We model Cenozoic temperature and ice volume changes using the Pacific benthic δ 18 O record and a global compilation of foraminiferal Mg/Ca data. In our model, the proportion of δ 18 O benthic variation reflecting temperature change over time is parameterized, and a benthic foraminiferal paleotemperature equation is used to estimate δ 18 O sw . Barystatic sea level (BSL) is derived using an ice-sheet model that defines temporal variability in the ratio of δ 18 O sw to BSL change. We calibrate parameters to align model output BSL and temperature variations with independent sea-level estimates and Mg/Ca-derived temperatures. Our approach is conceptually similar to previous efforts to decompose δ 18 O benthic using Mg/Ca data as temperature constraint, but differs through our application of the ice-sheet model and a Bayesian inversion framework. Our results indicate a modestly sized Antarctic ice sheet is present through most of the Paleocene and Early Eocene. Large Antarctic and modest Northern Hemisphere ice sheets (NHIS) developed after the Eocene-Oligocene transition, though the NHIS melted during most interglacial periods and through the Miocene Climate Optimum. Milankovitch forcing produced 100 kyr BSL variability that increased from ~5 m in the Paleocene to 30–40 m through the Oligocene and Early to early Middle Miocene, before diminishing to 20–30 m in the late Middle to Late Miocene. The amplitude rose again to ~40 m in the Early Pliocene and has increased to 80–100 m 100 kyr over the past Myr. Constructive interference of precession, obliquity, and eccentricity produces large variations in deep sea paleotemperature and BSL, especially at a ~100 kyr periodicity.

We evaluate lead-lag relationships between warming associated with the Paleocene-Eocene thermal maximum (PETM) and the attendant carbon isotope excursion (CIE) recorded in sedimentary archives from the mid-Atlantic continental margin. Cores from the New Jersey coastal plain (NJCP) provide thick (up to 15 m), rapidly deposited shelf PETM sections recording a 6-8 degrees C warming based on the TEX86 paleothermometer. Updip cores from Medford, NJ provide the most expanded CIE onset, associated with a gradual lithologic change from uppermost Paleocene glauconitic sands to the lowermost Eocene kaolinitic Marlboro Clay. The relative thickness of these transitional sediments and the CIE onset allow for high-resolution stable isotopic (bulk sediment, foraminifera, and organic carbon) and lipid biomarker analyses. The TEXH86-derived temperature records from Medford cores show no warming prior to the CIE onset, with the carbon isotopic decrease in phase with temperature. Previous studies of more downdip PETM sections on the NJCP suggested that warming preceded the CIE, consistent with a thermal trigger for carbon release. Re-evaluation of published records and Bayesian analysis of TEXH86-derived temperature and delta 13C from five NJCP sites do not indicate a statistically discernible lead or lag of carbon injection and warming. Though we can not preclude that a lead or lag exists, our analysis suggests that a synchronous CIE onset and warming is the most likely scenario on the NJ paleoshelf.

The release of over 4500 Gt (gigatonnes) of carbon at the Paleocene–Eocene boundary provides the closest geological analog to modern anthropogenic CO2 emissions. The cause(s) of and responses to the resulting Paleocene–Eocene Thermal Maximum (PETM) and attendant carbon isotopic excursion (CIE) remain enigmatic and intriguing despite over 30 years of intense study. CIE records from the deep sea are generally thin due to its short duration and slow sedimentation rates, and they are truncated due to corrosive bottom waters dissolving carbonate sediments. In contrast, PETM coastal plain sections along the US mid-Atlantic margin are thick, generally having an expanded record of the CIE. Drilling here presents an opportunity to study the PETM onset to a level of detail that could transform our understanding of this important event. Previous drilling in this region provided important insights, but existing cores are either depleted or contain stratigraphic gaps. New core material is needed for well-resolved marine climate records. To plan new drilling, members of the international scientific community attended a multi-staged, hybrid scientific drilling workshop in 2022 designed to maximize not only scientifically and demographically diverse participation but also to protect participants' health and safety during the global pandemic and to reduce our carbon footprint. The resulting plan identified 10 sites for drill holes that would penetrate the Cretaceous–Paleogene (K–Pg) boundary, targeting the pre-onset excursion (POE), the CIE onset, the rapidly deposited Marlboro Clay that records a very thick CIE body, and other Eocene hyperthermals. The workshop participants developed several primary scientific objectives related to investigating the nature and the cause(s) of the CIE onset as well as the biotic effects of the PETM on the paleoshelf. Additional objectives focus on the evidence for widespread wildfires and changes in the hydrological cycle, shelf morphology, and sea level during the PETM as well as the desire to study both underlying K–Pg sediments and overlying post-Eocene records of extreme hyperthermal climate events. All objectives address our overarching research question: what was the Earth system response to a rapid carbon cycle perturbation?

We reconstruct the subtropical North Atlantic water column structure during the Miocene Climate Optimum warming (MCO; 17–14.8 Ma) and the Middle Miocene Climate Transition cooling (MMCT; 14.8–12.8 Ma) by analyzing δ18O and δ13C in four species of foraminifera (surface dwellers Dentoglobigerina altispira and Trilobatus quadrilobatus, thermocline dweller Dentoglobigerina venezuelana, and benthic Planulina wuellerstorfi) from Site 558 (37.8°N). At the end of the MCO, δ18O of surface and thermocline dwellers increased by >1‰, suggesting at least 2°C cooling in the upper ocean as ice growth increased global δ18Osw by ∼0.5‰. The difference in δ18O values between thermocline and surface-dwelling species increased during the MMCT, coinciding with the development of a largely permanent East Antarctic Ice Sheet, and persisted into the Late Miocene. We interpret this increase in vertical δ18O gradient as a strengthening of the thermocline due to intensification of subtropical gyre circulation in response to the MMCT cooling.

This dataset includes pore water chemical data and headspace gas data from Site J1003 taken on the south Chilean Margin. Tab 3 includes Na and K data used in geothermometry calculations. Data have been used in a preprint manuscript uploaded at EarthArXiv (https://doi.org/10.31223/X5X92N), which is currently in revision at Nature Communications Earth & Environment.

Submarine groundwater discharge is increasingly recognized as an important component of the oceanic geochemical budget, but knowledge of the distribution of this phenomenon is limited. To date, reports of meteoric inputs to marine sediments are typically limited to shallow shelf and coastal environments, whereas contributions of freshwater along deeper sections of tectonically active margins like the Chilean Margin have generally been attributed to silicate diagenesis, mineral dehydration, or methane hydrate dissociation. Here we report that substantial pore water freshening on the south Chilean Margin reflects deep and focused contributions of meteorically modified geothermal groundwater, which has infiltrated marine sediments through regional fault systems. Geochemical fingerprinting of pore water data from Site J1003, recovered during D/V JOIDES Resolution Expedition 379T, highlights mixing between this fresh groundwater endmember and seawater, and provides the first constraints on the depth of geothermal groundwater reservoirs in the Aysén region of Patagonia. Collectively, our results identify an unappreciated locus of deep submarine groundwater and geothermal discharge along active margins, with potential implications for coastal biogeochemical processes and tectonic instability.

Abstract Sediment cores recently collected from the Chilean Margin during D/V JOIDES Resolution Expedition 379T (JR100) document variability in shipboard‐generated records of the green/blue (G/B) ratio. These changes show a strong coherence with benthic foraminiferal δ18O, Antarctic ice core records, and sediment lithology (e.g., higher diatom abundances in greener sediment intervals), suggesting a climate‐related control on the G/B. Here, we test the utility of G/B as a proxy for diatom productivity at Sites J1002 and J1007 by calibrating G/B to measured biogenic opal. Strong exponential correlations between measured opal% and the G/B were found at both sites. We use the empirical regressions to generate high‐resolution records of opal contents (opal%) on the Chilean Margin. Higher productivity tends to result in more reducing sedimentary conditions. Redox‐sensitive sedimentary U/Th generally co‐varies with the reconstructed opal% at both sites, supporting the association between sediment color, sedimentary U/Th, and productivity. Lastly, we calculated opal mass accumulation rate (MAR) at Site J1007 over the last ∼150,000 years. The G/B‐derived opal MAR record from Site J1007 largely tracks existing records derived from traditional wet‐alkaline digestion from the south and eastern equatorial Pacific (EEP) Ocean, with a common opal flux peak at ∼50 ka suggesting that increased diatom productivity in the EEP was likely driven by enhanced nutrient supply from the Southern Ocean rather than dust inputs as previously suggested. Collectively, our results identify the G/B ratio as a useful tool with the potential to generate reliable, high‐resolution paleoceanographic records that circumvent the traditionally laborious methodology.

Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.

AbstractLacustrine sedimentary records and the proxies contained within them are valuable archives of past climate. However, the resolution of these records is frequently coarse or contains a high degree of uncertainty, making it difficult to resolve how climatic variability impacts the ecosystems on which humans depend. The goal of this study is to couple recent sediment cores sampled at centimeter-scale resolution with paleo- and historical information about lake levels to document how changes in the paleoenvironment impact the paleoecology of a rift basin lake. We present multiproxy data from three short cores collected from Ferguson's Gulf (FG), a shallow embayment connected to the western shore of Lake Turkana, Kenya. Five distinct biozones were interpreted on the basis of ostracods and geochemistry (δ18O, δ13C, and major elements), spanning the Little Ice Age (LIA) to the modern. Overall, ostracod total abundance and assemblage diversity decreased up-core, with the largest total abundance and genera diversity occurring during the LIA. This fits with regional datasets that indicate the Eastern Branch of the East African Rift System was wetter during the LIA than it is today. This also suggests that human impact in and around Lake Turkana has weakened the resiliency of the ecosystems in FG.

The mid-Atlantic coastal plain (eastern United States) preserves high-resolution records of the Paleocene-Eocene Thermal Maximum (PETM) and attendant carbon isotope excursion (CIE), though preservation is highly variable from site to site. Here, we use a dip transect of expanded (as much as 15 m thick) PETM sections from the New Jersey coastal plain to build a cross-shelf PETM depositional model that explains the variability of these records. We invoke enhanced delivery of fine-grained sediments, due to the rapid environmental changes associated with this hyperthermal event, to explain relatively thick PETM deposits. We utilize δ13Cbulk, percent CaCO3, and percent coarse fraction (>63 μm) data, supported by biostratigraphic records, to correlate sites along a paleoslope dip transect. Updip cores from Medford, New Jersey, preserve expanded sections of the initiation of the PETM and the earliest portion of the CIE. Medial sites (Wilson Lake, Millville) preserve an expanded CIE body, and downdip Bass River records the CIE recovery. We interpret this pattern to reflect the progradation of clinoform foresets across the paleoshelf via fluid mud, similar to modern high-sediment-supply rivers and adjacent muddy shelves (e.g., the Amazon, Mahakam [Indonesia], and Ayeyarwady [Myanmar] Rivers). Our subaqueous-clinoform delta model explains the pattern of the CIE records and provides a framework for future PETM studies in the region.

Due to their large heat and moisture storage capabilities, the tropics are fundamental in modulating both regional and global climate. Furthermore, their thermal response during past extreme warming periods, such as super interglacials, is not fully resolved. In this regard, we present high-resolution (analytical) foraminiferal geochemical (delta O-18 and Mg/Ca) records for the last 1800 kyr from the shallow (487 m) Inner Sea drift deposits of the Maldives archipelago in the equatorial Indian Ocean. Considering the diagenetic susceptibility of these proxies, in carbonate-rich environments, we assess the integrity of a suite of commonly used planktonic and benthic foraminifera geochemical datasets (Globigerinoides ruber (white), Globigerinita glutinata (with bulla), Pulleniatina obliquiloculata (with cortex) and Cibicides mabahethi) and their use for future paleoceanographic reconstructions. Using a combination of spot Secondary Ion Mass Spectrometer, Electron Probe Micro-Analyzer and Scanning Electron Microscope image data, it is evident that authigenic overgrowths are present on both the external and internal test (shell) surfaces, yet the degree down-core as well as the associated bias is shown to be variable across the investigated species and proxies. Given the elevated authigenic overgrowth Mg/Ca (similar to 12-22 mmol/mol) and delta O-18 values (closer to the benthic isotopic compositions) the whole-test planktonic G. ruber (w) geochemical records are notably impacted beyond similar to 627.4 ka (24.7 mcd). Yet, considering the setting (i.e. bottom water location) for overgrowth formation, the benthic foraminifera delta O-18 record is markedly less impacted with only minor diagenetic bias beyond similar to 790.0 ka (28.7 mcd). Even though only the top of the G. ruber (w) and C. mabahethirecords (wholetest data) would be suitable for paleo-reconstructions of absolute values (i.e. sea surface temperature, salinity, seawater delta O-18), the long-term cycles, while dampened, appear to be preserved. Furthermore, planktonic species with thicker-tests (i.e. P. obliquiloculata (w/c)) might be better suited, in comparison to thinner-test counter-parts (i.e. G. glutinata (w/b), G. ruber (w)), for traditional whole-test geochemical studies in shallow, carbonate-rich environments. A thicker test equates to a smaller overall bias from the authigenic overgrowth. Overall, if the diagenetic impact is constrained, as done in this study, these types of diagenetically altered geochemical records can still significantly contribute to studies relating to past tropical seawater temperatures, latitudinal scale ocean current shifts and South Asian Monsoon dynamics. (C) 2020 Elsevier B.V. All rights reserved.

Studies of ancient sea levels provide insights into the mechanisms and rates of sea level changes due to tectonic processes (e.g., ocean crust production) and climatic variations (e.g., insolation due to Earth's orbital changes and atmospheric CO2). Global mean sea level (GMSL) changes since the Middle Eocene (ca. 48 million years ago [Ma]) have been primarily driven by ice volume changes paced on astronomical timescales (2400, 1200, 95/125, 41, and 19/23 thousand years [kyr]), modulated by changes in atmospheric CO2. During peak warm intervals (e.g., Early Eocene Climatic Optimum 56-48 Ma and the early Late Cretaceous ca. 100-80 Ma), atmospheric CO2 was high and Earth was more than 5 degrees C warmer and mostly ice-free, contributing similar to 66 m of GMSL rise from ice alone. However, even in the warmest times (e.g., Early Eocene, ca 50 Ma), growth and decay of small ice sheets (<25 m sea level equivalent) likely drove sea level changes that inundated continents and controlled the record of shallow-water deposits. Ice sheets were confined to the interior of Antarctica prior to the Oligocene and first reached the Antarctic coast at 34 Ma, with the lowest sea levels -20 +/- 10 m relative to modern GMSL. Following a near ice-free Miocene Climatic Optimum (17-13.8 Ma), a permanent East Antarctic Ice Sheet (EAIS) developed in the Middle Miocene (ca. 13.8 Ma). During the Pliocene (4-3 Ma), CO2 was similar to 2020 CE (Common Era) and sea levels stood similar to 22 +/- 10 m above present, requiring significant loss of the Greenland Ice Sheet (similar to 7 m of sea level), West Antarctic Ice Sheet (similar to 5 m after isostatic compensation), and vulnerable portions of the EAIS. The small Northern Hemisphere ice sheets of the Eocene to Pliocene expanded into continental scale in the Quaternary (past 2.55 million years). Sea level reached its lowest point (similar to 130 m below present) during the Last Glacial Maximum (ca. 27-20 thousand years before 1950 [ka]), episodically rose during the deglaciation (ca. 20-11 ka) at rates that at times were in excess of 47 mm yr(-1) (vs. modern rates of 3.2 mm yr(-1)), and progressively slowed during the Early to Middle Holocene from ca. 11 ka until similar to 4 ka. During the Late Holocene (last 4.2 kyr, including the CE), GMSL only exhibited multi-centennial variability of +/- 0.1 m. The modern episode of GMSL rise began in the late nineteenth century, with most of the twentieth century rise attributable to global warming and ice melt. Under moderate emissions scenarios, GMSL is likely to rise 0.4-1.0 m in this century, with ancient analogs suggesting a longer term (centennial to millennial scale) equilibrium rise of similar to 10 m. Under higher emissions scenarios, twenty-first century GMSL will rise greater than 2 m, and in the long term, tens of meters cannot be excluded.