The boron isotope (δ11B) proxy for seawater pH is a tried and tested means to reconstruct atmospheric CO2in the geologic past, but uncertainty remains over how to treat species‐specific calibrations that link foraminiferal δ11B to pH estimates prior to 22 My. In addition, no δ11B‐based reconstructions of atmospheric CO2exist for wide swaths of the Oligocene (33–23 Ma), and large variability in CO2reconstructions during this epoch based on other proxy evidence leaves climate evolution during this period relatively unconstrained. To add to our understanding of Oligocene and early Miocene climate, we generated new atmospheric CO2estimates from new δ11B data from fossil shells of surface‐dwelling planktic foraminifera from the mid‐Oligocene to early Miocene (∼28–18 Ma). We estimate atmospheric CO2of ∼680 ppm for the mid‐Oligocene, which then evolves to fluctuate between ∼500–570 ppm during the late Oligocene and between ∼420–700 ppm in the early Miocene. These estimates tend to trend higher than Oligo‐Miocene CO2estimates from other proxies, although we observe good proxy agreement in the late Oligocene. Reconstructions of CO2fall lower than estimates from paleoclimate model simulations in the early Miocene and mid Oligocene, which indicates that more proxy and/or model refinement is needed for these periods. Our species cross‐calibrations, assessing δ11B, Mg/Ca, δ18O, and δ13C, are able to pinpoint and evaluate small differences in the geochemistry of surface‐dwelling planktic foraminifera, lending confidence to paleoceanographers applying this approach even further back in time.
As the majority of fossil fuel carbon dioxide (CO2) emissions originate from cities, the use of novel techniques to leverage available satellite observations of CO2and proxy species to constrain urban CO2is of great importance. In this study, we seek to empirically determine relationships between satellite observations of CO2and the proxy species nitrogen dioxide (NO2), applying these relationships to NO2fields to generate NO2‐derived CO2fields (NDCFs) from which CO2emissions can be estimated. We first establish this method using simulations of CO2and NO2for the cities of Buenos Aires, Melbourne, and Mexico City, finding that the method is viable throughout the year. For the same three cities, we next calculate empirical relationships (slopes) between co‐located observations of NO2from the Tropospheric Monitoring Instrument and Snapshot Area Mode observations of CO2from Orbiting Carbon Observatory‐3. Applying varying combinations of slopes to generate NDCFs, we evaluate methodological uncertainties for each slope application method and use a simple mass balance method to estimate CO2emissions from NDCFs. We demonstrate monthly urban CO2emissions estimates that are comparable to emissions inventory estimates. We additionally prove the utility of our method by demonstrating how large uncertainties at a grid cell level (equivalent to ∼1–3 ppm) can be reduced substantially when aggregating emissions estimates from NDCFs generated from all NO2swaths (about 1%–6%). Rather than rely on prior knowledge of emission ratios, our method circumvents such assumptions and provides a valuable observational constraint on urban CO2emissions.
more » « less- PAR ID:
- 10407798
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 128
- Issue:
- 6
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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