Abundance patterns and isotopic signals of morphotypes of Globigerinoides ruber

The chemical composition of shells of the planktonic foraminifer Globigerinoides ruber (white) is frequently used to determine past sea surface conditions. Recently, it has been shown that arbitrarily defined morphotypes within this species exhibit different chemical and isotopic signatures. Here, we investigate the occurrence through time and in space of morphological types of G. ruber (white) in late Quaternary and Holocene sediments of the central and the eastern Mediterranean Sea. In 115 samples representing two distinct time intervals (MIS 1-2 and MIS 9-12) at ODP Site 964 and the piston core GeoTü-SL96, we have defined three morphological types within this species and determined their relative abundances and stable isotopic composition. A quantitative analysis of morphological variation within G. ruber (white) in four samples revealed that the subjectively defined morphotypes occupy separate segments of a continuous and homogenous morphospace. We further show that the abundance of the morphotypes changes significantly between glacials and interglacials and that the three morphotypes of G. ruber show significant offsets in their stable isotopic composition. These offsets are consistent within glacial and interglacial stages but their sign is systematically reversed between the two Sites. Since the isotopic shifts among the three G. ruber morphotypes are systematic and often exceed 1per mil, their understanding is essential for the interpretation of all G. ruber-based proxy records for the paleoceanographic development of the Mediterranean during the late Quaternary.

Volcaniclastic layers in ODP Site 202-1241

This study presents a record of dissolution from the eastern equatorial Pacific (EEP) that extends to 2.1 Ma, based on sediments from Ocean Drilling Program (ODP) Site 1241. A new benthic oxygen isotope record was developed in order to provide the stratigraphic framework for the Pleistocene section of the core. The isotope record extends back to 2.1 Ma, covering MIS 1-80, and has a sampling resolution of 2 kyr from 0 to 360 kyr and 5 kyr from 360 to 2100 kyr. Dissolution at ODP Site 1241 is characterized through the use of percent coarse fraction (%CF) and shell fragmentation records. These records indicate that %CF in the EEP is recording a dissolution signal dominated by the 41-kyr and 100-kyr climate cycles, and that preservation maxima lag glacial maxima by 9-14 kyr at the major orbital periods. The dissolution signals observed in the ODP Site 1241 record can be correlated across the Pacific and likely record the response to basinwide changes in carbonate chemistry. The dissolution fluctuations and d13C signal observed at ODP Site 1241 are consistent with both the [Shackleton, 1977] and [Toggweiler et al., 2006, doi:10.1029/2005PA001154] hypotheses that explain changes in the global carbon cycle during glacial-interglacial transitions.

Seawater carbonate chemistry, processes and elements during experiments with planktonic foraminifera Orbulina universa, 2004

We investigate the sensitivity of U/Ca, Mg/Ca, and Sr/Ca to changes in seawater [CO3[2-]] and temperature in calcite produced by the two planktonic foraminifera species, Orbulina universa and Globigerina bulloides, in laboratory culture experiments. Our results demonstrate that at constant temperature, U/Ca in O. universa decreases by 25 +/- 7% per 100 µmol [CO3[2-]] kg**-1, as seawater [CO3[2-]] increases from 110 to 470 µmol kg**-1. Results from G. bulloides suggest a similar relationship, but U/Ca is consistently offset by ~+40% at the same environmental [CO3[2-]]. In O. universa, U/Ca is insensitive to temperature between 15°C and 25°C. Applying the O. universa relationship to three U/Ca records from a related species, Globigerinoides sacculifer, we estimate that Caribbean and tropical Atlantic [CO3[2-]] was 110 +/- 70 µmol kg**-1 and 80 +/- 40 µmol kg**-1 higher, respectively, during the last glacial period relative to the Holocene. This result is consistent with estimates of the glacial-interglacial change in surface water [CO3[2-]] based on both modeling and on boron isotope pH estimates. In settings where the addition of U by diagenetic processes is not a factor, down-core records of foraminiferal U/Ca have potential to provide information about changes in the ocean's carbonate concentration.