The Influence of Water Mass Mixing and Particle Dissolution on the Silicon Cycle in the Central Arctic Ocean

We present dissolved and particulate biogenic silica isotopes (δ³⁰DSi, δ³⁰bSi, respectively) from intermediate to deep waters along GEOTRACES transect GN04 in the Central Arctic Ocean (CAO) to investigate in detail the relative influence of water mass mixing and particle flux on the silicon (Si) cycle in the AO. Comparing the δ³⁰DSi with the water mass composition derived from Optimum Multiparameter analysis, we are able to show dominant Atlantic Water (AW) influence at the stations close to the Fram Strait (St. 32, 40, δ³⁰DSi = 1.51±0.11‰, 2SEM, n=3) and the only small δ³⁰DSi modification when compared to the AW endmember value from a previous study in the North Atlantic (δ³⁰DSi = 1.55‰, de Souza et al., 2012). Dense Arctic Atlantic Water, dominating from 200 to 500 m water depth (except for stations 32, 40, where it was present only at 500 m), is marked by heavier δ³⁰DSi of 1.62±0.06‰ (2SEM, n=21). Additionally, higher δ³⁰bSi of 1.64±0.13‰ (2SEM, n=7) determined at this depth are most likely due to influence of entraining waters from the shelves that underwent productivity and Si utilization and were transported laterally into the CAO. Intermediate and deep waters in the Eurasian Basin generally show a ~0.23‰ lower δ³⁰DSi compared to waters from the Canadian Basin. Particle dissolution at greater depths does not play a major role in setting the δ³⁰DSi of deep waters due to the low biogenic silica concentrations at these greater depths. Outflowing water masses from the AO present different δ³⁰DSi, with lower values around 1.46‰ originating from the CAO and influencing predominantly Denmark Strait Overflow Water and Iceland Scotland Overflow Water, and higher values around 2‰ originating from the Canadian AO influencing predominantly Labrador Sea Water. Those signatures correspond to the δ³⁰DSi found in the North Atlantic. Consequently, the AO potentially presents several isotopically different endmembers that contribute to the deep water formed in the North Atlantic.