Stable isotope signals from brines in the Barents Sea: Implications for brine formation during the last glaciation

Abstract

The δ 18 O and δ 13 C values of benthic foraminifera from the cold stadials of the last glacial period in the Nordic seas are low, whereas the values from the warm interstadials are high. The low values have been attributed to brine formation carrying a low stable isotope signal from the surface water into deep water, as occurs around Antarctica today. Brines are often considered to have played a major role for the abrupt millennial-scale climate shifts during the last glaciation. However, very little is known of the isotopic composition of modern brines in the Northern Hemisphere, greatly hampering the interpretation of past data. Here we report on the oxygen and carbon isotope composition of benthic foraminifera in two cores from a brine-influenced shelf environment in Storfjorden, Svalbard, in the Barents Sea. The results indicate that brines with sufficient density to contribute significantly to intermediate and deep water are formed from cold, salty waters and have high δ 18 O and δ 13 C values. Brines with low δ 18 O values formed from cold, fresher water have relatively low density, and they are unable to penetrate the deeper parts of the Arctic and Nordic seas. This indicates that the low benthic δ 18 O and δ 13 C values obtained from the Nordic seas during stadials cannot be attributed to brines. The implication is that brines did not contribute significantly to the millennial-scale climate shifts.