Saúl González-Lemos

Decrease in coccolithophore calcification and CO2 since the middle Miocene

Marine algae are instrumental in carbon cycling and atmospheric carbon dioxide (CO2) regulation. One group, coccolithophores, uses carbon to photosynthesize and to calcify, covering their cells with chalk platelets (coccoliths). How ocean acidification influences coccolithophore calcification is strongly debated, and the effects of carbonate chemistry changes in the geological past are poorly understood. This paper relates degree of coccolith calcification to cellular calcification, and presents the first records of size-normalized coccolith thickness spanning the last 14 Myr from tropical oceans. Degree of calcification was highest in the low-pH, high-CO2 Miocene ocean, but decreased significantly between 6 and 4 Myr ago. Based on this and concurrent trends in a new alkenone ɛp record, we propose that decreasing CO2 partly drove the observed trend via reduced cellular bicarbonate allocation to calcification. This trend reversed in the late Pleistocene despite low CO2, suggesting an additional regulator of calcification such as alkalinity.

New evidence of sea-level lowstands and paleoenvironment during MIS 6 and 4 in the Cantabrian coastal karst: The Cobiheru cave (North Iberia)

The geomorphological evolution of the Cobiheru Cave shows the influence of the non-carbonate coastal mountain ranges on coastal karst evolution, as well as the temporal distribution of the cold-adapted fauna sites in the Cantabrian Coast. Geomorphological observation and U/Th dating lead to the construction of an evolution model. The model comprises two episodes of cave deposition occurred at ca. 60–70 and 130–150u2009ka, linked to cold climate conditions, global sea-level lowstands and the erosion of alluvial fans that covered the karst. Moreover, the comparison between the Cobiheru record and some raised beaches identified in previous studies sets the beginning of the sea-level lowering in the Cantabrian Sea during the MIS 5-4 transition. Two palaeoenvironments are inferred based on finding Equus ferus and Elona quimperiana. A wet deciduous forest would have been developed on the emerged marine terrace of the Cobiheru Cave since at least the Middle Pleistocene, and an open landscape with scarce vegetation would have been present at ca. 65u2009ka. The erosional event identified in the Cobiheru Cave helps to understand the temporal distribution of cold-adapted mammals located in the Asturias region. The probable sites of cold-adapted fauna developed in caves and alluvial fans would have disappeared after 65u2009ka. Therefore, palaeontological and palaeoclimate research based on cold-adapted mammals suggests the occurrence of an hiatus in the palaeontological record prior to 50u2009ka. This article is protected by copyright. All rights reserved.