ALBERT

Description: Repeated automated runs of signal alignment were used both to obtain an average fit (age model) and confidence intervals (uncertainties) for two marine sediment records from the southwest South Atlantic. A global and regional δ18O stack (LR04 and SL14, respectively) were used to transfer ages to the two records employing calibrated radiocarbon ages as chronological control points using the automated Match algorithm. A similar correlation between the two records is found both when the two records are correlated using the age model obtained and using δ18O correlation, validating the age models obtained by repeated automated tuning. The use of Termination I and Biozone Y/Z as chronological control points for the last deglaciation on high-resolution records is discussed here. The availability of uncertainties allowed more accurate interpretations. It is possible to observe that Biozone Y/Z is diachronous even on regional scale. Meanwhile Termination I is approximately synchronous on the regional scale but it is diachronous on the global scale. Although the stratigraphic events considered in this investigation are not globally synchronous and therefore not ideal control points for age models of high-resolution records, timing stratigraphic events in different locations has great relevance for investigations on triggering and propagation of climatic events and detailed understanding of climatic change mechanisms.

Description: This paper introduces an integrated Neogene microfossil biostratigraphic chart developed within post-merger BP for the Gulf of Mexico Basin and is the first published industrial framework "fully-tuned" to orbital periodicities. Astronomical-tuning was accomplished through a 15-year research program on ODP Leg 154 sediments (offshore NE Brazil) with sampling resolution for calcareous nannofossils and planktonic foraminifera about 20 k.y. and 40 k.y. (thousand year), respectively. This framework extends from the Late Oligocene (25.05 Ma) to Recent at an average Chart Horizon resolution for the Neogene of 144 k.y., approximately double that of published Gulf of Mexico biostratigraphic charts and a five-fold increase over the highest resolution global calcareous microfossil biozonation. Such resolution approximates that of 4th to 5th order parasequences and is a critical component in the verification of seismic correlations between mini-basins in the deep-water Gulf of Mexico. Its utility in global time-scale construction and correlation has been proven, in part, by application of the scheme in full to internal research for the Oligocene-Miocene boundary interval on the Global Boundary Stratotype Section and Point (GSSP) in northern Italy and offshore wells in the eastern Mediterranean Sea. This step change in Neogene resolution, now at the level of cyclostratigraphy (the orbital periodicity of eccentricity) and the magnetostratigraphic chron, demonstrates the potential for calcareous microfossil biostratigraphy to more consistently reinforce correlations of these time scale parameters. The integration of microfossil disciplines, consistent taxonomies, and rigorous analytical methodologies are all critical to obtaining and reproducing this new level of biostratigraphic resolution.

Description: Paleoceanographic reconstructions from the Brazil Current are scarce and lack the required temporal resolution to appropriately represent its variability during key periods of the last glacial-interglacial cycles. Here, we present the first high-temporal resolution multiproxy reconstruction of the Brazil Current at 24 °S covering the last 185 ka. During the last and penultimate glacial periods, our Mg/Ca-derived sea surface temperature (SST) record shows a strong cooling at ca. 47 and ca. 156 ka, respectively, that is followed by a warming trend from late-Marine Isotope Stage (MIS) 3 to MIS 1 and from late-MIS 6 to MIS5e, respectively. Importantly, the Brazil Current warmed uninterruptedly towards Termination I (II) after the low SST at ca. 47 and ca. 156 ka, with no SST minima during the Last Glacial Maximum or penultimate glacial maximum. The reason for the strong cooling and the warming trend during late-MIS 3 and late-MIS 6 could reside in the favorable obliquity configuration. However, this mechanism is not sufficient to sustain the warming observed for the rest of the last and penultimate glacial periods. We propose that the change in the Atlantic meridional overturning circulation (AMOC), as described in the literature, from a 'warm' to a 'cold mode' for MIS 2 and MIS 6 is responsible for the accumulation of warm waters in the subtropical western South Atlantic, preventing SST minima during the last and penultimate glacial maxima in the region. Change in benthic d13C corroborates that a fundamental modification in the AMOC mode might have triggered the heat accumulation. Our data also show a sudden increase in SST and surface salinity during the last glacial descent (MIS 4), indicating that the western portion of the subtropical gyres may have acted as a heat and salt reservoir, while higher latitude climates transited to a glacial background. Our findings imply that the AMOC 'cold mode' induces heat storage in the subtropical western South Atlantic and, because of that, the last two regional SST minima occurred out-of-phase with the glacial maxima of higher latitudes.

Description: Expansions of coastal upwelling spots along the Brazilian coast were previously reported for Marine Isotope Stage (MIS) 5, but open questions remain regarding the climatic mechanisms and the periodicity of such changes. Based on two marine sediment cores, we provide evidence for multiple intensifications of the upwelling regime off the Southeast Brazilian margin (SBM) during several interglacials and highlight the major role of eccentricity as the responsible forcing. In addition, we show a two-step change in the upwelling regime across the Mid-Brunhes Event (MBE) and an increase in the amplitude of upwelling variability after this climatic transition. Our findings point to substantial modifications of the upwelling regions during several glacial-interglacial transitions that probably altered the regional marine productivity regime and the carbon budget.

Description: The supercontinent cycle is a key oscillation of the Earth system with alternating aggregation and breakup of the supercontinent. It is important to know how Earth's climate system changes with this significant oscillation. Here, we demonstrate a unified picture of Earth's climate history since 4.4 billion years before present by deriving temperature, sea level, biodiversity, CO2, and geomagnetic intensity curves from a large number of Precambrian datasets. There were significant oscillations of temperature, sea level, biodiversity and geomagnetic intensity during the Precambrian period. Temperature oscillated by 20-60 oC, sea level rose and fell by 100-200 meters, and geomagnetic intensity oscillated by about 50% of its mean value. Temperature, sea level and geomagnetic intensity showed good in-phase relationship and tended to slightly lead orogenesis of the supercontinent cycle. We found that d13C captures well the Phanerozoic mass extinction events, and Precambrian biodiversity history showed seven "super mass extinction events".

Description: Thermocline temperature and seawater d18O reconstruction during Termination II and the Last Interglacial for the core GL-1090, in the western South Atlantic. The intensification of the Agulhas Leakage (AL) during glacial Terminations has long been proposed as a necessary mechanism to return the Atlantic Meridional Overturning Circulation (AMOC) to its interglacial mode. However, the lack of records showing the downstream evolution of the AL signal and the substantial temporal differences between AL intensification and resumption of deep-water convection cast doubt on the importance of this mechanism to the overturning. Here, we analyze a combination of new and previously published data related to Mg/Ca-derived temperatures and ice volume-corrected seawater δ18O records (δ18OIVC-SW as a proxy for ocean relative salinity changes) that demonstrate the propagation of the AL signal via surface and thermocline waters to the western South Atlantic (Santos Basin) during glacial Termination II and the early Last Interglacial. The saline AL waters were temporally stored in the upper subtropical South Atlantic until they were abruptly released in two steps into the North Atlantic via the surface and thermocline at ca. 129 and 123 ka BP, respectively. Within age uncertainties, these two steps are coeval with the resumption of convection in the Labrador and Nordic Seas during the Last Interglacial. We propose a mechanism whereby both an active AL and a favorable ocean-atmosphere configuration in the tropical Atlantic were required to allow the flux of AL waters into the North Atlantic, where they then contributed to enhancing the AMOC during the Last Interglacial period. Our results provide a framework that connects AL strengthening to the AMOC intensifications that follow glaciations.