Canadian research at the University of Massachusetts Amherst uses ancient lake sediments to extend the climate record.
Climatologists took advantage of the unique properties of sediments from the bottom of the Sawtooth Lake in Canada’s high Arctic and have extended the record of Atlantic surface temperature from around 100 to 2,900 years. This shows that the warmest interval during this period was the last 10 years.
A team led by Francois Lapointe and Raymond Bradley at the Climate System Research Center at the University of Massachusetts Amherst and Pierre Francus at the University of Québec-INRS analyzed “perfectly preserved” annual sediment layers in the lake on the northern island of Ellesmere in Nunavut that contained titanium left over from centuries of rock weathering. By measuring the titanium concentration in the various layers, scientists can estimate the relative temperature and atmospheric pressure over time.
The newly expanded record shows that the coldest temperatures were found between about AD 1400 and 1600, and the warmest interval only occurred in the past decade, the authors report. Francus adds: “Our unique data set represents the first reconstruction of surface temperatures of the Atlantic Ocean in the last 3,000 years. This will enable climatologists to better understand the mechanisms behind long-term changes in the behavior of the Atlantic Ocean.”
When temperatures are cool over the North Atlantic, a relatively low pressure pattern is noted across much of the Canadian High Arctic and Greenland. This is linked to slower snowmelt in this region and higher levels of titanium in the sediments. The opposite is true when the ocean is warmer – atmospheric pressure is higher, snowmelt is rapid, and titanium concentration is decreasing.
Lapointe says: “With the help of these strong connections it was possible to understand how the surface temperatures of the Atlantic Sea have changed over the past 2,900 years. This makes it the longest recording currently available. ”Details were published on October 12, 2020 in Procedure of the National Academy of Sciences.
The researchers report that their newly reconstructed record correlates significantly with several other independent sediment records from the Atlantic, stretching from northern Iceland to off the coast of Venezuela, confirming their reliability as a proxy for long-term variability in sea temperatures over a wide range of the Atlantic. The record is also similar to European temperatures over the past 2000 years.
Variations in sea surface temperatures known as the Atlantic Multidecadal Oscillation (AMO) are also related to other major climatic upheavals such as droughts in North America and the severity of hurricanes. However, since measurements of sea surface temperatures only go back about a century, little is known about the exact length and variability of the AMO cycle.
Global warming in the Arctic is now two or three times faster than the rest of the planet due to greenhouse gas emissions from burning fossil fuels. Warming can be amplified or dampened by natural climate variability, such as changes in the surface temperature of the North Atlantic, which appear to vary over cycles of around 60-80 years.
Lapointe, who has conducted extensive field research in the Canadian Arctic for the past decade, notes, “In recent summers it has been common for high pressure atmospheric systems – clear sky conditions – to prevail in the region. The maximum temperatures often reached 20 degrees Celsius68 degrees FahrenheitThis had irreversible effects on the snowpack, glaciers, ice caps and permafrost. “
Bradley adds, “The surface waters of the Atlantic have been consistently warm since about 1995. We don’t know if conditions will shift towards a cooler phase anytime soon, which would take some of the strain off the Arctic’s accelerated warming. If the warming of the Atlantic continues, atmospheric conditions can be expected in the coming decades that will encourage greater melting of the Canadian Arctic ice caps and the Greenland ice sheet. “
In 2019, the Greenland ice sheet lost more than 500 billion tons of mass, a record, and this was accompanied by unprecedented, sustained high pressure atmospheric conditions. “
Lapointe notes, “Conditions like these are currently not properly captured by global climate models, which underestimates the potential impact of future warming in Arctic regions.”
Reference: “Annual Resolved Variability of Atlantic Surface Temperature Over the Last 2,900 Years” by Francois Lapointe, Raymond S. Bradley, Pierre Francus, Nicholas L. Balascio, Mark B. Abbott, Joseph S. Stoner, Guillaume St-Onge and Arnaud De Coninck and Thibault Labarre, October 12, 2020, Procedure of the National Academy of Sciences.
DOI: 10.1073 / pnas.2014166117