Multi‐scale transgressive–regressive cycles from the mid‐Jurassic were recognised in the Central Lusitanian Basin, Portugal. These cycles allow the depositional evolution of the basin to be better understood and aid in the construction of stratigraphic sequences composed of three hierarchies. The stacking pattern of high‐frequency transgressive–regressive sequences forms larger clusters that define medium‐frequency transgressive–regressive sequences. Likewise, the stacking pattern of medium‐frequency transgressive–regressive sequences generates two Bathonian–early Callovian low‐frequency transgressive–regressive sequences. Integration of several methods supported the interpretation of facies associations representing clastic deposition in offshore to shoreface environments and carbonate sediments in outer to inner ramp settings. New data from calcareous nannofossils and dinoflagellate assemblages constrained the interval's Bathonian–early Callovian age, thus unveiling the Middle–Upper Jurassic disconformity and filling the Middle Jurassic stratigraphic record gap in the Central Lusitanian Basin. This study may be helpful for similar successions in Tethyan domains and comparable depositional settings elsewhere.
Antarctica is one of the most vulnerable regions to climate change on Earth and studying the past and present responses of this polar marine ecosystem to environmental change is a matter of urgency. Sedimentary ancient DNA (sedaDNA) analysis can provide such insights into past ecosystem-wide changes. Here we present authenticated (through extensive contamination control and sedaDNA damage analysis) metagenomic marine eukaryote sedaDNA from the Scotia Sea region acquired during IODP Expedition 382. We also provide a marine eukaryote sedaDNA record of ~1 Mio. years and diatom and chlorophyte sedaDNA dating back to ~540 ka (using taxonomic marker genes SSU, LSU, psbO). We find evidence of warm phases being associated with high relative diatom abundance, and a marked transition from diatoms comprising <10% of all eukaryotes prior to ~14.5 ka, to ~50% after this time, i.e., following Meltwater Pulse 1A, alongside a composition change from sea-ice to open-ocean species. Our study demonstrates that sedaDNA tools can be expanded to hundreds of thousands of years, opening the pathway to the study of ecosystem-wide marine shifts and paleo-productivity phases throughout multiple glacial-interglacial cycles.
The Southern Ocean paleoceanography provides key insights into how iron fertilization and oceanic productivity developed through Pleistocene ice-ages and their role in influencing the carbon cycle. We report a high-resolution record of dust deposition and ocean productivity for the Antarctic Zone, close to the main dust source, Patagonia. Our deep-ocean records cover the last 1.5 Ma, thus doubling that from Antarctic ice-cores. We find a 5 to 15-fold increase in dust deposition during glacials and a 2 to 5-fold increase in biogenic silica deposition, reflecting higher ocean productivity during interglacials. This antiphasing persisted throughout the last 25 glacial cycles. Dust deposition became more pronounced across the Mid-Pleistocene Transition (MPT) in the Southern Hemisphere, with an abrupt shift suggesting more severe glaciations since ~0.9 Ma. Productivity was intermediate pre-MPT, lowest during the MPT and highest since 0.4 Ma. Generally, glacials experienced extended sea-ice cover, reduced bottom-water export and Weddell Gyre dynamics, which helped lower atmospheric CO2 levels.
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