0.593906 |       0.405704 |       0.373535 |          1.52252 |         0.422686 |         0.466826 |    2.0938  |    3.1447  |   0.562048 |   0.463881 | 0.234204 | 0.476275 |     0.390396 |     0.595555 |  nan      |                    0.422824 |     0.294721 |   0.622021 |
| 2025Q1     | 0.376193 |   0.712626 |   0.604254 |       0.432756 |       0.536578 |          2.21596 |         0.580119 |         0.591788 |    2.69539 |    3.32973 |   0.824022 |   0.692935 | 0.297852 | 0.673126 |     0.474917 |     0.505771 |  nan      |                    0.472143 |     0.271055 |   0.634368 |
| 2025Q2     | 0.586443 |   0.91306  |   0.768801 |       0.590395 |       0.810694 |          2.18309 |         0.84232  |         1.24034  |    4.36114 |    4.38811 |   2.59219  |   1.40029  | 0.656925 | 1.32357  |     0.91589  |     0.962905 |   21.0486 |                    0.566423 |     0.367223 |   0.921352 |
| 2025Q3     | 0.343732 |   0.637652 |   0.699562 |       0.476294 |       0.757779 |          2.77171 |         0.651085 |         0.589823 |   13.2696  |   11.8667  |   2.27952  |   3.32532  | 0.319275 | 0.649195 |     0.56203  |     0.614875 |  nan      |                    0.419024 |     0.343666 |   0.627906 |
| 2025Q4     | 0.285594 |   0.519815 |   0.431246 |       0.288273 |       0.339615 |          2.32145 |         0.527534 |         0.489277 |    4.52746 |    5.29383 |   0.957656 |   1.26867  | 0.231938 | 0.488529 |     0.378762 |     0.442039 |  nan      |                    0.341309 |     0.28596  |   0.433947 |
| 2026Q1     | 0.408616 |   0.759452 |   0.72764  |       0.764275 |       0.681055 |          2.31307 |         0.700347 |         0.97185  |    2.54059 |    3.13046 |   0.768091 |   0.70799  | 0.465202 | 0.650165 |     0.378682 |     0.43569  |  nan      |                    0.595994 |     0.285268 |   0.494263 |
| Grand Mean | 0.417285 |   0.778942 |   0.754196 |       0.54442  |       0.536668 |          2.08277 |         0.581437 |         0.621158 |    2.75962 |    4.0333  |   0.834817 |   0.820161 | 0.336461 | 0.616417 |     0.521817 |     0.63257  |   22.101  |                    0.509899 |     0.324855 |   0.693243 |

VIIRS Pixel Coverage Summary

GAB {'lat_km': 100.18799999999983, 'lon_km': 236.14039282935244, 'area_km2': 23658.43367678712, 'expected_pixels': 1478.652104799195}
Ceduna W {'lat_km': 100.18799999999983, 'lon_km': 84.45069361866571, 'area_km2': 8460.946092266866, 'expected_pixels': 528.8091307666791}
Ceduna E {'lat_km': 200.37599999999966, 'lon_km': 93.3608076236846, 'area_km2': 18707.26518840339, 'expected_pixels': 1169.204074275212}
Pt Lincoln W {'lat_km': 178.11200000000014, 'lon_km': 73.48130770267028, 'area_km2': 13087.902677538019, 'expected_pixels': 817.9939173461262}
Pt Lincoln E {'lat_km': 200.37599999999966, 'lon_km': 73.39338185392326, 'area_km2': 14706.272282361702, 'expected_pixels': 919.1420176476064}
Spencer Gulf N {'lat_km': 155.84799999999984, 'lon_km': 139.4028962077236, 'area_km2': 21725.662568181284, 'expected_pixels': 1357.8539105113302}
Spencer Gulf C {'lat_km': 66.79200000000016, 'lon_km': 110.22196155400673, 'area_km2': 7361.945256115235, 'expected_pixels': 460.1215785072022}
Spencer Gulf S {'lat_km': 77.92399999999952, 'lon_km': 109.35870090910547, 'area_km2': 8521.667409641082, 'expected_pixels': 532.6042131025677}
SVG - NW {'lat_km': 77.92399999999952, 'lon_km': 38.55462068911782, 'area_km2': 3004.3302625787987, 'expected_pixels': 187.77064141117492}
SVG - NE {'lat_km': 77.92399999999952, 'lon_km': 44.062423644703465, 'area_km2': 3433.520300089852, 'expected_pixels': 214.59501875561574}
SVG - SW {'lat_km': 66.79200000000016, 'lon_km': 40.98439194469068, 'area_km2': 2737.4295067697863, 'expected_pixels': 171.08934417311164}
SVG - SE {'lat_km': 66.79200000000016, 'lon_km': 40.98439194468809, 'area_km2': 2737.4295067696135, 'expected_pixels': 171.08934417310084}
KI - W {'lat_km': 100.18799999999983, 'lon_km': 90.23076422948498, 'area_km2': 9040.039806623625, 'expected_pixels': 565.0024879139766}
KI - E {'lat_km': 100.18799999999983, 'lon_km': 90.23076422948498, 'area_km2': 9040.039806623625, 'expected_pixels': 565.0024879139766}
Victor - W {'lat_km': 89.05599999999968, 'lon_km': 63.121684790097184, 'area_km2': 5621.364760666875, 'expected_pixels': 351.33529754167967}
Victor - E {'lat_km': 89.05599999999968, 'lon_km': 71.95634710042403, 'area_km2': 6408.144447375339, 'expected_pixels': 400.5090279609587}
Lk Alex {'lat_km': 44.52799999999984, 'lon_km': 45.37001311025132, 'area_km2': 2020.2359437732637, 'expected_pixels': 126.26474648582898}
Victor Harbour-Mt Gambier {'lat_km': 211.50799999999984, 'lon_km': 132.56279752558572, 'area_km2': 28038.092179041563, 'expected_pixels': 1752.3807611900977}
Mt Gambier {'lat_km': 111.32, 'lon_km': 174.23988004162143, 'area_km2': 19396.383446233296, 'expected_pixels': 1212.273965389581}
Pt Fairy {'lat_km': 111.32, 'lon_km': 174.23988004162143, 'area_km2': 19396.383446233296, 'expected_pixels': 1212.273965389581}

Technical Notes

VIIRS Sensor Capabilities:

• Operational: 2011-present (Suomi-NPP), 2017-present (NOAA-20)
• Resolution: 750m (superior to MODIS 1000m)
• Calibration: Stable, no orbital drift (unlike aging MODIS)
• Algorithm: Standard NASA OC3 chlorophyll-a retrieval
• Validation: Well-established for coastal waters globally

Not Benthic Reflectance:

• Upper Spencer Gulf depth: 20-40m (adequate for ocean color sensing)
• Gulf St Vincent North depth: 15-30m (adequate for ocean color sensing)
• VIIRS algorithm corrects for shallow-water reflectance
• 13-year temporal stability rules out bottom-type changes
• Southern regions (similar depths) show low stable values
• Spike events (9.11 mg/m³) impossible from benthic reflectance

Not Cloud/Atmospheric Artifacts:

• 13-year consistent pattern (thousands of clear-sky observations)
• Multiple independent overpasses (NPP + NOAA-20)
• Standard atmospheric correction applied
• Pattern matches known circulation (counter-clockwise GSV)
• Independent validation: In-situ sampling during 2025 crisis confirmed satellite values

What is Chlorophyll-a?

Chlorophyll-a is the green pigment found in all photosynthetic algae and plants. In ocean water, measuring chlorophyll-a tells us how much algae (phytoplankton) is present. It's the standard indicator used worldwide to monitor algal blooms.

Understanding the Measurements (mg/m³)

Chlorophyll-a Level	Interpretation	Water Quality
0.1 - 1.0 mg/m³	Normal oceanic levels	🟢 Healthy
1.0 - 2.0 mg/m³	Slightly elevated	🟡 Acceptable
2.0 - 5.0 mg/m³	Moderate bloom conditions	🟠 Concerning
5.0 - 10.0 mg/m³	Severe bloom	🔴 Harmful
> 10.0 mg/m³	Extreme bloom / toxic potential	🔴 Crisis

What Causes High Chlorophyll?

Algae need nutrients (primarily nitrogen and phosphorus) to grow. Excessive nutrients from:

• Wastewater discharge
• Agricultural fertilizer runoff
• Industrial waste
• Urban stormwater
• Waste management facilities

Nitrogen Isotope Fingerprinting

• Sample seagrass/algae tissue from north-south transects
• δ15N signatures differentiate: organic waste (+8 to +20‰), treated sewage (+15 to +22‰), natural marine (+3 to +7‰)
• Definitive source apportionment
• For details, see: https://pubmed.ncbi.nlm.nih.gov/23602260/

Lake Alexandrina

• Refer to the "Chlorophyll-a Time Series Viewer" for an alternative visualisation
• This uses a merged dataset from two satellites (still VIIRS, but NRT) for improved gap filling
• Or just drive down Point Sturt road and see for yourself :)

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Last updated: Wed 15 Apr 2026 14:15:04 ACST