Decoupling of surface ocean hydrology and Greenland ice core records in the eastern North Atlantic during the last glacial inception

MIS 4, a key paleoclimatic interval for the last glacial inception, is characterized by a rapid CO₂ drop of approx. ~28ppm and a large drop in temperature (as seen in Antarctic ice cores). SSTs in the North Atlantic are thought to be coupled to AMOC strength, whereby various proxies suggest a weaker and shoaled AMOC during the transition from MIS5a to MIS4. Furthermore, several millennial events also occurred during MIS 4, including Heinrich Stadial 6 and DO events 16-19. MIS 4 is thus an ideal interval to study and eventually to disentangle, glacial-interglacial and millennial variability.

Here, we present high resolution planktonic and benthic foraminifera geochemical data from several marine sediment cores from the Iberian Margin (including stable isotope and trace element data). The Iberian Margin is a prime location to study millennial-scale climate variability as isotope records of planktonic and benthic foraminifera simultaneously recorded rapid climate change expressed in Greenland and Antarctic ice cores, respectively, during the last glacial period. However, our results so far, suggest that surface ocean response at this site does not track Greenland temperature, as would be expected for this region of the North Atlantic. Perhaps the most striking, our planktic Mg/Ca record shows a late onset of rapid MIS 4 cooling at the start of Heinrich 6, and no clear millennial variability signal. This is in agreement with SST reconstructed using alkenones (Pailler and Bard, 2002) and planktonic foraminifera faunal assemblages (Salgueiro et al., 2010) from nearby core sites. Local d18O seawater reconstructions imply major hydrological changes in the region, which is supported by the “dry event” seen in speleothems from North Eastern Iberia (Perez-Mehias et al., 2019) and Italy (Columbu et al., 2020), just before Heinrich 6. We propose that the observed changes may reflect changes in regional ocean and atmospheric circulation patterns such as the interaction of the strength and position of the Azores Current, Iberian Poleward Current and the Subtropical Gyre, which in turn could depend on the larger scale AMOC and wind driven surface ocean changes due to glacial-interglacial and millennial variability. Further links to moisture transport, ice sheet growth and carbon cycle are yet to be investigated.

 

References

Columbu, A., Chiarini, V., Spötl, C., Benazzi, S., Hellstrom, J., Cheng, H. and De Waele, J., 2020. Speleothem record attests to stable environmental conditions during Neanderthal–modern human turnover in southern Italy. Nature Ecology & Evolution, 4(9), pp.1188-1195.

Pailler, D. and Bard, E., 2002. High frequency palaeoceanographic changes during the past 140 000 yr recorded by the organic matter in sediments of the Iberian Margin. Palaeogeography, Palaeoclimatology, Palaeoecology, 181(4), pp.431-452.

Pérez-Mejías, C., Moreno, A., Sancho, C., Martín-García, R., Spötl, C., Cacho, I., Cheng, H. and Edwards, R., 2019. Orbital-to-millennial scale climate variability during Marine Isotope Stages 5 to 3 in northeast Iberia. Quaternary Science Reviews, 224, p.105946.

Salgueiro, E., Voelker, A., de Abreu, L., Abrantes, F., Meggers, H. and Wefer, G., 2010. Temperature and productivity changes off the western Iberian margin during the last 150 ky. Quaternary Science Reviews, 29(5-6), pp.680-695.