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  • 1
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    Microzooplankton grazing along the Western Antarctic Peninsula (2013)
    Inter-Research
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Inter-Research, 2013. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Aquatic Microbial Ecology 70 (2013): 215-232, doi:10.3354/ame01655.
    Description: The significance of microzooplankton as grazers in pelagic ecosystems has been established, yet relatively few studies of microzooplankton grazing, compared to that of macrozooplankton, have been conducted in the Southern Ocean. We report phytoplankton and bacterial growth and grazing mortality rates along the Western Antarctic Peninsula (WAP), a region of rapid climate change. Growth and grazing rates were determined by dilution experiments at select stations along the WAP in January of 2009 to 2011 and in the nearshore waters near Palmer Station in February and March 2011. Microzooplankton exerted higher grazing pressure on bacteria compared to phytoplankton along the WAP and also selectively grazed on smaller phytoplankton (picoautotrophs and nanophytoplankton) and on the more actively growing (high nucleic acid) bacterial cells. Among all phytoplankton size classes, growth rates ranged from undetectable (i.e. not significant; NS) to 0.99 d-1, grazing mortality rates were NS to 0.56 d-1, and microzooplankton removed 〈100% of daily phytoplankton production in all but one experiment. For high and low nucleic acid content bacteria, growth rates were NS to 0.95 d-1, and grazing mortality rates were NS to 0.43 d-1; microzooplankton often removed 〉100% of daily bacterial production. There was a significant (albeit weak) exponential relationship between temperature and phytoplankton mortality, although the range of experimental temperatures was small. The present study provides a reference point of microzooplankton grazing impact along the WAP in the summer and contributes valuable information to studies modeling the flow of carbon through the WAP food web, improving our ability to predict climate-induced changes in the WAP ecosystem.
    Description: The Palmer LTER is supported by National Science Foundation award ANT-0823101 from the Division of Polar Programs Antarctic Organisms and Ecosystems Program. Additional funding to support the participation of L.M.G. on a Palmer LTER cruise was provided by A. G. ‘Casey’ Duplantier Jr. and the 1st Advantage Federal Credit Union of Newport News, Virginia, USA.
    Keywords: Microzooplankton ; Protozoa ; Grazing ; Western Antarctic Peninsula ; Southern Ocean ; Climate
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    Climate forcing for dynamics of dissolved inorganic nutrients at Palmer Station, Antarctica : an interdecadal (1993–2013) analysis (2016)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Biogeosciences 121 (2016): 2369–2389, doi:10.1002/2015JG003311.
    Description: We analyzed 20 years (1993–2013) of observations of dissolved inorganic macronutrients (nitrate, N; phosphate, P; and silicate, Si) and chlorophyll a (Chl) at Palmer Station, Antarctica (64.8°S, 64.1°W) to elucidate how large-scale climate and local physical forcing affect the interannual variability in the seasonal phytoplankton bloom and associated drawdown of nutrients. The leading modes of nutrients (N, P, and Si empirical orthogonal functions 1, EOF1) represent overall negative anomalies throughout growing seasons, showing a mixed signal of variability in the initial levels and drawdown thereafter (low-frequency dynamics). The second most common seasonal patterns of nitrate and phosphate (N and P EOF2) capture prolonged drawdown events during December–March, which are correlated to Chl EOF1. Si EOF2 captures a drawdown event during November–December, which is correlated to Chl EOF2. These different drawdown patterns are shaped by different sets of physical and climate forcing mechanisms. N and P drawdown events during December–March are influenced by the winter and spring Southern Annular Mode (SAM) phase, where nutrient utilization is enhanced in a stabilized upper water column as a consequence of SAM-driven winter sea ice and spring wind dynamics. Si drawdown during November–December is influenced by early sea ice retreat, where ice breakup may induce abrupt water column stratification and a subsequent diatom bloom or release of diatom cells from within the sea ice. Our findings underscore that seasonal nutrient dynamics in the coastal WAP are coupled to large-scale climate forcing and related physics, understanding of which may enable improved projections of biogeochemical responses to climate change.
    Description: U.S. National Science Foundation Grant Numbers: OPP-9011927, 9632763, 0217282, 0823101, GEO-PLR 1440435; NASA ROSES Grant Number: NNX14AL86G
    Description: 2017-03-17
    Keywords: Nutrient drawdown ; Phytoplankton bloom ; Climate variability ; Western Antarctic Peninsula ; Palmer LTER ; Biogeochemistry
    Repository Name: Woods Hole Open Access Server
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  • 3
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    Effect of continental shelf canyons on phytoplankton biomass and community composition along the western Antarctic Peninsula (2015)
    Inter-Research
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marine Ecology Progress Series 524 (2015): 11-26, doi:10.3354/meps11189.
    Description: The western Antarctic Peninsula is experiencing dramatic climate change as warm, wet conditions expand poleward and interact with local physics and topography, causing differential regional effects on the marine ecosystem. At local scales, deep troughs (or canyons) bisect the continental shelf and act as conduits for warm Upper Circumpolar Deep Water, with reduced seasonal sea ice coverage, and provide a reservoir of macro- and micronutrients. Shoreward of many canyon heads are Adélie penguin breeding colonies; it is hypothesized that these locations reflect improved or more predictable access to higher biological productivity overlying the canyons. To synoptically assess the potential impacts of regional bathymetry on the marine ecosystem, 4 major canyons were identified along a latitudinal gradient west of the Antarctic Peninsula using a high-resolution bathymetric database. Biological-physical dynamics above and adjacent to canyons were compared using in situ pigments and satellite-derived sea surface temperature, sea ice and ocean color variables, including chlorophyll a (chl a) and fucoxanthin derived semi-empirically from remote sensing reflectance. Canyons exhibited higher sea surface temperature and reduced sea ice coverage relative to adjacent shelf areas. In situ and satellite-derived pigment patterns indicated increased total phytoplankton and diatom biomass over the canyons (by up to 22 and 35%, respectively), as well as increases in diatom relative abundance (fucoxanthin:chl a). While regional heterogeneity is apparent, canyons appear to support a phytoplankton community that is conducive to both grazing by krill and enhanced vertical export, although it cannot compensate for decreased biomass and diatom relative abundance during low sea ice conditions.
    Description: We acknowledge support from the National Aeronautics and Space Administration Ocean Bio - logy and Biogeochemistry Program (NNX14AL86G) and the National Science Foundation Polar Programs awards 0823101 (Antarctic Organisms and Ecosystems Program) and 1440435 (Antarctic Integrated System Science) to the Palmer LTER program.
    Keywords: Western Antarctic Peninsula ; Canyons ; Phytoplankton ; Diatoms ; Remote sensing ; Adélie penguin habitat ; Sea ice
    Repository Name: Woods Hole Open Access Server
    Type: Article
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