Annual cycles of nutrients and oxygen in the upper layers of the North Atlantic Ocean

Monthly climatologies of nutrients and oxygen in the upper North Atlantic Ocean are analyzed and used to estimate the rates of spring-summer new production and remineralization. The annual cycle of surface nutrients is characterized by a spring-summer biological drawdown and a fall-winter increase due to vertical mixing. The drawdown is accompanied by maximum oxygen supersaturations. In the subsurface layer (100-200 m), the decrease of oxygen concentrations during the spring-summer period reflects the remineralization of organic matter. The spring-summer drawdown of surface nutrients implies new production rates that are high in the high latitudes (around 40 g C/m² on average), and low in the low and temperate latitudes (about 15 g C/m² on average). In the subsurface layer, respiration rates are computed from the oxygen concentration decrease during the spring-summer period. Results show that most of the new production in the low latitudes, and half or less of it in the high latitudes, is remineralized above 200 m. The spring-summer new production in the North Atlantic Ocean is estimated to be 1.3 Pg C. Considering that the spring-summer production that is not mineralized in the top 200 m of the ocean is mainly composed of particulate organic matter the spring-summer export at 200 m is estimated to be between 0.4 and 0.6 Pg C for the whole North Atlantic Ocean.