Observing shelf sea oxygen dynamics with autonomous observation systems

Hull, Tom (2020) Observing shelf sea oxygen dynamics with autonomous observation systems. Doctoral thesis, University of East Anglia.

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Abstract

This thesis provides new estimates for net community production (NCP) from two North Sea regions, using high temporal resolution oxygen measurements from a long-term monitoring buoy and from a fleet of submarine gliders during a pilot monitoring program. The buoy study reveals a net-heterotrophic system (O2 NCP = (−5.0 �} 2.5) molm−2 a−1), despite a highly productive spring phytoplankton bloom (maximum O2 NCP >(485 �} 129) mmolm−2 d−1). The glider study uses both oxygen and nitrate mass-balances and demonstrates new production rates consistent with Redfield (an O:N ratio of 8.7) during the Spring bloom (O2 NCP = (232 �} 12) molm−2 d−1, NO3 - NCP = (26.8 �} 0.7) mmolm−2 d−1).

In addition, bottom mixed layer oxygen dynamics are explored using an array of seabed landers in the Celtic Sea. The oxygen fluxes, including respiration, are calculated and compared with incubation studies performed during the same observation campaign. The bottom mixed layer oxygen consumption is shown to be broadly similar to that as calculated by the incubation studies (O2 NCP ranged between 30 mmolm−2 d−1 to 47 mmolm−2 d−1). However, the time series reveals temporal variations which are missed with the incubations, including post-bloom increases in consumption and possible re-suspension-driven events. There is also evidence for large persistent vertical fluxes of oxygen.

For shelf sea oxygen time series based NCP estimation, the largest source of uncertainty is derived from the determination of a representative water mass with which to perform an analysis, and the subsequent integration of oxygen observations. Spatial heterogeneity is often overlooked in both open-ocean and shelf-sea based studies. It is shown that the choice of which fluxes need to be quantified, and the length scales that observations should be integrated over, is highly dependent on the dynamics of the particular study region.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Chris White
Date Deposited: 15 Dec 2021 10:19
Last Modified: 15 Dec 2021 10:19
URI: https://ueaeprints.uea.ac.uk/id/eprint/82691
DOI:

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