What was done
Noting that satellite altimetry data have shown sea level change to be characterized by an uneven spatial structure, with positive trends in some regions and negative trends in others (Cazenave et al., 2004), the authors constructed maps of Sea Level Anomalies (SLAs) for the extratropical North Atlantic and North Pacific Oceans that they obtained from merged Topex/Poseidon-Jason-1+ERS-1/2 altimetry data for the period October 1992 to July 2003, after which they used Empirical Orthogonal Function (EOF) analysis to identify dominant modes of interannual SLA variability.

What was learned
Volkov and van Aken found that "the spatial patterns of the observed sea level trends in both oceans [were] identical to the spatial patterns of the EOFs-1 of the interannual SLA data," and that "the year-to-year variations of sea level showed coherence between the North Atlantic Oscillation, El Niņo/La Niņa and Pacific Decadal Oscillation events and respective gyre-scale changes."

What it means
In the words of the two Dutch scientists, "the results of this work suggest that the recently reported local trends of sea level are not necessarily related to the global sea level rise, but may be part of interdecadal fluctuations."  This conclusion is reminiscent of the upper-ocean heat content findings of Levitus et al. (2005), who concluded that "phenomena associated with the variability of the 0-700 m global ocean heat content integral for 1956-2003 are characterized by gyre and basin-scale spatial variability and time-scales approximately decadal and longer," which variability, in their words, "is dominated by the reversal of polarity of the Pacific Decadal Oscillation in the late-1970s and El Niņo phenomana."

References
Cazenave, A., Minh, K.D. and Gennero, M.C.  2004.  Present-day sea-level rise: From satellite and in-situ observations to physical causes.  In: Hwang, C., Shum, C. and Li, J., Eds.  Satellite Altimetry for Geodesy, Geophysics and Oceanography 23.

Levitus, S., Antonov, J.I., Boyer, T.P., Garcia, H.E. and Locarnini, R.A.  2005.  EOF analysis of upper ocean heat content, 1956-2003.  Geophysical Research Letters 32: 10.1029/2005GL023606.