Program

As ocean ecosystems rapidly change in response to climate change and other drivers, the ability to predict the ocean’s productivity, particularly in remote and inhospitable regions of the ocean, becomesincreasingly critical.  Ships are limited in range and duration of observations, and typically miss key episodic events that may be disproportionally important in setting annual cycles or documenting harmful bloom events.  The maturation of underwater glider and float technology for observing the ocean’s ecosystems and biogeochemistry offers a powerful solution to the paucity of ship-based observations.  Two case studies will be presented that highlight the power of autonomous platforms to measure various components of marine productivity.  One is from the subpolar North Atlantic bloom, which is one of the most remarkable features on the planet, with an almost explosive ‘greening’ of the oceans. Athree-monthcomprehensive study of the initiation and demise of the spring bloom was undertaken in 2008 with integrated measurements from aLagrangianfloat, underwater gliders and ships, observations from satellites, and analyses from models. The diatom-dominated bloom began in mid April when the water column stabilized, not by solar warming, but rather by eddy-driven slumping of horizontal density gradients. The resulting bloom was patchy in biomass and phytoplankton diversity, despite high, non-limiting concentrations of macronutrients. Magnitudes and relative proportions of net community productivity (NCP, determined from autonomous budgets of O2 and NO3) and net phytoplankton productivity (NPP, computed from ship-based photosynthetic parameters and float-based biomass and light) diverged as the bloom evolved, with higher fractions of particulate organic carbon (POC) consumed within the mixed layer as the bloom aged. Export productivity (EP, derived as the difference between NCP and accumulation rate of POC) was of similar magnitude during the May diatom bloom and June picophytoplankton bloom. An eddy-driven subduction event was observed, indicating transport of otherwise non-sinking POC along isopycnals to depths of > 200 m. These striking export events reinforce the value of a persistent, distributed presence afforded by a network of autonomous platforms to catch and follow key, transient events. A second case study was carried out from August through September 2014 in the Beaufort Sea, with gliders that navigated through open water, the marginal ice zone, and under the ice. Changing NPP in the Arctic, particularly in the spring when ship measurements under the ice are not possible, can be best assessed through autonomous observations.