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Hodell, DA, Kanfoush SL, Shemesh A, Crosta X, Charles CD, Guilderson TP.  2001.  Abrupt cooling of Antarctic surface waters and sea ice expansion in the South Atlantic sector of the Southern Ocean at 5000 cal yr B.P. Quaternary Research. 56:191-198.   10.1006/qres.2001.2252   AbstractWebsite

Antarctic surface waters were warm and ice free between 10,000 and 5000 cal yr B.P., as judged from ice-rafted debris and microfossils in a piston core at 53 degreesS in the South Atlantic. This evidence shows that about 5000 cal yr B.P., sea surface temperatures cooled, sea ice advanced, and the delivery of ice-rafted detritus (IRD) to the subantarctic South Atlantic increased abruptly. These changes mark the end of the Hypsithermal and onset of Neoglacial conditions. They coincide with an early Neoglacial advance of mountain glaciers in South America and New Zealand between 5400 and 4900 cal yr B.P., rapid middle Holocene climate changes inferred from the Taylor Dome Ice Core (Antarctica), cooling and increased IRD in the North Atlantic, and the end of the African humid period. The near synchrony and abruptness of all these climate changes suggest links among the tropics and both poles that involved nonlinear response to gradual changes in Northern Hemisphere insolation. Sea ice expansion in the Southern Ocean may have provided positive feedback that hastened the end of the Hypsithermal and African humid periods in the middle Holocene. (C) 2001 University of Washington.

Carilli, JE, Charles CD, Garren M, McField M, Norris RD.  2013.  Baseline shifts in coral skeletal oxygen isotopic composition: a signature of symbiont shuffling? Coral Reefs. 32:559-571.   10.1007/s00338-012-1004-y   AbstractWebsite

Decades-long records of the stable isotopic composition of coral skeletal cores were analyzed from four sites on the Mesoamerican Reef. Two of the sites exhibited baseline shifts in oxygen isotopic composition after known coral bleaching events. Changes in pH at the calcification site caused by a change in the associated symbiont community are invoked to explain the observed shift in the isotopic composition. To test the hypothesis that changes in symbiont clade could affect skeletal chemistry, additional coral samples were collected from Belize for paired Symbiodinium identification and skeletal stable isotopic analysis. We found some evidence that skeletal stable isotopic composition may be affected by symbiont clade and suggest this is an important topic for future investigation. If different Symbiodinium clades leave consistent signatures in skeletal geochemical composition, the signature will provide a method to quantify past symbiont shuffling events, important for understanding how corals are likely to respond to climate change.

Charles, CD, Froelich PN, Zibello MA, Mortlock RA, Morley JJ.  1991.  Biogenic Opal in Southern Ocean Sediments Over the Last 450,000 Years: Implications for Surface Water Chemistry and Circulation. Paleoceanography. 6:697-728.   10.1029/91pa02477   AbstractWebsite

We present records of biogenic opal percentage and burial rate in 12 piston cores from the Atlantic and Indian sectors of the Southern Ocean. These records provide a detailed, quantitative description of changing patterns of opal deposition over the last 450 kyr. The striking regional coherence of these records suggests that dissolution in the deep sea and sediment pore waters does not obscure the surface productivity signal, and therefore these opal time series can be used in combination with other surface water tracers to make inferences about the chemistry and circulation of the Southern Ocean under different global climate conditions. Three broad depositional patterns can be distinguished. Northernmost records (39 degrees-42 degrees S latitude) are characterized by enhanced opal burial during glacial periods and strong 41 kyr periodicity. Records from cores just north of the present Antarctic Polar Front (46 degrees-49 degrees S) show even larger increases in opal burial rate during glacial intervals, but have variance concentrated in the 100 and 23 kyr bands. Southern most records (51 degrees-55 degrees S) are completely out of phase with those to the north, with greatly reduced opal burial rates during glacial periods. Taken as a whole, the opal records show no evidence for the increased total Antarctic productivity predicted by recent geochemical models of atmospheric CO2 variability. T he areal expansion of Southern Ocean sea ice over the present zone of high siliceous productivity provides one plausible explanation for the glacial-interglacial opal patterns. The excess silica not taken up in this zone during glacial periods would contribute to greater nutrient availability and thus higher productivity in the subantarctic region. However, local circulation changes may act to modify this basic signal, possibly accounting for the observed differences in the opal variance spectra.

Flores, JA, Marino M, Sierro FJ, Hodell DA, Charles CD.  2003.  Calcareous plankton dissolution pattern and coccolithophore assemblages during the last 600 kyr at ODP Site 1089 (Cape Basin, South Atlantic): paleoceanographic implications. Palaeogeography Palaeoclimatology Palaeoecology. 196:409-426.   10.1016/s0031-0182(03)00467-x   AbstractWebsite

Coccolithophore assemblages at ODP Site 1089 in the southern Cape Basin (similar to41degreesS) were used to reconstruct surface-water conditions for the late Quaternary (Marine Isotope Stages (MIS) 1-15) in a region of strong hydrographic gradients in the southeast Atlantic. Stratigraphic control was provided by oxygen isotope stratigraphy and calcareous nannofossil events that are thought to be synchronous over a broad range of latitudes. The greatest coccolith abundances occurred at glacial terminations and, to a lesser degree, during glacial stages. Conversely, coccolithophores were the least abundant during the transition between interglacial to glacial stages, when calcium carbonate dissolution was strong. With the exception of these intervals, coccolith preservation is moderate to good, allowing study of the assemblages. The total abundance of coccolithophores and calcium carbonate variations at Site 1089 result both from variations in dissolution and carbonate production. During terminations, for example, the greatest calcium carbonate concentrations occurred at the same time as a moderate-to-poor preservation of coccoliths and foraminifers. Carbonate production was relatively high during these intervals. However, during terminations IV and V. maxima in carbonate production in the ocean were linked to high-dissolution processes at Site 1089. This trend is not observed for terminations I, II and III [Hodell et al., Earth Planet. Sci. Lett. 192 (2001) 109-124]. The interval from MIS 9 to 13 is coincident with high abundances of highly calcified species such as Gephyrocapsa caribbeanica. Here we discuss the contribution of this ubiquitous species to the production of calcium carbonate and their paleoecological significance. Except for occasional coccolith-barren intervals during interglacial periods, subtropical coccolith species were present continuously at ODP Site 1089 during the late Pleistocene. This suggests that the Polar Front has been south of Site 1089 for the last 600 kyr. (C) 2003 Elsevier Science B.V. All rights reserved.

Naqvi, WA, Charles CD, Fairbanks RG.  1994.  Carbon and Oxygen Isotopic Records of Benthic Foraminifera From the Northeast Indian-Ocean - Implications on Glacial-Interglacial Atmospheric CO2 Changes. Earth and Planetary Science Letters. 121:99-110.   10.1016/0012-821x(94)90034-5   AbstractWebsite

We present here continuous records of delta(18)O and delta(13)C in benthic foraminifera, extending well into the last ice age, in two piston cores from the Andaman Sea (sill depth similar to 1.3 km) and the Bay of Bengal (3 km). These show that, contrary to the previous reports, the glacial to interglacial shift in delta(13)C,at mid-depths in the Northeast Indian Ocean was indistinguishable from the mean oceanic delta(13)C change, negating a more vigorous renewal of intermediate waters globally during the glacial time. The corresponding delta(13)C Shift in deep waters is estimated to be about 50% larger than that reported previously. Jointly with some recent data from the Pacific, our results indicate a modest glacial-Holocene shift in the intermediate to deep water chemical gradients in the Indo-Pacific as a whole, implying that it was perhaps not the dominant mechanism for the glacial-interglacial atmospheric CO2 variations. Also, in conflict with previous work, our measurements suggest significant cooling of both the intermediate and deep waters during the glacial time. The high-resolution records from the Andaman Sea help reconstruct paleoenvironmental changes at intermediate depths during the last deglaciation. Rapid increases in delta(13)C occurring in two stages during the early deglaciation appear to have been caused by the fluctuations in the North Atlantic Deep Water production. A negative excursion in delta(13)C during the mid-deglaciation is ascribed to enhanced nutrient regeneration at mid-depths associated with the greatly intensified summer monsoon around the Pleistocene-Holocene boundary.

Cobb, KM, Charles CD, Hunter DE.  2001.  A central tropical Pacific coral demonstrates Pacific, Indian, and Atlantic decadal climate connections. Geophysical Research Letters. 28:2209-2212.   10.1029/2001gl012919   AbstractWebsite

While instrumental and proxy-based climate records describe significant decadal-scale climate variability throughout the tropical Pacific, Indian, and Atlantic Oceans, the processes responsible for these variations and their interactions are not readily apparent from the observations. A new 112-yr coral-based sea surface temperature (SST) reconstruction from Palmyra Island in the central tropical Pacific (CTP) exhibits strong decadal variability with an amplitude of roughly 0.3 degreesC. A 12-13yr-period signal in this coral record is highly coherent with long equatorial Atlantic and Indian Ocean climate records, implying a unified phenomenon. The Atlantic pattern suggests that it may fall under direct influence of anomalous SST in the CTP, as it does over interannual timescales, while the Indian Ocean pattern exhibits maximum response during the switch between warm/cold states in the tropical Pacific. The results demonstrate that the CTP has played a significant role in determining the expression of global decadal climate variability over the twentieth century.

Ninnemann, US, Charles CD.  2002.  Changes in the mode of Southern Ocean circulation over the last glacial cycle revealed by foraminiferal stable isotopic variability. Earth and Planetary Science Letters. 201:383-396.   10.1016/s0012-821x(02)00708-2   AbstractWebsite

Benthic foraminiferal oxygen and carbon isotopic records from Southern Ocean sediment cores show that during the last glacial period, the South Atlantic sector of the deep Southern Ocean filled to roughly 2500 m with water uniformly low in VC, resulting in the appearance of a strong mid-depth nutricline similar to those observed in glacial northern oceans. Concomitantly, deep water isotopic gradients developed between the Pacific and Atlantic sectors of the Southern Ocean; the delta(13)C of benthic foraminifera in Pacific sediments remained significantly higher than those in the Atlantic during the glacial episode. These two observations help to define the extent of what has become known as the 'Southern Ocean low delta(13)C problem'. One explanation for this glacial distribution of delta(13)C calls upon surface productivity overprints or changes in the microhabitat of benthic foraminifera to lower glacial age delta(13)C values. We show here, however, that glacial-interglacial delta(13)C shifts are similarly large everywhere in the deep South Atlantic, regardless of productivity regime or sedimentary environment. Furthermore, the degree of isotopic decoupling between the Atlantic and Pacific basins is proportional to the magnitude of delta(13)C change in the Atlantic on all time scales. Thus, we conclude that the profoundly altered distribution of delta(13)C in the glacial Southern Ocean is most likely the result of deep ocean circulation changes. While the characteristics of the Southern Ocean delta(13)C records clearly point to reduced North Atlantic Deep Water input during glacial periods, the basinal differences suggest that the mode of Southern Ocean deep water formation must have been altered as well. (C) 2002 Elsevier Science B.V. All rights reserved.

Charles, CD, LynchStieglitz J, Ninnemann US, Fairbanks RG.  1996.  Climate connections between the hemisphere revealed by deep sea sediment core ice core correlations. Earth and Planetary Science Letters. 142:19-27.   10.1016/0012-821x(96)00083-0   AbstractWebsite

Correlation of Southern Ocean deep sea sediment core records with ice core records of polar climate delineates with unprecedented detail the relationship between high latitude climate and the ocean's thermohaline circulation over the last 80,000 years. Our observations suggest that, while North Atlantic Deep Water variability manifests itself clearly in Southern Ocean nutrient proxy records over periods as short as 500 yr, this deep water variability did not promote a direct link between climate variability in the high latitudes of the two hemispheres on millennial timescales. In particular, the proxy records indicate that, on average, northern hemisphere climate fluctuations lagged those of the southern hemisphere by 1500 yr.

Kanfoush, SL, Hodell DA, Charles CD, Janecek TR, Rack FR.  2002.  Comparison of ice-rafted debris and physical properties in ODP Site 1094 (South Atlantic) with the Vostok ice core over the last four climatic cycles. Palaeogeography Palaeoclimatology Palaeoecology. 182:329-349.   10.1016/s0031-0182(01)00502-8   AbstractWebsite

Visual counts of ice-grafted debris (IRD), foraminifera, and radiolaria were made for similar to1500 samples in Site 1094 spanning the last four climatic cycles (marine isotope stages 1-11). Most, but not all, of the IRD variability is captured by whole-core physical properties including magnetic susceptibility and gamma-ray attenuation bulk density. Glacial periods are marked by high IRD abundance and millennial-scale variability, which may reflect instability of ice shelves in the Weddell Sea region. Each interglacial period exhibits low IRD and high foraminiferal abundance during the early part of the interglacial, indicating relatively warm sea-surface temperatures and reduced influence of sea ice. IRD increases and foraminiferal abundances decrease during the latter part of each interglacial, indicating a return to more glacial-like conditions. Glacial terminations I and V are each characterized by a step-wise reduction in ice-rafting punctuated by a brief pulse in IRD delivery and reversal in delta(18)O. The coarse fraction of the sediment is dominated by ash and radiolaria, and the relative abundance of these components is remarkably similar to the concentration of Na+ in Vostok. Each of these variables is believed to be controlled mainly by sea-ice cover, thereby providing a means for sediment-ice core correlation. (C) 2002 Elsevier Science B.V. All rights reserved.

Hodell, DA, Charles CD, Ninnemann US.  2000.  Comparison of interglacial stages in the South Atlantic sector of the southern ocean for the past 450 kyr: implifications for Marine Isotope Stage (MIS) 11. Global and Planetary Change. 24:7-26.   10.1016/s0921-8181(99)00069-7   AbstractWebsite

Oxygen and carbon isotopic gradients in surface waters were reconstructed for the past 450 kyr by analysis of the planktic foraminifer Neogloboquadrina pachyderma in cores located at approximately 43 degrees, 47 degrees, and 54 degrees S across the Polar Frontal Zone in the South Atlantic sector of the Southern Ocean. Comparison of the oxygen isotopic records for peak interglacial conditions during the past 450 kyr reveals that Marine Isotope Stage (MIS) ii was not substantially warmer than other interglacials at high southern latitudes, although the period of warmth lasted longer. The carbonate and carbon isotope chemistry of surface and deep water represent the truly distinctive aspects of Stage 11 in the Southern Ocean. Peak carbonate production occurred at high southern latitudes during MIS 11, resulting in light-colored, high-carbonate sediments deposited throughout the Southern Ocean above the lysocline. Carbon isotopic values of benthic foraminifera in cores bathed by Circumpolar Deep Water (CPDW) were highest during MIS11, suggesting strong input of North Atlantic Deep Water (NADW) to the Southern Ocean. Planktic delta(13)C values at high southern latitudes were also highest during MIS Il, which may reflect upwelling of CPDW with a greater contribution of NADW, lower whole-ocean nutrient inventories, higher gas exchange rates, and/or lowered alkalinity of Antarctic surface waters (resulting from carbonate precipitation south of the Polar Front). (C) 2000 Elsevier Science B.V. All rights reserved.

Zaunbrecher, LK, Cobb KM, Beck JW, Charles CD, Druffel ERM, Fairbanks RG, Griffin S, Sayani HR.  2010.  Coral records of central tropical Pacific radiocarbon variability during the last millennium. Paleoceanography. 25   10.1029/2009pa001788   AbstractWebsite

The relationship between decadal to centennial changes in ocean circulation and climate is difficult to discern using the sparse and discontinuous instrumental record of climate and, as such, represents a large uncertainty in coupled ocean-atmosphere general circulation models. We present new modern and fossil coral radiocarbon (Delta(14)C) records from Palmyra (6 degrees N, 162 degrees W) and Christmas (2 degrees N, 157 degrees W) islands to constrain central tropical Pacific ocean circulation changes during the last millennium. Seasonally to annually resolved coral Delta(14)C measurements from the 10th, 12th-17th, and 20th centuries do not contain significant interannual to decadal-scale variations, despite large changes in coral delta(18)O on these timescales. A centennial-scale increase in coral radiocarbon from the Medieval Climate Anomaly (similar to 900-1200 AD) to the Little Ice Age (similar to 1500-1800) can be largely explained by changes in the atmospheric Delta(14)C, as determined with a box model of Palmyra mixed layer Delta(14)C. However, large 12th century depletions in Palmyra coral Delta(14)C may reflect as much as a 100% increase in upwelling rates and/or a significant decrease in the Delta(14)C of higher-latitude source waters reaching the equatorial Pacific during this time. SEM photos reveal evidence for minor dissolution and addition of secondary aragonite in the fossil corals, but our results suggest that coral Delta(14)C is only compromised after moderate to severe diagenesis for these relatively young fossil corals.

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.

Mortyn, PG, Charles CD, Ninnemann US, Ludwig K, Hodell DA.  2003.  Deep sea sedimentary analogs for the Vostok ice core. Geochemistry Geophysics Geosystems. 4   10.1029/2002gc000475   AbstractWebsite

Many applications of the Vostok ice core depend critically on the ability to make stratigraphic ties to marine records in the adjacent Southern Ocean. Here we present oxygen isotopic records from high accumulation rate sites in the South Atlantic sector of the Southern Ocean, collected for the purpose of complementing the recently extended deltaD record from the Vostok ice core. The combination of several planktonic foraminiferal delta(18)O records from northern subantarctic piston cores demonstrates that all of the millennial-scale oscillations expressed in the Vostok ice core over the last 60 ky are also present in marine records. The observations also support the assumption that the millennial-scale oscillations common to both marine and ice archives are synchronous, thus providing a rationale for extending the marine-ice core comparison through the last 400,000 years, making use of a marine drilled core (ODP Site 1089). By aligning the phase of these common abrupt events, we anchor the Vostok chronology to an orbitally tuned marine sediment chronology-a refinement that allows examination of a variety of paleoclimatological issues such as the relationship between deep ocean variability and Antarctic polar climate. For example, this exercise suggests that, over at least the 4 major deglaciation events, the primary (orbital scale) changes in the chemistry and, most likely, the temperature of the deep Southern ocean were synchronous with changes in atmospheric pCO(2) and polar air temperatures. We also find that the deuterium excess in the ice core resembles marine (foraminiferal) delta(13)C records and that the deuterium excess is synchronous with an "anomalous'' foraminiferal delta(18)O signal ( the residual between normalized versions of Vostok deltaD and foraminiferal delta(18)O). These observations demand a tight link between the Vostok isotopic record and the air-sea interaction of the subantarctic zone.

Cobb, KM, Charles CD, Cheng H, Edwards RL.  2003.  El Nino/Southern Oscillation and tropical Pacific climate during the last millennium. Nature. 424:271-276.   10.1038/nature01779   AbstractWebsite

Any assessment of future climate change requires knowledge of the full range of natural variability in the El Nino/Southern Oscillation (ENSO) phenomenon. Here we splice together fossil-coral oxygen isotopic records from Palmyra Island in the tropical Pacific Ocean to provide 30-150-year windows of tropical Pacific climate variability within the last 1,100 years. The records indicate mean climate conditions in the central tropical Pacific ranging from relatively cool and dry during the tenth century to increasingly warmer and wetter climate in the twentieth century. But the corals also document a broad range of ENSO behaviour that correlates poorly with these estimates of mean climate. The most intense ENSO activity within the reconstruction occurred during the mid-seventeenth century. Taken together, the coral data imply that the majority of ENSO variability over the last millennium may have arisen from dynamics internal to the ENSO system itself.

Fairbanks, RG, Evans MN, Rubenstone JL, Mortlock RA, Broad K, Moore MD, Charles CD.  1997.  Evaluating climate indices and their geochemical proxies measured in corals. Coral Reefs. 16:S93-S100.   10.1007/s003380050245   AbstractWebsite

Standard ocean/climate indices such as the Nino-3 sea surface temperature (SST) index, based on sparse instrumental data, and atmospheric indices such as the Southern Oscillation Index (SOI), may now be substituted and/or extended by coral-based indices. Several elements or their isotopes are incorporated in coral aragonitic skeletons at predictable concentrations, some of which are temperature or salinity dependent. The availability of century-old corals, at key oceanographic sites, permits the establishment of a network of proxy climate indices.

Mortlock, RA, Charles CD, Froelich PN, Zibello MA, Saltzman J, Hays JD, Burckle LH.  1991.  Evidence for Lower Productivity in the Antarctic Ocean During the Last Glaciation. Nature. 351:220-223.   10.1038/351220a0   AbstractWebsite

BOTH increased biological productivity and more efficient uptake of upwelled nutrients in high-latitude oceans have been proposed 1-5 as mechanisms responsible for the glacial reduction in atmospheric concentrations of carbon dioxide deduced from ice-core measurements 6-8. These glacial models invoke more efficient 'biological pumping' of carbon into the deep sea by increasing the uptake of 'excess' biolimiting nutrients in the Antarctic surface ocean 9 or by reorganizing chemical circulation patterns within the ocean 10,11. Here we challenge this conventional view with new evidence from tracers of palaeoproductivity preserved in Antarctic sediments. Records of the accumulation rates of diatom shells, the ratio of germanium to silicon in diatomaceous opal and the carbon isotope ratio in foraminiferal carbonate all suggest lower glacial productivity and less efficient uptake of nutrients. Although alternative interpretations are possible, our results support previous studies that indicate lower glacial productivity in the Southern Ocean 12,13 and raise new questions about the role of ocean productivity in models of the causes (or remedies) for changes in atmospheric concentrations of carbon dioxide.

Charles, CD, Fairbanks RG.  1992.  Evidence From Southern-Ocean Sediments for the Effect of North-Atlantic Deep-Water Flux on Climate. Nature. 355:416-419.   10.1038/355416a0   AbstractWebsite

The Southern Ocean is perhaps the only region where fluctuations in the global influence of North Atlantic Deep Water (NADW) can be monitored unambiguously in single deep-sea cores. A carbon isotope record from benthic foraminifera in a Southern Ocean core reveals large and rapid changes in the flux of NADW during the last deglaciation, and an abrupt increase in the NADW production rate which immediately preceded large-scale melting of the Northern Hemisphere ice sheets. This sudden strengthening of the NADW thermohaline cell provides strong evidence for the importance of NADW in glacial-interglacial climate change.

Roach, LD, Charles CD, Field DB, Guilderson TP.  2013.  Foraminiferal radiocarbon record of northeast Pacific decadal subsurface variability. Journal of Geophysical Research-Oceans. 118:4317-4333.   10.1002/jgrc.20274   AbstractWebsite

The decadal dynamics of the subsurface North Pacific Ocean are largely inaccessible beyond sparse instrumental observations spanning the last 20 years. Here we present a approximate to 200 year long record of benthic foraminiferal radiocarbon (C-14), extracted at biennial resolution from the annually laminated sediments at the Santa Barbara Basin (SBB) depocenter (approximate to 600 m). The close match between core top benthic foraminiferal C-14 values and the C-14 of seawater dissolved inorganic carbon (DIC) suggests that benthic foraminifera faithfully capture the bottom water radiocarbon concentrations, as opposed to that of the deeper (>0.5 cm) sediment porewater zone. The full time series of benthic foraminiferal C-14 displays significant variability on decadal timescales, with excursions on the order of 40. These excursions are overprinted by a unidirectional trend over the late 20th century that likely reflects the sedimentary incorporation of bomb radiocarbon (via remineralized particulate organic carbon). We isolate this trend by means of a one-dimensional oxidation model, which considers the possible contribution of remineralized particles to the total ambient carbon pool. This oxidation model also considers the possible influence of carbon with a variety of sources (ages). Though variable oxidation of preaged carbon could exert a strong influence on benthic foraminiferal radiocarbon variability, the totality of evidence points to the vertical density structure along the Southern California Margin (SCM) as the primary driver of the SBB benthic foraminiferal C-14 record. For example, intervals characterized by significantly lower C-14 values correspond to periods of enhanced upwelling and subsurface equatorward flow along the SCM.

Channell, JET, Stoner JS, Hodell DA, Charles CD.  2000.  Geomagnetic paleointensity for the last 100 kyr from the sub-antarctic South Atlantic: a tool for inter-hemispheric correlation. Earth and Planetary Science Letters. 175:145-160.   10.1016/s0012-821x(99)00285-x   AbstractWebsite

We report relative paleointensity proxy records from four piston cores collected near the Agulhas Ridge and Meteor Rise (South Atlantic). The mean sedimentation rate of the cores varies from 24 cm/kyr to 11 cm/kyr. The two cores with mean sedimentation rates over 20 cm/kyr record positive remanence inclinations at 40-41 ka coeval with the Laschamp Event. Age models are based on oxygen isotope data from three of the cores, augmented by radiocarbon ages from nearby Core RC11-83, and by correlation of paleointensity records for the one core with no oxygen isotope data. The relative paleointensity proxy records are the first from the South Atlantic and from the high to mid-latitude southern hemisphere. Prominent paleointensity lows at similar to 40 ka and similar to 65 ka, as well as many other features, can be correlated to paleointensity records of comparable resolution from the northern hemisphere. The records are attributable, in large part, to the global-scale field, and therefore have potential for inter-hemispheric correlation at a resolution difficult to achieve with isotope data alone. (C) 2000 Elsevier Science B.V. All rights reserved.

Charles, CD, Fairbanks R.  1990.  Glacial to interglacial changes in the isotopic gradients of southern ocean surface water. The Geologic History of Polar oceans: Arctic Vs Antarctic NATO/ASI series. ( Bleil U, Thiede J, Eds.). Abstract
Charles, CD, Rind D, Jouzel J, Koster RD, Fairbanks RG.  1994.  Glacial-Interglacial Changes in Moisture Sources for Greenland - Influences on the Ice Core Record of Climate. Science. 263:508-511.   10.1126/science.263.5146.508   AbstractWebsite

Large, abrupt shifts in the O-18/O-16 ratio found in Greenland ice must reflect real features of the climate system variability. These isotopic shifts can be viewed as a result of air temperature fluctuations, but determination of the cause of the changes-the most crucial issue for future climate concerns-requires a detailed understanding of the controls on isotopes in precipitation. Results from general circulation model experiments suggest that the sources of Greenland precipitation varied with different climate states, allowing dynamic atmospheric mechanisms for influencing the ice core isotope shifts.

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.

Cobb, KM, Westphal N, Sayani HR, Watson JT, Di Lorenzo E, Cheng H, Edwards RL, Charles CD.  2013.  Highly variable El Nino-Southern Oscillation throughout the Holocene. Science. 339:67-70.   10.1126/science.1228246   AbstractWebsite

The El Nino-Southern Oscillation (ENSO) drives large changes in global climate patterns from year to year, yet its sensitivity to continued anthropogenic greenhouse forcing is uncertain. We analyzed fossil coral reconstructions of ENSO spanning the past 7000 years from the Northern Line Islands, located in the center of action for ENSO. The corals document highly variable ENSO activity, with no evidence for a systematic trend in ENSO variance, which is contrary to some models that exhibit a response to insolation forcing over this same period. Twentieth-century ENSO variance is significantly higher than average fossil coral ENSO variance but is not unprecedented. Our results suggest that forced changes in ENSO, whether natural or anthropogenic, may be difficult to detect against a background of large internal variability.

Charles, CD, Hunter DE, Fairbanks RG.  1997.  Interaction between the ENSO and the Asian monsoon in a coral record of tropical climate. Science. 277:925-928.   10.1126/science.277.5328.925   AbstractWebsite

The oxygen isotopic composition of a banded coral from the western equatorial Indian Ocean provides a 150-year-long history of the relation between the El Nino-Southern Oscillation (ENSO) phenomenon and the Asian monsoon. Interannual cycles in the coral time series were found to correlate with Pacific coral and instrumental climate records, suggesting a consistent linkage across ocean basins, despite the changing frequency and amplitude of the ENSO. However, decadal variability that is characteristic of the monsoon system also dominates the coral record, which implies important interactions between tropical and midlatitude climate variability. One prominent manifestation of this interaction is the strong amplitude modulation of the quasi-biennial cycle.

Herguera, JC, Herbert T, Kashgarian M, Charles C.  2010.  Intermediate and deep water mass distribution in the Pacific during the Last Glacial Maximum inferred from oxygen and carbon stable isotopes. Quaternary Science Reviews. 29:1228-1245.   10.1016/j.quascirev.2010.02.009   AbstractWebsite

Intermediate ocean circulation changes during the last Glacial Maximum (LGM) in the North Pacific have been linked with Northern Hemisphere climate through air sea interactions, although the extent and the source of the variability of the processes forcing these changes are still not well resolved. The ventilated volumes and ages in the upper wind driven layer are related to the wind stress curl and surface buoyancy fluxes at mid to high latitudes in the North Pacific. In contrast, the deeper thermohaline layers are more effectively ventilated by direct atmosphere-sea exchange during convective formation of Subantarctic Mode Waters (SAMW) and Antarctic Intermediate Waters (AAIW) in the Southern Ocean, the precursors of Pacific Intermediate Waters (PIW) in the North Pacific. Results reported here show a fundamental change in the carbon isotopic gradient between intermediate and deep waters during the LGM in the eastern North Pacific indicating a deepening of nutrient and carbon rich waters. These observations suggest changes in the source and nature of intermediate waters of Southern Ocean origin that feed PIW and enhanced ventilation processes in the North Pacific, further affecting paleoproductivity and export patters in this basin. Furthermore, oxygen isotopic results indicate these changes may have been accomplished in part by changes in circulation affecting the intermediate depths during the LGM. (C) 2010 Elsevier Ltd. All rights reserved.