From the Geekbench 2 benchmark description page:
Memory benchmarks measure not only the performance of the underlying memory hardware, but also the performance of the functions provided by the operating system used to manipulate memory.
- Read Sequential loads values from memory into registers.
- Write Sequential stores values from registers into memory.
- Stdlib Allocate allocates and deallocates blocks of memory of varying sizes using functions from the C Standard Library.
- Stdlib Write writes a constant value to a block of memory using functions from the C Standard Library.
- Stdlib Copy copies values from one block of memory to another using functions from the C Standard Library.
I'm guessing that because Geekbench is (in some parts) testing how quickly it can load data from CPU registers into RAM, that test would (of course) be slower with a reduced CPU clock. And, of course, as harrymc mentioned, reduced CPU speed would make the whole test run slower.
In general, score-based benchmarks like Geekbench tell you very little about how your system is running. There's very little way to isolate "memory performance" as a separate entity, since there are so many variables and most of them are directly related to the performance of the rest of your system.