Transport of carbon and nutrients through the Herald Canyon in the Arctic Ocean

The Arctic Ocean has experienced large changes in the last decades. A question is how these changes impact the carbon cycle and specifically the air-sea flux of carbon dioxide. One process relevant to the latter is the sedimentation of organic matter to the deep waters, a process that is dependent on the supply of nutrients. Substantial amounts of nutrients and carbon enter the Arctic Ocean from the Pacific Ocean through Bering Strait, distributed over three main pathways. Water with low salinities and nutrient concentrations takes an eastern route along the Alaskan coast, as Alaska Coastal Water. A central pathway has intermediate salinity and nutrient concentrations, while the most nutrient rich water enters Bering Strait on its western side. Towards the Arctic Ocean the flow of these water masses is subject to strong topographic steering within the Chukchi Sea with volume transports modulated by the wind field. It has been speculated that most of the nutrient rich water enters the deep Arctic Ocean through Herald Canyon. In this contribution we use data from several sections crossing Herald Canyon collected in 2008 and 2014. The bottom of the canyon has the highest nutrient concentrations, likely as a result of addition from the degradation of organic matter at the sediment surface. We compute the flux of nutrients (nitrate, phosphate, and silicate) and dissolved inorganic carbon in different water masses as identified by their T-S characteristics by combining hydrographic and nutrient observations with ADCP and surface drift data. Even if there are some general similarities between the years, there are differences in both the T-S and nutrient characteristics. The conclusion is that this region needs to be monitored over a longer time frame to deduce the temporal variability and potential trends.