Temporal and spatial length scales in δ18O observations (D5.5)

This deliverable is a report on the analysis undertaken to determine the length scales and timescales of oxygen isotope (δ¹⁸O) variations in the surface ocean based on observations. We find that there are multiple length scales, up to three (depending on the length of the segment being analysed). We characterise these length scales as being eddy (typically 100-300km), an intermediate scale (500-700 km) and a gyre scale (1000-1500 km). The spatial distribution of the decorrelation length scales indicate the pervasiveness of eddies in the Southern Ocean, while longer length scales depict the zonal nature of the Antarctic Circumpolar Current as well as the structure of the Ross and Weddell gyres. The differences in the spatial patterns suggest that at the largest scales, the decorrelation length scales are anisotropic, with meridional length scales mostly featuring the circumpolar current, while northward scales indicating the northward spreading of the Subantarctic Mode Waters. Regarding the decorrelation timescales, unfortunately, the available time series in the Southern Ocean can only suggest some interannual variability, but the amount of observations is not enough to identify the structure or driver of such variability. Scales associated with oxygen isotopes are similar to those for salinity, whereas there are some differences with temperature.