Planktonic foraminifers and shelled pteropods in the Barents Sea: Seasonal distribution and contribution to the carbon pump of the living fauna, and foraminiferal development during the last three millennia

Abstract

The Arctic Ocean in general and the Barents Sea specifically, are highly affected by the human induced carbon dioxide (CO2) emissions and increasing temperatures. Atlantification, caused by an increase in warm Atlantic Water inflow, and polar amplification, caused by a higher impact of the increasing temperatures at high latitudes, have already been observed. Moreover, the Barents Sea has been described as a hotspot for ocean acidification. Ocean acidification is the decrease of pH, calcium carbonate saturation state, and carbonate ion concentration due to an increase in CO2 uptake from the atmosphere by the ocean. This alteration of the carbonate chemistry of the water affects the marine biota, especially planktonic marine calcifiers. They are organisms living in the water column with a shell made of calcium carbonate (CaCO3). They contribute significantly to the carbon cycle by exporting mainly CaCO3 from the surface water to the seabed when they die. The main goal of this thesis is to study the distribution of marine calcifiers (planktonic foraminifers and shelled pteropods) in the Barents Sea and the adjacent Arctic Basin. We have (1) investigated their distribution patterns and contribution to carbon dynamics in the north Svalbard margin and in a seasonal basin in the northern Barents Sea; and (2) reconstructed the foraminiferal production and preservation patterns from the late Holocene in sediment cores from the northern and southern Barents Sea. The results from this thesis show that pteropods are important contributors to the carbon dynamics in all seasons in the northern Barents Sea and northern Svalbard margin. Due to the higher sensitivity of their shells compared to foraminifers, they are more likely to be affected by ocean acidification. Moreover, the abundance of foraminifers in the sediment suggests higher productivity in the southern than in the northern Barents Sea. The almost zero abundances observed in the northern Barents Sea core, combined with the seasonality of marine calcifiers, the water carbonate chemistry, and the presence of agglutinated foraminifers suggest dissolution of CaCO3 in the sediment. Due to the use of their shells in paleoceanography, further investigations of CaCO3 dissolution are needed to use them as proxies for the reconstruction of the paleoenvironmental and paleoclimatic conditions in the Barents Sea.