We present an optically detected mechanical accelerometer that achieves a sensitivity of 100 ng(n)/root Hz over a bandwidth of 10 kHz and is traceable. We have incorporated a Fabry-Perot fiber-optic micro-cavity that is currently capable of measuring the test-mass displacement with sensitivities of 200 am/root Hz, and whose length determination enables traceability to the International System of Units. The compact size and high mQ-product achieved combined with the high sensitivity and simplicity of the implemented optical detection scheme highlight our device and this category of accelerometers, outlining a path for high sensitivity reference acceleration measurements and observations in seismology and gravimetry. (C) 2014 AIP Publishing LLC.