Chilly reminders of a centuries-long cold snap can be found deep within the Pacific, a new study finds. According to the results, ongoing cooling observed in Pacific deep-ocean temperatures indicates that the deep Pacific is still adjusting to the surface cooling that occurred during the Little Ice Age, which began nearly 1,000 years ago. The common-era climate anomaly known as the Little Ice Age brought significantly colder year-round temperature averages to many parts of the globe and is recognized in paleoclimate and historical records worldwide. Historic climate events such as these impact the sea surface temperatures, and due to how the ocean circulates, it's been theorized that signals related to anomalies like the Little Ice Age are perhaps preserved like memories in the creeping waters of the overturning deep Pacific. However, whether these signals are predictable or detectable, let alone accurately characterize past surface conditions, remains unclear, according to the authors. Geoffrey Gebbie and Peter Huybers combine an ocean circulation model with modern and historical measurements to detect and quantify the influence of Little Ice Age cooling on the Pacific's deep interior and find that the cooling currently observed in the deep Pacific can be explained by the ongoing introduction of cooler waters, which were last on the surface during the cold years of the Little Ice Age. Gebbie and Huybers' model prediction is largely corroborated by temperature changes identified between measurements taken during the 1870s HMS Challenge expedition and modern temperature observations. Furthermore, the results underscore the deep ocean's role in the planetary heat budget and suggest that the heat loss in the deep Pacific since 1750 offsets nearly a quarter of global heat gain in the upper ocean, according to the authors.
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Journal
Science