Constraints on Late Paleozoic Ocean Response to Climate Change Based on Brachiopod δ11B and 87Sr/86Sr
Abstract
In order to understand the possible effects of climate change on present day oceans, it is important to determine how marine systems responded to climate change in the past. This study uses δ11B values from well-preserved Carboniferous and Permian brachiopods as well as models to examine chemical trends in seawater and how these relate to long- and short-term climate changes. Our results show that δ11B rises rapidly going into the Carboniferous from a low of 10‰ to a high of 17‰ and remains relatively stable through the Carboniferous, despite the initiation of glaciation in the Mid Carboniferous. At the Carboniferous-Permian boundary, δ11B declines into the Early Permian before reaching a low at the Sakmarian. This decline in δ11B is coincident with the decrease in 87Sr/86Sr through this interval, which corresponds to evidence for aridity going into the Permian. We hypothesize that a reduction in silicate weathering drives an increase in atmospheric pCO2 and a subsequent lowering of ocean pH going into the Permian. This is consistent with our interpretation of the Carboniferous-Permian boundary, as a major mechanism for controlling seawater boron isotope composition is the adsorption of borate on clays, removing isotopically light boron and thus leaving seawater boron isotopically heavy. Therefore, at lower pH seawater should become isotopically lighter as this mechanism for removal is reduced. These hypotheses are supported by our initial modeling results of the B and Sr isotopic budgets of the ocean during the Late Paleozoic.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFMPP14A..06L
- Keywords:
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- 1622 Earth system modeling;
- GLOBAL CHANGE;
- 4912 Biogeochemical cycles;
- processes;
- and modeling;
- PALEOCEANOGRAPHY;
- 4914 Continental climate records;
- PALEOCEANOGRAPHY;
- 4924 Geochemical tracers;
- PALEOCEANOGRAPHY