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We present 850$\mu$m polarization observations of the L1689 molecular cloud,part of the nearby Ophiuchus molecular cloud complex, taken with the POL-2polarimeter on the James Clerk Maxwell Telescope (JCMT). We observe threeregions of L1689: the clump L1689N which houses the IRAS 16293-2422protostellar system, the starless clump SMM-16, and the starless core L1689B.We use the Davis-Chandrasekhar-Fermi method to estimate plane-of-sky fieldstrengths of $366\pm 55$ $\mu$G in L1689N, $284\pm 34$ $\mu$G in SMM-16, and$72\pm 33$ $\mu$G in L1689B, for our fiducial value of dust opacity. Thesevalues indicate that all three regions are likely to be magneticallytrans-critical with sub-Alfv\'{e}nic turbulence. In all three regions, theinferred mean magnetic field direction is approximately perpendicular to thelocal filament direction identified in $Herschel$ Space Telescope observations.The core-scale field morphologies for L1689N and L1689B are consistent with thecloud-scale field morphology measured by the $Planck$ Space Observatory,suggesting that material can flow freely from large to small scales for thesesources. Based on these magnetic field measurements, we posit that accretionfrom the cloud onto L1689N and L1689B may be magnetically regulated. However,in SMM-16, the clump-scale field is nearly perpendicular to the field seen oncloud scales by $Planck$, suggesting that it may be unable to efficientlyaccrete further material from its surroundings.

JCMT POL-2 and BISTRO Survey observations of magnetic fields in the L1689 molecular cloud