This data set includes absolute counts and relative abundances of diatom species from samples collected during cruises LMG0502 and NBP0603 on the research vessels LM Gould and NB Palmer. Sediment samples were collected using a Smith-McIntyre grab sampler and kasten corer. These sediments are stored at the Antarctic Marine Geology Research Facility at Florida State University. Quantitative slides ... for microscopic analyses were prepared at 1-10 cm intervals from all cores collected, and from all surface samples. These slides are stored at Colgate University. Water samples were collected from the uncontaminated seawater line during these same cruises. These samples were filtered and phytoplankton counts were completed. Diatom count data from both sediment and water sample analyses are available in Excel format from the Principal Investigator. The spreadsheets include latitude, longitude and water depth for all the sediment samples. Additional physical oceanographic data are available for all the phytoplankton data. This includes information regarding sea surface temperature and salinity, pCO2sw, transmissivitysw and underway surface fluorometry. Additionally, observational data concerning the local distribution of sea ice and glacial ice are recorded.