10:45 AM - 12:15 PM
[BCG07-P07] Photic-zone euxinia and transitions of primary producers caused by the global warming at the Permian-Triassic boundary
Keywords:P/Tr boundary event, end-Permian mass extinction, photic-zone euxinia, 1-D upper ocean ecosystem model
At the Permian-Triassic boundary (P/Tr boundary; 252Ma), a large environmental change occurred due to an eruption of Siberian Trap (e.g. Reichow et al., 2009). This igneous activity supplied much amount of greenhouse gases into the atmosphere. This promoted the nutrient supply from the continents and the primary productivity in the ocean, leading to an ocean anoxic event (OAE) (Winguth and Winguth, 2012). The OAE at the P/Tr boundary was so extensive that ~10% of the ocean floor was deoxygenated (Kipp and Tissot, 2022), causing the large mass extinction of marine species (Wignall and Twitchett, 1996). Furthermore, the existence of biomarkers that indicate the presence of green sulfur bacteria was confirmed in the sediments deposited from shallow water, which suggests uprising sulfidic water into the photic zone (e.g., Grice et al., 2005; Hays et al., 2007). In addition, it has been discussed that activities of terrestrial life may have been affected by the release of hydrogen sulfide (H2S) from the ocean caused by the photic-zone euxinia (Kump et al., 2005). However, the conditions for the photic-zone euxinia at the P/Tr boundary and the behaviors of primary producers in such conditions have not been quantitatively demonstrated. For this reason, the impact of the photic-zone euxinia on the activity of the ocean ecosystem was unclear.
Here, we use the high-resolution surface ocean ecosystem model (e.g., Haga et al., JpGU 2019), which can reproduce the transition of redox conditions of the surface ocean and primary producers (algae, cyanobacteria, and green sulfur bacteria). We investigate the behaviors of primary producers, changes in the depth of redoxcline, and conditions for the photic-zone euxinia against a global-mean surface temperature and a local upwelling rate. We also discuss the impacts of changes in ocean redox conditions on the atmospheric compositions and the activity of terrestrial life by estimating the supply rate of H2S to the atmosphere.
We show that, as the surface temperature increases and/or the upwelling rate becomes faster, the nutrient supply from the deep ocean increases, leading to higher primary production. Specifically, when the global average temperature exceeds ~18 deg. C, the photic-zone euxinia occurs and the activity of green sulfur bacteria becomes dominant compared with the activities of algae and cyanobacteria. This result supports the occurrence of the photic-zone euxinia at the P/Tr boundary because the global mean temperature around this period is estimated to be ~28.6 deg. C (Scotese et al., 2021). We further show that an upwelling rate faster than 1000-2000 m/yr is required to increase the supply rate of H2S to the atmosphere. In the present ocean, such a high upwelling rate is limited to some coastal or equatorial upwelling regions. Thus, the release of H2S to the continental area due to the photic-zone euxinia may have, at least, had a regional influence in the activity of terrestrial life at the P/Tr boundary.
Here, we use the high-resolution surface ocean ecosystem model (e.g., Haga et al., JpGU 2019), which can reproduce the transition of redox conditions of the surface ocean and primary producers (algae, cyanobacteria, and green sulfur bacteria). We investigate the behaviors of primary producers, changes in the depth of redoxcline, and conditions for the photic-zone euxinia against a global-mean surface temperature and a local upwelling rate. We also discuss the impacts of changes in ocean redox conditions on the atmospheric compositions and the activity of terrestrial life by estimating the supply rate of H2S to the atmosphere.
We show that, as the surface temperature increases and/or the upwelling rate becomes faster, the nutrient supply from the deep ocean increases, leading to higher primary production. Specifically, when the global average temperature exceeds ~18 deg. C, the photic-zone euxinia occurs and the activity of green sulfur bacteria becomes dominant compared with the activities of algae and cyanobacteria. This result supports the occurrence of the photic-zone euxinia at the P/Tr boundary because the global mean temperature around this period is estimated to be ~28.6 deg. C (Scotese et al., 2021). We further show that an upwelling rate faster than 1000-2000 m/yr is required to increase the supply rate of H2S to the atmosphere. In the present ocean, such a high upwelling rate is limited to some coastal or equatorial upwelling regions. Thus, the release of H2S to the continental area due to the photic-zone euxinia may have, at least, had a regional influence in the activity of terrestrial life at the P/Tr boundary.