Investigating hyperthermals occurring during the Early Eocene Climate Optimum

Abstract

In this work, we present a new high-resolution planktic carbon (δ13C) and oxygen (δ18O) isotopes record for Acarinina spp. and Subbotina spp. from ODP Site 1263 located in the Walvis Ridge. We cover the period following the Paleocene Eocene Thermal Maximum (PETM) ~54 Ma until the end of the Early Eocene Climate Optimum (EECO) at ~49 Ma. The δ13C results of the benthic dwelling species N. truempyi and surface species Acarinina spp. confirm the occurrence of all hyperthermals but with varying isotopic excursion between the two. The δ13C values for Acarinina spp. are combined with the δ13C values for N. truempyi by linear regression to calculate their covariance. The values of the slopes indicate a clear relationship between all hyperthermals occurring before the problematic interval (first group), excluding the H1 hyperthermal, that presents a low covariance. On the other hand, all the hyperthermals occurring after the ‘problematic interval’ (second group) have a higher covariance, excluding the P hyperthermal that present a low covariance. The values found in this study (δ13C for Acarinina spp. vs. N. truempyi δ13C) indicate that high productivity in the surface ocean probably impacted the values of δ13C for Acarinina spp. in the first group of hyperthermals. On the contrary, the second group presents smaller variations between the benthic and planktic species resulting in an almost linear relationship, indicating a probable drop in productivity compared to the pre ‘problematic interval’ hyperthermals. Also, this study identifies a period of probable high productivity after the H2 hyperthermal because of the presence of high δ13C values only in the Acarinina spp. curve.