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Lal, D, Charles C.  2007.  Deconvolution of the atmospheric radiocarbon record in the last 50,000 years. Earth and Planetary Science Letters. 258:550-560.   10.1016/j.epsl.2007.04.016   AbstractWebsite

Here we identify the principal causes of changes in the atmospheric Delta(14)C record by removing the influence of two discrete large changes in the geomagnetic field between 45 and 30 kyr. The marked transitions in the Delta(14)C record during this period can be interpreted as being the result of either "zero magnetic field" for periods of the order of 6500 y and 600 y at similar to 40 kyr and 32 kyr B.P, respectively, or for longer durations if the field was non-zero for appreciable time during the event. Once the effect of these events has been removed, the residual Delta(14)C record shows a plateau with nearly constant value at similar to 300 parts per thousand during 28-17 kyr B.P, followed by a sharp decrease in Delta(14)C between 17 kyr B.P. and the present, to a Delta(14)C value of similar to 0 parts per thousand. Estimated global paleomagnetic fields derived from paleointensity measurements in deep sea sediments (SINT-800, NAPIS-75 and Sumatra Basin) can only explain a maximum of 50% of this residual Delta(14)C record during 30-0 kyr B.P. We propose that the remainder must have resulted from changes in oceanic circulation leading to isolation of >= 20% of oceanic radiocarbon inventory from large scale mixing with the atmosphere during 28-17 kyr B.P. Subsequent inclusion of this carbon may be responsible in part for the decrease between 17 kyr B.P. to the present, to a Delta(14)C value of similar to 0 parts per thousand. We also note that the deconvoluted Delta(14)C record during the past 15,000 y B.P. seems to be primarily influenced by the changes in the atmospheric CO(2) concentrations. These possibilities have been discussed in previous works, but our results here point to a seemingly cyclical change in carbon exchange that was initiated prior to the Last Glacial Maximum. (c) 2007 Elsevier B.V. All rights reserved.

Lal, D, Charles C, Vacher L, Goswami JN, Jull AJT, McHargue L, Finkel RC.  2006.  Paleo-ocean chemistry records in marine opal: Implications for fluxes of trace elements, cosmogenic nuclides (Be-10 and Al-26), and biological productivity. Geochimica Et Cosmochimica Acta. 70:3275-3289.   10.1016/j.gca.2006.04.004   AbstractWebsite

Here, we provide evidence suggesting that marine (diatom) opal contains not only a high fidelity record of dissolved oceanic concentrations of cosmic ray-produced radionuclides, Be-10 and Al-26, but also a record of temporal variations in a large number of trace elements such as Ti, Fe, Zn and Mn. This finding is derived from measurements in purified biogenic opal that can be separated from detrital materials using a newly developed technique based on surface charge characteristics. Initial results from a sediment core taken near the present-day position of the Antarctic Polar Front (ODP Site 1093) show dramatic changes in the intrinsic concentrations of, Be, Al, Ti, Fe, Mn and Zn in the opal assemblages during the past similar to 140 kyr BP. The results imply appreciable climatically controlled fluctuations in the level of bioreactive trace elements. The time series of total Be. Al, Ti, Fe and 10Be in the sediment core are all well correlated with each other and with dust records in the polar ice cores. The observations suggest that a significant flux of these trace metals to oceans is contributed by the aeolian dust, in this case, presumably from the Patagonia. This observation also allows determination of fluxes of dust-contributed Be-10 to the Antarctica ice sheets. However. our data show that the relationships among the various metals are not perfectly linear. During periods of higher dissolved concentrations of trace elements (indicated by Fe and Ti) the relative concentrations of bioreactive elements, Be, Al, Mn and Zn are decreased. By contrast. the Fe/Zn and Fe/Mn ratios decrease significantly during each transition from cold to warm periods. The relative behavior could be consistent with any of the following processes: (i) enhanced biological productivity due to greater supply of the bioreactive elements (e.g. Zn) during cold periods (ii) increased biological and inorganic scavenging of particle active elements (e.g. Be and Al) during early interglacial periods (iii) differential uptake/removal of the metals by the various diatom taxa whose relative productivity or growth rate changes with large scale climate. In any case. with one sedimentary phase and in single sedimentary sections, we now have the potential to compare directly a proxy for aeolian input of micronutrients (e.g. Fe or Ti), with a proxy for production (e.g. Al-26/Al ratios). We expect that studies of the temporal records of trace elements and cosmogenic nuclides in contrasting regions of upwelling and productivity, which exhibit different sensitivities to global climate fluctuations and micronutrient inputs, would lead to a direct and comprehensive test of ideas such as the hypothesis of iron control of atmospheric carbon dioxide [Martin, J.H., 1990. Glacial-interglacial CO2 change: the iron hypothesis. Paleoceanography 5, 1-13]. Our present data from a single site do not show that increases in dissolved Fe concentrations, per se, were responsible for increased biological productivity. However, a much clearer picture of the effect of increased dust fluxes should emerge when we have data for trace elements and the cosmogenic nuclides, 10Be and 26 Al from various oceanic provinces. (c) 2006 Elsevier Inc. All rights reserved.

Linsley, BK, Wu HC, Rixen T, Charles CD, Gordon AL, Moore MD.  2017.  SPCZ zonal events and downstream influence on surface ocean conditions in the Indonesian Throughflow region. Geophysical Research Letters. 44:293-303.   10.1002/2016gl070985   AbstractWebsite

Seasonal surface freshening of the Makassar Strait, the main conduit of the Indonesian Throughflow (ITF), is a key factor controlling the ITF. Here we present a 262year reconstruction of seasonal sea-surface-salinity variability from 1742 to 2004 Common Era by using coral O-18 records from the central Makassar Strait. Our record reveals persistent seasonal freshening and also years with significant truncations of seasonal freshening that correlate exactly with South Pacific Convergence Zone (SPCZ) zonal events >4000km to the east. During these events, the SPCZ dramatically rotates similar to 15 degrees north to near the equator and stronger westward flowing South Pacific boundary currents force higher-salinity water through the Makassar Strait in February-May halting the normal seasonal freshening in the strait. By these teleconnections, our Makassar coral O-18 series provides the first record of the recurrence interval of these zonal SPCZ events and demonstrates that they have occurred on a semiregular basis since the mid-1700s.

Lynch-Stieglitz, J, Curry WB, Oppo DW, Ninneman US, Charles CD, Munson J.  2006.  Meridional overturning circulation in the South Atlantic at the last glacial maximum. Geochemistry Geophysics Geosystems. 7   10.1029/2005gc001226   AbstractWebsite

The geostrophic shear associated with the meridional overturning circulation is reflected in the difference in density between the eastern and western margins of the ocean basin. Here we examine how the density difference across 30 degrees S in the upper 2 km of the Atlantic Ocean ( and thus the magnitude of the shear associated with the overturning circulation) has changed between the last glacial maximum and the present. We use oxygen isotope measurements on benthic foraminifera to reconstruct density. Today, the density in upper and intermediate waters along the eastern margin in the South Atlantic is greater than along the western margin, reflecting the vertical shear associated with the northward flow of surface and intermediate waters and the southward flowing North Atlantic Deep Waters below. The greater density along the eastern margin is reflected in the higher delta(18)O values for surface sediment benthic foraminifera than those found on the western margin for the upper 2 km. For the last glacial maximum the available data indicate that the eastern margin foraminifera had similar delta(18)O to those on the western margin between 1 and 2 km and that the gradient was reversed relative to today with the higher delta(18)O values in the western margin benthic foraminifera above 1 km. If this reversal in benthic foraminifera delta(18)O gradient reflects a reversal in seawater density gradient, these data are not consistent with a vigorous but shallower overturning cell in which surface waters entering the Atlantic basin are balanced by the southward export of Glacial North Atlantic Intermediate Water.

Lynch-Stieglitz, J, Fairbanks RG, Charles CD.  1994.  Glacial-interglacial history of Antarctic Intermediate Water: Relative strengths of Antarctic versus Indian Ocean sources. Paleoceanography. 9:7-29.   10.1029/93PA02446   AbstractWebsite

Sediment cores from the southern continental margin of Australia are near the formation region of Antarctic Intermediate Water (AAIW) and Subantarctic Mode Water and record the changes in these water masses from the last glacial maximum through the present. Carbon and oxygen isotopes were measured on the benthic foraminiferal species Planulina wuellerstrorfi for both the Recent and last glacial maximum sections of the cores and were then used to reconstruct temperature and carbon isotopic water column profiles. The glacial oxygen isotope profile indicates a vertical temperature structure for this region similar to that in today's Subantarctic Zone. Although intermediate water δ13C cannot be used as a nutrient tracer in this region because of the large influence of air-sea carbon isotopic exchange on this water mass, δ13C can be used as a water mass tracer. Today, AAIW properties reflect contributions from cool, fresh Antarctic Surface Waters (2/3) and warm, salty waters from the Indian Ocean (1/3). When examined in conjuction with the glacial δ13C and δ18C data from the north Indian and Southern Oceans, our data suggest a much reduced contribution of North Indian Ocean intermediate water to glacial Antarctic Intermediate Water relative to the contribution of Antarctic Surface Water. This fresher, cooler glacial Antarctic Intermediate Water would be distributed to the intermediate-depth ocean, thus decreasing the transport of salt produced in the North Indian Ocean to the rest of the world's oceans. Combined with evidence for a reduced influence of North Atlantic Deep Water, these results suggest major changes in the pathways for the redistribution of heat and salt in the glacial ocean.