Shell size variation of pteropod Heliconoides inflatus: inferences on Indian Ocean carbonate chemistry during late Quaternary

Abstract

The current study is an effort to understand the relationship between the average shell size and Limacina Dissolution Index (LDX) of pteropod species, Heliconoides inflatus as a metric for shell calcification using several cores, ranging in age from recent to 1.2 Myr. The current study is based on the variability of H. inflatus average shell size, LDX, and fragmentation ratio (FR) and their correlation among different spatial and temporal sediment core records from the Northern Indian Ocean. Results suggest that in the cores collected above the Aragonite lysocline (Aly) and the Aragonite Compensation Depth (ACD) (SPC 05, 06, 09, 11, 12, 13, 14, and NGHP-17), the average shell size values exhibited larger shells during the stadials/glacial periods (Little Ice Age (LIA), Marine Isotope Stages (MIS) 3, 6, 10 − 9 transition etc.) which corresponds to lower LDX values. However, the cores beyond the ACD (SK168, AAS11, and RVS2) show larger shell size values during the warm interstadials (e.g., Bølling–Allerød) with higher FR. The variability in shell size and LDX shows an indication of the carbonate ion saturation in the water column over glacial/interglacial time scales and the impact of changing atmospheric CO₂ in the atmosphere. However, the factors adding to the carbonate ion saturation within the water column could be varied physiographically. The calcification proxy complements the dissolution proxies and reveals that the most intense aragonite dissolution occurred during the Holocene and interstadials/interglacials.