Exceptional Agulhas leakage prolonged interglacial warmth during MIS 11c in Europe

Abstract

The transport of warm and saline surface water from the Indo-Pacific Ocean into the South Atlantic ("Agulhas leakage") influences the Atlantic Meridional Overturning Circulation (AMOC), which in turn exerts control on European climate. Paleoceanographic data document a remarkably strong Agulhas leakage at the end of marine isotope stage (MIS) 11c interglacial (~400 ka B.P.), which is one of the best orbital analogues for the Holocene. Here we assess the potential influence of this exceptional Agulhas leakage on North Atlantic climate based on a compilation of marine and terrestrial proxy records from the Iberian margin and continental Europe. We show that a~5 ka long warm period persisted across Europe beyond the MIS 11c climatic optimum. This warm period is testified by increases in foraminifer-derived sea surface temperatures on the Iberian margin, a spread of temperate trees on Iberia, and the expansion both of evergreen trees and thermophilous diatom taxa in Central European lowlands. Paradoxically, this warming coincides with an insolation minimum, implying that orbital forcing can be excluded as the underlying cause. We conclude that persistent warmth during weak insolation at the end of MIS 11c in Europe may have been triggered by strengthened Agulhas leakage, which stimulated a vigorous AMOC and increased the northward transport of warm surface waters to higher latitudes via the North Atlantic Current. The close analogy of the present and MIS 11c orbital forcing underlines the possibility that the present-day increase of the Agulhas leakage, although driven by different forcing than MIS 11c, may considerably affect future climates across Europe.

Response of the North Atlantic surface and intermediate ocean structure to climate warming of MIS 11

“…This time interval was therefore defined as the regional climate optimum30. The pattern revealed in core M23414 is in accordance with Antarctic ice-core31, terrestrial7, and marine162132333435 records, which all show that the climate optimum occurred in the middle of MIS 11ss. Such a late occurrence of the climate optimum during MIS 11ss is different from the Holocene and the last interglacial when temperature rose immediately after the deglaciations.…”

“…Although a vigorous Atlantic Meridional Overturning Circulation (AMOC) is usually inferred for MIS1113141516, interglacials as such were not free of notable climate instabilities as reflected in surface and deep waters of the North Atlantic1718. In spite of minor variability evident in some terrestrial records1920, the peak of MIS 11, i.e.…”

“…In spite of minor variability evident in some terrestrial records1920, the peak of MIS 11, i.e. MIS 11 sensu stricto (ss), is generally regarded as a rather stable interglacial period, at least on an interglacial time scale131621. However, if the GIS was indeed continuously releasing meltwater during the course of this rather long interglacial8, there could also have been notable effects on the vertical ocean structure as well as on ocean circulation and climate.…”

Palaeotemperature estimation in the Holsteinian Interglacial (MIS 11) based on oxygen isotopes of aquatic gastropods from eastern Poland

“…They require further comparisons and high resolution studies, but the palaeolake records from eastern Poland appears of crucial importance for MIS 11 sharing many similarities with other European sequences of that age (Turner 1970;Müller 1974;Meyer 1974;Nitychoruk 1995, 1996;Dabkowski et al 2012;Koutsodendris et al 2012). They show the main palaeoecological trends through the Holsteinian in the central and northwestern part of the continent (Koutsodendris et al 2012(Koutsodendris et al , 2013Candy et al 2014) providing valuable reference data for supra-regional correlations (e.g., Nitychoruk 1995, 1996;Nitychoruk et al 2005;Koutsodendris et al 2012Koutsodendris et al , 2014.…”

Potential of space-borne GNSS reflectometry to constrain simulations of the ocean circulation

“…These Agulhas rings travel northwest into the central and northern Atlantic and influence the Gulf Stream, the North Atlantic Current and finally the Atlantic meridional overturning circulation (Beal et al 2011;Ruehs et al 2013). By this tele-connection the South African current system has an important impact on past, present and future climate (Weijer and van Sebille 2014;Koutsodendris et al 2014). The strength and variability of the Agulhas system and the amount of leaked heat and salt are highly unknown (Beal et al 2011).…”