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Absolute melatonin levels between from 18:00 to 24:00 in Montevideo (red) and Antarctica (blue). Melatonin levels were obtained at 1-h intervals. The expected nocturnal increase in melatonin levels in both locations was observed. Antarctic diurnal melatonin levels (18:00–21:00 h) were very low (rarely > 7 pg/mL) and significantly different from the respective Montevideo values from 18:00 to 20:00 h (Wilcoxon signed-rank test: ** p < 0.01). Black dots represent outliers.
