[Eoas-seminar] PhD Dissertation - Luis Rodriguez-Marrero

Tue Oct 27 14:50:28 EDT 2026

Good afternoon,

Please join us for Luis Rodriguez-Marrero's Dissertation on Monday, November 2, 2026 at 10 AM in EOAS 6067.

Title: Quantifying changes in mean climate and its uncertainty over the Holocene in coral geochemical proxies from the central tropical Pacific

Name: Luis Rodriguez-Marrero
Date: November 2, 2026
Time: 10:00 AM
Room: EOAS 6067
Major Professor: Dr. Alyssa Atwood
Zoom: https://fsu.zoom.us/j/93153095685<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Ffsu.zoom.us%2Fj%2F93153095685&data=05%7C02%7Ceoas-seminar%40lists.fsu.edu%7Cb3e797dc6e644579883608df345b2bb5%7Ca36450ebdb0642a78d1b026719f701e3%7C0%7C0%7C639287238306596830%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=OCy5CBCUewvPuiQAXlVMjFQoBa6e8mXeinu7ZcDySsE%3D&reserved=0>

Abstract: The central tropical Pacific is a major driver of global climate variability, as exemplified by the El Niño/Southern Oscillation (ENSO), which has far-reaching impacts on ecosystems and billions of people around the globe. How this region may change in the future under global warming is still unknown and represents a major source of uncertainty in future climate projections. Furthermore, the short instrumental record and scarcity of paleoclimate records from the equatorial Pacific Ocean limit our understanding of climate variability and change in this region prior to the mid-20th century. Sub-fossil corals from Kiritimati Atoll in the central equatorial Pacific provide precisely dated and monthly resolved records of past sea surface temperatures (SST) and sea surface salinity (SSS)/seawater δ¹⁸O in the region. However, non-climatic processes such as diagenesis and coral vital effects introduce significant uncertainty in such records. This dissertation provides an overview of the sources of uncertainty in coral δ¹⁸O and trace element (Sr/Ca, Sr-U) records, quantifies this uncertainty, and develops a set of tools to minimize their effects on coral-based paleoclimate reconstructions. These tools are then used to reconstruct changes in central Pacific SST and seawater δ¹⁸O over the last 7,000 years to present.

We first present a new framework to minimize the uncertainty in mean coral δ18O records from Kiritimati using a multivariate regression model that incorporates four commonly measured properties in coral δ18O records. We apply this model to a large ensemble of coral δ18O records from Kiritimati spanning the Holocene and find that 38% of the variance in the mean coral δ18O values is accounted for by a combination of four commonly measured indicators of diagenesis and coral physiology. Isolating and correcting for these factors reduces the centennial scale variance in mean coral δ18O values by 65% and reduces the uncertainty in the Holocene trend by 18%. The revised coral δ18O reconstruction is then used to infer long term changes in central equatorial Pacific SSTs and hydroclimate over the Holocene.

We then test a recent paleothermometry technique (Sr-U) against the traditional Sr/Ca paleothermometry technique in four overlapping modern corals from Kiritimati and Jarvis Islands in the central equatorial Pacific. Our replication study indicates that the Sr-U paleothermometer does not consistently outperform Sr/Ca in estimating mean SSTs from this region. We further develop robust uncertainty estimates for mean SST reconstructions using the inverse prediction framework for a proxy-SST calibration. Individual Sr/Ca-derived SST reconstructions have an uncertainty of 0.7°C (1s) while Sr-U-derived SST reconstructions from Kiritimati have an uncertainty of 1.2°C (1s).  We demonstrate that this uncertainty can be reduced through ensemble averaging across multiple coral records, wherein the standard error decreases as the ensemble size increases (as [cid:2fc948df-48fb-4de7-8b0d-432a0a33da50] ). This ensemble averaging technique has important implications for reconstructing mean climate from the fossil coral record.

Lastly, we apply these findings to an ensemble of paired coral Sr/Ca and δ18O records from Kiritimati to quantitatively reconstruct changes in mean SST and seawater δ18O in the central equatorial Pacific over the last 7,000 years to present. Our Sr/Ca reconstruction shows no significant SST trend over the Holocene, consistent with existing multi-proxy reconstructions and transient climate model simulations. When paired with our coral δ¹⁸O reconstruction, the reconstructions indicate that large seawater δ18O changes (0.078‰/kyr) occurred in this region over the mid- to late-Holocene, likely driven by drier conditions in the region during the mid-Holocene. These findings are consistent with a La Niña like mean state and/or a northern/southern meridional shift of the Pacific Intertropical Convergence Zone.

These results provide an improved set of mean climate reconstructions with associated uncertainties from the central equatorial Pacific over the Holocene. Our results show the potential of using large ensembles of paired sub-fossil coral Sr/Ca and δ18O records to produce climate reconstructions on long (millennial) time scales and highlight the use of replication studies over the instrumental period to robustly quantify uncertainties in the fossil coral record. These reconstructions illuminate important new aspects of hydroclimate change over the mid-Holocene to present day in this dynamically important region of the planet.

Best,
Adea

Adea Arrison

Sr. Academic Program Specialist

Department of Earth, Ocean & Atmospheric Science

[cid:323aebd8-babc-4f64-8192-f625b8033b20]<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.eoas.fsu.edu%2F&data=05%7C02%7Ceoas-seminar%40lists.fsu.edu%7Cb3e797dc6e644579883608df345b2bb5%7Ca36450ebdb0642a78d1b026719f701e3%7C0%7C0%7C639287238306904822%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=ngOnZS8emkERg8UhHjxSkyjKESadC6%2BCzoMFVnLXbyE%3D&reserved=0>

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