Heat Transport Affects the Atlantic Ocean

With the help of ultra-precise measurements of natural radionuclides in the ocean sediments a team led by environmental physicists at Heidelberg University studied the ocean's strength of circulation and revealed new information about the past of the "Atlantic heat pump."

The heat transport in the past in the Atlantic Ocean was much stronger than compared to the present time.

"Thanks to the Gulf Stream and its northern branches, it is much warmer here than at the same latitudes in North America. Without the ocean's heat transport, which is comparable to that of a million large power plants, temperatures in Northern and Western Europe would be considerably cooler," explained Dr. Jörg Lippold, lead author of the study from Heidelberg University's Institute of Environmental Physics.

"Using two exotic representatives of the periodic table from core samples of Atlantic deep sea sediment, we were able to quantitatively determine this return flow for the first time," said the Heidelberg researcher. 

The researchers focused at two isotopes protactinium-231 and thorium-230 that are produced from the radioactive decay of uranium that are found naturally in the sea water. Thorium deposits directly in the sediment at the ocean's floor while protactinium follows the circulation and is taken by the deep sea current from the North Atlantic. The strength of the circulation is dependent on the proportion of the two elements in the sediment ergo.

Approximately 20,000 years ago, around the time of the largest global ice coverage, less proctactinium-231 was measured. According to Lippold, this points to an increase in the Atlantic circulation, which is also supported by model calculations.

"The oceans are the key to the Earth's climate system. There is approximately 50 times more CO₂bound in the Earth's oceans than in the atmosphere, with 1,000 times more heat storage capacity," said Lippold. "With the Ocean circulating more quickly then, it could also extract and store more CO₂ from the atmosphere."

"If the Ocean warms in the course of climate change and the density of the waters of the North Atlantic drops due to melt water or increased precipitation, the heat pump could weaken. Paradoxically, this could cause cooling in Europe while the rest of the world heats up," explained the Heidelberg environmental physicist.

The results of the study are published in the journal Nature Geoscienc