Tropical North Atlantic sea surface temperature variability over the last 2000 years: High-resolution foraminiferal Mg/Ca records from the Cariaco Basin, Venezuela
Wurtzel, Jennifer Beth
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There are critical gaps in our understanding of tropical Atlantic climate variability on sub-decadal to centennial time scales for the past two millennia. This is in part due to the limited spatial and temporal extent of the instrumental record, but also due to a lack of tropical proxy records of sufficient length and resolution to establish a baseline range of variability, to which we can compare modern signals. This study presents a high-resolution marine sediment-derived reconstruction of seasonal tropical Atlantic SSTs from the Cariaco Basin, Venezuela, spanning the past two millennia that are correlated with instrumental sea surface temperatures (SSTs) for the period of overlap. Two seasonally-representative species of foraminifera were picked at 3-4 year sample resolution for Mg/Ca analysis. Using Globigerina bulloides and Globigerinoides ruber, quantitative SST records were generated for winter and summer, respectively. The results demonstrate that the rate and magnitude of temperature changes in the twentieth century, while remarkable, are not unprecedented. Despite the apparent success of the calibrations to instrumental SSTs described, examination of the long-term results suggest the signal recorded by the respective species is more complicated than originally thought. Anti-phasing between G. bulloides and G. ruber temperatures throughout large portions of the record indicates that G. bulloides may not be consistently representative of a surface signal, but rather often records a subsurface signal that is anti-correlated with the surface. This makes sense in the context of Atlantic meridional overturning circulation (AMOC) variations, for which an anti-correlated relationship between the surface and subsurface has been observed in modeling studies. Thus, it would appear that multidecadal- and centennial-scale temperature variability in the tropical Atlantic are related to AMOC fluctuations and its associated northward heat transport that in turn may be driven by solar variability.