Vertical Land Movements and Sea Level Changes on South Georgia, South Atlantic Ocean: Results from 7 Years of Geodetic and Oceanographic Observations on a Remote Island

Scientific Conference (2020, December 16)

South Georgia Island in the South Atlantic Ocean, is a small remote land mass that supports various ground-based instrumental observations (Global Navigation Satellite System (GNSS), tide gauge ... [more ▼]

South Georgia Island in the South Atlantic Ocean, is a small remote land mass that supports various ground-based instrumental observations (Global Navigation Satellite System (GNSS), tide gauge, meteorological and seismic) in an otherwise largely under sampled oceanic region. Moreover, the South Atlantic Ocean plays an important role in global ocean circulation, con-necting the deep thermohaline circulation of the North Atlantic and Indian Oceans, whilst also linking to the Antarctic Circumpolar Current in the South, where the lack of continental barriers allows a free exchange of water between the major ocean basins. Hence, South Georgia po-tentially lies within a region susceptible to climatic changes before these can be felt further afield. In 2013 and 2014 a total of five GNSS stations were installed covering the area of the main island (approximately 170 x 50 km) with two of those being located close to the King Edward Point (KEP) Research Station and the GLOSS tide gauge (ID 187). Furthermore, precise levelling campaigns in 2013, 2014, 2017 and 2020 supported the analysis of local ground instabilities near the tide gauge. Through these activities the tide gauge datum within the Permanent Ser-vice for Mean Sea Level (PSMSL) has been established, which in turn, makes the derived KEP mean sea level (MSL) record highly valuable for long-term studies and satellite altimetry cali-brations. In this study, we will present the vertical land movement estimates from seven years of GNSS observations, five precise levelling campaigns, and will discuss their impact on the sea level record from the KEP tide gauge and nearby satellite altimetry sea surface heights. Our results confirm uplift all over South Georgia Island while the area at KEP and particularly the jetty with tide gauge are subsiding relative to the rest of the island. Using this information we correct the MSL record for the vertical land movements and investigate its signals together with those from nearby satellite altimetry tracks. [less ▲]

Present-Day Land and Sea Level Changes around South Georgia Island: Results from Precise Levelling, GNSS, Tide Gauge and Satellite Altimetry Measurements

Scientific Conference (2019, July 25)

South Georgia Island, the main land outcrop on the South Georgia microcontinent (SGM), is located approximately 1,400 km east of the Falkland Islands and approximately 1,400 km northeast of the ... [more ▼]

South Georgia Island, the main land outcrop on the South Georgia microcontinent (SGM), is located approximately 1,400 km east of the Falkland Islands and approximately 1,400 km northeast of the northernmost tip of the Antarctic peninsular. The SGM is believed to lie south of the North Scotia Ridge (NSR), which forms the boundary to the South America Plate, while to the south it is bordered by the Scotia Plate (SP). In its sub-Antarctic location, the island is largely covered by mountain glaciers which have been reported to be retreating due to climatic change. Furthermore, during past glaciation periods the island and its shelf area, stretching much of the SGM, have been ice covered as was revealed by scarring of the sub-oceanic topography. Together with ongoing tectonics along the NSR and recent seismicity at the SP boundary, these processes have the ability to produce significant uplift on local to regional scales. With its mid-ocean location in the Southern Atlantic Ocean South Georgia Island is in a key position for the oceanic and geodetic global monitoring networks. As these net-works suffer from a Hemisphere imbalance with the number of stations in the Northern Hemisphere outnumbering those in the Southern Hemisphere, operating these stations to the highest standards is of key scientific value. It is of particular interest to monitor the tide gauge (GLOSS ID 187) at King Edward Point (KEP) for vertical land movements to establish a continuous record of its datum within the Permanent Service for Mean Sea Level (PSMSL), which in turn makes it useful for long-term sea level studies and satellite altimetry calibrations. With the establishment of five GNSS stations on the islands by teams from Luxembourg, the UK and the USA during 2013 to 2015, and the scientific analysis of these data within a global network of stations, it has now become possible to study present-day vertical land movements and their impacts. Furthermore, together with four precise levelling campaigns of the KEP benchmark network in 2013, 2014 and two in 2017, it has also been possible to investigate the very local character of the vertical motions near KEP, i.e. the stability of the jetty upon which the tide gauge is mounted. In this study, we will present the still preliminary results from the GNSS and levelling measurements and will discuss their impact on the sea level record from the KEP tide gauge. Our measurements show that while South Georgia Island and the area around KEP are rising, the jetty and tide gauge are subsiding, leading to a lower magnitude of the observed sea level change than expected from satellite altimetry. In order to improve the agreement between these measurements both local and regional vertical land movements need to be monitored. [less ▲]

Vertical Land Movements and Sea Level Changes around South Georgia Island

Poster (2018, April 09)

South Georgia Island in the Southern Atlantic Ocean is a key location for the seismic, geomagnetic and oceanic global monitoring networks. In its sub-Antarctic location, the island is largely covered by ... [more ▼]

South Georgia Island in the Southern Atlantic Ocean is a key location for the seismic, geomagnetic and oceanic global monitoring networks. In its sub-Antarctic location, the island is largely covered by mountain glaciers which have been reported to be retreating due to climatic change. Furthermore, during past glaciation periods the island and its shelf area have been ice covered as was revealed by scarring of the sub-oceanic topography. Together with ongoing tectonics along the North Scotia Ridge, these processes have the ability to produce significant uplift on local to regional scales, affecting the measurements of the tide gauge (GLOSS ID 187) at King Edward Point (KEP). Furthermore, with its mid-ocean location, the tide gauge is of particular interest to satellite altimetry calibrations over the Southern Atlantic and Southern Oceans. With the establishment of five GNSS stations on the islands during 2013 to 2015 and the scientific analysis of these data within the global network of stations of the International GNSS Service Tide Gauge Benchmark Monitoring (TIGA) working group, it has now become possible to study present-day vertical land movements of the region and their impacts on, for example, regional sea level. Furthermore, together with four precise levelling campaigns of the KEP benchmark network in 2013, 2014 and two in 2017, it has also been possible to investigate the very local character of the vertical motions near KEP, ie. the stability of the jetty upon which the tide gauge is mounted. In this study, we will present the still preliminary results from the GNSS and levelling measurements and will discuss their impact on the sea level record from the KEP tide gauge. Our measurements show that while South Georgia Island and the area around KEP are rising, the jetty and tide gauge are subsiding, leading to a disagreement in the observed sea level change from the tide gauge and satellite altimetry. In order to improve the agreement between these sea level measurements both local and regional vertical land movements need to be monitored. [less ▲]

Calibration of the Tide Gauge at King Edward Point, South Georgia Island, South Atlantic Ocean

Poster (2015, June 27)

In 2008 a new pressure tide gauge with Global Sea Level Observing System Number 187 was installed at King Edward Point (KEP), South Georgia Island, South Atlantic Ocean. This installation was carried out ... [more ▼]

In 2008 a new pressure tide gauge with Global Sea Level Observing System Number 187 was installed at King Edward Point (KEP), South Georgia Island, South Atlantic Ocean. This installation was carried out as part of the Antarctic Circumpolar Current Levels by Altimetry and Island Measurements (ACCLAIM) programme. In 2013 the KEP Geodetic Observatory was established in support of various scientific applications including the monitoring of vertical land movements at KEP. Currently, the observatory consists of two state-of-the-art Global Navigation Satellite System (GNSS) stations with local benchmark networks. This ties all benchmarks and the tide gauge into the International Terrestrial Reference Frame 2008, and allows the establishment of a local height datum in a global height system through the use of a global gravitational model. In 2014 a tide board was added to the tide gauge, which, together with the GNSS and levelling observations, now enables a calibration of the tide gauge. This will make it possible to include the KEP tide gauge in the Permanent Service for Mean Sea Level (PSMSL) database. In this study, we will present the results from the calibration of the tide gauge using the GNSS observations from the KEP Geodetic Observatory for the period from February 2013 to present, the levelling campaigns in 2013 and 2014, and geoid undulations derived from a seamless combination of the latest Gravity Observation Combination (GOCO) 05S and Earth Gravitational Model (EGM) 2008 models. [less ▲]