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 (δ¹³C_leaf) records the balance of CO₂ supply through stomata and the demand by photosynthesis. The positive correlation between δ¹³C_leaf and temperature and negative correlation between δ¹³C_leaf 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 δ¹³C_leaf and δ¹⁸O_leaf (r=0.88; p<0.001; n=24) indicates that stomatal closure during warm dry periods explains seasonal variation in δ¹³C_leaf. We observed significant differences between winter and summer seasons for both δ¹⁸O_leaf and δ¹³C_leaf and among study locations for δ¹⁸O_leaf but not δ¹³C_leaf. 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 δ¹⁸O_leaf further suggests that relative humidity is the main driver of the δ¹⁸O_leaf. 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.

中文翻译：

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作为南大西洋新的古气候代名词的黄柏（Pos flabellata）（tus草）的现代标定

在南大西洋，陆地古气候记录很少，这限制了为当前全球变化提供史前背景的机会。丛草Poa flabellata在福克兰群岛和其他亚南极岛屿的海岸上大量生长。它形成了广泛的泥炭记录，为重建高分辨率区域气候记录提供了一个有希望的机会。沉积在这些泥炭中的叶和根组织的同位素组成具有记录随时间变化的降水，温度和相对湿度的潜力，但是这些关系对于黄叶P. bellbellata是未知的。在这里，我们测量了P. flabellata的同位素组成和降水，并探索福克兰群岛四个研究地点与季节性温度和湿度变化的关系。我们揭示碳该季节间差异和叶的氧稳定同位素α -纤维素活P.胆草与月平均温度和相对湿度相关。叶的碳同位素组成α -纤维素（δ ¹³ C ^_叶）记录的平衡CO ₂供给通孔和通过光合作用的需求。之间的正相关性δ ¹³ Ç_叶 和温度之间的负相关δ¹³ C_叶片和相对湿度表明，在温暖干燥的条件下，相对于气孔供应， CO _2的光合作用需求增加。另外，之间的正相关性δ ¹³ Ç_叶和δ ¹⁸ ö_叶（ [R = 0.88 ; p <0.001 ; ñ = 24）表示在预热期间干旱期的是气孔关闭解释季节变化δ ¹³ Ç_叶。我们观察到冬季和夏季之间显著差异两个δ ¹⁸ Ø_叶和δ ¹³ Ç_叶和研究地点为中δ ¹⁸ ö_叶但不δ ¹³ Ç_叶。δ ^18个月复合沉淀的O值分别为季节之间和研究地点之间相似，但风暴路径和季节性风的纬向起源的特性。之间的弱相关性 δ ¹⁸ ö按月复合沉淀和δ ¹⁸ ö_叶进一步表明，相对湿度是的主要驱动δ ¹⁸ ö_叶。中的氧同位素根 α -纤维素没有反映，或仅部分地反射（在一项研究中位置），δ ¹⁸ Ó沉淀。总的来说，这项研究支持使用由黄叶疫霉形成的泥炭记录来填补我们对南半球气候动态长期趋势的认识上的重大空白。