In the North Atlantic, cold, relatively salty water sinks in the icy Labrador and Greenland seas, forming North Atlantic Deep Water (NADW). This circulates through the global ocean, driving ocean overturning and global heat transport and, thus, impacting global climate. As one of the most climatically sensitive regions on Earth,...
Modern upwelling conditions and corresponding oceanographic properties are investigated and reconstructed for the Late Quaternary. The oceanographic conditions considered influence diatom ecology and the record of fossil diatom frustules in the sediments.
Diatoms from modern sediments are evaluated as paleoceanographic proxies and transfer functions (TFs) are calibrated using the Imbrie...
Ocean Drilling Program (ODP) Leg 138 was designed to study the late Neogene paleoceanography of the equatorial Pacific Ocean at time scales of thousands to millions of years. Crucial to this objective was the acquisition of continuous, high-resolution sedimentary records. It is well known that between successive advanced piston corer...
The primary objective of Leg 138 was to provide detailed information about the ocean's response to global climate change
during the Neogene. Two north south transects were drilled (95° and 110°W) within the region of equatorial divergence driven
upwelling (and thus high accumulation rates and resolution) and spanning the major...
Northeast Pacific Ocean sediments were analyzed to determine the past
relationship between northeast Pacific sea surface conditions and the climate on the
adjacent continent, the Pacific Northwest of North America. Studies of modern
ocean-atmosphere interactions demonstrate the significant effect sea surface conditions
and atmospheric circulation in the Northeast Pacific Ocean...
High-resolution records of δ¹⁸0 and relative abundances of planktonic foraminifers were generated for ODP Leg 138 Site 846 for the past 800 k.y., with an average sampling interval of 3.6 k.y. The time scale was constructed by correlating the benthic δ¹⁸0 record to the SPECMAP and ODP Site 677 δ¹⁸0...
Paleoclimate records from glacial Indian and Pacific oceans sediments document millennial-scale fluctuations of subsurface dissolved oxygen levels and denitrification coherent with North Atlantic temperature oscillations. Yet the mechanism of this teleconnection between the remote ocean basins remains elusive. Here we present model simulations of the oxygen and nitrogen cycles that...
Marine sediment core OC1706B-02J ( 46° 15.4178 N, 125° 42.4543 W, at water depth 2263m), was collected on the lower continental slope near the base of the Willapa Canyon. It is a rapidly accumulating site (~30cm/kyr) located near the thrust front of the Cascadia Subduction Zone. The site is also...
Recent works have investigated use of the hydrogen isotopic composition of C₃₇ alkenones (δD[subscript K37s]), lipid biomarkers of certain haptophyte microalgae, as an independent paleosalinity proxy. I discuss herein the factors impeding such an application and identify the potential alternative use of δD[subscript K37s] measurements as a proxy for non-thermal,...
This dissertation explores one overarching question relevant to the
paleoclimate of the latest Pleistocene glacial cycle (approximately the last
130,000 years): “How did spatial and temporal evolution of ocean
temperature, both at the surface and interior, relate to other parts of the
climate system in the late Pleistocene?” Results from...
Sediments of the central Chile margin record changes in ocean circulation and
continental erosion associated with large–scale climate change. Here Antarctic–
influenced Southern Ocean currents flow equatorward, forming a link between the high–
and low–latitude oceans. Part of this link, Antarctic Intermediate Water, is an important
conduit that ventilates South...
The Global Overturning Circulation (GOC) is a major component of the global climate system. Understanding its behavior is pertinent to our prediction of climate change in the future. The lack of long-term observations of GOC in the modern instrumental era necessitates studies of GOC using paleoceanographic records. Of great interest...
Westward transport of water vapor across the Panama Isthmus helps to
maintain the salinity contrast between the Atlantic and Pacific Oceans, important in
thermohaline circulation and global climate. Relatively low sea-surface salinities and a
strong, shallow pycnocline in the eastern Pacific warm pool (EPWP) region near
Central America reflect high...
The distribution of barite (BaSO₄) in marine sediments has long been studied as a proxy for paleoproductivity. While pure barite is known to be a stable mineral in oxic sediments, it is also known that variations in the Sr/Ba ratio influence its solubility and liability during early diagenesis. To extract...
Marine sediments exceptionally rich in organic carbon, known as black shales, occur globally but intermittently in well correlated Cretaceous successions. The presence of black shales indicates that sporadic, ocean-wide interruption of normal respiration of marine organic matter during oxygen-deficient conditions has occurred. Submarine volcanism on a massive scale, related to...
Methane derived authigenic carbonate (MDAC) precipitation occurs within marine sediments as a byproduct of the microbial anaerobic oxidation of methane (AOM). While these carbonates form in chemical and isotopic equilibrium with the fluids from which they precipitate, burial diagenesis and recrystallization can overprint these signals. Plane polarized light (PPL) and...
This thesis describes the development of a rare earth element (REE) proxy for paleoceanographic studies of climate change. This work was done in three stages with the goal: (1) To develop a cleaning method that overcomes the problems of REE readsorption; (2) To measure pore water REEs for evaluation of...
The Cretaceous was a period of extreme climatic conditions accompanied
by major perturbations in ocean-atmosphere biogeochemical cycles. One of the
most intriguing features is the sporadic interruption of normal marine pelagic
sediment deposition by organic rich sediments deposited during oxygen-deficient
conditions (ocean anoxic events OAEs). A current model for the...
Ocean circulation is an important component in Earth's climate system. Predicting future climate and circulation changes requires an improved understanding of the past relationship between climate and ocean currents. The neodymium isotope composition (εNd) of water masses is frequently used as a quasi-conservative tracer to reconstruct ocean circulation. The current...
Throughout the Holocene, appreciable changes in bathymetry are hypothesized to have resulted in large changes to tidal datums in coastal and estuarine areas. An understanding of tidal change is an important contribution to the knowledge of relative historical sea-level change and future coastal planning. To test this hypothesis, the Advanced...
Deep-sea bamboo coral (Isidella sp.) SE000901A from the southern Oregon coast (water depth 1048m) provides a high-resolution record of variability of North Pacific Intermediate Water (NPIW) and carbon rain to the sea floor, related to coastal upwelling, from 1808 to 2000AD. Counting of annual layers in magnesium to calcium (Mg/Ca)...
Many trace elements (e.g., Zn, Cd, Mo) are essential phytoplankton micronutrients, making them crucial to the marine ecosystem and ultimately the carbon cycle. Because of this association trace metals are also utilized in paleoceanographic studies (e.g., Mo, Cd). However, not much is known about what controls the cycling of these...
Planktonic foraminiferal faunas of the southeast Pacific indicate that sea surface temperatures (SST) have
varied by as much as 8–10°C in the Peru Current, and by ~5–7°C along the equator, over the past 150,000 years.
Changes in SST at times such as the Last Glacial Maximum reflect incursion of high-latitude...
We present a new hypothesis to explain the millennial-scale temperature variability recorded in ice cores known as Dansgaard-Oeschger (DO) cycles. We propose that an ice shelf acted in concert with sea ice to set the slow and fast timescales of the DO cycle, respectively. The abrupt warming at the onset...
An interlaboratory study of Mg/Ca and Sr/Ca ratios in three commercially available carbonate reference
materials (BAM RS3, CMSI 1767, and ECRM 752-1) was performed with the participation of
25 laboratories that determine foraminiferal Mg/Ca ratios worldwide. These reference materials containing
Mg/Ca in the range of foraminiferal calcite (0.8 mmol/mol to...
Factor analysis of radiolarian species from the tops of 34 gravity
cores in the area extending from 5°N to 45°N, 95°W to 155°W, yields
five factor assemblages which are related to the present surface circulation:
1) a Pacific Equatorial Water assemblage; 2) a California
Current assemblage; 3) a North Equatorial...
The primary Mg/Ca ratio of foraminiferal shells is a potentially valuable paleoproxy for sea surface
temperature (SST) reconstructions. However, the reliable extraction of this ratio from sedimentary calcite
assumes that we can overcome artifacts related to foraminiferal ecology and partial dissolution, as well as
contamination by secondary calcite and clay....
Stable oxygen and stable carbon isotopes of foraminifera are widely applied in paleoceanographic reconstructions. Oxygen and carbon isotopes are typically measured using pooled sample analysis (i.e., the combination of several shells) or single-shell analysis (typically restricted to heavier shells that weigh above 10 µg). With pooled sample analysis, where many...
Sedimentary sections recovered during the Deep Sea Drilling Project and the Ocean
Drilling Program provide the opportunity to study the evolution of Neogene climate at high
resolution overtime periods spanning millions of years. Two components of the paleodlimatic
system, eastern equatorial Pacific carbonate sedimentation and global ice volume, were
examined...
The mass accumulation rates of sedimentary components (carbonate, organic carbon, opal, barite, reactive phosphate, iron, terrigenous minerals, etc.) are used in many paleoceanographic reconstructions to learn about temporal and spatial changes in surficial Earth processes including wind stress and direction, oceanic circulation, weathering rates, marine productivity and ecosystem structure, climate...
A three-dimensional, process-based model of the ocean’s carbon and nitrogen cycles, including
13C and 15N isotopes, is used to explore effects of idealized changes in the soft-tissue biological pump. Results
are presented from one preindustrial control run (piCtrl) and six simulations of the Last Glacial Maximum
(LGM) with increasing values...
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paleoceanography and at the
heart of the problem to explain the low atmospheric CO2 concentration, which was ~190
Glacial periods exhibit abrupt Dansgaard-Oeschger (DO) climatic oscillations that are thought to be linked to instabilities in the Atlantic meridional overturning circulation (AMOC). Great uncertainty remains regarding the dynamics of the DO cycle, as well as controls on the timing and duration of individual events. Using ice core data we...
The rise in atmospheric CO₂ during Heinrich Stadial 1 (HS1; 14.5–17.5 kyr B.P.) may have been driven by the release of carbon from the abyssal ocean. Model simulations suggest that wind-driven upwelling in the Southern Ocean can liberate ¹³C-depleted carbon from the abyss, causing atmospheric CO₂ to increase and the δ¹³C...
Much uncertainty exists about the state of the oceanic and atmospheric circulation in the tropical Pacific over the last glacial cycle. Studies have been hampered by the fact that sediment cores suitable for study were concentrated in the western and eastern parts of the tropical Pacific, with little information from...
Water mass exchange between the Arctic Ocean and the Norwegian-Greenland Seas has played an important role for the Atlantic thermohaline circulation and Northern Hemisphere climate. We reconstruct past water mass mixing and erosional inputs from the radiogenic isotope compositions of neodymium (Nd), lead (Pb), and strontium (Sr) at Ocean Drilling...
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PUBLICATIONS
Paleoceanography
RESEARCH ARTICLE
10.1002/2015PA002843
Key Points:
• Yermak
Assessing impacts of future anthropogenic carbon emissions is currently impeded by uncertainties in our knowledge of equilibrium climate sensitivity to atmospheric carbon dioxide doubling. Previous studies suggest 3 K as best estimate, 2–4.5 K as the 66% probability range, and non-zero probabilities for much higher values, the latter implying a...
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. Schmittner, A. J. Weaver, J Climate 17, 2033 (Jun, 2004). 257
48. W. B. Curry, D. W. Oppo, Paleoceanography
Reconstructions of the El Niño–Southern Oscillation (ENSO) are often created using the oxygen isotopic ratio in tropical coral skeletons (δ¹⁸O). However, coral δ¹⁸O can be difficult to interpret quantitatively, as it reflects changes in both temperature and the δ¹⁸O value of seawater. Small-scale (10–100 km) processes affecting local temperature and...
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variability in a regional ocean modeling framework: Implications for coral proxy records
Paleoceanography
Ocean Drilling Program (ODP) Leg 202 has opened a new window
into understanding late Paleogene and Neogene global environmental
change by providing high-quality sediment sequences from a previously
unsampled region, the eastern South Pacific. Eleven sites (1232–
1242) that record variations on timescales ranging from decades to tens
of millions...
Here we present the first downcore results for a new paleoproxy, the Mn/Ca ratio of foraminiferal calcite, applied to sediment accumulated in the extreme Eastern Tropical North Pacific (ETNP) over the last 30,000 years. The Mn/Ca results are compared to oxygen isotopes and sea surface temperature calculated from Mg/Ca. We...
Sea surface temperatures (SST) and inorganic continental input over the last 25,000 years (25 ka) are reconstructed in the far eastern equatorial Pacific (EEP) based on three cores stretching from the equatorial front (~0.01°N, ME0005-24JC) into the cold tongue region (~3.6°S; TR163-31P and V19-30). We revisit previously published alkenone-derived SST...
We examine the 0–100 Ma paleoceanographic record retained in pelagic clay from the South Pacific Gyre (SPG) by analyzing 47 major, trace, and rare earth elements in bulk sediment in 206 samples from seven sites drilled during Integrated Ocean Drilling Program Expedition 329. We use multivariate statistical analyses (Q-mode factor analysis...
The production of carbon and export to deep ocean sediments is linked to carbon partitioning between the ocean and atmosphere and is a key driver of climate change over the glacial-interglacial transition. Yet conflicting reconstructions create barriers to understanding changes to the carbon system over this important climate transition. Production...
To investigate the dynamics of the Atlantic meridional overturning circulation (AMOC) on
timescales longer than the observational records, model-data comparisons of past AMOC variability
are imperative. However, this remains challenging because of dissimilarities between different proxy-based
AMOC tracers and the difficulty of comparing these to model output. We present an...
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overturning circulation: Toward a more direct model‐data comparison.
Paleoceanography, 30(2), 95-117. doi
The sensitivity of the tropics to climate change, particularly the amplitude of glacial‐to‐interglacial changes in sea surface temperature (SST), is one of the great controversies in paleoclimatology. Here we reassess faunal estimates of ice age SSTs, focusing on the problem of no‐analog planktonic foraminiferal assemblages in the equatorial oceans that...
A three-dimensional, process-based model of the ocean’s carbon and nitrogen cycles, including
13C and 15N isotopes, is used to explore effects of idealized changes in the soft-tissue biological pump. Results
are presented from one preindustrial control run (piCtrl) and six simulations of the Last Glacial Maximum
(LGM) with increasing values...
Full Text:
- SchmittnerComplementaryConstraintsCarbonSupportingInfo.doc
1
Paleoceanography
Supporting Information for
Complementary Constraints from
Reconstructions of the El Niño–Southern Oscillation (ENSO) are often created using the oxygen isotopic ratio in tropical coral skeletons (δ¹⁸O). However, coral δ¹⁸O can be difficult to interpret quantitatively, as it reflects changes in both temperature and the δ¹⁸O value of seawater. Small-scale (10–100 km) processes affecting local temperature and...
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Paleoceanography
Supporting Information for
Characterizing Seawater Oxygen Isotopic Variability in a Regional
Changes in the field of publishing and in scholarly communication have been impacting the distribution of scientific knowledge for years. The economics of publishing continues to have an impact on subscribers’ ability to maintain access and therefore the readership of established publications may diminish or look for legitimate alternatives to...
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