Continuous shipboard measurements of oceanic δ¹⁸O, δD and δ¹³CDIC along a transect from New Zealand to Antarctica using cavity ring-down isotope spectrometry

• Published in: Journal of Marine Systems
• Main Authors: Bass, A.M., Munksgaard, N.C., O'Grady, D., Williams, M.J.M., Bostock, H.C., Rintoul, S.R., Bird, M.I.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2014
• Subjects: Oxygen isotopes; hydrogen isotopes; dissolved inorganic carbon; Antarctica; sea-ice; Southern Ccean; Polar front; Sub-tropical front; Sub-Antarctic front; Antarctic; New Zealand; The Antarctic; Antarc*; Sea ice
• Online Access: http://hdl.handle.net/2440/123379; https://doi.org/10.1016/j.jmarsys.2014.04.003

Cavity ring-down spectrometers, with automated sampling interfaces, were deployed to allow measurements of water isotopes (δ¹⁸O, δD) and dissolved inorganic carbon (δ¹³CDIC) stable isotope ratios at high temporal resolution along a transect from New Zealand to the Antarctic continental shelf. Measurements every 10 min for δ¹⁸O and δD, 15 min for DIC yielded 2499 and 2289 discrete measurements respectively. High resolution data enabled the delineation of water mass boundaries as well as revealing insights into surface hydrological and biological processes. δ¹⁸O, δD, and δ¹³CDIC decreased southwards, dropping by approximately 1.0‰, 7.0‰, and 0.5‰, respectively. Though the decline in δ¹³CDIC with latitude was generally linear, the drop in δ¹⁸O and δD was punctuated by areas of rapid, significant change corresponding to the Sub-Tropical, Sub-Antarctic and Polar Fronts. North of the Sub-Antarctic Front (approx. 54.5°S) the dominant control on water and DIC isotopes was the precipitation–evaporation balance and the contribution of upwelling waters, respectively. Further south, in close proximity to the sea ice and on the Antarctic shelf, water isotope values were more variable and predominantly influenced by the melting/freezing of sea-ice coupled to inputs from glacial/snow melt water. Local increases in δ¹³CDIC were likely due to photosynthetic enrichment of the DIC pool. Using this new instrumentation has provided one of the most comprehensive oceanic transect data sets yet achieved and illustrates the potential of these methods to delineate discrete water masses and advance our knowledge of both water and inorganic carbon cycling processes in the ocean. This methodology, combining high-resolution isotopic measurements with hydrographic data, has significant benefits in modelling water mixing in locations with multiple sources and controlling processes. Adrian M. Bass, Niels C. Munksgaard, Damien O’Grady, Michael J.M. Williams, Helen C. Bostock, Stephen R. Rintoul, Michael I. Bird