First phytoplankton community assessment of the Kong Håkon VII Hav, Southern Ocean, during austral autumn

[摘要] We studied phytoplankton and protozooplankton community composition based on light microscopy, flow cytometry, and photosynthetic pigment data in the Atlanticsector of the Southern Ocean during March 2019 (early austral autumn).Sampling was focused on the area east of the prime meridian in the Kong Håkon VII Hav, including Astrid Ridge, Maud Rise, and a south–north transect at 6 ∘  E. Phytoplankton community composition throughoutthe studied area was characterized by oceanic diatoms typical of theiron-depleted high-nutrient, low-chlorophyll (HNLC) Southern Ocean. Topography and wind-driven iron supply likely sustained blooms dominated by the centric diatom Chaetoceros dichaeta at Maud Rise and at a station north of the 6 ∘  E transect.For the remainder of the 6 ∘  E transect, diatom composition was similar to the previously mentioned bloom stations, but flagellates dominatedin abundance, suggesting a post-bloom situation and likely top-down control by krill on the bloom-forming diatoms. Among flagellates, species withhaptophyte-type pigments were the dominating group. At Astrid Ridge, overallabundances were lower and pennate diatoms were more numerous than centric diatoms, but the community composition was nevertheless typical of HNLC areas. The observations described here show that C. dichaeta can form blooms beyond the backgroundbiomass level and also fuels both carbon export and upper trophic levels within HNLC areas. This study is the first thorough assessment ofphytoplankton communities in this region and can be compared to otherseasons in future studies.

[学科分类] 大气科学