Heavy silicon isotopic composition of silicic acid and biogenic silica in Arctic waters over the Beaufort shelf and the Canada Basin

• Published in: Global Biogeochemical Cycles
• Main Authors: Varela, D., Brzezinski, M., Beucher, C., Jones, J., Giesbrecht, K., Lansard, B., Mucci, A.
• Other Authors: British Columbia, School of Earth and Ocean Sciences Victoria (SEOS), University of Victoria Canada (UVIC), University of California Santa Barbara (UC Santa Barbara), University of California (UC), Department of Ecology, Evolution and Marine Biology Santa Barbara (EEMB), University of California (UC)-University of California (UC), Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Océan et Interfaces (OCEANIS), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Research Centre on the Dynamics of the Earth System (GEOTOP), École Polytechnique de Montréal (EPM)-McGill University = Université McGill Montréal, Canada -Université de Montréal (UdeM)-Université du Québec en Abitibi-Témiscamingue (UQAT)-Université du Québec à Rimouski (UQAR)-Concordia University Montreal -Université du Québec à Montréal = University of Québec in Montréal (UQAM)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2016
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces; environment; Arctic Ocean; canada basin; Mackenzie river; Sea ice
• Online Access: https://hal.science/hal-02881295; https://hal.science/hal-02881295/document; https://hal.science/hal-02881295/file/2015GB005277.pdf; https://doi.org/10.1002/2015GB005277

International audience The silicon isotopic composition of silicic acid (δ 30 Si(OH) 4) and biogenic silica (δ 30 Si-bSiO 2) were measured for the first time in marine Arctic waters from the Mackenzie River delta to the deep Canada Basin in the late summer of 2009. In the upper 100 m of the water column, δ 30 Si(OH) 4 signals (+1.82‰ to +3.08‰) were negatively correlated with the relative contribution of Mackenzie River water. The biogenic Si isotope fractionation factor estimated using an open system model, 30 ε = À0.97 ± 0.17‰, agrees well with laboratory and global-ocean estimates. Nevertheless, the δ 30 Si dynamics of this region may be better represented by closed system isotope models that yield lower values of 30 ε, between À0.33‰ and À0.41‰, depending on how the contribution of sea-ice diatoms is incorporated. In the upper 400 m, δ 30 Si-bSiO 2 values were among the heaviest ever measured in marine suspended bSiO 2 (+2.03‰ to +3.51‰). A positive correlation between δ 30 Si-bSiO 2 and sea-ice cover implies that heavy signals can result from isotopically heavy sea-ice diatoms introduced to pelagic assemblages. Below the surface bSiO 2 production zone, the δ 30 Si(OH) 4 distribution followed that of major water masses. Vertical δ 30 Si(OH) 4 profiles showed a minimum (average of +1.84 ± 0.10‰) in the upper halocline (125-200 m) composed of modified Pacific water and heavier average values (+2.04 ± 0.11‰) in Atlantic water (300-500 m deep). In the Canada Basin Deep Water (below 2000 m), δ 30 Si(OH) 4 averaged +1.88 ± 0.12‰, which represents the most positive value ever measured anywhere in the deep ocean. Since most Si(OH) 4 enters the Arctic from shallow depths in the Atlantic Ocean, heavy deep Arctic δ 30 Si(OH) 4 signals likely reflect the influx of relatively heavy intermediate Atlantic waters. A box model simulation of the global marine δ 30 Si(OH) 4 distribution successfully reproduced the observed patterns, with the δ 30 Si(OH) 4 of the simulated deep Arctic Ocean being the heaviest of all ...