Deep Ocean Temperatures used to be 10 to 15 degrees warmer
My March 8th post shows a chart illustrating deep ocean temperatures for the last 100 million years. At the website Global Climate Change Student Guide, the original home of the chart, I also found the following excerpt comparing prehistoric deep ocean temperatures with today:
… evidence from oxygen isotope records (Douglas & Woodruff, 1981) revealed that deep sea ocean temperatures were at least 10°C to 15°C warmer than they are today (see Figure 5.6). Early Cenozoic sea surface temperatures around Antarctica were also considerably warmer than today (Shackleton & Kennet, 1975) .
The early Eocene (55 to 50Ma) was the warmest period during the Cenozoic. Various climatic indices suggest that tropical conditions extended 10° to 15° of latitude poleward of their present limits.