Relationship of benthic foraminiferal diversity to paleoproductivity in the Neogene Caribbean

Abstract

Diversity trends 8.3–2.5 Ma in Caribbean deep-sea foraminifera, as interpreted from the indices Fisher's α and the Information Index [ H( S)] parallel paleoproductivity proxies (benthic foraminiferal infaunal/epifaunal species ratio, benthic foraminifer accumulation rates and flux of organic carbon to the seafloor). Paleoproductivity never reached a eutrophic threshold value above which we would predict opposite trends of high paleoproductivity and low diversity, consistent with stressful conditions. Instead, results are similar to those from other studies of oligotrophic settings that show a positive and statistically significant correlation between paleoproductivity and diversity. The correlations between current intensity and watermass oxygenation with diversity are negative and statistically significant. These results are also borne out by Principal Component Analysis (PCA). Intervals of increased relative abundance of Epistominella exigua, a proxy for seasonality of phytodetrital input to the seafloor, coincide with increased diversity, suggesting that pulsed paleoproductivity enhanced the diversity signal in the Caribbean. Diversity and paleoproductivity peaked in the Caribbean at 7.9 Ma, and declined thereafter due to the cut off of the nutrient-rich Pacific deep waters (< 1000 m) into the Caribbean. From 7.6 to 4.2 Ma, both diversity and paleoproductivity increased. With the complete closure of the Caribbean–Pacific seaway at 4.2 Ma, both diversity and paleoproductivity gradually decreased from a high at 4.2 Ma to moderate values until the end of the study interval at 2.5 Ma. Major intervals of significant shifts in Caribbean diversity and paleoproductivity were also confirmed with SHEBI analysis that displays a diverging trend between the Pacific and Caribbean sites since 7.9 Ma, with the Caribbean displaying decreasing values. In summary, in the Caribbean, decreased paleoproductivity due to the gradual constriction and the final closure of the Central American Seaway (CAS) led to decreased deep-sea benthic foraminiferal diversity and that both benthic foraminiferal diversity and paleoproductivity maintained a positive relationship.