Dankdude
Well-Known Member
Lake Sediments
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
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.
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
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.
