Abstract
Abstract. The Bering Sea is a highly productive ecosystem, supporting a variety of fish, seabird, and marine mammal populations, as well as large commercial fisheries. Due to its unique shelf geometry and the presence of seasonal sea ice, the processes controlling productivity in the Bering Sea ecosystem span the pelagic water column, the benthic sea floor, and the sympagic sea ice environments. The Bering Ecosystem Study Nutrient-Phytoplankton-Zooplankton (BESTNPZ) model has been developed to simulate the lower-trophic-level processes throughout this region. Here, we present a version of this lower-trophic-level model coupled to a three-dimensional regional ocean model for the Bering Sea. We quantify the model's ability to reproduce key physical features of biological importance as well as its skill in capturing the seasonal and interannual variations in primary and secondary productivity over the past several decades. We find that the ocean model demonstrates considerable skill in replicating observed horizontal and vertical patterns of water movement, mixing, and stratification, as well as the temperature and salinity signatures of various water masses throughout the Bering Sea. Along the data-rich central portions of the southeastern Bering Sea shelf, it is also able to capture the mean seasonal cycle of primary production. However, its ability to replicate domain-wide patterns in nutrient cycling, primary production, and zooplankton community composition, particularly with respect to the interannual variations that are important when linking variation in productivity to changes in longer-lived upper-trophic-level species, remains limited. We therefore suggest that near-term application of this model should focus on the physical model outputs, while model development continues to elucidate potential mechanisms controlling nutrient cycling, bloom processes, and trophic dynamics.
Highlights
The Bering Sea is a highly productive ecosystem
While our physical model domain extends into the northern Gulf of Alaska, the biological model was never intended to simulate this region, and for this validation we assume that all regions south of the Aleutian Islands or east of the Alaska Peninsula are outside the biological domain of the Bering Ecosystem Study NutrientPhytoplankton-Zooplankton (BESTNPZ) model
The BESTNPZ model coupled to the Bering10K regional ocean model demonstrates considerable skill in replicating observed horizontal and vertical patterns of water movement, mixing, and stratification, as well as the temperature and salinity signatures of various water masses throughout the Bering Sea
Summary
The Bering Sea is a highly productive ecosystem. Its broad, shallow eastern shelf reaches widths of over 500 km, with an average depth of only 70 m, leading to a long growing season and high annual primary production (Rho and Whitledge, 2007). Tidal mixing along the continental shelf break leads to a highly productive off-shelf region, often referred to as the “Green Belt”, where the confluence of nitrate from the deep basin and iron from the shelf are mixed into the euphotic zone (Springer et al, 1996). This high primary productivity across the shelf and slope in turn supports a wide variety of pelagic and benthic predators, which support fisheries that land nearly half of the US annual catch (National Marine Fisheries Service, 2017; Fissel et al, 2017). This skill assessment reveals the model’s strengths and weaknesses in reproducing historical patterns across the entire Bering Sea domain and serves as a baseline to which further model improvements can be compared
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