Air pressure was measured with a Vaisala PTB220A digital barometer designed to operate over a wide pressure and temperature range . A comparison of the pressure data to ECMWF operational analysis confirmed the suspicion that the measurements were off for months after the passing of the deepest low, on 24 October 2008, possibly due to water in the sensor inlet. The error was not just a bias error; in addition, during the first half the pressure was too high, while during the second half the magnitudes of extreme were too small and the extrema were not all accounted for. From 1 February 2009 the measurements were in agreement with ECMWF analysis (not shown). To avoid any confusion the pressure data from 24 October 2008 to 1 February 2009 are removed from the data set. The buoy measurements of mean sea level pressure are shown in Fig. , with the exception of the erroneous data. During the deployment, the average pressure was 1009 hPa, varying from a minimum of 941 hPa to a maximum of 1047 hPa. Note that the maximum was measured on 13 February 2008 and a local minimum of 950 hPa a week later, on 21 February 2008, emphasizing the variability of the synoptic situation in the region.

Air temperature was measured at 3.5 m height with a OCEANOR/Omega temperature sensor, a robust and compact sensor. The thermistor element was protected by a sun radiation screen . The lowest temperature measurement was -9.5 ∘C and the highest 10.9 ∘C, a span of about 20 ∘C (see Fig. ). During late autumn, winter and spring the temperature variations were much greater than during the summer and early autumn. The temperature variations during the cool seasons are related to the variation in weather regimes, from northerly cold air outbreaks to warm air advection by synoptic cyclones moving into the area from the south . The highest temperatures were measured in late summer, mainly in August and September 2008, while temperatures below -5 ∘C were measured most frequently in February, followed closely by January and March.

The wind speed, wind gust and wind direction were measured at 4 m height with a Gill WindSonic wind sensor . It has been shown that during rough seas, due to sheltering effects and elevation changes, wind measurement by buoys can be negatively biased e.g.. Here, no attempt is made to compensate for a potential bias in the data set; that is left to the user.

The maximum measured wind was 19.3 ms-1 and the maximum gust 29.8 ms-1. The gust factor was in general below 1.5. There was a significant lower wind speed during the summer months than the winter months (see Fig. ). The monthly mean wind speed was the highest in February 2008 and lowest in June 2009 (see Table ).

The wind rose in Fig.  shows that the most common wind directions were northerly to northeasterly, approximately 30 % of the time, and the least common wind directions were westerly to northwesterly. This is in accordance with wind directional frequency in Iceland (not shown).

The relative humidity was measured at 3.5 m height with a Vaisala HMP 45A relative humidity sensor based on the capacitive thin film polymer HUMICAP 180 . As the measurements were made over the sea the relative humidity was in general high with the lowest measurement at 50 % (see Fig. ). In all cases of relative humidity below 55 % the air temperature was below freezing and in most cases winds were light. The mean relative humidity was 87 %.

Water temperature was measured at 1.5 m depth with the Aanderaa DCS 4100R current speed and water temperature sensor. The temperature was measured using a temperature-dependent crystal-oscillator circuit . After 17 April 2009 all measurements from the current sensor were invalid. The water temperature measurements were thus made over 16 consecutive months. The lowest temperature was measured in spring and the highest from the end of July until mid-September. The rise in temperature during late spring and early summer was slower than the fall in the autumn (see Fig. ). The lowest and highest monthly means were in April and August 2008. The air temperature is also shown in the figure. The amplitude of the water temperature variations is much less than that of the air temperature. The differences between the water temperature and the air temperature, Tw-T, were calculated, and on a monthly basis the difference varied between 0.5 and 3.3 ∘C, with the least difference during summer months but large variation during the winter months, related to different air mass impacting the area.

Current speed and direction were measured at 1.5 m depth with the Aanderaa DCS 4100R current speed and water temperature sensor. The sensor used the Doppler shift principle and together with orientation from the internal compass determined current speed and direction . As mentioned earlier, after the compass and the GPS sensor broke down on 17 April 2009 all current measurements are missing. As stated in Sect.  the buoy was anchored at 68.47∘ N, 9.27∘ W and drifted inside a circle with a diameter of approximately 2 km. Here, no adjustments are made to the measured ocean currents, but a user of the ocean data may want to consider doing corrections. The mean current speed was 13 cms-1 and the maximum 52 cms-1. The monthly mean current speed varied from 8.8 cms-1 in May 2008 to 17.2 cms-1 in February 2008. By convention, current directions are defined opposite to wind directions; northerly current moves toward north while northerly wind is coming from north. The most common current directions were southwesterly (toward southwest) and easterly directions (toward east) least common (see Fig. ).

The wave parameters are measured with Fugro OCEANOR Wavesense, a robust integrated wave sensor and data logger. Accelerometers, rate gyros and magnetometers were mounted orthogonally to provide the basic data. These data were then used as input to algorithms, which calculated heave, roll, pitch, surge, sway and compass time series. Significant wave height, wave direction, wave period and a number of other statistical parameters were then found from these time series . Figure  shows the frequency of wave directions. By convention, wave directions are defined in the same way as wind directions. The most common directions were northeasterly to east-northeasterly, a slight clockwise rotation from the most common wind directions (see Fig. ). The least common wave direction was northwesterly. Figure  shows the significant wave height (the mean height of the highest one-third of the waves) and the spectral peak period (the wave period with the highest energy) and Fig.  the highest wave height and the mean wave period (the mean of all wave periods). Both wave height and wave periods have an annual variation with minimum during summer and maximum during winter, as well as more variability during winter. The monthly mean significant wave height varied from 1.2 to 3.9 m and the monthly mean maximum wave height from 1.7 to 5.9 m.