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Patterns in Stable Isotope Values of Nitrogen and Carbon in Particulate Matter from the Northwest Atlantic Continental Shelf, from the Gulf of Maine to Cape Hatteras
Citation:
Oczkowski, A., B. Kreakie, Rick Mckinney, AND J. Prezioso. Patterns in Stable Isotope Values of Nitrogen and Carbon in Particulate Matter from the Northwest Atlantic Continental Shelf, from the Gulf of Maine to Cape Hatteras. Frontiers in Marine Science. Frontiers, Lausanne, Switzerland, 3:252, (2016).
Impact/Purpose:
Here we analyze nitrogen and carbon stable isotope values in particulate matter, collected over more than a decade. We used standard spatial statistical techniques (kriging, random forest) to consider the isotope data set in the context of other ecological variables. The resultant information provides important background data from which to consider continental shelf nutrient dynamics.
Description:
Stable isotope measurements of nitrogen and carbon (15N, 13ddC) are often used to characterize estuarine, nearshore, and open ocean ecosystems. Reliable information about the spatial distribution of base-level stable isotope values, often represented by primary producers, is critical to interpreting values in these ecosystems. While base-level isotope data are generally readily available for estuaries, nearshore coastal waters, and the open ocean, the continental shelf is less studied. To address this, and as a first step toward developing a surrogate for base-level isotopic signature in this region, we collected surface and deep water samples from the United States’ eastern continental shelf in the Western Atlantic Ocean, from the Gulf of Maine to Cape Hatteras, periodically between 2000 and 2013. During the study, particulate matter 15dN values ranged from 0.8 to 17.4‰, and 13dC values from −26.4 to −15.6‰over the region. We used spatial autocorrelation analysis and random forest modeling to examine the spatial trends and potential environmental drivers of the stable isotope values. We observed general trends toward lower values for both nitrogen and carbon isotopes at the seaward edge of the shelf. Conversely, higher 15dN and 13dC values were observed on the landward edge of the shelf, in particular in the southern portion of the sampling area. Across all sites, the magnitude of the difference between the 15dN of subsurface and surface particulate matter (PM) significantly increased with water depth (r2 = 0.41, df = 35, p < 0.001), while 13dC values did not change. There were significant positive correlations between 15dN and 13dC values for surface PM in each of the three marine ecoregions that make up the study area. Stable isotope dynamics on the shelf can inform both nearshore and open ocean research efforts, reflecting regional productivity patterns and, even possibly, large-scale climate fluctuations.
