Iron Limitation and Uneven Grazing Pressure on Phytoplankton Co‐Lead the Seasonal Species Succession in the Ross Ice Shelf Polynya. Issue 3 (10th March 2023)

• Record Type: Journal Article
• Authors: Zhang, Yongli; Zhao, Wei; Wei, Hao; Yang, Wei; Luo, Xiaofan
• Is Part Of: Journal of geophysical research. Volume 128:Issue 3(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-03-10
• Subjects: Ross Ice Shelf Polynya -- seasonal species succession -- Phaeocystis antarctica -- iron‐limited conditions -- grazing process -- sensitivity experiments; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2022JC019026
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: The seasonal species succession of phytoplankton from Phaeocystis antarctica to diatoms in the Ross Ice Shelf Polynya (RISP) plays a fundamental role in food webs and ecosystem functioning. Previous studies have revealed that this seasonal succession is affected by differences in light, iron demand, aggregation, and subsequent sinking between these two taxa. This study further investigated the dominant process of species succession by analyzing the results of a bulk mixed‐layer ecosystem model. The mechanism of processes leading to the replacement by diatoms differs from that for triggering the initial P. antarctica bloom. Light triggered the spring bloom dominated by P. antarctica in iron‐rich surface water, which is resupplied by winter convective mixing from the lower layer pool. After reaching its maximum in mid‐November, the biomass of P. antarctica declined progressively due to the severe iron limitation. Seasonal species succession can be enhanced by a small amount of predation on P. antarctica by microzooplankton. The long‐term iron enrichment promotes the transition by supporting diatom growth. The balance between bottom‐up and top‐down processes plays a critical role in shaping the phytoplankton composition and promoting the seasonal species succession in the iron‐limited upper mixed layer of the RISP. Plain Language Summary: Understanding how living things in the high‐latitude Southern Ocean are impacted by climate change requires knowledge of how the base of food webs (i.e., marine plants) responds to the environment and predators nowadays. It is especially important to understand the natural behaviors of plants in individual regions that are highly productive and less affected by human activities. The southern Ross Sea is one such region, which remains ice‐free all year round and iron‐limited during the growing seasons. Typical of this environment is the sequential occurrence of two plant species, but it is not known why they flourish in order. In this study, numerical simulations give us an idea of the different responses of the two plants to irradiance, water temperature, iron concentrations, and predators at different periods of the growing season. The simulations show us that low light conditions favor one species to grow first, iron limited its growth, then the predator's feeding on this species gives another species a chance to grow thereafter. The comparison of feeding process and iron‐limiting effects on plants according to the simulations highlights the balance between growth and ingestion in regulating the base of food webs in this unique environment. Key Points: Seasonal species succession of phytoplankton from Phaeocystis antarctica to diatoms has been well reproduced by the 0‐D ecosystem model Iron‐depleted environment drives the transition by iron‐limiting the P. antarctica growth Seasonal species succession can be enhanced by a small amount of predation on P. antarctica by microzooplankton