Expanded ocean minimum zones in the oceans during the Paleocene/Eocene Thermal Maximum indicated by I/Ca in planktic Foraminifera

Author(s): Zhou, Xiaoli; Thomas, Ellen; Rickaby, Rosalind E. M.; Winguth, Arne M. E.; Lu, Zunli
Author Affiliation(s): Primary:
Syracuse University, Department of Earth Sciences, Syracuse, NY, United States
Yale University, United States
University of Oxford, United Kingdom
University of Texas at Arlington, United States
Volume Title: Geological Society of America, 2014 annual meeting & exposition
Source: Abstracts with Programs - Geological Society of America, 46(6), p.580; Geological Society of America, 2014 annual meeting & exposition, Vancouver, BC, Canada, Oct. 19-22, 2014. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0016-7592 CODEN: GAAPBC
Note: In English
Summary: Forecasting ocean deoxygenation due to global warming is challenging. Information on deoxygenation during past global warming, e.g., the Paleocene Eocene Thermal Maximum (PETM, ∼55.5 Ma), may help, but is hampered by a lack of sensitive proxies. The iodine to calcium ratio (I/Ca) in calcite is a proxy for paleo-redox conditions, because oxidized (iodate), but not reduced iodine (iodide) is incorporated. Total iodine (sum of iodate and iodide) in the present oceans is around 0.45 mmol/L, thus iodate and iodide concentration are inversely correlated. The vertical iodate concentration profile in the oceans is influenced by productivity and the presence/absence of an oxygen minimum zone. If there is no OMZ, the iodate concentration increases downwards from the mixed layer. If there is a shallow OMZ, the iodate concentration decreases from the mixed layer down to the upper OMZ. When the top of the OMZ is deeper, the iodate concentration may increase downwards from the mixed layer, decreasing to zero in the OMZ. We use I/Ca in planktic foraminifera and compare our data with modeled oxygen levels. Shallowing OMZs should cause a decrease in planktic foraminiferal I/Ca, with lower values in thermocline than in mixed layer calcifiers. Changes in I/Ca in mixed-layer relative to thermocline dwellers reflect changes in the iodate depth gradient, related to the vertical extent of OMZs. At sites in the open ocean Pacific (865), Weddell Sea (690), SE Atlantic (1262, 1263) and Indian Ocean (738), I/Ca values in monogeneric mixed layer and thermocline dwelling planktic foraminifera decreased over the PETM, probably indicative of widespread deoxygenation in the upper ocean waters, more pronounced in the Atlantic and Indian than in the Pacific Ocean. The mean difference in I/Ca of thermocline and mixed-layer dwellers varies geographically, and is positively correlated to the minimum oxygen levels in the water column estimated from climate modeling. Reconstructed iodate gradients indicate that deoxygenation was widespread in all oceans during the PETM, due to vertical and potentially lateral expansion of Oxygen Minimum Zones, which may have influenced pelagic ecosystems through vertical compression of the zone above the OMZ.
Year of Publication: 2014
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Alkaline earth metals; Atlantic Ocean; Calcium; Cenozoic; East Pacific; Foraminifera; Halogens; I/Ca; Invertebrata; Iodine; Kerguelen Plateau; Leg 113; Leg 119; Leg 143; Leg 208; Marine environment; Maud Rise; Metals; Microfossils; Mid-Pacific Mountains; North Pacific; Northeast Pacific; ODP Site 1262; ODP Site 1263; ODP Site 690; ODP Site 738; ODP Site 865; Ocean Drilling Program; Pacific Ocean; Paleo-oceanography; Paleocene-Eocene Thermal Maximum; Paleoenvironment; Paleogene; Planktonic taxa; Protista; South Atlantic; Southern Ocean; Tertiary; Walvis Ridge; Weddell Sea
Coordinates: N182624 N182626 W1793320 W1793321
S650938 S650937 E0011218 E0011218
S271100 S271100 E0013500 E0013400
S624233 S624232 E0824715 E0824714
Record ID: 2015049456
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States