Autonomous Observations of Coupled Physical-Biological Processes in the Ice-covered Arctic Ocean over Diel to Annual Scales

In 2015 a five-year program was completed to outfit eight Ice-Tethered Profilers (ITPs) with novel bio-optical/biogeochemical sensor suites and deploy these in perennially ice-covered regions of the Arctic Ocean. This project represents an important new approach for obtaining biological and bio-physical observations, over diel to annual scales, in extremely difficult-to-sample under-ice ocean ecosystems such as in the Arctic Ocean. These ITPs, deployed in the central Arctic and Beaufort Gyre, carried sensors for chlorophyll fluorescence, optical scattering, CDOM fluorescence, and incident solar radiation in addition to a standard conductivity-temperature-depth sensor and dissolved oxygen. These systems have generated unique, long-term and high-resolution time series of under-ice irradiance, algal biomass, particulate scattering, and organic matter concentrations in the top 800m of the Arctic Ocean, with profiles conducted up to four times daily during most of the annual cycle. Two of these systems operated for twelve months, capturing the entire annual trend in bio-optical properties in the central Arctic Ocean and Beaufort Sea. These observations were used to estimate the timing and duration of the under-ice algal growing season, the subsequent export of particulate organic matter later in the season, the occurrence of intermittent physical perturbations that affect biological and bio-optical distributions (such as under-ice eddies), and the impact of long- and short-term fluctuations in under-ice insolation. Such high-resolution profiling in time enables a more accurate assessment of the timing and magnitude of such intermittent events, down to the time scale of less than a single day. These initial eight profilers provide some of the highest-resolution observations of basic seasonality in fundamental biological and bio-physical dynamics in perennially ice-covered regions of the Arctic Ocean, and demonstrate the utility of autonomous long-term observing in the deep central Arctic. Automated systems capable of long-term operation under polar sea ice are an essential part of any ‘global’ ocean observing system.