Cascadia margin sediments contain a rich reservoir of carbon derived both from terrestrial input and sea surface productivity. A portion of this carbon exists as solid gas hydrate within sediment pore spaces which previous studies have shown to be a methane reservoir of substantial size on both the Vancouver Island and Oregon portions of the Cascadia margin. Multichannel seismic reflection profiles on the Cascadia margin show the widespread presence of Bottom Simulating Reflectors (BSRs) within the sediment column, indicating the gas hydrate reservoir extends from the deformation front at 3000 m depth to the upper limit of gas hydrate stability near 500 m water depth. In this study, we compile an inventory of methane bubble plume sites on the Cascadia margin identified in investigations carried out for a range of interdisciplinary goals that also include sites volunteered by commercial fishermen. High plume density anomalies are associated with both the continental shelf (<180 m) and the depth of the upper limit of methane hydrate stability depth (MHSD) that occurs near 500 m in the NE Pacific. The observed anomalies on the Cascadia slope may be due to the warming of seawater at intermediate depths, suggesting that modern climate change has begun to destabilize the climate-sensitive hydrate reservoir within the Cascadia margin sediments. Reanalysis of similar plume images on the North American Atlantic slope suggests a lack of correlation between observed plume depths and the MHSD for much of the latitudinal range.

Gas hydrates, pervasive in continental margin sediments, are expected to release methane in response to ocean warming, but the geographic range of dissociation and subsequent flux of methane to the ocean are not well constrained. Sediment column thermal models based on observed water column warming trends offshore Washington (USA) show that a substantial volume of gas hydrate along the entire Cascadia upper continental slope is vulnerable to modern climate change. Dissociation along the Washington sector of the Cascadia margin alone has the potential to release 45-80 Tg of methane by 2100. These results highlight the importance of lower latitude warming to global gas hydrate dynamics and suggest that contemporary warming and downslope retreat of the gas hydrate reservoir occur along a larger fraction of continental margins worldwide than previously recognized.

Upper-ocean turbulence is central to the exchanges of heat, momentum, and gasses across the air/sea interface, and therefore plays a large role in weather and climate. Current understanding of upper-ocean mixing is lacking, often leading models to misrepresent mixed-layer depths and sea surface temperature. In part, progress has been limited due to the difficulty of measuring turbulence from fixed moorings which can simultaneously measure surface fluxes and upper-ocean stratification over long time periods. Here we introduce a direct wavenumber method for measuring Turbulent Kinetic Energy (TKE) dissipation rates, ϵ, from long-enduring moorings using pulse-coherent ADCPs. We discuss optimal programming of the ADCPs, a robust mechanical design for use on a mooring to maximize data return, and data processing techniques including phase-ambiguity unwrapping, spectral analysis, and a correction for instrument response. The method was used in the Salinity Processes Upper-ocean Regional Study (SPURS) to collect two year-long data sets. We find the mooring-derived TKE dissipation rates compare favorably to estimates made nearby from a microstructure shear probe mounted to a glider during its two separate two-week missions for (10−8) ≤ ϵ ≤ (10−5) m2 s−3. Periods of disagreement between turbulence estimates from the two platforms coincide with differences in vertical temperature profiles, which may indicate that barrier layers can substantially modulate upper-ocean turbulence over horizontal scales of 1-10 km. We also find that dissipation estimates from two different moorings at 12.5 m, and at 7 m are in agreement with the surface buoyancy flux during periods of strong nighttime convection, consistent with classic boundary layer theory.

This paper describes high‐resolution in situ observations of temperature and, for the first time, of salinity in the uppermost skin layer of the ocean, including the influence of large surface blooms of cyanobacteria on those skin properties. In the presence of the blooms, large anomalies of skin temperature and salinity of 0.95°C and −0.49 practical salinity unit were found, but a substantially cooler (−0.22°C) and saltier skin layer (0.19 practical salinity unit) was found in the absence of surface blooms. The results suggest that biologically controlled warming and inhibition of salinization of the ocean's surface occur. Less saline skin layers form during precipitation, but our observations also show that surface blooms of Trichodesmium sp. inhibit evaporation decreasing the salinity at the ocean's surface. This study has important implications in the assessment of precipitation over the ocean using remotely sensed salinity, but also for a better understanding of heat exchange and the hydrologic cycle on a regional scale.

Turbulence kinetic energy (TKE) drives the mixing of heat, momentum, and gases within and between the ocean and atmosphere, making it an important parameter in studies of weather and climate. In the Ocean Boundary Layer (OBL), the region of the upper ocean defined by nearly uniform density and active vertical mixing, it is generated primarily by wind, waves, and buoyant convection and lost through viscous dissipation into heat. Production can generally be assumed to equal dissipation and thus the rate of TKE dissipation (ε) serves as a means for quantifying turbulence in a system.Measurements of ε are difficult to make in the field and we rely instead on parameterizations for ε based on the TKE production terms that it balances. Such parameterizations have been traditionally developed using Monin-Obukhov similarity theory (MOST), a form of dimensional analysis applied to the boundary layers of the atmosphere and ocean (Monin & Obukhov, 1959) with which ε can be scaled using wind stress and surface buoyancy flux. The lack of an explicit wave scaling in MOST, however, puts into question its applicability to the OBL, where wave breaking and Langmuir turbulence can be leading sources of TKE. Langmuir turbulence, in particular, is thought to affect the OBL on a global scale and contribute to systematic biases in mixed layer depth and sea surface temperature in global climate models (Belcher et al., 2012). A new scaling framework that

Estimates of turbulence kinetic energy (TKE) dissipation rate (ε) are key in understanding how heat, gas, and other climate‐relevant properties are transferred across the air‐sea interface and mixed within the ocean. A relatively new method involving moored pulse‐coherent acoustic Doppler current profilers (ADCPs) allows for estimates of ε with concurrent surface flux and wave measurements across an extensive length of time and range of conditions. Here, we present 9 months of moored estimates of ε at a fixed depth of 8.4 m at the Stratus mooring site (20°S, 85°W). We find that turbulence regimes are quantified similarly using the Obukhov length scale (LM) $({L}_{M})$ and the newer Langmuir stability length scale (LL) $({L}_{L})$, suggesting that ocean‐side friction velocity ()u∗ $\left({u}_{\ast }\right)$ implicitly captures the influence of Langmuir turbulence at this site. This is illustrated by a strong correlation between surface Stokes drift ()us $\left({u}_{s}\right)$ and u∗ ${u}_{\ast }$ that is likely facilitated by the steady Southeast trade winds regime. In certain regimes, u∗3κz $\frac{{u}_{\ast }^{3}}{\kappa z}$, where κ $\kappa $ is the von Kármán constant and z $z$ is instrument depth, and surface buoyancy flux capture our estimates of ε $\varepsilon $ well, collapsing data points near unity. We find that a newer Langmuir turbulence scaling, based on us ${u}_{s}$ and u∗ ${u}_{\ast }$, scales ε well at times but is overall less consistent than u∗3κz $\frac{{u}_{\ast }^{3}}{\kappa z}$. Monin‐Obukhov similarity theory (MOST) relationships from prior studies in a variety of aquatic and atmospheric settings largely agree with our data in conditions where convection and wind‐driven current shear are both significant sources of TKE, but diverge in other regimes.

High Salinity Shelf Water (HSSW) is a precursor to Antarctic Bottom Water (AABW), a water mass that facilitates the sequestration of atmospheric heat and carbon into the deep ocean. The salinity of HSSW in the Ross Sea is sensitive to both local and broader regional forcing, with implications for the density of downstream AABW and the ocean’s ability to buffer against climate change. One poorly constrained source of HSSW variability in this region is its rate of production within Terra Nova Bay (TNB) in the western Ross Sea. Here, we use an unprecedented set of near-surface salinity, current velocity, and acoustic surface tracking timeseries, collected from a mooring in TNB in austral winter 2017, to estimate HSSW production rates. In one of few studies at the resolution of individual katabatic wind events, we find that HSSW production rates correlate with katabatic wind event frequency in early winter and with frequency, strength, and duration in late winter, suggesting a complex dependence on polynya dynamics. We calculate an average HSSW production rate of ~0.6 Sverdrups (106 m3 s-1)that allows us to validate an approach for estimating production rates from parametrized net surface heat fluxes, which we use to examine interannual variability in production rates across the decade. Though further mooring-based estimates are needed for confirmation, results suggest HSSW production in TNB has been mostly increasing since 2015 and could play a previously unrecognized role in the recently observed recovery of HSSW salinity in this region.

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