Ocean sediment data - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 185

petrographic composition of the ice rafted debris (IRD) in these sediments
reveals the place of the ice's origin and allows a reconstruction of the surface
currents of the past. Since the motion of icebergs and sea ice is controlled by the
atmospheric and oceanic circulation, the dispersal paths of IRD from known
sources permit the reconstruction of the past ocean surface currents and winds.''
Bischof (2000) shows some impressive graphs of lithologic diversity, grams of
lithic grain per gram of sediment, and the size of the largest dropstone in ice
rafted debris over a time period that spans the Last Glacial Maximum and the
Holocene. In each case there is a dramatic drop in these variables over a relatively
short time at the end of the last ice age.
Ice-rafted debris provides additional information that complements ocean
sediment data based on biologically induced isotope variations. While ice-rafted
debris tends to be limited to the most recent ice age and its aftermath, it provides
information on ocean currents and winds that could not be inferred from conven-
tional sediment data or ice cores. One of the interesting findings from ice-rafted
debris is that surface currents in the Norwegian Sea generally switched from
northwards during interglacials to southwards during glacials. Evidently, this
propelled polar climates southward during glacial periods. What is not clear is
whether this was a cause or an effect of glaciation.
Bond et al. (2001) utilized ice-rafted debris to study patterns of climate varia-
tion during the Holocene and reported a 1,500-year cycle that some think persisted
in a weak form down to the recent past (MWP and LIA).