Description: The state of Atlantic Meridional Overturning Circulation (AMOC) is influenced by both the strength and the location of the Mediterranean Outflow (MOW) plume in the Gulf of Cadiz. To evaluate the influence of MOW on AMOC over deglaciations, precise and accurate salinity and temperature reconstructions are needed. For this purpose, we measured Mg/Ca and clumped isotopes of several benthic foraminiferal species at IODP Site U1390 in the Gulf of Cadiz. The clumped isotope results of Cibicidoides pachyderma, Uvigerina mediterranea and Pyrgo spp. are consistent between species and record no significant difference in Glacial to Holocene DWT. Over the deglaciation, the Mg/Ca-based temperatures derived from U. mediterranea indicate three periods of MOW absence at site U1390. Mg/Ca-based temperatures of Hoeglundina elegans and C. pachyderma are on average 6 °C too cold when compared to the present core-top temperature, which we explain by a carbonate ion effect on these epibenthic species related to the high alkalinity of the MOW. Combining DWT estimates with the benthic oxygen isotope data and considering different relationships between seawater oxygen isotopes and salinity, we infer a salinity decrease of MOWby 3 to 8 units over the deglaciation, and 4 units during S1, accounting for the global d18O depletion due to the decrease in ice volume. Our findings confirm that the Mediterranean Sea accumulates excess salt during a glacial low stand, and suggest that this salt surged into the Atlantic over the deglaciation, presumably during HS1.

Description: For a short time interval (c. 1.2 Myr) during the early middle Eocene (~49 Myr), the central Arctic Ocean was episodically densely covered by the freshwater fern Azolla, implying sustained freshening of surface waters. Coeval Azolla fossils in neighboring Nordic seas were thought to have been sourced from the Arctic. The recognition of a different Azolla species in the North Sea raised doubts about this hypothesis. Here we show that no less than five Azolla species had coeval blooms and spread in the Arctic and NW European regions. A likely trigger for these unexpected Azolla blooms is high precipitation prevailing by the end of the warmest climates of the Early Eocene Climatic Optimum (EECO).

Description: Relative to the present day, meridional temperature gradients in the Early Eocene age (~56-53 Myr ago) were unusually low, with slightly warmer equatorial regions (Pearson et al., 2007, doi:10.1130/G23175A.1 ) but with much warmer subtropical Arctic (Sluijs et al., 2008, doi:10.1029/2007PA001495) and mid-latitude (Sluijs et al., 2007, doi:10.1038/nature06400) climates. By the end of the Eocene epoch (~34 Myr ago), the first major Antarctic ice sheets had appeared (Zachos et al., 1992, doi:10.1130/0091-7613(1992)020〈0569:EOISEO〉2.3.CO;2; Barker et al., 2007, doi:10.1016/j.dsr2.2007.07.027), suggesting that major cooling had taken place. Yet the global transition into this icehouse climate remains poorly constrained, as only a few temperature records are available portraying the Cenozoic climatic evolution of the high southern latitudes. Here we present a uniquely continuous and chronostratigraphically well-calibrated TEX86 record of sea surface temperature (SST) from an ocean sediment core in the East Tasman Plateau (palaeolatitude ~65° S). We show that southwest Pacific SSTs rose above present-day tropical values (to ~34° C) during the Early Eocene age (~53 Myr ago) and had gradually decreased to about 21° C by the early Late Eocene age (~36 Myr ago). Our results imply that there was almost no latitudinal SST gradient between subequatorial and subpolar regions during the Early Eocene age (55-50 Myr ago). Thereafter, the latitudinal gradient markedly increased. In theory, if Eocene cooling was largely driven by a decrease in atmospheric greenhouse gas concentration Zachos et al. (2008, doi:10.1038/nature06588), additional processes are required to explain the relative stability of tropical SSTs given that there was more significant cooling at higher latitudes.