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

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 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 α-cellulose of living P. flabellata 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 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 explains 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 were similar between seasons and among study locations, yet 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 a significant gap in our knowledge of the long-term trends in Southern Hemisphere climate dynamics.

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Isotopic Composition of Precipitation in a Southeastern Region of Brazil during the Action of the South Atlantic Convergence Zone

Atmosphere ◽

10.3390/atmos12040418 ◽

2021 ◽

Vol 12 (4) ◽

pp. 418

Author(s):

Cleber Santos ◽

Rayonil Carneiro ◽

Camilla Borges ◽

Didier Gastmans ◽

Laura Borma

Keyword(s):

Isotopic Composition ◽

Hydrological Cycle ◽

Statistical Tests ◽

Spatial Scales ◽

South Atlantic Convergence Zone ◽

South Atlantic ◽

Southeastern Brazil ◽

Convergence Zone ◽

The South ◽

Hysplit Model

The use of stable isotopes of hydrogen and oxygen is a tool widely used to trace water paths along the hydrological cycle, providing support for understanding climatic conditions in different spatial scales. One of the main synoptic scale events acting in southeastern Brazil is the South Atlantic Convergence Zone (SACZ), which causes a large amount of precipitation from southern Amazonia to southeastern Brazil during the southern summer. In order to determine the isotopic composition of precipitation during the action of SACZ in São Francisco Xavier in southeastern Brazil, information from the Weather Forecasting and Climate Studies Center of the National Institute for Space Research (CPTEC) was used regarding SACZ performance days, the retrograde trajectories of the HYSPLIT model, and images from the GOES-16 satellite, in addition to the non-parametric statistical tests by Spearman and Kruskal–Wallis. A high frequency of air mass trajectories from the Amazon to southeastern Brazil was observed when the SACZ was operating. During the SACZ events, the average isotopic composition of precipitation was more depleted, with a δ18O of −9.9‰ (±2.1‰), a δ2H of −69.3‰ (±17.9‰), and d-excess of 10.1‰ (±4.0‰). When disregarding the SACZ performance, the annual isotopic composition can present an enrichment of 1.0‰ for δ18O and 8.8‰ for the δ2H. The long-term monitoring of trends in the isotopic composition of precipitation during the SACZ events can assist in indicating the evapotranspiration contribution of the Amazon rainforest to the water supply of southeastern Brazil.

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Barry Gough. The Falkland Islands/Malvinas: The Contest for Empire in the South Atlantic. Atlantic Highlands, N.J.: Athlone. 1992. Pp. xvi, 212. $65.00

The American Historical Review ◽

10.1086/ahr/99.2.699 ◽

1994 ◽

Keyword(s):

South Atlantic ◽

Falkland Islands ◽

The South

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Regional Manifestations of Late Quaternary Climate Change and Archaeological Site Burial Along the South Atlantic Coastal Plain

Early Human Life on the Southeastern Coastal Plain ◽

10.5744/florida/9781683400349.003.0010 ◽

2018 ◽

pp. 193-235 ◽

Cited By ~ 1

Author(s):

Christopher R. Moore ◽

Mark J. Brooks ◽

I. Randolph Daniel ◽

Andrew H. Ivester ◽

James K. Feathers ◽

...

Keyword(s):

Coastal Plain ◽

Late Quaternary ◽

Archaeological Site ◽

South Atlantic ◽

Atlantic Coastal Plain ◽

Luminescence Dating ◽

The South ◽

Ams Radiocarbon Dating ◽

Paleoclimate Records ◽

Atlantic Coastal

Archaeological site investigations on the South Atlantic Coastal Plain have revealed stratified cultural remains in sand deposits of mixed aeolian and fluvial origins, aeolian sand sheets and dunes, alluvial terraces, and Carolina Bay rims. These sites are typically shallow but have yielded discernible archaeostratigraphy within sand dominated deposits by using luminescence dating (OSL), AMS radiocarbon dating, and close interval sediment sampling. Periods of site burial are linked to regional and global paleoclimate records, including Bond events, and provide broader reconstructions for human ecology and periods of site burial.

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