We apply a multi-proxy approach to marine sediment core CDH-89 (western equatorial Atlantic, WEA) to investigate ITCZ variability during the penultimate deglaciation. Planktonic foraminiferal assemblages were used to calculate the RN/Gg ratio, defined as %Neogloboquadrina / (%Neogloboquadrina + %Globigerina glutinata), providing insights into upper-ocean structure. We further reconstructed surface hydrography using a suite of oxygen-isotope–based proxies, including Neogloboquadrina dutertrei δ¹⁸O, Globigerinoides ruber (white, sensu stricto) δ¹⁸O, and the interspecies gradient Δδ¹⁸O (N. dutertrei – G. ruber). In addition, we estimated seawater isotopic composition (δ¹⁸O_SW) for both species (N. dutertrei δ¹⁸O_SW and G. ruber δ¹⁸O_SW), as well as the interspecies difference Δδ¹⁸O_SW (N. dutertrei – G. ruber), to infer past salinity variations. Sea-surface temperature was reconstructed using N. dutertrei Mg/Ca-derived calcification temperatures, and we calculated the interspecies temperature gradient ΔTemperature (N. dutertrei – G. ruber) to provide additional constraints on upper-ocean thermal structure.

Method details:Row 7: δ18O, seawater, reconstructed (Subsurface): Calculated using δ18O and temperature values derived from N. dutertrei. An offset of 0.27 ‰ was used for practical comparison between VPDB and VSMOW isotope reference scales (Hut, 1987). The temperature component was removed from N. dutertrei δ18O values using the paleotemperature equation of Shackleton (1974).Row 8: δ18O, seawater, reconstructed (Surface): Calculated using δ18O and temperature values derived from G. ruber. An offset of 0.27 ‰ was used for practical comparison between VPDB and VSMOW isotope reference scales (Hut, 1987). The temperature component was removed from G. ruber δ18O values using the paleotemperature equation of Shackleton (1974).Row 11: Species-specific calibration equation for N. dutertrei (350–450 μm) from Anand et al. (2003).Row 12: Neogloboquadrina dutertrei, temperature - Globigerinoides ruber white sensu stricto, temperature.