Stable oxygen isotope composition of benthic foraminifera from sediments of the Skagerrak, North Sea

Benthic foraminiferal tests of a sediment core from southwestern Skagerrak (northeastern North Sea, 420 m water depth) were investigated for their ratio of stable oxygen isotopes. During modern times sudden drops in temperature and salinity of Skagerrak deep waters point to advection-induced cascades of colder and denser central North Sea waters entering the Skagerrak. These temperature drops, which are recorded in benthic foraminiferal tests via the stable oxygen isotopic composition, were used to reconstruct deep-water renewal in the Skagerrak. In a second step we will show that, at least during the last 1200 years, Skagerrak deep-water renewal is triggered by the negative phase of the North Atlantic Oscillation (NAO). The NAO exerts a strong influence on the climate of northwestern Europe. It is currently under debate if the long-term variability of the NAO is capable of influencing Northern Hemisphere climate on long timescales. The data presented here cannot reinforce these speculations. Our data show that most of the 'Little Ice Age' was dominated by comparably warm deep-water temperatures. However, we did find extraordinary strong temperature differences between central North Sea waters and North Atlantic water masses during this time interval.

Quantitative coccolithophore analyses in sediment core MD01-2446

Quantitative coccolithophore analyses were performed in core MD01-2446, located in the mid-latitude North Atlantic, to reconstruct climatically induced sea-surface water conditions throughout Marine Isotope Stages (MIS) 14-9. The data are compared to new and available paleoenvironmental proxies from the same site as well as other nearby North Atlantic records that support the coccolithophore signature at glacial-interglacial to millennial climate scale. Total coccolithophore absolute abundance increases during interglacials but abruptly drops during the colder glacial phases and deglaciations. Coccolithophore warm-water taxa (wwt) indicate that MIS11c and MIS9e experienced warmer and more stable conditions throughout the whole photic zone compared to MIS13. MIS11 was a long-lasting warmer and stable interglacial characterized by a climate optimum during MIS11c when a more prominent influence of the subtropical front at the site is inferred. The wwt pattern also suggests distinct interstadial and stadial events lasting about 4-10 kyr. The glacial increases of Gephyrocapsa margereli-G. muellerae 3-4 µm along with higher values of Corg, additionally supported by the total alkenone abundance at Site U1313, indicate more productive surface waters, likely reflecting the migration of the polar front into the mid-latitude North Atlantic. Distinctive peaks of G. margereli-muellerae (> 4 µm), C. pelagicus pelagicus, Neogloboquadrina pachyderma left coiling, and reworked nannofossils, combined with minima in total nannofossil accumulation rate, are tracers of Heinrich-type events during MIS12 and MIS10. Additional Heinrich-type events are suggested during MIS12 and MIS14 based on biotic proxies, and we discuss possible iceberg sources at these times. Our results improve the understanding of mid-Brunhes paleoclimate and the impact on phytoplankton diversity in the mid-latitude North Atlantic region.