Transport matrices from standard ocean-model output and quantifying circulation response to climate change

• Published in: Ocean Modelling
• Main Authors: Chamberlain, MA, Matear, RJ, Holzer, M, Bi, D, Marsland, SJ
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2019
• Subjects: 14 Life Below Water; anzsrc-for: 0405 Oceanography; anzsrc-for: 0911 Maritime Engineering; Antarc*; Antarctic
• Online Access: http://hdl.handle.net/1959.4/unsworks_63269; https://unsworks.unsw.edu.au/bitstreams/46902d6c-0140-4290-94c9-3d1d57c1e828/download; https://doi.org/10.1016/j.ocemod.2019.01.005

A method to construct transport matrices from standard ocean-model output, such as mean volume fluxes and mixed-layer depths, is presented. These transport matrices enable highly efficient calculation of deep-water tracer fields that otherwise require long integrations with forward time-stepping ocean models. Comparisons of matrix solutions for ideal mean water age demonstrate that the transport matrices are reasonably accurate representations of the transport in the parent ocean models. Tracer fields calculated using transport matrices provide simple circulation metrics that can be compared to observations. We compare matrix-computed radiocarbon distributions from two versions of ACCESS ocean models with observations. We find matrices based on both models produce realistic circulations; the radiocarbon distribution based on ACCESS forced with CORE climatology fits observations better in the deep Pacific, whereas the fully coupled ACCESS1.3 model fits observations better in the deep Atlantic. When applied to the circulations of ACCESS1.3 climate-change experiments, the transport-matrix solutions show an increase in radiocarbon depletion, or water age, in the projected ocean circulation for the 2090s under the RCP8.5 scenario. By computing the water-mass fractions last ventilated from specific regions, we diagnose a corresponding progressive shutdown in Antarctic Bottom Water formation. The volumetric decrease in Antarctic waters in the global ocean is compensated by an increase in waters last ventilated in the subantarctic and southern subtropics.