Holocene Indian Ocean sea level, Antarctic melting history and past Tsunami deposits inferred using sea level reconstructions from the Sri Lankan, Southeastern Indian and Maldivian coasts

Abstract

Holocene sea level change in the northern Indian Ocean was studied using geochemical and geophysical approaches. Molluscs were sub-sampled for radiocarbon dating from sediment cores retrieved from a south Sri Lankan coastal lagoon. They were then combined with previously published sediment core radiocarbon ages from the same lagoon. We observe a ~20-fold reduction in sedimentation rates at around 4 ka, attributed to a decrease in the rate of sea level rise. Previously reported radiocarbon ages based on total organic matter in the lagoon show remarkable agreement with our new dates suggesting stable and homogeneous sedimentation during the last 8 ka. Comparison of down core age trends of both data sets reveal that sediments are older than coeval molluscs, except for the horizons adjacent to the paleo Tsunami layers, indicating fresh and younger sediments are provided during Tsunami events, which could become a new proxy for identifying paleo Tsunamis. Compilation of previously reported sea level indicators from Sri Lanka, Southeastern India and the Maldives, together with predicted sea level obtained from a glacio-hydro-isostatic adjustment model (GIA), suggest that 3e4m of global sea level equivalent ice sheet melting occurred during the Mid Holocene due to the retreat of the Antarctic and/or Greenland ice sheets. Previous works suggests late Holocene (ca. 4 ka) climate anomalies in both the low and high latitudes. We suggest the low latitude climate anomaly, transmitted via atmosphere to the high latitude during the late Holocene, seems to have induced changes in polar ice sheets.