Seasonal variation of surface seawater radiocarbon in the Andaman Sea as recorded in coral

Corals provide high-resolution radiocarbon record of the surface ocean. These high-resolution records can provide understanding of the surface ocean conditions and processes regulating these conditions. A Porites coral from the Andaman Sea was investigated for its high-resolution radiocarbon record between 2007 and 2014. The radiocarbon measurement of the coral shows a post-bomb period decline trend (2.7‰ yr-1) along with seasonal variations. A positive correlation is observed between the seasonal radiocarbon changes and the stable oxygen isotope values of the coral. The coral registers the seasonal changes in mixed layer depth and sea surface temperature between the monsoon and non-monsoon periods. Recent radiocarbon values of the Andaman Sea surface water have been found to be higher compared to the contemporary atmospheric radiocarbon values.

10Be depositional flux variation in the central Indian Ocean during the last 43 ka

The advent of Accelerator Mass Spectrometer (AMS) enhanced the application of meteoric ¹⁰Be (half-life of 1.39 Ma) as a tracer for understanding earth surface processes on thousand to million-year time scales. However, for the majority of applications, an adequate understanding of the ¹⁰Be depositional flux is a prerequisite. A number of efforts have been made to understand both spatial and temporal variation of ¹⁰Be depositional flux. Yet, due to the limited globally distributed dataset and modulation of the ¹⁰Be signal by local processes, a significant offset is observed between model-derived and measured deposition rates of ¹⁰Be. In this study, an attempt has been made to determine the ¹⁰Be depositional flux from a marine sediment core from the central Indian Ocean chronologically constrained with the AMS radiocarbon dating and ¹⁰Be concentration measured with AMS. The ¹⁰Be depositional flux estimates using weak leaching method are found to be nearly 44% lower compared to the strong leaching method. The calculated ¹⁰Be depositional flux during the Holocene varies between 9.63 and 13.01 × 10⁵ atoms/cm²/yr, which is 2-28% lower compared to the modeled depositional flux for the region. The difference observed in ¹⁰Be depositional flux could be due to the local processes (such as boundary scavenging, changing rate of sediment deposition at the location) affecting ¹⁰Be deposition into the sediment column or offset associated with the model estimations. The changes in ¹⁰Be depositional flux and the ¹⁰Be/⁹Be ratio have been reconstructed up to 43 ka. An increase in the ¹⁰Be/⁹Be ratio during 28 to 43 ka is observed due to the lower geomagnetic field intensity during the period. A high-resolution ¹⁰Be/⁹Be ratio reconstruction shows a peak at 41.2 ka, which can be attributed to the Laschamp event.

Production rate variation and changes in sedimentation rate of marine core dated with meteoric 10Be and 14C

The first measurement of meteoric beryllium-10 (¹⁰Be) using Accelerator Mass Spectrometer (AMS) is reported from PRL-AURiS (Physical Research Laboratory-Accelerator Unit for Radioisotope Studies). Strategically, the meteoric ¹⁰Be dating method can date events as old as 10 Myr, and its accuracy while dating marine sediment cores has been well tested with magnetic methods. An attempt is made for a comparative study between radiocarbon (¹⁴C) and meteoric ¹⁰Be dating methods from a 6 m long sediment core collected from the equatorial Indian Ocean. The core was dated using both radiocarbon and meteoric ¹⁰Be and results showed remarkable similarity for both methods in terms of the sedimentation rate. A continuous age offset observed within 50 kyr could be due to a continuous influx of sediment with low ¹⁰Be content and that may have caused the meteoric ¹⁰Be ages to be younger. The sedimentation rate calculated by changing the ¹⁰Be depositional flux rate from 1.5 to 2.5 × 10^-2 atoms.cm^-2.s^-1 shows large variation, indicating the choice of appropriate ¹⁰Be depositional flux rate for the region. Additionally, being the first meteoric beryllium-10 measurements using AURiS, we have also discussed and reported the laboratory protocols and efficiency based on repeat standard and blank measurements.