ALBERT

Description: Previous stable oxygen isotopic data from surface-dwelling foraminifera indicate that Eocene tropical sea surface temperatures (SSTs) were significantly lower than at present. Here we show that stable isotopic analyses ({delta}18O, {delta}13C) of the late mid-Eocene mixed-layer dweller Morozovella spinulosa are consistent with mid-Eocene mid-latitude SSTs close to, or slightly lower than modern temperatures at Blake Nose, western North Atlantic. In contrast, isotopic analyses of the benthic foraminifer, Nuttalides truempyi reveal a gradual fall in mean bottom-water temperatures from 8 to 7 {degrees}C over c. 500 ka years. These deep intermediate-water temperatures are significantly higher than modern ones and are similar to intermediate- and bottom-water temperatures recorded from earlier in Palaeogene and late Cretaceous time. Large shifts are seen in the {delta}18O and {delta}13C values of the planktonic foraminifers, of up to 1{per thousand} and 2.6{per thousand}, respectively, that probably reflect temperature and nutrient fluctuations controlled by regional changes in upwelling intensity and runoff. The surface to benthos {delta}18O gradient decreases from 3{per thousand} PDB to a minimum of c. 0.5{per thousand} PDB over 400 ka, which could relate to the intensity of upwelling. Spectral analysis reveals precessional forcing in the foraminiferal {delta}18O records, which shows the direct influence of low-latitude insolation on surface-water stratification. Monsoonal wind systems may have forced the upwelling cycles and/or freshwater input. The benthic foraminifer {delta}18O record also contains the obliquity cycle, in addition to the precessional cycles, indicating the inheritance of mid- and high-latitude forcing to subtropical deep waters.