Weddell Sea Phytoplankton Blooms Modulated by Sea Ice Variability and Polynya Formation

Abstract

Seasonal sea ice retreat is known to stimulate Southern Ocean phytoplankton blooms, but depth‐resolved observations of their evolution are scarce. Autonomous float measurements collected from 2015–2019 in the eastern Weddell Sea show that spring bloom initiation is closely linked to sea ice retreat timing. The appearance and persistence of a rare open‐ocean polynya over the Maud Rise seamount in 2017 led to an early bloom and high annual net community production. Widespread early ice retreat north of Maud Rise in 2017, however, had a similar effect, suggesting that the polynya most impacted the timing of bloom initiation. Still, higher productivity rates at Maud Rise relative to the surrounding region are observed in all years, likely supported by flow‐topography interactions. The longer growing season in 2017–2018 also allowed for separation of distinct spring and fall bloom signals, the latter of which was primarily subsurface and associated with mixed‐layer deepening.

Changes in Phytoplankton Communities Along the Northern Antarctic Peninsula: Causes, Impacts and Research Priorities

“…Consequently, phytoplankton growth rates increase, particularly in the marginal sea ice zones (Arrigo et al, 2017;Schofield et al, 2018). Recent continuous high-resolution measurements (e.g., using autonomous floats) have also confirmed the importance of seasonal ice retreat for the timing and intensity of phytoplankton blooms (von Berg et al, 2020). Therefore, the beginning of sea ice melting in spring (September-November) linked to the increase of daylight length (Vernet et al, 2012), is the main factor that triggers phytoplankton blooms in the NAP (Varela et al, 2002;Garibotti et al, 2005b).…”

“…Autonomous in situ measurements will also allow for in-depth studies of the dynamics between phytoplankton and sea ice. While a few studies using floats already exist in marginal ice zones (e.g., Moreau et al, 2020;von Berg et al, 2020), further works would help reveal how phytoplankton changes with sea ice retreat at finer scales. Ocean color remote sensing, i.e., satellite-based measurements of visible light reflected off the upper ocean, will be essential toward studying the NAP ecosystem.…”

Phenology and Environmental Control of Phytoplankton Blooms in the Kong Håkon VII Hav in the Southern Ocean

“…It should be noted that the detected bloom initiation may be regarded as the bloom climax if considering the bloom biomass as vertically integrated estimates instead of surface observations, and that the winter ("strict") onset of the vertically integrated bloom could occur earlier (Llort et al, 2015; see Table 1 and Supplementary Material section 2 for definitions). A recent study concentrating on biogeochemical (BGC) Argo floats providing vertical profile observations every 10-days at Maud Rise, from 2014 to 2019, indeed shows that biomass seemingly increases as early as in November with rapid increases in December (the bloom onset is not marked in their Figure 2), and that bloom climaxes in December-January (von Berg et al, 2020). Further, the detected bloom initiation in this study (i.e., climax) should correspond to favorable environmental conditions (bottom-up control) (Brody et al, 2013;Llort et al, 2015), which are discussed in the next subsections.…”

“…Furthermore, there are inherent limitations to satellite remote sensing data, such as the limited depth of the observations or array of variables provided, that can only be overcome by combining other data sources to the analysis, such as the in situ data described here. Therefore our study can contribute to new understanding, with the specific aim to characterize this area which has seldom received detailed attention besides the Maud Rise area (e.g., von Berg et al, 2020). The objectives of this paper are to describe the phytoplankton bloom phase, timing, and magnitude as observed during the autumn cruise and from the long-term ocean color remote sensing records; to explain the observed bloom patterns based on the environmental controlling factors of the bloom development, namely sea ice cover, light and MLD, and tidally induced mixing; and to delineate regional bloom regimes.…”

Self‐Shading and Meltwater Spreading Control the Transition From Light to Iron Limitation in an Antarctic Coastal Polynya

“…The seasonal succession from light to iron limitation reflects previous modeling results in the ASP (Oliver et al, 2019), as well as observations from the West Antarctic Peninsula (Arrigo et al, 2017) and the Weddell Sea (von Berg et al, 2020). We use the transition from light to iron limitation described above on a spatially averaged basis to examine differences across the domain.…”