Grasse
Patricia
Grasse
Patricia
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ArticleIsotopic characterization of water masses in the Southeast Pacific Region: paleoceanographic implications(American Geophysical Union, 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, DierkIn 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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ArticleNutrient and silicon isotope dynamics in the Laptev Sea and implications for nutrient availability in the Transpolar Drift(American Geophysical Union, 2022-09-07) Laukert, Georgi ; Grasse, Patricia ; Novikhin, A. ; Povazhnyi, V. ; Doering, Kristin ; Hölemann, Jens ; Janout, Markus ; Bauch, Dorothea ; Kassens, Heidemarie ; Frank, MartinRealistic prediction of the near‐future response of Arctic Ocean primary productivity to ongoing warming and sea ice loss requires a mechanistic understanding of the processes controlling nutrient bioavailability. To evaluate continental nutrient inputs, biological utilization, and the influence of mixing and winter processes in the Laptev Sea, the major source region of the Transpolar Drift (TPD), we compare observed with preformed concentrations of dissolved inorganic nitrogen (DIN) and phosphorus (DIP), silicic acid (DSi), and silicon isotope compositions of DSi (δ30SiDSi) obtained for two summers (2013 and 2014) and one winter (2012). In summer, preformed nutrient concentrations persisted in the surface layer of the southeastern Laptev Sea, while diatom‐dominated utilization caused intense northward drawdown and a pronounced shift in δ30SiDSi from +0.91 to +3.82‰. The modeled Si isotope fractionation suggests that DSi in the northern Laptev Sea originated from the Lena River and was supplied during the spring freshet, while riverine DSi in the southeastern Laptev Sea was continuously supplied during the summer. Primary productivity fueled by river‐borne nutrients was enhanced by admixture of DIN‐ and DIP‐rich Atlantic‐sourced waters to the surface, either by convective mixing during the previous winter or by occasional storm‐induced stratification breakdowns in late summer. Substantial enrichments of DSi (+240%) and DIP (+90%) beneath the Lena River plume were caused by sea ice‐driven redistribution and remineralization. Predicted weaker stratification on the outer Laptev Shelf will enhance DSi utilization and removal through greater vertical DIN supply, which will limit DSi export and reduce diatom‐dominated primary productivity in the TPD.