Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Spatiotemporal evolution of theMEEMD trends of ocean surface chla in theNorth Atlantic 2014 and 2016, respectively. j, Spatial structure of chla increase based on the time-unvarying l boxes refer to the North Gulf Stream region, the subpolar gyre region, and the region near the
decomposition (MEEMD) method (Wu et al., 2009), which is based on ensemble empirical mode decomposition (EEMD) (Wu and Huang, 2009) and empirical mode decomposition (EMD) (Wu and Huang, 2004; Huang et al., 1998).
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