11:45 AM - 12:00 PM
[MIS18-21] Chemical weathering and volcanism during the early Paleogene hothouse constrained from the marine osmium isotope record in the central North Pacific Ocean
Keywords:osmium isotopes, Paleogene, hyperthermals, Paleocene-Eocene Thermal Maximum, chemical weathering, North Atlantic Igneous Province
Early Paleogene is characterized by a progressive global warming on multi-million-year scale, which was punctuated by a series of further warming events called ‘hyperthermals’ of a geologically short time scale (104–105 yr) [1]. These hyperthermal events were accompanied by distinct negative carbon isotope excursions, implying massive injections of isotopically light carbon to the Earth’s surficial system [2]. Notably, the Paleocene-Eocene Thermal Maximum (PETM), the severest global warming among the early Paleogene hyperthermals, is believed to be associated with the North Atlantic Igneous Province (NAIP) [3,4].
Osmium isotope ratio (187Os/188Os) of seawater is controlled by the mixture of radiogenic Os flux from continental crusts and unradiogenic Os flux from mantle-like components (i.e., seafloor hydrothermal fluids, juvenile basalt, and cosmic dust). Therefore, given that the cosmic dust flux was almost constant in a relatively short interval, the marine osmium isotope ratio can fluctuate by the changes in chemical weathering of continental rocks and/or a large-scale volcanic activity [5-7].
Chemical weathering of continental silicate rocks could have played an important role for the recovery from the Paleogene hyperthermals. Previous studies indicated that the enhanced chemical weathering of continental rocks consumed the atmospheric CO2 during the PETM, based on the seawater Os isotope record [5,6]. Moreover, negative shift of marine Os isotope ratio just before the PETM was recently reported from the Arctic Ocean and Peri-Tethys, which suggests a close relationship between the eruption of NAIP and the PETM [6]. However, the marine Os isotope record during the early Paleogene, including the PETM and the following hyperthermals, has not been reconstructed from the pelagic region of the Pacific Ocean.
To verify that the changes in chemical weathering intensity of continental rocks and eruption of NAIP influenced on the marine Os system as the global signature, we analyzed 187Os/188Os of deep-sea sediment samples recording multiple hyperthermals (PETM, Eocene Thermal Maximum (ETM) 2 and ETM3 [8]) at Ocean Drilling Program Site 1215 Hole A in the central North Pacific Ocean. Based on the analytical results, we will discuss the changes in chemical weathering intensity of continental silicates for each hyperthermal event and the relationship between the PETM and the NAIP volcanism.
[1] Zachos et al. (2008) Nature 451, 279-283. [2] Lunt et al. (2011) Nature Geoscience 4, 775-778. [3] Svensen et al. (2004) Nature 429, 542-545. [4] Gutjahr et al. (2017) Nature 548, 573-577. [5] Ravizza et al. (2001) Paleoceanography 16, 155-163. [6] Dickson et al. (2015) Palaeogeography, Palaeoclimatology, Palaeoecology 438, 300-307. [7] Kuwahara et al. (2021) Scientific Reports 11, 5695. [8] Leon-Rodriquez and Dickens (2010) Palaeogeography, Palaeoclimatology, Palaeoecology 298, 409-420.
Osmium isotope ratio (187Os/188Os) of seawater is controlled by the mixture of radiogenic Os flux from continental crusts and unradiogenic Os flux from mantle-like components (i.e., seafloor hydrothermal fluids, juvenile basalt, and cosmic dust). Therefore, given that the cosmic dust flux was almost constant in a relatively short interval, the marine osmium isotope ratio can fluctuate by the changes in chemical weathering of continental rocks and/or a large-scale volcanic activity [5-7].
Chemical weathering of continental silicate rocks could have played an important role for the recovery from the Paleogene hyperthermals. Previous studies indicated that the enhanced chemical weathering of continental rocks consumed the atmospheric CO2 during the PETM, based on the seawater Os isotope record [5,6]. Moreover, negative shift of marine Os isotope ratio just before the PETM was recently reported from the Arctic Ocean and Peri-Tethys, which suggests a close relationship between the eruption of NAIP and the PETM [6]. However, the marine Os isotope record during the early Paleogene, including the PETM and the following hyperthermals, has not been reconstructed from the pelagic region of the Pacific Ocean.
To verify that the changes in chemical weathering intensity of continental rocks and eruption of NAIP influenced on the marine Os system as the global signature, we analyzed 187Os/188Os of deep-sea sediment samples recording multiple hyperthermals (PETM, Eocene Thermal Maximum (ETM) 2 and ETM3 [8]) at Ocean Drilling Program Site 1215 Hole A in the central North Pacific Ocean. Based on the analytical results, we will discuss the changes in chemical weathering intensity of continental silicates for each hyperthermal event and the relationship between the PETM and the NAIP volcanism.
[1] Zachos et al. (2008) Nature 451, 279-283. [2] Lunt et al. (2011) Nature Geoscience 4, 775-778. [3] Svensen et al. (2004) Nature 429, 542-545. [4] Gutjahr et al. (2017) Nature 548, 573-577. [5] Ravizza et al. (2001) Paleoceanography 16, 155-163. [6] Dickson et al. (2015) Palaeogeography, Palaeoclimatology, Palaeoecology 438, 300-307. [7] Kuwahara et al. (2021) Scientific Reports 11, 5695. [8] Leon-Rodriquez and Dickens (2010) Palaeogeography, Palaeoclimatology, Palaeoecology 298, 409-420.