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Publication Date
9 May 2022

Observations of Declining Primary Production in the Western Bering Strait



The shallow (~50 m deep), narrow (~85 km wide) Bering Strait is the sole marine link between the Pacific and Arctic Oceans and represents a critical northward throughflow of freshwater, nutrients, and heat into Arctic waters from lower latitudes (Woodgate and Peralta-Ferriz, 2021). Three water masses enter the Chukchi Sea through the Bering Strait from the Pacific: Anadyr Water (AW), Bering Shelf Water (BSW), and Alaskan Coastal Water (ACW) (Coachman et al., 1975). The western Bering Strait in particular has long been known to be a region of consistently high primary productivity throughout the spring and summer open-water season (Sambrotto et al., 1984; Springer and McRoy, 1993; Brown et al., 2011). This productivity is sustained through the delivery of high-nutrient AW waters via the northern branch of the bifurcated Bering Slope Current (Clement Kinney et al., 2009, 2022; Lowry et al., 2015; Pickart et al., 2016) also causes the Chukchi Sea to the north to be one of the most productive shelves in the Arctic (Hill et al., 2018). Western Bering Strait waters are clearly differentiated from lower productivity waters observed in the eastern Bering Strait that are characterized by relatively low-nutrient, freshwater-dominated ACW (Woodgate and Aagaard, 2005; Lee et al., 2007). However, time series of satellite observations over the last two decades have revealed statistically significant early season (June) declining trends in chlorophyll-a concentrations and primary productivity in the western Bering Strait. In particular, June chlorophyll-a concentrations have declined by ~58%, and June primary productivity has declined by ~34% over the 2003–2020 period. These declining trends appear to be associated with reductions in sea ice cover and increases in primary production upstream in the Gulf of Anadyr during May, with potential implications for decreased nutrient availability downstream in the western Bering Strait during June. To investigate the recent biological change in the Bering Strait, we compiled a satellite-based time series of chlorophyll-a concentrations derived from Aqua-Moderate Resolution Imaging Spectroradiometer (Aqua-MODIS) calibrated radiances using two algorithms: the OC3m algorithm that was developed at NASA Goddard Space Flight Center (GSFC) and makes use of band ratios and in situ measurements (O’Reilly et al., 1998) and the CI algorithm that makes use of reflectance differences in conjunction with a model (Hu et al., 2012). 

Frey, Karen E., Jaclyn Clement Kinney, Larry V. Stock, and Robert Osinski. 2022. “Observations Of Declining Primary Production In The Western Bering Strait”. Oceanography 35. doi:10.5670/oceanog.2022.123.
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