3:30 PM - 3:45 PM
[MIS14-26] Ocean circulation changes in early Eocene Hothouse inferred from deep-sea sediment silicification
Keywords:ocean circulation, deep-sea sediment, early Eocene, hyperthermal events, silica cycle, IODP
Ocean overturning circulation plays a critical role in Earth’s climate system. During the early Eocene (ca. 56–47 Ma), the warmest period of the Cenozoic era, vigorous meridional overturning circulation likely sustained long-term global warmth by transporting oceanic heat from low to high latitudes [1,2]. However, changes in circulation during transient global warming events in this Hothouse climate, known as hyperthermals, remain poorly understood.
In this study, we measured bulk chemical composition of deep-sea sediment samples containing the Paleocene-Eocene Thermal Maximum (PETM) and multiple early Eocene hyperthermal events, drilled at IODP Site U1553 in the South Pacific [3] and ODP Site 1209 in the central North Pacific. We also compiled the data from ODP Site 752 in the southern Indian Ocean and Site 738 in the Indian sector of Southern Ocean [4]. Our results showed that the bulk SiO2/Al2O3 ratio, reflecting non-detrital silica deposition, temporarily increased during these events, including the PETM, in the South Pacific (IODP Site U1553) and Indian Oceans (ODP Sites 752 and 738), which was a phenomenon originally reported only from the Atlantic Ocean [5]. Contrarily, sediment silicification was not observed in the central North Pacific (ODP Site 1209).
To explore the causal relationship between the spatial heterogeneity of sediment silicification and paleoenvironmental changes during the hyperthermal events, we constructed a global ocean silica cycle model that explicitly separates the Atlantic, Indian, and North and South Pacific Ocean basins, modified from a configuration of ocean circulation in the LOSCAR carbon cycle model [6]. Numerical experiments on the ocean silica cycle revealed that transient deep-water outflows from the North Pacific to other ocean basins, likely accompanied by intensification of the global meridional overturning circulation, could reproduce the observed spatially heterogeneous silicification of seafloor sediments. The coherence between circulation changes and hyperthermals suggests that overturning circulation responded to Earth’s orbital eccentricity maxima. Changes in oceanic heat transport resulting from this reorganization may have caused or amplified high-frequency climatic fluctuations during the early Eocene.
[1] Thomas et al. (2014) Paleoceanography 29, 454–469. [2] Zhang et al. (2022) Paleoceanography and Paleoclimatology 37, e2021PA004329. [3] Niederbockstruck et al. (2024) Paleoceanography and Paleoclimatology 39, e2023PA004801. [4] Yasukawa et al. (2017) Scientific Reports 7, 11304. [5] Penman et al. (2019) Paleoceanography and Paleoclimatology 34, 287–299. [6] Zeebe (2012) Geoscientific Model Development 5, 149–166.
In this study, we measured bulk chemical composition of deep-sea sediment samples containing the Paleocene-Eocene Thermal Maximum (PETM) and multiple early Eocene hyperthermal events, drilled at IODP Site U1553 in the South Pacific [3] and ODP Site 1209 in the central North Pacific. We also compiled the data from ODP Site 752 in the southern Indian Ocean and Site 738 in the Indian sector of Southern Ocean [4]. Our results showed that the bulk SiO2/Al2O3 ratio, reflecting non-detrital silica deposition, temporarily increased during these events, including the PETM, in the South Pacific (IODP Site U1553) and Indian Oceans (ODP Sites 752 and 738), which was a phenomenon originally reported only from the Atlantic Ocean [5]. Contrarily, sediment silicification was not observed in the central North Pacific (ODP Site 1209).
To explore the causal relationship between the spatial heterogeneity of sediment silicification and paleoenvironmental changes during the hyperthermal events, we constructed a global ocean silica cycle model that explicitly separates the Atlantic, Indian, and North and South Pacific Ocean basins, modified from a configuration of ocean circulation in the LOSCAR carbon cycle model [6]. Numerical experiments on the ocean silica cycle revealed that transient deep-water outflows from the North Pacific to other ocean basins, likely accompanied by intensification of the global meridional overturning circulation, could reproduce the observed spatially heterogeneous silicification of seafloor sediments. The coherence between circulation changes and hyperthermals suggests that overturning circulation responded to Earth’s orbital eccentricity maxima. Changes in oceanic heat transport resulting from this reorganization may have caused or amplified high-frequency climatic fluctuations during the early Eocene.
[1] Thomas et al. (2014) Paleoceanography 29, 454–469. [2] Zhang et al. (2022) Paleoceanography and Paleoclimatology 37, e2021PA004329. [3] Niederbockstruck et al. (2024) Paleoceanography and Paleoclimatology 39, e2023PA004801. [4] Yasukawa et al. (2017) Scientific Reports 7, 11304. [5] Penman et al. (2019) Paleoceanography and Paleoclimatology 34, 287–299. [6] Zeebe (2012) Geoscientific Model Development 5, 149–166.