The Prince Edward Islands (PEIs) Archipelago are situated in a prime location for the study of ecosystem response to intrinsic climate variability in the Southern Ocean and the impact of climate change. They are positioned in the Polar Frontal Zone, which is constrained by the subAntarctic Front and the Antarctic Polar Front, all of which are part of the strong, uninterrupted Antarctic Circumpolar Current (ACC). Due to its remoteness and challenging accessibility, there is a severe lack of data in the Southern Ocean and at the PEIs. The existing data are only available as single points observations or snapshots from past research cruises. This study thus makes use of 23 years (1993 – 2016) of satellite and reanalysis data to determine the annual/interannual and long-term variability of Sea Surface Temperature (SST), wind forcing and surface circulation at the PEIs and determine whether natural modes of climate variability like the El Niño Southern Oscillation (ENSO), Southern Annular Mode (SAM) or SemiAnnual Oscillation (SAO) were affecting these parameters. SST, wind speed, wind stress curl and the Ekman current did not express any long-term trend. A significant increasing but very small trend was only perceived in the geostrophic current and total surface current which was concluded to not be associated with the intensification of the ACC caused by a more positive SAM phase. The anomalies in SST showed striking interannual variability at a periodicity of 0.8, 2.8 and 7.5 years showing a similar pattern to that of ENSO with a periodicity of 1.5, 2.9 and 6 years. There has however been no relationship established between SST and any of the climate modes, but the Antarctic Circumpolar Wave (ACW), which is one of ENSO's teleconnection, could be responsible for the interannual changes seen in the SST anomalies. The anomalies in wind speed did not show any apparent periodicity and no relationship with ENSO. More so, while the impact of SAM and SAO has been seen on the westerly wind belt which governs the latitude of the PEIs, no correlation was established between the wind speed at the islands and SAM or SAO. The anomalies in wind stress curl presented no visible interannual variability but some sign of short-term variability. There was also no link 2 established between wind stress curl at the PEIs and any of the climate modes. Finally, a periodicity of 1.3 and 4 years was seen in the geostrophic current anomalies which also coincided with the pattern of ENSO but only showed minor correlation with ENSO. The ACW was deduced to perhaps also be responsible for the surface currents anomalies since the ACW is primarily propagated within the ACC. The trends perceived in the parameters considered for this study and the impact of climate modes on them appeared to be different to patterns which has been historically observed across the Southern Ocean. This further confirms the fact that the neighbouring oceanography and surface wind speed variability surrounding the PEIs differ from other regions of the Southern Ocean, most probably due to the frequent mesoscale instability such as eddies and frontal movement influencing the region. The impact of climate change on the PEIs ecosystem thus cannot be expected to be the same as the rest of the Southern Ocean.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uct/oai:localhost:11427/36569 |
| Date | 29 June 2022 |
| Creators | Toolsee, Tesha |
| Contributors | Lamont, Tarron, Rouault, Mathieu |
| Publisher | Faculty of Science, Department of Oceanography |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Master Thesis, Masters, MSc |
| Format | application/pdf |
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