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Sanchez, SC, Charles CD, Carriquiry JD, Villaescusa JA.  2016.  Two centuries of coherent decadal climate variability across the Pacific North American region. Geophysical Research Letters. 43:9208-9216.   10.1002/2016gl069037   AbstractWebsite

The decadal variability of the Pacific Ocean and North American hydroclimate are subjects of immediate concern for society, yet the length of the instrumental record limits full mechanistic understanding of this variability. Here we introduce a 178year, seasonally resolved coral oxygen isotopic record from Clarion Island (18 degrees N, 115 degrees W), a sampling a subtropical region that is strongly influenced by the decadal-scale fluctuations of the North Pacific Gyre Oscillation and a region that serves as a critical locus for the communication of climate anomalies with the tropics. This Mexican Pacific coral record is highly correlated to coral records from the central tropical Pacific and tree ring records from western North America. Significant changes in the amplitude of oceanic decadal variability in the early nineteenth century are mirrored in the drought reconstructions in western North America. The spatial manifestation of this relationship was relatively invariant, despite notable changes in the climatic mean state.

Schrag, DP, Adkins JF, McIntyre K, Alexander JL, Hodell DA, Charles CD, McManus JF.  2002.  The oxygen isotopic composition of seawater during the Last Glacial Maximum. Quaternary Science Reviews. 21:331-342.   10.1016/s0277-3791(01)00110-x   AbstractWebsite

High-resolution oxygen and hydrogen isotope measurements were made on pore fluids from deep-sea sediments from sites in the North and South Atlantic. The data provide direct measurements of changes in the isotopic composition of bottom waters during the Last Glacial Maximum (LGM). Results from Ocean Drilling Program (ODP) Site 981 in the North Atlantic, currently bathed in North Atlantic Deep Water (NADW) reproduces previous results from the Ceara and Bermuda Rises, constraining the glacial-interglacial change in delta(18)O of the deep Atlantic to be 0.7-0.8parts per thousand. Results from Site 984, which is located north of Site 981 and at a shallower water depth, yield a similar value (0.8parts per thousand), providing insight into the properties of Glacial North Atlantic Intermediate Water (GNAIW). Sites from ODP Leg 177 in the South Atlantic span the modern boundary between northern and southern sources of deep water. Data from the northern site (1088) yield a similar result to sites in the tropical and North Atlantic (0.7parts per thousand). At the southern site (1093), located south of the polar front, the change is substantially larger (1.1parts per thousand), representing the change in delta(18)O of southern source waters since the LGM. These results confirm previous estimates that the global average change in delta(18)O of seawater is 1.0+/-0.1parts per thousand. Hydrogen isotopes measured on pore fluids from three sites are consistent with the oxygen isotopes from these locations, giving further support to these results. At all sites studied, the temperature of the deep ocean during the LGM, calculated by combining the pore fluid results with oxygen isotope data from benthic foraminifera, was within VC of the freezing point of seawater. (C) 2001 Elsevier Science Ltd. All rights reserved.

Shemesh, A, Hodell D, Crosta X, Kanfoush S, Charles C, Guilderson T.  2002.  Sequence of events during the last deglaciation in Southern Ocean sediments and Antarctic ice cores. Paleoceanography. 17   10.1029/2000pa000599   AbstractWebsite

[1] The last glacial to interglacial transition was studied using down core records of stable isotopes in diatoms and foraminifera as well as surface water temperature, sea ice extent, and ice-rafted debris (IRD) concentrations from a piston core retrieved from the Atlantic sector of the Southern Ocean. Sea ice is the first variable to change during the last deglaciation, followed by nutrient proxies and sea surface temperature. This sequence of events is independent of the age model adopted for the core. The comparison of the marine records to Antarctic ice CO2 variation depends on the age model as C-14 determinations cannot be obtained for the time interval of 29.5-14.5 ka. Assuming a constant sedimentation rate for this interval, our data suggest that sea ice and nutrient changes at about 19 ka B. P. lead the increase in atmospheric pCO(2) by approximately 2000 years. Our diatom-based sea ice record is in phase with the sodium record of the Vostok ice core, which is related to sea ice cover and similarly leads the increase in atmospheric CO2. If gas exchange played a major role in determining glacial to interglacial CO2 variations, then a delay mechanism of a few thousand years is needed to explain the observed sequence of events. Otherwise, the main cause of atmospheric pCO(2) change must be sought elsewhere, rather than in the Southern Ocean.

Shemesh, A, Macko SA, Charles CD, Rau GH.  1993.  Isotopic Evidence for Reduced Productivity in the Glacial Southern-Ocean. Science. 262:407-410.   10.1126/science.262.5132.407   AbstractWebsite

Records of carbon and nitrogen isotopes in biogenic silica and carbon isotopes in planktonic foraminifera from deep-sea sediment cores from the Southern Ocean reveal that the primary production during the last glacial maximum was lower than Holocene productivity. These observations conflict with the hypothesis that the low atmospheric carbon dioxide concentrations were introduced by an increase in the efficiency of the high-latitude biological pump. Instead, different oceanic sectors may have had high glacial productivity, or alternative mechanisms that do not involve the biological pump must be considered as the primary cause of the low glacial atmospheric carbon dioxide concentrations.

Shemesh, A, Charles CD, Fairbanks RG.  1992.  Oxygen Isotopes in Biogenic Silica - Global Changes in Ocean Temperature and Isotopic Composition. Science. 256:1434-1436.   10.1126/science.256.5062.1434   AbstractWebsite

A record of oxygen isotopes in biogenic silica from a deep-sea sediment core from the Southern Ocean reveals that marine diatoms retain their primary isotopic composition after burial. As a result, the marine diatom record can be combined with data on coexisting planktonic foraminifera to monitor past surface temperature and isotopic composition of seawater. The coupling of these two records allows the solution of two paleotemperature equations for each core interval. Data from a South Atlantic core show that the average delta-O-18 during the glacial period at this site was higher by about 1.3 per mil than average Holocene values, and that average glacial-age temperatures were not significantly different from average Holocene values.

Stoner, JS, Channell JET, Hodell DA, Charles CD.  2003.  A similar to 580 kyr paleomagnetic record from the sub-Antarctic South Atlantic (Ocean Drilling Program Site 1089). Journal of Geophysical Research-Solid Earth. 108   10.1029/2001jb001390   AbstractWebsite

We report geomagnetic directional paleosecular variation, relative paleointensity proxies and oxygen isotope data from the upper 88 m composite depth (mcd) at South Atlantic Ocean Drilling Program (ODP) Site 1089 (40degrees56.2'S, 9degrees53.64'E, 4620 m water depth). The age model is provided by high-resolution oxygen isotope stratigraphy, augmented by radiocarbon dates from the upper 8 mcd of nearby piston core RC11-83. Mean sedimentation rates at Site 1089 are in the range of 15 to 20 cm/kyr. Two intervals during the Brunhes Chron, at similar to29.6 mcd (similar to190 ka) and at similar to48 mcd (similar to335 ka), have component magnetization directions with positive (reverse polarity) inclination; however, the excursional directions are heavily overprinted by the postexcursional field. Magnetite is the dominant carrier of magnetic remanence, and occurs in the pseudosingle-domain (PSD) grain size. An additional higher-coercivity magnetic carrier, characterized by low unblocking temperatures (<350&DEG;C), is assumed to be authigenic pyrrhotite. A decrease in magnetization intensity down core is mirrored by a reduction in pore water sulfate, indicating diagenetic reduction of magnetite. Despite down-core changes in magnetic mineralogy, normalized intensity records from Site 1089 are comparable with high-resolution paleointensity records from the North Atlantic (e.g., ODP Sites 983 and 984). Sediment properties and sedimentation patterns within the Cape (Site 1089) and Iceland (Sites 983 and 984) Basins are distinctly different at both millennial and orbital timescales and therefore preclude lithologic variability from being the source of this correlation. Variations in normalized intensity from Site 1089 therefore appear to reflect changes in global-scale geomagnetic field intensity.