The warm Atlantic water continued to flow into the icy Nordic seas during the coldest periods of the last Ice Age.
Fossil foraminifera measure temperature.
An Ice Age may sound as a stable period of cold weather, but the name can be deceiving. In the high latitudes of the Northern Hemisphere, the period was characterized by considerable climate changes. Cold periods (stadials) switched abruptly to warmer periods (interstadials) and back.
It is considered by many that during cold periods of the last Ice Age the warm Atlantic water had terminated its flow into the Nordic Seas during the glacial period, says Mohamed Ezat, PhD at Centre for Arctic Gas hydrate, Environment and Climate (CAGE) at UiT, The Arctic University of Norway.
The study, published in Geology
, documented that bottom water actually grew to a temperature of up to 5⁰C at 1200m depth
in the Nordic seas during the cold stadials. Cold bottom water temperatures of 0.5⁰C was detected during the warm interstadials, which is not dissimilar to what we experience today.
How was this possible?
So the air was getting colder, but the deep ocean water was getting warmer during some of the coldest periods of the Ice Age
. How is this possible?
Colloquially referred to as the Gulf Stream, the warm North Atlantic Current is partly to blame for our mild North European winters. It flows into the Nordic seas, where it cools down in winter and releases heat into the atmosphere. It becomes denser and sinks to the bottom of the Nordic seas. It creates a significant part of the global circulatory system of ocean currents.
Cold, deep water from the small area of the Nordic seas, less than 1% of the global ocean, travels the entire planet and returns as warm surface water. This has remained a fairly stable process for the last 10,000 years. The events here are significant for the entire ocean system. However, if we go back to the Ice Age
things were quite different, says professor Tine Rasmussen from CAGE. The reason is that ice sheets across Scandinavia and North America produced a substantial amount of fresh melt water from icebergs. This means that the surface water could not reach the required density to sink‒ this is a process that relies on salinity. The warm Atlantic water was saltier, and thus heavier and subducted at depth and reached to the bottom, actually heating up beneath a lid of ice and melt water, that prevented the release of heat into the atmosphere.
Warm water was present, but deep under the cold, icy surface. So the climate experience was colder
, as the atmospheric records from Greenland ice cores display. But what eventually happened, is that warm water reached a critical point, surged upwards to the surface, and contributed to the abrupt warming of the surface water and atmosphere, says, Ezat.
Methane hydrates belong to a group of substances called clathrates - substances in which one molecule type forms a crystal-like cage structure and encloses another type of molecule. If the cage-forming molecule is water, it is called a hydrate. If the molecule trapped in the water cage is a gas, it is a gas hydrate, in this case methane hydrate.
Methane hydrates can only form under very specific physical, chemical and geological conditions. High water pressures and low temperatures provide the best conditions for methane hydrate formation. Methane hydrates primarily occur on the continental slopes, those areas where the continental plates meet the deep-sea regions. With rising ocean temperatures, methane is increasingly escaping from deep ocean floors. Methane is also 21 more times capable of trapping heat in the atmosphere than carbon dioxide.
Recent discoveries verify trapped methane is now being released from many areas of the globe, both in oceans and on land, and at a faster rate than anticipated. This is part of a natural earth cycle and a possible contributing precursor to ice age rebound.
See also: Hundreds of methane plumes erupting along U.S. Atlantic coast