4:30 PM - 4:45 PM
[MIS14-30] Response of the marine productivity to the Eocene hyperthermals: Insights from Ba stable isotope records of Northwestern Pacific carbonate sediments
Keywords:Eocene hyperthermals, Paleocene-Eocene Thermal Maximum (PETM), Ba stable isotope, Marine productivity, Carbon cycle
The late Paleocene to early Eocene is a period known for repeated occurrences of transient global warming events, referred to as "hyperthermals" including the Paleocene-Eocene Thermal Maximum (PETM) [1]. These warming events have attracted great attention because they provide clues for understanding and predicting ongoing climate change. However, the response of the Earth's surface system to the hyperthermals remain unclear.
We focused on marine productivity, which plays a vital role in the Earth's carbon cycle, and aimed to elucidate the responses of marine productivity to the hyperthermals. Previous studies have proposed a hypothesis that warm climate during the hyperthermals triggered an increase in marine productivity, which in turn enhanced carbon transport to the deep ocean and sediments through carbon fixation by marine organisms. This process could have functioned as a negative feedback mechanism, called "productivity feedback", which mitigates warm climates [2]. However, owing to the considerable uncertainties in conventional proxies (e.g., barite accumulation rate, BAR), there are many challenges in reconstructing past marine productivity. Consequently, the relationship between the hyperthermals and marine productivity, including whether the productivity feedback worked during these warming events, remains poorly understood.
In this study, we employ Ba stable isotope ratios (δ138/134Ba), a non-conventional proxy for past marine productivity [3,4]. This proxy is based on isotopic fractionation between barite (BaSO4), which precipitates during organic matter decomposition, and seawater. As barite preferentially incorporates isotopically light Ba, increased in productivity and enhanced barite precipitation in the surface ocean lead to the depletion of light Ba in ambient seawater, thereby seawater δ138/134Ba increases. The isotopic signatures of seawater were subsequently recorded in the marine sediments. By utilizing this isotopic systematics, we reconstructed the Ba stable isotope record of seawater from the late Paleocene to the early Eocene to investigate the response of marine productivity to the hyperthermals and its implications for the carbon cycle.
In this presentation, we report Ba stable isotope ratios and bulk chemical compositions of deep-sea carbonate sediments from Ocean Drilling Program (ODP) Site 1209 on Shatsky Rise in the western North Pacific. Based on these geochemical data, we discuss the relationship between the hyperthermals and marine productivity.
[1] Westerhold et al. (2018) Paleoceanogr. Paleoclimatol. 33, 626-642. [2] Bains et al. (2000) Nature 407, 171–174. [3] Bridgestock et al. (2019) Earth Planet. Sci. Lett. 510, 53-63. [4] Miyazaki et al. (2023) Geochem. J. 57, GJ2301.
We focused on marine productivity, which plays a vital role in the Earth's carbon cycle, and aimed to elucidate the responses of marine productivity to the hyperthermals. Previous studies have proposed a hypothesis that warm climate during the hyperthermals triggered an increase in marine productivity, which in turn enhanced carbon transport to the deep ocean and sediments through carbon fixation by marine organisms. This process could have functioned as a negative feedback mechanism, called "productivity feedback", which mitigates warm climates [2]. However, owing to the considerable uncertainties in conventional proxies (e.g., barite accumulation rate, BAR), there are many challenges in reconstructing past marine productivity. Consequently, the relationship between the hyperthermals and marine productivity, including whether the productivity feedback worked during these warming events, remains poorly understood.
In this study, we employ Ba stable isotope ratios (δ138/134Ba), a non-conventional proxy for past marine productivity [3,4]. This proxy is based on isotopic fractionation between barite (BaSO4), which precipitates during organic matter decomposition, and seawater. As barite preferentially incorporates isotopically light Ba, increased in productivity and enhanced barite precipitation in the surface ocean lead to the depletion of light Ba in ambient seawater, thereby seawater δ138/134Ba increases. The isotopic signatures of seawater were subsequently recorded in the marine sediments. By utilizing this isotopic systematics, we reconstructed the Ba stable isotope record of seawater from the late Paleocene to the early Eocene to investigate the response of marine productivity to the hyperthermals and its implications for the carbon cycle.
In this presentation, we report Ba stable isotope ratios and bulk chemical compositions of deep-sea carbonate sediments from Ocean Drilling Program (ODP) Site 1209 on Shatsky Rise in the western North Pacific. Based on these geochemical data, we discuss the relationship between the hyperthermals and marine productivity.
[1] Westerhold et al. (2018) Paleoceanogr. Paleoclimatol. 33, 626-642. [2] Bains et al. (2000) Nature 407, 171–174. [3] Bridgestock et al. (2019) Earth Planet. Sci. Lett. 510, 53-63. [4] Miyazaki et al. (2023) Geochem. J. 57, GJ2301.