Variability of surface water characteristics and Heinrich‐like events in the Pleistocene midlatitude North Atlantic Ocean: Biomarker and XRD records from IODP Site U1313 (MIS 16–9)

Abstract

[1] A reconstruction of Milankovitch to millennial-scale variability of sea surface temperature (SST) and sea surface productivity in the Pleistocene midlatitude North Atlantic Ocean (marine isotope stage (MIS) 16-9) and its relationship to ice sheet instability was carried out on sediments from Integrated Ocean Drilling Program (IODP) Site U1313. This reconstruction is based on alkenone and n-alkane concentrations, U 37 K 0 index, total organic carbon (TOC) and carbonate contents, X-ray diffraction data, magnetic susceptibility, and accumulation rates. Increased input of ice-rafted debris occurred during MIS 16, 12, and 10, characterized by high concentrations of dolomite, quartz, and feldspars and elevated accumulation rates of terrigenous matter. Minimum input values of terrigenous matter, on the other hand, were determined for MIS 13 and 11. Peak values of dolomite, coinciding with quartz, plagioclase, and kalifeldspar peaks and maxima in long-chain n-alkanes indicative for land plants, are interpreted as Heinrich-like events related to sudden instability of the Laurentide Ice Sheet during early and late (deglacial) phases of the glacials. The coincidence of increased TOC values with elevated absolute concentrations of alkenones suggests increased glacial productivity, probably due to a more southern position of the Polar Front. Alkenone-based SST reached absolute maxima of about 19°C during MIS 11.3 and absolute minima of <10°C during MIS 12 and 10. Within MIS 11, prominent cooling events (MIS 11.22 and 11.24) occurred. The absolute SST minima recorded directly before and after the glacial maxima MIS 10.2 and 12.2 are related to Heinrich-like event meltwater pulses, as supported by the coincidence of SST minima and maxima in C 37:4 alkenones and dolomite. These sudden meltwater pulses, especially during terminations IV and V, probably caused a collapse of phytoplankton productivity as indicated by the distinct drop in alkenone concentrations. Ice sheet disintegration and subsequent surges and outbursts of icebergs and meltwater discharge may have been triggered by increased insolation in the northern high latitudes.

The meridional temperature gradient in the eastern North Atlantic during MIS 11 and its link to the ocean–atmosphere system

“…Additionally, European ice-sheet expansion was very large during MIS 12 (Donner, 1995), a fact which might help to explain not only the exceptional length of Termination V (Oppo et al, 1998;Bauch et al, 2000;Billups et al, 2004;Healey and Thunell, 2004;de Abreu et al, 2005) but also the difference in SST dynamics between polar and middle/low latitudes as revealed by us for the early interglacial phase. Our foraminiferal and alkenone SST data clearly demonstrate that the subtropical and the temperate climate zones experienced abrupt warming in accordance with insolation changes directly after Termination V. Such an early response to warming agrees with other investigations from the N. Atlantic (Oppo et al, 1998;McManus et al, 1999;de Abreu et al, 2005;Stein et al, 2009;Voelker et al, 2010;Rodrigues et al, 2011) and continental surroundings (Desprat et al, 2005;Nitychoruk et al, 2005;de Vernal and Hillaire-Marcel, 2008). On the contrary, the steep SST rise as registered in the Nordic Seas much later (around 410 ka) was driven, at least partially, by the second insolation peak (Fig.…”

“…Moreover, in the middle latitudes not only quantitative SST reconstructions but also analysis of relative abundances of the rare thermophilic species implies that the middle latitudes were also warmer during MIS 11c than during the Holocene (Kandiano and Bauch, 2003;. These results are consistent with other SST records published so far (Table 4; Ruddiman et al, 1989;Martrat et al, 2007;Lawrence et al, 2009;Stein et al, 2009;Rodrigues et al, 2011). An exception is Site 980 which shows very similar SST values for MIS 1 and MIS 11 (McManus et al, 1999).…”

“…So far, direct high-resolution SST records in the North Atlantic during MIS 11c are still very scarce (de Abreu et al, 2005;Kandiano and Bauch, 2007;Martrat et al, 2007;Stein et al, 2009;Voelker et al, 2010). In order to examine SST gradients in the North Atlantic a submeridional transect of five core sites was selected for the current investigations.…”

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 IODP Site U1313 alkenone curve in the dis cussed inter val shows three interstadials af ter a ma jor warm peak, with rel a tively sim i lar mag ni tude as at Ossówka, but it suf fers from lower res o lu tion (Stein et al, 2009). How ever, SST lev els of the third one (16°C) are in this case the same as the tem per a ture of the stadial be tween the first and the sec ond interstadial.…”

“…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).…”