Fig 1.
Map of the northern Bering Sea study area.
Two DBO areas are indicated in red and the black text corresponds to individually sampled stations within each DBO transect marked by the blue circles. The stations are grouped as DBO1 (n = 5: SLIP-1, SLIP-2, SLIP-3, SLIP-4, SLIP-5) and DBO2 (n = 8: BCL-6A, BCL-6C, UTBS-1, UTBS-2, UTBS-3, UTBS-4, UTBS-5, DBO2.7). The bathymetry is reproduced from GEBCO Sheet G.08 compiled by R.L. Fisher of the Scripps Institution of Oceanography and extracted from the GEBCO Digital Atlas published by the British Oceanographic Data Centre on behalf of the IOC and IHO, 2003.
Fig 2.
Examples of sea surface phytoplankton phenology curves using NASA MODIS Aqua chlorophyll a concentration.
The examples listed are (a) DBO2 station UTBS-2 in 2013, (b) UTBS-4 in 2013, and (c) DBO1 station SLIP-1 in 2015. The dark circles and label indicate time 1, 2, and 3 (t1, t2, t3, respectively) that were recorded for each bloom curve for the Day of Year (DOY) and chlorophyll a concentrations, at the day of year of the start, peak, and end of bloom (shown in plot (a) only). The metrics were recorded for each separate bloom (determined to be individual curves that rose at least 0.5 mg/m3 from its t1). Therefore, the second bloom pictured here was separately assigned t1, t2, and t3 in red. The yellow shaded bars represent the date range of all July cruise sampling 2013–2019 (DOY 194–199). The bloom stage was recorded for each bloom that corresponded to the time of cruise sampling. Therefore, the examples shown are (a) Early Bloom, (b) Post Bloom, and (c) No Bloom stages at the time of sampling.
Table 1.
Field measured vs. remotely sensed life stage classification accuracy assessment of phytoplankton stage.
Fig 3.
The aggregated counts of bloom stages identified for all of the stations within DBO1 and DBO2 for both the remotely sensed (RS) and cruise-collected (field) pheophytin proportion methods.
EB = Early Bloom, PB = Post Bloom, NaN = missing data, NB = No Bloom for observations outside of a bloom cycle. The aggregation was performed using all available years of data (i.e. years that failed the minimum observations criteria for satellite time series are classified here as “RS NaN”).
Fig 4.
Sea ice breakup dates for DBO1 (a) and DBO2 (b) over the time series. Bars are missing at some 2018 DBO1 stations because winter sea ice did not form and no breakup date was observed.
Fig 5.
Daily sea ice concentrations (blue) and MODIS chlorophyll a (green) time series curves at the DBO1 stations.
Fig 6.
Daily sea ice concentrations (blue) and MODIS chlorophyll a (green) time series curves at the DBO2 stations.
Table 2.
Statistical summary for pheophytin proportions of total chlorophyll a + pheophytin measured in high vs. low sea ice station years for the DBO1 and DBO2 stations (n = 13) in the northern Bering Sea.
Fig 7.
Transect views of pheophytin proportion based on combined chlorophyll a and pheophytin concentrations measured in units μg/L at each collected depth.
The annual latitudinal transects show DBO1 stations on the left and DBO2 stations to the right. Note: cruise samples for most DBO2 stations were missing in 2019. Figure constructed using Ocean Data View (version 5.3; [46]).
Fig 8.
Pheophytin proportion time series.
Depth integrated (a, c) and surface (b, d) pheophytin proportions at each station in DBO1 (a, b) and DBO2 (c, d) over time.