Particle flux, carbon sequestration and the role of mesoscale spatial variability in the Iceland Basin

• Main Author: Baker, Chelsey Adrianne
• Format: Thesis
• Language: English
• Published: University of Southampton 2019
• Subjects: Iceland
• Online Access: https://eprints.soton.ac.uk/441939/; https://eprints.soton.ac.uk/441939/1/Baker_Chelsey_PhD_Thesis_June_2020.pdf

Organic carbon sequestration is driven by the biological carbon pump (BCP), which transfers organic‐rich biomass and detritus to the deep ocean, storing carbon on climatically significant timescales. The BCP exports 5 – 11 Gt C yr‐1 globally into the interior ocean and 0.33 – 0.66 Gt C yr‐1 reaches 2000 m depth. Understanding the functioning of the BCP, and the factors controlling the magnitude and composition of particle flux to the deep ocean in the current climate system, is crucial to detecting and predicting future changes. Records of deep ocean particle flux are usually limited to a single mooring in one location. Uniquely, this study utilises four sediment traps deployed below 2000 m in a mesoscale spatial array in the Iceland Basin (60 °N, 20 °W) from November 2006 to June 2008. In this thesis, the effects of spatial variability and particle flux composition on the magnitude of carbon sequestered in the deep ocean Iceland Basin will be investigated and the observed spatial variability in the context of upper ocean biological and physical processes will be explored. In the first results chapter of this thesis, the flux of organic carbon to the deep ocean Iceland Basin is quantified for the first time. The mean annual particulate organic carbon (POC) flux to 2000 m in the Iceland Basin is 101.7 (± 12.3) mmol m‐2 yr‐1, which is lower than the global average. The data indicate considerable mesoscale spatial variability, evidenced by differences in POC flux captured by the 4 sediment traps. Averaging POC fluxes over increasingly long temporal scales, decreases the magnitude of the observed mesoscale spatial variability, particularly for time scales > 1 month. The influence of localised spatial variability on observed POC fluxes should be considered when investigating particle fluxes at given locations, or using individual traps, for less than annual timescales. However, reassuringly, mesoscale spatial processes likely do not impact deep ocean annual carbon budgets derived from long‐term time‐series, such ...