NABOS is part of the Arctic Observing Network and is funded by the National Science foundation and the National Oceanic and Atmospheric Administration.
Since the early 2000s, the goal of NABOS has been to compile a cohesive picture of climatic changes in the Eurasian and Makarov basins of the Arctic Ocean. NABOS works to understand:
- how boundary currents transport Atlantic Water
- how Atlantic Water interacts with shelf waters, the deep basin interior, and the upper ocean
- changes in upper ocean circulation within these basins
NABOS survey types
Extensive measurements are planned reaching from Svalbard to the Lomonosov Ridge and eastward into the Makarov Basin, both to answer fundamental questions about circulation and transformation of Atlantic Water (AW), and to provide context for the oceanographic, biological, and chemical sampling programs.
Ship-based sampling will include conductivity-temperature-depth (CTD)/rosette and geochemistry sampling and attendant sea-ice and atmospheric observations. Repeated cross-sections, some of which were initiated as early as 2002, have proved to be a powerful tool for detecting and documenting the climate change signal [e.g. Polyakov et al. 2005, 2011a,b].
There are, however, some important additions to the routine NABOS survey. Two cross-sections at 90°E and 160°E will be expanded further north to merge with the two NPEO sections (Fig. 1). This addition links our observations with another Arctic Observing Network (AON) element, NPEO, and provides the large-scale spatial coverage that is much needed for data interpretation.
Higher (~several km) spatial density of sampling is planned for the shelf edge vicinity and coarser sampling (~10-15km) will be used over the slope area, thus resolving fast lateral changes of water properties at the shelf margins. In the basin interior the sampling will be even coarser (~50km).
CTD observations will be complemented with lowered Acoustic Doppler Current Profiler (LADCP) measurements. These will be compared to XCP velocity profiles at selected stations on the 160°E and 90°E line.
Chemical tracers can be used in conjunction with temperature-salinity (T-S) measurements to address variability in halocline water formation and circulation [McLaughlin et al. 2004; Woodgate et al. 2005; Itoh et al. 2007; Alkire et al. 2010]. By combining high-resolution measurements of the NO parameter and focused bottle chemistry sampling, variability in the halocline can be studied.
Fractional contributions of meteoric water, net sea-ice melt, and AW will be calculated via a simple water-type analysis [Ostlund and Hut 1984; Schlosser et al. 1994; Yamamoto-Kawaii et al. 2008] incorporating conservative tracers (salinity, δ18O, and total alkalinity). The fractions of these water types will be used to assess the contribution of shelf waters to halocline layers. Combined with sensor-based, high-resolution measurements of NO, temperature, and salinity, these data will be used to gauge the role of shelf waters in halocline layer formation.
While the deployment of nitrate and dissolved oxygen sensors on moorings M1, M5, and M9 should capture the temporal variability in NO at fixed locations, particularly the seasonal cycles of biological production versus respiration and sea-ice melt and formation, the multi-disciplinary cruises will provide unparalleled detail about the distribution of both NO and freshwater sources over the Siberian shelf/slope and Eurasian Basin (EB).
Together, these data should help to elucidate variability in the role of shelf waters in halocline ventilation in both time and space. An aggressive chemical sampling program is essential to the success of the analysis. For example, samples for nutrient determination (nitrate, nitrite, ammonia, phosphate, and silicate), chlorophyll and dissolved inorganic carbon/total alkalinity will be collected. Highly accurate DIC and TA data will be also collected allowing changes in oceanic CO2 to be documented. Bottle samples of nitrate and dissolved oxygen are necessary for sensor calibration. Salinity and stable oxygen isotopes (δ18O) will be utilized to separate and quantify fractional contributions of net sea-ice melt, meteoric water, and AW as described above. Total alkalinity (TA) samples, collected as part of the carbon biogeochemistry program, will also serve to supplement the limited number of stable oxygen isotope samples available to estimate contributions of net sea-ice melt and meteoric water [Anderson et al. 1994, 2004; Yamamoto-Kawaii et al. 2005].