ALBERT

Description: Global climate cooled from the early Eocene hothouse (~52-50 Ma) to the latest Eocene (~34 Ma). At the same time, the tectonic evolution of the Southern Ocean was characterized by the opening and deepening of circum-Antarctic gateways, which affected both surface- and deep-ocean circulation. The Tasmanian Gateway played a key role in regulating ocean throughflow between Australia and Antarctica. Southern Ocean surface currents through and around the Tasmanian Gateway have left recognizable tracers in the spatiotemporal distribution of plankton fossils, including organic-walled dinoflagellate cysts. This spatiotemporal distribution depends on both the physico-chemical properties of the water masses and the path of surface-ocean currents. The extent to which climate and tectonics have influenced the distribution and composition of surface currents and thus fossil assemblages has, however, remained unclear. In particular, the contribution of climate change to oceanographic changes, superimposed on long-term and gradual changes induced by tectonics, is still poorly understood. To disentangle the effects of tectonism and climate in the southwest Pacific Ocean, we target a climatic deviation from the long-term Eocene cooling trend, the Middle Eocene Climatic Optimum (MECO; ~40 Ma). This 500-thousand-year-long phase of global warming was unrelated to regional tectonism, and thus provides a test case to investigate the ocean's physiochemical response to climate change alone. We reconstruct changes in surface-water circulation and temperature in and around the Tasmanian Gateway during the MECO through new palynological and organic geochemical records from the central Tasmanian Gateway (Ocean Drilling Program Site 1170), the Otway Basin (southeastern Australia) and the Hampden Beach section (New Zealand). Our results confirm that dinocyst communities track specific surface-ocean currents, yet the variability within the communities can be driven by superimposed temperature change. Together with published results from the east of the Tasmanian Gateway, our new results suggest a shift in surface-ocean circulation during the peak of MECO warmth. Simultaneous with high sea-surface temperatures in the Tasmanian Gateway area, pollen assemblages indicate warm temperate rainforests with paratropical elements along the southeastern margin of Australia. Finally, based on new age constraints we suggest that a regional southeast Australian transgression might have been coincident with the MECO.

Description: The Atlantic Meridional Overturning Circulation (AMOC) helps regulate the transport and storage of a large reservoir of heat and carbon, and therefore plays an essential role in climate change past and present1. Authigenic uranium deposition in deep-sea sediments is a sensitive redox tracer2,3 that can shed light on bottom water oxygen, carbon storage and, in certain circumstances, water mass distributions in the deep ocean4-7. Here, we combine new and published authigenic uranium data to reconstruct oxygenation since the last ice age in the east and west basins of the North Atlantic Ocean. Overall, the glacial deep North Atlantic was less well oxygenated compared to the Holocene, suggesting a higher ocean carbon inventory and important contribution to the global sequestration of CO2. We find that lower oxygen levels occurred in the deepest locations in the western basin, while substantially lower-oxygen waters were present throughout the northeast Atlantic. Our findings indicate that lower oxygen levels and correspondingly greater carbon storage were persistent features of the last glaciation and deglaciation in the deep North Atlantic Ocean, particularly in the eastern basin. This zonal emphasis is likely related to the farther advance and greater infilling in the east of deep waters originating from the Southern Ocean.

Description: The data set has been obtained on gravity core M125-67-4 from off the Jequitinhonha River, East Brazil. The obtained proxies described the hydrological conditions in the river's hinterland over the past ~ 5000 years as measure of fluctuations in the South American Summer Monsoon intensity. XRF-derived K/Al ratios and mineral phases determined by XRD reflect weathering state in the hinterland; high K/Al ratio and low kaolinite contents indicate dry conditions (and vice versa for low K/Al and high kaolinite conditions). Hydrogen isotopes are interpreted to primarily reflect precipitation amount, with low values indicating more precipitation.

Description: Multi-proxy records from two deep-sea sediment cores (IODP 353-U1446 and U1448) of the stable oxygen isotope composition (N. dutertrei) and trace element ratios (G. ruber ss, N. dutertrei) measured in planktic foraminifera, foraminiferal percent abundance and bulk sediment elemental variations gained from portable-XRF. These records are inferred to capture Indian Summer Monsoon river runoff across Marine Isotope Stage 5/6 (70-140 thousand years ago).

Description: We collected pelagic sediments from Holes A and B of IODP Site 342-U1407 that accumulated on the Southeast Newfoundland Ridge that spanned the Early Cenomanian to Early Turonian. In this study, we reconstruct the paleoceanographic changes before, during, and after Oceanic Anoxic Event 2 (OAE2) to isolate the triggers behind the widespread deposition of organic matter (OM) during this time. We combined the stable isotopes of bulk organic carbon, total organic carbon, total inorganic carbon, major and trace elements, and abundances of microfossils (benthic foraminiferal, biserial heterohelicid foraminifera, and radiolarians) to characterize the sediments. Biomarker indices were also calculated to determine the source and thermal maturity of the OM.

Description: The latest Cenomanian to early Turonian sedimentary record recovered at IODP Site 369-U1513 in the Mentelle Basin (SE Indian Ocean, paleolatitude about 60°S at 85 Ma) is studied to interpret the paleoceanographic evolution across the Oceanic Anoxic Event 2 (OAE 2) in the Southern Hemisphere. Here we present the planktonic and benthic foraminifera, radiolaria and calcispheres distribution and absolute abundances, the calcareous nannofossils distribution, the CaCO3 content, the bulk carbonate carbon and oxygen stable isotope data and the Total Organic Carbon values from IODP Holes 369-U1513A and 369-U1513D. The data presented here permit interpretation of the dynamics of the water mass stratification and document a reduced water mass stratification with alternating episodes of enhanced surface water productivity and variations of the thickness of the mixed layer across the OAE 2.

Description: The data include temperature proxy data (TEX86, MBT, brGMGT-I, NLR) and palynology (dinocyst assemblage data) for two coastal sections in the Australo-Antarctic Gulf. The stratigraphy of these sections is described in Frieling et al. (2018). The new data were generated to provide detailed multi-proxy temperature reconstructions for the region. A combination of organic geochemistry (lipid biomarker) analyses and palynology (mainly dinoflagellate cysts (dinocyst)) were conducted. A paper describing the results has been submitted (doi supplied when available). Sediment samples were acquired (by hand) during a field campaign to the coastal outcrop section at Point Margaret, Australia (-38.724667 N, 143.176389 E, 0m elevation) 14-28th of February 2016. Core samples from the Latrobe-1 borehole (-38.693056 N, 143.150000 E; drilled in 1963, ca. 20m elevation) were acquired from the geological survey core repository (Melbourne) during the same trip. From these sediment samples we quantified isoprenoid and branched glycerol dialkyl glycerol tetraethers (isoGDGTs) and branched glycerol monoalkyl glycerol tetraethers (brGMGTs) from organic total lipid extracts using ultra high performance liquid chromatography – mass spectrometry (UHPLC-MS) analyses. Furthermore, we used standard palynological techniques to obtain nearest living relative data from pollen and spore assemblages (methodology follows Huurdeman et al. 2021). Dinoflagellate cyst (dinocyst) assemblages were analysed from the same residues and here provided as relative abundances of ecogroups. All measurements and analyses were conducted in the organic geochemistry and palynology labs at Utrecht University, Netherlands between 2016 and 2018.

Description: The cyclic growth and decay of continental ice sheets can be reconstructed from the history of global sea level. Sea level is relatively well-constrained for the Last Glacial Maximum (LGM, 26,500-19,000 years ago, 26.5-19 ka) and the ensuing deglaciation. However, sea-level estimates for the period of ice-sheet growth before the LGM vary by 〉 60 m, an uncertainty comparable to the sea-level equivalent of the contemporary Antarctic Ice Sheet. Here we constrain sea level prior to the LGM by reconstructing the flooding history of the shallow Bering Strait since 46 ka. Our data constraint on Bering Strait flooding are nitrogen isotope measurements in organic matter bound in the planktonic foraminifer Neogloboquadrina pachyderma from four sediment cores in the Arctic Ocean, dating back to ~50,000 years before present. These data extend the previous measurements of Farmer et al., 2021 (https://doi.org/10.1038/s41561-021-00789-y). We additionally provide new Bayesian age-depth models for each sediment core based on existing radiocarbon (14C) measurements on N. pachyderma. The nitrogen isotope data are compared with a suite of reconstructions of global mean sea-level and relative sea level at the Bering Strait from glacial isostatic adjustment modeling covering the last 120,000 years.

Description: The Paleocene-Eocene Thermal Maximum (PETM) is the most studied global warming event of a series of Paleocene-Eocene carbon cycle perturbations called hyperthermals. PETM origins have been associated with volcanic-related carbon emissions; however, other carbon cycle feedbacks were required to develop a large hyperthermal such as the PETM. The orbital configuration in which the PETM occurred is still unclear despite possible orbital controls on the PETM triggering. This dataset contains X-Ray Fluorescence (XRF) data (Fe, Ca, and Si) from Contessa Road (Italy), a sedimentary section with reduced calcium carbonate dissolution compared to deep ocean sites. Astrochronological age models and probabilistic assessments reveal that the PETM onset appeared close to both short and long eccentricity maxima, which suggests that orbitally controlled insolation variations may have thermally destabilized carbon reservoirs that worked as PETM positive carbon cycle feedbacks.