TY - JOUR T1 - Cooling of Northwest Atlantic slope waters during the Holocene JF - Geophysical Research Letters Y1 - 2007 A1 - Sachs, J. P. KW - circulation KW - deposition KW - ice KW - labrador sea KW - ocean KW - oscillation KW - sea-surface KW - stratigraphy KW - Temperature KW - variability AB - [1] Climate of the last 11,000 years, the Holocene, is usually described as warm and stable. Benchmark temperature records from central Greenland ice cores show none of the large, abrupt variations that characterized the prior 100,000 years of glacial climate. Nor do they show any substantial trend, indicating at most 1 degrees-3 degrees C of cooling. Here we show that the slope waters east of the United States and Canada cooled 4 degrees-10 degrees C during the Holocene. Declining insolation, increasing convection in the Labrador Sea, and equatorward shifting of the Gulf Stream path may have caused the cooling. VL - 34 SN - 0094-8276 IS - 3 N1 - 136deTimes Cited:35 Cited References Count:33 JO - Geophys Res Lett ER - TY - JOUR T1 - A Sediment Budget for Southern Lake-Michigan - Source and Sink Models for Different Time Intervals JF - Journal of Great Lakes Research Y1 - 1994 A1 - Colman, S. M. A1 - Foster, D. S. KW - deposition KW - erosion KW - Holocene KW - lake michigan KW - sediment budget KW - sediments AB - We have constructed a sediment budget for the southern Lake Michigan basin for sand and for mud during three time periods: the past 100, 5,000, and 10,000 years. For the modern (100-year) sediment budget, accountable sediment sources add up to 93 percent of the calculated sinks. The mud budget has a source deficit of about 40%, probably due to errors in mu&sand ratios and (or) to other sources not included in our model, especially erosion of the lake floor, which accompanies bluff recession. Two terms dominate the modem sediment-budget equation: (1) bluff erosion, which is an order of magnitude larger than either rivers or aerosols as a source, and (2) deposition in the deep basin, which is more than two orders of magnitude greater as a sink than suspended sediment transport out of the basin. About half of the sand derived from bluff erosion is deposited in the deep lake; the other half must be deposited in nearshore sand bodies, beaches, and dunes. Despite the uncertainties in our estimates of sediment sources and sinks, the attempt to reconstruct sediment budgets for time intervals of 100, 5,000, and 10,000 years leads to important insights about erosion and sedimentation processes. Bluff erosion is the dominant source of both sand and mud in the basin. The deep lake floor is the primary sink for mud, whereas both the deep lake and nearshore areas are important sinks for sand. On a long-term basis, rates of bluff erosion have progressively decreased and are apparently independent of anthropogenic effects. Rates of sediment accumulation in the lake basin mirror the decrease in rates of bluff erosion for prehistoric time, but have increased markedly since human settlement, probably because of anthropogenic effects on river and aerosolic inputs. VL - 20 SN - 0380-1330 IS - 1 N1 - Nl348Times Cited:17 Cited References Count:29 JO - J Great Lakes Res ER - TY - JOUR T1 - Illumination of a Black-Box - Analysis of Gas-Composition during Graphite Target Preparation JF - Radiocarbon Y1 - 1992 A1 - McNichol, A. P. A1 - Gagnon, A. R. A1 - Jones, G. A. A1 - Osborne, E. A. KW - deposition AB - We conducted a study of relative gas composition changes of CO2, CO and CH4 during the formation of graphite targets using different temperatures, catalysts and methods. Reduction with H-2 increases the reaction rate without compromising the quality of the AMS target produced. Methane is produced at virtually any temperature, and the amount produced is greater at very low temperatures. The reduction of CO to graphite is very slow when H-2 is not included in the reaction. VL - 34 SN - 0033-8222 IS - 3 N1 - Kf389Times Cited:63 Cited References Count:10 JO - Radiocarbon ER -