The variability of Southern Ocean sea-surface temperatures (SST) are important to understanding coastal biology yet are poorly known amongst biologists. We compare sea temperatures at a constant depth (10–20 m) at coastal localities both sides of the Polar Front (PF), around the Scotia-Arc, the West Antarctic Peninsula and at high oceanic latitudes (around the margins of East Antarctica). We assess the wider context of these values by investigating minimum and maximum temperatures and ranges throughout the Southern Ocean using remotely sensed SST data. Data to date show weekly, daily and hourly variation in shallow sea temperature can be one-third of total annual variability (in the summer) but can be very constant (in winter). From comparison across scales in time and space, the strong seasonal signal is the most striking feature of Antarctic shallow sea temperatures even at highest oceanic latitude sites. The winter sea temperatures at localities within the PF are similar (near freezing), but upper temperatures and thus the annual range vary predictably with latitude in a cline. This amounts to 0.2 °C annual range/100 km of latitude between 54°S and 67°S. The annual range in sea temperatures is little different at SubAntarctic islands, whether they are north or south of the PF.