科研之友
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摘要
The Gully is a large shelf-edge submarine canyon located on the eastern Scotian Shelf which has long been recognized as an area rich in marine life. This paper analyses the available nutrient (nitrate, silicate and phosphate) data for The Gully, including the new information collected since The Gully was designated a potential Marine Protected Area in 1998, and reports on nutrient climatology, nutrient transports and transport mechanisms, and surface nutrient distributions with a focus on how nutrient behaviour may or may not be different in The Gully than observed elsewhere on the Scotian Shelf. Seasonal cycles for nutrients in The Gully show the general patterns expected for nutrients in temperate coastal waters. The concentrations of all three nutrients in the surface layer (z <= 50 m) are relatively high in late fall and winter. Nitrate and silicate levels fall rapidly during the spring bloom and remain low during the summer and fall. Nitrate is more severely depleted than silicate. Phosphate levels are also lower in summer than in winter, but not depleted in summer, which is consistent with a nitrogen limited ecosystem. Attenuated versions of these seasonal cycles for the three nutrients are evident in the intermediate layer (50 < z <= 100 m), with substantial quantities of nutrients remaining in the summer. Little evidence of a seasonal cycle is seen in deeper waters (z > 100 m). These nutrient concentrations and seasonal cycles are similar to those found elsewhere on the shelf. A more detailed examination of nutrient concentrations in The Gully shows that higher nitrate, silicate and phosphate levels occur at the head of The Gully compared to the mouth, and on the Sable Bank side of The Gully compared to the Banquereau side. These observations are consistent with a trapping of nutrients associated with the counter-clockwise circulation within The Gully, which could fuel more primary productivity in The Gully than on the adjacent shelf. Nutrient levels determined from surface samples collected at high frequency while survey vessels were underway showed anomalously high surface concentrations of nitrate and silicate that were consistent with the areas where the interaction of gully currents with the bottom topography at the head of The Gully and breaking internal waves along the north-east edge of The Gully would enhance vertical mixing. Calculations of transports of nutrients through The Gully show that similar to 5% of the external inputs of nitrate to the eastern Scotian Shelf are supplied through The Gully in winter, and similar to 25% flow through The Gully in summer. Calculations based on these physical processes and the observed nutrient levels show that such mechanisms have the potential to increase production substantially in The Gully compared to other areas of the shelf.
- 出版日期2005-6
