The characteristics and trends of rainfall on sub-Antarctic Marion Island and associated air circulation patterns
- Authors: Mapuka, Fortunate Nomsa
- Date: 2020
- Language: English
- Type: Thesis , Masters , MSc(Geography)
- Identifier: http://hdl.handle.net/10353/18698 , vital:42725
- Description: Marion Island (46°54ʹS, 37°45ʹE) located in the Southern Ocean possesses one of the most oceanic climates on earth and sensitive to climate change. Climatologically, the sub-Antarctic is inadequately represented in the climate literature and this research therefore attempts to establish the recent changes that have occurred on Marion Island with regards to annual rainfall totals, monthly rainfall, rain days and non-rain days during the period from 1980 to 2018. This study found that annual rainfall has decreased by 24% from 2196.7 mm to 1678.57 mm from 1980 to 2018 and that the last decade (2010-2018) is the driest on record. The decrease in annual rainfall on Marion Island can be directly linked to the decreases recorded in monthly and daily rainfall. Rainfall in autumn has reduced by 35% over the last 40 years and the decrease in autumn rainfall is in part directly related to an increase in anticyclonic air circulation during which Marion Island is not influenced by any mid-latitudinal depressions. The frequency of rain days measured on Marion Island significantly decreased. Daily rainfall measuring less than 5 mm of rain a day contribute 50% of the total number of rain days. However, these high frequency low depth rainfall days contribute very little rainfall to annual totals. On Marion Island rain days that measure 10 mm and above contribute 65% of the total annual rainfall and it is also these type of high magnitude rain days that have significantly decreased since 1980. Multi-day consecutive rain events contribute the greatest proportion of rainfall to the annual rainfall totals (~40%). Linear statistics shows that the contribution to rainfall amount from these multi-day rainfall has halved since 1980. The frequency of non-rain days and consecutive non-rain days have significantly increased. The increased frequency of anticyclonic air circulation over Marion Island and the decrease of the traveling low-pressure systems affecting Marion Island are the probable cause of the increase in non-rain days. It is suggested that this increase in consecutive non-rain days has the most significant impact on the island’s biodiversity and landscape
- Full Text:
- Date Issued: 2020
- Authors: Mapuka, Fortunate Nomsa
- Date: 2020
- Language: English
- Type: Thesis , Masters , MSc(Geography)
- Identifier: http://hdl.handle.net/10353/18698 , vital:42725
- Description: Marion Island (46°54ʹS, 37°45ʹE) located in the Southern Ocean possesses one of the most oceanic climates on earth and sensitive to climate change. Climatologically, the sub-Antarctic is inadequately represented in the climate literature and this research therefore attempts to establish the recent changes that have occurred on Marion Island with regards to annual rainfall totals, monthly rainfall, rain days and non-rain days during the period from 1980 to 2018. This study found that annual rainfall has decreased by 24% from 2196.7 mm to 1678.57 mm from 1980 to 2018 and that the last decade (2010-2018) is the driest on record. The decrease in annual rainfall on Marion Island can be directly linked to the decreases recorded in monthly and daily rainfall. Rainfall in autumn has reduced by 35% over the last 40 years and the decrease in autumn rainfall is in part directly related to an increase in anticyclonic air circulation during which Marion Island is not influenced by any mid-latitudinal depressions. The frequency of rain days measured on Marion Island significantly decreased. Daily rainfall measuring less than 5 mm of rain a day contribute 50% of the total number of rain days. However, these high frequency low depth rainfall days contribute very little rainfall to annual totals. On Marion Island rain days that measure 10 mm and above contribute 65% of the total annual rainfall and it is also these type of high magnitude rain days that have significantly decreased since 1980. Multi-day consecutive rain events contribute the greatest proportion of rainfall to the annual rainfall totals (~40%). Linear statistics shows that the contribution to rainfall amount from these multi-day rainfall has halved since 1980. The frequency of non-rain days and consecutive non-rain days have significantly increased. The increased frequency of anticyclonic air circulation over Marion Island and the decrease of the traveling low-pressure systems affecting Marion Island are the probable cause of the increase in non-rain days. It is suggested that this increase in consecutive non-rain days has the most significant impact on the island’s biodiversity and landscape
- Full Text:
- Date Issued: 2020
Towards a reconstruction of Marion Island’s glacial history
- Authors: Rudolph, Elizabeth
- Date: 2020
- Subjects: Glacial landforms Geomorphological mapping
- Language: English
- Type: Thesis , Doctoral , PhD (Geography)
- Identifier: http://hdl.handle.net/10353/18531 , vital:42581
- Description: Southern Hemisphere glacial chronologies can provide valuable insights into interactions between glaciation and past climate changes. The sub-Antarctic Islands provide a valuable terrestrial record of glacial chronologies for the Southern Hemisphere, since they are unique, not only in size and topography, but also in oceanic situation when compared to other continental landmasses (e.g. Antarctica or Patagonia). On sub-Antarctic Marion Island, southern Indian Ocean, the exact timing and extent of the local Last Glacial Maximum is not yet known as glacial reconstructions have mostly been based on palynological proxies and relative-age dating techniques. This study presents 29 cosmogenic 36Cl exposure ages of deglaciated bedrock surfaces and moraine deposits from Marion Island. In addition, a comprehensive glacial-geomorphological map, which in conjunction with exposure ages provide improved temporal and spatial constraints for the island’s glacial history. Results show that the ice reached a local Last Glacial Maximum before 56 ka ago and retreated, with minor stillstands, until ~17 ka. This early deglaciation left island surfaces below 850 m a.s.l. ice-free after ~19 ka, and any subsequent advances during the Late Glacial or Holocene cooling periods would have been restricted to the interior. This glacial chronology is similar to that of some other sub-Antarctic Islands (e.g. the Kerguelen archipelago, Auckland and Campbell islands, and possibly South Georgia) and a number of other Southern Hemisphere glaciers (e.g. in Patagonia and New Zealand) and adds to evidence that suggest the Southern Hemisphere was in a glacial maximum earlier than the global LGM. A combination of climatic drivers such as declining temperatures, a northward migration of oceanic fronts and the Southern Hemisphere Westerly Winds (causing precipitation changes), as well as the physiography of Marion Island, created optimal conditions for glacier growth during Marine Isotope Stage 4 (MIS 4; ~65 ka ago) instead of the global LGM in MIS 2 (~18 ka). These findings redefine the glacial history of Marion Island, and have implications for future investigations on post-glacial landscape development and ecological succession.
- Full Text:
- Date Issued: 2020
- Authors: Rudolph, Elizabeth
- Date: 2020
- Subjects: Glacial landforms Geomorphological mapping
- Language: English
- Type: Thesis , Doctoral , PhD (Geography)
- Identifier: http://hdl.handle.net/10353/18531 , vital:42581
- Description: Southern Hemisphere glacial chronologies can provide valuable insights into interactions between glaciation and past climate changes. The sub-Antarctic Islands provide a valuable terrestrial record of glacial chronologies for the Southern Hemisphere, since they are unique, not only in size and topography, but also in oceanic situation when compared to other continental landmasses (e.g. Antarctica or Patagonia). On sub-Antarctic Marion Island, southern Indian Ocean, the exact timing and extent of the local Last Glacial Maximum is not yet known as glacial reconstructions have mostly been based on palynological proxies and relative-age dating techniques. This study presents 29 cosmogenic 36Cl exposure ages of deglaciated bedrock surfaces and moraine deposits from Marion Island. In addition, a comprehensive glacial-geomorphological map, which in conjunction with exposure ages provide improved temporal and spatial constraints for the island’s glacial history. Results show that the ice reached a local Last Glacial Maximum before 56 ka ago and retreated, with minor stillstands, until ~17 ka. This early deglaciation left island surfaces below 850 m a.s.l. ice-free after ~19 ka, and any subsequent advances during the Late Glacial or Holocene cooling periods would have been restricted to the interior. This glacial chronology is similar to that of some other sub-Antarctic Islands (e.g. the Kerguelen archipelago, Auckland and Campbell islands, and possibly South Georgia) and a number of other Southern Hemisphere glaciers (e.g. in Patagonia and New Zealand) and adds to evidence that suggest the Southern Hemisphere was in a glacial maximum earlier than the global LGM. A combination of climatic drivers such as declining temperatures, a northward migration of oceanic fronts and the Southern Hemisphere Westerly Winds (causing precipitation changes), as well as the physiography of Marion Island, created optimal conditions for glacier growth during Marine Isotope Stage 4 (MIS 4; ~65 ka ago) instead of the global LGM in MIS 2 (~18 ka). These findings redefine the glacial history of Marion Island, and have implications for future investigations on post-glacial landscape development and ecological succession.
- Full Text:
- Date Issued: 2020
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