Foraminiferal reconstruction of barium distributions in water masses of the glacial oceans

Foraminiferal Ba can be used to reconstruct the distribution of deeply regenerated chemical components in past oceans. The Ba contents of benthic foraminifera recovered from cores in the Atlantic Ocean indicate that waters deeper than 2900 m had ∼30–60% higher Ba during the last glacial maximum (LGM). These changes are consistent with previously observed glacial nutrient enrichments based on foraminiferal Cd and δ 13 C. Increases in deepwater nutrient contents in the Atlantic can be explained by reductions in North Atlantic Deep Water formation during the LGM. Ba/Ca of benthic foraminifera from the glacial sections of intermediate depth Atlantic cores are equal to or lower than Holocene values. This Ba evidence argues against the Mediterranean as a greatly increased source to Atlantic intermediate waters during the LGM, since the Mediterranean is enriched in Ba today and apparently remained enriched during the LGM. Benthic foraminiferal Ba from the glacial sections of cores from the eastern equatorial Pacific suggest that deep waters of the Glacial Pacific were about 25% lower in Ba (at ∼3000 m). Taken together, the foraminiferal evidence indicates that the Ba content of deep waters of the Atlantic, Antarctic, and Pacific were similar at the LGM. Since foraminiferal Cd distributions indicate that Cd remained significantly lower in the deep Atlantic relative to the Pacific at the last glacial maximum, a seven‐box ocean model is used to explore several scenarios for reconciling LGM Ba and Cd distributions. While the changed distribution of both tracers suggests diminishment in the flux of nutrient depleted waters to the deep Atlantic during the LGM, increased Atlantic upwelling rates and consequently enhanced Ba particle fluxes can account for the the lack of Ba fractionation between the deep Atlantic and Pacific. The model suggests that Ba can be transferred efficiently to the deep Atlantic by enhanced upwelling because the vast majority of the Ba is regenerated in the deep Atlantic box.