Planktic calcifiers: from living assemblages to proxies in the Arctic Ocean

Abstract

Planktic foraminifers, pteropods, and coccolithophores are marine calcifiers, organisms living in the water column and found throughout all oceans, with shells made of calcium carbonate. Because of their shell, they play an important role in the carbon cycle exporting calcium carbonate from the upper ocean to the sea floor when they die and sink. If no dissolution occurs on the water column or within the sediment, their shells are found intact in the fossil record. Those are extensively used as proxies to reconstruct paleoenvironments and as biostratigraphic tools.

Compared to other regions, little is known about the living faunas and annual variability and how they are reflected in Arctic Ocean sediments. Here we aim to combine data from living to fossil assemblages and from different regions in the Arctic, including the Barents Sea and Arctic Basin, and the Fram Strait. In the northern Barents Sea, we observed that pteropods drive the calcium carbonate production in the upper 100 meters of the water column. However, due to the more fragile aragonitic shell (compared to the calcitic shells of foraminifers and coccolithophores), they are rarely found in the sediments and barely used as proxies in the global ocean. In sediments from the northern Barents Sea north of the polar front, we found very low, almost zero, abundances of fossil planktic foraminifers in the upper 20 cm in the sediment despite an abundant living population in the overlaying water column through different seasons and years. Hence, studying the present assemblages is key to understanding processes, such as calcium carbonate dissolution, relevant for a more accurate interpretation of the fossil faunas. The presence and abundance of plates from coccolithophores are as the foraminifers also used in biostratigraphy in long sediment cores. In the Arctic, the first appearance datum of the species Gephyrocapsa (or Emiliania) huxleyi (c. 268 ka) and the last appearance datum of Pseudoemiliania lacunosa (c. 458 ka) have been previously used for biostratigraphy to better constrain the age models of sediment cores. In our current study, we aim to use the presence and absence of these species as age indicators for MIS 5 and MIS 11 in a 12-meter long sediment core from the Fram Strait.