may be nothing down there,looks man made,no really sure how old it is but one thing is for sure the sea is rising..
Current sea-level rise is about 3 mm/year worldwide. According to the National Oceanic and Atmospheric Administration (NOAA), "this is a significantly larger rate than the sea-level rise averaged over the last several thousand years", and the rate may be increasing.[2] This rise in sea levels around the world potentially affects human populations (e.g., those living in coastal regions and on islands)[3] and the natural environment (e.g., marine ecosystems).[4] Between 1870 and 2004, global average sea levels rose 195 mm (7.7 in), 1.46 mm (0.057 in) per year.[5] From 1950 to 2009, measurements show an average annual rise in sea level of 1.7 ± 0.3 mm per year, with satellite data showing a rise of 3.3 ± 0.4 mm per year from 1993 to 2009,[6] a faster rate of increase than previously estimated.[7] It is unclear whether the increased rate reflects an increase in the underlying long-term trend.[