Define CDW for end of backward particle tracking

[PaulSpence]

What definitions of CDW that work based on T, S, and or density ... in models or obs?

Below is some literature providing various options for defining CDW.

[PaulSpence]

Morrison, A., Hogg, A. M., England, M., & Spence, P. (2020). Warm circumpolar deep water transport toward Antarctica driven by local dense water export in canyons. Science Advances, 6(18), eaav2516. https://doi.org/10.1126/sciadv.aav2516

32.40<CDW<32.56 kg/m3

Unfortunately, there are no self-evident definitions, because the temperature, salinity, and density of the water masses vary considerably around the Antarctic continent. We therefore strive to keep the definitions simple and widely applicable by using only density thresholds to separate water masses [following ([13], [17], [24], [31])]. The DSW density cutoff is chosen to capture the maximum possible offshore transport across the 1000-m isobath (e.g., as shown in Fig. 2B). The density threshold separating CDW and AASW is chosen to select the majority of the warmest, oldest waters on the continental slope. This is done using a temperature-salinity plot, as shown in fig. S7 for the circumpolar case.

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[PaulSpence]

Tamsitt, V., England, M. H., Rintoul, S. R., & Morrison, A. K. (2021). Residence time and transformation of warm Circumpolar Deep Water on the Antarctic continental shelf. Geophysical Research Letters, 48, e2021GL096092. https://doi.org/10.1029/2021GL096092 On the shelf and slope

32.4 < CDW< 32.56 kg/m3

As CDW properties vary around the shelf and slope, it is difficult to choose a universal temperature and salinity definition to capture the onshore CDW in all shelf regions. Therefore, we define particles as modified CDW (mCDW) if their initial potential density anomaly referenced to 1,000 m ( ) lies between 32.4 and 32.56 kg m−3 (Morrison et al., 2020), and note that this includes a range of temperatures from near freezing to 2°C.

[PaulSpence]

Ribeiro, N., Herraiz-Borreguero, L., Rintoul, S. R., McMahon, C. R., Hindell, M., Harcourt, R., & Williams, G. (2021). Warm modified Circumpolar Deep Water intrusions drive ice shelf melt and inhibit Dense Shelf Water formation in Vincennes Bay, East Antarctica. Journal of Geophysical Research: Oceans, 126, e2020JC016998. https://doi.org/10.1029/2020JC016998

For modified CDW 28.0 < mCDW< 28.7 kg/m3 and -1.7<mCDW<1.5 oC

There is some variability in the nomenclature and properties used to define water masses around the coastal margin of Antarctica, especially in regions of AABW production (Jacobs et al., 1970; Kitade et al., 2014; Williams et al., 2016). We follow the water mass definitions of Williams et al. (2016) and Silvano et al. (2017), using neutral density to distinguish the three classic offshore water masses of Antarctic Surface Water (AASW), CDW, and AABW. Water mass transformations driven by ice-ocean-atmosphere interactions over the continental shelf produce three additional water masses: Winter Water (WW), DSW and Ice Shelf Water (ISW), whose properties are described in Table 1

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