Inorganic carbon time series at Ocean Weather Station M in the Norwegian Sea

Abstract. Dissolved inorganic carbon (C_T) has been collected at Ocean Weather Station M (OWSM) in the Norwegian Sea since 2001. Seasonal variations in (C_T) are confined to the upper 50 m, where the biology is active, and below this layer no clear seasonal signal is seen. From winter to summer the surface (C_T) concentration typical drop from 2140 to about 2040 μmol kg⁻¹, while a deep water (C_T) concentration of about 2163 μmol kg⁻¹ is measured throughout the year. Observations show an annual increase in salinity normalized carbon concentration (nC_T) of 1.3±0.7 μmol kg⁻¹ yr⁻¹ in the surface layer, which is equivalent to a pCO₂ increase of 2.6±1.2 μatm yr⁻¹, i.e. larger than the atmospheric increase in this area (2.1±0.2 μatm yr^-1). Observations also show an annual increase in the deep water nC_T of 0.57±0.24 μmol kg⁻¹ yr⁻¹, of which about 15% is due to inflow of old Arctic water with larger amounts of remineralised matter. The remaining part has an anthropogenic origin and sources for this might be Greenland Sea surface water, Iceland Sea surface water, and/or recirculated Atlantic Water. By using an extended multi linear regression method (eMLR) it is verified that anthropogenic carbon has entered the whole water column at OWSM.