Geology topics

Harry J. Dowsett

Publications and source records attributed to Harry J. Dowsett.

At least 19 recordsLinked to original sources

USGS2026

Correcting a systematic bias in an ocean drilling project site 882 alkenone sea surface temperature record

Reconstructions of sea surface temperature (SST) in the geologic record are fundamental to our understanding of Earth's climate history and the evaluation of Earth's climate sensitivity to greenhouse gas forcing. SSTs are reconstructed with a variety of methods, including alkenone biomarker lipids produced by certain coccolithophore algae. One such alkenone SST reconstruction from the subpolar northwest Pacific Ocean Drilling Program (ODP) Site 882 (50.21° N, 167.35° E, 3244 m water depth) has played a large role in shaping the paleoclimate science community's view of global climate warmth during the Late Pliocene (3.6–2.6 million years ago) and the subsequent cooling that characterized the intensification of Northern Hemisphere Glaciation (Haug, 1995; Haug et al., 2005; Martínez-Garcia et al., 2010). First, we have found that the values reported in the PANGAEA archive for this ODP Site 882 alkenone dataset were inaccurately reported as U K' 37 values when they are instead U K 37 ( https://doi.org/10.1594/PANGAEA.315092 , Haug and Sarnthein, 2005). This error in the archived data table resulted in the incorporation of inaccurate absolute SST estimates by several studies that applied U K' 37 calibrations to this ODP Site 882 dataset (e.g., Brennan et al., 2022; Clark et al., 2024, 2025; Tierney et al., 2019, 2025b). Second, using other published data from ODP Site 882 (Studer et al., 2012) and nearby Site 883 (51.11° N, 167.46° E, 2384 m water depth; Herbert et al., 2016; Novak et al., 2024), we show that the original Haug (1995) alkenone SST record at ODP Site 882 systematically reports an amplified range of absolute SST values compared to the more recently generated data. This observation is consistent with the known concentration-dependent biases of the gas chromatography chemical ionization mass spectrometry (GC-CI-MS) analytical method used by the original ODP Site 882 study (Chaler et al., 2000, 2003; Haug, 1995; Hefter, 2008; Rosell-Mele et al., 1995). These concentration-dependent analytical biases complicate applying a uniform correction to the entire Haug (1995) dataset. However, we are able to leverage the published datasets to propose a correction and quantification of uncertainty for a subset of the Haug (1995) dataset measured at similar on-column analyte abundance. For these samples, we find an average analytical uncertainty equivalent to ±2.05 °C , which is greater than and in addition to the typical ±1.4 °C 1 σ prediction uncertainty of the U K' 37 sea surface temperature proxy. We then discuss the implications of the corrected dataset for our understanding of late Neogene and Quaternary climate in the Kuroshio Extension region.

Climate of the Past↗

USGS2026

Pliocene (Piacenzian) planktic foraminiferal biogeography: Insights into how planktic biogeography is linked to climate and socioeconomic impacts on marine ecosystems

The Piacenzian Age (3.60–2.58 Ma) of the Pliocene Epoch was characterized by globally warmer climates, higher sea levels, and atmospheric CO 2 similar to present. Utilizing a robust dataset of 2,101 samples and over 637,000 foraminifer specimens from 77 deep-sea core sites worldwide, we document planktic foraminifer biogeography and biodiversity during the mid-Piacenzian Warm Period (mPWP). Cluster analysis and multidimensional scaling reveal five major bioregions: tropical, warm subtropical, transitional, polar, and a distinct North Atlantic polar bioregion. Each bioregion was dominated by characteristic species with well-established temperature preferences. Analyses demonstrate higher species richness and evenness in low and mid-latitudes, with increased diversity associated with periods of climatic warming and poleward expansion of warm water assemblages. The long-term stability of biogeographic patterns underscores ecological conservatism but also highlights potential vulnerability to rapid anthropogenic climate change. Our findings emphasize the critical role of planktic foraminifers in reconstructing past ocean conditions and offer valuable insights into links between planktic biogeography, climate, and socioeconomic impacts on marine ecosystems. This work advances our understanding of marine ecosystem responses to climate extremes and provides a foundation for future regional and temporal analyses of planktic foraminifer biogeography under global change scenarios.

Frontiers in Earth Science↗

USGS2026

Early Pliocene (Zanclean) sea surface temperature for PlioMIP3

Paleoclimate researchers have been comparing Pliocene environmental data to paleoclimate model results since the 1980s. The Pliocene Model Intercomparison Project (PlioMIP) began in 2008 with a focus on the Late Pliocene. Here we assess the availability and utility of sea surface temperature (SST) data for verification of Pliocene Model Intercomparison Project (PlioMIP3) Early Pliocene (Zanclean) experiments. We analyze published data in terms of quantity and spatial distribution. Only SST estimates derived using alkenone paleo thermometry are reported, and all estimates are based upon the same temperature calibration. Sea surface temperature data are selected from within three distinct time intervals: The early Zanclean 5.3 Ma – 4.2 Ma time slab, and two time slices within the early Zanclean, chosen by PlioMIP3 at 4.870 Ma and 4.474 Ma. Results show the early Zanclean time slab contains 2055 individual estimates. Approximately ∼ 80% of these estimates come from Sites 609, 642, 846, 847, 882, 907, and 1146. There are 17 sites with a total of 42 estimates within the 4.474 Ma ±10 kyr time slice, and 15 sites with a total of 47 data points within the 4.870 Ma ±10 kyr interval. The sparse spatial and temporal distribution of Zanclean data, relative to the data available for the mid Piacenzian, makes point-by-point data model comparison suspect. We suggest interpreting model output against lower resolution long term trends in proxy data, and comparison of models through temperature gradients, may be the most useful application of currently available data. Integrating Zanclean age coastal plain sequences within data model comparison schemes, for increased understanding of regional climate impacts, also holds great potential.

Global and Planetary Change↗

USGS2025

Calcareous nannofossil biostratigraphy and floral response to environmental changes recorded in the Pliocene Yorktown Formation, southeastern Virginia, USA

The Pliocene Yorktown Formation, deposited on the U.S. Mid-Atlantic Coastal Plain, has played an important role in advancing our knowledge of Pliocene paleoclimate. To refine the age and paleoenvironment of the Yorktown Formation, we analyzed the calcareous nannofossil assemblage and compared it with variations in lithology and calculated sea surface temperature (SST) from previous studies. The Yorktown Formation in the studied sections consists of, in ascending order, the Sunken Meadow, Rushmere, Morgarts Beach, and Moore House members. Sediment samples were collected from these units and analyzed for calcareous nannoplankton assemblages. The last occurrences of both Reticulofenestra pseudoumbilicus (3.82 Ma) and Sphenolithus spp. (3.61 Ma) were recognized within the Sunken Meadow Member. Discoaster tamalis and Discoaster surculus sporadically occurred within the Rushmere Member, but no specimens of the genus Sphenolithus were recorded, suggesting that this unit was deposited sometime between 3.61–2.76Ma. Rare occurrences of the genus Discoaster made it difficult to constrain the age of the Morgarts Beach and Moore House members, but they are most likely deposited before re-entrance of small Gephyrocapsa (ca. 2.5 Ma), supporting previous age estimates based on planktic foraminiferal biostratigraphy and variation in alkenone-based sea-surface temperature estimates. The abrupt decline of both cold-water species ( Coccolithus pelagicus ) and coastal species ( Helicosphaera spp.) is associated with a rise in SST within the Rushmere Member just below the Morgarts Beach Member, and it may reflect a rapid transgression following the global sea-level low stand associated with Marine Isotope Stage (MIS)M2.

Virginia↗

USGS2025

The conundrum of taxonomic uniformitarianism in planktic foraminifera

Planktic foraminiferal species distributions in the modern ocean track environmental features like sea surface temperature (SST). Species shift their distributions as the marine environment changes, providing an analogue for past behaviour. Stationarity of species' ecological tolerances is therefore a first-order assumption of all palaeoenvironmental reconstructions based upon modern analogue methods. In this paper we test the hypothesis that planktic foraminifer species temperature preferences did not change between the Late Pliocene and present, using a dataset which contains faunal abundance data and alkenone palaeotemperature data from the same samples. Our dataset includes 463 samples from 29 localities. Pliocene relative abundances of four taxa ( Globigerina bulloides , Globigerinita glutinata , Neogloboquadrina pachyderma and Neogloboquadrina incompta ) are compared to SST estimates of the same age derived using the alkenone unsaturation ratio ( U K ' 37 ) palaeothermometer. Core-top abundances of the same taxa were compared to pre-industrial SST. Our Pliocene data are generally concordant with previous work. Pliocene SST responses and those of the pre-industrial are similar, supporting the hypothesis that temperature preferences of planktic foraminifera have been relatively stable since the Late Pliocene. This documentation of stationarity of planktic foraminiferal species' temperature tolerances is helpful in identifying situations where environmental variables other than temperature (e.g. salinity or productivity) exhibit a first-order control on faunal diversity. Our results support the notion of taxonomic uniformitarianism and therefore provide additional confidence in using planktic foraminifera to evaluate both regional and global climate change.

Palaeontology↗

USGS2025

Molluscan isotope sclerochronology in marine palaeoclimatology: Taxa, technique and timespan issues

Study of the accretionary biomineralised hardparts of organisms (sclerochronology) can make a useful contribution to palaeoclimatology. Ontogenetic sequences of isotopic data (δ 18 O and Δ 47 values) from the shells of marine molluscs are a source of information on seasonal sea-surface temperatures that can be used for detailed and rigorous evaluation of the outputs of numerical climate models. In situations where there is significant seasonality, and where shell preservation is adequate, accurate information about winter and summer surface temperature can be obtained from shallow-water benthic forms (bivalves and gastropods), in particular the early ontogeny of fast-growing species. Accurate information about winter surface temperature can also be obtained from individuals that lived at mid-shelf depths (20–40 m), but summer seafloor values from these need upward adjustment to derive a plausible surface temperature if thermal stratification of the water column occurs in this season. Ontogenetic δ 18 O profiles from planktonic pteropod gastropods are a potential source of insight into seasonal surface temperatures in the ocean basins; these organisms merit investigation for provision of information to complement shelf data. Temperature profiles constructed from shell δ 18 O require an estimate of the δ 18 O value of ambient seawater, which can be derived by back-calculation from the Δ 47 -temperature supplied by the same shell material. Alternatively, through appropriate sampling and data processing, seasonal temperatures can be obtained directly from Δ 47 profiles. Climate parameters are defined in terms of the mean state over a period of 30 consecutive years, a statistic (e.g., for seasonal temperatures) which can be derived from the long isotopic temperature records obtainable from bivalve species that live for many tens or hundreds of years. Efforts should be made to acquire such records, especially averaged data from crossdated shells, to specify climate parameters for precise times in the past. Information for precise times would be of particular value for icehouse intervals like the late Cenozoic, characterised by high frequency (high amplitude) climate fluctuation. Short records from non-crossdated shells can nevertheless provide useful insights into climate, particularly if a large dataset is obtained, supplying a reliable picture of the mean state and range of variation in climate parameters over the interval represented by the shells.

Quaternary Science Reviews↗

USGS2025

The stratigraphic record of the mid-Piacenzian warm period on the Atlantic Coastal Plain

Anthropogenic climate change is an existential threat to our planet, impacting everything from the delicate balance of ecosystems to the availability of vital resources. Coastal regions, particularly vulnerable to the impacts of climate change due to rising sea levels and changing weather patterns, are experiencing increased erosion, flooding, and habitat loss. Understanding how coastal regions responded to past warming is crucial for developing effective adaptation and mitigation strategies. One past interval commonly used to examine and compare with climate model projections of near future conditions is the mid-Piacenzian Warm Period (MPWP) which occurred between*3.3 and 3.0 Ma. Here we review the stratigraphy of Atlantic Coastal Plain (ACP) sediments to determine the stratigraphic position of the MPWP by evaluating ages based upon existing and new planktic foraminifer occurrence data calibrated to the current geologic time scale (GTS2020). We identify geologic formations representing pre-, syn-, and post-MPWP environments. The Sunken Meadow Member of the Yorktown Formation in Virginia and North Carolina and the Wabasso beds in the subsurface of Georgia and Florida both fall within Planktic Foraminiferal Zone PL1 and represent pre-MPWP Pliocene deposits. Parts of the Yorktown Formation in southeastern Virginia and northern North Carolina, the Duplin Formation in North Carolina and South Carolina, and the Raysor Formation in South Carolina and Georgia, fall within Planktic Foraminiferal Zone PL3 and were deposited following a major regression associated with a global drop in sea level during Marine Isotope Stage (MIS) M2 and represent syn-MPWP deposits. Representing the immediately post-MPWP climate conditions (Planktic Foraminiferal Zone PL5) are the Chowan River, Bear Bluff, and Cypresshead Formations. This work provides a record of the MPWP from Georgia to Virginia and provides a stratigraphic framework within which the impacts of a profound global warming on the east coast of the United States can be assessed.

Georgia, North Carolina, South Carolina, Virginia↗

USGS2024

Isotopic evidence against North Pacific Deep Water formation during late Pliocene warmth

Several modelling and observational studies suggest deep water formation in the subpolar North Pacific as a possible alternative mode of thermohaline circulation that occurred in the warm Pliocene, a time when global atmospheric partial pressure of carbon dioxide was like the modern atmosphere (~400 ppm). We test this hypothesis by measuring the δ 13 C of the benthic foraminifer Cibicidoides wuellerstorfi collected from northernmost Pacific mid-Piacenzian Warm Period (3.264–3.025 Myr ago) sediments. The data reveal progressively more isotopically negative dissolved inorganic carbon along a northward Equator-to-pole transect, the opposite of the expected Pliocene Pacific meridional overturning circulation signal. C. wuellerstorfi δ 13 C is also often more positive at the deeper Ocean Drilling Program (ODP) site 887 compared with the shallower ODP site 883, suggesting ‘bottom-up’ ventilation of the deep Pacific Ocean. We then present alkenone sea surface temperature and export-productivity data from ODP site 883, which suggest that late Pliocene subarctic North Pacific carbonate sedimentation was, at least in part, probably due to higher coccolithophore export production, rather than North Pacific Deep Water formation as previously argued. Therefore, we suggest it is unlikely that North Pacific Deep Water formation occurred in the mid-Piacenzian Warm Period, although a shallower overturning cell cannot be ruled out.

Nature Geoscience↗

USGS2024

Modeling the mid-Piacenzian warm climate using the water isotope-enabled Community Earth System Model (iCESM1.2-ITPCAS)

The mid-Piacenzian Warm Period (MPWP, ~ 3.264–3.025 Ma) is the most recent example of a persistently warmer climate in equilibrium with atmospheric CO 2 concentrations similar to today. Towards studying patterns and dynamics of a warming climate the MPWP is often compared to today. Following the Pliocene Model Intercomparison Project, Phase 2 (PlioMIP2) protocol we prepare a water isotope-enabled Community Earth System Model (iCESM1.2) simulation that is warmer and wetter than the PlioMIP2 multi-model ensemble (MME). While our simulation resembles PlioMIP2 MME in many aspects we find added insights. (1) Considerable warmth at high latitudes exceeds previous simulations. Polar amplification (PA) is comparable to proxies, enabled by iCESM1.2’s high climate sensitivity and a distinct method of ocean initialization. (2) Major driver of warmth is the downward component of clear-sky surface long-wave radiation (Δ T rlds_clearsky ). (3) In iCESM1.2 modulated dominance of dynamic (δDY) processes causes different low-latitude (~ 30 S°–10°N) precipitation response than the PlioMIP2 MME, where thermodynamic processes (δTH) dominate. (4) Modulated local condensation leads to lower δ18O p across tropical Indian Ocean and surrounding Asian-African-Australian monsoon regions. (5) We find contrasting changes in tropical atmospheric circulations (Hadley and Walker cells). Anomalous regional meridional (zonal) circulation, forced by changes in tropical-subtropical (tropical) diabatic processes, presents a more comprehensive perspective than explaining weakened and expanded Hadley circulation (strengthened and westward-shifted Walker circulation) via static stability. (6) Enhanced Atlantic meridional overturning circulation owes to a closed Bering Strait.

Climate Dynamics↗

USGS2024

Decomposition of physical processes controlling EASM precipitation changes during the mid-Piacenzian: New insights into data–model integration

The mid-Piacenzian warm period (MPWP, ~3.264–3.025 Ma) has gained widespread interest due to its partial analogy with future climate. However, quantitative data–model comparison of East Asian Summer Monsoon (EASM) precipitation during the MPWP is relatively rare, especially due to problems in decoding the imprint of physical processes to climate signals in the records. In this study, pollen-based precipitation records are reconstructed and compared to the multi-model ensemble mean of the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2). We find spatially consistent precipitation increase in most simulations but a spatially divergent change in MPWP records. We reconcile proxy data and simulation by decomposing physical processes that control precipitation. Our results 1) reveal thermodynamic control of an overall enhancement of EASM precipitation and 2) highlight a distinct control of thermodynamic and dynamical processes on increases of tropical and subtropical EASM precipitation, reflecting the two pathways of water vapor supply that enhance EASM precipitation, respectively.

npj Climate and Atmospheric Science↗

USGS2024

Benthic foraminiferal community changes across the Miocene climatic optimum Identified by SHEBI analysis (SHE analysis for biozone identification), Calvert Cliffs, Maryland, USA

The Calvert Cliffs, MD, an iconic section of Middle Miocene strata, have been well studied both paleontologically and stratigraphically for over a century. However, few studies of the Calvert Cliffs have looked at the benthic foraminifera. This study uses SHEBI analysis (SHE analysis for biozone identification) of benthic foraminiferal assemblages to analyze community change in the Calvert and Choptank formations of the Calvert Cliffs deposited during the Miocene Climatic Optimum (MCO; 17–14.8 Ma) and the Middle Miocene Climate Transition (MMCT; 14.8–13.8 Ma). SHE analysis differs from traditional analytical methods by defining communities based on changes in diversity rather than the relative abundance of individual species. This study uses SHE analysis on a composite section of benthic foraminiferal assemblages from three vertical transects that span the MCO and MMCT. Two communities were identified from the studied strata. Community 1 was deposited during the MCO and includes incised valley fill (IVF), transgressive system tract (TST), and highstand system tract (HST) deposits. Community 2, deposited during the MMCT, is composed of samples from TST, HST, IVF, and another HST. The assemblages of community 1 are representative of an inner to middle shelf environment whereas those of community 2 are representative of an inner shelf environment. The two foraminiferal communities differentiated by SHE analysis indicate a high relative sea level in the Salisbury Embayment during the warm MCO followed by a decrease in sea level during the subsequent cooler MMCT.

Maryland↗

USGS2024

What the cliffs near America’s earliest settlements tell us about climate change

Climate change is a big problem for natural habitats, people, and the systems that support society, including roads, water supply, electrical grids, and phone and internet connections. It’s an important theme in politics, economics, and culture. Scientists make computer models to show what the climate might be like in the future, and it looks very different from what we are used to. Scientists can also learn about the future climate by looking at geological records from the past. About 3 million years ago, most of the US east coast was under water. Sediments that collected on the ocean floor show what the ocean environment was like back then. Some of these sediments are now exposed above water as bluffs along the James River near colonial Jamestown in southeastern Virginia, and they hold many clues as to what Earth may look like in the future.

Virginia↗

USGS2024

Pliocene Model Intercomparison Project Phase 3 (PlioMIP3) – Science plan and experimental design

The Pliocene Model Intercomparison Project (PlioMIP) was initiated in 2008. Over two phases PlioMIP has helped co-ordinate the experimental design and publication strategy of the community, which has included an increasing number of climate models and modelling groups from around the world. It has engaged with palaeoenvironmental scientists to foster new data synthesis supporting the construction of new model boundary conditions, as well as to facilitate new data-model comparisons. The work has advanced our understanding of Pliocene climates and environments, enhanced our knowledge regarding the ability of complex climate and Earth System models to accurately simulate climate change, and helped to refine our estimates of how sensitive the climate system is to forcing conditions. In this community protocol paper, we outline the scientific plan for PlioMIP Phase 3 (PlioMIP3). This plan provides the required guidance to participating modelling groups from around the world to successfully set up and perform PlioMIP3 climate model experiments. The project is open to new participants from the scientific community (both from the climate modelling and geosciences communities). In PlioMIP3, we retain the PlioMIP2 Core experiments ( Eoi 400 , E 280 ) and extend the Core requirements to include either an experiment focussed on the Early Pliocene or an alternative Late Pliocene simulation (or both). These additions (a) allow a comparison of Early and Late Pliocene warm intervals and help build research connections and synergy with the MioMIP (Miocene Model Intercomparison Project - also known as DeepMIP-Miocene) and PlioMioVAR projects (Pliocene-Miocene Variability Working Group), and (b) create an alternative time slice simulation for 3.205 Ma (MIS KM5c) through removal of some of the largest palaeogeographic differences introduced between PlioMIP1 and 2 resulting in minimal land-sea mask variations from the modern. In addition, we present ten optional experiments designed to enhance our assessment of climate sensitivity and to explore the uncertainty in greenhouse gas-related forcing. For the first time, we introduce orbital sensitivity experiments into the science plan, as well as simulations incorporating dynamic vegetation-climate feedbacks and an experiment designed to examine the potential significance of East Antarctic Ice Sheet boundary condition uncertainty. These changes enhance palaeo-to-future scientific connections and enable an exploration of the significance of palaeogeographic uncertainties on climate simulations.

Global and Planeatary Change↗

USGS2024

Formation of vertical columnar seismic structures and seafloor depressions by groundwater discharge in the drowned Miami Terrace platform and overlying deep-water carbonates, southeastern Florida

The presence of vertical cross-formational fluid migration passageways within sedimentary basins can profoundly impact aquifer and reservoir fluid-flow and their identification is fundamental to informing management of subsurface fluid resources (groundwater, oil, gas). In an onshore and offshore southeastern part of Florida, 2D/3D seismic-reflection and bathymetry data document ∼153 vertical columnar structures composed of reflection disruptions up to 790 m in the height and averaging 360 m in diameter, and ∼219 subcircular to circular seafloor depressions up to 1334 m wide. Our study focuses on these features found within the offshore shallow-marine carbonate Miami Terrace platform, which drowned approximately at the end of the middle Miocene, and within overlying Plio-Quaternary deep-water carbonate slope and drift deposits. Most columnar structures are rooted in stratiform aquifers of the Miami Terrace platform and associated with faults or fault intersections produced by Eocene and circa late Miocene tectonics. The columns commonly terminate within the platform or as subcircular depressions along an amalgamated karstic and drowning unconformity at the platform top. The columns typically stretch upwards from a zone of deep karst cavity collapse through the Miami Terrace platform with upward decreasing sag on internal reflections. Following drowning and Plio-Quaternary partial burial of the Miami Terrace platform by deep-water deposits, the subcircular depressions and faults along the platform top were points of origin for a second phase of column growth upward into the deep-water deposits. The continuation of deep platform cavity collapse and column evolution produced pockmarks along paleo-seafloors within the deep-water deposits and at the present-day sea floor. The Plio-Quaternary pockmarks formed at water depths too deep to suggest an origin related to meteoric karst above or near sea level, but rather their formation is suggested to be related to cyclic sea level falls that drove increased groundwater head and density gradients, and seafloor discharge of offshore freshened groundwater sourced from the underlying platform. Plausibly, mixing of freshened groundwater and seawater at the seafloor discharge sites drove dissolution of the host deep-water deposits, which together with erosion by groundwater venting and current scouring formed the pockmarks. Seaward of the Plio-Quaternary seafloor pockmarks, at the late-middle Miocene upper slope of the Miami Terrace platform and along the regional karst/drowning unconformity is a slope-parallel band of ∼189 densely distributed subcircular seafloor depressions with diameters up to 1334 m at water depths up to ∼660 m. It is plausible that along the upper slope, faults and fractures produced by gravity-driven slope instability and possibly tectonics formed a dense network of fluid passageways that promoted upward artesian freshened groundwater flow to sites of discharge where mixing with seawater generated limestone dissolution and the depressions. But tectonic uplift may have forced emersion and initial meteoric sinkhole formation circa late Miocene with later enhancement by freshened groundwater discharge and bottom current erosion.

Florida↗

USGS2024

Revisiting the physical processes controlling the tropical atmospheric circulation changes during the Mid-Piacenzian Warm Period

The Mid-Piacenzian Warm Period (MPWP; 3.0–3.3 Ma), a warm geological period about three million years ago, has been deemed as a good past analog for understanding the current and future climate change. Based on 12 climate model outputs from Pliocene Model Intercomparison Project Phase 2 (PlioMIP2), we investigate tropical atmospheric circulation (TAC) changes under the warm MPWP and associated underlying mechanisms by diagnosing both atmospheric static stability and diabatic processes. Our findings underscore the advantage of analyzing atmospheric diabatic processes in elucidating seasonal variations of TAC compared to static stability assessments. Specifically, by diagnosing alterations in diabatic processes, we achieve a quantitative understanding and explanation the following TAC changes (incl. Strength and edge) during the MPWP: the weakened (annual, DJF, JJA) Northern Hemisphere and (DJF) Southern Hemisphere Hadley circulation (HC), reduced (annual, DJF) Pacific Walker circulation (PWC) and enhanced (annual, JJA) Southern Hemisphere HC and (JJA) PWC, and westward shifted (annual, DJF, JJA) PWC. We further addressed that the increasing bulk subtropical static stability and/or decreasing vertical shear of subtropical zonal wind - two crucial control factors for changes in subtropical baroclinicity - may promote HC widening, and vice versa. Consequently, our study of spatial diabatic heating and cooling, corresponding to upward and downward motions within the TAC, respectively, provides a new perspective for understanding the processes controlling seasonal TAC changes in response to surface warming.

Quaternary International↗

USGS2023

The relative stability of planktic foraminifer thermal preferences over the past 3 million years

Stationarity of species’ ecological tolerances is a first-order assumption of paleoenvironmental reconstruction based upon analog methods. To test this and other assumptions used in quantitative analysis of foraminiferal faunas for paleoceanographic reconstruction, we analyzed paired alkenone unsaturation ratio ( U 37 K ′ )   "> U K ′ 37 ) 37′) sea surface temperature (SST) estimates and relative abundances of planktic foraminifera within Late Pliocene assemblages. We established Pliocene temperature preferences for nine species in the North Atlantic: Dentoglobigerina altispira, Globorotalia menardii, Globoconella puncticulata, Neogloboquadrina atlantica, Neogloboquadrina incompta, Neogloboquadrina pachyderma, Trilobatus sacculifer, Globigerinita glutinata, and Globigerina bulloides. We compared these to the temperature preferences of the same extant species, and in the three cases where the species are now extinct ( Dentoglobigerina altispira, Neogloboquadrina atlantica, and Globoconella puncticulata ), comparisons were made to either the descendant species or other modern species commonly used as analogs. In general, the taxa tested show similar temperature responses in both Late Pliocene and present-day (core-top) distributions. The data from these comparisons are mostly encouraging, supporting past paleoceanographic conclusions, and are otherwise valuable for testing previous taxonomic grouping decisions that are often necessary for interpreting the paleoenvironment based upon Pliocene foraminiferal assemblages.

Geosciences↗

USGS2023

Planktic foraminifera

Planktic foraminifera are single-celled marine organisms that secrete calcium carbonate tests. They live in the ocean's photic zone, and when they die, their tests, each about the size of a grain of sand, collect on the ocean floor. The geographic distribution of planktic foraminifera is mostly governed by the temperature and salinity of the ocean surface, and species assemblages are generally arranged in latitudinal bands from polar to tropical, with more species occupying warmer waters. Their ubiquity in the world's oceans since the Cretaceous Period makes them ideal biostratigraphic markers, and their sensitivity to environmental changes makes them excellent proxies of past ecological, oceanographic and climatic history.

Book chapter↗

USGS2023

Early Pliocene (Zanclean) stratigraphic framework for PRISM5/PlioMIP3 time slices

Global reconstructions of Pliocene climate provide important insights into how the climate system operates under elevated temperatures and atmospheric CO2 levels. These reconstructions have been used extensively in paleoclimate modeling experiments for comparison to simulated conditions, and as boundary conditions.Most previous work focused on the Late Pliocene interval known as the mid Piacenzian Warm Period (mPWP), the interval originally identified by the U.S. Geological Survey Pliocene Research, Interpretation and Synoptic Mapping Project (PRISM) as the PRISM interval or Mid Pliocene Warm Period. The term Mid Pliocene Warm Period is a misnomer due to changes to the geological time scale, and its use should be discontinued. The Pliocene Model Intercomparison Project (PlioMIP), now in its third phase, is expanding to include a focus on the Early Pliocene (Zanclean). PlioMIP3 experiments will allow comparison of environmental and climatic conditions before and after closure of the Central American Seaway (CAS). PlioMIP3 used the annual insolation pattern at the top of the atmosphere to determine time slices in the Zanclean that have orbital configurations that are most similar to modern. Two have been selected by PlioMIP and adopted by PRISM for inclusion in future studies: PRISM5.1 (4.474 Ma) and PRISM5.2 (4.870 Ma). Here we establish the stratigraphic framework for these Early Pliocene time slices and furnish information to help locate these intervals in proxy records of paleoenvironmental data using oxygen isotope stratigraphy, paleomagnetic stratigraphy, biostratigraphy, and biochronology (calibrated planktic foraminifer and calcareous nannofossil events).

Stratigraphy↗