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Abstract: Bioturbation on Antarctica’s Explorers Cove Seafloor:
Why Animal Activity has a Greater Impact on the Sedimentary Record
than Animal Abundance
Little is known about the sedimentologic and taphonomic processes occurring under semi-permanent sea ice in Explorers Cove (EC), Antarctica. We analyzed the amount of seafloor bioturbation by point-counting disruption on a cm-scale grid superimposed on 26 quadrants (1m2) and by assessing the Bedding Plane Bioturbation Index (BPBI) for each quadrant. All quadrants had BPBI of 5 and averaged 77% points disrupted. Two epifaunal animals, the scallop, Adamussium colbecki, and the ophiuroid, Ophionotus victoriae, are responsible for this disruption. A. colbecki produces “divots” 3 cm deep. O. victoriae leaves 2 mm deep imprints.
Bioturbation rate is a function of animal density and animal activity. Range of scallops per 20 m2 transect (n=16) is 4 to 192. Rates of animal activity are poorly constrained. The estimated minimum number of divots that A. colbecki would produce is 2m- 2y-1, the maximum 24m-2y-1. This translates to 157 to 1884 cm2 reworked per m2y-1. O. victoriae is estimated to disrupt 281 to 5900 cm2 per m2y-1. The activities of O. victoriae and A. colbecki together could produce a 100% bioturbated quadrant in 5 to 61 years, consistent with the absence of lamination in EC cores.
Bioturbation by A. colbecki and O. victoriae is pervasive in EC quadrants and decoupled from the abundance of these organisms. As demonstrated in this study, the record of animal activity is more likely to be encountered in the stratigraphic record than is skeletal material. This underscores the importance of linking animals to their bioturbation when documenting climate change.