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<p>Polynyas and their adjacent seasonal ice zones (SIZs) represent the most productive regions in the Southern Ocean, supporting unique food webs that are highly sensitive to climate change. Understanding the dynamics of phytoplankton and the carbon pool in these areas is crucial for assessing the role of the Southern Ocean in global carbon cycling. During the late stage of an algal bloom, seawater samples at 14 stations were collected in the Amundsen Sea Polynya (ASP) and adjacent SIZ. Using nutrients, phytoplankton pigments, organic carbon (OC), remote sensing data, and physicochemical measurements, as well as CHEMTAX model simulations, we investigated the response of the phytoplankton crops, taxonomic composition, and OC pool to environmental factors. Our analyses revealed that hydrodynamic regimes of the polynya, adjacent SIZs and open sea were regulated by the regionally varying intrusion of Circumpolar Deep Water, photosynthetically active radiation and sea ice melt water. The ASP exhibited the highest seasonal nutrient utilization rates [Δ<i>N</i> = (1 059 ± 386) mmol/m<sup>2</sup>, Δ<i>P</i> = (50 ± 17) mmol/m<sup>2</sup> and ΔSi = (956 ± 904) mmol/m<sup>2</sup>], while the open sea had lower rates. The integrated chlorophyll <i>a</i> (Chl <i>a</i>) concentration at depths of 0–200 m ranged from 20.4 mg/m<sup>2</sup> to 1 420.0 mg/m<sup>2</sup> and peaked in the polynya. In the study area, Haptophytes <i>P. antarctica</i> was the dominant functional group (34% ± 27%), and diatoms acted as a secondary contributor (23% ± 14%). The major functional group and particulate OC (POC) contributor varied from diatoms (36% ± 12%) in the open sea to haptophytes (48% ± 31%) in the polynya waters. Strong light conditions and microelement limitations promoted the dominance of <i>P. antarctica</i> (low Fe forms) dominance in the ASP. The strong correlations between the POC and Chl <i>a</i> depth-integrated concentration suggest that the POC was primarily derived from phytoplankton, while dissolved OC (DOC) was influenced by consumer activity and water mass transport. In addition, the transport of OC in the upper 200 m of the water column within the ASP was quantified, revealing the predominantly westward fluxes for both DOC (9.0 mg OC / (m<sup>2</sup>·s)) and POC (7.2 mg OC / (m<sup>2</sup>·s)). The latitudinal transport exhibited the northward transport of DOC (8.1 mg OC / (m<sup>2</sup>·s)) and southward transport of POC (4.3 mg OC / (m<sup>2</sup>·s)) movement. These findings have significant implications for enhancing our understanding of how hydrodynamics influence OC cycling in polynya regions.</p>

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Spatial dynamics of phytoplankton assemblages and organic carbon stock in the highly productive Amundsen Sea Polynya and adjacent seasonal ice zone

  • 期刊论文

  • 发表日期：

    2025年4月1日

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  • Dong Li,
  • Jun Zhao,
  • Ji Hu,
  • Jianming Pan,
  • Jianfeng He,
  • Yongming Sun,
  • Peisong Yu,
  • Xufeng Yang,
  • Cai Zhang,
  • Haifeng Zhang,
  • Weiping Sun,
  • Gaojing Fan

摘要

Polynyas and their adjacent seasonal ice zones (SIZs) represent the most productive regions in the Southern Ocean, supporting unique food webs that are highly sensitive to climate change. Understanding the dynamics of phytoplankton and the carbon pool in these areas is crucial for assessing the role of the Southern Ocean in global carbon cycling. During the late stage of an algal bloom, seawater samples at 14 stations were collected in the Amundsen Sea Polynya (ASP) and adjacent SIZ. Using nutrients, phytoplankton pigments, organic carbon (OC), remote sensing data, and physicochemical measurements, as well as CHEMTAX model simulations, we investigated the response of the phytoplankton crops, taxonomic composition, and OC pool to environmental factors. Our analyses revealed that hydrodynamic regimes of the polynya, adjacent SIZs and open sea were regulated by the regionally varying intrusion of Circumpolar Deep Water, photosynthetically active radiation and sea ice melt water. The ASP exhibited the highest seasonal nutrient utilization rates [ΔN = (1 059 ± 386) mmol/m2, ΔP = (50 ± 17) mmol/m2 and ΔSi = (956 ± 904) mmol/m2], while the open sea had lower rates. The integrated chlorophyll a (Chl a) concentration at depths of 0–200 m ranged from 20.4 mg/m2 to 1 420.0 mg/m2 and peaked in the polynya. In the study area, Haptophytes P. antarctica was the dominant functional group (34% ± 27%), and diatoms acted as a secondary contributor (23% ± 14%). The major functional group and particulate OC (POC) contributor varied from diatoms (36% ± 12%) in the open sea to haptophytes (48% ± 31%) in the polynya waters. Strong light conditions and microelement limitations promoted the dominance of P. antarctica (low Fe forms) dominance in the ASP. The strong correlations between the POC and Chl a depth-integrated concentration suggest that the POC was primarily derived from phytoplankton, while dissolved OC (DOC) was influenced by consumer activity and water mass transport. In addition, the transport of OC in the upper 200 m of the water column within the ASP was quantified, revealing the predominantly westward fluxes for both DOC (9.0 mg OC / (m2·s)) and POC (7.2 mg OC / (m2·s)). The latitudinal transport exhibited the northward transport of DOC (8.1 mg OC / (m2·s)) and southward transport of POC (4.3 mg OC / (m2·s)) movement. These findings have significant implications for enhancing our understanding of how hydrodynamics influence OC cycling in polynya regions.