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Moore, MD, Charles CD, Rubenstone JL, Fairbanks RG.  2000.  U/Th-dated sclerosponges from the Indonesian Seaway record subsurface adjustments to west Pacific winds. Paleoceanography. 15:404-416.   10.1029/1999pa000396   AbstractWebsite

Stable isotope records from sclerosponges collected at 10-20 m depth in the Indonesian Seaway and Solomon Islands are particularly well suited for reconstructing century-scale trends in ambient temperature variability and the oceanic uptake of fossil fuel carbon. Basal U/Th dates demonstrate that the sclerosponges analyzed are 85-100 years old. Isotopic records from the Indonesian specimens suggest a strong subsurface cooling over the past 20 years that is not manifested in either surface instrumental or shallower coral proxy records. However, analysis of observed subsurface temperatures in Indonesia, observed winds in the west Pacific, and simulated subsurface temperatures from a steady state general circulation model hindcast forced by observed winds combine to suggest that thermocline adjustments could account for at least part of the recent cooling inferred from the Indonesian sclerosponges. If so, the sclerosponge data suggests that, on average, the west Pacific thermocline has shoaled significantly over at least the past 2 decades.

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.

Mortyn, P, Charles CD, Hodell DA.  2002.  Southern Ocean upper water column structure over the last 140 kyr with emphasis on the glacial terminations. Global and Planetary Change. 34:241-252.   10.1016/s0921-8181(02)00118-2   AbstractWebsite

We use delta(18)0 and delta(13)C isotopic records from both shallow- and deep-dwelling planktonic foraminiferal species to describe the transition of surface water column structure over the last two glacial terminations in the Atlantic sector of the Southern Ocean between 41degreesS-50degreesS. The delta(18)O differences between deep- and shallow-dwelling foraminifera are typically less pronounced before and during a termination than they are following a termination. Additionally, delta(13)C minima occur during terminations that may be linked to changes in thermohaline circulation mode. These observations collectively point toward water column structural changes that vary from relatively unstratified to relatively stratified during the course of a typical climate transition. The data can potentially be explained by southward retreats of surface water masses that previously advanced to the north during a typical glacial (i.e. frontal migration). Some of the delta(18)O phenomena can also be explained by subduction, entrainment, and advection of continental ice meltwater from higher latitudes. In either case, the glacial subantarctic between 41degreesS-50degreesS was less thermally stratified than it is today. (C) 2002 Elsevier Science B.V. All rights reserved.

Mortyn, PG, Charles CD.  2003.  Planktonic foraminiferal depth habitat and delta O-18 calibrations: Plankton tow results from the Atlantic sector of the Southern Ocean. Paleoceanography. 18   10.1029/2001pa000637   AbstractWebsite

[1] Plankton tows conducted in the Atlantic sector of the Southern Ocean allow analysis of the influence of water column structure on planktonic foraminiferal abundance and delta(18)O composition. Foraminiferal abundance varies by several orders of magnitude across a large gradient in sea surface temperature and other hydrographic features, demonstrating high sensitivity of foraminiferal populations to regional differences in water properties. The depth of maximum abundance for key species such as Globigerina bulloides and Neogloboquadrina pachyderma is not constant from station to station. The pattern suggests that their abundance and shell chemistry are tied to density horizons or other conditions (such as food availability) that become more sharply defined with depth in the northern subantarctic. The consistent observation of Globorotalia inflata and Globoratalia truncatulinoides as relatively deep-dwelling species confirms their utility as indicators of upper thermocline properties. In delta(18)O all species are observed to be isotopically lighter than predicted from water properties, but the species-specific offset is fairly uniform at all stations. These observations define the utility of multispecies delta(18)O for reconstructing temperature and density stratification from past surface oceans.

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.