Graco Michelle

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Last Name
Graco
First Name
Michelle
ORCID
0000-0002-6193-3256

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Isotopic characterization of water masses in the Southeast Pacific Region: paleoceanographic implications

2021-12-23 , Reyes-Macaya, Dharma , Hoogakker, Babette , Martínez-Méndez, Gema , Llanillo, Pedro J. , Grasse, Patricia , Mohtadi, Mahyar , Mix, Alan C. , Leng, Melanie J. , Struck, Ulrich , McCorkle, Daniel C. , Troncoso, Macarena , Gayo, Eugenia M. , Lange, Carina B. , Farias, Laura , Carhuapoma, Wilson , Graco, Michelle , Cornejo-D’Ottone, Marcela , De Pol-Holz, Ricardo , Fernandez, Camila , Narváez, Diego , Vargas, Cristian A. , García-Araya, Francisco , Hebbeln, Dierk

In this study, we used stable isotopes of oxygen (δ18O), deuterium (δD), and dissolved inorganic carbon (δ13CDIC) in combination with temperature, salinity, oxygen, and nutrient concentrations to characterize the coastal (71°–78°W) and an oceanic (82°–98°W) water masses (SAAW—Subantarctic Surface Water; STW—Subtropical Water; ESSW—Equatorial Subsurface water; AAIW—Antarctic Intermediate Water; PDW—Pacific Deep Water) of the Southeast Pacific (SEP). The results show that δ18O and δD can be used to differentiate between SAAW-STW, SAAW-ESSW, and ESSW-AAIW. δ13CDIC signatures can be used to differentiate between STW-ESSW (oceanic section), SAAW-ESSW, ESSW-AAIW, and AAIW-PDW. Compared with the oceanic section, our new coastal section highlights differences in both the chemistry and geometry of water masses above 1,000 m. Previous paleoceanographic studies using marine sediments from the SEP continental margin used the present-day hydrological oceanic transect to compare against, as the coastal section was not sufficiently characterized. We suggest that our new results of the coastal section should be used for past characterizations of the SEP water masses that are usually based on continental margin sediment samples.

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Article

Global variability in seawater Mg:Ca and Sr:Ca ratios in the modern ocean

2020-07-17 , Lebrato, Mario , Garbe-Schonberg, Dieter , Müller, Marius N. , Blanco-Ameijeiras, Sonia , Feely, Richard A. , Lorenzoni, Laura , Molinero, Juan-Carlos , Bremer, Karen , Jones, Daniel O. B. , Iglesias-Rodriguez, M. Debora , Greeley, Dana , Lamare, Miles D. , Paulmier, Aurelien , Graco, Michelle , Cartes, Joan , Barcelos e Ramos, Joana , de Lara, Ana , Sanchez-Leal, Ricardo , Jimenez, Paz , Paparazzo, Flavio E. , Hartman, Susan , Westernströer, Ulrike , Küter, Marie , Benavides, Roberto , da Silva, Armindo F. , Bell, Steven , Payne, Chris , Olafsdottir, Solveig R. , Robinson, Kelly , Jantunen, Liisa M. , Korablev, Alexander , Webster, Richard J. , Jones, Elizabeth M. , Gilg, Olivier , Bailly du Bois, Pascal , Beldowski, Jacek , Ashjian, Carin J. , Yahia, Nejib D. , Twining, Benjamin S. , Chen, Xue-Gang , Tseng, Li-Chun , Hwang, Jiang-Shiou , Dahms, Hans-Uwe , Oschlies, Andreas

Seawater Mg:Ca and Sr:Ca ratios are biogeochemical parameters reflecting the Earth–ocean–atmosphere dynamic exchange of elements. The ratios’ dependence on the environment and organisms' biology facilitates their application in marine sciences. Here, we present a measured single-laboratory dataset, combined with previous data, to test the assumption of limited seawater Mg:Ca and Sr:Ca variability across marine environments globally. High variability was found in open-ocean upwelling and polar regions, shelves/neritic and river-influenced areas, where seawater Mg:Ca and Sr:Ca ratios range from ∼4.40 to 6.40 mmol:mol and ∼6.95 to 9.80 mmol:mol, respectively. Open-ocean seawater Mg:Ca is semiconservative (∼4.90 to 5.30 mol:mol), while Sr:Ca is more variable and nonconservative (∼7.70 to 8.80 mmol:mol); both ratios are nonconservative in coastal seas. Further, the Ca, Mg, and Sr elemental fluxes are connected to large total alkalinity deviations from International Association for the Physical Sciences of the Oceans (IAPSO) standard values. Because there is significant modern seawater Mg:Ca and Sr:Ca ratios variability across marine environments we cannot absolutely assume that fossil archives using taxa-specific proxies reflect true global seawater chemistry but rather taxa- and process-specific ecosystem variations, reflecting regional conditions. This variability could reconcile secular seawater Mg:Ca and Sr:Ca ratio reconstructions using different taxa and techniques by assuming an error of 1 to 1.50 mol:mol, and 1 to 1.90 mmol:mol, respectively. The modern ratios’ variability is similar to the reconstructed rise over 20 Ma (Neogene Period), nurturing the question of seminonconservative behavior of Ca, Mg, and Sr over modern Earth geological history with an overlooked environmental effect.

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Article

Global perspectives on observing ocean boundary current systems

2019-08-08 , Todd, Robert E. , Chavez, Francisco P. , Clayton, Sophie A. , Cravatte, Sophie , Goes, Marlos Pereira , Graco, Michelle , Lin, Xiaopei , Sprintall, Janet , Zilberman, Nathalie , Archer, Matthew , Arístegui, Javier , Balmaseda, Magdalena A. , Bane, John M. , Baringer, Molly O. , Barth, John A. , Beal, Lisa M. , Brandt, Peter , Calil, Paulo H. R. , Campos, Edmo , Centurioni, Luca R. , Chidichimo, Maria Paz , Cirano, Mauro , Cronin, Meghan F. , Curchitser, Enrique N. , Davis, Russ E. , Dengler, Marcus , deYoung, Brad , Dong, Shenfu , Escribano, Ruben , Fassbender, Andrea , Fawcett, Sarah E. , Feng, Ming , Goni, Gustavo J. , Gray, Alison R. , Gutiérrez, Dimitri , Hebert, Dave , Hummels, Rebecca , Ito, Shin-ichi , Krug, Marjolaine , Lacan, Francois , Laurindo, Lucas , Lazar, Alban , Lee, Craig M. , Lengaigne, Matthieu , Levine, Naomi M. , Middleton, John , Montes, Ivonne , Muglia, Michael , Nagai, Takeyoshi , Palevsky, Hilary I. , Palter, Jaime B. , Phillips, Helen E. , Piola, Alberto R. , Plueddemann, Albert J. , Qiu, Bo , Rodrigues, Regina , Roughan, Moninya , Rudnick, Daniel L. , Rykaczewski, Ryan R. , Saraceno, Martin , Seim, Harvey E. , Sen Gupta, Alexander , Shannon, Lynne , Sloyan, Bernadette M. , Sutton, Adrienne J. , Thompson, LuAnne , van der Plas, Anja K. , Volkov, Denis L. , Wilkin, John L. , Zhang, Dongxiao , Zhang, Linlin

Ocean boundary current systems are key components of the climate system, are home to highly productive ecosystems, and have numerous societal impacts. Establishment of a global network of boundary current observing systems is a critical part of ongoing development of the Global Ocean Observing System. The characteristics of boundary current systems are reviewed, focusing on scientific and societal motivations for sustained observing. Techniques currently used to observe boundary current systems are reviewed, followed by a census of the current state of boundary current observing systems globally. The next steps in the development of boundary current observing systems are considered, leading to several specific recommendations.