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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.

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.

Perez, ME, Charles CD, Berger WH.  2001.  Late Quaternary productivity fluctuations off Angola: evidence from benthic foraminifers, Site 1079. Proceedings of the Ocean Drilling Program Scientific Results. 175   10.2973/odp.proc.sr.175.213.2001   Abstract

Benthic foraminifer accumulation rates (BFAR) >150 ┬Ám and species composition were used to reconstruct the late Quaternary productivity in the Mid-Angola Basin at Ocean Drilling Program Site 1079. In general, BFAR values indicate higher productivity during glacial periods than during interglacials. Spectral analysis of the BFAR record shows that benthic foraminifers were sensitive to climate forcing at 100- and 23-k.y. periodicities. These results are similar to those observed in nearby regions, as described by the Geo-Bremen group. The benthic foraminiferal fauna is dominated by low oxygen-tolerant infaunal species, with Bolivina pseudopunctata and Bolivina dilatata as the most abundant species. B. pseudopunctata appears to be well correlated with marine organic carbon (Corg), whereas B. dilatata tends to increase when the influx of terrigenous organic matter dominates the environment. Furthermore, the spikiness in the abundance of B. pseudopunctata suggests that this species may be opportunistic and may respond to threshold values in environmental conditions.