Arctic Ocean benthic foraminifera preservation and Mg/Ca ratios : Implications for bottom water palaeothermometry

• Main Author: Barrientos, Natalia
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Stockholms universitet, Institutionen för geologiska vetenskaper 2018
• Subjects: Arctic Ocean; benthic foraminifera; Mg/Ca-temperature; calcite preservation; Climate Research; Klimatforskning; Geochemistry; Geokemi; Oceanography; Hydrology and Water Resources; Oceanografi; hydrologi och vattenresurser; Environmental Sciences; Miljövetenskap; Geosciences; Multidisciplinary; Multidisciplinär geovetenskap; Arctic; Chukchi Sea; Morris Jesup Rise; Chukchi; Climate change; Foraminifera*; Lomonosov Ridge
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-155089

Reconstructions of Arctic Ocean palaeotemperatures are needed to disentangle natural variability from anthropogenic changes and understand the role of ocean heat transport in forcing or providing feedbacks on Arctic climate change. Despite known complications with calcareous microfossil preservation in Arctic Ocean sediments, calcareous benthic foraminifera can be common in interglacial sequences. However, thus far they have been underutilized in palaeoceanographic studies. This thesis explores the application of the Mg/Ca palaeothermometry proxy for reconstructing bottom water temperatures (BWT) in the Arctic Ocean during the late Quaternary. This method, which is supported by previous empirical studies demonstrating a strong temperature control on trace Mg inclusion into foraminiferal shell calcite, has been applied in many ocean regions and time intervals. Until now its application in the Arctic Ocean has been sparingly explored. The results of this doctoral thesis are based on benthic foraminifera retrieved from marine sediment cores covering a wide geographical Arctic Ocean area including both the shallow and vast continental shelves and slopes to the intermediate-to-deep waters of the Lomonosov Ridge and Morris Jesup Rise. These provide the first benthic foraminifera Mg/Ca ratios from the central Arctic Ocean region. In the first study, mechanisms that could affect Mg incorporation in Arctic benthic foraminifera are investigated using oceanographic field data and six 'live' modern Arctic species (Elphidium clavatum, Nonionella labradorica, Cassidulina neoteretis, Oridorsalis tener, Cibicidoides wuellerstorfi and Quinqueloculina arctica). The result is new species-specific Mg/Ca–BWT field calibrations that provide important constraints at the cold end of the BWT spectrum (-2 to 1°C) (Paper I). Using the new Mg/Ca–BWT equation for E. clavatum, a palaeotemperature record was generated for the late Holocene (past ca. 4100 yr) from the western Chukchi Sea. The data showed BWT fluctuations from -2 to 1°C that ...