Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • Problem Description
• Data Files
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Discrete samples of triple oxygen isotopes (TOI) were collected from the surface Niskin bottles on the CTD-rosette system at all stations as well as on some cruises from the underway system between stations. Samples were collected in custom-made ~500-mL sample bottles which were pre-poisoned with 100 µl of saturated mercuric chloride solution and filled with around 300 mL of seawater from the underway system or from the Niskin at each station (Stanley et al., 2015). Samples were brought to Woods Hole Oceanographic Institution where they were analyzed for TOI with a custom-made processing line and a Thermofisher MAT 253 isotope ratio mass spectrometer as detailed in Stanley et al (2015), that was based on the method of Barkan and Luz (2003). The same samples were also analyzed for O2/Ar which yielded rates of NCP from discrete data as well as an independent method for calibrating the EIMS (see associated dataset). Corrections for the effect of argon on the triple oxygen isotope ratio and the effect of varying sizes of the sample vs. reference standard were made for every sample. Typical lab Reproducibilities from duplicate samples collected on these cruises ranged from 4 to 8 per meg for 17Δ, 0.008 to 0.03 per mil for δ17O, and 0.008 to 0.05 per mil for δ18O depending on the cruise. Confirmation that the water from the underway system was representative of the oceanic TOI signature of dissolved oxygen was obtained by comparing samples collected from the underway system to those collected concurrently from the surface Niskin bottle. 

From these samples, GOP is calculated in units of mmol O2 m-2 d-1 following Eq. 7 in  Prokopenko et al., (2011). The photosynthetic end member used was the average of the phytoplankton value determined by Barkan and Luz (2011); Vienna Standard Mean Ocean Water (VSMOW) was used for the isotopic composition of oxygen in H2O. The actual isotopic composition of H2O was measured in a subset of samples to see if corrections needed to be made (Manning et al., 2017a). It was found to be very similar to VSMOW, leading to an error of less than 10% in GOP due to isotopic water variations. NCP was calculated from the O2/Ar ratios measured in each sample by assuming steady state, neglecting horizontal and vertical advection, and therefore using :NCP = ((O2/Ar)smpl/(O2/Ar)eq-1)*[O2]eq*k*ρ  where (O2/Ar)smpl represents the ratio of O2 to Ar ion currents detected by the EIMS after being calibrated with bottle data, and (O2/Ar)eq represents the ratio of equilibrium concentrations of the gases determined from the gases’ solubility (Garcia and Gordon 1992; Hamme and Emerson 2004) at the seawater temperature and salinity, [O2]eq represents the equilibrium concentration of O2 at the relevant temperature and salinity (mmol kg-1), k is the weighted gas transfer velocity (m d-1), and ρ is the density of seawater (kg m-3) (Millero and Poisson 1981).  For both GOP and NCP, the weighted gas transfer velocity was calculated as a time-weighted average from over the past 60 d calculated as described in Reuer et al. (2007), with the gas exchange parameterization of Stanley et al. (2009) and wind speeds from NCEP Reanalysis (Kalnay et al., 1996; Kistler et al., 2001).

NSF award abstract:

The continental shelf break of the Middle Atlantic Bight supports a productive and diverse ecosystem. Current paradigms suggest that this productivity is driven by several upwelling mechanisms at the shelf break front. This upwelling supplies nutrients that stimulate primary production by phytoplankton, which in turn leads to enhanced production at higher trophic levels. Although local enhancement of phytoplankton biomass has been observed in some circumstances, such a feature is curiously absent from time-averaged measurements, both from satellites and shipboard sampling. Why would there not be a mean enhancement in phytoplankton biomass as a result of the upwelling? One hypothesis is that grazing by zooplankton prevents accumulation of biomass on seasonal and longer time scales, transferring the excess production to higher trophic levels and thereby contributing to the overall productivity of the ecosystem. However, another possibility is that the net impact of these highly intermittent processes is not adequately represented in long-term means of the observations, because of the relatively low resolution of the in-water measurements and the fact that the frontal enhancement can take place below the depth observable by satellite. The deployment of the Ocean Observatories Initiative (OOI) Pioneer Array south of New England has provided a unique opportunity to test these hypotheses. The combination of moored instrumentation and autonomous underwater vehicles will facilitate observations of the frontal system with unprecedented spatial and temporal resolution. This will provide an ideal four-dimensional (space-time) context in which to conduct a detailed study of frontal dynamics and plankton communities needed to examine mechanisms controlling phytoplankton populations in this frontal system. This project will also: (1) promote teaching, training and learning via participation of graduate and undergraduate students in the research , (2) provide a broad dissemination of information by means of outreach in public forums, printed media, and a video documentary of the field work, and (3) contribute to improving societal well-being and increased economic competitiveness by providing the knowledge needed for science-based stewardship of coastal ecosystems, with particular emphasis on connecting with the fishing industry through the Commercial Fisheries Research Foundation.

The investigators will conduct a set of three cruises to obtain cross-shelf sections of physical, chemical, and biological properties within the Pioneer Array. Nutrient distributions will be assayed together with hydrography to detect the signature of frontal upwelling and associated nutrient supply. The investigators expect that enhanced nutrient supply will lead to changes in the phytoplankton assemblage, which will be quantified with conventional flow cytometry, imaging flow cytometry (Imaging FlowCytobot, IFCB), optical imaging (Video Plankton Recorder, VPR), traditional microscopic methods, and pigment analysis. Zooplankton will be measured in size classes ranging from micro- to mesozooplankton with the IFCB and VPR, respectively, and also with microscopic analysis. Biological responses to upwelling will be assessed by measuring rates of primary productivity, zooplankton grazing, and net community production. These observations will be synthesized in the context of a coupled physical-biological model to test the two hypotheses that can potentially explain prior observations: (1) grazer-mediated control and (2) undersampling. Hindcast simulations will also be used to diagnose the relative importance of the various mechanisms of upwelling. The intellectual merit of this effort stems from our interdisciplinary approach, advanced observational techniques, and integrated analysis in the context of a state-of-the-art coupled model. The project will address longstanding questions regarding hydrodynamics and productivity of an important ecosystem, leading to improved understanding of physical-biological interactions in a complex continental shelf regime. Given the importance of frontal systems in the global coastal ocean, it is expected that knowledge gained will have broad applicability beyond the specific region being studied.