Abstract
Abstract. Integrated Ocean Drilling Program (IODP) Expedition 318 recovered a ∼ 170 m long Holocene organic-rich sedimentary sequence at Site U1357. Located within the narrow but deep Adélie Basin close to the Antarctic margin, the site accumulated sediments at exceptionally high sedimentation rates, which resulted in extraordinary preservation of the organic sedimentary component. Here, we present an overview of 74 different mainly marine microfossil taxa and/or types found within the organic component of the sediment, which include the remains of unicellular and higher organisms from three eukaryotic kingdoms (Chromista, Plantae, and Animalia). These remains include phytoplanktonic (phototrophic dinoflagellates and prasinophytes) and very diverse zooplanktonic (heterotrophic dinoflagellates, tintinnids, copepods) organisms. We illustrate each marine microfossil taxon or type identified by providing morphological details and photographic images, which will help with their identification in future studies. We also review their ecological preferences to aid future (palaeo)ecological and (palaeo)environmental studies. The planktonic assemblage shows a high degree of endemism related to the strong influence of the sea-ice system over Site U1357. In addition, we found the remains of various species of detritus feeders and bottom-dwelling scavengers (benthic foraminifers and annelid worms) indicative of high export productivity at Site U1357. This study shows the potential of organic microfossil remains for reconstructing past environmental conditions, such as sea-ice cover and (export) productivity.
Highlights
Site U1357 was drilled as part of the Integrated Ocean Drilling Program (IODP) Expedition 318 and is located in the Adélie Basin downwind and downcurrent from the Mertz Glacier Polynya
Organic microplankton remains are less commonly used for reconstructing past environmental conditions in the Southern Ocean because not all organic remains are able to withstand lithification processes and/or oxygen degradation, the organic microplankton remains of Site U1357 are exceptionally well preserved
We explain on a superordinate level the relationship between the microfossils in the sediments and their species living in the water column from which they originate and how we can interpret these in terms of environmental conditions
Summary
Site U1357 was drilled as part of the Integrated Ocean Drilling Program (IODP) Expedition 318 and is located in the Adélie Basin downwind and downcurrent from the Mertz Glacier Polynya. Polynyas are seasonal openings within the sea ice formed through the vertical mixing of warmer subsurface waters or through advection from the coast by wind or currents (Arrigo et al, 1998a; Arrigo and van Dijken, 2003; Morales Maqueda et al, 2004). In the case of thecate dinoflagellates the tabulation of the cyst (paratabulation) reflects the tabulation (plate arrangement) of the theca, which is unique for each species (Evitt, 1985). In these cysts, the archaeopyle is often formed through the loss of a distinct set of paraplates, which is used for classification (Fensome et al, 1993). Because the biological species is unknown for many dinoflagellate cysts, we apply the classification of dinoflagellate cysts and primarily list the dinoflagellate cyst taxa below unless the dinoflagellate cyst has none, in which case we use “Cyst of (biological taxon)”
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