A 1000-year-long record of diatom production and climate variability from the Gulf of Tehuantepec (Eastern Tropical North Pacific)

We examined the productivity variability in diatom assemblages during two contrasting climatological periods: the Medieval Warm Period (MWP) and the Little Ice Age (LIA), in the Gulf of Tehuantepec (GT), Eastern Tropical North Pacific. The GT is an important fisheries region in Southern Mexico, largely dependent on ocean productivity. Climatologically, the GT is seasonally affected by a strong north-wind regime and the Intertropical Convergence Zone interactions. These winds promote intense mixing and upwelling in winter to spring months and stratification conditions during the rest of the year; therefore, this climatic variability is expected to have been affected by the MWP and LIA conditions. The MWP (~784 to ~1426 CE) was characterized by the predominance of a warm-water and low-productivity assemblage formed by Neodelphineis pelagica, Thalassionema nitzschioides var. parvum , Thalassiosira eccentrica , Thalassiosira oestrupii , Cyclotella litoralis , Thalassiosira lineata , Fragilariopsis doliolus , Nitzschia interruptestriata and other minor taxa. Early LIA (~1436 to ~1620 CE) was characterized by the predominance of a cold-water and high-productivity diatom assemblage constituted by Chaetoceros spores, Thalassionema nitzschioides , Thalassionema bacillare , Lioloma pacificum, and Thalassiosira nanolineata . Comparing the MWP diatom assemblage to that from the Current Warm Period (1850 CE to present, as reported in a previously published study in the GT) showed that the last 150 years have been the warmest in the integrated ~1400-year GT record.