Stratification of surface waters during the last glacial millennial climatic events: a key factor in subsurface and deep-water mass dynamics
- 1UMR 5805, EPOC (Environnements et Paléoenvironnements Océaniques et Continentaux), Université de Bordeaux, 33615 Pessac, France
- 2UMR 6538, Domaines Océaniques, IUEM-UBO, 29280 Plouzané, France
- 3UMR 8212, LSCE (Laboratoire des Sciences du Climat et de l'Environnement), CEA/CNRS-INSU/UVSQ, 91198 Gif-sur-Yvette CEDEX, France
- anow at: UMR 7329, Géoazur, Université de Sophia Antipolis, 06560 Valbonne, France
- bnow at: UQAM, Université du Québec à Montreal, Montréal, Québec H3C 3P8, Canada
- cnow at: Laboratoire Péagos, Département Dynamiques des écosystèmes côtiers, IFREMER Brest, Technopôle Brest Iroise, 29280 Plouzané, France
Abstract. The last glacial period was punctuated by abrupt climatic events with extrema known as Heinrich and Dansgaard–Oeschger events. These millennial events have been the subject of many paleoreconstructions and model experiments in the past decades, but yet the hydrological processes involved remain elusive. In the present work, high-resolution analyses were conducted on the 12–42 ka BP section of core MD99-2281 retrieved southwest of the Faeroe Islands, and combined with analyses conducted in two previous studies (Zumaque et al., 2012; Caulle et al., 2013). Such a multiproxy approach, coupling micropaleontological, geochemical and sedimentological analyses, allows us to track surface, subsurface, and deep hydrological processes occurring during these rapid climatic changes. Records indicate that the coldest episodes of the studied period (Greenland stadials and Heinrich stadials) were characterized by a strong stratification of surface waters. This surface stratification seems to have played a key role in the dynamics of subsurface and deep-water masses. Indeed, periods of high surface stratification are marked by a coupling of subsurface and deep circulations which sharply weaken at the beginning of stadials, while surface conditions progressively deteriorate throughout these cold episodes; conversely, periods of decreasing surface stratification (Greenland interstadials) are characterized by a coupling of surface and deep hydrological processes, with progressively milder surface conditions and gradual intensification of the deep circulation, while the vigor of the subsurface northward Atlantic flow remains constantly high. Our results also reveal different and atypical hydrological signatures during Heinrich stadials (HSs): while HS1 and HS4 exhibit a "usual" scheme with reduced overturning circulation, a relatively active North Atlantic circulation seems to have prevailed during HS2, and HS3 seems to have experienced a re-intensification of this circulation during the middle of the event. Our findings thus bring valuable information to better understand hydrological processes occurring in a key area during the abrupt climatic shifts of the last glacial period.