Fig 1.
Conceptual diagram for three phytoplankton bloom types.
Solid line, dashed line, and dotted line represent under-ice (UI) bloom, probable under-ice (PUI) bloom, and marginal ice zone (MIZ) bloom following the date of sea ice retreat (DSR), respectively. This conceptual diagram was modified from Lowry et al. [13].
Fig 2.
Bathymetry map of the Pacific Arctic.
Abbreviations: SLI, St. Lawrence Island; BS, Bering Strait; NS, Norton Sound; KS, Kotzebue Sound.
Fig 3.
Description of the parametric Gaussian model.
Abbreviations: chla0, background chla; chlam, amplitude of chla peak; tm, date of chla peak; σ, days for which chla exceeded half of chla peak.
Table 1.
Settings for the parametric Gaussian function.
Fig 4.
Spatial patterns in sea-ice climatology.
(A) Average date of sea-ice retreat (DSR) and (B) interannual trend (Mann-Kendall test, p < 0.05) in DSR for 2003–2019. White represents areas with insignificant (Mann-Kendall test, p ≥ 0.05) temporal trend during the period.
Fig 5.
Spatial variations in average chlorophyll-a (chla) concentrations for 2003–2019.
(A) Entire open-water period (sea-ice concentration below 50%) and (B) marginal ice zone (MIZ) retreat period.
Fig 6.
Frequency plots of collated chla time-series during the MIZ retreat period.
(A) UI blooms, (B) PUI blooms, and (C) MIZ blooms.
Fig 7.
Results of the sensitivity analysis for the bloom type classification.
(A) UI, and (B) PUI, and MIZ blooms. Modeled chla time-series from 30 days prior to DSR until 30 days after DSR using five randomly-selected chla concentrations during the MIZ retreat period are shown as gray lines. Black circles represent sample chla time-series during the MIZ retreat period. The accuracy indicates the rate of correct identification for each bloom type.
Fig 8.
Spatial distribution of spring phytoplankton bloom types.
(A) Dominant bloom type, and number of years from 2003 through 2019 with observations of (B) UI, (C) PUI, and (D) MIZ blooms. White represents areas where none of the years 2003–2019 satisfied our criteria.
Table 2.
Summary statistics for proportions of each bloom type in the Pacific Arctic.
Fig 9.
Proportion of each bloom type and number of observable pixels within ten-day DSR range steps.
Blue, yellow and red bars represent proportions of UI, PUI, and MIZ blooms, respectively. White dots indicate number of observable pixels.
Fig 10.
Interannual variations in proportions of each bloom type for 2003–2019.
Solid and dashed lines represent statistically significant (p < 0.05) and insignificant trends, respectively.