Oceanographic observations (CTD, DOM fluorescence and nutrients) in the Nansen Sound fjord system of the eastern Canadian Arctic Archipelago in August 2024 and May 2025

In 2025, measurements were collected using an RBRconcerto³ CTD featuring a sensor accuracy of ±0.002°C and ±0.003 S/m. Practical salinity was derived from seawater conductivity and temperature in accordance with the Practical Salinity Scale of 1978 (PSS-78). All CTD casts were restricted to a maximum depth of 522 m.

CDOM fluorescence (excitation/emission = 370/460 nm) was measured using a Wet Labs ECO fluorometer with a sensor sensitivity of 0.09 parts per billion (ppb). Nitrate profiles were obtained via a Sea-Bird Scientific SUNA V2 Optical Nitrate Sensor, which utilizes UV light absorption spectrum characteristics. According to the manufacturer's specifications, the nitrate measurements are accurate to ±10% of the reading.

All profiles were binned at 1-meter intervals, and a 7-meter moving average was applied to the CDOM and nitrate profiles. Water samples were collected from 2 L Niskin bottles lowered through the ice. Nutrient samples (nitrate, phosphate and silicate) were collected in acid-washed 15 mL Falcon tubes by filtering via an acid-washed syringe through a Swinnex-mounted pre-combusted (450°C for 5 hours) GF/F filter.

Sample vials were rinsed with a small volume of sample before filling and then were frozen at –20°C. Finally, samples were analysed at the Université Laval using a continuous colourimetric method adapted from Hansen and Koroleff (1999) on a continuous-flow AutoAnalyzer III (Bran and Luebbe GmbH). Final data are reported in μmol/l. Oceanographic surveys discovered Pacific Summer Water within Nansen Sound, marked by a –1.08 °C subsurface temperature maximum.

Tracked by nutrient tracers, this water mass is distinct from the overlying Polar Surface Water. It does not cross the Canadian Arctic Archipelago (CAA) shelf directly due to unique physical properties. Instead, simulations reveal it is routed along the CAA continental margin by a southwestward diversion of the Transpolar Pacific water branch.