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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-487
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-487
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 30 Jan 2020

Submitted as: research article | 30 Jan 2020

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This preprint is currently under review for the journal BG.

Modern calibration of Poa flabellata (Tussac grass) as a new paleoclimate proxy in the South Atlantic

Dulcinea V. Groff1,2, David G. Williams3, and Jacquelyn L. Gill1,2 Dulcinea V. Groff et al.
  • 1Climate Change Institute, University of Maine, Orono, ME 04469, USA
  • 2School of Biology and Ecology, University of Maine, Orono, Me 04469, USA
  • 3Department of Botany, University of Wyoming, Laramie, WY 82071, USA

Abstract. Terrestrial paleoclimate records are rare in the South Atlantic, limiting opportunities to provide a prehistoric context for current global changes. The tussock grass, Poa flabellata, grows abundantly along the coasts of the Falkland Islands and other sub-Antarctic islands. It forms extensive peat records, providing a promising opportunity to reconstruct high-resolution regional climate records. The isotopic composition of leaf and root tissues deposited in these peats has the potential to record variation in precipitation, temperature, and relative humidity over time, but these relationships are unknown for P. flabellata. Here, we investigate the isotopic composition of P. flabellata plants and precipitation and explore seasonal relationships with temperature and humidity across 4 study locations in the Falkland Islands. We reveal that inter-seasonal differences in carbon and oxygen stable isotopes of leaf α-cellulose of living P. flabellata significantly correlated with monthly mean temperature and relative humidity. The carbon isotope composition of leaf α-cellulose (δ13Cleaf) records the balance of CO2 supply through stomata and the demand by photosynthesis. The positive correlation between δ13Cleaf and temperature and negative correlation between between δ13Cleaf and relative humidity suggest that photosynthetic demand for CO2 relative to stomatal supply is enhanced when conditions are warm and dry. Further, the positive correlation between δ13Cleaf and δ18Oleaf (r = 0.88, p < 0.001, n = 24) indicates that stomatal closure during warm dry periods explain seasonal variation in δ13Cleaf. We observed significant differences between winter and summer seasons for both δ18Oleaf and δ13Cleaf, and among study locations for δ18Oleaf, but not δ13Cleaf. δ18O values of monthly composite precipitation did not differ between seasons or among study locations, yet is characteristic of the latitudinal origin of storm tracks and seasonal winds. The weak correlation between δ18O in monthly composite precipitation and δ18Oleaf further suggests that relative humidity is the main driver of the δ18Oleaf. The oxygen isotopes in root α-cellulose did not reflect, or only partially reflected (at one study location), the δ18O in precipitation. Overall, this study supports the use of peat records formed by P. flabellata to fill in a significant gap in our knowledge of the long-term trends in Southern Hemisphere climate dynamics.

Dulcinea V. Groff et al.

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Dulcinea V. Groff et al.

Data sets

Datasets for leaf and root stable isotopes of cellulose D. V. Groff, D. G. Williams, and J. L. Gill https://doi.org/10.5281/zenodo.3104573

Dulcinea V. Groff et al.

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Latest update: 25 Feb 2020
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Short summary
Tussock grasses that grow along coastlines of the Falkland Islands are slow to decay, and build up thick peat layers over thousands of years. Grass fragments found in ancient peat can be used to reconstruct past climate because grasses can preserve a record of growing conditions in their leaves. We found that modern living tussock grasses in the Falkland Islands reliably record temperature and humidity in their leaves and the peat they form can be used to understand past climate change.
Tussock grasses that grow along coastlines of the Falkland Islands are slow to decay, and build...
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