Element concentrations and stable isotope record of planktonic foraminifera of sediment cores from the northeastern Brazilian Continental Margin

Detailed 14C AMS data and isotope based stratigraphies from high-resolution paleoceanographic records for the last 22 ka of cores from the upper continental slope off NE Brazil reveal sedimentation rates of up to 100 cm per 1000 yr. Variations in the sediment composition relate to changes in the input of terrigenous material. The sedimentation is controlled by sea level and by the climatic regime of the hinterland. Short-term changes in the tropical wind field may act as a climatic trigger. The zonality of the SE trades was probably increased and the monsoonal activity over Africa reduced during the Younger Dryas period.

Age determination and stable isotope ratios of three sediment cores from the Great Belt

The marine transgression Into the Baltic Sea through the Great Belt took place around 9,370 calibrated C-14-years B.P. The sedimentary sequence from the early brackish phase and the change to marine conditions has been investigated in detail through C-14-datings, and oxygen and carbon isotope measurements, and is interpreted by comparison with modern analogs. The oldest brackish sediments are the strongly laminated clays and silts rich in organic carbon followed by non-laminated heavily bioturbated silts. The bedding and textural characteristics and stable isotope analyses on Ammonia beccarii (dextral) and A. beccarii (sinistral) show that the deposltlonal conditions respond to a change at about 9,100 cal. a B.P. from an unstratified brackish water environment in the initial stage of the Littorina Transgression to a thermohaline layered milieu in the upper unit. The oxygen isotope results indicate that the bottom waters of this latter period had salinities and temperatures comparable to the present day Kiel Bay waters. The isotopic composition of the total organic carbon and the d13C-values of A. beccarii reveal a gradual change from an initially lacustrine/terrestrial provenance toward a brackish/marine dominated depositional environment. A stagnation of the sea level at around 9,100 to 9,400 B.P. is indicated.

Stable isotope stacks from GRIP and GISP ice cores

Recent efforts to link the isotopic composition of snow in Greenland with meteorological and climatic parameters have indicated that relatively local information such as observed annual temperatures from coastal Greenland sites, as well as more synoptic scale features such as the North Atlantic Oscillation (NAO) and the temperature seesaw between Jakobshaven, Greenland, and Oslo, Norway, are significantly correlated with d18O and dD values from the past few hundred years measured in ice cores. In this study we review those efforts and then use a new record of isotope values from the Greenland Ice Sheet Project 2 and Greenland Ice Core Project sites at Summit, Greenland, to compare with meteorological and climatic parameters. This new record consists of six individual annually resolved isotopic records which have been average to produce a Summit stacked isotope record. The stacked record is significantly correlated with local Greenland temperatures over the past century (r=0.471), as well as a number of other records including temperatures and pressures from specific locations as well as temperature and pressure patterns such as the temperature seesaw and the North Atlantic Oscillation. A multiple linear regression of the stacked isotope record with a number of meteorological and climatic parameters in the North Atlantic region reveals that five variables contribute significantly to the variance in the isotope record: winter NAO, solar irradiance (as recorded by sunspot numbers), average Greenland coastal temperature, sea surface temperature in the moisture source region for Summit (30°-20°N), and the annual temperature seesaw between Jakobshaven and Oslo. Combined, these variables yield a correlation coefficient of r=0.71, explaining half of the variance in the stacked isotope record.