UC Santa Barbara

Climate states of warm and cold periods have varied on approximately 100,000 year cycles for the last million years. These climate states are represented in similar patterns of global sea level observed in five to seven individual records of sea level over 800-kyr. These records were combined into a 800-kyr long global stack using principal components analysis. A record of δ18O of benthic foraminiferal calcite shows a correlation of 0.9 to the sea level stack (PC1), suggesting a strong sea level influence in the calcite, but a 2-kyr lag with respect to the calcite record suggests that deep ocean temperature precedes the sea level response. Sea level change is estimated to account for nearly 45% of the 100-kyr power of benthic δ18O.

The principal component analysis also captured regional variation in the sea level records in PC2 and PC3. Regional variations in δ18O of seawater during the modern/Holocene and Last Glacial Maximum (LGM), respectively, may help us to understand ocean and atmospheric circulation associated with these extreme climate changes. A simple three-box model of the Atlantic Ocean was compared to surface and deep gradients in δ18O of seawater from paleoclimate proxy measurements. First, parameters were tuned to realistic modern values that matched modern δ18O of seawater observations. The estimated LGM parameters did not fit the proxy evidence for a surface gradient change of -0.04 per mil or a vertical gradient change of 0.36 per mil. However, the error in the proxy surface and vertical gradient change estimates is quite large (+/-0.29 per mil and +/-0.14 per mil, respectively). An improved fit to the data was achieved by slowing the overturning circulation while increasing Arctic runoff to a modern value. The results of this study suggest that additional LGM δ18O of seawater measurements are needed to constrain ocean and atmospheric circulation changes.