Sub-challenge: Change in average temperature at surface, 500 metre depth and bottom on a grid over past 10 years and 50 years.
For this sub-challenge enough data was available to complete it, data used came from U.S. NOAA. The data is has been averaged. No clashes were found in the data. It was chosen to interpret ‘grid’ as a gridded map for optimal viewing. However, one must keep in mind that historical Arctic data more than a few decades ago is very different than modern data due to the changes in sampling methods (e.g. invention of the CTD, and initiation of polar orbiting satellites) and sample locations from individual expeditions to full polar coverage. Archival data is increasingly being merged into digital forms so that historical conditions can be reconstructed. Older data are becoming more available as more reanalysis data sets become available. As more historical data becomes available in digital forms, we expect reanalyses of more types of ice information to become available.
This challenge is to find data showing the change in average temperature for the surface (z=0m), 500m depth and bottom over past 10 and 50 years on a grid. Hydrographic data are available from the U.S. National Oceanic and Atmospheric Administration (NOAA) / National Oceanographic Data Center (NODC). The World Ocean Database (WOD) (Boyer et al, 2009) contains the world's largest collection of quality controlled salinity and temperature profiles and these data are freely available. The World Ocean Atlas (WOA) (Locarinini, Mishonov et al. 2010) provides objectively analysed climatological means based on data from WOD. The challenge in the Arctic water is that there are few observations, especially winter. We have downloaded data from WOD, but to obtain good measures of change in northern sea temperatures based on these data requires careful analysis. This subject is discussed in a recently published paper (Seidov, Antonov et al. 2015). In this paper decadal variability of hydrography of northern water is discussed based on data from WOD and WOA. (A high resolution regional climatology for the Arctic is available from these analysis (http://www.nodc.noaa.gov/OC5/regional_climate/arctic/)). To provide the change in ocean average temperature maps for 10 and 50 years we have used the decadal means available from the WOA. The quality of these averages depend on data coverage as mentioned and we refer to (Seidov, Antonov et al. 2015) for a more thorough discussion. Data are available from WOA for the periods 1955-64, 1965-74, 1975-84, 1985-94, 1995-2004 and 2005-2012. There is a large decadal variability in the ocean, and to calculate consistent change for the 10 and 50 year period we use the difference between two the most recent available averages to calculate the 10 year change (Figure 2-1). For the 50 year period we use change between 2005-2012 and 1955-1965 (Figure 2-1).
Figure 1: Change in temperature (°C) calculated as differences between the average over 2005-2012 and average over 1995-2004 (left panels) and 1955-1965 (right panels) from surface (top panels), at 500 m (middle panels) and bottom (lower panels). Some artificial land occurs for bottom estimates due to interpolation challenges.
- Boyer, P., J.I. Anaatove, O.K. Baranova, H.E. Garcia, D.R. Johnson, T.P. Locarinini, A.V. Mishonov, D.K. O'Brien, D. Seidov, I. Smolyar, M.M. Zweng (2009). World Ocean Database, 2009. U.S. Government Printing Office, National Oceanic and Atmospheric Administration.
- Locarinini, T., A. Mishonov, J. Antonov, T. Boyer and H. E. Garcia (2010). NOAA NESDIS Atlas. U.S. Government Printing Office, National Oceanic and Atmospheric Administration. 68: 184.
- Seidov, D., J. I. Antonov, K. M. Arzayus, O. K. Baranova, M. Biddle, T. P. Boyer, D. R. Johnson, A. V. Mishonov, C. Paver and M. M. Zweng (2015). "Oceanography north of 60°N from World Ocean Database." Progress in Oceanography 132: 153-173.