Progress toward a multi-basin calibration for quantifying deep sea calcite preservation in the tropical/subtropical world ocean

The development of a quantitative and multi-basin deep sea calcite preservation proxy is important for a better understanding of the marine carbonate system, both in modern sediments and in down core work. We present CaCO3 preservation data from 89 core top samples in tropical and subtropical areas of the Pacific, Atlantic and Indian Oceans. We observe that the Globorotalia menardii Fragmentation Index (MFI) has potential to trace deep sea CaCO3 dissolution quantitatively across the tropical/subtropical world ocean. This is evident in the robust relationship between MFI and bottom water calcite under-saturation in six depth transects with markedly different bottom water CO32− saturation states. We also found a strong relationship between MFI and modeled estimates of percent CaCO3 dissolved at our core top locations. Corroboration for MFI's dissolution trend in the subtropics comes from the concurrent drop in size-normalized shell weight of Globorotalia truncatulinoides specimens with increasing CO32− under-saturation, and the dissolution driven drop in Mg/Ca measurements from tests of three foraminifer species: G. truncatulinoides, Globigerina conglobatus and Globorotalia hirsuta. MFI's core top calibration is further corroborated by the fragmentation trend of foraminifers that prefer higher latitudes like Globigerina bulloides, G. truncatulinoides and Neogloboquadrina pachyderma. Our observations suggest that MFI is coming closer to meeting the criteria for an ideal calcite dissolution proxy with world-wide applicability.