Beschreibung: Reconstructions of global mean sea level from earlier warm periods in Earth’s history can help constrain future projections of sea level rise. Here we report on the sedimentology and age of a geological unit in central Patagonia, Argentina, that we dated to the Early Pliocene (4.69–5.23 Ma, 2σ) with strontium isotope stratigraphy. The unit was interpreted as representative of an intertidal environment, and its elevation was measured with differential GPS at ca. 36 m above present-day sea level. Considering modern tidal ranges, it was possible to constrain paleo relative sea level within  ±2.7 m (1σ). We use glacial isostatic adjustment models and estimates of vertical land movement to calculate that, when the Camarones intertidal sequence was deposited, global mean sea level was 28.4 ± 11.7 m (1σ) above present. This estimate matches those derived from analogous Early Pliocene sea level proxies in the Mediterranean Sea and South Africa. Evidence from these three locations indicates that Early Pliocene sea level may have exceeded 20m above its present level. Such high global mean sea level values imply an ice-free Greenland, a significant melting of West Antarctica, and a contribution of marine-based sectors of East Antarctica to global mean sea level.

Beschreibung: Global mean sea level was 28.4 ± 11.7 m higher than at present during the Early Pliocene, at atmospheric CO2 levels of no more than 450 ppm and temperatures of 2–3 ∘C above preindustrial levels, suggests a reconstruction from Patagonia.

Beschreibung: National Science Foundation (NSF) https://doi.org/10.13039/100000001

Beschreibung: Highlights • Core-log-seismic correlation allows to assign ages to the Scotia Sea seismic record. • Major implications are derived on the relation between regional and global events. • The main stratigraphic events are much younger than previously proposed. • Three major phases for the regional oceanography are observed from late Miocene. • These phases appear to be closely linked to the Antarctic Ice Sheet dynamics. Scotia Sea and the Drake Passage is key towards understanding the development of modern oceanic circulation patterns and their implications for ice sheet growth and decay. The sedimentary record of the southern Scotia Sea basins documents the regional tectonic, oceanographic and climatic evolution since the Eocene. However, a lack of accurate age estimations has prevented the calibration of the reconstructed history. The upper sedimentary record of the Scotia Sea was scientifically drilled for the first time in 2019 during International Ocean Discovery Program (IODP) Expedition 382, recovering sediments down to ∼643 and 676 m below sea floor in the Dove and Pirie basins respectively. Here, we report newly acquired high resolution physical properties data and the first accurate age constraints for the seismic sequences of the upper sedimentary record of the Scotia Sea to the late Miocene. The drilled record contains four basin-wide reflectors – Reflector-c, -b, -a and -a' previously estimated to be ∼12.6 Ma, ∼6.4 Ma, ∼3.8 Ma and ∼2.6 Ma, respectively. By extrapolating our new Scotia Sea age model to previous morpho-structural and seismic-stratigraphic analyses of the wider region we found, however, that the four discontinuities drilled are much younger than previously thought. Reflector-c actually formed before 8.4 Ma, Reflector-b at ∼4.5/3.7 Ma, Reflector-a at ∼1.7 Ma, and Reflector-a' at ∼0.4 Ma. Our updated age model of these discontinuities has major implications for their correlation with regional tectonic, oceanographic and cryospheric events. According to our results, the outflow of Antarctic Bottom Water to northern latitudes controlled the Antarctic Circumpolar Current flow from late Miocene. Subsequent variability of the Antarctic ice sheets has influenced the oceanic circulation pattern linked to major global climatic changes during early Pliocene, Mid-Pleistocene and the Marine Isotope Stage 11.

Beschreibung: Early Pleistocene Marine Isotope Stage (MIS)-31 (1.081–1.062 Ma) is a unique interval of extreme global warming, including evidence of a West Antarctic Ice Sheet (WAIS) collapse. Here we present a new 1,000-year resolution, spanning 1.110–1.030 Ma, diatom-based reconstruction of primary productivity, relative sea surface temperature changes, sea-ice proximity/open ocean conditions and diatom species absolute abundances during MIS-31, from the Scotia Sea (59°S) using deep-sea sediments collected during International Ocean Discovery Program (IODP) Expedition 382. The lower Jaramillo magnetic reversal (base of C1r.1n, 1.071 Ma) provides a robust and independent time-stratigraphic marker to correlate records from other drill cores in the Antarctic Zone of the Southern Ocean (AZSO). An increase in open ocean species Fragilariopsis kerguelensis in early MIS-31 at 53°S (Ocean Drilling Program Site 1,094) correlates with increased obliquity forcing, whereas at 59°S (IODP Site U1537; this study) three progressively increasing, successive peaks in the relative abundance of F. kerguelensis correlate with Southern Hemisphere-phased precession pacing. These observations reveal a complex pattern of ocean temperature change and sustained sea surface temperature increase lasting longer than a precession cycle within the Atlantic sector of the AZSO. Timing of an inferred WAIS collapse is consistent with delayed warmth (possibly driven by sea-ice dynamics) in the southern AZSO, supporting models that indicate WAIS sensitivity to local sub-ice shelf melting. Anthropogenically enhanced impingement of relatively warm water beneath the ice shelves today highlights the importance of understanding dynamic responses of the WAIS during MIS-31, a warmer than Holocene interglacia

Beschreibung: Ice loss in the Southern Hemisphere has been greatest over the past 30 years in West Antarctica. The high sensitivity of this region to climate change has motivated geologists to examine marine sedimentary records for evidence of past episodes of West Antarctic Ice Sheet (WAIS) instability. Sediments accumulating in the Scotia Sea are useful to examine for this purpose because they receive iceberg-rafted debris (IBRD) sourced from the Pacific- and Atlantic-facing sectors of West Antarctica. Here we report on the sedimentology and provenance of the oldest of three cm-scale coarse-grained layers recovered from this sea at International Ocean Discovery Program Site U1538. These layers are preserved in opal-rich sediments deposited ∼1.2 Ma during a relatively warm regional climate. Our microCT-based analysis of the layer's in-situ fabric confirms its ice-rafted origin. We further infer that it is the product of an intense but short-lived episode of IBRD deposition. Based on the petrography of its sand fraction and the Phanerozoic 40Ar/39Ar ages of hornblende and mica it contains, we conclude that the IBRD it contains was likely sourced from the Weddell Sea and/or Amundsen Sea embayment(s) of West Antarctica. We attribute the high concentrations of IBRD in these layers to “dirty” icebergs calved from the WAIS following its retreat inland from its modern grounding line. These layers also sit at the top of a ∼366-m thick Pliocene and early Pleistocene sequence that is much more dropstone-rich than its overlying sediments. We speculate this fact may reflect that WAIS mass-balance was highly dynamic during the ∼41-kyr (inter)glacial world. Key Points - We present the first provenance data generated for Pleistocene-aged iceberg-rafted debris deposited in Iceberg Alley - We conclude that prominent iceberg-rafted debris layers deposited at Pirie Basin Site U1538 ∼1.2 Ma were sourced from West Antarctica - They represent intense suborbitally-paced episodes of iceberg discharge from tidewater glaciers, most likely in the Weddell Embayment

Beschreibung: 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.

Beschreibung: We present high-resolution late Pliocene (~2.7-3.5 Ma) benthic foraminiferal stable isotope records from eastern equatorial Atlantic ODP Site 959 (δ^13^C and δ^18^O) and ODP Site 662 (δ^13^C). The complementary δ^18^O record from Site 662 was published in Lisiecki and Raymo (2005; doi:10.1029/2004PA001071). Site 959 data was generated using the epibenthic species Cibicides wuellerstorfi and stable isotope analysis was performed at Utrecht University in 2016 on either a Thermo-Finnigan Kiel III automated preparation system coupled to a Thermo-Finnigan MAT 253 mass spectrometer, or a Thermo Finnigan GasBench-II carbonate preparation device coupled to a Thermo Finnigan Delta-V mass spectrometer. Site 662 data was generated using Cibicides wuellerstorfi when possible, and alternatively, a combination of Cibicides species (Cibicides spp.) was used. Stable isotope analysis was performed in the early 1990s at Massachusetts Institute of Technology using a VG Prism mass spectrometer. These new records are combined with previously published benthic δ¹³C and δ¹⁸O records. By assuming that both δ¹³C and δ¹⁸O behave as conservative tracers, we estimate the isotopic end-members of deep Atlantic water masses. At least three endmembers are needed to explain the spatial δ¹³C-δ¹⁸O variability in the deep North Atlantic Ocean: two Northern Component Water (NCW) and one Southern Component Water (SCW) water masses. We use a ternary mixing model to quantify the mixing proportions between SCW and NCW in the deep Atlantic ocean.

Beschreibung: This dataset contains single-shell stable isotope data (d18O and d13C), shell weights, ages, and preservation states of Cibicidoides shells spanning MIS 1-2 from ODP Site 929, Ceara Rise (5.976°N, -43.740°E, 4357 m water depth). Sediment samples were processed following standard procedures. From each 〉63µm sediment sample, all specimens of the genera Cibicidoides and Uvigerina were picked from the 〉150 µm size fraction. Using a binocular microscope, each individual Cibicidoides and Uvigerina specimen was critically evaluated for preservation quality. Details of the Foraminiferal Preservation Index (FPI) can be found in the corresponding publication. In short, an initial score (IS) of 5 is applied to an ideal specimen with clearly defined whorls, sutures, pores, and other surface features. A shell with an IS score of 3 usually contains enlarged pores and "smoothed" looking surface features, including sutures and surface ornamentation. An IS score of 4 is assigned to specimens with more subtly smoothed features, and/or slightly enlarged pores. From the IS3-5 value for a given specimen, deductions of 1-2 points are applied to generate its final score (FS). A deduction of 1 point is applied for either a missing or fractured chamber, and/or evidence of slight dissolution. A deduction of 2 points is applied for extensive missing or fractured chambers, and/or evidence of extensive dissolution. For example, an assigned FS1 value for a specimen could be the result of highly smoothed surface features, with some combination of extensive dissolution pockmarks and/or one to several fractured/missing chambers (i.e. IS3 - 2 = FS1). The letter "A" assigned to the final score indicates that the appearance of the shell is glassy, "B" is assigned to pseudo-glassy shells, and "C" to frosty specimens. Specimens of varying preservation quality were purposely chosen for single-shell stable isotope analyses. Each specimen was weighed, and shells featuring narrow mass ranges were selected for individual analytical runs of d18O and d13C which allows for the optimization of instrument tuning. Single Cibicidoides shells were analyzed on a Thermo Delta V Kiel IV dual inlet mass spectrometer at the Lamont-Doherty Earth Observatory, and were corrected relative to the NBS-19 calcite standard. Average precision on these analyses was better than 0.08‰ for δ18O and better than 0.06‰ for δ13C. The age model is based on published stable isotope records (Bickert et al., 1997; Billups et al., 1998) tuned to the deep sea benthic d18O stack (Lisiecki and Raymo, 2005; Ahn et al., 2017).

Beschreibung: This dataset contains single-shell stable isotope data (d18O and d13C), shell weights, ages, and preservation states of Cibicidoides shells spanning MIS 9-10 from ODP Site 1089 north of Agulhas Ridge (-40.936°N, 9.894°E, 4620 m water depth). Sediment samples were processed following standard procedures. From each 〉63µm sediment sample, all specimens of the genera Cibicidoides and Uvigerina were picked from the 〉150 µm size fraction. Using a binocular microscope, each individual Cibicidoides and Uvigerina specimen was critically evaluated for preservation quality. Details of the Foraminiferal Preservation Index (FPI) can be found in the corresponding publication. In short, an initial score (IS) of 5 is applied to an ideal specimen with clearly defined whorls, sutures, pores, and other surface features. A shell with an IS score of 3 usually contains enlarged pores and “smoothed” looking surface features, including sutures and surface ornamentation. An IS score of 4 is assigned to specimens with more subtly smoothed features, and/or slightly enlarged pores. From the IS3-5 value for a given specimen, deductions of 1-2 points are applied to generate its final score (FS). A deduction of 1 point is applied for either a missing or fractured chamber, and/or evidence of slight dissolution. A deduction of 2 points is applied for extensive missing or fractured chambers, and/or evidence of extensive dissolution. For example, an assigned FS1 value for a specimen could be the result of highly smoothed surface features, with some combination of extensive dissolution pockmarks and/or one to several fractured/missing chambers (i.e. IS3 – 2 = FS1). The letter “A” assigned to the final score indicates that the appearance of the shell is glassy, “B” is assigned to pseudo-glassy shells, and “C” to frosty specimens. Specimens of varying preservation quality were purposely chosen for single-shell stable isotope analyses. Each specimen was weighed, and shells featuring narrow mass ranges were selected for individual analytical runs of d18O and d13C which allows for the optimization of instrument tuning. Single Cibicidoides shells were analyzed on a Thermo Delta V Kiel IV dual inlet mass spectrometer at the Lamont-Doherty Earth Observatory, and were corrected relative to the NBS-19 calcite standard. Average precision on these analyses was better than 0.08‰ for δ18O and better than 0.06‰ for δ13C. The age model is based on the published stable isotope record (Hodell et al. 2001) tuned to the deep sea benthic d18O stack (Lisiecki and Raymo, 2005; Ahn et al., 2017).