What was done
Using a well-established radiolarian-based transfer function, the authors developed a mean annual sea surface temperature (SST) history of the last 10,500 years based on data derived from the top 390 cm of a gravity core recovered from the western slope of the northern Okinawa Trough (29°13.93'N, 128°53'E) of the East China Sea.

What was learned
Early in the Holocene, between 10,500 and 8500 calendar years before present (cal. yr BP), mean annual SST gradually rose from ~23.5 to ~25.2°C, but then declined abruptly to ~24.0°C at about 8200 cal. yr BP. The middle portion of the Holocene that followed was relatively stable, with a mean SST of ~24.7°C, after which a dramatic cooling to ~23.6°C occurred at about 3100 cal. yr BP that lasted until about 2600 cal. yr BP, largely coincident with what is known as the "third Neoglaciation" of Europe. This cold interval was followed by the Roman Warm Period (~2600-1700 cal. yr BP), when SSTs rose to ~24.8°C. Then came the Dark Ages Cold Period, when SSTs dropped to ~23.8°C, after which temperatures during the Medieval Warm Period (~1250-750 cal. yr BP) returned to ~24.8°C, only to decline to ~24.2°C during the Little Ice Age (~600-300 cal. yr BP). Immediately thereafter, it began to warm once again; but the warming was short-lived, with the temperature actually reversing course and falling slightly below the Little Ice Age minimum value of ~24.2°C at about AD 1950, where the SST history terminates.

What it means
This SST record from the East China Sea clearly reveals the millennial-scale cycling of climate that has left its mark on numerous paleoclimatic proxies throughout the world; and it suggests that the near-identical peak SSTs of the East China Sea during both the Medieval and Roman Warm Periods were probably significantly greater than those of today, which have likely had insufficient time to once again reverse course and warm to such an elevated level from their lowest level of the past 1300 years.