| Autor: |
Miller, Lisa A., Burgers, Tonya M., Burt, William J., Granskog, Mats A., Papakyriakou, Tim N. |
| Zdroj: |
Geophysical Research Letters; January 2019, Vol. 46 Issue: 1 p235-243, 9p |
| Abstrakt: |
Summer near‐surface seawater sampling in the Canadian Arctic revealed potential for significant errors (nearly 0.1 μmol·(m‐2s‐1)) in CO2fluxes calculated from measured air‐sea CO2gradients. River runoff and sea ice melt strongly stratify these waters, often resulting in surface mixed layers only a few meters thick and isolated from waters sampled by shipboard underway systems. Samples collected with the underway system, rosette, and small boats exposed substantial near‐surface gradients in CO2partial pressure (pCO2) over the top 7 m at many stations. Distributions of temperature, salinity, and fluorescence indicated that the sources of the CO2system gradients varied between stations, precluding simple corrections to align subsurface data with shallower conditions. Overall, the strong summertime sink of atmospheric CO2implied by the underway data was not supported by shallower data. Large quantities of sea ice melt and river runoff in the Arctic Ocean form thin layers of fresh water at the surface that are isolated from deeper water. However, standard methods of sampling surface waters from ships draw water from 2 to 7 m below the surface, which can cause errors in air‐sea CO2fluxes calculated from measured seawater CO2concentrations. We have quantified the potential error for waters of the coastal Arctic Ocean by measuring CO2concentrations in samples collected near the surface using different methods from both large ships and small boats. We found that large errors could result from shipboard sampling at some stations. In particular, measuring the CO2concentration from automated instruments that draw water from below the ship's hull systematically overestimated atmospheric CO2absorption by the ocean. In stratified Arctic Ocean waters, sampling depth can introduce large errors into air‐sea CO2flux estimates at individual stationsData from an underway system generally overestimated the summer atmospheric CO2drawdown in the Canadian Arctic Archipelago |
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