Oh, thanks - played a bit more with nm:
arm-none-eabi-nm -S --size-sort -r core-firmware.elf --radix decimal --debug-syms --special-syms --synthetic | grep -e " [BbDd] "
gives a list with all RAM blocks, along with their decimal size, largest block first 
However, the total of these amounts to 8k only, 7k of them for the largest 9 blocks.
Where’s the 6k difference to the 14k gcc reports for bss+data coming from?
536874336 00002064 B spark_protocol
536871296 00001064 d impure_data
536872364 00001032 D _malloc_av
536877640 00001024 B wlan_tx_buffer
536878664 00001024 B wlan_rx_buffer
536873776 00000352 B User_Func_Lookup_Table
536873500 00000256 B USART_Rx_Buffer
536874132 00000200 B User_Var_Lookup_Table
536877288 00000176 B expandedKey