Spatial and temporal scales of chlorophyll variability using high-resolution glider data

In the Southern Ocean, increasing evidence from recent studies is highlighting the need for high-resolution sampling at fine spatial (meso- to sub-mesoscale) and temporal scales (intra-seasonal) in order to understand longer-term variability of phytoplankton and the controlling physical and biogeochemical processes. Here, highresolution glider data (3 hourly, 2 km horizontal resolution) and satellite ocean colour data (2-4 km) from the Sub-Antarctic zone (SAZ) were used to 1) quantify the dominant scales of variability of the glider time series, 2) determine the minimum sampling frequency required to adequately characterise the glider time series and 3) discriminate how much of the variability measured with a glider is the result of temporal variations versus spatial patchiness. Results highlight the important role of signals shorter than 10 days in characterising surface chlorophyll (chl-a) variability, particularly in spring (97%) and to a lesser degree in summer (27%). These small scales of variability were also evident in the physical indices of SST, wind stress and mixed layer depth. Further analysis revealed that sampling at high frequencies (< 10 days) are required to adequately resolve and characterise the seasonal and intra-seasonal mean state and variability of chl-a in the SAZ. Spatial analysis found that surface chl-a is patchier than surface temperature, as previously found in the North Atlantic. In addition, our seasonal analyses found that patchiness at smaller scales decreases in summer (relative to spring) indicative of a more homogeneous phytoplankton distribution. A spring comparison of the glider and concurrent satellite data at similar spatial scales suggests that the chl-a variability captured by the glider is generally larger than observed in the remote sensing images and may be driven by daily fluctuations.