Microstructure mixing observations and finescale parameterizations in the Beaufort Sea

Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 51(1), (2021): 19-35, https://doi.org/10.1175/JPO-D-19-0233.1.In the Beaufort Sea in September of 2015, concurrent mooring and microstructure observations were used to assess dissipation rates in the vicinity of 72°35′N, 145°1′W. Microstructure measurements from a free-falling profiler survey showed very low [O(10−10) W kg−1] turbulent kinetic energy dissipation rates ε. A finescale parameterization based on both shear and strain measurements was applied to estimate the ratio of shear to strain Rω and ε at the mooring location, and a strain-based parameterization was applied to the microstructure survey (which occurred approximately 100 km away from the mooring site) for direct comparison with microstructure results. The finescale parameterization worked well, with discrepancies ranging from a factor of 1–2.5 depending on depth. The largest discrepancies occurred at depths with high shear. Mean Rω was 17, and Rω showed high variability with values ranging from 3 to 50 over 8 days. Observed ε was slightly elevated (factor of 2–3 compared with a later survey of 11 profiles taken over 3 h) from 25 to 125 m following a wind event which occurred at the beginning of the mooring deployment, reaching a maximum of ε= 6 × 10−10 W kg−1 at 30-m depth. Velocity signals associated with near-inertial waves (NIWs) were observed at depths greater than 200 m, where the Atlantic Water mass represents a reservoir of oceanic heat. However, no evidence of elevated ε or heat fluxes was observed in association with NIWs at these depths in either the microstructure survey or the finescale parameterization estimates.This work was supported by NSF Grants PLR 14-56705 and PLR-1303791 and by NSF Graduate Research Fellowship Grant DGE-1650112

Tracking icebergs with time-lapse photography and sparse optical flow, LeConte Bay, Alaska, 2016–2017

We present a workflow to track icebergs in proglacial fjords using oblique time-lapse photos and the Lucas-Kanade optical flow algorithm. We employ the workflow at LeConte Bay, Alaska, where we ran five time-lapse cameras between April 2016 and September 2017, capturing more than 400 000 photos at frame rates of 0.5–4.0 min−1. Hourly to daily average velocity fields in map coordinates illustrate dynamic currents in the bay, with dominant downfjord velocities (exceeding 0.5 m s−1 intermittently) and several eddies. Comparisons with simultaneous Acoustic Doppler Current Profiler (ADCP) measurements yield best agreement for the uppermost ADCP levels (∼ 12 m and above), in line with prevalent small icebergs that trace near-surface currents. Tracking results from multiple cameras compare favorably, although cameras with lower frame rates (0.5 min−1) tend to underestimate high flow speeds. Tests to determine requisite temporal and spatial image resolution confirm the importance of high image frame rates, while spatial resolution is of secondary importance. Application of our procedure to other fjords will be successful if iceberg concentrations are high enough and if the camera frame rates are sufficiently rapid (at least 1 min−1 for conditions similar to LeConte Bay).This work was funded by the U.S. National Science Foundation (OPP-1503910, OPP-1504288, OPP-1504521 and OPP-1504191).Ye

Does Puget Sound have a long-term memory?

More than a decade of high-resolution, full-water column data collected by profiling UW ORCA/NANOOS moorings in several Puget Sound Basins are used to investigate interannual variability of near-surface and deep water properties. Although there are no significant trends in temperature, salinity, density and dissolved oxygen spanning the last decade, measurements show steady and relatively strong trends in these variables over periods of 3 to 5 years in both South Sound near bottom waters and in south Hood Canal deep water. For example, the annual minimum density in south Hood Canal deep water increased four years in a row from 2006 to 2009, then this trend reversed for three years. In Carr Inlet the annual maximum deep temperature increased five years in a row from 2011 to 2015, with deep salinity following a similar trend. As these trends are significantly longer than expected flushing and residence times (\u3c year), this hints at potential interannual dynamical feedbacks, longer-term system “memory”, and/or similar trends in ocean and atmospheric forcing. Using archived National Data Buoy Center, National Weather Service and UW Atmospheric Sciences data we explore and report on potential factors contributing to these trends

Double diffusion, shear instabilities, and heat impacts of a pacific summer water intrusion in the Beaufort Sea

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Fine, E., MacKinnon, J., Alford, M., Middleton, L., Taylor, J., Mickett, J., Cole, S., Couto, N., Boyer, A., & Peacock, T. Double diffusion, shear instabilities, and heat impacts of a pacific summer water intrusion in the Beaufort Sea. Journal of Physical Oceanography, 52(2), (2022): 189–203, https://doi.org/10.1175/jpo-d-21-0074.1.Pacific Summer Water eddies and intrusions transport heat and salt from boundary regions into the western Arctic basin. Here we examine concurrent effects of lateral stirring and vertical mixing using microstructure data collected within a Pacific Summer Water intrusion with a length scale of ∼20 km. This intrusion was characterized by complex thermohaline structure in which warm Pacific Summer Water interleaved in alternating layers of O(1) m thickness with cooler water, due to lateral stirring and intrusive processes. Along interfaces between warm/salty and cold/freshwater masses, the density ratio was favorable to double-diffusive processes. The rate of dissipation of turbulent kinetic energy (ε) was elevated along the interleaving surfaces, with values up to 3 × 10−8 W kg−1 compared to background ε of less than 10−9 W kg−1. Based on the distribution of ε as a function of density ratio Rρ, we conclude that double-diffusive convection is largely responsible for the elevated ε observed over the survey. The lateral processes that created the layered thermohaline structure resulted in vertical thermohaline gradients susceptible to double-diffusive convection, resulting in upward vertical heat fluxes. Bulk vertical heat fluxes above the intrusion are estimated in the range of 0.2–1 W m−2, with the localized flux above the uppermost warm layer elevated to 2–10 W m−2. Lateral fluxes are much larger, estimated between 1000 and 5000 W m−2, and set an overall decay rate for the intrusion of 1–5 years.This work was supported by ONR Grant N00014-16-1-2378 and NSF Grants PLR 14-56705 and PLR-1303791, NSF Graduate Research Fellowship Grant DGE-1650112, as well as by the Postdoctoral Scholar Program at Woods Hole Oceanographic Institution, with funding provided by the Weston Howland Jr. Postdoctoral Scholarship

Regional and temporal variability in Puget Sound zooplankton: bottom-up links to juvenile salmon

We use data from the Puget Sound Zooplankton Monitoring Program to explore patterns of spatial and interannual variability in zooplankton communities in response to environmental change during 2014-2017. This program is a collaborative effort involving 10 tribal, county, state, federal, academic, and nonprofit entities initiated via the Salish Sea Marine Survival Project with the goal of understanding the key role of zooplankton in food webs and ecosystems. Large interannual differences in the environment over this period strong effects on zooplankton community structure and abundance. 2014 began as a fairly normal year in Puget Sound until the Pacific Warm Anomaly event nicknamed “The Blob” began to affect the region during late summer and fall. Unprecedented warm anomalies occurred in summer 2015, persisting through 2016. Off the coast of Washington and Oregon, clear effects on zooplankton community structure were observed, with rare oceanic species occurring in coastal samples concurrent with decreased overall biomass. In sharp contrast, few rare species were collected in Puget Sound, and zooplankton increased in 2015 and 2016 relative to 2014, including increases in nearly all taxa that are important juvenile salmon prey. A few taxa, most notably the dinoflagellate Noctiluca and numerous species of small jellyfish, decreased during the warm years, and shifts in the seasonal phenology of some taxa were observed. These and other findings from the Puget Sound Zooplankton Monitoring Program will be presented in the context of the implications of environmental change for juvenile salmon growth and survival

Patterns and variability in ocean acidification conditions in Puget Sound and the Strait of Juan de Fuca

The Washington Ocean Acidification Center is working with NOAA and other partners to increase understanding of ocean acidification dynamics and spatial variability in the Salish Sea, and how these correlate with planktonic responses. These data are critical for assessing water quality, areas with higher or lower OA stress, and to understand effects on the food web. Two main strategies are employed; seasonal ship cruises provide spatial coverage and the ability to collect plankton, while mooring buoys provide information on mechanisms and the range of variation due to the high-resolution and constant coverage they provide. Results show a strong degree of depth, seasonal, and spatial variation in pH and aragonite saturation state. In general, the lowest pH and aragonite saturation state values are at depth, particularly in stratified areas, though this can shift during seasonal localized upwelling, e.g., Southern Hood Canal, and in mixed water columns, e.g., the Main Basin. Seasonal patterns are spatially diverse, with stratified areas exhibiting strong vertical gradients with depth during summer and more homogenous conditions during winter; well-mixed areas show less variation year-round. This implies that species encounter quite different OA conditions in various parts of the Salish Sea between the seasons. Mooring CO2 data reveal higher variation during late fall through early spring at sites within the Salish Sea, due to winter mixing of stratified waters, yet the reverse pattern off the Washington coast, due to summer upwelling. In both cases, these mechanisms (winter mixing and summer upwelling) operate across a gradient, bringing relatively deeper lower pH / aragonite saturation state waters in contact with surface waters with higher values. Such changes in the spatial and depth distribution of corrosive conditions have broad implications for sensitive marine life

Autonomous Seawater \u3ci\u3ep\u3c/i\u3eCO\u3csub\u3e2\u3c/sub\u3e and pH Time Series From 40 Surface Buoys and the Emergence of Anthropogenic Trends

Ship-based time series, some now approaching over 3 decades long, are critical climate records that have dramatically improved our ability to characterize natural and anthropogenic drivers of ocean carbon dioxide (CO2) uptake and biogeochemical processes. Advancements in autonomous marine carbon sensors and technologies over the last 2 decades have led to the expansion of observations at fixed time series sites, thereby improving the capability of characterizing sub-seasonal variability in the ocean. Here , we present a data product of 40 individual autonomous moored surface ocean pCO2 (partial pressure of CO2) time series established between 2004 and 2013, 17 also include autonomous pH measurements. These time series characterie a wide range of surface ocean carbonate conditions in diffferent oceanic (17 sites), coastal (13 sites), and coral reef (10 sites) regimes. A time of trend emergence (ToE) methodology applied ot the time series that exhibit well-constrained daily to interannual variability and an estimate of decadal variability indicates that the length of sustained observations necessary to detect statistically significant anthropogenic trends varies by marine environment. The ToE estisites, and 9 to 22 years at the coral reef sites. Only two open ocean pCO2 and pH range from 8 to 15 years at the open ocean sites, 16 to 41 years at the coastal sites, and 9 to 22 years at the coral reef sites. Only two open ocean pCO2 time series, Woods Hole Oceanographic Institution Hawaii Ocean Time-series Station (WHOTS) in the subtropical North Pacific and Stratus n the South Pacific gyre, have been deployed longer than the estimated trend detection time and, for these, deseasoned monthly means show estimated anthropogenic trends of 1.9 ± 0.3 and 1.6 ± 0.3 μatm yr-1, respectively. In the future, it is possible that updates to this product will allow for the estimation of anthropogenic trends at more sites; however, the product currently provides a valuable tool in an accessible format for evaluating climatology and natural variability of surface ocean carbonate chemistry in a variety of regions. Data are available at https://doi.org/10.7289/V5DB8043 and https://www.nodc.noaa.gov/ocads/oceans/Moorings/ndp097.html (Sutton et al., 2018)

Turbulent entrainment fluxes within the eastern Pacific warm pool

Thesis (Ph. D.)--University of Washington, 2007.Mechanisms controlling turbulent entrainment fluxes, or vertical turbulent fluxes at the mixed layer base (z = -h), and the specific influence of heat entrainment on SST within the eastern Pacific warm pool (EPWP) are investigated using a 19-day timeseries of upper-ocean and atmospheric measurements collected in September 2001 at 10°N, 95°W, co-located buoy measurements, and a semi-empirical entrainment model. Buoyancy entrainment scaled with the cube of the friction velocity, u*, and the inverse finescale (8-m) gradient Richardson number at z = -h, Ri-1(-h), with the variance of the latter largely due to both near-inertial and sub-inertial shear. These two parameters explained more than half of buoyancy entrainment variance over the 19-day timeseries. Surface buoyancy flux also modulated entrainment with heavy rainfall and intense solar radiation suppressing and buoyant convection generating entrainment. Variability of vertical gradients of temperature and salinity at z = -h due to coincident large surface heat and freshwater (rainfall) fluxes and the comparable roles of temperature and salinity in determining the stratification at h were also found to modulate entrainment heat and salt fluxes produced by elevated turbulence at h.The 19-days of entrainment observations allowed the evaluation and modification of the Ni-iler and Kraus (1977) (N-K) entrainment parameterization, which was used with mooring buoy measurements to obtain entrainment estimates over 2001. The three empirically-motivated modifi cations reduced the base N-K model root-mean-square error by 35% and mean bias from +40% to less than +2%. Mixed layer temperature budget inferences and entrainment model results indicate that changes in h associated with Ekman pumping and Rossby waves strongly controls entrainment and, thus, SST. Large entrainment heat fluxes and large resultant drops in SST occur when Ekman pumping decreases h, exposing the concentrated temperature gradients at z = -h to stronger, surface-forced turbulence. With changes in depth-averaged mixed layer temperature due to entrainment inversely proportional to h, shoaling h also amplifies the effect of these fluxes on SST changes. Entrainment may account for most of the cooling needed to offset the net annual ∼23°C of warming that would result from the divergence of the surface and penetrative heat fluxes acting alone, and, thus, strongly controls the region's SST

Tracking Salish Sea Environmental Changes in Real-Time

Using existing and freely available real-time environmental measurements in the Salish Sea and on the Washington shelf including mooring observations, atmospheric measurements, and river flow measurements, we developed five metrics to help understand and track primary factors contributing to changes in Salish Sea water properties, and, thus, potential ecological changes. These metrics, which include estuarine flow speed, river and rain effect on salinity, water-column oxygen availability, ocean boundary conditions, and heating or cooling of the water by the atmosphere, are intended to inform resource managers, scientists, health officials, and others on how key climate and ocean factors are influencing the present state of the Salish Sea. Climatologies are developed for all metrics to place the current conditions in the context of past observations. A “dashboard” website hosted by NANOOS describes these metrics and presents plots of the metrics that are updated weekly (http://www.nanoos.org/products/ps_metrics/home.php). This project was initially developed as a Puget Sound Ecosystem Monitoring Program (PSEMP) project with funding from the Puget Sound Partnership