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Gas transfer velocities in Norwegian fjords and the adjacent North Atlantic waters

Banko-Kubis Hanne M., Wurl Oliver, Mustaffa Nur Ili Hamizah, Ribas-Ribas Mariana

Oceanologia

2019

No. 61 (4)

460--470

We investigated air-sea carbon dioxide (CO2) transfer in situ to determine the role of wind and turbulence in forcing gas transfer. In situ gas transfer velocities of CO2 were measured with a floating chamber technique along the Norwegian coast and inside the Sogne- and Trondheimsfjord. Gas transfer velocities were related to wind speed and turbulence, but neither wind speed nor turbulence can satisfactorily predict gas transfer velocity. However, comparison to existing wind-based parameterizations showed that the data from this study have a similar trend. Generally, we measured higher transfer velocities than the parameterizations predict. In the North Atlantic, we measured transfer velocities of up to 54.9 cm h-1 versus predicted transfer velocities of 6.3 cm h-1 at a wind speed of 3.7 m s-1. In addition, we observed that measurements of transfer velocities at wind speeds below 4 m s-1 are higher than predictions. Wind-based parameterizations are lacking data in the low wind regime for validation, and we provide 25 data points for this critical wind speed range. Overall, results indicate that Norwegian fjords and the adjacent North Atlantic are sinks for atmospheric CO2 during summer, with uptake rates of -9.6 ± 7.6 μmol m-2 min-1 and -4.1 ± 1.7 μmol m-2 min-1, respectively. Due to the low partial pressure of CO2 in the upper water layer of the stratified fjords (down to 150.7 μatm), the Sogne- and Trondheimsfjord absorb 196 tons of carbon per day during the summer.

Monthly dynamics of carbon dioxide exchange across the sea surface of the Arctic Ocean in response to changes in gas transfer velocity and partial pressure of CO2 in 2010

Wróbel I.

Oceanologia

2017

No. 59 (4)

445--459

The Arctic Ocean (AO) is an important basin for global oceanic carbon dioxide (CO2) uptake, but the mechanisms controlling air–sea gas fluxes are not fully understood, especially over short and long timescales. The oceanic sink of CO2 is an important part of the global carbon budget. Previous studies have shown that in the AO differences in the partial pressure of CO2 (Δp CO2) and gas transfer velocity (k) both contribute significantly to interannual air–sea CO2 flux variability, but that k is unimportant for multidecadal variability. This study combined Earth Observation (EO) data collected in 2010 with the in situ p CO2 dataset from Takahashi et al. (2009) (T09) using a recently developed software toolbox called FluxEngine to determine the importance of k and Δp CO2 on CO2 budgets in two regions of the AO – the Greenland Sea (GS) and the Barents Sea (BS) with their continental margins. Results from the study indicate that the variability in wind speed and, hence, the gas transfer velocity, generally play a major role in determining the temporal variability of CO2 uptake, while variability in monthly Δp CO2 plays a major role spatially, with some exceptions.