0 0.5 1 TINnorm -20 -15 -10 -5 0 5 10 15 20 dbar shallower than peak dT/dz Jul-Sep Midl Shelf Composite TIN norm rel to peak dT/dz -0.2 -0.1 0 0.1 0.2 mmol N m-3 d-1 -20 -15 -10 -5 0 5 10 15 20 0 10 20 30 40 50 60 70 80 90 100 Days Since 1 July 0 5 10 15 20 25 30 35 TINdeep [ mol l-1] Deep (>50 dbar) TIN concentrations, SE Middle Shelf Jul-Sep • Researchers at NOAA PMEL and AFSC are currently working on a compendium of CTD (1974- present) and nutrient (2001- present) data based on NOAA sampling in Alaska waters. • This will include EcoFOCI and predecessor programs at PMEL, along with data from the BASIS program at AFSC. • Here, we show an example application: investigating the nutricline on the SE Bering Sea middle shelf. • A strong thermocline there is a consistent feature in summer. • The compendium data are used to demonstrate the composite structure relative to this thermocline, post-spring bloom. • We use total inorganic nitrogen TIN = NO3+NO2+NH4 to characterize the nutricline (Lomas et al. 2012). Data are referenced to the thermocline in each profile. • Composites at left are based on 991 casts in 18 years (2003-2020) of sampling on middle shelf in July-Sept (red). • E Bering Shelf is among most densely sampled areas for nutrients in the compendium. • Coverage extends into Chukchi (not shown) and Gulf of Alaska (partially shown). • Observed subsurface chl maxima – e.g., shown here at M2 site (green, above) in 2019 sampled by prawler instrument (Nielsen et al., 2023) – are often also coincident with or just above thermocline. • Confirmed in composite (right) of data in vertical coordinates relative to thermocline. Compare with profile of convergence of turb. flux at left. Conditions at M2 site in 2019 Bloom Thermocline Convergence of vertical turbulent flux, assuming constant Kz applied to composite • Composite deep concentrations (right) increase with day of year. • Suggests that replenishment due to biogeochemical processes in lower layer outpaces upward mixing. • Though, likely some geographic variability on the middle shelf that needs to be more fully accounted for in sampling. Data Compilation An Example Summer The Composite Deep Layer The Composite Nutricline Composite Fitted Data Composite Fitted (descriptive) • The composite nutricline in these profiles is almost exactly centered on depth of peak dT/dz. • Here TINnorm = TIN / TINdeep (avg of bottles ≥50 dbar in each profile). • The mean summer profile implies nutrients are being supplied to upper half of nutricline. And, being depleted in lower half. • ~0.5 mmol N per day total supplied to a 5-meter region in upper nitricline, if Kz ~ 10-5 m2 s-1 and is constant, and TINdeep ~ 15 micromol kg-1 • Results support the common assumptions that thermocline and nutricline are coincident, and that nutrients are often depleted in surface layer, and imply a vertical structure of nutrient supply under certain conditions/assumptions. Data are to be described in: Mordy C, Pelland N, Stabeno P, Bell S, Cheng W, Eisner L, Farley E, Gann J, Hermann A, Nielsen J, Proctor P, Wisegarver E. A fifty-year compendium of hydrographic data in Alaska waters by the U.S. National Oceanic and Atmospheric Administration. Data manuscript in preparation. Other references: Nielsen J, Pelland N, Bell S, Lomas M, Eisner L, Stabeno P, Harpold C, Stalin S, Mordy C (2023) Seasonal Dynamics of Primary Production in the Southeastern Bering Sea Assessed Using Continuous Temporal and Vertical Dissolved Oxygen and Chlorophyll-a Measurements. JGR: Oceans, 128, e2022JC01907. Lomas M, Moran S, Casey J, Bell D, Tiahlo M, Whitefield J, et al. (2012). Spatial and seasonal variability of primary production on the eastern Bering Sea shelf. DSR-II, 65–70, 126–140 The composite southeast Bering Sea shelf nutricline, within a multi-decade compendium of NOAA Alaska hydrography Noel Pelland1,3, Jens Nielsen1,3, Calvin Mordy1,2, Phyllis Stabeno2, Shaun Bell2, Wei Cheng1,2, Al Hermann1,2, Lisa Eisner3, Jeanette Gann3 1.