We can look at marine sediment cores to see if this is an unusual or normal occurrence. (antarcticglaciers.org)
Like marine sediment cores, an ice core provides a vertical timeline of past climates stored in ice sheets and mountain glaciers. (earthobservatory.nasa.gov)
Analysing new data from marine sediment cores taken from the deep South Atlantic, between the southern tip of South America and the southern tip of Africa, the researchers discovered that during the last ice age, deep ocean currents in the South Atlantic varied essentially in unison with Greenland ice - core temperatures. (sciencedaily.com)