Dust record from the EPICA Dome C ice core, Antarctica, covering 0 to 800 kyr BP

Dust can affect the radiative balance of the atmosphere by absorbing or reflecting incoming solar radiation and it can be a source of micronutrients, such as iron, to the ocean. It has been suggested that production, transport, and deposition of dust is influenced by climatic changes on glacial-interglacial timescales. Here we present a high-resolution aeolian dust record from the EPICA Dome C ice core in East Antarctica, which provides an undisturbed climate sequence over the last eight climatic cycles. We find that there is a significant correlation between dust flux and temperature records during glacial periods that is absent during interglacial periods. Our data suggests that dust flux is increasingly correlated with Antarctic temperature as climate becomes colder. We interpret this as progressive coupling of Antarctic and lower latitudes climate. Limited changes in glacial-interglacial atmospheric transport time Mahowald et al. (1999, doi:10.1029/1999JD900084), Jouzel et al. (2007, doi:10.1126/science.1141038), and Werner et al. (2002, doi:10.1029/2002JD002365) suggest that the sources and lifetime of dust are the major factors controlling the high glacial dust input. We propose that the observed ~25-fold increase in glacial dust flux over all eight glacial periods can be attributed to a strengthening of South American dust sources, together with a longer atmospheric dust particle life-time in the upper troposphere resulting from a reduced hydrological cycle during the ice ages.

Natural remanent magnetization (NRM) from ODP Site 1263 covering magnetochron C20r and C21n and high-resolution bulk carbon isotope (d13C) records from Sites 702 and 1263

To explore cause and consequences of past climate change, very accurate age models such as those provided by the astronomical timescale (ATS) are needed. Beyond 40 million years the accuracy of the ATS critically depends on the correctness of orbital models and radioisotopic dating techniques. Discrepancies in the age dating of sedimentary successions and the lack of suitable records spanning the middle Eocene have prevented development of a continuous astronomically calibrated geological timescale for the entire Cenozoic Era. We now solve this problem by constructing an independent astrochronological stratigraphy based on Earth's stable 405 kyr eccentricity cycle between 41 and 48 million years ago (Ma) with new data from deep-sea sedimentary sequences in the South Atlantic Ocean. This new link completes the Paleogene astronomical timescale and confirms the intercalibration of radioisotopic and astronomical dating methods back through the Paleocene-Eocene Thermal Maximum (PETM, 55.930 Ma) and the Cretaceous-Paleogene boundary (66.022 Ma). Coupling of the Paleogene 405 kyr cyclostratigraphic frameworks across the middle Eocene further paves the way for extending the ATS into the Mesozoic.

A foraminiferal d18O record of sediment core GT90-3 covering the last 2,200 years

For many years the Torino Cosmogeophysics group has been studying sediment cores drilled from the Gallipoli Terrace in the Gulf of Taranto (Ionian Sea) and deposited in the last millennia. The gravity core GT90-3, in which the 18O series was measured, was drilled from the Gallipoli Terrace in the Gulf of Taranto (Ionian Sea) at 39°45'53''N, 17°53'33''E. It was extracted at a depth of 178 m and its length is 3.57 m. Thanks to its geographical location, the Gallipoli Terrace is a favourable site for climatic studies based on marine sediments, because of its closeness to the volcanically active Campanian area, a region that is unique in the world for its detailed historical documentation of volcanic eruptions. Tephra layers corresponding to historical eruptions were identified along the cores, thus allowing for accurate dating and determination of the sedimentation rate. The measurements performed in different cores from the same area showed that the sedimentation rate is uniform across the whole Gallipoli Terrace. We measured the oxygen isotope composition d18O of planktonic foraminifera. These measurements provided a high-resolution 2,200-year-long record. We sampled the core using a spacing of 2.5 mm corresponding to 3.87 years. Each sample of sediment (5 g) was soaked in 5% calgon solution overnight, then treated in 10% H2O2 to remove any residual organic material. Subsequently it was washed with a distilled-water jet through a sieve with a 150 µm mesh. The fraction > 150 µm was kept and oven-dried at 5°C. The planktonic foraminifera Globigerinoides ruber were picked out of the samples under a microscope. For each sample, 20-30 specimens were selected from the fraction comprised between 150 µm and 300 µm. The use of a relatively large number of specimens for each sample reduces the isotopic variability of individual organisms, giving a more representative d18O value. The stable isotope measurements were performed using a VG-PRISM mass spectrometer fitted with an automated ISO-CARB preparation device. Analytical precision based on internal standards was better than 0.1 per mil. Calibration of the mass spectrometer to VPDB scale was done using NBS19 and NBS18 carbonate standards. The strategic location of the drilling area makes this record a unique tool for climate and oceanographic studies of the Central Mediterranean.

CO2 concentration and stable isotope ratios of three Antarctic ice cores covering the period from 149.4 - 1.5 kyr before 1950

We present new d13C measurements of atmospheric CO2 covering the last glacial/interglacial cycle, complementing previous records covering Terminations I and II. Most prominent in the new record is a significant depletion in d13C(atm) of 0.5 permil occurring during marine isotope stage (MIS) 4, followed by an enrichment of the same magnitude at the beginning of MIS 3. Such a significant excursion in the record is otherwise only observed at glacial terminations, suggesting that similar processes were at play, such as changing sea surface temperatures, changes in marine biological export in the Southern Ocean (SO) due to variations in aeolian iron fluxes, changes in the Atlantic meridional overturning circulation, upwelling of deep water in the SO, and long-term trends in terrestrial carbon storage. Based on previous modeling studies, we propose constraints on some of these processes during specific time intervals. The decrease in d13C(atm) at the end of MIS 4 starting approximately 64 kyr B.P. was accompanied by increasing [CO2]. This period is also marked by a decrease in aeolian iron flux to the SO, followed by an increase in SO upwelling during Heinrich event 6, indicating that it is likely that a large amount of d13C-depleted carbon was transferred to the deep oceans previously, i.e., at the onset of MIS 4. Apart from the upwelling event at the end of MIS 4 (and potentially smaller events during Heinrich events in MIS 3), upwelling of deep water in the SO remained reduced until the last glacial termination, whereupon a second pulse of isotopically light carbon was released into the atmosphere.