Wind speed influence on phytoplankton bloom dynamics in the Southern Ocean Marginal Ice Zone

Abstract

[1] Analysis of satellite ocean color and wind speed data within the seasonal ice zone (SIZ) of the Southern Ocean sheds light on the physical processes that influence phytoplankton biomass distributions. A compilation of monthly averaged chlorophyll and percent sea ice cover data within the SIZ from 1997 to 2005 has been compared with monthly average wind speed data from 1999 to 2005. The size of the marginal ice zone (MIZ, areas of recent ice retreat) was fairly consistent from year to year, always peaking in December, with a mean area of 6.0 million km 2 . The mean area within the MIZ with phytoplankton blooms (chlorophyll exceeding 0.8 mg/m 3 ) was 0.36 million km 2 . While the bloom areal extent seems small compared to the MIZ, in reality, because of gaps in the chlorophyll data, blooming regions comprise a much larger fraction of the MIZ. Considering only areas with valid chlorophyll data, the percentage of the MIZ with blooms was 17%, 21%, and 24% for the months of December, January, and February, respectively. December always has the largest MIZ area, but MIZ mean chlorophyll concentrations sometimes do not peak until February. Wind speed strongly impacts phytoplankton bloom dynamics within the MIZ. There is an inverse relation between wind speed and bloom occurrence, with blooms largely suppressed at high wind speeds. At low wind speeds ($5 m/s), blooms are observed over about one third of the MIZ. Blooms are also much more frequent near the continent than in offshore waters, likely due to increased iron availability. Open ocean phytoplankton blooms in the Southern Ocean are likely to become iron-light co-limited except in regions where the mixed layer depth is relatively shallow.

Southern Ocean Phytoplankton in a Changing Climate

“…Storms, wind mixing, and waves deepen mixed depths in the MIZ, reducing the light availability and inhibiting bloom development ( Figure 7B) (Venables and Meredith, 2014). As a result, blooms only cover 17-24% of the MIZ over summer with maximum coverage of only 0.36 million km 2 in December (Savidge et al, 1996;Fitch and Moore, 2007). Evidence from culture studies and blooms in the Ross Sea indicate that Phaeocystis sp.…”

“…Phytoplankton blooms in the MIZ are patchy in space and time (Smith and Nelson, 1986). They generally occur in shallow mixed layers where wind speeds are <5 m s −1 (Fitch and Moore, 2007). Storms, wind mixing, and waves deepen mixed depths in the MIZ, reducing the light availability and inhibiting bloom development ( Figure 7B) (Venables and Meredith, 2014).…”

“…It is an area of high productivity that accounts for the majority of the springsummer phytoplankton blooms (Figure 2) (Arrigo et al, 2008b). The area of the MIZ varies greatly over spring and summer, ranging from 6 million km 2 in December to ∼0.2 million km 2 by March (Fitch and Moore, 2007). Sea ice formation in the winter scavenges phytoplankton cells into the ice and concentrates iron from the surface water Boyd, 2002;Lannuzel et al, 2010Lannuzel et al, , 2016.…”

The effects of dilution and mixed layer depth on deliberate ocean iron fertilization: 1-D simulations of the southern ocean iron experiment (SOFeX)

“…These lowered growth rates are still sufficient to offset losses to grazing and other processes. Fitch and Moore (2007) recently found an inverse correlation between bloom occurrence and wind speed in the Southern Ocean marginal ice zone.…”

The Role of Confluence in Shaping Water Quality Parameters on Example of the Flow-Through Lake Bikcze (Eastern Poland)

“…Slightly higher chl-a variability was recorded in the part between the deepest point of the lake and the outflow; the direction and the orientation of the vector was consistent with the wind direction (SW), during the measurement period. Wind may influence the phytoplankton distribution (expressed as chlorophyll) [37,38].…”