Methodology:

The Jurassic ice core was drilled in the austral summer 2012/2013 CE to a depth of 140m using the British Antarctic Survey (BAS) electromechanical, 104 mm diameter drill. An ice chronology was established for this core based on the annual cycles of hydrogen peroxide (H2O2) and the non-sea salt component of sulphate (nssSO42-). The estimated dating error was <+/-7 months for each year and with no accumulated error. Diatom samples were obtained by filtering meltwater from annual layers of the Jurassic ice core. Jurassic ice core meltwater was filtered through 1.0 micro-meter pore size filters, which were later imaged using a Quanta-650F Scanning Electron Microscope (SEM) at the Earth Sciences Department, University of Cambridge. Diatom identification and ecological associations were based on published Southern Ocean databases and references therein (Armand et al., 2005; Hasle and Syvertsen, 1997; Cefarelli et al., 2010; Zielinski and Gersonde, 1997).

Data collection:

Quanta-650F Scanning Electron Microscope (SEM) at the Earth Sciences Department, University of Cambridge.

Data quality:

Diatom samples were processed and analysed according to the methods and constraints outlined in Tetzner et al. (2021) and Tetzner et al. (2025). Annual layer meltwater from Jurassic ice core was filtered using polycarbonate membrane filters with a pore diameter of 1.0 ?m. After filtration, the filters were scanned using a Scanning Electron Microscope (SEM). One-third of the filter area was scanned, in line with the observations from Tetzner et al. (2021) and Tetzner et al. (2025), which noted that diatoms tend to have a homogeneous spatial distribution when the counts over one-third of the filter area are six or more. The main diatom assemblage composition was established from the identified species and groups with abundances higher than 2.0% of the whole assemblage.