Sediment instability on the Portuguese continental margin under abrupt glacial climate changes (last 60 kyr)

• Published in: The ISME Journal
• Main Authors: Martín Lebreiro, Susana, Voelker, A. H. L., Vizcaino, A., Abrantes, Fátima G., Alt-Epping, Ulrich, Jung, S., Thouveny, Nicolas, Gràcia i Mont, Eulàlia
• Other Authors: European Commission, European Science Foundation, Laboratório Nacional de Energia e Geologia (Portugal)
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2009
• Subjects: turbidite; sediment; millennial climate variability; Portuguese margin; AMOC; Heinrich; Dansgaard-Oeschger; bulk delta18 O carbonate; cambio climático; Portugal; Geología Glacial; Antarctic; Greenland; Antarc*; Antarctica
• Online Access: http://hdl.handle.net/10261/277074; https://doi.org/10.1016/j.quascirev.2009.08.007; https://doi.org/10.13039/501100000780; https://doi.org/10.13039/501100000782

It is well established that orbital scale sea-level changes generated larger transport of sediments into the deep-sea during the last glacial maximum than the Holocene. However, the response of sedimentary processes to abrupt millennial-scale climate variability is rather unknown. Frequency of distal turbidites and amounts of advected detrital carbonate are estimated off the Lisbon–Setu´ bal canyons (core MD03- 2698, at 4602 mwd), within a chronostratigraphy based on radiometric ages, oxygen isotopes and paleomagnetic key global anomalies. We found that: 1) higher frequency of turbidites concurred with Northern Hemisphere coldest temperatures (Greenland Stadials [GS], including Heinrich [H] events). But more than that, an escalating frequency of turbidites starts with the onset of global sea-level rising (and warming in Antarctica) and culminates during H events, at the time when rising is still in its early-mid stage, and the Atlantic Meridional Overturning Circulation (AMOC) is re-starting. This short time span coincides with maximum gradients of ocean surface and bottom temperatures between GS and Antarctic warmings (Antarctic Isotope Maximum; AIM 17, 14, 12, 8, 4, 2) and rapid sea-level rises. 2) Trigger of turbidity currents is not the only sedimentary process responding to millennial variability; land-detrital carbonate (with a very negative bulk d18O signature) enters the deep-sea by density-driven slope lateral advection, accordingly during GS. 3) Possible mechanisms to create slope instability on the Portuguese continental margin are sea-level variations as small as 20 m, and slope friction by rapid deep and intermediate re-accommodation of water masses circulation. 4) Common forcing mechanisms appear to drive slope instability at both millennial and orbital scales. Marine Geology Research Unit, Laboratório Nacional de Energia e Geologia, Portugal Departamento de Investigación y Prospectiva Geocientífica, Instituto Geológico y Minero de España, España Unitat de Tecnologia Marina, Centre ...