Solar insolation changes are amongst various factors that affect sea-surface temperature, which in turn modulate global climate. Out of all the oceanic regions, equatorial region receives the maximum solar insolation and thus is the locale for the warmest waters. However, how the equatorial sea-surface temperature affects global climate, is still not clear.
Long-term past seawater temperature records are required to understand the effect of temporal changes in equatorial sea-surface temperature on the global climate. Various techniques are used to estimate past seawater temperatures. Here, the equatorial sea-surface temperatures of the last 150,000 years BP as estimated from Magnesium/ Calcium (Mg/Ca) ratio of the foraminiferal shells, have been compiled in order to get an update of the past sea-surface temperature changes in the equatorial region.
It is inferred that the average cooling during the Last Glacial Maximum (LGM) (the interval dated from ~ 19–23 kyr BP (19-23 thousand years before present) during the last glacial period, when the ice-sheets covered maximum area) was ~ 2.3°C as compared to the Holocene. The LGM–Holocene sea-surface temperature difference was not uniform throughout the studied cores, which implies that the surface equatorial temperature gradient during LGM was different than that at present.
The equatorial surface waters were warmest during marine isotopic stage (MIS) 5.5, even warmer than that at present. However, the pattern of cooling and amount of drop in surface temperature during various substages of MIS 5 was not uniform throughout the equatorial oceans. During MIS 4, several regions of the surface equatorial ocean were warmer than that during MIS 3. The study further shows that surface equatorial oceans during MIS 3 were as cold as during MIS 2.
The paper can be downloaded below –