Directly Measuring Physical and Biogeochemical Proxies of the Kuparuk and Sagavanirktok Rivers during the Spring Freshet, in Adjacent Ice-covered Coastal Arctic Waters

The spring freshet is a critical seasonal transition in coastal Arctic marine ecosystems: an ephemeral annual event that occurs during a narrow window of one to several weeks which contributes not only a substantial pulse of riverine freshwater into adjacent coastal ecosystems but also dissolved and particulate organic carbon (DOC and POC) derived terrestrially from a given river’s watershed. Observing the physical and biogeochemical contributions of spring freshets in real-time remains a substantial challenge, especially in areas where the coastal ocean remains ice-covered during the freshet event. This observational challenge limits our ability to assess riverine impacts on coastal Arctic ecosystems on complete annual time scales. We present observational data from a spring-summer field study in 2018 and 2019, in and around Stefansson Sound in the coastal Beaufort Sea, where we developed and deployed a suite of new custom-designed ice buoys outfitted with sensors to detect and measure the incoming freshet, including optical proxies for DOC and POC. We deployed this suite of buoys inshore of the barrier islands surrounding Prudhoe Bay and Foggy Island Bay in mid-April and May while sea ice conditions were still safe for access. Buoys that survived the subsequent spring freshet event provided novel time series of optical and hydrographic variables throughout the course of the Kuparuk and Sagavanirktok freshets over several months, sometimes remaining operational until well after ice-out. These two particular rivers exhibited differences in the optical signatures of their freshets, suggesting that such simple optical approaches may be valuable in characterizing the duration, spatial extents, and possibly DOC & POC contribution by different rivers such as these, directly while sea ice cover still exists. Buoys that were later recovered allowed us to assess influences of biofouling and other factors on the quality of these optical proxy data.