This dataset contains sample preparation parameters and stable carbon and oxygen isotope measurements from IODP Site 306-U1312, located in the North Atlantic Ocean north of the Azores Islands (42°50.2'N, 23°38.2'W; 3554 m water depth). The record spans Marine Isotope Stages 38 to 46 during the Early Pleistocene and includes wet weight, dry weight, sand fraction weight, and stable isotope data obtained from planktonic and benthic foraminifera. Sediment samples were processed following the standard procedures of the Sedimentology and Micropaleontology Laboratory of the Divisão de Geologia e Georecursos Marinhos (DivGM), Instituto Português do Mar e da Atmosfera (IPMA). Samples were weighed before and after freeze-drying to determine dry weight, washed through a 63 μm sieve, and the coarse fraction was dried and weighed. Stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotope measurements were performed on the planktonic foraminifer Globigerina bulloides and the benthic foraminifera Cibicidoides wuellerstorfi at the Leibniz Laboratory for Radiometric Dating and Stable Isotope Research (Kiel University, Germany) using a Finnigan MAT 253 mass spectrometer coupled to a Kiel IV carbonate preparation device. Isotope values are reported relative to the Vienna Pee Dee Belemnite (VPDB) standard. The age model is based on correlation of the benthic δ¹⁸O record to the LR04 benthic isotope stack. The dataset provides stable isotope and sample preparation data for IODP Site 306-U1312 and serves as a chronological framework for paleoceanographic and micropaleontological investigations in the North Atlantic during the Early Pleistocene.