Paleoclimate

Last Glacial Maximum

The Last Glacial Maximum spanning the period between about 25,000 and 20,000 years ago was characterized by global atmospheric temperatures 3-6 degrees colder than today, atmospheric carbon dioxide concentrations 80-90ppm lower than preindustrial values, and extended ice sheets and sea ice. The drop in temperature and the expansion of ice sheets are linked to the drop in carbon dioxide, which reduced the greenhouse radiative feedback. Isotope proxies suggest that the missing carbon dioxide ended up in the abyssal ocean, but it remains an open question how this happened. We have shown that the large-scale ocean circulation changed dramatically during glacial periods and sequestered large amounts of carbon in the abyss. We are now trying to quantify whether the amount of carbon trapped in the abyss is quantitatively consistent with the observed drop in atmospheric carbon dioxide.

Now working on this theme: Sandy Gregorio, Louis-Philippe Nadeau, Anne Willem Omta.

Previously working on this theme: Malte Jansen.

Eocene

The early parts of the Eocene Epoch, between 56 and 49 million years ago, were characterized by equable climates with little to no ice and a smaller than present difference in temperature from the equator to the poles. A multitude of proxies support the presence of a warmer equable climate: fossils native to warm climates, such as crocodiles, located in the higher latitudes, the presence at the high-latitudes of frost-intolerant flora such as palm trees, fossils of snakes found in the tropics that would require much higher average temperatures to sustain them. Isotope proxies indicate sea surface temperatures in the tropics as high as 35 °C and bottom water temperatures around 10 °C. With these bottom water temperatures, temperatures in areas where deep-water forms near the poles are unable to be much cooler than the bottom water temperatures. While an increase in atmospheric carbon dioxide values to 700 – 900 ppm appears to explain the warm ocean temperatures, the presence of crocodiles and frost-intolerant flora in continental interiors remains a puzzle. Our group is trying to understand how the high-latitude continental remained above freezing in winter.

Previously working on this theme: Luca Filippi.