Climatic and Topographic Control of the Stable Isotope Values of Rivers on the South Island of New Zealand. Issue 5 (19th May 2021)

• Record Type: Journal Article
• Authors: Lachniet, Matthew S.; Moy, Christopher M.; Riesselman, Christina; Stephen, Haroon; Lorrey, Andrew M.
• Is Part Of: Paleoceanography and paleoclimatology. Volume 36:Issue 5(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-05-19
• Subjects: climate dynamics -- New Zealand -- oxygen isotopes -- paleoaltimetry -- paleoclimate -- rivers; Paleoceanography -- Periodicals; Paleoclimatology -- Periodicals; 551.46
• DOI: 10.1029/2021PA004220
• Languages: English
• ISSNs: 2572-4517

Abstract

Abstract: We show that climate and topography control the spatial distribution of stable isotope values on the South Island of New Zealand, based on a spatially dense ( n = 193) river isotopic survey. Our data show a δ 18 O minimum in isotope values east of the Southern Alps that demonstrates topographically driven continentality associated with the Southern Alps, which intersect the prevailing, moisture‐laden westerlies. Our data define a South Island surface water line of δ 2 H = 8.17 (±0.26) × δ 18 O + 10.57 (±2.04), which is identical within 95% confidence intervals to the global and New Zealand meteoric water lines established from monthly precipitation samples. The observed river δ 18 O values are strongly correlated with annual temperature range and winter temperature. Strongest correlations are between δ 18 O and mean minimum winter temperatures ( r > 0.7 for June, July, August), with gradients of 0.58–0.66‰ /°C. Based on a multiple regression analysis of δ 18 O against climate data, we present a river δ 18 O model and isoscape that demonstrate the control of continentality and moisture source on New Zealand surface water isotope spatial patterns. Model validation against previously published river samples shows skill in predicting river δ 18 O values (root‐mean‐square error = 0.83), confirming that the spatial variations in river δ 18 O (and δ 2 H) are robust to sampling period and reflect continental, precipitation source and temperature effects. Our data suggest that oxygen or hydrogen isotope paleoclimate proxies derived from rivers or open‐system lakes on the South Island should be sensitive to winter temperature. Plain Language Summary: We investigated the spatial variations in oxygen and hydrogen stable isotopes in rivers on the South Island of New Zealand and show that they are strongly controlled by the presence of the Southern Alps. Indicators of continental climates, such as seasonal temperature range and temperature of the coldest months are strongly related to measured oxygen isotope values of river waters. We show that winter temperature and continentality are the dominant control on New Zealand South Island river oxygen isotope values, and they result in minimum values in the lee of the highest portion of the Southern Alps. We also show that river deuterium excess values are controlled by Pacific Ocean versus Tasman Sea moisture sources. Key Points: Survey of spatial river δ 18 O values on New Zealand's South Island shows strong correlations to winter temperature and continentality Lowest river δ 18 O values are present in the most continental locations in the lee of the high Southern Alps Data are useful for interpreting isotopic paleoclimate proxy records related to surface waters