Cross-shelf transport and exchange between a temperate shelf sea and the North Atlantic Ocean

• Main Author: Ruiz Castillo, E
• Format: Thesis
• Language: unknown
• Published: University of Liverpool Repository 2019
• Subjects: North Atlantic
• Online Access: https://dx.doi.org/10.17638/03046560; https://livrepository.liverpool.ac.uk/id/eprint/3046560

Shelf seas are relatively small regions. They account for 9% of the ocean's area and less than 0.5% of the ocean's volume (Simpson and Sharples, 2012). Despite their relatively small size shelf seas play a key role in global biogeochemical cycles. It is estimated that 20% of the global ocean annual primary production (Behrenfield et al., 2005) and 79% of the total CO2 oceanic intake occurs in shelf seas (Jahnke, 2010). The physics governing cross-shelf transport and exchange between the shelf and the ocean impact the shelf sea biogeochemical cycles. For instance, the NW European shelf is generally seen as a net carbon sink (Hartman et al., 2018) with carbon thought to be exported from the shelf into the ocean (Thomas et al., 2004; Painter et al., 2017). In addition, it is estimated that globally about 56-58% and 85-90% of the phosphorus and nitrogen required by shelf seas to maintain high productivity are supplied from the ocean (Liu et al., 2010). Therefore, understanding the mechanisms governing transport, both within the shelf and in shelf-ocean exchange, will help to better comprehend how the high productivity of shelf seas is supported and how export of shelf seas contributes to the global carbon cycles. This thesis focuses on the temperate and wide Celtic Sea, where it is unclear how nutrients supplied either at the shelf break or near the coast are transported into the interior of the shelf to sustain primary productivity or, conversely how carbon is exported from the shelf to drive net shelf sea absorption of atmospheric CO2. This research particularly focuses on the mechanisms supplying and transporting nutrients onto and across the Celtic Sea. Results indicate that throughout summer, due to wind-driven dynamics, nutrients are chiefly supplied from the North Atlantic onto the outer Celtic Sea and on the shelf, nutrients are advected across the shelf in the bottom mixed layer. At the shelf edge off-shelf export in the bottom layer was found to be negligible. In the interior of the Celtic Sea evidence of stratification being maintained by wind-driven advection of relatively high salinity waters in the bottom layer was observed in late-autumn 2014 and spring 2015.