Isotope Data

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 (benthic) temperatures (indicative of low and high latitude areas respectively) is much higher today than it was in the Late Cretaceous.

These records for planktic and benthic forams 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; the benthic record reflects conditions at the high-latitude source regions of deep-water masses.

The data suggest general cooling in the Pacific throughout the Late Cretaceous from a high temperature peak in the Albian/Cenomanian.

Temperature 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.

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