What was done
The authors studied petrographical and geochemical properties of three stalagmites (STAL-B7-1, STAL-B7-5 and STAL-B7-7) found in B7-Cave in Sauerland, Northwest Germany, from which they developed a climatic history that covers the last 17,600 years.

What was learned
In the words of the authors, their three stalagmite records "resemble records from an Irish stalagmite (McDermott et al., 1999)," which has also been described by McDermott et al. (2001).  With respect to their own records, for example, Niggemann et al. explicitly note that they provide evidence for the existence of the Little Ice Age, the Medieval Warm Period and the Roman Warm Period, which also implies the existence of what McDermott et al. (2001) call the Dark Ages Cold Period that separated the Medieval and Roman Warm Periods, as well as the unnamed cold period that preceded the Roman Warm Period.

What it means
More and more data from more and more caves, as well as many other types of proxy climate data, continue to testify of the reality of the millennial-scale oscillation of climate that has reverberated throughout the Holocene and beyond.  The wealth of corroborative information contained in these records suggests there is nothing unusual, unprecedented or unexpected about the 20th-century warming that has ushered in the Modern Warm Period.

References
McDermott, F., Frisia, S., Huang, Y., Longinelli, A., Spiro, S., Heaton, T.H.E., Hawkesworth, C., Borsato, A., Keppens, E., Fairchild, I., van Borgh, C., Verheyden, S. and Selmo, E.  1999.  Holocene climate variability in Europe: evidence from delta¹⁸O, textural and extension-rate variations in speleothems.  Quaternary Science Reviews 18: 1021-1038.

McDermott, F., Mattey, D.P. and Hawkesworth, C.  2001.  Centennial-scale Holocene climate variability revealed by a high-resolution speleothem delta¹⁸O record from SW Ireland.  Science 294: 1328-1331.