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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.

Ninneman, US, Charles CD.  1999.  Origin of global millenial scale climate events: constraints from the Southern Ocean deep sea sedimentary record. Mechanisms of global climate change at millennial time scales. 112( Clark PU, Webb RS, Keigwin LD, Eds.).:99-112., Washington, D.C.: American Geophysical Union Abstract
Ninnemann, US, Charles CD.  1997.  Regional differences in Quaternary Subantarctic nutrient cycling: Link to intermediate and deep water ventilation. Paleoceanography. 12:560-567.   10.1029/97pa01032   AbstractWebsite

Several fundamental issues regarding carbon cycling in the glacial oceans rest on the development: of reliable descriptions of high southern latitude surface waters, Here we compare new Subantarctic planktonic foraminiferal delta(13)C records with previously published records to demonstrate two distinct regional patterns over glacial cycles: (1) a lour-amplitude signal (similar to 0.7 parts per thousand), previously observed in the Indian (primarily in Globigerina bulloides), that also dominates the Pacific, and (2) a higher-amplitude signal, previously observed in Neogloboquadrina Pachyderma, that is confined to the Atlantic and western Indian sectors. The near observations from the Southeast Pacific, a primary region of Antarctic Intermediate Water (AAIW) formation, strengthen the suggestion that intermediate water acted as a conduit for transferring delta(13)C variability to low latitudes, because the timing and amplitude of the Indo-Pacific low-amplitude delta(13)C changes are similar to those observed in planktonic records from the tropical Pacific and Atlantic. A new benthic foraminiferal delta(13)C record from intermediate depths in the South Atlantic is also similar to the Southeast Pacific surface water records, further demonstrating that this link between high- and low-latitude surface: waters might be maintained. The widespread Indo-Pacific Subantarctic surface water signal is obscured in records from the Atlantic sector by the large glacial-interglacial delta(13)C signal (>1.0 parts per thousand) that is most likely the result of nutrient changes related to variable North Atlantic Deep Water (NADW) production, pachyderma delta(13)C records is not matched in a new C, bulloides delta(13)C record. The confined regional extent of the high-amplitude signal and the discrepancy between the two species suggest that most of the excess nutrients in the glacial Atlantic (inferred from delta(13)C) may be removed seasonally by increased production in the Subantarctic.

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.

Nurhati, IS, Cobb KM, Charles CD, Dunbar RB.  2009.  Late 20th century warming and freshening in the central tropical Pacific. Geophysical Research Letters. 36   10.1029/2009gl040270   AbstractWebsite

Global climate models and analyses of instrumental datasets provide a wide range of scenarios for future tropical Pacific climate change, limiting the accuracy of regional climate projections. Coral records provide continuous reconstructions of tropical Pacific climate trends that are difficult to quantify using the short, sparse instrumental datasets available from the tropical Pacific. Here, we present coral-based reconstructions of late 20th century sea-surface temperature and salinity trends from several islands in the central tropical Pacific. The coral data reveal warming trends that increase towards the equator, implying a decrease in equatorial upwelling in the last decades. Seawater freshening trends on the southern edge of the Inter-Tropical Convergence Zone suggest a strengthening and/or an equatorward shift of the convergence zone. Together, the new coral records support a late 20th century trend towards "El Nino-like" conditions in the tropical Pacific, in line with the majority of coupled global climate model projections. Citation: Nurhati, I. S., K. M. Cobb, C. D. Charles, and R. B. Dunbar (2009), Late 20th century warming and freshening in the central tropical Pacific, Geophys. Res. Lett., 36, L21606, doi:10.1029/2009GL040270.