Interpretation of the data
Oxygen isotope record of foraminifera from the central North Pacific
for the Mid-Late Cretaceous and its comparison with the present day. Oxygen
isotope ratio scale is shown on the left vertical
axis; the corresponding temperature scales for the ocean are shown on the right.
Notice how with decreasing oxygen isotope values, ocean temperature increases. Also
that the difference in temperature between surface (planktic) and deep water
(indicative of low and high latitude areas respectively) is much higher today
than it was in the Late Cretaceous.
These records for planktic and
from subtropical sites in the North Pacific illustrate the major features of
palaeoclimate changes over the Late Cretaceous.
The planktic record reflects
temperature and oxygen isotope ratio variations in low-latitude surface waters;
record reflects conditions at the high-latitude source regions of deep-water
The data suggest general cooling in the Pacific throughout the Late
Cretaceous from a high temperature peak in the
trends in deep waters are correlated with those of surface waters. However,
bottom waters were considerably warmer than at present. This suggests that
latitudinal contrast in ocean temperatures is higher today than in the Late
Cretaceous resulting from apparent cooling at high latitudes. The climate in
the Late Cretaceous was obviously less varied across the Earth's surface than
it is today.
Return to the Isotope Evidence page.