Ecosystem scale CO2 and CH4 fluxes were measured using the eddy covariance method with three eddy covariance (EC) towers in Barrow (CMDL (71.3225269N, -156.6091798W), BEO (71.2810016N, -156.6123454W), and BES (71.280881N, -156.596467W), one EC tower in Atqasuk (ATQ, 70.4696228N, -157.4089471W), and one EC tower in Ivotuk (IVO, 68.48649N, -155.75022N). The EC towers in CMDL, BEO, and BES, and ATQ wereupgraded during the summer and fall of 2013 to include closed-path LGRanalysers (FGGA, Los Gatos Research, Mountain View, CA, USA), LI-7200(LICOR, Lincoln, NE, USA) (CMDL, ATQ, and IVO), LI-7700 (in IVO inApril 2013, and at CMDL in June 2011), a uSonic-3 Class-A (METEK GmbH,Elmshorn, Germany) sonic anemometer (ATQ, and IVO), and CSAT-3D(Campbell Scientific, Logan, Utah, USA) sonic anemometer (BEO, BES,ATQ, and IVO) which were installed in summer and fall 2013. A widerange of meteorological variables were measured at each of the five ECtowers, including: photosynthetic active radiation (PAR), which wasmeasured with quantum sensors (LI-190, Li-COR, Nebraska, USA) in allsites; net radiation recorded using a net radiometer (REBS Q7, in BES,BEO, CMDL, and ATQ, and an NR Lite Kipp & Zonen, Delft, TheNetherlands, in IVO); incoming solar radiation measured usingpyranometers (CMP3, Kipp & Zonen) in all sites; air temperatureand relative humidity (RH) measured with a Vaisala HMP 45 (in CMDL,BES, BEO, and ATQ), and a Vaisala 155a in IVO (and in BEO after 2013)(Vaisala, Helsinki, Finland); soil heat flux at -2 to -5 cm depthmeasured in 4-6 locations in all sites with REBS HFT3 (REBS Inc.,Seattle, Washington, USA); soil temperatures at different depths (atsurface, -1, -5, -10, -20, and -30 cm depth in BES, at -5, -15, and -30 cm in four profiles in ATQ, and at the surface, -5, -15, -30, and -40 cm in four profiles in IVO) measured with thermocouples (eithertype-T or type-E, Omega Engineering, Stamford, Connecticut, USA); soilmoisture measured with CS616 (Campbell Scientific, Logan, Utah, USA)inserted perpendicularly (0-30 cm) or diagonally in different soillayers (0-10 cm, and -20/-30 cm) in BES, or at horizontally atdifferent depths in the soil (-5, -15, and -30 cm in two differentprofiles in ATQ, and in three profiles in IVO). More details on thesemeasurements are detailed in Zona et al. (2016) and Goodrich et al.(2016). Snow depth was measured with Sonic Ranging Sensor in BEO/BES,ATQ, and IVO with a Campbell Scientific model SR50A-L snow senor(Campbell Scientific, Logan, Utah, USA).
