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Hartmann, AC, Carilli JE, Norris RD, Charles CD, Deheyn DD.  2010.  Stable isotopic records of bleaching and endolithic algae blooms in the skeleton of the boulder forming coral Montastraea faveolata. Coral Reefs. 29:1079-1089.   10.1007/s00338-010-0667-5   AbstractWebsite

Within boulder forming corals, fixation of dissolved inorganic carbon is performed by symbiotic dinoflagellates within the coral tissue and, to a lesser extent, endolithic algae within the coral skeleton. Endolithic algae produce distinctive green bands in the coral skeleton, and their origin may be related to periods of coral bleaching due to complete loss of dinoflagellate symbionts or "paling" in which symbiont populations are patchily reduced in coral tissue. Stable carbon isotopes were analyzed in coral skeletons across a known bleaching event and 12 blooms of endolithic algae to determine whether either of these types of changes in photosynthesis had a clear isotopic signature. Stable carbon isotopes tended to be enriched in the coral skeleton during the initiation of endolith blooms, consistent with enhanced photosynthesis by endoliths. In contrast, there were no consistent delta(13)C patterns directly associated with bleaching, suggesting that there is no unique isotopic signature of bleaching. On the other hand, isotopic values after bleaching were lighter 92% of the time when compared to the bleaching interval. This marked drop in skeletal delta(13)C may reflect increased kinetic fractionation and slow symbiont recolonization for several years after bleaching.

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.

Hodell, DA, Venz KA, Charles CD, Ninnemann US.  2003.  Pleistocene vertical carbon isotope and carbonate gradients in the South Atlantic sector of the Southern Ocean. Geochemistry Geophysics Geosystems. 4   10.1029/2002gc000367   AbstractWebsite

[1] We demonstrate that the carbon isotopic signal of mid-depth waters evolved differently from deep waters in the South Atlantic sector of the Southern Ocean during the Pleistocene. Deep sites (>3700 m) exhibit large glacial-to-interglacial variations in benthic delta(13)C, whereas the amplitude of the delta(13)C signal at Site 1088 ( 2100 m water depth) is small. Unlike the deep sites, at no time during the Pleistocene were benthic delta(13)C values at Site 1088 lower than those of the deep Pacific. Reconstruction of intermediate-to-deep delta(13)C gradients (Delta(13)C(I-D)) supports the existence of a sharp chemocline between 2100 and 2700 m during most glacial stages of the last 1.1 myr. This chemical divide in the glacial Southern Ocean separated well-ventilated water above similar to2500 m from poorly ventilated water below. The Delta(13)C(I-D) signal parallels the Vostok atmospheric pCO(2) record for the last 400 kyr, lending support to physical models that invoke changes in Southern Ocean deep water ventilation as a mechanism for changing atmospheric pCO2. The emergence of a strong 100-kyr cycle in Delta(13)C(I-D) during the mid-Pleistocene supports a change in vertical fractionation and deep-water ventilation rates in the Southern Ocean, and is consistent with possible CO(2)-forcing of this climate transition.

Hodell, DA, Charles CD, Sierro FJ.  2001.  Late Pleistocene evolution of the ocean's carbonate system. Earth and Planetary Science Letters. 192:109-124.   10.1016/s0012-821x(01)00430-7   AbstractWebsite

We demonstrate that the carbonate record from a single site (Ocean Drilling Program Site 1089) in the deep South Atlantic represents a qualitative, high-resolution record of the temporal evolution of the carbonate saturation state of the deep sea. The record is especially notable because it is free from many of the complications that limit other records (low sedimentation rates, blurring by chemical erosion, bioturbation, etc.). The pattern of carbonate variability is characteristic of Indo-Pacific cores with high-carbonate glacials and low-carbonate interglacials. Wt% carbonate lags changes in benthic delta O-18 by an average of similar to 7.6 kyr, and carbonate variations are in-phase with the rate of change (first derivative) of benthic delta O-18. Intense dissolution occurs at the transition from interglacial to glacial periods and increased preservation occurs during deglaciations. These observations represent two fundamentally different responses of the marine carbonate system. The lagged response of carbonate to 6180 reflects a steady-state mass balance process whereby the lysocline adjusts to maintain alkalinity balance between riverine input and marine burial. The Site 1089 carbonate signal is remarkably similar to inferred changes in the Sr/Ca of seawater for the past 250 kyr, which implies that both carbonate dissolution and seawater Sr/Ca may be controlled by sea level-induced changes in the location of carbonate deposition (shelf-basin fractionation) during glacial to interglacial cycles. The transient change in preservation during the transitions into and out of glacial stages reflects a response of the carbonate system to a redistribution of alkalinity and DIC in the ocean (i.e. carbonate compensation). Comparison of the Site 1089 carbonate and Vostok pCO(2) records suggests a role of deep-sea [CO32-] variations for governing at least some second-order features of the atmospheric pCO, signal. In order to quantify this role, however, measurement of indices of dissolution along a true depth transect. will be required to estimate the magnitudes of changes in deep-sea [CO32-]. (C) 2001 Elsevier 3 Science B.V. All rights reserved.

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.

Hodell, DA, Venz KA, Charles CD, Sierro FJ.  2002.  The mid-Brunhes transition in ODP sites 1089 and 1090. Earth's climate and orbital eccentricity : the marine isotope stage 11 question. 137( Droxler AW, Poore RZ, Burckle LH, Eds.)., Washington, DC: American Geophysical Union Abstract
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.