Knor Lucie A. C. M.

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Knor
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Lucie A. C. M.
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  • Article
    Hawaii coastal seawater CO2 network: A statistical evaluation of a decade of observations on tropical coral reefs.
    (Frontiers Media, 2019-05-07) Terlouw, Gerianne J. ; Knor, Lucie A. C. M. ; De Carlo, Eric H. ; Drupp, Patrick S. ; Mackenzie, Fred T. ; Li, Yuan Hui ; Sutton, Adrienne J. ; Plueddemann, Albert J. ; Sabine, Christopher L.
    A statistical evaluation of nearly 10 years of high-resolution surface seawater carbon dioxide partial pressure (pCO2) time-series data collected from coastal moorings around O’ahu, Hawai’i suggest that these coral reef ecosystems were largely a net source of CO2 to the atmosphere between 2008 and 2016. The largest air-sea flux (1.24 ± 0.33 mol m−2 yr−1) and the largest variability in seawater pCO2 (950 μatm overall range or 8x the open ocean range) were observed at the CRIMP-2 site, near a shallow barrier coral reef system in Kaneohe Bay O’ahu. Two south shore sites, Kilo Nalu and Ala Wai, also exhibited about twice the surface water pCO2 variability of the open ocean, but had net fluxes that were much closer to the open ocean than the strongly calcifying system at CRIMP-2. All mooring sites showed the opposite seasonal cycle from the atmosphere, with the highest values in the summer and lower values in the winter. Average coastal diurnal variabilities ranged from a high of 192 μatm/day to a low of 32 μatm/day at the CRIMP-2 and Kilo Nalu sites, respectively, which is one to two orders of magnitude greater than observed at the open ocean site. Here we examine the modes and drivers of variability at the different coastal sites. Although daily to seasonal variations in pCO2 and air-sea CO2 fluxes are strongly affected by localized processes, basin-scale climate oscillations also affect the variability on interannual time scales.
  • Article
    Quantifying net community production and calcification at Station ALOHA near Hawai‘i: Insights and limitations from a dual tracer carbon budget approach
    (American Geophysical Union, 2023-07-02) Knor, Lucie A. C. M. ; Sabine, Christopher L. ; Sutton, Adrienne J. ; White, Angelicque E. ; Potemra, James T. ; Weller, Robert A.
    A budget approach is used to disentangle drivers of the seasonal mixed layer carbon cycle at Station ALOHA (A Long-term Oligotrophic Habitat Assessment) in the North Pacific Subtropical Gyre (NPSG). The budget utilizes data from the WHOTS (Woods Hole—Hawaii Ocean Time-series Site) mooring, and the ship-based Hawai'i Ocean Time-series (HOT) in the NPSG, a region of significant oceanic carbon uptake. Parsing the carbon variations into process components allows an assessment of both the proportional contributions of mixed layer carbon drivers and the seasonal interplay of drawdown and supply from different processes. Annual net community production reported here is at the lower end of previously published data, while net community calcification estimates are 4- to 7-fold higher than available sediment trap data, the only other estimate of calcium carbonate export at this location. Although the observed seasonal cycle in dissolved inorganic carbon in the NPSG has a relatively small amplitude, larger fluxes offset each other over an average year. Major supply comes from physical transport, especially lateral eddy transport throughout the year and entrainment in the winter, offset by biological carbon uptake in the spring. Gas exchange plays a smaller role, supplying carbon to the surface ocean between Dec-May and outgassing in Jul-Oct. Evaporation-precipitation (E-P) is variable with precipitation prevailing in the first half and evaporation in the second half of the year. The observed total alkalinity signal is largely governed by E-P with a somewhat stronger net calcification signal in the wintertime.