(Table T1) Bulk calcium carbonate content of ODP Hole 194-1198A sediments

Weight percent calcium carbonate (wt% CaCO3) content was determined on 328 samples from Ocean Drilling Program Hole 1198A. Two intervals were analyzed, one within lithologic Subunit IA between 14.52 and 41.13 meters below seafloor (mbsf) (25 cm sampling interval) and one within Subunit IB between 67.42 and 100.12 mbsf (15-30 cm interval), allowing the comparison of the nature of cyclic siliciclastic-carbonate variations during the late and early Pleistocene. Overlap with a previously analyzed interval in Hole 1198A illustrates the good agreement in data generated by differing methodologies and extends the continuous record of bulk wt% CaCO3 from 0 to 41.13 mbsf. Although Subunits 1A and 1B exhibit nearly the same variability, from 93% to 63% and 94% to 68%, respectively, Subunit 1A is characterized by a longer cycle length.

Stable isotope record, carbonate and organic carbon content of the Miocene section of IODP Site 321-U1337

The Miocene Climatic Optimum (~17-14.7 Ma) represents one of several major interruptions in the long-term cooling trend of the past 50 million years. To date, the processes driving high-amplitude climate variability and sustaining global warmth during this remarkable interval remain highly enigmatic. We present high-resolution benthic foraminiferal and bulk carbonate stable isotope records in an exceptional, continuous, carbonate-rich sedimentary archive (Integrated Ocean Drilling Program Site U1337, eastern equatorial Pacific Ocean), which offer a new view of climate evolution over the onset of the Climatic Optimum. A sharp decline in d18O and d13C at ~16.9 Ma, contemporaneous with a massive increase in carbonate dissolution, demonstrates that abrupt warming was coupled to an intense perturbation of the carbon cycle. The rapid recovery in d13C at ~16.7 Ma, ~200 k.y. after the beginning of the MCO, marks the onset of the first carbon isotope maximum within the long-lasting "Monterey Excursion". These results lend support to the notion that atmospheric pCO2 variations drove profound changes in the global carbon reservoir through the Climatic Optimum, implying a delicate balance between changing CO2 fluxes, rates of silicate weathering and global carbon sequestration. Comparison with a high-resolution d13C record spanning the onset of the Cretaceous Oceanic Anoxic Event 1a (~120 Ma ago) reveals common forcing factors and climatic responses, providing a long-term perspective to understand climate-carbon cycle feedbacks during warmer periods of Earth's climate with markedly different atmospheric CO2 concentrations.

Fig. 2: Comparison of the number of grains counted in a sieve analysis

The distribution of ice rafted debris (IRD) is an important parameter in glaciomarine sediments. A simple method is presented allowing the determination of the IRD-content by counting the gravel fraction of the X-radiographs which are generally taken during sarnpling. In comparison with sieve analyses corresponding values are obtained by both methods. However, more information can be made available in a shorter time by this method.

Comparison of glacial/interglacial carbonate concentrations in Atlantic sediments

To assess the regional effects of glaciation on sedimentation in the Atlantic Ocean we compare sediment types, distributions, and rates between Recent (core top) and last glacial maximum (LGM: ~18,000 years B.P.) stratigraphic levels. Based upon smear slides and carbonate analyses in 178 cores we find that glacial age carbonate content is generally lower than Recent. During both the Recent and LGM, carbonate content shows an east/west asymmetry with western basins exhibiting lower carbonate values. Input of ice-rafted detritus into the North Atlantic during LGM time interrupts this topographic control on carbonate distribution considerably farther south than at present; in the South Atlantic this effect is minor. Comparison of LGM and Recent sediment distributions indicates that the LGM seafloor was dominated by biogenic oozes, calcareous clays, and clays, while the Recent is dominated by biogenic oozes and marls. Coarse-grained detritus is much more prevalent in LGM sediments, derived not only from glacial input but also from fluvial and aeolian sources. Sedimentation rates, calculated from LGM to Recent sediment thickness in cores, are <4 cm/1000 yr for most of the ocean. Higher rates are typical of the continental margin off the Amazon River, the North American Basin, and a small region off west equatorial Africa.