Stable Water Isotopes across a Transect of the Southern Alps, New Zealand

Abstract

Stable water isotope concentrations were obtained from samples of stream water at 29 sites in a west–east transect across the Southern Alps of New Zealand, where westerly conditions dominate the precipitation regime. The samples were taken from small catchment streams during a time of extended recession as a means of collecting time and space averages of the source precipitation. The isotopic concentrations from sites at either end of the transect lead to a drying ratio estimate of 22%–34% for this region of the Southern Alps. The isotope concentrations increased from west to east, indicating that precipitation in the lee area originates from higher and/or colder condensation than on the windward side. The transect was divided into three regions according to the deuterium-excess (d excess) results. Increasing d-excess values on the windward side of the mountains were speculated to be a result of some unknown combination of reducing relative evapotranspiration, increasing recycling of water vapor, and increasing nonequilibrating condensation from high-intensity precipitation. Low d-excess values in the region immediately lee of the mountains were consistent with below-cloud evaporation associated with increased hydrometeor drift into the drier lee side. High d excess in the more distant lee side was attributed to a secondary source of moisture (from the east and south). The information gained has supported current concepts of the precipitation processes dominant in the region and has provided additional quantitative measurements with which to validate future precipitation modeling efforts.

Linking interannual river flow river variability across New Zealand to the Southern Annular Mode, 1979–2011

“…Given its similar geographic setting to that of BoPHB, and the SAM river flow association described above for that region as well as CWLNI and LoSI, it would appear that orographic forcing or blocking or steering play a fundamental role in controlling the hydrological outcome of strong positive and negative phases of SAM across New Zealand via its control on precipitation delivery. This claim lends credence to the hydrological implications of climatological research conducted on zonal precipitation gradients across NZ (Chater & Sturman, ; Kerr, Srinivasan, & Rutherford, ; Webster, Kingston, & Kerr, ). Further, the posited significance of distinct synoptic scale configurations of atmospheric circulation for river flow across New Zealand is supported by work conducted for similar geographical settings that evaluate the importance of orography in determining hydrological outcomes arising from contrasting phases of large scale modes of climatic variability (Luce, Abatzoglou, & Holden, ; Mass, Johnson, Warner, & Vargas, ; Siler, Roe, & Durran, ; Viale & Nunez, ).…”

“…Although statistically significant concurrent correlations were not found between SAM index values and river flow for the CTB region, the sign of the monthly and one season ahead correlations are strongly suggestive of CTB high flows being consequential on a positive SAM phase (Tables 4 and 5). Given its similar geographic setting to that of BoPHB, and the SAM river flow association described above for that region as well as CWLNI and LoSI, it would appear that orographic forcing or blocking or steering play a fundamental role in controlling the hydrological outcome of strong positive and negative phases of SAM across New Zealand via its precipitation gradients across NZ (Chater & Sturman, 1998;Kerr, Srinivasan, & Rutherford, 2015;Webster, Kingston, & Kerr, 2015). Further, the posited significance of distinct synoptic scale configurations of atmospheric circulation for river flow across New Zealand is supported by work conducted for similar geographical settings that evaluate the importance of orography in determining hydrological outcomes arising from contrasting phases of large scale modes of climatic variability (Luce, Abatzoglou, & Holden, 2013;Mass, Johnson, Warner, & Vargas, 2015;Siler, Roe, & Durran, 2013;Viale & Nunez, 2011).…”

Climatic and Topographic Control of the Stable Isotope Values of Rivers on the South Island of New Zealand

“…To further assess model performance, we compiled 127 independently measured streams with δ 18 O and/or δ 2 H values from the published literature (Blackstock, 2011;Kerr et al, 2015;Stewart et al, 1983) including the 24 rivers reported above (Table S2) to calculate the statistical fit, and mean and standard deviation of the residuals. The Stewart et al (1983) δ 2 H data, collected in the 1970s and 1980s, were converted to δ 18 O values according to our local surface water line equation from Figure 2.…”

“…A more comprehensive suite of river water isotope values was presented by Stewart et al (1983), who measured δ 2 H values in 61 rivers on the South Island, with most samples located near the coasts. Additionally, Kerr et al (2015) sampled 29 closely spaced sites in a transect from the Tasman Sea to near the alpine divide. These three studies indicate that river isotope values vary significantly across the South Island, but large areas remain unsampled.…”

Late Quaternary Climate Variability and Change from Aotearoa New Zealand Speleothems: Progress in Age Modelling, Oxygen Isotope Master Record Construction and Proxy-Model Comparisons

“…Data from a network of precipitation isotope monitoring sites in New Zealand demonstrate a strong control of temperature, altitude, and precipitation amount on precipitation δ 18 O values [57]. Highest mean annual δ 18 O values are found at lower latitudes and altitudes and near the coasts, with lowest δ 18 O values in the lee of the Southern Alps on the South Island where northwesterly air masses experience the greatest fractional rainout [59]. In the Waikato area near the Waitomo cave sites, seasonal precipitation δ 18 O values are inversely correlated with rainfall amount, which is consistent with the "amount effect" [34].…”