Nicole K Murray

University of Illinois Urbana-Champaign

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Jessica L. Conroy

University of Illinois Urbana-Champaign

Fernando Echeverría

Charles Darwin Foundation

K. M. Cobb

Brown University

Eric C. Grimm

Illinois State Museum

A. R. Muñoz

University of Illinois Urbana-Champaign

Kate O’Brien

Xavier University

Jun Hu

Xiamen University

Aiden I. G. Schore

University of Illinois Urbana-Champaign

David Chillagana

Charles Darwin Foundation

Georgina Falster

Australian National University

Cooperative Institutions

University of Illinois Urbana-Champaign

Charles Darwin Foundation

Charles Darwin University

Georgia Institute of Technology

Illinois State Museum

University of Minnesota

University of Arizona

University of Washington

University of Colorado Boulder

University of Colorado System

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Water Isotope Systematics: Improving Modern and Paleoclimate Interpretations II Poster

AGU Fall Meeting 2021 (2021)

Bradley Markle Georgina Falster Jun Hu Nicole K Murray

Paleoclimatology

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Equatorial Undercurrent Influence on Surface Seawater δ ¹⁸ O Values in the Galápagos

Geophysical Research Letters (2023)

Jessica L. Conroy Nicole K Murray Gillian S. Patterson Aiden I. G. Schore Ima Ikuru

Abstract Stable isotopes of oxygen (δ 18 O) in seawater reflect the combined influences of ocean circulation and atmospheric moisture balance. However, it is difficult to disentangle disparate ocean and atmosphere influences on modern seawater δ 18 O values, partly because continuous time series of seawater δ 18 O are rare. Here we present a nearly nine‐year, continuous record of seawater δ 18 O values from the Galápagos. Seawater δ 18 O values faithfully track sea surface salinity and salinity along the equator at 50 m depth. Zonal current velocity within the Equatorial Undercurrent (EUC), directly west of the Galápagos, is strongly correlated with Galápagos surface seawater δ 18 O values with a 1‐month lag. Reconstructions of Galápagos seawater δ 18 O values could thus provide a window into past variations in the strength of the EUC, an important influence on large‐scale tropical Pacific climate.

10.1029/2022gl102074

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Holocene relationships between climate, waterfowl, and lacustrine nutrient cycling at Kettle Lake, North Dakota, USA

The Holocene (2023)

Nicole K Murray Jessica L. Conroy Kate O’Brien Eric C. Grimm Joseph J. Donovan

Avian populations can substantially influence lacustrine nutrient loading and biogeochemical cycling through guano deposition. Here, we examine the influence of climate-forced avian migration throughout the Holocene on Kettle Lake, North Dakota, using stable nitrogen and carbon isotope values (δ 15 N, δ 13 C) of lake sediment organic matter. Carbon content and δ 13 C values are negatively correlated with δ 15 N and appear to be driven by changes in charcoal abundance and watershed vegetation, respectively. We find enriched δ 15 N values when the guano mineral struvite is present in the lake sediment core in the early to Mid-Holocene. A strong δ 15 N-percent Nitrogen content relationship during periods with struvite, relative to periods without struvite, indicates that guano deposition from mass bird visitations altered past nitrogen cycle processes, likely through enhanced denitrification. These results attest to the ability of waterfowl to alter lacustrine N-cycling in a mid-continental North American lake, and indicate that paleo-N data in this particular lake are recording a unique history that does not necessarily represent regional paleoenvironmental conditions. However, a significant, positive relationship between δ 15 N and Ambrosia and Amaranthaceae pollen abundance suggests avian visitation and its impacts on the N-cycle occurred during periods of anomalously wet summers superimposed on the background conditions of early to Mid-Holocene drought.

Guano

Biogeochemical Cycle

Cycling

Macrofossil

10.1177/09596836231176490

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Machine Learning Solutions to Regional Surface Ocean δ¹⁸O‐Salinity Relationships for Paleoclimatic Reconstruction

Paleoceanography and Paleoclimatology (2023)

Nicole K Murray A. R. Muñoz Jessica L. Conroy

Abstract Stable isotope‐based reconstructions of past ocean salinity and hydroclimate depend on accurate, regionally constrained relationships between the stable oxygen isotopic composition of seawater (δ 18 O sw ) and salinity in the surface ocean. An increasing number of δ 18 O sw observations suggest greater spatial variability in this relationship than previously considered, highlighting the need to reassess these relationships on a global scale. Here, we use available, paired δ 18 O sw and salinity data ( N = 11,119) to create global interpolations of each variable. We then use a self‐organizing map, a specialized form of machine learning, to define 19 regions with unique δ 18 O sw ‐salinity relationships in the surface (<50 m) ocean. Inclusion of atmospheric moisture‐related variables and oceanic tracer data in additional self‐organizing map experiments indicates global surface δ 18 O sw ‐salinity spatial patterns are strongly forced by the atmosphere, as the SOM spatial output is highly similar despite no overlapping input data. Our approach is a useful update to the previously delimited regions, and highlights the utility of neural network pattern extraction in spatiotemporally sparse data sets.

TRACER

10.1029/2023pa004612

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Western Pacific Warm Pool δ¹⁸O Response to the El Niño‐Southern Oscillation

Geophysical Research Letters (2025)

Nicole K Murray Jessica L. Conroy Patrick L. Colin K. M. Cobb David Noone

Abstract Tropical Pacific seawater and precipitation stable oxygen isotope data aid in understanding modern oceanic and atmospheric interactions, and these data are particularly valuable as they are archived in isotope‐based paleoclimate records. However, the absence of modern seawater isotope time series limits the ability to identify the atmospheric influences on these data, precluding robust paleoclimate interpretations. We present a new 10 year sub‐monthly record of seawater and precipitation stable oxygen isotope values (δ 18 O sw and δ 18 O p ) from Koror, Palau. Our dataset indicates that temporally, δ 18 O sw is strongly influenced by local δ 18 O p. Both monthly δ 18 O sw and δ 18 O p are highly correlated with outgoing longwave radiation across the tropical Pacific, reflecting a Walker Circulation imprint on the surface ocean. Changes in the Palau δ 18 O sw —salinity relationship correspond to NINO3.4 variability, indicating a difference in how these variables record El Niño Southern Oscillation (ENSO) information, but demonstrating the utility of δ 18 O sw to reconstruct ENSO variability in the western tropical Pacific.

Oscillation (cell signaling)

10.1029/2024gl113366

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