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

Groff, Dulcinea V.; Williams, David G.; Gill, Jacquelyn L.

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 subantarctic 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 measured the isotopic composition of P. flabellata and precipitation and explore relationships with seasonal temperature and humidity variations across four study locations in the Falkland Islands. We reveal that inter-seasonal differences in carbon and oxygen stable isotopes of leaf inline-formulaα-cellulose of living P. flabellata correlated with monthly mean temperature and relative humidity. The carbon isotope composition of leaf inline-formulaα-cellulose (inline-formulaδ13Cinline-formulaleaf) records the balance of inline-formulaCO2 supply through stomata and the demand by photosynthesis. The positive correlation between inline-formulaδ13Cinline-formulaleaf and temperature and negative correlation between inline-formulaδ13Cinline-formulaleaf and relative humidity suggest that photosynthetic demand for inline-formulaCO2 relative to stomatal supply is enhanced when conditions are warm and dry. Further, the positive correlation between inline-formulaδ13Cinline-formulaleaf and inline-formulaδ18Oinline-formulaleaf (inline-formular=0.88; inline-formulap<0.001; inline-formulan=24) indicates that stomatal closure during warm dry periods explains seasonal variation in inline-formulaδ13Cinline-formulaleaf. We observed significant differences between winter and summer seasons for both inline-formulaδ18Oinline-formulaleaf and inline-formulaδ13Cinline-formulaleaf and among study locations for inline-formulaδ18Oinline-formulaleaf but not inline-formulaδ13Cinline-formulaleaf. inline-formulaδ18O values of monthly composite precipitation were similar between seasons and among study locations, yet characteristic of the latitudinal origin of storm tracks and seasonal winds. The weak correlation between inline-formulaδ18O in monthly composite precipitation and inline-formulaδ18Oinline-formulaleaf further suggests that relative humidity is the main driver of the inline-formulaδ18Oinline-formulaleaf. The oxygen isotopes in root inline-formulaα-cellulose did not reflect, or only partially reflected (at one study location), the inline-formulaδ18O in precipitation. Overall, this study supports the use of peat records formed by P. flabellata to fill a significant gap in our knowledge of the long-term trends in Southern Hemisphere climate dynamics.

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Groff, Dulcinea V. / Williams, David G. / Gill, Jacquelyn L.: Modern calibration of Poa flabellata (tussac grass) as a new paleoclimate proxy in the South Atlantic. 2020. Copernicus Publications.

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Rechteinhaber: Dulcinea V. Groff et al.

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