Jan Even Øie Nilsen

Simulated North Atlantic-Nordic Seas water mass exchanges in an isopycnic coordinate OGCM

[1] The variability in the volume exchanges between the North Atlantic and the Nordic Seas during the last 50 years is investigated using a synoptic forced, global version of the Miami Isopycnic Coordinate Ocean Model (MICOM). The simulated volume fluxes agree with the existing observations. The net volume flux across the FaroeShetland Channel (FSC) is positively correlated with the net flux through the Denmark Strait (DS; R = 0.74 for 3 years low pass filtering), but negatively correlated with the net flux across the Iceland-Faroe Ridge (IFR; R = 0.80). For the Atlantic inflow across the FSC and IFR, the correlation is R = 0.59. For the transports through the FSC and DS, the simulation suggests that an atmospheric pattern resembling the North Atlantic Oscillation is the main driving force for the variations, involving Ekman fluxes and barotropic adjustment. The model also shows a 0.7 Sv reduction of the Atlantic inflow to the Nordic Seas since the late 50’s. INDEX TERMS: 4215 Oceanography: General: Climate and interannual variability (3309); 4255 Oceanography: General: Numerical modeling; 9315 Information Related to Geographic Region: Arctic region; 1635 Global Change: Oceans

The Nordic Seas carbon budget: Sources, sinks, and uncertainties

[1] A carbon budget for the Nordic Seas is derived by combining recent inorganic carbon data from the CARINA database with relevant volume transports. Values of organic carbon in the Nordic Seas’ water masses, the amount of carbon input from river runoff, and the removal through sediment burial are taken from the literature. The largest source of carbon to the Nordic Seas is the Atlantic Water that enters the area across the Greenland-Scotland Ridge; this is in particular true for the anthropogenic CO2. The dense overflows into the deep North Atlantic are the main sinks of carbon from the Nordic Seas. The budget show that presently 12.3 ± 1.4 Gt C yr −1 is transported into the Nordic Seas and that 12.5 ± 0.9 Gt C yr −1 is transported out, resulting in a net advective carbon transport out of the Nordic Seas of 0.17 ± 0.06 Gt C yr −1 . Taking storage into account, this implies a net air-to-sea CO2 transfer of 0.19 ± 0.06 Gt C yr −1 into the Nordic Seas. The horizontal transport of carbon through the Nordic Seas is thus approximately two orders of magnitude larger than the CO2 uptake from the atmosphere. No difference in CO2 uptake was found between 2002 and the preindustrial period, but the net advective export of carbon from the Nordic Seas is smaller at present due to the accumulation of anthropogenic CO2.

Measurement of the velocity-profile in and above a forest of Laminaria hyperborea

Abstract The aim of this study is to resolve the mechanism of damping of surface waves above bottom vegetation. A field experiment has been carried out, where the horizontal velocities were measured in and above a kelp forest of Laminaria hyperborea (Gunnerus)Foslie, using ultrasonic current-meters. The results from the experiment are presented as periodograms of kinetic energy-density at several levels, and as the correlation of energy at two levels. The main conclusion is that the attenuation extends throughout the whole water column. The long waves exhibit only a slight (5–8%) reduction of velocity-amplitude within the kelp forest.

Quantifying mesoscale eddies in the Lofoten Basin

The Lofoten Basin is the most eddy rich region in the Norwegian Sea. In this paper, the characteristics of these eddies are investigated from a comprehensive database of nearly two decades of satellite altimeter data (1995–2013) together with Argo profiling floats and surface drifter data. An automated method identified 1695/1666 individual anticyclonic/cyclonic eddies in the Lofoten Basin from more than 10,000 altimeter-based eddy observations. The eddies are found to be predominantly generated and residing locally. The spatial distributions of lifetime, occurrence, generation sites, size, intensity, and drift of the eddies are studied in detail. The anticyclonic eddies in the Lofoten Basin are the most long-lived eddies (>60 days), especially in the western part of the basin. We reveal two hotspots of eddy occurrence on either side of the Lofoten Basin. Furthermore, we infer a cyclonic drift of eddies in the western Lofoten Basin. Barotropic energy conversion rates reveals energy transfer from the slope current to the eddies during winter. An automated colocation of surface drifters trapped inside the altimeter-based eddies are used to corroborate the orbital speed of the anticyclonic and cyclonic eddies. Moreover, the vertical structure of the altimeter-based eddies is examined using colocated Argo profiling float profiles. Combination of altimetry, Argo floats, and surface drifter data is therefore considered to be a promising observation-based approach for further studies of the role of eddies in transport of heat and biomass from the slope current to the Lofoten Basin.

Northern North Atlantic Sea Level in CMIP5 Climate Models: Evaluation of Mean State, Variability, and Trends against Altimetric Observations

AbstractThe northern North Atlantic comprises a dynamically complex area with distinct topographic features, making it challenging to model oceanic features with global climate models. As climate models form the basis for assessment reports of future regional sea level rise, model evaluation is important. In this study, the representation of regional sea level in this area is evaluated in 18 climate models that contributed to phase 5 of the Coupled Model Intercomparison Project. Modeled regional dynamic height is compared to observations from an altimetry-based record over the period 1993–2012 in terms of mean dynamic topography, interannual variability, and linear trend patterns. As models are expected to reproduce the location and magnitude but not the timing of internal variability, the observations are compared to the full 150-yr historical simulations using 20-yr time slices. This approach allows one to examine modeled natural variability versus observed changes and to assess whether a forced signal ...