Sedimentary processes in the Discovery Gap (Central–NE Atlantic): An example of a deep marine gateway

• Published in: Deep Sea Research Part I: Oceanographic Research Papers
• Main Authors: Glazkova, T., Rodríguez Tovar, Francisco J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2021
• Subjects: Deep-water sedimentation; Bottom currents; Paleocirculation; Antarctic bottom water; Contourites; Deep marine gateways; Discovery gap; Central-NE Atlantic; Antarctic; The Antarctic; Holloway; Antarc*
• Online Access: http://hdl.handle.net/10481/74737; https://doi.org/10.1016/j.dsr.2021.103681

This project was done within the framework of "The Drifters" Research Group at Royal Holloway University of London (RHUL). The authors thank the captain, crew and onboard scientific team of the 43rd cruise onboard the R/V Akademik Nikolaj Strakhov. Research by RT was funded by Projects CGL2015-66835-P and PID2019-104625RB-100 (Secretaria de Estado de I + D + I, Spain), B-RNM-072-UGR18 (FEDER Andalucia) and P18-RT-4074 (Junta de Andalucia). Research by EL was supported through the CGL2016-80445-R (AEI/FEDER, UE) SCORE projects. The field research, stable isotope interpretation, and the age model construction were carried out within framework of the state assignment of IO RAS (theme No. 0128-2021-0012). Hydrological data processing and core ANS43006_A analysis (CaCO3, MS, and XRF) were supported by the Russian Science Foundation (grant No. 19-1700246). The SBE 19plus V2 SeaCAT hydrophysical probe (Sea-Bird Electronics, United States) used during the expedition was kindly provided by the Moscow State University. We thank the editor and the two anonymous reviewers for their comments and suggestions which have helped us to improve the original submitted version of this work. We would also like to thank L. Bashirova for the insightful discussion which has improved the final version of this manuscript. Paleoceanographic studies of abyssal bottom currents are often complicated by low current speeds and sedimentation rates, resulting in sediment condensation or erosion. However, increased rates of erosion and deposition may occur where bottom current velocities change as they pass through deep marine gaps and gateways. Despite this, the depositional processes in these gateways and their paleoceanographic implications remain poorly understood. Based on new sedimentological, hydrological and geophysical (high resolution seismic and bathymetry) data from Discovery Gap (Azores–Gibraltar Fracture Zone) collected during the 43rd cruise of the R/ V Akademik Nikolaj Strakhov in 2019, the key sedimentary processes occurring in the Late Quaternary have been determined. Two depressions with depths exceeding 5300 m in the centre and south of Discovery Gap have been identified, the latter filled with contouritic deposits. These depressions are separated by a roughly N–S trending central sill at 4860 m and a sediment filled terrace at 4720 m water depth. Elongated NE–SW trending highs and sills, are present in the north and south of the study area. Their importance in controlling the flow of water through Discovery Gap is determined by the presence of erosion at the base of these highs with adjacent sheeted or mounded contourite drifts. Pelagic, hemipelagic, reworked pelagic/hemipelagic and fine-grained contourite sedimentary facies have been identified. The sedimentary facies associations point to remarkable variability in the Antarctic Bottom Water (AABW), linked to glacial–interglacial changes, and its intermittent influence in Discovery Gap during the Quaternary. During glacial intervals (MIS 6, 4 and 2) and at their terminations there was enhanced bottom current activity coeval with higher terrigenous content, and increased carbonate dissolution. The results of this study improve our understanding of sedimentary processes in abyssal environments and highlight the value of the sedimentary record in deep marine gateways for interpreting the interaction of bottom water with abyssal morphology. Future work in other modern deep gaps is essential to shed more light on how deep gaps form and to fully reconstruct deep-water paleocirculation within oceanic basins. Spanish Government CGL2015-66835-P PID2019-104625RB-100 FEDER Andalucia B-RNM-072-UGR18 Junta de Andalucia P18-RT-4074 SCORE projects CGL2016-80445-R Russian Science Foundation (RSF) 19-1700246