To deduce paleoclimatic changes attributable to variability in the sea ice, a long-term record of sea-ice is required, beyond the time period covered by direct instrumental monitoring. A recent proxy for Arctic Ocean sea-ice has been developed based on the analysis of an isomer of C25, also known as IP25 (Ice proxy with 25 carbo atoms). In addition, other phytoplankton - derive biomarkers such as brassicasterol (Phytoplankton marker - IP25 index; PIP25) are employed to confirm sea ice change deductions for the past 500 years.
