Schooled: Warmth-Sensitive Fish Teach Us They Swam In A 4-5°C Warmer Ocean About 5000 Years Ago

Extensive hake (fish) skeletal remains in ocean waters too cold for this species to occupy today suggest past ocean temperatures were several degrees warmer.

Fish habitats are limited by specific temperature boundaries. In a new study, for example,  Wheeland  and Morgan (2020) found there was a pronounced ocean warming from the 1980s to late 1990s off the coasts of Greenland. This temperature shift changed the distribution of halibut habitat. Since then, however, there has been no net warming in the study region (through 2016).

Image Source: Wheeland  and Morgan, 2020

In a new study, Bas et al. ( 2020)  document a large presence of a temperature-sensitive fish species (hake) at 53°S (southernmost South America) when current hake venture no further south than 47°S. This latitude differential for hake habitat suggests the ocean was 4-5°C warmer than today about 5000 years ago (Mid-Holocene).

Image Source: Bas et al., 2020

Evidence for anomalously cold present-day sea surface temperatures in southern South America relative to past millennia has also been documented by Caniupán et al., 2014. This region’s temperatures may actually be nearly the coldest of the last 10,000 years – cooler than the temperature depths reached during the “global Little Ice Age”.

Image Source: Caniupán et al., 2014