Air sea temperature decoupling in western Europe during the last interglacial glacial transition

Transcription

1 María Fernanda Sánchez Goñi, Edouard Bard, Amaelle Landais, Linda Rossignol, Francesco d Errico SUPPLEMENTARY INFORMATION DOI: /NGEO1924 Air sea temperature decoupling in western Europe during the last interglacial glacial transition Supplementary Information Present-day environmental setting At present, the western European margin is primarily affected by the strength and direction of the northwesterlies and the North Atlantic subtropical gyre dynamic 1. The western Iberian margin is locally influenced in summer by upwelling events that generate a southward surface circulation while downwelling in winter develops a northward surface circulation 2-3. At latitudes above 40 N, the atmospheric configuration results in year-round wet climate, with annual precipitation at ~1000 mm, and a mean annual temperature of 10 C allowing for the development of the Atlantic mixed Quercus (oak) forest 4. In southwestern Iberia, between 36 and 40 N, precipitation is concentrated in autumn and winter (Pann<600 mm). Cool winters (minimal winter temperatures ranging between 5 and - 1 C) and hot, dry summers promote the development of Mediterranean forest. Modern sea surface conditions along the western European margin between 37 N and 45 N are characterized by mean annual temperatures ranging from 18 C to 14.5 C, respectively. Table S1 Stratigraphic events identified by 5-6 and dated after Svensson et al., 2008, Shackleton et al., 2000 and 2003, Sanchez Goñi et al., 2012 used to: a) develop the linear interpolation model of core MD , and b) the age models of the other western NATURE GEOSCIENCE 1

2 European margin cores. These chronologies are based on the correlation of identified and dated forest increases in MD to the same identified forest increases in cores MD and MD a Event stratigraphy Reference MD References Depth (cm) D-O 12* Shackleton et al., Svensson et al., D-O 14* Shackleton et al., Svensson et al., D-O 17* Shackleton et al., Svensson et al., MIS 5a lightest value Shackleton et al Shackleton et al., 2000, MIS 5e/5d Shackleton et al Sanchez Goñi et al., Age ka b Event stratigraphy MD Age ka MD MD Depth (cm) Depth (cm) Depth (cm) Forest increase (D-O 12) Forest increase (D-O 14) Forest increase (D-O 17) HS 6 (strong N. pachyderma (s) increase) Forest increase (Stadial II/Ognon II) Forest increase (Stadial I/Ognon I) Forest increase (Mélisey II/St Germain II) Forest decrease (St Germain 1c/Mélisey II) Figure S1 Comparison of a) summer and winter foraminifera-based SST records and the percentage curve of subtropical and temperate planktonic foraminifera with b) pollen percentage records of different taxa from core MD retrieved in the Bay of Biscay. Grey bands indicate warm/temperate phases in western France. The clear identification of 2

3 the Ognon II Interstadial after the abrupt increase of the Atlantic forest pollen percentages demonstrates that this interstadial is a real climate event and not the result of pollen reworking as previously suggested 7. HS 6 indicate Heinrich Stadial 6. Grey bands indicate warm phases. 3

4 Figure S2 Constrained Correspondence Analysis (CCA) showing the sample scores on the ordination space for the pollen record of core MD and using foraminifera-based summer (jas) SST as constraining variable. The CCA between the five main pollen ecological groups, Atlantic forest, Picea, Abies, Ericaceae (heathlands), grasslands and semi-desert, and, using summer SST as constraining variables statistically confirmed our observations. Numbers refer to sample ages in thousands of years (ka). 4

5 Figure S3 a) Temperature record of Greenland 8-10 compared with the western European margin palaeoclimatic records for the interval ka: b) M (Bay of Biscay): Atlantic forest pollen percentages, foraminifera-based SST, benthic foraminifera δ 18 O and IRD concentrations (grey surface), c) MD (northwestern Iberian margin): Atlantic forest and Ericaceae (heathlands) pollen percentages, foraminifera- and Uk 37 -based SST, benthic foraminifera δ 18 O, IRD concentrations (grey surface) and N. pachyderma (s) percentages (black line). Note the tight correlation between the Ericaceae and the foraminifera-based SST records that show heathland expansion at the expense of the Atlantic forest contraction when SST are relatively warm, higher than 9 C in summer, and e) MD (southwestern Iberian margin): pollen percentages, Uk 37 -based SST, benthic foraminifera δ 18 O, IRD concentrations (grey surface) and N. pachyderma (s) percentages (black line). The onset of HS (Heinrich Stadial) 6 in the south westernmost site is marked by the strong increase in N. pachyderma (s). C19 is marked by the slight occurrence of IRD in the northern cores. MIS refers to Marine Isotopic Stages. 5

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7 Figure S4 Comparison between summer SST reconstruction curves for core MD This figure shows no substantial differences between the two curves apart from a tendency of SIMMAX (green line) to smooth SST between 80 and 73 ka. The SIMMAX SST estimates fully confirm persistent warm conditions in the Bay of Biscay during the MIS5e/4 transition. We have used MAT (black line) instead of SIMMAX because it has been shown that the former accurately reconstruct SST 11. 7

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