Neoichnology of high energy deep-sea environments: A tool to improve gateways characterization

Abstract

Neoichnology of high energy deep-sea environments: A tool to improve gateways characterization  Olmo Miguez-Salas1, Francisco J. Rodríguez-Tovar2 1Department of Marine Zoology, Senckenberg Research Institute and Natural History Museum, 60325 Frankfurt, Germany.2 Department of Stratigraphy and Paleontology, University of Granada, 18071 Granada, Spain  Evolution of ocean gateways determines significant changes in deep-water dynamics affecting depositional and ecological conditions. Particularly, variations in deep-water circulation associated to closing and opening gateways induce changes in hydrodynamic energy, rate of sedimentation, organic matter availability, salinity, oxygenation, etc., affecting benthic community. Modern biogenic structures (lebensspuren), as reflecting the behavior of the tracemaker to environmental conditions (i.e., depositional and ecological) reveal as a useful tool to interpret processes affecting deep-sea depositional settings. The exploration of these deep-sea environments and the in-situ observation of tracemakers require the expensive and time-consuming deployment of short-range observation gear, in many cases with inherent limitations, such as restricted fields of view in both spatial and temporal scales. However, in recent years neoichnological information from marine epibenthic lebensspuren (i.e., traces on the seafloor) has been obtained from videos or still images captured by cameras on autonomous and remotely operated underwater vehicles transiting on or above the seafloor. This new information reveals of major interest, especially in high-energy deep-sea environments, which can be correlated with those related to gateways and paleo-gateways.In this study we present three cases that exemplify how lebensspuren features are related to deep-sea environments that have high-energy conditions: 1) Rosette-shape traces (RST) related to echiuran feeding activities. We study two locations of the Porcupine Abyssal Plain (NE Atlantic) where the seafloor consistency is different due to sporadic high energetic gravity flows as well as the local dominant megabenthos feeding group (e.g., suspension vs. deposit feeders). The seafloor consistency appeared not to affect RST morphology while the dominant feeding group seemed to control rosette areal coverage. 2) At an abyssal site in the NE Pacific ('Station M'), high-energy periods associated with benthic storms have been related to the impoverishment of lebensspuren abundance and diversity. The local-scale erosion and re-suspension of unconsolidated surface sediment inhibits the formation of previous softground traces and led to the redistribution of organic matter resources but the trace maker remained in the deep-sea station. These findings offer a new perspective where absence of traces may not imply tracemakers absence during quick (<1 day) energetic episodes at the deep-sea. 3) At an abyssal site with a dune field in the Bering Sea, lebensspuren abundance and diversity varies from the abyssal area to the dune field. Changes in the abundance of dwelling structures seem to be related to the high energetic conditions typical of deep-sea dunes.