Influence of timing of sea ice retreat on phytoplankton size during marginal ice zone bloom period on the Chukchi and Bering shelves
The size structure and biomass of a phytoplankton community during the spring bloom period can affect the energy use of higher-trophic-level organisms through the predator–prey body size relationships. The timing of the sea ice retreat (TSR) also plays a crucial role in the seasonally ice-covered ma...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-01-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/13/115/2016/bg-13-115-2016.pdf |
| Summary: | The size structure and biomass of a phytoplankton community during the spring
bloom period can affect the energy use of higher-trophic-level organisms
through the predator–prey body size relationships. The timing of the sea ice
retreat (TSR) also plays a crucial role in the seasonally ice-covered marine
ecosystem, because it is tightly coupled with the timing of the spring bloom.
Thus, it is important to monitor the temporal and spatial distributions of a
phytoplankton community size structure. Prior to this study, an ocean colour
algorithm was developed to derive phytoplankton size index <i>F</i><sub>L</sub>,
which is defined as the ratio of chlorophyll <Ei>a</Emphasis> (chl <Emphasis Type="Italic">a</i>) derived from cells
larger than 5 µm to the total chl <i>a</i>, using satellite remote
sensing for the Chukchi and Bering shelves. Using this method, we analysed
the pixel-by-pixel relationships between <i>F</i><Subscript>L</Subscript> during the marginal ice
zone (MIZ) bloom period and TSR over the period of 1998–2013. The influences
of the TSR on the sea surface temperature (SST) and changes in ocean heat
content (ΔOHC) during the MIZ bloom period were also investigated. A
significant negative relationship between <i>F</i><sub>L</sub> and the TSR was widely
found in the shelf region during the MIZ bloom season. However, we
found a significant positive (negative) relationship between the SST (ΔOHC) and TSR. Specifically, an earlier sea ice retreat was associated with
the dominance of larger phytoplankton during a colder and weakly stratified
MIZ bloom season, suggesting that the duration of the nitrate supply, which
is important for the growth of large-sized phytoplankton in this region (i.e.
diatoms), can change according to the TSR. In addition, under-ice
phytoplankton blooms are likely to occur in years with late ice retreat,
because sufficient light for phytoplankton growth can pass through the ice
and penetrate into the water columns as a result of an increase in solar
radiation toward the summer solstice. Moreover, we found that both the length
of the ice-free season and the annual median of <i>F</i><sub>L</sub> positively
correlated with the annual net primary production (APP). Thus, both the
phytoplankton community composition and growing season are important for the
APP in the study area. Our findings showed a quantitative relationship
between the interannual variability of <i>F</i><sub>L</sub>, the TSR, and the APP,
which suggested that satellite remote sensing of the phytoplankton community
size structure is suitable to document the impact of a recent rapid sea ice
loss on the ecosystem of the study region. |
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| ISSN: | 1726-4170 1726-4189 |