Buoyant macroalgal transport of benthic epiphytic diatoms into deep-sea Southern Ocean sediments; a new proxy for antarctic paleoenvironmental change and an unresolved component of the Antarctic pelagic ecosystem

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doi: 10.1130/abs/2016AM-287899
Author(s): Harwood, David M.
Author Affiliation(s): Primary:
University of Nebraska-Lincoln, Earth and Atmospheric Sciences, Lincoln, NE, United States
Volume Title: Geological Society of America, 2016 annual meeting & exposition
Source: Abstracts with Programs - Geological Society of America, 48(7); Geological Society of America, 2016 annual meeting & exposition, Denver, CO, Sep. 25-28, 2016. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0016-7592 CODEN: GAAPBC
Note: In English
Summary: A distinctive assemblage of epiphytic diatoms is recovered from Neogene Southern Ocean abyssal sediments, far removed from shallow coastal waters where they are important elements of coastal benthic ecosystems. Epiphytic diatoms maintained a position in the euphotic zone attached to buoyant macroalgal (seaweed) rafts. The stratigraphic occurrence of large, benthic epiphytic diatoms of genera Arachnoidiscus, Isthmia, Rhabdonema, Gephyra, Trigonium, and smaller Achnanthes, Cocconeis, Grammatophora, and Rhaphoneis in sediment cores from Southern Ocean abyssal plain reflects times when macroalgae were abundant in the Southern Ocean. The discontinuous stratigraphic occurrence of the epiphytes (often exceeding 10% of the total diatom flora) amongst the background of planktonic diatoms suggests environmental changes induced by either warm or cold events that controlled the production and/or release of the macroalgae and their attached epiphytes into the deep-sea. Well-resolved climate cycles in IODP Site U1356 (Pliocene) and Site U1361 (Miocene) help to develop this new proxy to identify times when floating macroalgal oases were an important feature of the 'pelagic' Southern Ocean realm, and helped deliver organic material to the deep sea. Macroalgae attach to coastal substrates with a holdfast, a multi-fingered structure that serves as an anchor and can raft large sedimentary particles into the deep-sea. Amphipods thrive in this community, grazing epiphytic diatoms and producing diatom-rich fecal pellets that sink rapidly to the abyssal seafloor. The epiphytic diatom occurrences offer an opportunity to develop a new paleobiological proxy to interpret Antarctic paleoenvironmental history, specifically to: (1) provide insight into Neogene extent of open marine shelves on the Wilkes Land margin; (2) infer intervals of substantial Neogene ice sheet retreat from interior Antarctic basins; (3) reassess interpretations of terrigenous sediment grains in the deep-sea, inferred previously to result from iceberg-rafting in the Southern Ocean that may also result from biological rafting; and (4) consider the timing for paleobiogeographic dispersal of invertebrate organisms living within macroalgal holdfast communities to Subantarctic islands.
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Algae; Cores; Diatoms; Expedition 318; IODP Site U1356; IODP Site U1361; Integrated Ocean Drilling Program; Marine sediments; Microfossils; Paleoenvironment; Plantae; Sediments; Southern Ocean
Coordinates: S631837 S631837 E1355956 E1355956
S642434 S642434 E1435312 E1435312
Record ID: 2017002062
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