Variations in mid-latitude North Atlantic surface water properties during the mid-Brunhes (MIS 9–14) and their implications for the thermohaline circulation

Abstract

Abstract. Stable isotope and ice-rafted debris records from three core sites in the mid-latitude North Atlantic (IODP Site U1313, MD01-2446, MD03-2699 are combined with records of ODP Sites 1056/1058 and 980 to reconstruct hydrographic conditions during the middle Pleistocene spanning Marine Isotope Stages (MIS) 9-14 (300-540 ka). Core MD03-2699 is the first high-resolution mid-Brunhes record from the North Atlantic's eastern boundary upwelling system covering the complete MIS 11c interval and MIS 13. The array of sites reflect western and eastern basin boundary current as well as north to south transect sampling of subpolar and transitional water masses and allow the reconstruction of transport pathways in the upper limb of the North Atlantic's circulation. Hydrographic conditions in the surface and deep ocean during peak interglacial MIS 9 and 11 were similar among all the sites with relative stable conditions and confirm prolonged warmth during MIS 11c also for the mid-latitudes. Sea surface temperature (SST) reconstructions further reveal that in the mid-latitude North Atlantic MIS 11c is associated with two plateaus, the younger one of Correspondence to: A. Voelker (antje.voelker@lneg.pt) which is slightly warmer. Enhanced subsurface northward heat transport in the eastern boundary current system, especially during early MIS 11c, is denoted by the presence of tropical planktic foraminifer species and raises the question how strongly it impacted the Portuguese upwelling system. Deep water ventilation at the onset of MIS 11c significantly preceded surface water ventilation. Although MIS 13 was generally colder and more variable than the younger interglacials the surface water circulation scheme was the same. The greatest differences between the sites existed during the glacial inceptions and glacials. Then a north -south trending hydrographic front separated the nearshore and offshore waters off Portugal. While offshore waters originated from the North Atlantic Current as indicated by the similarities between the records of IODP Site U1313, ODP Site 980 and MD01-2446, nearshore waters as recorded in core MD03-2699 derived from the Azores Current and thus the subtropical gyre. Except for MIS 12, Azores Current influence seems to be related to eastern boundary system dynamics and not to changes in the Atlantic overturning circulation.

Terrestrial versus marine archives: biostratigraphical correlation of the Middle Pleistocene lacustrine records from central Europe and their equivalents in the deep-sea cores from the Portuguese margin

“…The high-res o lu tion re cord of core MD03-2699 un doubt edly stands out among the few ones available (Voelker et al, 2010;Rodrigues et al, 2011). It is as tounding that each stadial/interstadial phase in the Ossówka core has its close equiv a lent in the alkenone curve as re gards both its rela tive mag ni tude and sed i men ta tion rate ( Fig.…”

“…1). They rep re sent dif fer ent hydrologic con di tions and pro ductiv ity re gimes: ODP Site 980 (the branch of NAC, sub po lar regime), IODP Site U1313 (the branch of NAC, mid-lat i tude regime), core MD01-2447 off shore of the Ibe rian Mar gin (southward recirculation of NAC), cores MD03-2699 and MD01-2443 in nearshore po si tions on the Ibe rian Mar gin (sub trop i cal Azores Cur rent and upwelling) and ODP Sites 1056/1058 (Gulf Stream) (McManus et al, 1999;Martrat et al, 2007;Voelker et al, 2010;Rodrigues et al, 2011).…”

“…The multispecies planktic d 18 O iso tope curves from core MD01-2443 (de Abreu et al, 2005) show so many vari a tions in the dis cussed pe riod that iden ti fi ca tion of clear trends is not pos si ble. Sim i larly, in the IODP Site U1313 re cords (Stein et al, 2009;Voelker et al, 2010), both ben thic and planktic d 18 O curves show a se ries of quick os cil la tions hard to cor re late with those at Ossówka. Sim ilar prob lems arise while ana lys ing re cords from the core MD03 --2669 and the ODP Sites 1056/1058 (Voelker et al, 2010).…”

“…In the ODP Site 980, the post-op ti mal part of MIS 11 is punc tu -ated by 2-4 un doubted interstadial ep i sodes (McManus et al, 1999), whereas the MD01-2446 re cord re flects 3 post -inter glacial warm and cold events with the de scend ing trend of SST (Voelker et al, 2010). How ever, even in these cases, pre cise esti ma tion of the SST level for stadials and interstadials is dif fi cult.…”

“…Hence, the in flu ence of con ti nen tal cli mate in east ern Po land is also an im por tant fac tor. Be cause the sur face wa ters at sites near Por tu gal "are de rived in one form or an other from the Gulf Stream and the North At lan tic Cur rent (NAC)'' (Voelker et al, 2010) the link be tween the cli mate in that area and this in Poland seems to be clear. As we can see from the At lan tic deep-sea cores, NAC in flu enced sub stan tially the weather in west ern and cen tral Eu rope in the mid dle and the Up per Pleisto cene.…”