Utilisation of radiocarbon and tephrochronology to constrain the oceanic circulation in the Southeast Pacific Ocean during the last 20,000 years

• Main Author: Martínez Fontaine, Consuelo
• Other Authors: Géosciences Paris Saclay (GEOPS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Université Paris-Saclay, Giuseppe Siani, Elisabeth Michel
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2021
• Subjects: Southern Volvanic Zone of the Andes; Tephrochronology; Radiocarbon; Paleoceanography; Southeast Pacific; Deglaciation; Zone volcanique sud des Andes; Téphrochronologie; Radiocarbone; Paléocéanographie; Pacifique Sud-Est; Déglaciation; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology; [SDU.STU.ST]Sciences of the Universe [physics]/Earth Sciences/Stratigraphy; [INFO.INFO-DB]Computer Science [cs]/Databases [cs.DB]; [INFO.INFO-IR]Computer Science [cs]/Information Retrieval [cs.IR]; Pacific; Southern Ocean
• Online Access: https://theses.hal.science/tel-03543983; https://theses.hal.science/tel-03543983/document; https://theses.hal.science/tel-03543983/file/94489_MARTINEZ_FONTAINE_2021_archivage.pdf

The ocean is thought to have an important role in glacial–interglacial cycles, by regulating the amount of CO₂ in the atmosphere. In particular, during the Last Glacial Maximum (~23,000–19,000 calendar years before present (cal years BP)), the deep ocean is thought to have accumulated CO₂, releasing it to the atmosphere during the last deglaciation (~18,000–11,000 cal years BP). The amount of CO₂ stored/released, the areas of the ocean where this would take place and the mechanisms leading to this storing/release, are currently being discussed and information worldwide is being produced to this aim. In this thesis I produce new records on ventilation changes of intermediate and deep waters in the Southeast Pacific (SEP) during the last ~22,000 years. Using ¹⁴C ages of paired benthic and planktic foraminifera in nine marine sediment cores in a transect between ~500–3,300 m and ~31–49° S, changes in oceanic circulation during the last deglaciation are interpreted. An important challenge in paleoceanograhy at the time is establishing robust chronologies for marine sediment cores, which is essential to integrate the information provided by paleoenvironmental records in different areas of the ocean, but also on land and ice caps. In order to explore how to improve the chronologies in the cores here studied, a tephrochronological record is produced in three of the cores. This study allowed to identify between one and three tephras (eruptions) in each core, aiding the robustness of their chronologies. From the produced records, the circulation in the SEP during the last 20,000 years reveals a more stratified glacial ocean, with the most ¹⁴C–depleted waters found in the deep Southern Ocean. During the deglaciation, important circulation changes are observed, indicating a more vigorous convection and the ventilation of deep waters in the Southern Ocean. Additionally, anomalously ¹⁴C–depleted values are observed during the deglaciation at depths bathed by Pacific Deep Waters, which might indicate the influence of ...