- Email: [email protected]
Diatom-based reconstruction of salinity in Lake St. Lucia, South Africa: A Holocene climate history
188
Abstracts / Quaternary International 404 (2016) 174e213
HOLOCENE MARINE RADIOCARBON RESERVOIR CORRECTION DELTA R FOR THE WEST COAST OF SOUTH AFRICA 1, *
2
3
4
1
G. Dewar , P. Reimer , J. Sealy , S. Woodborne . Department of Anthropology, University of Toronto, Canada; 2 Archaeology and Palaeoecology, School of Geography, Archaeology and Palaeoecology, Queen's University Belfast, UK; 3 Archaeology Department, University of Cape Town, South Africa; 4 iThemba Laboratories, South Africa. E-mail address: [email protected].
In order to calibrate radiocarbon ages based on samples with a marine carbon component it is important to know the marine carbon reservoir correction or DR value. This study measured the DR on both known-age pre bomb marine shells and paired marine and terrestrial samples from two regions on the west coast of South Africa: the southwestern Cape and Namaqualand. Pooling the data by region produces DR values that are similar enough to use a west coast weighted mean DR of 146 ± 85 14C years to correctly calibrate marine shell or mixed marine and terrestrial 14C ages. There are however temporal differences in DR throughout the Holocene, which we compare with proxy data for upwelling and sea surface temperatures. Keywords: marine reservoir effect, radiocarbon dates, southern Africa, west coast
A NEW LATE HOLOCENE POLLEN RECORD FROM EILANDVLEI, SOUTH AFRICA N. Du Plessis*, M.E. Meadows, L.J. Quick, K.L. Kirsten. Department of Environmental and Geographical Science, University of Cape Town, South Africa. E-mail address: [email protected].
It is a well-known fact that the South African palaeoenvironmental record is fairly limited, mainly due to the fact that environmental conditions do not favour the preservation of proxy data sources. This being said, new evidence is emerging from the Wilderness Embayment along the Southern Cape coast of South Africa. This area is of particular interest from a palaeoclimate perspective due to its location within the year round rainfall zone of South Africa, while the presence of both Fynbos and Afrotemperate forest within this region further highlights the importance of studies in the area. This study presents a new late Holocene pollen and charcoal record from Eilandvlei, extending from ca. 3 800 cal yr BP to the present. The sequence is dominated by fynbos, most notably Ericaceae and Restionaceae, with the single largest contributor to the assemblage being the succulent/drought resistant element ChenoAm-type. Significantly increased levels of ChenoAm-type is evident for the period ca. 3200 cal yr BP to ca. 2600 cal yr BP, indicating a major marine event in the area. The record further encompasses the arrival of European colonists in the region ca. 1800 AD, marked by the appearance of Pinus, with subsequent notable fluctuations in other taxa, e.g. Podocarpus and Stoebe-type, possibly the expression of the anthropogenic effect on the landscape. This high resolution record thus highlights significant, albeit short term, fluctuations in climate and vegetation patterns along the southern coast of South Africa and adds to the inadequate records available for the region thus far. Keywords: late Holocene, palynology, Southern Cape, Wilderness
SPATIAL PATTERNS OF MODERN DIATOM DISTRIBUTION IN THE EILANDVLEI CATCHMENT, WILDERNESS, SOUTH AFRICA J. Fell 1, *, K.L. Kirsten 1, P. Frenzel 2, S. Meschner 2, M. Zabel 3, M.E. Meadows 1. 1 Department of Environmental and Geographical Science, University of Cape Town, South Africa; 2 Institute of Geosciences, Friedrich Schiller University Jena, Germany; 3 MARUM e Zentrum für marine Umweltwissenschaften, University of Bremen, Germany. E-mail address: [email protected].
Diatom species compositions are often distributed along environmental gradients and are influenced by a number of environmental parameters. The spatial patterns of modern diatoms can be combined with palaeolimnology to provide a powerful means to assess ecological change in coastal lake systems on multiple time scales. The modern distribution of diatom assemblages in surficial sediments in the Eilandvlei catchment was studied in order to ascertain spatial patterns and explore the main environmental parameters responsible for community structure. Canonical correspondence analysis revealed that among four measured environmental variables; salinity and conductivity accounted for most of the variance in the diatom data. The species composition of the catchment was found to be dominated by brackish species. In general, the brackish species' Cocconeis placentula, Amphora coffeaeformis and Planothidium delicatulum were prevalent among all sites in the catchment, indicating the brackish nature of the system. Geographic Information System techniques were used in the analysis of the distribution of diatom species. Diatoms were classed by salinity preferences into brackish, fresh and marine taxa and their spatial distribution was analysed relative to water temperature and salinity distributions. The community pattern gave an accurate representation of ecological conditions of the sampling sites, displaying salinity and temperature gradients through the catchment. Brackish species were most abundant through the estuary while marine species were concentrated through sections of Eilandvlei and Rondevlei. Freshwater species were found at low abundances through the system. The distribution of the three classes of diatoms suggests that this assemblage is structured by salinity. This distribution of modern diatoms can provide useful analogues to interpret palaeoenvironmental reconstructions in the region in the future. Keywords: benthic diatoms, modern distribution, South Africa, salinity gradient
DIATOM-BASED RECONSTRUCTION OF SALINITY IN LAKE ST. LUCIA, SOUTH AFRICA: A HOLOCENE CLIMATE HISTORY M. Gomes 1, *, M. Humphries 2, K.L. Kirsten 3, D. Drake 1. 1 School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, South Africa; 2 School of Chemistry, University of the Witwatersrand, South Africa; 3 Department of Environmental and Geographical Science, University of Cape Town, South Africa. E-mail address: [email protected].
Coastal water bodies on the east coast of South Africa contain sedimentary deposits that provide potential archives of long-term, highresolution climate change. Lake St. Lucia, on the north coast of KwaZuluNatal, is the largest coastal lagoon system in South Africa and has international recognition as a UNESCO World Heritage Site. The St. Lucia system evolved from fluvial origins and today is underlain by a intricate network of buried river channels that reflect almost continual deposition since the start of the Holocene. Recorded data for the last 50 years show that St. Lucia has been subject to extreme salinity fluctuations driven by drought and flood events. Hence, the environmental sensitivity of St. Lucia to climate-driven water balances makes it an ideal site to investigate changes in salinity associated with palaeoclimate variability. Two 15.9 m cores have been extracted from the Lake St. Lucia in order to provide a detailed account of the hydrological cycle during the Holocene. One core was obtained from False Bay and the other from North Lake and provided a basal age of ca. 8300 cal yrs BP, and ca. 7000 cal yrs BP, respectively. The main focus of this study is to present a high-resolution reconstruction of the salinity history of Lake St. Lucia using diatoms, in order to understand the hydrological evolution of this system. Findings from this research will contribute to a larger multiproxy study that aims to provide a more detailed understanding of the characteristics and timing of palaeoenvironmental change in the summer rainfall zone of South Africa. Keywords: Lake St. Lucia, palaeoclimate, Holocene, summer rainfall region
* Corresponding author.
Abstracts / Quaternary International 404 (2016) 174e213
HOLOCENE MARINE RADIOCARBON RESERVOIR CORRECTION DELTA R FOR THE WEST COAST OF SOUTH AFRICA 1, *
2
3
4
1
G. Dewar , P. Reimer , J. Sealy , S. Woodborne . Department of Anthropology, University of Toronto, Canada; 2 Archaeology and Palaeoecology, School of Geography, Archaeology and Palaeoecology, Queen's University Belfast, UK; 3 Archaeology Department, University of Cape Town, South Africa; 4 iThemba Laboratories, South Africa. E-mail address: [email protected].
In order to calibrate radiocarbon ages based on samples with a marine carbon component it is important to know the marine carbon reservoir correction or DR value. This study measured the DR on both known-age pre bomb marine shells and paired marine and terrestrial samples from two regions on the west coast of South Africa: the southwestern Cape and Namaqualand. Pooling the data by region produces DR values that are similar enough to use a west coast weighted mean DR of 146 ± 85 14C years to correctly calibrate marine shell or mixed marine and terrestrial 14C ages. There are however temporal differences in DR throughout the Holocene, which we compare with proxy data for upwelling and sea surface temperatures. Keywords: marine reservoir effect, radiocarbon dates, southern Africa, west coast
A NEW LATE HOLOCENE POLLEN RECORD FROM EILANDVLEI, SOUTH AFRICA N. Du Plessis*, M.E. Meadows, L.J. Quick, K.L. Kirsten. Department of Environmental and Geographical Science, University of Cape Town, South Africa. E-mail address: [email protected].
It is a well-known fact that the South African palaeoenvironmental record is fairly limited, mainly due to the fact that environmental conditions do not favour the preservation of proxy data sources. This being said, new evidence is emerging from the Wilderness Embayment along the Southern Cape coast of South Africa. This area is of particular interest from a palaeoclimate perspective due to its location within the year round rainfall zone of South Africa, while the presence of both Fynbos and Afrotemperate forest within this region further highlights the importance of studies in the area. This study presents a new late Holocene pollen and charcoal record from Eilandvlei, extending from ca. 3 800 cal yr BP to the present. The sequence is dominated by fynbos, most notably Ericaceae and Restionaceae, with the single largest contributor to the assemblage being the succulent/drought resistant element ChenoAm-type. Significantly increased levels of ChenoAm-type is evident for the period ca. 3200 cal yr BP to ca. 2600 cal yr BP, indicating a major marine event in the area. The record further encompasses the arrival of European colonists in the region ca. 1800 AD, marked by the appearance of Pinus, with subsequent notable fluctuations in other taxa, e.g. Podocarpus and Stoebe-type, possibly the expression of the anthropogenic effect on the landscape. This high resolution record thus highlights significant, albeit short term, fluctuations in climate and vegetation patterns along the southern coast of South Africa and adds to the inadequate records available for the region thus far. Keywords: late Holocene, palynology, Southern Cape, Wilderness
SPATIAL PATTERNS OF MODERN DIATOM DISTRIBUTION IN THE EILANDVLEI CATCHMENT, WILDERNESS, SOUTH AFRICA J. Fell 1, *, K.L. Kirsten 1, P. Frenzel 2, S. Meschner 2, M. Zabel 3, M.E. Meadows 1. 1 Department of Environmental and Geographical Science, University of Cape Town, South Africa; 2 Institute of Geosciences, Friedrich Schiller University Jena, Germany; 3 MARUM e Zentrum für marine Umweltwissenschaften, University of Bremen, Germany. E-mail address: [email protected].
Diatom species compositions are often distributed along environmental gradients and are influenced by a number of environmental parameters. The spatial patterns of modern diatoms can be combined with palaeolimnology to provide a powerful means to assess ecological change in coastal lake systems on multiple time scales. The modern distribution of diatom assemblages in surficial sediments in the Eilandvlei catchment was studied in order to ascertain spatial patterns and explore the main environmental parameters responsible for community structure. Canonical correspondence analysis revealed that among four measured environmental variables; salinity and conductivity accounted for most of the variance in the diatom data. The species composition of the catchment was found to be dominated by brackish species. In general, the brackish species' Cocconeis placentula, Amphora coffeaeformis and Planothidium delicatulum were prevalent among all sites in the catchment, indicating the brackish nature of the system. Geographic Information System techniques were used in the analysis of the distribution of diatom species. Diatoms were classed by salinity preferences into brackish, fresh and marine taxa and their spatial distribution was analysed relative to water temperature and salinity distributions. The community pattern gave an accurate representation of ecological conditions of the sampling sites, displaying salinity and temperature gradients through the catchment. Brackish species were most abundant through the estuary while marine species were concentrated through sections of Eilandvlei and Rondevlei. Freshwater species were found at low abundances through the system. The distribution of the three classes of diatoms suggests that this assemblage is structured by salinity. This distribution of modern diatoms can provide useful analogues to interpret palaeoenvironmental reconstructions in the region in the future. Keywords: benthic diatoms, modern distribution, South Africa, salinity gradient
DIATOM-BASED RECONSTRUCTION OF SALINITY IN LAKE ST. LUCIA, SOUTH AFRICA: A HOLOCENE CLIMATE HISTORY M. Gomes 1, *, M. Humphries 2, K.L. Kirsten 3, D. Drake 1. 1 School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, South Africa; 2 School of Chemistry, University of the Witwatersrand, South Africa; 3 Department of Environmental and Geographical Science, University of Cape Town, South Africa. E-mail address: [email protected].
Coastal water bodies on the east coast of South Africa contain sedimentary deposits that provide potential archives of long-term, highresolution climate change. Lake St. Lucia, on the north coast of KwaZuluNatal, is the largest coastal lagoon system in South Africa and has international recognition as a UNESCO World Heritage Site. The St. Lucia system evolved from fluvial origins and today is underlain by a intricate network of buried river channels that reflect almost continual deposition since the start of the Holocene. Recorded data for the last 50 years show that St. Lucia has been subject to extreme salinity fluctuations driven by drought and flood events. Hence, the environmental sensitivity of St. Lucia to climate-driven water balances makes it an ideal site to investigate changes in salinity associated with palaeoclimate variability. Two 15.9 m cores have been extracted from the Lake St. Lucia in order to provide a detailed account of the hydrological cycle during the Holocene. One core was obtained from False Bay and the other from North Lake and provided a basal age of ca. 8300 cal yrs BP, and ca. 7000 cal yrs BP, respectively. The main focus of this study is to present a high-resolution reconstruction of the salinity history of Lake St. Lucia using diatoms, in order to understand the hydrological evolution of this system. Findings from this research will contribute to a larger multiproxy study that aims to provide a more detailed understanding of the characteristics and timing of palaeoenvironmental change in the summer rainfall zone of South Africa. Keywords: Lake St. Lucia, palaeoclimate, Holocene, summer rainfall region
* Corresponding author.