A total of 31 paired under-ice irradiance measurements and ice core samples were collected from 12 ice stations in the 115-130 degrees E sector off East Antarctica in September and early October 2007 during the Sea Ice Physics and Ecosystem eXperiment (SIPEX). Sampled ice floes were several 100 meters to several kilometres in diameter and were all composite first-year sea ice floes showing ... different degrees of deformation. The SIPEX bio-optical sampling sites were chosen such that their immediate surroundings (20 m) showed no snow cover disturbances, were level, and free of surface deformations.
On each sampling site we deployed a TriOS Ramses ACC VIS radiometer (cosine receptor, 180 degree field of view) 0.15 m beneath the subsurface of the ice floe through an access hole (0.11 m diameter) using a retractable L-shaped stainless steel arm. The hole-effect on the light measurements was assumed to be negligible due the position of the radiometer 1.2 m north (i.e. directed towards the sun) of the access hole. Under-ice high-resolution (300-900 nm, 3.3 nm band-width) irradiance spectra were recorded with a laptop computer using TriOS MSDA_XE software version 7.5.1. At each site, snow thickness was measured with a ruler (10 replicate measurements) and one ice core was collected, using a manual Kovacs Mark II ice core system (0.09 m core diameter), directly above the radiometer location. Ice floe freeboard was determined with a ruler from the sampling hole. The length of the ice core was recorded and the ice core was placed in a clean polyethylene container and transported back to the ship's laboratories. On the ship sampled ice cores were melted at 4 degrees C in the dark within 24 - 36 hours of collection. After the ice cores had melted, the samples were gently mixed and subsamples were taken for a) determination of ice algal pigment concentration and composition, and b) determination of particulate absorption.