## 2 Observations  
Field data were obtained from a profiling instrument platform deployed at the Martha's Vineyard Coastal Observatory (MVCO) south of Martha's Vineyard, MA, USA, at the 12-m isobath in the summer of 2011, as part of the Office of Naval Research (ONR)-funded Optics and Acoustics and Stress In Situ (OASIS) experiment [43]. The platform was mounted on a pivoting arm that profiled every 20 min from 10 cm to 2 m above bottom. The platform was equipped with variety of optical and acoustical sensors. Here we discuss data from a Sequoia LISST 100-X (Sequoia Scientific, Bellevue, WA, USA), a EcoBB2f (WETLabs, Philomath, OR, USA) triplet measuring dissolved organic fluorescence and backscattering at two wavelengths (532 and 650 nm), and a WETLabs AC-9 spectral absorption and beam attenuation meter. Water was pumped from an intake at the tip of the arm into the 10-cm pathlength sampling volume of the AC-9. An automatic valve periodically routed the water sample through a 0.2-\(\upmu\)m filter to remove particulates, leaving the dissolved fraction, to obtain calibration-independent particulate properties [44]. Shear velocity \(u_{sc}\) [cm/s] associated with mean flow in the bottom boundary layer (BBL) was inferred from a pair of acoustic Doppler velocimeter (Sontek, San-Diego, CA, USA) measurements (cf. [45]), and model estimates of the wave-current combined maximum shear velocity in the wave boundary layer (relevant to sediment resuspension) were determined using a version of the Grant-Madsen model [46; 47]. We have plotted sign(\(u\)) \(u_{sc}\) in Figure 2, where \(u\) is the east-west component of the current velocity, to differentiate flood (east, positive) from ebb (west, negative). The location is dominated by the east-west semi-diurnal tidal currents, northward swell, and periodic storms (Figure 2). The measurements discussed here were taken in the bottom boundary layer, which is mostly well mixed. Waves and currents varied during the experiment, and we have selected four periods with distinctly different forcing and optical responses (Figure 2). Two periods (Maria and Ophelia) were associated with offshore passage of hurricanes and arrival of swell waves at the study site. Another period (Spring tides) was associated with moderate wave conditions and strong spring tidal currents. The fourth period (Calm) was characterized by low waves and weaker near tidal currents. For each of the four periods identified in Figure 2, we show the distribution of the following optical properties (or properties inferred from optical measurements):  
1. Beam attenuation \(c_{p}\)(650) [m\({}^{-1}\)] measured by the AC-9 and particulate backscattering coefficient (\(b_{bp}\)(650) [m\({}^{-1}\)] measured by the EcoBB2F provide proxies of particulate concentration (e.g., [5], where higher values associated with higher particle concentrations. 2. Exponent of the power-law fits of the particulate beam attenuation \(\gamma_{cp}\) [dimensionless] and backscattering \(\gamma_{bbp}\) [dimensionless] (\(c_{p}=c_{p}(\lambda_{0})(\lambda/\lambda_{0})^{-\gamma_{cp}}\), with an analogous formula for \(\gamma_{bbp}\)provide proxies for size distribution in the finer sizes (e.g., [13]). Lower values are associated with larger size averaged particles. \(\gamma_{cp}\) is biased towards the smaller (0.5 to 10 \(\upmu\)m) particles in the population [9], and \(\gamma_{bbp}\) may be more sensitive to larger particles [15]. 3. Sauter diameter \(D_{s}\) [\(\upmu\)m] is determined from the ratio of LISST measurements of volume and area concentrations, summed over size classes \(i\) as \(D_{s}=1.5\sum V_{i}/\sum A_{i}\) and reciprocal of particle density \(\rho_{a}{}^{-1}=\sum V_{i}/c_{p}\) [m ppm\({}^{-1}\) = \(\upmu\)m], using the LISST-based \(c_{p}\). Both are proxies for packing: larger values of \(D_{s}\) indicate larger, less-dense particle populations, and larger values of \(\rho_{a}{}^{-1}\) also indicate less-dense particle populations. 4.