Lake sediments are not as widespread nor do they record as long a history as sea floor sediments. However they record very valuable information about the climate on the world's landmasses. Once again, this is another mutually-supporting, correlatable line of evidence about past Earth climate changes, before man was involved.
Read about these documented historical, often abrupt, and severe climate changes. They were obviously caused by something (the sun?) other than mankind burning oil and coal. Are today's apparent slight global warming and climate changes abnormal and unusual? NO Are they something to get all panicked about? Not likely. Are we in the midst of a climate crises? All of our climate history tells us we're going through nothing unusual, it has all happened before. It is only the computer climate models that are unusual. Why are so many people trying to scare us?
The Physical Evidence of Earth's Unstoppable 1,500-Year Climate Cycle
Findings from analysis of lake sediments reinforces those from seabed sediments. Some examples:
In Switzerland, the remains of tiny aquatic creatures in the sediments of Lake Neufchatel showed Swiss temperatures fell by 1.5° C during the shift from the Medieval Warming to the Little Ice Age.34 The authors note that mean annual temperatures during the warming were “on average higher than at present.”
In southwest Alaska, the University of Illinois’ F. S. Hu analyzed the silica produced by living organisms, organic carbon and organic nitrogen in lake sediments. He found the climate shifts have been similar in the subpolar regions of both the North Atlantic and North Pacific — “possibly because of sun-ocean-climate linkages.”35
In West Africa, sediments from Cameroon’s Lake Ossa show that the climate oscillates with the 1,500-year cycle in the northern and southern movements of the Intertropical Convergence Zone.36 Francis Nguetsop of the French National Museum of Natural History says his lake sediment core showed southward shifts of the zone were marked by low precipitation in the northern subtropics (Nigeria and Ghana) and high precipitation in the subequatorial zone (Zaire and Tanzania).37
"Sediments from dry lakebeds show 1,500-year cycles of droughts and floods."
In East Africa,Belgium’s DirkVerschuren built an 1,100-year rainfall-drought history for Kenya’s Lake Naivasha, based on 1) sediments, 2) fossil diatoms and 3) midge species and numbers.38 “In tropical Africa,” Verschuren says, “the data indicate that, over the past millennium, equatorial east Africa has alternated between contrasting climate conditions, with significantly drier climate than today during the ‘Medieval Warm Period’ (1000–1270) and a relatively wet climate during the ‘Little Ice Age’ (1270–1850) that was interrupted by three prolonged dry episodes.”
In Africa’s Central Highlands, sediment cores from Lake Victoria show a 1,400- to 1,500-year spacing of precipitation-evaporation fluctuations over the past 10,000 years.39
In a lake high on Mount Kenya, Weizmann Institute researchers retrieved a six-foot core of sediment that accumulated between 2250 B.C. and A.D. 750. The team analyzed the ratio of oxygen isotopes in the algae skeletons (called biogenic opal). The largest anomaly was a rapid warming — 4° C — during the 800 years between 350 B.C. and A.D. 450, reflecting a warmer climate in equatorial East Africa.40 Was this the Roman Warming? The researchers noted warming during the same period in the Swedish part of Lapland and in the northeastern St. Elias Mountains of Alaska and the Canadian Yukon.
In Central America, near the abandoned Mayan cities, lake sediment cores testify to a prolonged drought during the cold Dark Ages that may have caused the collapse of the entire Mayan culture.41 A team from the University of Florida, led by David Hodell, recently confirmed evidence of a Yucatan drought from 800 to 1000, based on the gypsum levels in a core from the muddy bottom of ancient Lake Chichancanab.42
Seabed cores from the Cariaco Basin just off the Venezuelan coast (in the same climatic region) echo the Mayan drought. Gerald Haug of the University of Southern California and Konrad Hughen of the Woods Hole Oceanographic Institute analyzed titanium concentrations; more titanium was associated with more rainfall.43
Mayan cities thrived in the Yucatan lowlands for 1,000 years — mostly during the Roman Warming era. In the cold Dark Ages, however, the Mayans suffered at least 100 years of low rainfall, punctuated by periods of three to nine years in a row with little or no rainfall.
"Climate shifts in the opposite direction in some regions."
In Argentina, a study of saline lake sediments from a high volcanic plateau found that rainfall and climate changed sharply when the world shifted from warm to cool and back again. The study team concluded, “The Little Ice Age stands as a significant climatic event in the Altiplano and South Amer-ica.”44
More Global Connections. A remarkable similarity in weather patterns has been documented for southeastern Africa’s Lake Malawi and the Cariaco Basin off the coast of Venezuela. Researchers studied sediment layers in Lake Malawi, and reconstructed a climate record by comparing the algae fossils and ratios of niobium to titanium over 25,000 years.45 More niobium indicated a dryer climate with the Intertropical Convergence Zone shifted to the south, so more volcanic ash was wind-blown from north of the lake. Knowing that both Lake Malawi and the Caribbean are impacted by the ITCZ, they found the reconstructed Malawi climate history “remarkably similar” to that of the Cariaco Basin since the Late Glacial period. They also found that the Lake Malawi record was often anti-phased to the Greenland climate record.
In central Chile, geochemicals, sediments and algae cyst populations from Laguna Aculeo showed a major increase in floods during 400 B.C. to A.D.200 (the pre-Roman cold era), 500 to 700 (the Dark Ages) and from 1300 to 1700 (the Little Ice Age). During cooling periods, westerly winds bring additional rainfall to the lake.46
Near Antarctica,on Signy Island, lake sediments clearly show the Roman Warming and the Dark Ages, the Medieval Warming, the Little Ice Age and the 20th century warming — which is cooler to date than the Medieval Warming.47
« Previous Study Home Next »