Wallace S Broecker

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Two hypotheses have been put forward to explain the large and abrupt climate changes that punctuated glacial time. One attributes such changes to reorganizations of the ocean's thermohaline circulation and the other to changes in tropical atmosphere-ocean dynamics. In an attempt to distinguish between these hypotheses, two lines of evidence are examined.(More)
The asynchronous relationship between millennial-scale temperature changes over Greenland and Antarctica during the last glacial period has led to the notion of a bipolar seesaw which acts to redistribute heat depending on the state of meridional overturning circulation within the Atlantic Ocean. Here we present new records from the South Atlantic that show(More)
he reconstruction of global temperatures during the last millennium can provide important clues for how climate may change in the future. A recent, widely cited reconstruction ( ) leaves the impression that the 20th century warming was unique during the last millennium. It shows no hint of the Medieval Warm Period (from around 800 to 1200 A.D.) during which(More)
vertebrate networks, only a small minority of signaling molecules (fibroblast growth factor, Nodal) and transcription factors (ZicL, FoxD, FoxA-a, Otx) affect the expression of a large fraction of the regulatory genes assayed. It will be interesting to test whether the majority of genes studied, which have few or no targets in the network, directly control(More)
The existence of the Big Dry event from 14.9 to 13.8 C kyrs in the Lake Estancia New Mexico record suggests that the deglacial Mystery Interval (14.5–12.4 14C kyrs) has two distinct hydrologic parts in the western USA. During the first, Great Basin Lake Estancia shrank in size and during the second, Great Basin Lake Lahontan reached its largest size. It is(More)
[1] The substantial lowering of tropical snowlines at the Last Glacial Maximum (LGM), circa 21 kya, is examined using a modified version of the single-cell tropical climate model of Betts and Ridgway [1989]. These authors concluded that it was difficult to reconcile the large depression of snowlines at the LGM with the small reduction in mean tropical(More)
Measurements of carbon-14 in small samples of methane from major biogenic sources, from biomass burning, and in "clean air" samples from both the Northern and Southern hemispheres reveal that methane from ruminants contains contemporary carbon, whereas that from wetlands, pat bogs, rice fields, and tundra is somewhat, depleted in carbon-14. Atmospheric(More)
[1] Paleonutrient proxies currently provide the strongest constraints on the past spatial distribution of deep water masses. We review the state of knowledge derived from the trace metal proxy Cd/Ca for the Atlantic Ocean during the Last Glacial Maximum (LGM). We compile published benthic foraminiferal Cd/Ca data, supplemented with new data, to reconstruct(More)
[1] Abstract: We make a case that the 20 ppm rise in atmospheric CO2 content over the last 8000 years was at least in part a consequence of the 500 Gt C increase in terrestrial biomass early in the present interglacial rather than of a 200 Gt C decrease in terrestrial biomass during the latter part of the Holocene as proposed by Indermühle et al. [1999]. In(More)
Deepwater formation in the North Atlantic by open-ocean convection is an essential component of the overturning circulation of the Atlantic Ocean, which helps regulate global climate. We use water-column radiocarbon reconstructions to examine changes in northeast Atlantic convection since the Last Glacial Maximum. During cold intervals, we infer a reduction(More)