Brine formation recorded by stable isotopes of Recent benthic foraminifera in Storfjorden, Svalbard: palaeoceanographical implications

• Published in: Boreas
• Main Authors: Mackensen, Andreas, Schmiedl, Gerhard
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2016
• Subjects: Arctic; Arctic Ocean; Svalbard; Foraminifera*; Nordic Seas; Storfjorden
• Online Access: http://dx.doi.org/10.1111/bor.12174; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fbor.12174; https://onlinelibrary.wiley.com/doi/pdf/10.1111/bor.12174

We discuss water oxygen isotopes (δ 18 O w ) and carbon isotopes of dissolved inorganic carbon (δ 13 C DIC ) of brine‐enriched shelf water ( BSW ) from Storfjorden (southern Svalbard) in comparison to Recent benthic foraminiferal δ 18 O c and δ 13 C c calcified in the same water. We determined relatively high δ 18 O w values of 0.15±0.03‰ VSMOW in BSW below sill depth at temperatures below −1.8 °C, and high δ 18 O c values of 3.90±0.18‰ VPDB . Such high BSW δ 18 O w cannot significantly deplete 18 O w contents of Arctic Ocean deep water; furthermore, such high δ 18 O c cannot be distinguished from δ 18 O c values of 3.82±0.12‰, calcified in warmer Arctic and Nordic seas intermediate and deeper waters. Today, in Storfjorden low benthic δ 13 C c and high δ 18 O c reflect the low δ 13 C DIC and relatively high δ 18 O w of BSW . High benthic δ 18 O c is in contrast to expected low δ 18 O c as brine rejection is widely thought to predominantly take place in surface water diluted by meteoric water with very low δ 18 O w . Low epibenthic δ 13 C c values of 0.50±0.12‰ partly reflect low δ 13 C DIC caused by enhanced uptake of atmospheric low δ 13 C CO 2 decreased by anthropogenic activities. An adjustment for preindustrial higher values would increase δ 13 C c by about 0.6‰. Therefore, in Storfjorden brine formed before the industrial era would be characterized by both high δ 13 C c as well as high δ 18 O c values of benthic foraminiferal calcite. Our data may cast doubt on scenarios that explain negative excursions in benthic foraminiferal stable isotope records from the Atlantic Ocean during cold stadials in the last glacial period by enhanced brine formation in Nordic seas analogously to modern processes in Storfjorden.