Resolving Apparent Conflicts between Oceanographic and Antarctic Climate Records and Evidence for a Decrease in pCO2 during the Oligocene through Early Miocene (34–16 Ma)

An apparent mismatch between published oxygen isotopic data and other paleoclimate proxies for the span from 26–16 Ma is resolved by calibration against global sea-level estimates obtained from backstripping continental margin stratigraphy. Ice-volume estimates from calibrated oxygen isotope data compare favorably with stratigraphic and palynological data from Antarctica, and with estimates of atmospheric pCO2 throughout the Oligocene to early Miocene (34–16 Ma). Isotopic evidence for an East Antarctic Ice Sheet (EAIS) as much as 30% larger than its present-day volume at glacial maxima during that span is consistent with seismic reflection and stratigraphic evidence for an ice sheet covering much of the Antarctic continental shelf at the same glacial maxima. Palynological data suggest long-term cooling during the Oligocene, with cold near-tundra environments developing along the coast at glacial minima no later than the late Oligocene. A possible mechanism for this long-term cooling is a decrease in atmospheric pCO2 from the middle Eocene to Oligocene, reaching near pre-industrial levels by the latest Oligocene, and remaining at those depressed levels throughout the Miocene

Is There a Role for Sequence Stratigraphy in Chronostratigraphy?

Sequence stratigraphy revolutionized the field of stratigraphy in the late 1970s and 1980s by providing an interpretive depositional framework for integrating diverse stratigraphic data at the scale of sedimentary basins. However, a lack of consensus on criteria for recognizing, mapping and hence dating sequence boundaries, interpretations of uneven quality, and doubts about the universal eustatic origin and global synchrony of unconformity-related sequences limit the usefulness of sequence stratigraphy in chronostratigraphy

Evaluating the Stratigraphic Response to Eustasy from Oligocene Strata in New Jersey

Previously published Oligocene eustatic records are compared with observed stratigraphic architecture at the New Jersey continental margin in order to evaluate the stratigraphic response to eustatic change. Lower to mid-Oligocene sequence boundaries (33.8–28.0 Ma) are associated with relatively long hiatuses (0.3–0.6 m.y.), in which sedimentation in many places terminated during eustatic falls and resumed early during eustatic rises. Upper Oligocene sequence boundaries are associated with relatively short hiatuses (less than 0.3 m.y.), and provide the best constraints on phase relations between sea-level forcing and margin response. The interval represented by each upper Oligocene sequence varies in dip profile. At updip locations, landward of the clinoform rollover in the underlying sequence boundary, sedimentation commenced after the eustatic low and terminated before the eustatic high (with partial erosion of any younger record). At downdip locations, sedimentation within each sequence was progressively delayed in a seaward direction, beginning during the eustatic rise and terminating near the eustatic low. Combining data from all available boreholes, ages of sequence boundaries (correlative surfaces) correspond closely with the timing of eustatic lows, and ages of condensed sections (intervals of sediment starvation) correspond with eustatic highs

Calibration between Eustatic Estimates from Backstripping and Oxygen Isotopic Records for the Oligocene

Eustatic estimates from the backstripping of Oligocene sections are compared quantitatively with δ18O data. Each of the nine Oligocene δ18O events (maxima) identified in previous studies correlates with a stratigraphically determined sea-level lowstand. Oxygen isotopic records from planktonic foraminifers from western equatorial Atlantic Ocean Drilling Program (ODP) Site 929 indicate an isotopic increase of 0.16‰ per 10 m decrease in the depth of the ocean (apparent sea level, ASL). Amplitudes of ASL change also correlate with moderate- and high-resolution benthic for a min i fer al δ18O records from ODP Sites 803 (western tropical Pacific) and 929 and from Deep Sea Drilling Project (DSDP) Site 522 (South Atlantic Ocean), with an isotopic change of 0.22‰ per 10 m of ASL change (r2 = 0.807 and 0.960, respectively), and with records from ODP Site 689 (Southern Ocean; 0.13‰ per 10 m of ASL change; r2 = 0.704). This correlation suggests that Southern Ocean deep-water temperature changes were smaller than tropical sea-surface temperature changes between million year–scale glacials and interglacials. It also suggests that the deep-sea Southern Ocean records may provide the best means to calibrate sea level to oxygen isotopes

Spatial Variations in a Condensed Interval between Estuarine and Open-Marine Settings: Holocene Hudson River Estuary and Adjacent Continental Shelf

An interval of stratigraphic condensation extending for 300 km from the fluvially dominated Hudson River estuary to the adjacent continental shelf reveals stratal relationships within an unconformity-related depositional sequence that are commonly difficult to resolve in seismic reflection profiles and outcrop. High-resolution side-scan sonar and bathymetry, more than 100 sediment cores ∼2 m long, and radioisotope (14C, 137Cs) age control show that much of the valley was filled by ca. 3 to 1 ka. The present rate of sediment accumulation averages 1 mm/yr, corresponding with a sea-level rise of ∼1.2 mm/yr relative to local bedrock. Condensation is manifested today by sedimentary bypass in most parts of the estuary and by the trapping of available sediment (1.2–5.6 × 105 t/yr [metric tons]) along narrow reaches and primarily in the vicinity of the estuarine turbidity maximum, a part of the estuary located upstream of the salinity intrusion ∼25 km from the mouth (3.0 × 105 t/yr). Shelf condensation is due to sediment starvation. The condensed interval merges updip with a nascent sequence boundary as the estuary reaches its final filling phase and downdip with the sequence boundary that developed at the Last Glacial Maximum. Delta progradation may take place as available shelf accommodation is filled, but such sediments are expected to be removed once sea level begins to fall. This sedimentation pattern, in which a condensed interval merges with different sequence boundaries, is consistent with the stratigraphic record of the Atlantic margin back to the Paleogene and may be typical of sediment-starved margins

Estuarine Processes and Their Stratigraphic Record: Paleosalinity and Sedimentation Changes in the Hudson Estuary (North America)

Paleosalinity estimates and rates of sedimentation inferred from core samples from the Hudson estuary for the interval between 6.4 and 1.3 ka indicate a possible role for the estuarine turbidity maximum (ETM) in influencing patterns of estuarine sedimentation at centennial to millennial time scales. Currently in the estuary, sedimentation is localized via sediment trapping particularly in the vicinity of the ETM, 13–26 km upstream from Battery Park (FBP) at the southern tip of Manhattan, in water depths greater than 4 m, and on the western side of the estuary. Data presented in this paper are from cores located within the segment of the estuary 29–50 km FBP. Age constraints are provided by C-14 dating. Paleoenvironmental interpretations are based upon paleosalinity estimates, grain size variability, and sedimentary structures. Paleosalinity was inferred on the basis of foraminiferal biofacies analysis and a new method for estimating summertime paleosalinity using oxygen isotope measurements in bivalve shell material. The isotopic analysis of a narrow size fraction (1.0–1.7 mm) representing summer growth of a single bivalve species (Gemma gemma) reduces the uncertainty related to annual changes in temperature. Data from ∼45 km FBP indicate a gradual decrease in summertime paleosalinity between 6.4 and 2.0 ka from 25–20‰ to 15–10‰ (the latter is similar to present-day values). These results are consistent with the conclusion of an earlier low-resolution study. Sedimentation rates are generally low and are similar to the rate of sea-level rise in the Hudson River. Lowest sedimentation rates are noted in short (lower than 2 m) cores from north of the Tappan Zee Bridge (40–50 km FBP from 2.4 ka to present); in shallow water (∼2 m at mean low water, core SD-11) ∼45 km FBP; and on the eastern side of the estuary from ∼50 to 29 km FBP. Exceptions are high sedimentation rates (up to four times background) observed in cores from the western flats (SD 30, ∼45 km FBP, 4.9 to 3.4 ka) in water depths of 4 m and from the western part of the main channel (P21.7 core, ∼32 km FBP, greater than 2.3 to ∼1.3 ka). We hypothesize that the observed pattern in sediment accumulation relates to a location for the ETM some 20 km upstream of its present position at 3 ka. Downstream migration of the ETM since 3 ka is ascribed to shoaling of the estuary, effectively squeezing the marine saltwater wedge in the same direction, and off marginal flats into the channel. Such shoaling would have enhanced the role of waves in mixing marine and fresher surface water, and reduced the effect of the ETM in focusing sediment accumulation. The results of this study are consistent with the idea that at any time, estuarine sedimentation is highly localized, suggesting a more complex depositional pattern than previously indicated in estuarine stratigraphic models

The Phanerozoic Record of Global Sea-Level Change

We review Phanerozoic sea-level changes [543 million years ago (Ma) to the present] on various time scales and present a new sea-level record for the past 100 million years (My). Long-term sea level peaked at 100 ± 50 meters during the Cretaceous, implying that ocean-crust production rates were much lower than previously inferred. Sea level mirrors oxygen isotope variations, reflecting ice-volume change on the 104- to 106-year scale, but a link between oxygen isotope and sea level on the 107-year scale must be due to temperature changes that we attribute to tectonically controlled carbon dioxide variations. Sea-level change has influenced phytoplankton evolution, ocean chemistry, and the loci of carbonate, organic carbon, and siliciclastic sediment burial. Over the past 100 My, sea-level changes reflect global climate evolution from a time of ephemeral Antarctic ice sheets (100 to 33 Ma), through a time of large ice sheets primarily in Antarctica (33 to 2.5 Ma), to a world with large Antarctic and large, variable Northern Hemisphere ice sheets (2.5 Ma to the present)

The Huanan Seafood Wholesale Market in Wuhan was the early epicenter of the COVID-19 pandemic

Understanding how severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in 2019 is critical to preventing zoonotic outbreaks before they become the next pandemic. The Huanan Seafood Wholesale Market in Wuhan, China, was identified as a likely source of cases in early reports but later this conclusion became controversial. We show the earliest known COVID-19 cases from December 2019, including those without reported direct links, were geographically centered on this market. We report that live SARS-CoV-2 susceptible mammals were sold at the market in late 2019 and, within the market, SARS-CoV-2-positive environmental samples were spatially associated with vendors selling live mammals. While there is insufficient evidence to define upstream events, and exact circumstances remain obscure, our analyses indicate that the emergence of SARS-CoV-2 occurred via the live wildlife trade in China, and show that the Huanan market was the epicenter of the COVID-19 pandemic

Relative sea-level rise around East Antarctica during Oligocene glaciation

During the middle and late Eocene (∼48-34 Myr ago), the Earth's climate cooled and an ice sheet built up on Antarctica. The stepwise expansion of ice on Antarcticainduced crustal deformation and gravitational perturbations around the continent. Close to the ice sheet, sea level rosedespite an overall reduction in the mass of the ocean caused by the transfer of water to the ice sheet. Here we identify the crustal response to ice-sheet growth by forcing a glacial-hydro isostatic adjustment model with an Antarctic ice-sheet model. We find that the shelf areas around East Antarctica first shoaled as upper mantle material upwelled and a peripheral forebulge developed. The inner shelf subsequently subsided as lithosphere flexure extended outwards from the ice-sheet margins. Consequently the coasts experienced a progressive relative sea-level rise. Our analysis of sediment cores from the vicinity of the Antarctic ice sheet are in agreement with the spatial patterns of relative sea-level change indicated by our simulations. Our results are consistent with the suggestion that near-field processes such as local sea-level change influence the equilibrium state obtained by an icesheet grounding line

Eocene cooling linked to early flow across the Tasmanian Gateway

The warmest global temperatures of the past 85 million years occurred during a prolonged greenhouse episode known as the Early Eocene Climatic Optimum (52–50 Ma). The Early Eocene Climatic Optimum terminated with a long-term cooling trend that culminated in continental-scale glaciation of Antarctica from 34 Ma onward. Whereas early studies attributed the Eocene transition from greenhouse to icehouse climates to the tectonic opening of Southern Ocean gateways, more recent investigations invoked a dominant role of declining atmospheric greenhouse gas concentrations (e.g., CO(2)). However, the scarcity of field data has prevented empirical evaluation of these hypotheses. We present marine microfossil and organic geochemical records spanning the early-to-middle Eocene transition from the Wilkes Land Margin, East Antarctica. Dinoflagellate biogeography and sea surface temperature paleothermometry reveal that the earliest throughflow of a westbound Antarctic Counter Current began ∼49–50 Ma through a southern opening of the Tasmanian Gateway. This early opening occurs in conjunction with the simultaneous onset of regional surface water and continental cooling (2–4 °C), evidenced by biomarker- and pollen-based paleothermometry. We interpret that the westbound flowing current flow across the Tasmanian Gateway resulted in cooling of Antarctic surface waters and coasts, which was conveyed to global intermediate waters through invigorated deep convection in southern high latitudes. Although atmospheric CO(2) forcing alone would provide a more uniform middle Eocene cooling, the opening of the Tasmanian Gateway better explains Southern Ocean surface water and global deep ocean cooling in the apparent absence of (sub-) equatorial cooling