Abstract:
Although currently the third largest delta system in the world in terms of sediment supply, and second in terms of carbon delivery, the offshore Ayeyarwady Delta has remained, until recently, largely unstudied. We report here on an investigation of the shelf area off the Ayeyarwady, including data from a research cruise conducted in December 2017. Sediment dispersal and accumulation in the adjacent Andaman Sea and Bay of Bengal are controlled by: seasonal variations in sediment input; reversing monsoon winds and circulation patterns; strong forcing by tides and waves; and tectonic uplift/subsidence west/east of the N-S trending Sagaing fault that bisects the delta. Maximum sediment accumulation rates of ~10 cm/y are observed in the foreset region of a subaqueous delta that is prograding into the Martaban Depression east of the Sagaing fault. Accumulation rates in other areas of the shelf surrounding the delta are typically ~1 cm/y. The extensive shallow (topset) region of the eastern Gulf of Martaban is characterized by deep (up to a meter) physical mixing of the seabed and reduced net accumulation rates. Frequent and deep re-oxidation of pore waters by tide and wave sediment resuspension likely forms the distinctive reddish-brown coloration of the sediments, and has important implications for carbon sequestration. The shelf (ramp) off the western mouths of the Ayeyarwady Delta is characterized by a relatively narrow nearshore (
