[1] Climate warming was significant from the mid-19th century to the mid-20th century and in recent decades at most northern high latitudes. Climate warming could induce permafrost degradation, which may have important impacts on hydrological, ecological, and biogeochemical processes and on northern communities and infrastructure. To assess the effects of climate change on permafrost, a process-based model of Northern Ecosystem Soil Temperature (NEST) was developed and utilized to simulate the ground thermal regime of the Canadian landmass at a resolution of a half-degree latitudelongitude since the end of the Little Ice Age (circa 1850). The simulated southern boundary of the permafrost for recent decades is similar to that of the current published map, and the simulated active layer thickness and the depth to permafrost base are comparable to site measurements. Simulation results show that climate change since the end of the Little Ice Age, especially during the 20th century, has induced degradation of permafrost in most of Canada: From the 1850s to the 1990s, the area underlain by permafrost was reduced by 5.4%; for those areas where permafrost existed in all the years throughout the period 1850-2002, the mean depth to the base of permafrost decreased (became shallower) by 3 m; the mean active layer thickness increased by 0.21 m, or 34%; and the mean depth to permafrost table increased by 0.39 m. Results also show that suprapermafrost taliks were formed and became larger and more frequent with climate warming in the southern permafrost region, which greatly enhanced permafrost thaw from the top and could have severe impacts on the landscape, hydrology, and ecosystems.
47 48 A high-resolution unstructured-grid global-regional nested ice-current coupled 49 FVCOM system was configured for the Arctic Ocean and used to examine the impact of 50 model resolution and geometrical fitting on the basin-coastal scale circulation and 51 transport in the pan-Arctic. With resolving steep bottom slope and irregular coastal 52 geometry, the model was capable of simulating the multi-scale circulation and its spatial 53 variability in the Arctic Basin and flow through the Bering Strait, Fram Strait and 54 Canadian Archipelago. The model-simulated annual-mean velocities were in good 55 agreement with observations within the measurement uncertainty and variability due to 56 insufficient sampling. The errors in the flow direction varied with the flow speed, larger 57 in the weak velocity zone and smaller as the velocity increased. In the upper 50-m layer, 58 the annual-mean circulation pattern was dominated by the wind-and ice-drifting-induced 59 anticyclonic circulation in the Arctic Basin and a relatively strong cyclonic slope current 60 along the edge of the continental shelf. In the deep 200-600-m layer, a relatively 61 permanent cyclonic circulation occurred along the steep bottom slope. These annual-62 mean circulations accounted for ~85% of the total kinetic energy variance. De-trending 63 the mean flow, an empirical orthogonal function (EOF) analysis showed that the semi-64 annual and seasonal variability of the sub-tidal flow was dominated by the first and 65 second modes that accounted for ~46% and ~30% of the total variance in the upper 50-m 66 layer and ~58% and 20% in the deep 200-600-m layer. Consistent with observations, the 67 AO-FVCOM-simulated cyclonic slope flow was characterized by a large positive 68 topostrophy. Sensitivity experiment results with various grid configurations suggested 69 that the currents over slopes, narrow straits and water passages featured topographic and 70 3 baroclinic frontal dynamical scales associated with bathymetric slope and internal Rossby 71 deformation radius. Over the Arctic slope, since these two scales are in the same order, 72 the along-slope current could be captured, as the cross-isobath model resolution was 73 refined to resolve the steep bottom topography. Under this condition, there is no need to 74 add Neptune forcing into the momentum equations. The accuracy of the estimation of the 75 transport through the strait and narrow water passage was affected by the model 76 resolution. In Fram Strait where the flow is characterized by strong lateral current shear 77 resulting from the Atlantic inflow and Arctic outflow, the transport estimation could have 78 a significant uncertainty due to both horizontal and vertical sampling resolutions.
A high‐resolution (up to 2 km), unstructured‐grid, fully coupled Arctic sea ice‐ocean Finite‐Volume Community Ocean Model (AO‐FVCOM) was employed to simulate the flow and transport through the Canadian Arctic Archipelago (CAA) over the period 1978–2013. The model‐simulated CAA outflow flux was in reasonable agreement with the flux estimated based on measurements across Davis Strait, Nares Strait, Lancaster Sound, and Jones Sounds. The model was capable of reproducing the observed interannual variability in Davis Strait and Lancaster Sound. The simulated CAA outflow transport was highly correlated with the along‐strait and cross‐strait sea surface height (SSH) difference. Compared with the wind forcing, the sea level pressure (SLP) played a dominant role in establishing the SSH difference and the correlation of the CAA outflow with the cross‐strait SSH difference can be explained by a simple geostrophic balance. The change in the simulated CAA outflow transport through Davis Strait showed a negative correlation with the net flux through Fram Strait. This correlation was related to the variation of the spatial distribution and intensity of the slope current over the Beaufort Sea and Greenland shelves. The different basin‐scale surface forcings can increase the model uncertainty in the CAA outflow flux up to 15%. The daily adjustment of the model elevation to the satellite‐derived SSH in the North Atlantic region outside Fram Strait could produce a larger North Atlantic inflow through west Svalbard and weaken the outflow from the Arctic Ocean through east Greenland.
[1] Moored current measurements were made at one mooring site in the northern Gulf of Tonkin for about 1 year during [1988][1989]. Analyses were performed to examine characteristics and variability of tidal and subtidal flows. Rotary spectra showed two peaks at diurnal and semidiurnal periods, with higher diurnal energy. Complex demodulations of diurnal and semidiurnal tidal currents indicated that the tidal current magnitudes varied significantly with seasons: more energetic in the stratified summer than in the vertically well-mixed winter. The observed subtidal currents were highly correlated with the surface wind in winter but not in summer; challenging the conceptual summertime anticyclonic circulation pattern derived using wind-driven homogenous circulation theory. The computed currents from a global ocean model were in good agreement with the observed currents. Similar to the current observations, the model-computed flow patterns were consistent with the conceptual wind-driven circulation pattern in winter but opposite in summer. Process-oriented experiments suggest that the summertime cyclonic circulation in the northern Gulf of Tonkin forms as a result of the combination of stratified wind-driven circulation and tidal-rectified inflow from Qiongzhou Strait. The interaction between the southwest monsoon and buoyancy-driven flow from Hong River can significantly intensify the cyclonic circulation near the surface, but its contribution to the vertically averaged flow of the cyclonic circulation is limited.
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