The ‘8.2 ka cooling event’ is the largest climatic excursion of the Holocene from the perspective of Greenland temperature change. Greenland temperature dropped by 3 deg.C, and methane declined by 80 ppbv, which suggest an important change in the hydrologic cycle.
During ca. 8220 to 7600 cal yr BP also called the ‘8.2 ka cooling event’ Greenland temperature dropped by 3 deg.C, and methane declined by 80 ppbv due to glacial outburst flood of freshwater from Lake Agassiz thorough the Hudson Bay into the North Atlantic.
It is one of the largest climatic excursions of the Holocene and an important change in the hydrologic cycle.
Scientists from Birbal Sahni Institute of Palaeosciences (BSIP) have found signature of this Abrupt Climate Change (ACC) or Rapid Climate Change (RCC) event of the North Atlantic, in the Core Monsoon Zone (CMZ), India (Figs. 1 & 2).
The team extracted a 1.2-meter-long sediment profile from Tuman Lake in Korba District, Chhattisgarh, located within the CMZ and analysed fossil pollen preserved in lake sediments. Each type of plant produces distinctive pollen grains. By identifying and counting 300 terrestrial pollen grains per sample, the researchers reconstructed past vegetation patterns and, in turn, inferred past climate conditions and constructed a high-resolution climate archive written in microscopic grains of pollen.
In a study published in the journal Quaternary International, the researchers interpretated that more tropical moist deciduous forest pollen indicated stronger monsoon rainfall and drier deciduous or herbaceous pollen indicated weaker monsoon conditions and identified weakened monsoon during the 8.2 ka interval. Also, using radiocarbon dating and statistical age-depth modelling, the team built a timeline stretching back over 8,200 years.
The weakened monsoon during the 8.2 ka interval suggests a powerful teleconnection or an atmospheric and oceanic link between the North Atlantic and the Indian Summer Monsoon. It indicated that cooling in Greenland caused disruptions in Atlantic circulation that may have shifted global wind belts and weakened monsoons in the Northern Hemisphere, thereby reducing rainfall over India.
