Atlantic Basin

Figure 16.2 Model-predicted latitudinal distribution in the North Atlantic Basin (a) estuarine denitrification (b) total nitrogen transport by rivers. (Modified from Seitzinger, 2000.)...

Prospero, J. M., Barrett, K., Church, T., Dentener, P., Duce, R. A., Galloway, J. N., Levy, H. II., Moody, J., and Quinn, P. (1996). Atmospheric deposition of nutrients to the North Atlantic Basin. In Nitrogen cycling in the North Atlantic Ocean and its watersheds report of the international SCOPE project (Howard, R. W., ed.), Kluwer, Dordrecht, pp. 27-74. 

Figure 13.5 Upper 500 m distributions of (A) nitrate (pmol kg ) and (B) DON (pmol kg ) along section A16 (North and South Atlantic basins occupied injanuary 2003 andjune 2005, respectively, with data combined from those cruises). Dots indicate sample depths. 

Figure 13-9 Schematic views of (A) meridional and vertical transport of nitrate in the upper Atlantic basin and (B) associated horizontal transport pathways. Nitrate-rich Circumpolar Deep Water (CDW) upwells in the Southern Hemisphere and the residual mean flow transports some of this upwelled water across the polar front into the regions of intermediate and mode water formation. Nitrate-rich Sub-Antarctic Mode Water (SAMW) and Antarctic Intermediate Water move northward in the thermocline, ultimately outcropping in the subpolar North Atlantic. Ekman transfer provides a source of nitrate to the subtropical gyre along with lateral and vertical eddy transport processes.

The Atlantic basin, particularly the North Atlantic, is the most studied of the global oceans, yet there are several important processes and issues remaining to be addressed. Arguably, the most important issue is the paucity of data from the South Atlantic. There have been excellent expeditionary efforts there (i.e., the WOCE sections and the South Atlantic Ventilation Experiment), so the hydrographic system and the nutrient provinces can now be assessed in greater detail. However there has been little focus on processes of the nitrogen cycle in the basin. 

Detailed analyses of foraminiferal Cd/Ca in North Atlantic sediment cores indicate that the depth distribution of nutrients was much more stratified below 1 Ion during the last glacial maximum than it is today (Fig. 7.15). While water below about 2.5 km was much more influenced by high nutrients from Southern sourced waters (AABW) (see above), shallow waters (<2 km) had lower nutrient concentrations than today. This result, coupled with the Pacific-Atlantic differences in nutrient concentrations, suggests that during the last glacial maximum NADW production occupied shallower depths in the North Atlantic Basin. 

Consequently, authors have developed the model of coupled nitrification/denitrification for continental shelf sediments to estimate the spatial distribution of denitrification throughout shelf regions in the North Atlantic basin. Using data from a wide range of continental shelf regions, authors found a linear relationship between denitrification and sediment oxygen uptake (Figure 20). 

The model-predicted average denitrification rate for continental shelf sediments in the North Atlantic Basin is 0.69 mmol N as N2 per m /day. Denitrification rates (per unit area) are highest for the continental shelf region in the western North Atlantic between Cape Hatteras and South Florida and lowest for Hudson Bay, the Baffin Island region, and Greenland (Figure 21). 

Figure 21. Model predicted rates of denitrification coupled to sediment nitrification for various continental shelf regions in the North Atlantic basin a) denitrification rates per unit area (mmol N as N2 perm /day), andb) N removal by region (mol N x j e.g.. Nova Scotia/Hattras...

Figure 22. Known. wurces and. sinks of N for continental shelf regions in the we.stern and eastern Atlantic Basin by latitudinal zone (Seilzinger and Gibiin. 1996).

Figure 4. Relationship between log of population density and log of total nitrogen export from regions of the North Atlantic basin (top, a) and of nitrate in the major world rivers (bottom, b). Both relationships are significant, but the relationship for nitrate fluxes in the World s rivers (bottom) is more significant, has lesser scatter and has a steeper slope. For TN fluxes in the North Atlantic basin (top), logTN = 2.2+0.35 og(population density) r = 0.45 p = 0.01. For nitrate fluxes in the World s rivers (bottom), logN03 = 1.15 + 0.621og (population density) r - 0.53 p — 0.00001 (Howarth, 1996).

Figure 5. Application of nitrogen in fertilizer and by atmospheric deposition ofFiOy to 13 of the watershed regions. Values are in kg N/km /year. Fertilizer inputs dominate net anthropogenic nitrogen inputs in most, but not all, regions of the North Atlantic basin (Howarth, 1996).

Figure 9, Schematic representation of nitrogen circulation within and between the terrestrial ecosystems, the groundwater systems, and the river system of the North Atlantic basin as a whole. Values In kg N/km /year. Width of arrows, although not strictly proportional,. suggests the relative magnitude of the corresponding fluxes (Howarth et al, /996).

Channel and remains a distinct water mass as far north as 40 N in the western North Atlantic basin. 

Kuypers M.M.M., Pancost R.D., Nijenhuis I.A., Sinninghe DamsteJ.S. (2002) Enhanced productivity led to increased organic carbon burial in the euxinic North Atlantic basin during the late Cenomanian oceanic anoxic event. Paleoceanogr. 17, 1051, doi 10.1029/222PA000569. 

European consumers compete with the US for natural gas supplies in the Atlantic Basin both import regions negotiate with exporters such as Trinidad Tobago, Qatar or Nigeria. Furthermore, LNG enables the redirection of cargoes between the two regions if price differentials allow for arbitrage benefits. 

The third reason to question the lEA projections arises from the fact that the six countries shown in the bottom half of Table 3.1 account for more than 90 percent of projected MENA gas exports in the 2010-30 period two countries - Algeria and Qatar - account for 70-90 percent of total exports. Should any political or geopolitical problems prevent these two countries from developing exports as anticipated in the table the consequences for European gas supplies and the Atlantic Basin (and global) LNG market will be significant. Saudi Arabia, the other major country... 

Since 2000, the LNG market in the Atlantic Basin has been transformed from a relatively limited and rigid set of bilateral trades into an increasingly liquid market with a much larger number of players. There are a number of reasons for this transformation ... 

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